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Kokossis D, Wei HJ, Gallitto M, Yoh N, McQuillan N, Tazhibi M, Berg X, Zhang X, Szalontay L, Gartrell R, Jovana P, Zhang Z, Molotkov A, Mintz A, Konofagou EE, Wu CC. Focused Ultrasound for Blood-Brain Barrier Opening and Delivery of Anti-PD1 in Diffuse Midline Gliomas. Int J Radiat Oncol Biol Phys 2023; 117:e523-e524. [PMID: 37785629 DOI: 10.1016/j.ijrobp.2023.06.1796] [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] [Indexed: 10/04/2023]
Abstract
PURPOSE/OBJECTIVE(S) Diffuse midline glioma with H3K27 mutation is a fatal pediatric brain tumor, most commonly arising in the brainstem. This tumor remains universally fatal, despite a multitude of clinical trials, with a median overall survival of only 9-12 months. While immune-checkpoint inhibitors (ICIs) have transformed the treatment landscape of multiple solid tumors, delivery past the blood brain barrier (BBB) remains challenging. Programmed cell death protein 1 (PD1) is an immune checkpoint protein expressed on the surface of activated T cells; interaction with its ligand, PDL1, is tumor-protective, dampening T cell response. Recent phase I clinical trials have shown that ICIs targeting proteins along the PD1/PDL1 axis are well tolerated in patients with DMG; however, efficacy remains low. The blood-brain barrier (BBB) poses a major challenge to the efficacious delivery of therapeutic agents with large molecular size, such as anti-PD1. We hypothesize that BBB opening (BBBO) using focused ultrasound (FUS), a form of non-ionizing acoustic radiation, can enhance delivery and efficacy of anti-PD1 for treatment of DMG. MATERIALS/METHODS We established a syngeneic mouse DMG model with intracranial injection of cell line 4423 (PDGFB+, H3.3K27M, p53-/-). Magnetic resonance imaging (MRI) was utilized to evaluate BBBO and tumor progression. We measured delivery of anti-PD1 after BBBO using Western Blot and 3D in vivo optical fluorescent imaging/CT (OI/CT) of Cy7 labeled anti-PD1. RESULTS We demonstrate that delivery of anti-PD1 can be enhanced over 3.5-fold after reversible BBBO with FUS and concurrent microbubble administration. OI/CT revealed enhanced real-time antibody distribution peritumorally. Furthermore, we demonstrate that combined treatment of FUS and anti-PD1 led to benefit in local control of tumor growth using volumetric analysis of MRI. Preliminary survival studies suggest a positive trend for overall survival. CONCLUSION Our results support that FUS-mediated BBBO can increase treatment efficacy of anti-PD1 in a DMG murine model, due to improved targeted delivery to the tumoral region after systemic antibody administration. We consider these findings strong rationale for further investigation of the therapeutic effects of combinatorial treatment using FUS-mediated BBBO and ICIs for the treatment of DMG.
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Affiliation(s)
- D Kokossis
- Columbia University Irving Medical Center, New York, NY
| | - H J Wei
- Department of Radiation Oncology, Columbia University Irving Medical Center, New York, NY
| | - M Gallitto
- Department of Radiation Oncology, Columbia University Irving Medical Center, New York, NY
| | - N Yoh
- Department of Neurological Surgery, Columbia University Irving Medical Center, New York, NY
| | - N McQuillan
- Department of Radiation Oncology, Columbia University Irving Medical Center, New York, NY
| | | | - X Berg
- Columbia University Irving Medical Center, New York, NY
| | - X Zhang
- Department of Pediatrics, Columbia University Irving Medical Center, New York, NY
| | - L Szalontay
- Department of Pediatrics Oncology, Columbia University Irving Medical Center, New York, NY
| | - R Gartrell
- Department of Pediatrics Oncology, Columbia University Irving Medical Center, New York, NY
| | - P Jovana
- Columbia University Irving Medical Center, New York, NY
| | - Z Zhang
- Department of Pediatrics, Columbia University Irving Medical Center, New York, NY
| | - A Molotkov
- Columbia University Irving Medical Center, New York, NY
| | - A Mintz
- Columbia University Irving Medical Center, New York, NY
| | - E E Konofagou
- Department of Biomedical Engineering, Columbia University, New York, NY
| | - C C Wu
- Herbert Irving Comprehensive Cancer Center, Columbia University Irving Medical Center, New York, NY
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Noel RL, Batts AJ, Ji R, Pouliopoulos AN, Bae S, Kline-Schoder AR, Konofagou EE. Natural aging and Alzheimer's disease pathology increase susceptibility to focused ultrasound-induced blood-brain barrier opening. Sci Rep 2023; 13:6757. [PMID: 37185578 PMCID: PMC10130033 DOI: 10.1038/s41598-023-30466-6] [Citation(s) in RCA: 4] [Impact Index Per Article: 4.0] [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: 01/01/2023] [Accepted: 02/23/2023] [Indexed: 05/17/2023] Open
