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Ambekar YS, Caiaffa CD, Wlodarczyk BJ, Singh M, Schill AW, Steele JW, Zhang J, Aglyamov SR, Scarcelli G, Finnell RH, Larin KV. Optical coherence tomography-guided Brillouin microscopy highlights regional tissue stiffness differences during anterior neural tube closure in the Mthfd1l murine mutant. Development 2024:dev.202475. [PMID: 38682273 DOI: 10.1242/dev.202475] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/03/2023] [Accepted: 04/18/2024] [Indexed: 05/01/2024]
Abstract
Neurulation is a highly synchronized biomechanical process leading to the formation of the brain and spinal cord, and its failure leads to neural tube defects (NTDs). Although we are rapidly learning the genetic mechanisms underlying NTDs, the biomechanical aspects are largely unknown. To understand the correlation between NTDs and tissue stiffness during neural tube closure (NTC), we imaged an NTD murine model using optical coherence tomography (OCT), Brillouin microscopy, and confocal fluorescence microscopy. Here, we associate structural information from OCT with local stiffness from the Brillouin signal of embryos undergoing neurulation. The stiffness of neuroepithelial tissues in Mthfd1l null embryos was significantly lower than that of wild-type embryos. Additionally, exogenous formate supplementation improved tissue stiffness and gross embryonic morphology in nullizygous and heterozygous embryos. Our results demonstrate the significance of proper tissue stiffness in normal NTC and pave the way for future studies on the mechanobiology of normal and abnormal embryonic development.
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Affiliation(s)
| | - Carlo Donato Caiaffa
- Center for Precision Environmental Health, Baylor College of Medicine, Houston, TX, USA
- Dell Pediatric Research Institute, Dell Medical School, University of Texas at Austin, TX, USA
| | - Bogdan J Wlodarczyk
- Center for Precision Environmental Health, Baylor College of Medicine, Houston, TX, USA
| | - Manmohan Singh
- Department of Biomedical Engineering, University of Houston, Houston, TX, USA
| | - Alexander W Schill
- Department of Biomedical Engineering, University of Houston, Houston, TX, USA
| | - John W Steele
- Center for Precision Environmental Health, Baylor College of Medicine, Houston, TX, USA
| | - Jitao Zhang
- Department of Biomedical Engineering, Wayne State University, Detroit, MI, USA
| | - Salavat R Aglyamov
- Department of Mechanical Engineering, University of Houston, Houston, TX, USA
| | - Giuliano Scarcelli
- Fischell Department of Bioengineering, University of Maryland, College Park, MD, USA
| | - Richard H Finnell
- Center for Precision Environmental Health, Baylor College of Medicine, Houston, TX, USA
| | - Kirill V Larin
- Department of Biomedical Engineering, University of Houston, Houston, TX, USA
- Molecular Physiology and Biophysics, Baylor College of Medicine, Houston, TX, USA
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Caiaffa CD, Ambekar YS, Singh M, Lin YL, Wlodarczyk B, Aglyamov SR, Scarcelli G, Larin KV, Finnell RH. Disruption of Fuz in mouse embryos generates hypoplastic hindbrain development and reduced cranial nerve ganglia. Dev Dyn 2024. [PMID: 38501709 DOI: 10.1002/dvdy.702] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/08/2023] [Revised: 02/07/2024] [Accepted: 02/20/2024] [Indexed: 03/20/2024] Open
Abstract
BACKGROUND The brain and spinal cord formation is initiated in the earliest stages of mammalian pregnancy in a highly organized process known as neurulation. Environmental or genetic interferences can impair neurulation, resulting in clinically significant birth defects known collectively as neural tube defects. The Fuz gene encodes a subunit of the CPLANE complex, a macromolecular planar polarity effector required for ciliogenesis. Ablation of Fuz in mouse embryos results in exencephaly and spina bifida, including dysmorphic craniofacial structures due to defective cilia formation and impaired Sonic Hedgehog signaling. RESULTS We demonstrate that knocking Fuz out during embryonic mouse development results in a hypoplastic hindbrain phenotype, displaying abnormal rhombomeres with reduced length and width. This phenotype is associated with persistent reduction of ventral neuroepithelial stiffness in a notochord adjacent area at the level of the rhombomere 5. The formation of cranial and paravertebral ganglia is also impaired in these embryos. CONCLUSIONS This study reveals that hypoplastic hindbrain development, identified by abnormal rhombomere morphology and persistent loss of ventral neuroepithelial stiffness, precedes exencephaly in Fuz ablated murine mutants, indicating that the gene Fuz has a critical function sustaining normal neural tube development and neuronal differentiation.
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Affiliation(s)
- Carlo Donato Caiaffa
- Center for Precision Environmental Health, Baylor College of Medicine, Houston, Texas, USA
- Department of Pediatrics, Dell Pediatric Research Institute, University of Texas at Austin Dell Medical School, Austin, Texas, USA
| | - Yogeshwari S Ambekar
- Department of Biomedical Engineering, University of Houston, Houston, Texas, USA
| | - Manmohan Singh
- Department of Biomedical Engineering, University of Houston, Houston, Texas, USA
| | - Ying Linda Lin
- Center for Precision Environmental Health, Baylor College of Medicine, Houston, Texas, USA
| | - Bogdan Wlodarczyk
- Center for Precision Environmental Health, Baylor College of Medicine, Houston, Texas, USA
| | - Salavat R Aglyamov
- Department of Biomedical Engineering, University of Houston, Houston, Texas, USA
| | - Giuliano Scarcelli
- Fischell Department of Bioengineering, University of Maryland, College Park, Maryland, USA
| | - Kirill V Larin
- Department of Biomedical Engineering, University of Houston, Houston, Texas, USA
- Department of Molecular Physiology and Biophysics, Baylor College of Medicine, Houston, Texas, USA
| | - Richard H Finnell
- Center for Precision Environmental Health, Baylor College of Medicine, Houston, Texas, USA
- Department of Molecular and Cellular Biology, Molecular and Human Genetics and Medicine, Baylor College of Medicine, Houston, Texas, USA
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Nair A, Zvietcovich F, Singh M, Weikert MP, Aglyamov SR, Larin KV. Optical coherence elastography measures the biomechanical properties of the ex vivo porcine cornea after LASIK. J Biomed Opt 2024; 29:016002. [PMID: 38223300 PMCID: PMC10787573 DOI: 10.1117/1.jbo.29.1.016002] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 09/15/2023] [Revised: 11/29/2023] [Accepted: 12/26/2023] [Indexed: 01/16/2024]
Abstract
Significance The biomechanical impact of refractive surgery has long been an area of investigation. Changes to the cornea structure cause alterations to its mechanical integrity, but few studies have examined its specific mechanical impact. Aim To quantify how the biomechanical properties of the cornea are altered by laser assisted in situ keratomileusis (LASIK) using optical coherence elastography (OCE) in ex vivo porcine corneas. Approach Three OCE techniques, wave-based air-coupled ultrasound (ACUS) OCE, heartbeat (Hb) OCE, and compression OCE were used to measure the mechanical properties of paired porcine corneas, where one eye of the pair was left untreated, and the fellow eye underwent LASIK. Changes in stiffness as a function of intraocular pressure (IOP) before and after LASIK were measured using each technique. Results ACUS-OCE showed that corneal stiffness changed as a function of IOP for both the untreated and the treated groups. The elastic wave speed after LASIK was lower than before LASIK. Hb-OCE and compression OCE showed regional changes in corneal strain after LASIK, where the absolute strain difference between the cornea anterior and posterior increased after LASIK. Conclusions The results of this study suggest that LASIK may soften the cornea and that these changes are largely localized to the region where the surgery was performed.
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Affiliation(s)
- Achuth Nair
- University of Houston, Department of Biomedical Engineering, Houston, Texas, United States
| | | | - Manmohan Singh
- University of Houston, Department of Biomedical Engineering, Houston, Texas, United States
| | - Mitchell P. Weikert
- Baylor College of Medicine, Cullen Eye Institute, Houston, Texas, United States
| | - Salavat R. Aglyamov
- University of Houston, Department of Mechanical Engineering, Houston, Texas, United States
| | - Kirill V. Larin
- University of Houston, Department of Biomedical Engineering, Houston, Texas, United States
- Baylor College of Medicine, Department of Physiology and Biophysics, Houston, Texas, United States
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Mekonnen T, Zevallos-Delgado C, Singh M, Aglyamov SR, Larin KV. Multifocal acoustic radiation force-based reverberant optical coherence elastography for evaluation of ocular globe biomechanical properties. J Biomed Opt 2023; 28:095001. [PMID: 37701876 PMCID: PMC10494982 DOI: 10.1117/1.jbo.28.9.095001] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/24/2023] [Revised: 08/01/2023] [Accepted: 08/28/2023] [Indexed: 09/14/2023]
Abstract
Significance Quantifying the biomechanical properties of the whole eye globe can provide a comprehensive understanding of the interactions among interconnected ocular components during dynamic physiological processes. By doing so, clinicians and researchers can gain valuable insights into the mechanisms underlying ocular diseases, such as glaucoma, and design interventions tailored to each patient's unique needs. Aim The aim of this study was to evaluate the feasibility and effectiveness of a multifocal acoustic radiation force (ARF) based reverberant optical coherence elastography (RevOCE) technique for quantifying shear wave speeds in different ocular components simultaneously. Approach We implemented a multifocal ARF technique to generate reverberant shear wave fields, which were then detected using phase-sensitive optical coherence tomography. A 3D-printed acoustic lens array was employed to manipulate a collimated ARF beam generated by an ultrasound transducer, producing multiple focused ARF beams on mouse eye globes ex vivo. RevOCE measurements were conducted using an excitation pulse train consisting of 10 cycles at 3 kHz, followed by data processing to produce a volumetric map of the shear wave speed. Results The results show that the system can successfully generate reverberant shear wave fields in the eye globe, allowing for simultaneous estimation of shear wave speeds in various ocular components, including cornea, iris, lens, sclera, and retina. A comparative analysis revealed notable differences in wave speeds between different parts of the eye, for example, between the apical region of the cornea and the pupillary zone of the iris (p = 0.003 ). Moreover, the study also revealed regional variations in the biomechanical properties of ocular components as evidenced by greater wave speeds near the apex of the cornea compared to its periphery. Conclusions The study demonstrated the effectiveness of RevOCE based on a non-invasive multifocal ARF for assessing the biomechanical properties of the whole eyeball. The findings indicate the potential to provide a comprehensive understanding of the mechanical behavior of the whole eye, which could lead to improved diagnosis and treatment of ocular diseases.
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Affiliation(s)
- Taye Mekonnen
- University of Houston, Department of Biomedical Engineering Houston, Texas, United States
| | | | - Manmohan Singh
- University of Houston, Department of Biomedical Engineering Houston, Texas, United States
| | - Salavat R. Aglyamov
- University of Houston, Department of Mechanical Engineering, Houston, Texas, United States
| | - Kirill V. Larin
- University of Houston, Department of Biomedical Engineering Houston, Texas, United States
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Caiaffa CD, Ambekar YS, Singh M, Lin YL, Wlodarczyk B, Aglyamov SR, Scarcelli G, Larin KV, Finnell R. Disruption of Fuz in mouse embryos generates hypoplastic hindbrain development and reduced cranial nerve ganglia. bioRxiv 2023:2023.08.04.552068. [PMID: 37577618 PMCID: PMC10418252 DOI: 10.1101/2023.08.04.552068] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 08/15/2023]
Abstract
The formation of the brain and spinal cord is initiated in the earliest stages of mammalian pregnancy in a highly organized process known as neurulation. Convergent and extension movements transforms a flat sheet of ectodermal cells into a narrow and elongated line of neuroepithelia, while a major source of Sonic Hedgehog signaling from the notochord induces the overlying neuroepithelial cells to form two apposed neural folds. Afterward, neural tube closure occurs by synchronized coordination of the surface ectoderm and adjacent neuroepithelial walls at specific axial regions known as neuropores. Environmental or genetic interferences can impair neurulation resulting in neural tube defects. The Fuz gene encodes a subunit of the CPLANE complex, which is a macromolecular planar polarity effector required for ciliogenesis. Ablation of Fuz in mouse embryos results in exencephaly and spina bifida, including dysmorphic craniofacial structures due to defective cilia formation and impaired Sonic Hedgehog signaling. In this work, we demonstrate that knocking Fuz out during embryonic mouse development results in a hypoplastic hindbrain phenotype, displaying abnormal rhombomeres with reduced length and width. This phenotype is associated with persistent loss of ventral neuroepithelial stiffness, in a notochord adjacent area at the level of the rhombomere 5, preceding the development of exencephaly in Fuz ablated mutants. The formation of cranial and paravertebral ganglia is also impaired in these embryos, indicating that Fuz has a critical function sustaining normal neural tube development and neuronal differentiation. SIGNIFICANCE STATEMENT Neural tube defects (NTDs) are a common cause of disability in children, representing the second most common congenital structural malformation in humans following only congenital cardiovascular malformations. NTDs affect approximately 1 to 2 pregnancies per 1000 births every year worldwide, when the mechanical forces folding the neural plate fails to close at specific neuropores located anteriorly (cranial) or posteriorly (caudal) along the neural tube, in a process known as neurulation, which happens throughout the third and fourth weeks of human pregnancy.