Abstract
Focused Ultrasound (FUS) paired with systemically-injected microbubbles (μB) is capable of transiently opening the blood-brain barrier (BBBO) for noninvasive and targeted drug delivery to the brain. FUS-BBBO is also capable of modulating the neuroimmune system, further qualifying its therapeutic potential for neurodegenerative diseases like Alzheimer's disease (AD). Natural aging and AD impose significant strain on the brain and particularly the BBB, modifying its structure and subsequently, its functionality. The emerging focus on treating neurodegenerative diseases with FUS-BBBO necessitates an investigation into the extent that age and AD affect the BBB's response to FUS. FUS-BBBO was performed with a 1.5-MHz, geometrically focused transducer operated at 450 kPa and paired with a bolus microbubble injection of 8 × 108 μB/mL. Here we quantify the BBBO, BBB closing (BBBC) timeline, and BBB permeability (BBBP) following FUS-BBBO in male mice with and without AD pathology, aged 10 weeks, one year, or two years. The data presented herein indicates that natural aging and AD pathology may increase initial BBBO volume by up to 34.4% and 40.7% respectively, extend BBBC timeline by up to 1.3 and 1.5 days respectively, and increase BBBP as measured by average Ktrans values up to 80% and 86.1% respectively in male mice. This characterization of the BBB response to FUS-BBBO with age and AD further clarifies the nature and extent of the functional impact of these factors and may offer new considerations for planning FUS-BBBO interventions in aged and AD populations.
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Affiliation(s)
- R L Noel
- Department of Biological Engineering, Columbia University, 351 Engineering Terrace, Mail Code 8904, 1210 Amsterdam Avenue, New York, NY, 10027, USA.
| | - A J Batts
- Department of Biological Engineering, Columbia University, 351 Engineering Terrace, Mail Code 8904, 1210 Amsterdam Avenue, New York, NY, 10027, USA
| | - R Ji
- Department of Biological Engineering, Columbia University, 351 Engineering Terrace, Mail Code 8904, 1210 Amsterdam Avenue, New York, NY, 10027, USA
| | - A N Pouliopoulos
- Department of Biological Engineering, Columbia University, 351 Engineering Terrace, Mail Code 8904, 1210 Amsterdam Avenue, New York, NY, 10027, USA
| | - S Bae
- Department of Biological Engineering, Columbia University, 351 Engineering Terrace, Mail Code 8904, 1210 Amsterdam Avenue, New York, NY, 10027, USA
| | - A R Kline-Schoder
- Department of Biological Engineering, Columbia University, 351 Engineering Terrace, Mail Code 8904, 1210 Amsterdam Avenue, New York, NY, 10027, USA
| | - E E Konofagou
- Department of Biological Engineering, Columbia University, 351 Engineering Terrace, Mail Code 8904, 1210 Amsterdam Avenue, New York, NY, 10027, USA.
- Department of Radiology, Columbia University, 622 West 168th Street, New York, NY, 10032, USA.
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Liu D, Munoz F, Sanatkhani S, Pouliopoulos AN, Konofagou E, Grinband J, VP F. Alteration of functional connectivity in the cortex and major brain networks of non-human primates following focused ultrasound exposure. bioRxiv 2023:2023.02.16.528741. [PMID: 36824864 PMCID: PMC9949083 DOI: 10.1101/2023.02.16.528741] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 02/18/2023]
Abstract
Focused ultrasound (FUS) is a non-invasive neuromodulation technology that is being investigated for potential treatment of neurological and psychiatric disorders. Focused ultrasound combined with microbubbles can temporarily open the intact blood-brain barrier (BBB) of animals and humans, and facilitate drug delivery. FUS exposure, either with or without microbubbles, has been demonstrated to alter the behavior of non-human primates, and previous work has demonstrated transient and long-term effects of FUS neuromodulation on functional connectivity using resting state functional MRI. However, it is unknown whether opening the BBB affects functional connectivity differently than FUS alone. Thus we applied FUS alone (neuromodulation) and FUS with microbubbles (BBB opening) in the dorsal striatum of lightly anesthetized non-human primates, and compared changes in functional connectivity in major brain networks. We found different alteration patterns between FUS neuromodulation and FUS-mediated BBB opening in several cortical areas, and we also found that applying FUS to a deep brain structure can alter functional connectivity in the default mode network and frontotemporal network.