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Mekonnen T, Schill AW, Zevallos-Delgado C, Singh M, Aglyamov SR, Larin KV. Reverberant optical coherence elastography using multifocal acoustic radiation force. Opt Lett 2023; 48:2773-2776. [PMID: 37262207 DOI: 10.1364/ol.482201] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/28/2022] [Accepted: 04/15/2023] [Indexed: 06/03/2023]
Abstract
In this study, we introduce a multifocal acoustic radiation force source that combines an ultrasound transducer and a 3D-printed acoustic lens for application in reverberant optical coherence elastography (Rev-OCE). An array of plano-concave acoustic lenses, each with an 11.8 mm aperture diameter, were used to spatially distribute the acoustic energy generated by a 1 MHz planar ultrasound transducer, producing multiple focal spots on a target plane. These focal spots generate reverberant shear wave fields detected by the optical coherence tomography (OCT) system. The effectiveness of the multifocal Rev-OCE system in probing mechanical properties with high resolution is demonstrated in layered gelatin phantoms.
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Mekonnen T, Zevallos-Delgado C, Zhang H, Singh M, Aglyamov SR, Larin KV. The lens capsule significantly affects the viscoelastic properties of the lens as quantified by optical coherence elastography. Front Bioeng Biotechnol 2023; 11:1134086. [PMID: 36970614 PMCID: PMC10034121 DOI: 10.3389/fbioe.2023.1134086] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/29/2022] [Accepted: 02/21/2023] [Indexed: 03/11/2023] Open
Abstract
The crystalline lens is a transparent, biconvex structure that has its curvature and refractive power modulated to focus light onto the retina. This intrinsic morphological adjustment of the lens to fulfill changing visual demands is achieved by the coordinated interaction between the lens and its suspension system, which includes the lens capsule. Thus, characterizing the influence of the lens capsule on the whole lens’s biomechanical properties is important for understanding the physiological process of accommodation and early diagnosis and treatment of lenticular diseases. In this study, we assessed the viscoelastic properties of the lens using phase-sensitive optical coherence elastography (PhS-OCE) coupled with acoustic radiation force (ARF) excitation. The elastic wave propagation induced by ARF excitation, which was focused on the surface of the lens, was tracked with phase-sensitive optical coherence tomography. Experiments were conducted on eight freshly excised porcine lenses before and after the capsular bag was dissected away. Results showed that the group velocity of the surface elastic wave, V, in the lens with the capsule intact (V=2.55±0.23 m/s) was significantly higher (p < 0.001) than after the capsule was removed (V=1.19±0.25 m/s). Similarly, the viscoelastic assessment using a model that utilizes the dispersion of a surface wave showed that both Young’s modulus, E, and shear viscosity coefficient, η, of the encapsulated lens (E=8.14±1.10 kPa,η=0.89±0.093 Pa∙s) were significantly higher than that of the decapsulated lens (E=3.10±0.43 kPa,η=0.28±0.021 Pa∙s). These findings, together with the geometrical change upon removal of the capsule, indicate that the capsule plays a critical role in determining the viscoelastic properties of the crystalline lens.
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Affiliation(s)
- Taye Mekonnen
- Department of Biomedical Engineering, University of Houston, Houston, TX, United States
| | | | - Hongqiu Zhang
- Department of Biomedical Engineering, University of Houston, Houston, TX, United States
| | - Manmohan Singh
- Department of Biomedical Engineering, University of Houston, Houston, TX, United States
| | - Salavat R. Aglyamov
- Department of Mechanical Engineering, University of Houston, Houston, TX, United States
| | - Kirill V. Larin
- Department of Biomedical Engineering, University of Houston, Houston, TX, United States
- *Correspondence: Kirill V. Larin,
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Lin X, Mekonnen T, Verma S, Zevallos-Delgado C, Singh M, Aglyamov SR, Gesteira TF, Larin KV, Coulson-Thomas VJ. Hyaluronan Modulates the Biomechanical Properties of the Cornea. Invest Ophthalmol Vis Sci 2022; 63:6. [PMID: 36478198 PMCID: PMC9733656 DOI: 10.1167/iovs.63.13.6] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
Abstract
Purpose Hyaluronan (HA) is a major constituent of the extracellular matrix (ECM) that has high viscosity and is essential for maintaining tissue hydration. In the cornea, HA is enriched in the limbal region and is a key component of the limbal epithelial stem cell niche. HA is upregulated after injury participating in the formation of the provisional matrix, and has a key role in regulating the wound healing process. This study investigated whether changes in the distribution of HA before and after injury affects the biomechanical properties of the cornea in vivo. Methods Corneas of wild-type (wt) mice and mice lacking enzymes involved in the biosynthesis of HA were analyzed before, immediately after, and 7 and 14 days after a corneal alkali burn (AB). The corneas were evaluated using both a ring light and fluorescein stain by in vivo confocal microscopy, optical coherence elastography (OCE), and immunostaining of corneal whole mounts. Results Our results show that wt mice and mice lacking HA synthase (Has)1 and 3 present an increase in corneal stiffness 7 and 14 days after AB without a significant increase in HA expression and absence of scarring at 14 days after AB. In contrast, mice lacking Has2 present a significant decrease in corneal stiffness, with a significant increase in HA expression and scarring at 14 days after AB. Conclusions Our findings show that the mechanical properties of the cornea are significantly modulated by changes in HA distribution following alkali burn.
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Affiliation(s)
- Xiao Lin
- College of Optometry, University of Houston, Houston, Texas, United States
| | - Taye Mekonnen
- Department of Biomedical Engineering, University of Houston, Houston, Texas, United States
| | - Sudhir Verma
- College of Optometry, University of Houston, Houston, Texas, United States,Department of Zoology, Deen Dayal Upadhyaya College, University of Delhi, Delhi, India
| | | | - Manmohan Singh
- Department of Biomedical Engineering, University of Houston, Houston, Texas, United States
| | - Salavat R. Aglyamov
- Department of Mechanical Engineering, University of Houston, Houston, Texas, United States
| | - Tarsis F. Gesteira
- College of Optometry, University of Houston, Houston, Texas, United States
| | - Kirill V. Larin
- Department of Biomedical Engineering, University of Houston, Houston, Texas, United States
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Mekonnen T, Lin X, Zevallos-Delgado C, Singh M, Aglyamov SR, Coulson-Thomas V, Larin KV. Longitudinal assessment of the effect of alkali burns on corneal biomechanical properties using optical coherence elastography. J Biophotonics 2022; 15:e202200022. [PMID: 35460537 PMCID: PMC11057918 DOI: 10.1002/jbio.202200022] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/29/2022] [Revised: 03/29/2022] [Accepted: 04/22/2022] [Indexed: 06/14/2023]
Abstract
Eye injury due to alkali burn is a severe ocular trauma that can profoundly affect corneal structure and function, including its biomechanical properties. Here, we assess the changes in the mechanical behavior of mouse corneas in response to alkali-induced injury by conducting longitudinal measurements using optical coherence elastography (OCE). A non-contact air-coupled ultrasound transducer was used to induce elastic waves in control and alkali-injured mouse corneas in vivo, which were imaged with phase-sensitive optical coherence tomography. Corneal mechanical properties were estimated using a modified Rayleigh-Lamb wave model, and results show that Young's modulus of alkali-burned corneas were significantly greater than that of their healthy counterparts on days 7 (p = 0.029) and 14 (p = 0.026) after injury. These findings, together with the changes in the shear viscosity coefficient postburn, indicate that the mechanical properties of the alkali-burned cornea are significantly modulated during the wound healing process.
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Affiliation(s)
- Taye Mekonnen
- Department of Biomedical Engineering, University of Houston, 3517 Cullen Blvd., Room 2027, Houston, TX 77204, USA
| | - Xiao Lin
- College of Optometry, University of Houston, 4901 Calhoun Road, Houston, TX 77204‑2020, USA
| | - Christian Zevallos-Delgado
- Department of Biomedical Engineering, University of Houston, 3517 Cullen Blvd., Room 2027, Houston, TX 77204, USA
| | - Manmohan Singh
- Department of Biomedical Engineering, University of Houston, 3517 Cullen Blvd., Room 2027, Houston, TX 77204, USA
| | - Salavat R. Aglyamov
- Department of Mechanical Engineering, University of Houston, Houston, TX 77204, USA
| | - Vivien Coulson-Thomas
- College of Optometry, University of Houston, 4901 Calhoun Road, Houston, TX 77204‑2020, USA
| | - Kirill V. Larin
- Department of Biomedical Engineering, University of Houston, 3517 Cullen Blvd., Room 2027, Houston, TX 77204, USA
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Zvietcovich F, Nair A, Singh M, Aglyamov SR, Twa MD, Larin KV. In vivo assessment of corneal biomechanics under a localized cross-linking treatment using confocal air-coupled optical coherence elastography. Biomed Opt Express 2022; 13:2644-2654. [PMID: 35774330 PMCID: PMC9203097 DOI: 10.1364/boe.456186] [Citation(s) in RCA: 13] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/15/2022] [Revised: 03/19/2022] [Accepted: 03/20/2022] [Indexed: 05/25/2023]
Abstract
The localized application of the riboflavin/UV-A collagen cross-linking (UV-CXL) corneal treatment has been proposed to concentrate the stiffening process only in the compromised regions of the cornea by limiting the epithelium removal and irradiation area. However, current clinical screening devices dedicated to measuring corneal biomechanics cannot provide maps nor spatial-dependent changes of elasticity in corneas when treated locally with UV-CXL. In this study, we leverage our previously reported confocal air-coupled ultrasonic optical coherence elastography (ACUS-OCE) probe to study local changes of corneal elasticity in three cases: untreated, half-CXL-treated, and full-CXL-treated in vivo rabbit corneas (n = 8). We found a significant increase of the shear modulus in the half-treated (>450%) and full-treated (>650%) corneal regions when compared to the non-treated cases. Therefore, the ACUS-OCE technology possesses a great potential in detecting spatially-dependent mechanical properties of the cornea at multiple meridians and generating elastography maps that are clinically relevant for patient-specific treatment planning and monitoring of UV-CXL procedures.
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Affiliation(s)
- Fernando Zvietcovich
- Department of Biomedical Engineering, University of Houston, Houston, Texas 77204, USA
- Department of Engineering, Pontificia Universidad Catolica del Peru, San Miguel, Lima 15088, Peru
| | - Achuth Nair
- Department of Biomedical Engineering, University of Houston, Houston, Texas 77204, USA
| | - Manmohan Singh
- Department of Biomedical Engineering, University of Houston, Houston, Texas 77204, USA
| | - Salavat R. Aglyamov
- Department of Mechanical Engineering, University of Houston, Houston, Texas 77204, USA
| | - Michael D. Twa
- College of Optometry, University of Houston, Houston, Texas 77204, USA
| | - Kirill V. Larin
- Department of Biomedical Engineering, University of Houston, Houston, Texas 77204, USA
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Nair A, Singh M, Aglyamov SR, Larin KV. Multimodal Heartbeat and Compression Optical Coherence Elastography for Mapping Corneal Biomechanics. Front Med (Lausanne) 2022; 9:833597. [PMID: 35479957 PMCID: PMC9037093 DOI: 10.3389/fmed.2022.833597] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/11/2021] [Accepted: 02/28/2022] [Indexed: 11/13/2022] Open
Abstract
The biomechanical properties of the cornea have a profound influence on the health, structural integrity, and function of the eye. Understanding these properties may be critical for diagnosis and identifying disease pathogenesis. This work demonstrates how two different elastography techniques can be combined for a multimodal approach to measuring corneal biomechanical properties. Heartbeat optical coherence elastography (Hb-OCE) and compression OCE were performed simultaneously to measure the stiffness of the cornea in an in vivo rabbit model. Measurements were further performed after collagen crosslinking to demonstrate how the combined technique can be used to measure changes in corneal stiffness and map mechanical contrast. The results of this work further suggest that measurements from Hb-OCE and compression OCE are comparable, meaning that Hb-OCE and compression OCE may be used interchangeably despite distinct differences in both techniques.
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Affiliation(s)
- Achuth Nair
- Biomedical Engineering, University of Houston, Houston TX, United States
| | - Manmohan Singh
- Biomedical Engineering, University of Houston, Houston TX, United States
| | | | - Kirill V. Larin
- Biomedical Engineering, University of Houston, Houston TX, United States
- Molecular Physiology and Biophysics, Baylor College of Medicine, Houston, TX, United States
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12
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Ambekar YS, Singh M, Schill AW, Zhang J, Zevallos-Delgado C, Khajavi B, Aglyamov SR, Finnell RH, Scarcelli G, Larin KV. Multimodal imaging system combining optical coherence tomography and Brillouin microscopy for neural tube imaging. Opt Lett 2022; 47:1347-1350. [PMID: 35290310 PMCID: PMC9088521 DOI: 10.1364/ol.453996] [Citation(s) in RCA: 9] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/21/2022] [Accepted: 02/03/2022] [Indexed: 06/14/2023]
Abstract
To understand the dynamics of tissue stiffness during neural tube formation and closure in a murine model, we have developed a multimodal, coaligned imaging system combining optical coherence tomography (OCT) and Brillouin microscopy. Brillouin microscopy can map the longitudinal modulus of tissue but cannot provide structural images. Thus, it is limited for imaging dynamic processes such as neural tube formation and closure. To overcome this limitation, we have combined Brillouin microscopy and OCT in one coaligned instrument. OCT provided depth-resolved structural imaging with a micrometer-scale spatial resolution to guide stiffness mapping by Brillouin modality. 2D structural and Brillouin frequency shift maps were acquired of mouse embryos at gestational day (GD) 8.5, 9.5, and 10.5 with the multimodal system. The results demonstrate the capability of the system to obtain structural and stiffness information simultaneously.
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Affiliation(s)
| | - Manmohan Singh
- Department of Biomedical Engineering, University of Houston, Houston, Texas, USA
| | - Alexander W. Schill
- Department of Biomedical Engineering, University of Houston, Houston, Texas, USA
| | - Jitao Zhang
- Department of Biomedical Engineering, Wayne State University, Detroit, Michigan, USA
| | | | - Behzad Khajavi
- Department of Biomedical Engineering, University of Houston, Houston, Texas, USA
| | - Salavat R. Aglyamov
- Department of Mechanical Engineering, University of Houston, Houston, Texas, USA
| | - Richard H. Finnell
- Departments of Molecular and Cell Biology, Molecular and Human Genetics, and Medicine, Baylor College of Medicine, Houston, Texas, USA
| | - Giuliano Scarcelli
- Fischell Department of Bioengineering, University of Maryland, College Park, Maryland, USA
| | - Kirill V. Larin
- Department of Biomedical Engineering, University of Houston, Houston, Texas, USA
- Department of Molecular Physiology and Biophysics, Baylor College of Medicine, Houston, Texas, USA
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Singh M, Schill AW, Nair A, Aglyamov SR, Larina IV, Larin KV. Ultra-fast dynamic line-field optical coherence elastography. Opt Lett 2021; 46:4742-4744. [PMID: 34598188 PMCID: PMC9121022 DOI: 10.1364/ol.435278] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/25/2021] [Accepted: 08/20/2021] [Indexed: 05/12/2023]
Abstract
In this work, we present an ultra-fast line-field optical coherence elastography system (LF-OCE) with an 11.5 MHz equivalent A-line rate. The system was composed of a line-field spectral domain optical coherence tomography system based on a supercontinuum light source, Michelson-type interferometer, and a high-speed 2D spectrometer. The system performed ultra-fast imaging of elastic waves in tissue-mimicking phantoms of various elasticities. The results corroborated well with mechanical testing. Following validation, LF-OCE measurements were made in in situ and in in vivo rabbit corneas under various conditions. The results show the capability of the system to rapidly image elastic waves in tissues.
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Affiliation(s)
- Manmohan Singh
- Biomedical Engineering, University of Houston, 3517 Cullen Blvd., Room 2027, Houston, Texas 77204, USA
| | - Alexander W. Schill
- Biomedical Engineering, University of Houston, 3517 Cullen Blvd., Room 2027, Houston, Texas 77204, USA
| | - Achuth Nair
- Biomedical Engineering, University of Houston, 3517 Cullen Blvd., Room 2027, Houston, Texas 77204, USA
| | - Salavat R. Aglyamov
- Mechanical Engineering, University of Houston, 4726 Calhoun Rd., N207 Engineering Building 1, Houston, Texas 77204, USA
| | - Irina V. Larina
- Molecular Physiology and Biophysics, Baylor College of Medicine, 1 Baylor Plaza, Houston, Texas 77030, USA
| | - Kirill V. Larin
- Biomedical Engineering, University of Houston, 3517 Cullen Blvd., Room 2027, Houston, Texas 77204, USA
- Molecular Physiology and Biophysics, Baylor College of Medicine, 1 Baylor Plaza, Houston, Texas 77030, USA
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Zvietcovich F, Singh M, Ambekar YS, Aglyamov SR, Twa MD, Larin KV. Micro Air-Pulse Spatial Deformation Spreading Characterizes Degree of Anisotropy in Tissues. IEEE J Sel Top Quantum Electron 2021; 27:6800810. [PMID: 33994766 PMCID: PMC8117953 DOI: 10.1109/jstqe.2020.3038633] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/04/2023]
Abstract
In optical coherence elastography (OCE), air-pulse stimulation has been widely used to produce propagation of mechanical waves for elastic characterization of tissues. In this paper, we propose the use of spatial deformation spreading (SDS) on the surface of samples produced by air-pulse stimulation for the OCE of transverse isotropic tissues. Experiments in isotropic tissue-mimicking phantoms and anisotropic chicken tibialis muscle were conducted using a spectral-domain optical coherence tomography system synchronized with a confocal air-pulse stimulation. SDS measurements were compared with wave speeds values calculated at different propagation angles. We found an approximately linear relationship between shear wave speed and SDS in isotropic phantoms, which was confirmed with predictions made by the numerical integration of a wave propagation model. Experimental measurements in chicken muscle show a good agreement between SDS and surface wave speed taken along and across the axis of symmetry of the tissues, also called degree of anisotropy. In summary, these results demonstrated the capabilities of SDS produced by the air-pulse technique in measuring the shear elastic anisotropy of transverse isotropic tissues.
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Affiliation(s)
- Fernando Zvietcovich
- Department of Biomedical Engineering, University of Houston, Houston, TX 77204 USA
| | - Manmohan Singh
- Department of Biomedical Engineering, University of Houston, Houston, TX 77204 USA
| | - Yogeshwari S Ambekar
- Department of Biomedical Engineering, University of Houston, Houston, TX 77204 USA
| | - Salavat R Aglyamov
- Department of Mechanical Engineering, University of Houston, Houston, TX 77204 USA
| | - Michael D Twa
- College of Optometry, University of Houston, Houston, TX 77204 USA
| | - Kirill V Larin
- Department of Biomedical Engineering, University of Houston, Houston, TX 77204 USA
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Rippy JR, Singh M, Aglyamov SR, Larin KV. Ultrasound Shear Wave Elastography and Transient Optical Coherence Elastography: Side-by-Side Comparison of Repeatability and Accuracy. IEEE Open J Eng Med Biol 2021; 2:179-186. [PMID: 34179823 PMCID: PMC8224461 DOI: 10.1109/ojemb.2021.3075569] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
Objective: We compare the repeatability and accuracy of ultrasound shear wave elastography (USE) and transient optical coherence elastography (OCE). Methods: Elastic wave speed in gelatin phantoms and chicken breast was measured with USE and OCE and compared with uniaxial mechanical compression testing. Intra- and Inter-repeatability were analyzed using Bland-Altman plots and intraclass correlation coefficients (ICC). Results: OCE and USE differed from uniaxial testing by a mean absolute percent error of 8.92% and 16.9%, respectively, across eight phantoms of varying stiffness. Upper and lower limits of agreement for intrasample repeatability for USE and OCE were ±0.075 m/s and −0.14 m/s and 0.13 m/s, respectively. OCE and USE both had ICCs of 0.9991. In chicken breast, ICC for USE was 0.9385 and for OCE was 0.9924. Conclusion: OCE and USE can detect small speed changes and give comparable measurements. These measurements correspond well with uniaxial testing.
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Abstract
Assessing the biomechanical properties of the cornea is crucial for detecting the onset and progression of eye diseases. In this work, we demonstrate the application of compression-based optical coherence elastography (OCE) to measure the biomechanical properties of the cornea under various conditions, including validation in an in situ rabbit model and a demonstration of feasibility for in vivo measurements. Our results show a stark increase in the stiffness of the corneas as IOP was increased. Moreover, UV-A/riboflavin corneal collagen crosslinking (CXL) also dramatically increased the stiffness of the corneas. The results were consistent across 4 different scenarios (whole CXL in situ, partial CXL in situ, whole CXL in vivo, and partial CXL in vivo), emphasizing the reliability of compression OCE to measure corneal biomechanical properties and its potential for clinical applications.
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Affiliation(s)
- Manmohan Singh
- Department of Biomedical Engineering, University of Houston, 3517 Cullen Blvd., Room 2027, Houston, TX 77204, USA
| | - Achuth Nair
- Department of Biomedical Engineering, University of Houston, 3517 Cullen Blvd., Room 2027, Houston, TX 77204, USA
| | - Salavat R. Aglyamov
- Department of Mechanical Engineering, University of Houston, 4726 Calhoun Rd., Room N207, Houston, TX 77204, USA
| | - Kirill V. Larin
- Department of Biomedical Engineering, University of Houston, 3517 Cullen Blvd., Room 2027, Houston, TX 77204, USA
- Molecular Physiology and Biophysics, Baylor College of Medicine, One Baylor Plaza, BCM335, Houston, TX 77030, USA
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Abstract
SIGNIFICANCE A novel imaging technology, dynamic optical coherence elastography (OCE), was adapted for clinical noninvasive measurements of corneal biomechanics. PURPOSE Determining corneal biomechanical properties is a long-standing challenge. Elasticity imaging methods have recently been developed and applied for clinical evaluation of soft tissues in cancer detection, atherosclerotic plaque evaluation, surgical guidance, and more. Here, we describe the use of dynamic OCE to characterize mechanical wave propagation in the human cornea in vivo, thus providing a method for clinical determination of corneal biomechanical properties. METHODS High-resolution phase-sensitive optical coherence tomography imaging was combined with microliter air-pulse tissue stimulation to perform dynamic elasticity measurements in 18 eyes of nine participants. Low-pressure (0.1 mmHg), spatiotemporally discreet (150 μm, 800 μs) tissue stimulation produced submicron-scale tissue deformations that were measured at multiple positions over a 1-mm2 area. Surface wave velocity was measured and used to determine tissue stiffness. Elastic wave propagation velocity was measured and evaluated as a function of IOP and central corneal thickness. RESULTS Submicron corneal surface displacement amplitude (range, 0.005 to 0.5 μm) responses were measured with high sensitivity (0.24 nm). Corneal elastic wave velocity ranged from 2.4 to 4.2 m/s (mean, 3.5; 95% confidence interval, 3.2 to 3.8 m/s) and was correlated with central corneal thickness (r = 0.64, P < .001) and IOP (r = 0.52, P = .02). CONCLUSIONS Phase-sensitive optical coherence tomography imaging combined with microliter air-pulse mechanical tissue stimulation has sufficient detection sensitivity to observe submicron elastic wave propagation in corneal tissue. These measurements enable in vivo corneal stiffness determinations that will be further studied for use with disease detection and for monitoring clinical interventions.
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Affiliation(s)
- Gongpu Lan
- School of Physics and Optoelectronic Engineering, Foshan University, Foshan, Guangdong, China
- University of Houston College of Optometry, Houston, Texas
| | | | - Kirill V. Larin
- Department of Biomedical Engineering, University of Houston, Houston, Texas
| | - Michael D. Twa
- University of Houston College of Optometry, Houston, Texas
- School of Optometry, University of Alabama at Birmingham, Birmingham, Alabama
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Zvietcovich F, Nair A, Ambekar YS, Singh M, Aglyamov SR, Twa MD, Larin KV. Confocal air-coupled ultrasonic optical coherence elastography probe for quantitative biomechanics. Opt Lett 2020; 45:6567-6570. [PMID: 33258863 PMCID: PMC10041740 DOI: 10.1364/ol.410593] [Citation(s) in RCA: 19] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/14/2023]
Abstract
We present an air-coupled ultrasonic radiation force probe co-focused with a phase-sensitive optical coherence tomography (OCT) system for quantitative wave-based elastography. A custom-made 1 MHz spherically focused piezoelectric transducer with a concentric 10 mm wide circular opening allowed for confocal micro-excitation of waves and phase-sensitive OCT imaging. Phantom studies demonstrated the capabilities of this probe to produce quasi-harmonic excitation up to 4 kHz for generation of elastic waves. Experimental results in ocular tissues showed highly detailed 2D and 3D elasticity mapping using this approach with great potential for clinical translation.
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Affiliation(s)
- Fernando Zvietcovich
- Department of Biomedical Engineering, University of Houston, Houston, Texas 77204, USA
| | - Achuth Nair
- Department of Biomedical Engineering, University of Houston, Houston, Texas 77204, USA
| | - Yogeshwari S. Ambekar
- Department of Biomedical Engineering, University of Houston, Houston, Texas 77204, USA
| | - Manmohan Singh
- Department of Biomedical Engineering, University of Houston, Houston, Texas 77204, USA
| | - Salavat R. Aglyamov
- Department of Mechanical Engineering, University of Houston, Houston, Texas 77204, USA
| | - Michael D. Twa
- College of Optometry, University of Houston, Houston, Texas 77204, USA
| | - Kirill V. Larin
- Department of Biomedical Engineering, University of Houston, Houston, Texas 77204, USA
- Corresponding author:
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Zvietcovich F, Nair A, Singh M, Aglyamov SR, Twa MD, Larin KV. Dynamic Optical Coherence Elastography of the Anterior Eye: Understanding the Biomechanics of the Limbus. Invest Ophthalmol Vis Sci 2020; 61:7. [PMID: 33141893 PMCID: PMC7645208 DOI: 10.1167/iovs.61.13.7] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022] Open
Abstract
Purpose Currently, the biomechanical properties of the corneo-scleral limbus when the eye-globe deforms are largely unknown. The purpose of this study is to evaluate changes in elasticity of the cornea, sclera, and limbus when subjected to different intraocular pressures (IOP) using wave-based optical coherence elastography (OCE). Special attention was given to the elasticity changes of the limbal region with respect to the elasticity variations in the neighboring corneal and scleral regions. Methods Continuous harmonic elastic waves (800 Hz) were mechanically induced in the sclera near the corneo-sclera limbus of in situ porcine eye-globes (n = 8). Wave propagation was imaged using a phase-sensitive optical coherence tomography system (PhS-OCT). The eyes were subjected to five different IOP-levels (10, 15, 20, 30, and 40 mm Hg), and spatially distributed propagation velocities were calculated along corneal, limbal, and scleral regions. Finite element analysis (FEA) of the same regions under the same excitation conditions were conducted for further validation of results. Results FEA demonstrated that the stiffness of the heterogeneous cornea-limbus-sclera transition can be characterized by phase velocity measurements of the elastic waves produced at 800 Hz in the anterior eye. Experimental results revealed that the wave speed in the limbus (cL = 6.5 m/s) is between the cornea (cc = 2.9 m/s) and sclera (cs = 10.0 m/s) at a physiological IOP level (15 mm Hg) and rapidly increases as the IOP level is increased, even surpassing the wave speed in the sclera. Finally, the change in elastic wave speed in the limbus (ΔcL∼18.5 m/s) was greater than in the cornea (Δcc ∼12.6 m/s) and sclera (Δcs∼8.1 m/s) for the same change in IOP. Conclusions We demonstrated that wave-based OCE can be utilized to assess limbus biomechanical properties. Moreover, experimental evidence showed that the corneo-scleral limbus is highly nonlinear compared to the cornea and sclera when the eye-globe is deformed by an increase of IOP. This may suggest that the limbus has enough structural flexibility to stabilize anterior eye shape during IOP changes.