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Affiliation(s)
- D Liu
- Dept. of Neuroscience, Columbia University, USA
- Zuckerman Mind Brain Behavior Institute, Columbia University, USA
| | - F Munoz
- Dept. of Neuroscience, Columbia University, USA
- Zuckerman Mind Brain Behavior Institute, Columbia University, USA
| | - S Sanatkhani
- Dept. of Neuroscience, Columbia University, USA
- Zuckerman Mind Brain Behavior Institute, Columbia University, USA
| | - A N Pouliopoulos
- Dept. of Surgical & Interventional Engineering, School of Biomedical Engineering & Imaging Science, King’s College London, UK
| | - E Konofagou
- Dept. of Biomedical Engineering, Columbia University, USA
- Dept. of Radiology, Columbia University, USA
| | - J Grinband
- Dept. of Radiology, Columbia University, USA
- Dept. of Psychiatry, Columbia University, USA
| | - Ferrera VP
- Dept. of Neuroscience, Columbia University, USA
- Zuckerman Mind Brain Behavior Institute, Columbia University, USA
- Dept. of Psychiatry, Columbia University, USA
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Munoz F, Meaney A, Gross A, Liu K, Pouliopoulos AN, Liu D, Konofagou EE, Ferrera VP. Long term study of motivational and cognitive effects of low-intensity focused ultrasound neuromodulation in the dorsal striatum of nonhuman primates. Brain Stimul 2022; 15:360-372. [PMID: 35092823 PMCID: PMC9419899 DOI: 10.1016/j.brs.2022.01.014] [Citation(s) in RCA: 18] [Impact Index Per Article: 9.0] [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: 08/06/2021] [Revised: 01/18/2022] [Accepted: 01/24/2022] [Indexed: 12/20/2022] Open
Abstract
Noninvasive brain stimulation using transcranial focused ultrasound (FUS) has many potential applications as a research and clinical tool, including incorporation into neural prosthetics for cognitive rehabilitation. To develop this technology, it is necessary to evaluate the safety and efficacy of FUS neuromodulation for specific brain targets and cognitive functions. It is also important to test whether repeated long-term application of FUS to deep brain targets improves or degrades behavioral and cognitive function. To this end, we investigated the effects of FUS in the dorsal striatum of nonhuman primates (NHP) performing a visual-motor decision-making task for small or large rewards. Over the course of 2 years, we performed 129 and 147 FUS applications, respectively, in two NHP. FUS (0.5 MHz @ 0.2-0.8 MPa) was applied to the putamen and caudate in both hemispheres to evaluate the effects on movement accuracy, motivation, decision accuracy, and response time. Sonicating the caudate or the putamen unilaterally resulted in modest but statistically significant improvements in motivation and decision accuracy, but at the cost of slower reaction times. The effects were dose (i.e., FUS pressure) and reward dependent. There was no effect on reaching accuracy, nor was there long-term behavioral impairment or neurological trauma evident on T1-weighted, T2-weighted, or susceptibility-weighted MRI scans. Sonication also resulted in significant changes in resting state functional connectivity between the caudate and multiple cortical regions. The results indicate that applying FUS to the dorsal striatum can positively impact the motivational and cognitive aspects of decision making. The capability of FUS to improve motivation and cognition in NHPs points to its therapeutic potential in treating a wide variety of human neural diseases, and warrants further development as a novel technique for non-invasive deep brain stimulation.
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Affiliation(s)
- F Munoz
- Dept. of Neuroscience, Columbia University, United States; Zuckerman Mind Brain Behavior Institute, Columbia University, United States.
| | - A Meaney
- Zuckerman Mind Brain Behavior Institute, Columbia University
| | | | - K Liu
- Dept. of Biomedical Engineering, Columbia University
| | | | - D Liu
- Dept. of Neuroscience, Columbia University,Zuckerman Mind Brain Behavior Institute, Columbia University
| | - EE Konofagou
- Dept. of Biomedical Engineering, Columbia University,Dept. of Radiology, Columbia University
| | - VP Ferrera
- Dept. of Neuroscience, Columbia University,Zuckerman Mind Brain Behavior Institute, Columbia University,Dept. of Psychiatry, Columbia University
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Galan-Acosta L, Sierra C, Leppert A, Pouliopoulos AN, Kwon N, Noel RL, Tambaro S, Presto J, Nilsson P, Konofagou EE, Johansson J. Recombinant BRICHOS chaperone domains delivered to mouse brain parenchyma by focused ultrasound and microbubbles are internalized by hippocampal and cortical neurons. Mol Cell Neurosci 2020; 105:103498. [PMID: 32389804 DOI: 10.1016/j.mcn.2020.103498] [Citation(s) in RCA: 12] [Impact Index Per Article: 3.0] [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: 11/06/2019] [Revised: 04/30/2020] [Accepted: 05/02/2020] [Indexed: 02/08/2023] Open
Abstract
The BRICHOS domain is found in human precursor proteins associated with cancer, dementia (Bri2) and amyloid lung disease (proSP-C). Recombinant human (rh) proSP-C and Bri2 BRICHOS domains delay amyloid-β peptide (Aβ) fibril formation and reduce associated toxicity in vitro and their overexpression reduces Aβ neurotoxicity in animal models of Alzheimer's disease. After intravenous administration in wild-type mice, rh Bri2, but not proSP-C, BRICHOS was detected in the brain parenchyma, suggesting that Bri2 BRICHOS selectively bypasses the blood-brain barrier (BBB). Here, our objective was to increase the brain delivery of rh proSP-C (trimer of 18 kDa subunits) and Bri2 BRICHOS (monomer to oligomer of 15 kDa subunits) using focused ultrasound combined with intravenous microbubbles (FUS + MB), which enables targeted and transient opening of the BBB. FUS + MB was targeted to one hemisphere of wild type mice and BBB opening in the hippocampal region was confirmed by magnetic resonance imaging. Two hours after FUS + MB brain histology showed no signs of tissue damage and immunohistochemistry showed abundant delivery to the brain parenchyma in 13 out of 16 cases given 10 mg/kg of proSP-C or Bri2 BRICHOS domains. The Bri2, but not proSP-C BRICHOS domain was detected also in the non-targeted hemisphere. ProSP-C and Bri2 BRICHOS domains were taken up by a subset of neurons in the hippocampus and cortex, and were detected to a minor extent in early endosomes. These results indicate that rh Bri2, but not proSP-C, BRICHOS, can be efficiently delivered into the mouse brain parenchyma and that both BRICHOS domains can be internalized by cell-specific mechanisms.
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Affiliation(s)
- L Galan-Acosta
- Department of Neurobiology, Care Sciences and Society (NVS), Division of Neurogeriatrics, Karolinska Institutet, 141 83 Huddinge, Sweden
| | - C Sierra
- Ultrasound and Elasticity Imaging Laboratory, Department of Biomedical Engineering, Columbia University, NY, New York, USA
| | - A Leppert
- Department of Neurobiology, Care Sciences and Society (NVS), Division of Neurogeriatrics, Karolinska Institutet, 141 83 Huddinge, Sweden
| | - A N Pouliopoulos
- Ultrasound and Elasticity Imaging Laboratory, Department of Biomedical Engineering, Columbia University, NY, New York, USA
| | - N Kwon
- Ultrasound and Elasticity Imaging Laboratory, Department of Biomedical Engineering, Columbia University, NY, New York, USA
| | - R L Noel
- Ultrasound and Elasticity Imaging Laboratory, Department of Biomedical Engineering, Columbia University, NY, New York, USA
| | - S Tambaro
- Department of Neurobiology, Care Sciences and Society (NVS), Division of Neurogeriatrics, Karolinska Institutet, 141 83 Huddinge, Sweden
| | - J Presto
- Department of Neurobiology, Care Sciences and Society (NVS), Division of Neurogeriatrics, Karolinska Institutet, 141 83 Huddinge, Sweden
| | - P Nilsson
- Department of Neurobiology, Care Sciences and Society (NVS), Division of Neurogeriatrics, Karolinska Institutet, 141 83 Huddinge, Sweden
| | - E E Konofagou
- Ultrasound and Elasticity Imaging Laboratory, Department of Biomedical Engineering, Columbia University, NY, New York, USA; Department of Radiology, Columbia University, NY, New York, USA
| | - J Johansson
- Department of Neurobiology, Care Sciences and Society (NVS), Division of Neurogeriatrics, Karolinska Institutet, 141 83 Huddinge, Sweden.