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Affiliation(s)
- Fernando Zvietcovich
- Department of Biomedical Engineering, University of Houston, Houston, Texas, United States
| | - Achuth Nair
- Department of Biomedical Engineering, University of Houston, Houston, Texas, United States
| | - Manmohan Singh
- Department of Biomedical Engineering, University of Houston, Houston, Texas, United States
| | - Salavat R Aglyamov
- Department of Mechanical Engineering, University of Houston, Houston, Texas, United States
| | - Michael D Twa
- College of Optometry, University of Houston, Houston, Texas, United States
| | - Kirill V Larin
- Department of Biomedical Engineering, University of Houston, Houston, Texas, United States
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Nair A, Singh M, Aglyamov SR, Larin KV. Heartbeat OCE: corneal biomechanical response to simulated heartbeat pulsation measured by optical coherence elastography. J Biomed Opt 2020; 25:1-9. [PMID: 32372574 PMCID: PMC7199791 DOI: 10.1117/1.jbo.25.5.055001] [Citation(s) in RCA: 18] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/16/2020] [Accepted: 04/24/2020] [Indexed: 05/04/2023]
Abstract
SIGNIFICANCE It is generally agreed that the corneal mechanical properties are strongly linked to many eye diseases and could be used to assess disease progression and response to therapies. Elastography is the most notable method of assessing corneal mechanical properties, but it generally requires some type of external excitation to induce a measurable displacement in the tissue. AIM We present Heartbeat Optical Coherence Elastography (Hb-OCE), a truly passive method that can measure the elasticity of the cornea based on intrinsic corneal displacements induced by the heartbeat. APPROACH Hb-OCE measurements were performed in untreated and UV-A/riboflavin cross-linked porcine corneas ex vivo, and a distinct difference in strain was detected. Furthermore, a partially cross-linked cornea was also assessed, and the treated and untreated areas were similarly distinguished. RESULTS Our results suggest that Hb-OCE can spatially map displacements in the cornea induced by small fluctuations in intraocular pressure, similar to what is induced by the heartbeat. CONCLUSIONS The described technique opens the possibility for completely passive and noncontact in vivo assessment of corneal stiffness.
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Affiliation(s)
- Achuth Nair
- University of Houston, Department of Biomedical Engineering, Houston, Texas, United States
| | - Manmohan Singh
- University of Houston, Department of Biomedical Engineering, Houston, Texas, United States
| | - Salavat R. Aglyamov
- University of Houston, Department of Mechanical Engineering, Houston, Texas, United States
| | - Kirill V. Larin
- University of Houston, Department of Biomedical Engineering, Houston, Texas, United States
- Address all correspondence to Kirill V. Larin, E-mail:
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Ambekar YS, Singh M, Zhang J, Nair A, Aglyamov SR, Scarcelli G, Larin KV. Multimodal quantitative optical elastography of the crystalline lens with optical coherence elastography and Brillouin microscopy. Biomed Opt Express 2020; 11:2041-2051. [PMID: 32341865 PMCID: PMC7173892 DOI: 10.1364/boe.387361] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/03/2020] [Revised: 02/27/2020] [Accepted: 03/05/2020] [Indexed: 05/03/2023]
Abstract
Assessing the biomechanical properties of the crystalline lens can provide crucial information for diagnosing disease and guiding precision therapeutic interventions. Existing noninvasive methods have been limited to global measurements. Here, we demonstrate the quantitative assessment of the elasticity of crystalline lens with a multimodal optical elastography technique, which combines dynamic wave-based optical coherence elastography (OCE) and Brillouin microscopy to overcome the drawbacks of individual modalities. OCE can provide direct measurements of tissue elasticity rapidly and quantitatively, but it is a challenge to image transparent samples such as the lens because this technique relies on backscattered light. On the other hand, Brillouin microscopy can map the longitudinal modulus with micro-scale resolution in transparent samples. However, the relationship between Brillouin-deduced modulus and Young's modulus is not straightforward and sample dependent. By combining these two techniques, we can calibrate Brillouin measurements with OCE, based on the same sample, allowing us to completely map the Young's modulus of the crystalline lens. The combined system was first validated with tissue-mimicking gelatin phantoms of varying elasticities (N = 9). The OCE data was used to calibrate the Brillouin shift measurements and subsequently map the Young's modulus of the phantoms. After validation, OCE and Brillouin measurements were performed on ex-vivo porcine lenses (N = 6), and the Young's modulus of the lenses was spatially mapped. The results show a strong correlation between Young's moduli measured by OCE and longitudinal moduli measured by Brillouin microscopy. The correlation coefficient R was 0.98 for the phantoms and 0.94 for the lenses, respectively. The mean Young's modulus of the anterior and posterior lens was 1.98 ± 0.74 kPa and 2.93 ± 1.13 kPa, respectively, and the Young's modulus of the lens nucleus was 11.90 ± 2.94 kPa. The results presented in this manuscript open a new way for truly quantitative biomechanical mapping of optically transparent (or low scattering) tissues in 3D.
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Affiliation(s)
| | - Manmohan Singh
- Department of Biomedical Engineering, University of Houston, Houston, TX 77030, USA
| | - Jitao Zhang
- Fischell Department of Bioengineering, University of Maryland, College Park, MD 20742, USA
| | - Achuth Nair
- Department of Biomedical Engineering, University of Houston, Houston, TX 77030, USA
| | - Salavat R. Aglyamov
- Department of Mechanical Engineering, University of Houston, Houston, TX 77030, USA
| | - Giuliano Scarcelli
- Fischell Department of Bioengineering, University of Maryland, College Park, MD 20742, USA
| | - Kirill V. Larin
- Department of Biomedical Engineering, University of Houston, Houston, TX 77030, USA
- Molecular Physiology and Biophysics, Baylor College of Medicine, Houston, TX 77030, USA
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Vekilov DP, Singh M, Aglyamov SR, Larin KV, Grande-Allen KJ. Mapping the spatial variation of mitral valve elastic properties using air-pulse optical coherence elastography. J Biomech 2019; 93:52-59. [PMID: 31300156 PMCID: PMC10575695 DOI: 10.1016/j.jbiomech.2019.06.015] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/19/2019] [Revised: 05/18/2019] [Accepted: 06/14/2019] [Indexed: 10/26/2022]
Abstract
The mitral valve is a highly heterogeneous tissue composed of two leaflets, anterior and posterior, whose unique composition and regional differences in material properties are essential to overall valve function. While mitral valve mechanics have been studied for many decades, traditional testing methods limit the spatial resolution of measurements and can be destructive. Optical coherence elastography (OCE) is an emerging method for measuring viscoelastic properties of tissues in a noninvasive, nondestructive manner. In this study, we employed air-pulse OCE to measure the spatial variation in mitral valve elastic properties with micro-scale resolution at 1 mm increments along the radial length of the leaflets. We analyzed differences between the leaflets, as well as between regions of the valve. We found that the anterior leaflet has a higher elastic wave velocity, which is reported as a surrogate for stiffness, than the posterior leaflet, most notably at the annular edge of the sample. In addition, we found a spatial elastic gradient in the anterior leaflet, where the annular edge was found to have a greater elastic wave velocity than the free edge. This gradient was less pronounced in the posterior leaflet. These patterns were confirmed using established uniaxial tensile testing methods. Overall, the anterior leaflet was stiffer and had greater heterogeneity in its mechanical properties than the posterior leaflet. This study measures differences between the two mitral leaflets with greater resolution than previously feasible and demonstrates a method that may be suitable for assessing valve mechanics following repair or during the engineering of synthetic valve replacements.
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Affiliation(s)
| | - Manmohan Singh
- University of Houston, Department of Biomedical Engineering, Houston, TX, United States
| | - Salavat R Aglyamov
- University of Houston, Department of Mechanical Engineering, Houston, TX, United States; University of Texas at Austin, Department of Biomedical Engineering, Austin, TX, United States
| | - Kirill V Larin
- University of Houston, Department of Biomedical Engineering, Houston, TX, United States
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Zhang H, Wu C, Singh M, Nair A, Aglyamov SR, Larin KV. Optical coherence elastography of cold cataract in porcine lens. J Biomed Opt 2019; 24:1-7. [PMID: 30864348 PMCID: PMC6444576 DOI: 10.1117/1.jbo.24.3.036004] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/05/2018] [Accepted: 02/19/2019] [Indexed: 05/08/2023]
Abstract
Cataract is one of the most prevalent causes of blindness around the world. Understanding the mechanisms of cataract development and progression is important for clinical diagnosis and treatment. Cold cataract has proven to be a robust model for cataract formation that can be easily controlled in the laboratory. There is evidence that the biomechanical properties of the lens can be significantly changed by cataract. Therefore, early detection of cataract, as well as evaluation of therapies, could be guided by characterization of lenticular biomechanical properties. In this work, we utilized optical coherence elastography (OCE) to monitor the changes in biomechanical properties of ex vivo porcine lenses during formation of cold cataract. Elastic waves were induced in the porcine lenses by a focused micro air-pulse while the lenses were cooled, and the elastic wave velocity was translated to Young's modulus of the lens. The results show an increase in the stiffness of the lens due to formation of the cold cataract (from 11.3 ± 3.4 to 21.8 ± 7.8 kPa). These results show a relation between lens opacity and stiffness and demonstrate that OCE can assess lenticular biomechanical properties and may be useful for detecting and potentially characterizing cataracts.
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Affiliation(s)
- Hongqiu Zhang
- University of Houston, Department of Biomedical Engineering, Houston, Texas, United States
| | - Chen Wu
- University of Houston, Department of Biomedical Engineering, Houston, Texas, United States
| | - Manmohan Singh
- University of Houston, Department of Biomedical Engineering, Houston, Texas, United States
| | - Achuth Nair
- University of Houston, Department of Biomedical Engineering, Houston, Texas, United States
| | - Salavat R. Aglyamov
- University of Houston, Department of Mechanical Engineering, Houston, Texas, United States
- University of Texas at Austin, Department of Biomedical Engineering, Austin, Texas, United States
| | - Kirill V. Larin
- University of Houston, Department of Biomedical Engineering, Houston, Texas, United States
- Address all correspondence to Kirill V. Larin, E-mail:
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Wu C, Aglyamov SR, Han Z, Singh M, Liu CH, Larin KV. Assessing the biomechanical properties of the porcine crystalline lens as a function of intraocular pressure with optical coherence elastography. Biomed Opt Express 2018; 9:6455-6466. [PMID: 31065442 PMCID: PMC6491010 DOI: 10.1364/boe.9.006455] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/10/2018] [Revised: 11/11/2018] [Accepted: 11/14/2018] [Indexed: 05/04/2023]
Abstract
In this study, we investigated the relationship between the biomechanical properties of the crystalline lens and intraocular pressure (IOP) using a confocal acoustic radiation force (ARF) and phase-sensitive optical coherence elastography (OCE) system. ARF induced a small displacement at the apex of porcine lenses in situ at various artificially controlled IOPs. Maximum displacement, relaxation rate, and Young's modulus were utilized to assess the stiffness of the crystalline lens. The results showed that the stiffness of the crystalline increased as IOP increased, but the lens stiffening was not as significant as the stiffening of other ocular tissues such as the cornea and the sclera. A mechanical hysteresis in the lens was also observed while cycling IOP, indicating that the viscoelastic response of the lens is crucial to fully understanding its biomechanical properties.