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Abstract
Image-guided monitoring of microbubble-based focused ultrasound (FUS) therapies relies on the accurate localization of FUS-stimulated microbubble activity (i.e. acoustic cavitation). Passive cavitation imaging with ultrasound arrays can achieve this, but with insufficient spatial resolution. In this study, we address this limitation and perform high-resolution monitoring of acoustic cavitation-mediated blood-brain barrier (BBB) opening with a new technique called power cavitation imaging. By synchronizing the FUS transmit and passive receive acquisition, high-resolution passive cavitation imaging was achieved by using delay and sum beamforming with absolute time delays. Since the axial image resolution is now dependent on the duration of the received acoustic cavitation emission, short pulses of FUS were used to limit its duration. Image sets were acquired at high-frame rates for calculation of power cavitation images analogous to power Doppler imaging. Power cavitation imaging displays the mean intensity of acoustic cavitation over time and was correlated with areas of acoustic cavitation-induced BBB opening. Power cavitation-guided BBB opening with FUS could constitute a standalone system that may not require MRI guidance during the procedure. The same technique can be used for other acoustic cavitation-based FUS therapies, for both safety and guidance.
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Affiliation(s)
- M T Burgess
- Department of Biomedical Engineering, Columbia University, New York, NY, United States of America
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7
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Kamimura HAS, Wang S, Wu SY, Karakatsani ME, Acosta C, Carneiro AAO, Konofagou EE. Chirp- and random-based coded ultrasonic excitation for localized blood-brain barrier opening. Phys Med Biol 2016; 60:7695-712. [PMID: 26394091 DOI: 10.1088/0031-9155/60/19/7695] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
Chirp- and random-based coded excitation methods have been proposed to reduce standing wave formation and improve focusing of transcranial ultrasound. However, no clear evidence has been shown to support the benefits of these ultrasonic excitation sequences in vivo. This study evaluates the chirp and periodic selection of random frequency (PSRF) coded-excitation methods for opening the blood-brain barrier (BBB) in mice. Three groups of mice (n = 15) were injected with polydisperse microbubbles and sonicated in the caudate putamen using the chirp/PSRF coded (bandwidth: 1.5–1.9 MHz, peak negative pressure: 0.52 MPa, duration: 30 s) or standard ultrasound (frequency: 1.5 MHz, pressure: 0.52 MPa, burst duration: 20 ms, duration: 5 min) sequences. T1-weighted contrast-enhanced MRI scans were performed to quantitatively analyze focused ultrasound induced BBB opening. The mean opening volumes evaluated from the MRI were mm3, mm3and mm3 for the chirp, random and regular sonications, respectively. The mean cavitation levels were V.s, V.s and V.s for the chirp, random and regular sonications, respectively. The chirp and PSRF coded pulsing sequences improved the BBB opening localization by inducing lower cavitation levels and smaller opening volumes compared to results of the regular sonication technique. Larger bandwidths were associated with more focused targeting but were limited by the frequency response of the transducer, the skull attenuation and the microbubbles optimal frequency range. The coded methods could therefore facilitate highly localized drug delivery as well as benefit other transcranial ultrasound techniques that use higher pressure levels and higher precision to induce the necessary bioeffects in a brain region while avoiding damage to the surrounding healthy tissue.
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Konofagou E. TU-EF-210-03: Real-Time Ablation Monitoring and Lesion Quantification Using Harmonic Motion Imaging. Med Phys 2015. [DOI: 10.1118/1.4925712] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022] Open
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Wang S, Olumolade OO, Sun T, Samiotaki G, Konofagou EE. Noninvasive, neuron-specific gene therapy can be facilitated by focused ultrasound and recombinant adeno-associated virus. Gene Ther 2014; 22:104-10. [PMID: 25354683 DOI: 10.1038/gt.2014.91] [Citation(s) in RCA: 98] [Impact Index Per Article: 9.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/18/2014] [Revised: 07/30/2014] [Accepted: 08/26/2014] [Indexed: 02/04/2023]
Abstract
Recombinant adeno-associated virus (rAAV) has shown great promise as a potential cure for neurodegenerative diseases. The existence of the blood-brain barrier (BBB), however, hinders efficient delivery of the viral vectors. Direct infusion through craniotomy is the most commonly used approach to achieve rAAV delivery, which carries increased risks of infection and other complications. Here, we report a focused ultrasound (FUS)-facilitated noninvasive rAAV delivery paradigm that is capable of producing targeted and neuron-specific transductions. Oscillating ultrasound contrast agents (microbubbles), driven by FUS waves, temporarily 'unlock' the BBB, allowing the systemically administrated rAAVs to enter the brain parenchyma, while maintaining their bioactivity and selectivity. Taking the advantage of the neuron-specific promoter synapsin, rAAV gene expression was triggered almost exclusively (95%) in neurons of the targeted caudate-putamen region. Both behavioral assessment and histological examination revealed no significant long-term adverse effects (in the brain and several other critical organs) for this combined treatment paradigm. Results from this study demonstrated the feasibility and safety for the noninvasive, targeted rAAV delivery, which might have open a new avenue in gene therapy in both preclinical and clinical settings.