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Affiliation(s)
- Chen Wu
- Department of Biomedical Engineering, University of Houston, Houston, TX 77204, USA
| | - Salavat R Aglyamov
- Department of Mechanical Engineering, University of Houston, Houston, TX 77204, USA
- Department of Biomedical Engineering, University of Texas, Austin, TX 78712, USA
| | - Zhaolong Han
- Department of Biomedical Engineering, University of Houston, Houston, TX 77204, USA
- School of Naval Architecture, Ocean and Civil Engineering, Shanghai Jiao Tong University, Shanghai 200240, China
| | - Manmohan Singh
- Department of Biomedical Engineering, University of Houston, Houston, TX 77204, USA
| | - Chih-Hao Liu
- Department of Biomedical Engineering, University of Houston, Houston, TX 77204, USA
| | - Kirill V Larin
- Department of Biomedical Engineering, University of Houston, Houston, TX 77204, USA
- Interdisciplinary Laboratory of Biophotonics, Tomsk State University, Tomsk, Russia
- Molecular Physiology and Biophysics, Baylor College of Medicine, TX 77584, USA
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Singh M, Han Z, Li J, Vantipalli S, Aglyamov SR, Twa MD, Larin KV. Quantifying the effects of hydration on corneal stiffness with noncontact optical coherence elastography. J Cataract Refract Surg 2018; 44:1023-1031. [PMID: 30049567 DOI: 10.1016/j.jcrs.2018.03.036] [Citation(s) in RCA: 25] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/31/2017] [Revised: 02/17/2018] [Accepted: 03/20/2018] [Indexed: 01/08/2023]
Abstract
PURPOSE To quantify the effects of the hydration state on the Young's modulus of the cornea. SETTING Biomedical Optics Laboratory, University of Houston, Houston, Texas, USA. DESIGN Experimental study. METHODS Noncontact, dynamic optical coherence elastography (OCE) measurements were taken of in situ rabbit corneas in the whole eye-globe configuration (n = 10) and at an artificially controlled intraocular pressure of 15 mm Hg. Baseline OCE measurements were taken by topically hydrating the corneas with saline for 1 hour. The corneas were then dehydrated topically with a 20% dextran solution for another hour, and the OCE measurements were repeated. A finite element method was used to quantify the Young's modulus of the corneas based on the OCE measurements. RESULTS The thickness of the corneas shrank considerably after topical addition of the 20% dextran solution (∼680 μm to ∼370 μm), and the OCE-measured elastic-wave speed correspondingly decreased (∼3.2 m/s to ∼2.6 m/s). The finite element method results showed an increase in Young's modulus (500 kPa to 800 kPa) resulting from dehydration and subsequent thinning. CONCLUSION Young's modulus increased significantly as the corneas dehydrated and thinned, showing that corneal geometry and hydration state are critical factors for accurately quantifying corneal biomechanical properties.
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Affiliation(s)
- Manmohan Singh
- From Biomedical Engineering (Singh, Li, Larin) and the College of Optometry (Vantipalli), Mechanical Engineering (Aglyamov), University of Houston, and Molecular Physiology and Biophysics (Larin), Baylor College of Medicine, Houston, Texas, and the School of Optometry (Twa) and Biomedical Engineering (Twa), University of Alabama at Birmingham, Birmingham, Alabama, USA; The School of Naval Architecture (Han), Ocean and Civil Engineering, Shanghai Jiao Tong University, Shanghai, China; Interdisciplinary Laboratory of Biophotonics (Larin), Tomsk State University, Tomsk, Russia
| | - Zhaolong Han
- From Biomedical Engineering (Singh, Li, Larin) and the College of Optometry (Vantipalli), Mechanical Engineering (Aglyamov), University of Houston, and Molecular Physiology and Biophysics (Larin), Baylor College of Medicine, Houston, Texas, and the School of Optometry (Twa) and Biomedical Engineering (Twa), University of Alabama at Birmingham, Birmingham, Alabama, USA; The School of Naval Architecture (Han), Ocean and Civil Engineering, Shanghai Jiao Tong University, Shanghai, China; Interdisciplinary Laboratory of Biophotonics (Larin), Tomsk State University, Tomsk, Russia
| | - Jiasong Li
- From Biomedical Engineering (Singh, Li, Larin) and the College of Optometry (Vantipalli), Mechanical Engineering (Aglyamov), University of Houston, and Molecular Physiology and Biophysics (Larin), Baylor College of Medicine, Houston, Texas, and the School of Optometry (Twa) and Biomedical Engineering (Twa), University of Alabama at Birmingham, Birmingham, Alabama, USA; The School of Naval Architecture (Han), Ocean and Civil Engineering, Shanghai Jiao Tong University, Shanghai, China; Interdisciplinary Laboratory of Biophotonics (Larin), Tomsk State University, Tomsk, Russia
| | - Srilatha Vantipalli
- From Biomedical Engineering (Singh, Li, Larin) and the College of Optometry (Vantipalli), Mechanical Engineering (Aglyamov), University of Houston, and Molecular Physiology and Biophysics (Larin), Baylor College of Medicine, Houston, Texas, and the School of Optometry (Twa) and Biomedical Engineering (Twa), University of Alabama at Birmingham, Birmingham, Alabama, USA; The School of Naval Architecture (Han), Ocean and Civil Engineering, Shanghai Jiao Tong University, Shanghai, China; Interdisciplinary Laboratory of Biophotonics (Larin), Tomsk State University, Tomsk, Russia
| | - Salavat R Aglyamov
- From Biomedical Engineering (Singh, Li, Larin) and the College of Optometry (Vantipalli), Mechanical Engineering (Aglyamov), University of Houston, and Molecular Physiology and Biophysics (Larin), Baylor College of Medicine, Houston, Texas, and the School of Optometry (Twa) and Biomedical Engineering (Twa), University of Alabama at Birmingham, Birmingham, Alabama, USA; The School of Naval Architecture (Han), Ocean and Civil Engineering, Shanghai Jiao Tong University, Shanghai, China; Interdisciplinary Laboratory of Biophotonics (Larin), Tomsk State University, Tomsk, Russia
| | - Michael D Twa
- From Biomedical Engineering (Singh, Li, Larin) and the College of Optometry (Vantipalli), Mechanical Engineering (Aglyamov), University of Houston, and Molecular Physiology and Biophysics (Larin), Baylor College of Medicine, Houston, Texas, and the School of Optometry (Twa) and Biomedical Engineering (Twa), University of Alabama at Birmingham, Birmingham, Alabama, USA; The School of Naval Architecture (Han), Ocean and Civil Engineering, Shanghai Jiao Tong University, Shanghai, China; Interdisciplinary Laboratory of Biophotonics (Larin), Tomsk State University, Tomsk, Russia
| | - Kirill V Larin
- From Biomedical Engineering (Singh, Li, Larin) and the College of Optometry (Vantipalli), Mechanical Engineering (Aglyamov), University of Houston, and Molecular Physiology and Biophysics (Larin), Baylor College of Medicine, Houston, Texas, and the School of Optometry (Twa) and Biomedical Engineering (Twa), University of Alabama at Birmingham, Birmingham, Alabama, USA; The School of Naval Architecture (Han), Ocean and Civil Engineering, Shanghai Jiao Tong University, Shanghai, China; Interdisciplinary Laboratory of Biophotonics (Larin), Tomsk State University, Tomsk, Russia.
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26
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Wang S, Singh M, Tran TT, Leach J, Aglyamov SR, Larina IV, Martin JF, Larin KV. Biomechanical assessment of myocardial infarction using optical coherence elastography. Biomed Opt Express 2018; 9:728-742. [PMID: 29552408 PMCID: PMC5854074 DOI: 10.1364/boe.9.000728] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/13/2017] [Revised: 12/26/2017] [Accepted: 12/27/2017] [Indexed: 05/18/2023]
Abstract
Myocardial infarction (MI) leads to cardiomyocyte loss, impaired cardiac function, and heart failure. Molecular genetic analyses of myocardium in mouse models of ischemic heart disease have provided great insight into the mechanisms of heart regeneration, which is promising for novel therapies after MI. Although biomechanical factors are considered an important aspect in cardiomyocyte proliferation, there are limited methods for mechanical assessment of the heart in the mouse MI model. This prevents further understanding the role of tissue biomechanics in cardiac regeneration. Here we report optical coherence elastography (OCE) of the mouse heart after MI. Surgical ligation of the left anterior descending coronary artery was performed to induce an infarction in the heart. Two OCE methods with assessment of the direction-dependent elastic wave propagation and the spatially resolved displacement damping provide complementary analyses of the left ventricle. In comparison with sham, the infarcted heart features a fibrotic scar region with reduced elastic wave velocity, decreased natural frequency, and less mechanical anisotropy at the tissue level at the sixth week post-MI, suggesting lower and more isotropic stiffness. Our results indicate that OCE can be utilized for nondestructive biomechanical characterization of MI in the mouse model, which could serve as a useful tool in the study of heart repair.
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Affiliation(s)
- Shang Wang
- Department of Molecular Physiology and Biophysics, Baylor College of Medicine, One Baylor Plaza, Houston, Texas 77030, USA
- Equal contribution
| | - Manmohan Singh
- Department of Biomedical Engineering, University of Houston, 3605 Cullen Boulevard, Houston, Texas 77204, USA
- Equal contribution
| | - Thuy Tien Tran
- Department of Molecular Physiology and Biophysics, Baylor College of Medicine, One Baylor Plaza, Houston, Texas 77030, USA
| | - John Leach
- Department of Molecular Physiology and Biophysics, Baylor College of Medicine, One Baylor Plaza, Houston, Texas 77030, USA
| | - Salavat R. Aglyamov
- Department of Mechanical Engineering, University of Houston, 4726 Calhoun Road, Houston, Texas 77204, USA
| | - Irina V. Larina
- Department of Molecular Physiology and Biophysics, Baylor College of Medicine, One Baylor Plaza, Houston, Texas 77030, USA
| | - James F. Martin
- Department of Molecular Physiology and Biophysics, Baylor College of Medicine, One Baylor Plaza, Houston, Texas 77030, USA
- The Texas Heart Institute, 6770 Bertner Avenue, Houston, Texas 77030, USA
| | - Kirill V. Larin
- Department of Molecular Physiology and Biophysics, Baylor College of Medicine, One Baylor Plaza, Houston, Texas 77030, USA
- Department of Biomedical Engineering, University of Houston, 3605 Cullen Boulevard, Houston, Texas 77204, USA
- Interdisciplinary Laboratory of Biophotonics, Tomsk State University, 36 Lenin Ave., Tomsk 634050, Russia
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Yoon H, Aglyamov SR, Emelianov SY. Dual-Phase Transmit Focusing for Multiangle Compound Shear-Wave Elasticity Imaging. IEEE Trans Ultrason Ferroelectr Freq Control 2017; 64:1439-1449. [PMID: 28708552 PMCID: PMC5668129 DOI: 10.1109/tuffc.2017.2725839] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/12/2023]
Abstract
Shear-wave elasticity imaging (SWEI) enables the quantitative assessment of the mechanical properties of tissue. In SWEI, the effective generation of acoustic radiation force is of paramount importance. Consequently, several research groups have investigated various transmit beamforming and pulse-sequencing methods. To further improve the efficiency of the shear-wave generation, and therefore, to increase the quality of SWEI, we introduce a technique referred to as "multiangle compound SWEI" (MAC-SWEI), which uses simultaneous multiangular push beams created by dual-phase transmit focusing. By applying a constant phase offset on every other element of an array transducer, dual-phase transmit focusing creates both main and grating lobes (i.e., multiangular push beams for pushing) to simultaneously generate shear waves with several wavefront angles. The shear waves propagating at different angles are separated by multidirectional filtering in the frequency domain, leading to the reconstruction of multiple spatially co-registered shear-wave velocity maps. To form a single-elasticity image, these maps are combined, while regions associated with known artifacts created by the push beams are omitted. Overall, we developed and tested the MAC-SWEI method using Field II quantitative simulations and the experiments performed using a programmable ultrasound imaging system. Our results suggest that MAC-SWEI with dual-phase transmit focusing may improve the quality of elasticity maps.
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28
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Singh M, Li J, Han Z, Wu C, Aglyamov SR, Twa MD, Larin KV. Investigating Elastic Anisotropy of the Porcine Cornea as a Function of Intraocular Pressure With Optical Coherence Elastography. J Refract Surg 2017; 32:562-7. [PMID: 27505317 DOI: 10.3928/1081597x-20160520-01] [Citation(s) in RCA: 43] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/21/2016] [Accepted: 04/12/2016] [Indexed: 01/02/2023]
Abstract
PURPOSE To evaluate the elastic anisotropy of porcine corneas at different intraocular pressures (IOPs) using a noncontact optical coherence elastography (OCE) technique. METHODS A focused air-pulse induced low amplitude (≤ 10 µm) elastic waves in fresh porcine corneas (n = 7) in situ in the whole eye globe configuration. A home-built phase-stabilized swept source optical coherence elastography (PhS-SSOCE) system imaged the elastic wave propagation at different stepped radial directions. A closed-loop feedback system was used to artificially control the IOP and the OCE measurements were repeated as the IOP was incrementally increased from 15 to 30 mm Hg in 5-mm Hg increments. RESULTS The OCE measurements demonstrated that the stiffness of the cornea increased as a function of IOP and elastic anisotropy of the cornea became more pronounced at higher IOPs. The standard deviation of the modified planar anisotropy coefficient increased from 0.72 ± 0.42 at an IOP of 15 mm Hg to 1.58 ± 0.40 at 30 mm Hg. CONCLUSIONS The presented noncontact OCE method was capable of detecting and assessing the corneal elastic anisotropy as a function of IOP. Due to the noninvasive nature and small amplitude of the elastic wave, this method may be able to provide further information about corneal health and integrity in vivo. [J Refract Surg. 2016;32(8):562-567.].
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29
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Singh M, Li J, Han Z, Vantipalli S, Liu CH, Wu C, Raghunathan R, Aglyamov SR, Twa MD, Larin KV. Evaluating the Effects of Riboflavin/UV-A and Rose-Bengal/Green Light Cross-Linking of the Rabbit Cornea by Noncontact Optical Coherence Elastography. Invest Ophthalmol Vis Sci 2017; 57:OCT112-20. [PMID: 27409461 PMCID: PMC4968774 DOI: 10.1167/iovs.15-18888] [Citation(s) in RCA: 33] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
Purpose The purpose of this study was to use noncontact optical coherence elastography (OCE) to evaluate and compare changes in biomechanical properties that occurred in rabbit cornea in situ after corneal collagen cross-linking by either of two techniques: ultraviolet-A (UV-A)/riboflavin or rose-Bengal/green light. Methods Low-amplitude (≤10 μm) elastic waves were induced in mature rabbit corneas by a focused air pulse. Elastic wave propagation was imaged by a phase-stabilized swept source OCE (PhS-SSOCE) system. Corneas were then cross-linked by either of two methods: UV-A/riboflavin (UV-CXL) or rose-Bengal/green light (RGX). Phase velocities of the elastic waves were fitted to a previously developed modified Rayleigh-Lamb frequency equation to obtain the viscoelasticity of the corneas before and after the cross-linking treatments. Micro-scale depth-resolved phase velocity distribution revealed the depth-wise heterogeneity of both cross-linking techniques. Results Under standard treatment settings, UV-CXL significantly increased the stiffness of the corneas by ∼47% (P < 0.05), but RGX did not produce statistically significant increases. The shear viscosities were unaffected by either cross-linking technique. The depth-wise phase velocities showed that UV-CXL affected the anterior ∼34% of the corneas, whereas RGX affected only the anterior ∼16% of the corneas. Conclusions UV-CXL significantly strengthens the cornea, whereas RGX does not, and the effects of cross-linking by UV-CXL reach deeper into the cornea than cross-linking effects of RGX under similar conditions.
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Affiliation(s)
- Manmohan Singh
- Department of Biomedical Engineering, University of Houston, Houston, Texas, United States
| | - Jiasong Li
- Department of Biomedical Engineering, University of Houston, Houston, Texas, United States
| | - Zhaolong Han
- Department of Biomedical Engineering, University of Houston, Houston, Texas, United States
| | | | - Chih-Hao Liu
- Department of Biomedical Engineering, University of Houston, Houston, Texas, United States
| | - Chen Wu
- Department of Biomedical Engineering, University of Houston, Houston, Texas, United States
| | - Raksha Raghunathan
- Department of Biomedical Engineering, University of Houston, Houston, Texas, United States
| | - Salavat R Aglyamov
- Department of Biomedical Engineering, University of Texas at Austin, Austin, Texas, United States
| | - Michael D Twa
- School of Optometry, University of Alabama at Birmingham, Birmingham, Alabama, United States
| | - Kirill V Larin
- Department of Biomedical Engineering, University of Houston, Houston, Texas, United States 5Interdisciplinary Laboratory of Biophotonics, Tomsk State University, Tomsk, Russia
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30
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Park S, Yoon H, Larin KV, Emelianov SY, Aglyamov SR. The impact of intraocular pressure on elastic wave velocity estimates in the crystalline lens. Phys Med Biol 2016; 62:N45-N57. [PMID: 27997379 DOI: 10.1088/1361-6560/aa54ef] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
Intraocular pressure (IOP) is believed to influence the mechanical properties of ocular tissues including cornea and sclera. The elastic properties of the crystalline lens have been mainly investigated with regard to presbyopia, the age-related loss of accommodation power of the eye. However, the relationship between the elastic properties of the lens and IOP remains to be established. The objective of this study is to measure the elastic wave velocity, which represents the mechanical properties of tissue, in the crystalline lens ex vivo in response to changes in IOP. The elastic wave velocities in the cornea and lens from seven enucleated bovine globe samples were estimated using ultrasound shear wave elasticity imaging. To generate and then image the elastic wave propagation, an ultrasound imaging system was used to transmit a 600 µs pushing pulse at 4.5 MHz center frequency and to acquire ultrasound tracking frames at 6 kHz frame rate. The pushing beams were separately applied to the cornea and lens. IOP in the eyeballs was varied from 5 to 50 mmHg. The results indicate that while the elastic wave velocity in the cornea increased from 0.96 ± 0.30 m s-1 to 6.27 ± 0.75 m s-1 as IOP was elevated from 5 to 50 mmHg, there were insignificant changes in the elastic wave velocity in the crystalline lens with the minimum and the maximum speeds of 1.44 ± 0.27 m s-1 and 2.03 ± 0.46 m s-1, respectively. This study shows that ultrasound shear wave elasticity imaging can be used to assess the biomechanical properties of the crystalline lens noninvasively. Also, it was observed that the dependency of the crystalline lens stiffness on the IOP was significantly lower in comparison with that of cornea.
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Affiliation(s)
- Suhyun Park
- Department of Biomedical Engineering, University of Texas at Austin, Austin, TX 78712, USA
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31
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Han Z, Li J, Singh M, Wu C, Liu CH, Raghunathan R, Aglyamov SR, Vantipalli S, Twa MD, Larin KV. Optical coherence elastography assessment of corneal viscoelasticity with a modified Rayleigh-Lamb wave model. J Mech Behav Biomed Mater 2016; 66:87-94. [PMID: 27838594 DOI: 10.1016/j.jmbbm.2016.11.004] [Citation(s) in RCA: 79] [Impact Index Per Article: 9.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/15/2016] [Revised: 10/27/2016] [Accepted: 11/02/2016] [Indexed: 01/22/2023]
Abstract
The biomechanical properties of the cornea play a critical role in forming vision. Diseases such as keratoconus can structurally degenerate the cornea causing a pathological loss in visual acuity. UV-A/riboflavin corneal collagen crosslinking (CXL) is a clinically available treatment to stiffen the cornea and restore its healthy shape and function. However, current CXL techniques do not account for pre-existing biomechanical properties of the cornea nor the effects of the CXL treatment itself. In addition to the inherent corneal structure, the intraocular pressure (IOP) can also dramatically affect the measured biomechanical properties of the cornea. In this work, we present the details and development of a modified Rayleigh-Lamb frequency equation model for quantifying corneal biomechanical properties. After comparison with finite element modeling, the model was utilized to quantify the viscoelasticity of in situ porcine corneas in the whole eye-globe configuration before and after CXL based on noncontact optical coherence elastography measurements. Moreover, the viscoelasticity of the untreated and CXL-treated eyes was quantified at various IOPs. The results showed that the stiffness of the cornea increased after CXL and that corneal stiffness is close to linear as a function of IOP. These results show that the modified Rayleigh-Lamb wave model can provide an accurate assessment of corneal viscoelasticity, which could be used for customized CXL therapies.
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Affiliation(s)
- Zhaolong Han
- Department of Biomedical Engineering, University of Houston, Houston, TX 77204, United States
| | - Jiasong Li
- Department of Biomedical Engineering, University of Houston, Houston, TX 77204, United States
| | - Manmohan Singh
- Department of Biomedical Engineering, University of Houston, Houston, TX 77204, United States
| | - Chen Wu
- Department of Biomedical Engineering, University of Houston, Houston, TX 77204, United States
| | - Chih-Hao Liu
- Department of Biomedical Engineering, University of Houston, Houston, TX 77204, United States
| | - Raksha Raghunathan
- Department of Biomedical Engineering, University of Houston, Houston, TX 77204, United States
| | - Salavat R Aglyamov
- Department of Biomedical Engineering, University of Texas at Austin, Austin, TX 78712, United States
| | - Srilatha Vantipalli
- College of Optometry, University of Houston, Houston, TX 77204, United States
| | - Michael D Twa
- School of Optometry, University of Alabama at Birmingham, Birmingham, AL 35233, United States
| | - Kirill V Larin
- Department of Biomedical Engineering, University of Houston, Houston, TX 77204, United States; Interdisciplinary Laboratory of Biophotonics, Tomsk State University, Tomsk, Russia; Department of Molecular Physiology and Biophysics, Baylor College of Medicine, Houston, TX 77030, United States.
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32
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Han Z, Singh M, Aglyamov SR, Liu CH, Nair A, Raghunathan R, Wu C, Li J, Larin KV. Quantifying tissue viscoelasticity using optical coherence elastography and the Rayleigh wave model. J Biomed Opt 2016; 21:90504. [PMID: 27653931 PMCID: PMC5028422 DOI: 10.1117/1.jbo.21.9.090504] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/14/2016] [Accepted: 08/30/2016] [Indexed: 05/02/2023]
Abstract
This study demonstrates the feasibility of using the Rayleigh wave model (RWM) in combination with optical coherence elastography (OCE) technique to assess the viscoelasticity of soft tissues. Dispersion curves calculated from the spectral decomposition of OCE-measured air-pulse induced elastic waves were used to quantify the viscoelasticity of samples using the RWM. Validation studies were first conducted on 10% gelatin phantoms with different concentrations of oil. The results showed that the oil increased the viscosity of the gelatin phantom samples. This method was then used to quantify the viscoelasticity of chicken liver. The Young’s modulus of the chicken liver tissues was estimated as E=2.04±0.88??kPa with a shear viscosity ?=1.20±0.13??Pa?s. The analytical solution of the RWM correlated very well with the OCE-measured phased velocities (R2=0.96±0.04). The results show that the combination of the RWM and OCE is a promising method for noninvasively quantifying the biomechanical properties of soft tissues and may be a useful tool for detecting disease.
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Affiliation(s)
- Zhaolong Han
- University of Houston, Department of Biomedical Engineering, 3605 Cullen Boulevard, Houston, Texas 77204, United States
| | - Manmohan Singh
- University of Houston, Department of Biomedical Engineering, 3605 Cullen Boulevard, Houston, Texas 77204, United States
| | - Salavat R. Aglyamov
- University of Texas at Austin, Department of Biomedical Engineering, 107 West Dean Keeton Street, Stop C0800, Austin, Texas 78712, United States
| | - Chih-Hao Liu
- University of Houston, Department of Biomedical Engineering, 3605 Cullen Boulevard, Houston, Texas 77204, United States
| | - Achuth Nair
- University of Houston, Department of Biomedical Engineering, 3605 Cullen Boulevard, Houston, Texas 77204, United States
| | - Raksha Raghunathan
- University of Houston, Department of Biomedical Engineering, 3605 Cullen Boulevard, Houston, Texas 77204, United States
| | - Chen Wu
- University of Houston, Department of Biomedical Engineering, 3605 Cullen Boulevard, Houston, Texas 77204, United States
| | - Jiasong Li
- University of Houston, Department of Biomedical Engineering, 3605 Cullen Boulevard, Houston, Texas 77204, United States
| | - Kirill V. Larin
- University of Houston, Department of Biomedical Engineering, 3605 Cullen Boulevard, Houston, Texas 77204, United States
- Tomsk State University, Interdisciplinary Laboratory of Biophotonics, 36 Lenin Avenue, Tomsk 634050, Russia
- Baylor College of Medicine, Molecular Physiology and Biophysics, One Baylor Plaza, Houston, Texas 77030, United States
- Address correspondence to: Kirill V. Larin, E-mail:
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33
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Singh M, Li J, Vantipalli S, Wang S, Han Z, Nair A, Aglyamov SR, Twa MD, Larin KV. Noncontact Elastic Wave Imaging Optical Coherence Elastography for Evaluating Changes in Corneal Elasticity Due to Crosslinking. IEEE J Sel Top Quantum Electron 2016. [PMID: 27547022 DOI: 10.1109/jqe.2016.2585338] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/04/2023]
Abstract
The mechanical properties of tissues can provide valuable information about tissue integrity and health and can assist in detecting and monitoring the progression of diseases such as keratoconus. Optical coherence elastography (OCE) is a rapidly emerging technique, which can assess localized mechanical contrast in tissues with micrometer spatial resolution. In this work we present a noncontact method of optical coherence elastography to evaluate the changes in the mechanical properties of the cornea after UV-induced collagen cross-linking. A focused air-pulse induced a low amplitude (μm scale) elastic wave, which then propagated radially and was imaged in three dimensions by a phase-stabilized swept source optical coherence tomography (PhS-SSOCT) system. The elastic wave velocity was translated to Young's modulus in agar phantoms of various concentrations. Additionally, the speed of the elastic wave significantly changed in porcine cornea before and after UV-induced corneal collagen cross-linking (CXL). Moreover, different layers of the cornea, such as the anterior stroma, posterior stroma, and inner region, could be discerned from the phase velocities of the elastic wave. Therefore, because of noncontact excitation and imaging, this method may be useful for in vivo detection of ocular diseases such as keratoconus and evaluation of therapeutic interventions such as CXL.
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Affiliation(s)
- Manmohan Singh
- Department of Biomedical Engineering at the University of Houston, Houston, TX 77204 USA
| | - Jiasong Li
- Department of Biomedical Engineering at the University of Houston, Houston, TX 77204 USA
| | | | - Shang Wang
- Department of Molecular Physiology and Biophysics at Baylor College of Medicine, One Baylor Plaza, Houston, TX 77030 USA
| | - Zhaolong Han
- Department of Biomedical Engineering at the University of Houston, Houston, TX 77204 USA
| | - Achuth Nair
- Department of Biomedical Engineering at the University of Houston, Houston, TX 77004 USA
| | - Salavat R Aglyamov
- Department of Biomedical Engineering, University of Texas at Austin, Austin, TX 78731 USA
| | - Michael D Twa
- School of Optometry at the University of Alabama at Birmingham, Birmingham, AL 35924
| | - Kirill V Larin
- Department of Biomedical Engineering at the University of Houston, Houston, TX 77004 USA and and the Interdisciplinary Laboratory of Biophotonics, Tomsk State University, Tomsk 634050, Russia, phone: 832-842-8834; fax: 713-743-0226
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34
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Singh M, Li J, Vantipalli S, Wang S, Han Z, Nair A, Aglyamov SR, Twa MD, Larin KV. Noncontact Elastic Wave Imaging Optical Coherence Elastography for Evaluating Changes in Corneal Elasticity Due to Crosslinking. IEEE J Sel Top Quantum Electron 2016; 22:6801911. [PMID: 27547022 PMCID: PMC4990138 DOI: 10.1109/jstqe.2015.2510293] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/02/2023]
Abstract
The mechanical properties of tissues can provide valuable information about tissue integrity and health and can assist in detecting and monitoring the progression of diseases such as keratoconus. Optical coherence elastography (OCE) is a rapidly emerging technique, which can assess localized mechanical contrast in tissues with micrometer spatial resolution. In this work we present a noncontact method of optical coherence elastography to evaluate the changes in the mechanical properties of the cornea after UV-induced collagen cross-linking. A focused air-pulse induced a low amplitude (μm scale) elastic wave, which then propagated radially and was imaged in three dimensions by a phase-stabilized swept source optical coherence tomography (PhS-SSOCT) system. The elastic wave velocity was translated to Young's modulus in agar phantoms of various concentrations. Additionally, the speed of the elastic wave significantly changed in porcine cornea before and after UV-induced corneal collagen cross-linking (CXL). Moreover, different layers of the cornea, such as the anterior stroma, posterior stroma, and inner region, could be discerned from the phase velocities of the elastic wave. Therefore, because of noncontact excitation and imaging, this method may be useful for in vivo detection of ocular diseases such as keratoconus and evaluation of therapeutic interventions such as CXL.