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Affiliation(s)
- S Wang
- Ultrasound and Elasticity Imaging Laboratory, Department of Biomedical Engineering, Columbia University, New York, NY, USA
| | - O O Olumolade
- Ultrasound and Elasticity Imaging Laboratory, Department of Biomedical Engineering, Columbia University, New York, NY, USA
| | - T Sun
- Ultrasound and Elasticity Imaging Laboratory, Department of Biomedical Engineering, Columbia University, New York, NY, USA
| | - G Samiotaki
- Ultrasound and Elasticity Imaging Laboratory, Department of Biomedical Engineering, Columbia University, New York, NY, USA
| | - E E Konofagou
- 1] Ultrasound and Elasticity Imaging Laboratory, Department of Biomedical Engineering, Columbia University, New York, NY, USA [2] Department of Radiology, Columbia University, New York, NY, USA
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Abstract
Ultrasonic strain imaging has been applied to echocardiography and carries great potential to be used as a tool in the clinical setting. Two-dimensional (2D) strain estimation may be useful when studying the heart due to the complex, 3D deformation of the cardiac tissue. Increasing the framerate used for motion estimation, i.e. motion estimation rate (MER), has been shown to improve the precision of the strain estimation, although maintaining the spatial resolution necessary to view the entire heart structure in a single heartbeat remains challenging at high MERs. Two previously developed methods, the temporally unequispaced acquisition sequence (TUAS) and the diverging beam sequence (DBS), have been used in the past to successfully estimate in vivo axial strain at high MERs without compromising spatial resolution. In this study, a stochastic assessment of 2D strain estimation precision is performed in vivo for both sequences at varying MERs (65, 272, 544, 815 Hz for TUAS; 250, 500, 1000, 2000 Hz for DBS). 2D incremental strains were estimated during left ventricular contraction in five healthy volunteers using a normalized cross-correlation function and a least-squares strain estimator. Both sequences were shown capable of estimating 2D incremental strains in vivo. The conditional expected value of the elastographic signal-to-noise ratio (E(SNRe|ε)) was used to compare strain estimation precision of both sequences at multiple MERs over a wide range of clinical strain values. The results here indicate that axial strain estimation precision is much more dependent on MER than lateral strain estimation, while lateral estimation is more affected by strain magnitude. MER should be increased at least above 544 Hz to avoid suboptimal axial strain estimation. Radial and circumferential strain estimations were influenced by the axial and lateral strain in different ways. Furthermore, the TUAS and DBS were found to be of comparable precision at similar MERs.
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Affiliation(s)
- E A Bunting
- Department of Biomedical Engineering, Columbia University, New York, NY, USA
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Konofagou E, Lee W, Ingrassia C. A theoretical performance assessment tool for myocardial elastography. Conf Proc IEEE Eng Med Biol Soc 2012; 2006:985-8. [PMID: 17282351 DOI: 10.1109/iembs.2005.1616582] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Abstract
The main purpose of this paper is to develop a theoretical tool in order to fundamentally characterize the performance of Myocardial Elastography and identify the optimal parameters to be used for the more reliable detection of ischemia or infarction. A complete representation of the left-ventricular function throughout an entire cardiac cycle was previously demonstrated through the use of a 3D finite-element analysis (FEA) model. This FEA model together with an ultrasound image formation model is used here in order to test the performance of 2D Myocardial Elastography at distinct phases of the cardiac cycle and at different states of myocardium, i.e., normal and ischemic, based on in vivo canine data. A previously developed 3D finite-element analysis (FEA) model of a normal canine left ventricle with 80 nodes and 40 elements was used to simulate all main phases of the cardiac cycle. The axial and lateral displacements within multiple image (x-y) planes across the left-ventricular volume were iteratively calculated and corrected to reduce the decorrelation noise. Given the excellent agreement between the FEA solution and the elastographic strains measured in 2D over an entire simulated cardiac cycle, Myocardial Elastography proves to be a reliable technique for the accurate assessment of the myocardial deformation in 2D at distinct phases of the cardiac cycle as well as detection of the ischemic region. Preliminary in vivo results of a standard short-axis view in a canine myocardium are shown validating the performance assessment using the proposed model.
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Affiliation(s)
- E Konofagou
- Associate Member, IEEE, departments of biomedical engineering and radiology of Columbia University, New York, NY 10032, USA (212-342-0863; fax: 212-342-5773; e-mail: )
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Konofagou E, Spalazzi J, Lu H. Elastographic Imaging of the Strain Distribution at the Anterior Cruciate Ligament and ACL-Bone Insertions. Conf Proc IEEE Eng Med Biol Soc 2012; 2006:972-5. [PMID: 17282348 DOI: 10.1109/iembs.2005.1616579] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Abstract
The anterior cruciate ligament (ACL) functions as a mechanical stabilizer in the tibiofemoral joint. Over 250,000 Americans each year suffer ACL ruptures and tears, making the ACL the most commonly injured knee ligament. Methods which permit the in situ monitoring of changes in ACL graft mechanical properties during healing are needed. A long term goal in ACL reconstruction is to regenerate the ACL-bone interface. To this end, an understanding of mechanical properties of the ligament-bone interface is needed. However, experimental determination has been difficult due the small length scale (<1 mm) involved and limited resolution of standard techniques. The current study uses elastography to characterize the functional properties of the ACL and the ACL-bone interface under applied load. In a first experiment, bovine joints were excised, cast in an agar gel matrix and externally compressed. In a second experiment, tibiofemoral joints were mounted on a MTS 858 Bionix Testing System. The ACL was loaded at different strain rates and tested to failure while RF data was collected at 5 MHz. For both tensile and compression testing, axial elastograms between successive RF frames were generated using cross-correlation and recorrelation techniques. When the ACL-bone complex was tested in the tibial alignment on the MTS system, compressive strains were found to dominate at the tibial insertion. Compressive strains were observed in the ligament proper when the transducer beam was aligned with respect to the insertion during loading.
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Affiliation(s)
- E Konofagou
- Associate Member, IEEE, Departments of Biomedical Engineering and Radiology of Columbia University, New York, NY 10032, USA (212-342-0863; fax: 212-342-5773; e-mail: )
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Okrasinski SJ, Ramachandran B, Konofagou EE. Assessment of myocardial elastography performance in phantoms under combined physiologic motion configurations with preliminary in vivo feasibility. Phys Med Biol 2012; 57:5633-50. [PMID: 22892701 PMCID: PMC3704133 DOI: 10.1088/0031-9155/57/17/5633] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
Myocardial elastography (ME) is a non-invasive, ultrasound-based strain imaging technique, which can detect and localize abnormalities in myocardial function. By acquiring radio-frequency (RF) frames at high frame rates, the deformation of the myocardium can be estimated, and used to identify regions of abnormal deformation indicative of cardiovascular disease. In this study, the primary objective is to evaluate the effect of torsion on the performance of ME, while the secondary objective is to image inclusions during different motion schemes. Finally, the phantom findings are validated with an in vivo human case. Phantoms of homogeneous stiffness, or containing harder inclusions, were fixed to a pump and motors, and imaged. Incremental displacements were estimated from the RF signals, and accumulated over a motion cycle, and rotation angle, radial strain and circumferential strain were estimated. Phantoms were subjected to four motion schemes: rotation, torsion, deformation, and a combination of torsion and deformation. Sonomicrometry was used as a gold standard during deformation and combined motion schemes. In the rotation scheme, the input and estimated rotation angle agree in both the homogeneous and inclusion phantoms. In the torsion scheme, the estimated rotation angle was found to be highest, closest to the source of torsion and lowest farthest from the source of torsion. In the deformation scheme, if an inclusion was not present, the estimated strain patterns accurately depicted homogeneity, while if an inclusion was present, abnormalities were observed which enabled detection of the inclusion. In addition, no significant rotation was detected. In the combined scheme, if an inclusion was not present, the estimated strain patterns accurately depicted homogeneity, while, if an inclusion was present, abnormalities were observed which enabled detection of the inclusion. Also, torsion was separated from the combined scheme and was found to be similar to the pure torsion findings. This study shows ME to be capable of accurately depicting and distinguishing between different types of motion schemes, and to be sensitive to stiffness changes in localized regions of tissue-mimicking phantoms under physiologic cardiac motion configurations, while strains estimated in the combined motion scheme were noisier than in individual motion schemes. Finally, ME was shown to be capable of distinguishing between deformation and rotation in a normal human heart in vivo.