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Affiliation(s)
| | | | | | - Shang Wang
- Department of Molecular Physiology and Biophysics at Baylor College
of Medicine, One Baylor Plaza, Houston, TX 77030 USA
| | - Zhaolong Han
- Department of Biomedical Engineering at the University of Houston,
Houston, TX 77204 USA
| | - Achuth Nair
- Department of Biomedical Engineering at the University of Houston,
Houston, TX 77004 USA
| | - Salavat R. Aglyamov
- Department of Biomedical Engineering, University of Texas at
Austin, Austin, TX 78731 USA
| | - Michael D. Twa
- School of Optometry at the University of Alabama at Birmingham,
Birmingham, AL 35924
| | - Kirill V. Larin
- Department of Biomedical Engineering at the University of Houston,
Houston, TX 77004 USA and and the Interdisciplinary Laboratory of
Biophotonics, Tomsk State University, Tomsk 634050, Russia, phone:
832-842-8834; fax: 713-743-0226
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35
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Aglyamov SR, Wang S, Emelianov SY, Larin KV. A three-dimensional solution for laser-induced thermoelastic deformation of the layered medium. ACTA ACUST UNITED AC 2016. [DOI: 10.1117/12.2213480] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022]
Affiliation(s)
| | - Shang Wang
- Baylor College of Medicine (United States)
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36
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Han Z, Li J, Singh M, Aglyamov SR, Wu C, Liu CH, Larin KV. Analysis of the effects of curvature and thickness on elastic wave velocity in cornea-like structures by finite element modeling and optical coherence elastography. Appl Phys Lett 2015; 106:233702. [PMID: 26130825 PMCID: PMC4464060 DOI: 10.1063/1.4922728] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/09/2015] [Accepted: 06/06/2015] [Indexed: 05/18/2023]
Abstract
Wave models that have been used to extract the biomechanical properties of the cornea from the propagation of an elastic wave are based on an assumption of thin-plate geometry. However, this assumption does not account for the effects of corneal curvature and thickness. This study conducts finite element (FE) simulations on four types of cornea-like structures as well as optical coherence elastography (OCE) experiments on contact lenses and tissue-mimicking phantoms to investigate the effects of curvature and thickness on the group velocity of an elastic wave. The elastic wave velocity as determined by FE simulations and OCE of a spherical shell section decreased from ∼2.8 m/s to ∼2.2 m/s as the radius of curvature increased from 19.1 mm to 47.7 mm and increased from ∼3.0 m/s to ∼4.1 m/s as the thickness of the agar phantom increased from 1.9 mm to 5.6 mm. Both the FE simulation and OCE results confirm that the group velocity of the elastic wave decreases with radius of curvature but increases with thickness. These results demonstrate that the effects of the curvature and thickness must be considered in the further development of accurate wave models for reconstructing biomechanical properties of the cornea.
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Affiliation(s)
- Zhaolong Han
- Department of Biomedical Engineering, University of Houston , Houston, Texas 77204, USA
| | - Jiasong Li
- Department of Biomedical Engineering, University of Houston , Houston, Texas 77204, USA
| | - Manmohan Singh
- Department of Biomedical Engineering, University of Houston , Houston, Texas 77204, USA
| | - Salavat R Aglyamov
- Department of Biomedical Engineering, University of Texas at Austin , Austin, Texas 78712, USA
| | - Chen Wu
- Department of Biomedical Engineering, University of Houston , Houston, Texas 77204, USA
| | - Chih-Hao Liu
- Department of Biomedical Engineering, University of Houston , Houston, Texas 77204, USA
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Aglyamov SR, Wang S, Karpiouk AB, Li J, Twa M, Emelianov SY, Larin KV. The dynamic deformation of a layered viscoelastic medium under surface excitation. Phys Med Biol 2015; 60:4295-312. [PMID: 25974168 DOI: 10.1088/0031-9155/60/11/4295] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
In this study the dynamic behavior of a layered viscoelastic medium in response to the harmonic and impulsive acoustic radiation force applied to its surface was investigated both theoretically and experimentally. An analytical solution for a layered viscoelastic compressible medium in frequency and time domains was obtained using the Hankel transform. A special incompressible case was considered to model soft biological tissues. To verify our theoretical model, experiments were performed using tissue-like gel-based phantoms with varying mechanical properties. A 3.5 MHz single-element focused ultrasound transducer was used to apply the radiation force at the surface of the phantoms. A phase-sensitive optical coherence tomography system was used to track the displacements of the phantom surface. Theoretically predicted displacements were compared with experimental measurements. The role of the depth dependence of the elastic properties of a medium in its response to an acoustic pulse at the surface was studied. It was shown that the low-frequency vibrations at the surface are more sensitive to the deep layers than high-frequency ones. Therefore, the proposed model in combination with spectral analysis can be used to evaluate depth-dependent distribution of the mechanical properties based on the measurements of the surface deformation.
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Affiliation(s)
- Salavat R Aglyamov
- Biomedical Engineering, University of Texas at Austin, Austin, TX 78731, USA
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Han Z, Li J, Singh M, Wu C, Liu CH, Wang S, Idugboe R, Raghunathan R, Sudheendran N, Aglyamov SR, Twa MD, Larin KV. Quantitative methods for reconstructing tissue biomechanical properties in optical coherence elastography: a comparison study. Phys Med Biol 2015; 60:3531-47. [PMID: 25860076 PMCID: PMC4409577 DOI: 10.1088/0031-9155/60/9/3531] [Citation(s) in RCA: 71] [Impact Index Per Article: 7.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
We present a systematic analysis of the accuracy of five different methods for extracting the biomechanical properties of soft samples using optical coherence elastography (OCE). OCE is an emerging noninvasive technique, which allows assessment of biomechanical properties of tissues with micrometer spatial resolution. However, in order to accurately extract biomechanical properties from OCE measurements, application of a proper mechanical model is required. In this study, we utilize tissue-mimicking phantoms with controlled elastic properties and investigate the feasibilities of four available methods for reconstructing elasticity (Young's modulus) based on OCE measurements of an air-pulse induced elastic wave. The approaches are based on the shear wave equation (SWE), the surface wave equation (SuWE), Rayleigh-Lamb frequency equation (RLFE), and finite element method (FEM), Elasticity values were compared with uniaxial mechanical testing. The results show that the RLFE and the FEM are more robust in quantitatively assessing elasticity than the other simplified models. This study provides a foundation and reference for reconstructing the biomechanical properties of tissues from OCE data, which is important for the further development of noninvasive elastography methods.
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Affiliation(s)
- Zhaolong Han
- Department of Biomedical Engineering, Cullen College of Engineering, University of Houston, Houston, TX 77204, USA
| | - Jiasong Li
- Department of Biomedical Engineering, Cullen College of Engineering, University of Houston, Houston, TX 77204, USA
| | - Manmohan Singh
- Department of Biomedical Engineering, Cullen College of Engineering, University of Houston, Houston, TX 77204, USA
| | - Chen Wu
- Department of Biomedical Engineering, Cullen College of Engineering, University of Houston, Houston, TX 77204, USA
| | - Chih-hao Liu
- Department of Biomedical Engineering, Cullen College of Engineering, University of Houston, Houston, TX 77204, USA
| | - Shang Wang
- Department of Biomedical Engineering, Cullen College of Engineering, University of Houston, Houston, TX 77204, USA
- Molecular Physiology and Biophysics, Baylor College of Medicine, Houston, TX 77030, USA
| | - Rita Idugboe
- Department of Biomedical Engineering, Cullen College of Engineering, University of Houston, Houston, TX 77204, USA
| | - Raksha Raghunathan
- Department of Biomedical Engineering, Cullen College of Engineering, University of Houston, Houston, TX 77204, USA
| | - Narendran Sudheendran
- Department of Biomedical Engineering, Cullen College of Engineering, University of Houston, Houston, TX 77204, USA
| | - Salavat R. Aglyamov
- Department of Biomedical Engineering, University of Texas at Austin, 107 W Dean Keeton Street, Austin, TX 78712, USA
| | - Michael D. Twa
- School of Optometry, University of Alabama, Birmingham, AL 35294 USA
| | - Kirill V. Larin
- Department of Biomedical Engineering, Cullen College of Engineering, University of Houston, Houston, TX 77204, USA
- Molecular Physiology and Biophysics, Baylor College of Medicine, Houston, TX 77030, USA
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Han Z, Aglyamov SR, Li J, Singh M, Wang S, Vantipalli S, Wu C, Liu CH, Twa MD, Larin KV. Quantitative assessment of corneal viscoelasticity using optical coherence elastography and a modified Rayleigh-Lamb equation. J Biomed Opt 2015; 20:20501. [PMID: 25649624 PMCID: PMC4315865 DOI: 10.1117/1.jbo.20.2.020501] [Citation(s) in RCA: 45] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/31/2014] [Accepted: 01/09/2015] [Indexed: 05/18/2023]
Abstract
We demonstrate the use of a modified Rayleigh–Lamb frequency equation in conjunction with noncontact optical coherence elastography to quantify the viscoelastic properties of the cornea. Phase velocities of air-pulse-induced elastic waves were extracted by spectral analysis and used for calculating the Young’s moduli of the samples using the Rayleigh–Lamb frequency equation (RLFE). Validation experiments were performed on 2% agar phantoms (n ¼ 3) and then applied to porcine corneas (n ¼ 3) in situ. The Young’s moduli of the porcine corneas were estimated to be ∼60 kPa with a shear viscosity ∼0.33 Pa · s. The results demonstrate that the RLFE is a promising method for noninvasive quantification of the corneal biomechanical properties and may potentially be useful for clinical ophthalmological applications.
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Affiliation(s)
- Zhaolong Han
- University of Houston, Department of Biomedical Engineering, Houston, Texas 77204, United States
| | - Salavat R. Aglyamov
- University of Texas at Austin, Department of Biomedical Engineering, Austin, Texas 78712, United States
| | - Jiasong Li
- University of Houston, Department of Biomedical Engineering, Houston, Texas 77204, United States
| | - Manmohan Singh
- University of Houston, Department of Biomedical Engineering, Houston, Texas 77204, United States
| | - Shang Wang
- University of Houston, Department of Biomedical Engineering, Houston, Texas 77204, United States
- Baylor College of Medicine, Department of Molecular Physiology and Biophysics, Houston, Texas 77030, United States
| | - Srilatha Vantipalli
- University of Houston, College of Optometry, Houston, Texas 77204, United States
| | - Chen Wu
- University of Houston, Department of Biomedical Engineering, Houston, Texas 77204, United States
| | - Chih-hao Liu
- University of Houston, Department of Biomedical Engineering, Houston, Texas 77204, United States
| | - Michael D. Twa
- University of Alabama, School of Optometry, Birmingham, Alabama 35294, United States
| | - Kirill V. Larin
- University of Houston, Department of Biomedical Engineering, Houston, Texas 77204, United States
- Baylor College of Medicine, Department of Molecular Physiology and Biophysics, Houston, Texas 77030, United States
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Manapuram RK, Aglyamov SR, Monediado FM, Mashiatulla M, Li J, Emelianov SY, Larin KV. In vivo estimation of elastic wave parameters using phase-stabilized swept source optical coherence elastography. J Biomed Opt 2012; 17:100501. [PMID: 23223976 PMCID: PMC3465019 DOI: 10.1117/1.jbo.17.10.100501] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/12/2023]
Abstract
We report a highly sensitive method based on phase-stabilized swept source optical coherence elastography (PhS-SSOCE) to measure elastic wave propagation in soft tissues in vivo. The waves were introduced using a mechanical stimulus and were assessed using the phase response of the swept source optical coherence tomography signal. The technique was utilized to measure age-related changes in elastic flexural wave velocity and attenuation in mice cornea in vivo. Results demonstrate that the wave velocity increases with animal age, supporting previous observations that stiffness of mice cornea gradually increases with age. Our studies suggest that the PhS-SSOCE technique could potentially be used to obtain biomechanical properties of ocular tissues in vivo.
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Affiliation(s)
- Ravi Kiran Manapuram
- University of Houston, Department of Mechanical Engineering, Engineering, Building 1, 4800 Calhoun Road, Houston, Texas 77204
| | - Salavat R. Aglyamov
- University of Texas at Austin, Department of Biomedical Engineering, BME Building, Austin, Texas 78712
| | - Floredes M. Monediado
- University of Houston, Department of Biomedical Engineering, SERC Building, 4800 Calhoun Road, Houston, Texas 77204
| | - Maleeha Mashiatulla
- University of Houston, Department of Biomedical Engineering, SERC Building, 4800 Calhoun Road, Houston, Texas 77204
| | - Jiasong Li
- University of Houston, Department of Biomedical Engineering, SERC Building, 4800 Calhoun Road, Houston, Texas 77204
| | - Stanislav Y. Emelianov
- University of Texas at Austin, Department of Biomedical Engineering, BME Building, Austin, Texas 78712
| | - Kirill V. Larin
- University of Houston, Department of Mechanical Engineering, Engineering, Building 1, 4800 Calhoun Road, Houston, Texas 77204
- University of Houston, Department of Biomedical Engineering, SERC Building, 4800 Calhoun Road, Houston, Texas 77204
- Address all correspondence to: Kirill V. Larin, University of Houston, Department of Mechanical Engineering, Engineering, Building 1, 4800 Calhoun Road, Houston, Texas 77204. E-mail:
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R. Aglyamov S, B. Karpiouk A, Mehrmohammadi M, Yoon S, Kim S, A. Ilinskii Y, A. Zabolotskaya E, Y. Emelianov S. Elasticity Imaging and Sensing Using Targeted Motion: From Macro to Nano. Curr Med Imaging 2012. [DOI: 10.2174/157340512799220599] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
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Abstract
From times immemorial manual palpation served as a source of information on the state of soft tissues and allowed detection of various diseases accompanied by changes in tissue elasticity. During the last two decades, the ancient art of palpation gained new life due to numerous emerging elasticity imaging (EI) methods. Areas of applications of EI in medical diagnostics and treatment monitoring are steadily expanding. Elasticity imaging methods are emerging as commercial applications, a true testament to the progress and importance of the field.In this paper we present a brief history and theoretical basis of EI, describe various techniques of EI and, analyze their advantages and limitations, and overview main clinical applications. We present a classification of elasticity measurement and imaging techniques based on the methods used for generating a stress in the tissue (external mechanical force, internal ultrasound radiation force, or an internal endogenous force), and measurement of the tissue response. The measurement method can be performed using differing physical principles including magnetic resonance imaging (MRI), ultrasound imaging, X-ray imaging, optical and acoustic signals.Until recently, EI was largely a research method used by a few select institutions having the special equipment needed to perform the studies. Since 2005 however, increasing numbers of mainstream manufacturers have added EI to their ultrasound systems so that today the majority of manufacturers offer some sort of Elastography or tissue stiffness imaging on their clinical systems. Now it is safe to say that some sort of elasticity imaging may be performed on virtually all types of focal and diffuse disease. Most of the new applications are still in the early stages of research, but a few are becoming common applications in clinical practice.
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Yoon S, Aglyamov SR, Karpiouk AB, Kim S, Emelianov SY. Estimation of mechanical properties of a viscoelastic medium using a laser-induced microbubble interrogated by an acoustic radiation force. J Acoust Soc Am 2011; 130:2241-8. [PMID: 21973379 PMCID: PMC3206915 DOI: 10.1121/1.3628344] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/03/2023]
Abstract
An approach to assess the mechanical properties of a viscoelastic medium using laser-induced microbubbles is presented. To measure mechanical properties of the medium, dynamics of a laser-induced cavitation microbubble in viscoelastic medium under acoustic radiation force was investigated. An objective lens with a 1.13 numerical aperture and an 8.0 mm working distance was designed to focus a 532 nm wavelength nanosecond pulsed laser beam and to create a microbubble at the desired location. A 3.5 MHz ultrasound transducer was used to generate acoustic radiation force to excite a laser-induced microbubble. Motion of the microbubble was tracked using a 25 MHz imaging transducer. Agreement between a theoretical model of bubble motion in a viscoelastic medium and experimental measurements was demonstrated. Young's modulii reconstructed using the laser-induced microbubble approach were compared with those measured using a direct uniaxial method over the range from 0.8 to 13 kPa. The results indicate good agreement between methods. Thus, the proposed approach can be used to assess the mechanical properties of a viscoelastic medium.
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Affiliation(s)
- Sangpil Yoon
- Department of Mechanical Engineering, The University of Texas at Austin, Austin, Texas 78712-1063, USA
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44
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Kim S, Aglyamov SR, Park S, O'Donnell M, Emelianov SY. An autocorrelation-based method for improvement of sub-pixel displacement estimation in ultrasound strain imaging. IEEE Trans Ultrason Ferroelectr Freq Control 2011; 58:838-43. [PMID: 21507761 PMCID: PMC3093758 DOI: 10.1109/tuffc.2011.1876] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/16/2023]
Abstract
In ultrasound strain and elasticity imaging, an accurate and cost-effective sub-pixel displacement estimator is required because strain/elasticity imaging quality relies on the displacement SNR, which can often be higher if more computational resources are provided. In this paper, we introduce an autocorrelation-based method to cost-effectively improve subpixel displacement estimation quality. To quantitatively evaluate the performance of the autocorrelation method, simulated and tissue-mimicking phantom experiments were performed. The computational cost of the autocorrelation method is also discussed. The results of our study suggest the autocorrelation method can be used for a real-time elasticity imaging system.
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Abstract
Nanoparticles are attracting considerable interest as contrast agents for many different imaging modalities. Moreover, imaging the events at the cellular and molecular level is possible by using nanoparticles that have the desired targeting moiety. Unfortunately, ultrasound imaging cannot visualize the nano-structures directly due to its limited spatial resolution and contrast. We present a new technique, pulsed magneto-acoustic imaging, capable of imaging magnetic nanoparticles indirectly. In this method, a high-strength pulsed magnetic field is used to induce motion within the magnetically labeled tissue and ultrasound is used to detect internal tissue motion. Experiments on tissue-mimicking phantoms and ex-vivo animal tissues demonstrated a clear contrast between normal and iron-laden samples labeled with 5 nm magnetic nanoparticles. In addition, the sensitivity of this new imaging technique was investigated for different concentrations of magnetic agents. The results of the study suggest that magnetic nanoparticles can be used as contrast agents in pulsed magneto-acoustic imaging. Furthermore, PMA imaging could become an imaging tool capable of visualizing the cellular and molecular composition of deep-lying structures.
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Affiliation(s)
- Mohammad Mehrmohammadi
- Department of Biomedical Engineering, University of Texas at Austin, Austin, TX 78712, USA
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46
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Karpiouk AB, Aglyamov SR, Ilinskii YA, Zabolotskaya EA, Emelianov SY. Assessment of shear modulus of tissue using ultrasound radiation force acting on a spherical acoustic inhomogeneity. IEEE Trans Ultrason Ferroelectr Freq Control 2009; 56:2380-7. [PMID: 19942525 PMCID: PMC3059155 DOI: 10.1109/tuffc.2009.1326] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/02/2023]
Abstract
An ultrasound-based method to locally assess the shear modulus of a medium is reported. The proposed approach is based on the application of an impulse acoustic radiation force to an inhomogeneity in the medium and subsequent monitoring of the spatio-temporal response. In our experimental studies, a short pulse produced by a 1.5-MHz highly focused ultrasound transducer was used to initiate the motion of a rigid sphere embedded into an elastic medium. Another 25 MHz focused ultrasound transducer operating in pulse-echo mode was used to track the displacement of the sphere. The experiments were performed in gel phantoms with varying shear modulus to demonstrate the relationship between the displacement of the sphere and shear modulus of the surrounding medium. Because the magnitude of acoustic force applied to sphere depends on the acoustic material properties and, therefore, cannot be used to assess the absolute value of shear modulus, the temporal behavior of the displacement of the sphere was analyzed. The results of this study indicate that there is a strong correlation between the shear modulus of a medium and spatio-temporal characteristics of the motion of the rigid sphere embedded in this medium.
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Affiliation(s)
- Andrei B. Karpiouk
- Department of Biomedical Engineering, University of Texas at Austin, Austin, TX
| | - Salavat R. Aglyamov
- Department of Biomedical Engineering, University of Texas at Austin, Austin, TX
| | - Yury A. Ilinskii
- Applied Research Laboratories, University of Texas at Austin, Austin, TX
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Kim S, Aglyamov SR, Emelianov SY. Display pixel-based synthetic aperture focusing method for intravascular ultrasound imaging. Annu Int Conf IEEE Eng Med Biol Soc 2009; 2009:475-478. [PMID: 19965127 DOI: 10.1109/iembs.2009.5335164] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/28/2023]
Abstract
An intravascular ultrasound image reconstruction technique that combines synthetic aperture focusing and display pixel-based focusing methods is presented. Although the synthetic aperture focusing method can improve intravascular ultrasound image quality, the final displayed images are usually blurry in the angular direction due to the limitations of the digital scan converter. The display pixel-based focusing method can eliminate blurring effects caused by the digital scan converter. Therefore, the image quality can be further improved by applying the display pixel-based focusing method to the synthetic aperture focusing method, especially for intravascular ultrasound images. The experimental studies were performed to evaluate display pixel-based synthetic aperture focusing method. The computational complexity of the display pixel-based synthetic aperture focusing method was discussed in comparison with that of the synthetic aperture focusing method.
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Affiliation(s)
- Seungsoo Kim
- Department of Biomedical Engineering, University of Texas at Austin, Austin, TX 78712 USA
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Karpiouk AB, Aglyamov SR, Mallidi S, Shah J, Scott WG, Rubin JM, Emelianov SY. Combined ultrasound and photoacoustic imaging to detect and stage deep vein thrombosis: phantom and ex vivo studies. J Biomed Opt 2008; 13:054061. [PMID: 19021440 DOI: 10.1117/1.2992175] [Citation(s) in RCA: 45] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/22/2023]
Abstract
Treatment of deep venous thrombosis (DVT)--a primary cause of potentially fatal pulmonary embolism (PE)--depends on the age of the thrombus. The existing clinical imaging methods are capable of visualizing a thrombus but cannot determine the age of the blood clot. Therefore, there is a need for an imaging technique to reliably diagnose and adequately stage DVT. To stage DVT (i.e., to determine the age of the thrombus, and therefore, to differentiate acute from chronic DVT), we explored photoacoustic imaging, a technique capable of noninvasive measurements of the optical absorption in tissue. Indeed, optical absorption of the blood clot changes with age, since maturation of DVT is associated with significant cellular and molecular reorganization. The ultrasound and photoacoustic imaging studies were performed using DVT-mimicking phantoms and phantoms with embedded acute and chronic thrombi obtained from an animal model of DVT. The location and structure of the clots were visualized using ultrasound imaging, while the composition, and therefore age, of thrombi were related to the magnitude and spatiotemporal characteristics of the photoacoustic signal. Overall, the results of our study suggest that combined ultrasound and photoacoustic imaging of thrombi may be capable of simultaneous detection and staging of DVT.
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Affiliation(s)
- Andrei B Karpiouk
- University of Texas at Austin, Department of Biomedical Engineering, Austin, Texas 78712, USA
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Aglyamov SR, Karpiouk AB, Bourgeois F, Ben-Yakar A, Emelianov SY. Ultrasound measurements of cavitation bubble radius for femtosecond laser-induced breakdown in water. Opt Lett 2008; 33:1357-9. [PMID: 18552957 PMCID: PMC2459242 DOI: 10.1364/ol.33.001357] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/18/2023]
Abstract
A recently developed ultrasound technique is evaluated by measuring the behavior of a cavitation bubble that is induced in water by a femtosecond laser pulse. The passive acoustic emission during optical breakdown is used to estimate the location of the cavitation bubble's origin. In turn, the position of the bubble wall is defined based on the active ultrasonic pulse-echo signal. The results suggest that the developed ultrasound technique can be used for quantitative measurements of femtosecond laser-induced microbubbles.
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Affiliation(s)
- Salavat R. Aglyamov
- Department of Biomedical Engineering, University of Texas at Austin, Austin, Texas 78712, USA
- Institute of Mathematical Problems of Biology, Russian Academy of Sciences, Pushchino, Moscow Region 142290, Russia
| | - Andrei B. Karpiouk
- Department of Biomedical Engineering, University of Texas at Austin, Austin, Texas 78712, USA
| | - Frederic Bourgeois
- Department of Mechanical Engineering, University of Texas at Austin, Austin, Texas 78712, USA
| | - Adela Ben-Yakar
- Department of Biomedical Engineering, University of Texas at Austin, Austin, Texas 78712, USA
- Department of Mechanical Engineering, University of Texas at Austin, Austin, Texas 78712, USA
| | - Stanislav Y. Emelianov
- Department of Biomedical Engineering, University of Texas at Austin, Austin, Texas 78712, USA
- Department of Mechanical Engineering, University of Texas at Austin, Austin, Texas 78712, USA
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50
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Abstract
An adaptive photoacoustic image reconstruction technique that combines coherence factor (CF) weighting and the minimum variance (MV) method is introduced. The backprojection method is widely used to reconstruct photoacoustic tomography images. Owing to the scattering of light, the quality of the photoacoustic imaging can be degraded. CF, an adaptive weighting technique, is known to improve the lateral resolution of photoacoustic images. In addition, an MV adaptive beamforming method can further improve the image quality by suppressing signals from off-axis directions. Experimental studies are performed to quantify the spatial resolution and contrast of the adaptive photoacoustic beamforming methods.
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