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Affiliation(s)
- S J Okrasinski
- Department of Biomedical Engineering, Columbia University, 622 West 168th St., Vanderbilt Clinic, New York, NY 10032, USA
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Khamdaeng T, Luo J, Vappou J, Terdtoon P, Konofagou EE. Arterial stiffness identification of the human carotid artery using the stress-strain relationship in vivo. Ultrasonics 2012; 52:402-11. [PMID: 22030473 PMCID: PMC4009743 DOI: 10.1016/j.ultras.2011.09.006] [Citation(s) in RCA: 85] [Impact Index Per Article: 7.1] [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: 07/05/2011] [Revised: 09/20/2011] [Accepted: 09/20/2011] [Indexed: 05/06/2023]
Abstract
Arterial stiffness is well accepted as a reliable indicator of arterial disease. Increase in carotid arterial stiffness has been associated with carotid arterial disease, e.g., atherosclerotic plaque, thrombosis, stenosis, etc. Several methods for carotid arterial stiffness assessment have been proposed. In this study, in vivo noninvasive assessment using applanation tonometry and an ultrasound-based motion estimation technique was applied in seven healthy volunteers (age 28±3.6years old) to determine pressure and wall displacement in the left common carotid artery (CCA), respectively. The carotid pressure was obtained using a calibration method by assuming that the mean and diastolic blood pressures remained constant throughout the arterial tree. The regional carotid arterial wall displacement was estimated using a 1D cross-correlation technique on the ultrasound radio frequency (RF) signals acquired at a frame rate of 505-1010Hz. Young's moduli were estimated under two different assumptions: (i) a linear elastic two-parallel spring model and (ii) a two-dimensional, nonlinear, hyperelastic model. The circumferential stress (σ(θ)) and strain (ɛ(θ)) relationship was then established in humans in vivo. A slope change in the circumferential stress-strain curve was observed and defined as the transition point. The Young's moduli of the elastic lamellae (E(1)), elastin-collagen fibers (E(2)) and collagen fibers (E(3)) and the incremental Young's moduli before ( [Formula: see text] ) and after the transition point ( [Formula: see text] ) were determined from the first and second approach, respectively, to describe the contribution of the complex mechanical interaction of the different arterial wall constituents. The average moduli E(1), E(2) and E(3) from seven healthy volunteers were found to be equal to 0.15±0.04, 0.89±0.27 and 0.75±0.29MPa, respectively. The average moduli [Formula: see text] and [Formula: see text] of the intact wall (both the tunica adventitia and tunica media layers) were found to be equal to 0.16±0.04MPa and 0.90±0.25MPa, respectively. The average moduli [Formula: see text] and [Formula: see text] of the tunica adventitia were found to be equal to 0.18±0.05MPa and 0.84±0.22MPa, respectively. The average moduli [Formula: see text] and [Formula: see text] of the tunica media were found to be equal to 0.19±0.05MPa and 0.90±0.25MPa, respectively. The stiffness of the carotid artery increased with strain during the systolic phase. In conclusion, the feasibility of measuring the regional stress-strain relationship and stiffness of the normal human carotid artery was demonstrated noninvasively in vivo.
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Affiliation(s)
- T Khamdaeng
- Department of Mechanical Engineering, Chiang Mai University, Chiang Mai, Thailand
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Vappou J, Luo J, Okajima K, Di Tullio M, Konofagou EE. Non-invasive measurement of local pulse pressure by pulse wave-based ultrasound manometry (PWUM). Physiol Meas 2011; 32:1653-62. [PMID: 21904023 DOI: 10.1088/0967-3334/32/10/012] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/23/2023]
Abstract
Central blood pressure (CBP) has been established as a relevant indicator of cardiovascular disease. Despite its significance, CBP remains particularly challenging to measure in standard clinical practice. The objective of this study is to introduce pulse wave-based ultrasound manometry (PWUM) as a simple-to-use, non-invasive ultrasound-based method for quantitative measurement of the central pulse pressure. Arterial wall displacements are estimated using radiofrequency ultrasound signals acquired at high frame rates and the pulse pressure waveform is estimated using both the distension waveform and the local pulse wave velocity. The method was tested on the abdominal aorta of 11 healthy subjects (age 35.7 ± 16 y.o.). PWUM pulse pressure measurements were compared to those obtained by radial applanation tonometry using a commercial system. The average intra-subject variability of the pulse pressure amplitude was found to be equal to 4.2 mmHg, demonstrating good reproducibility of the method. Excellent correlation was found between the waveforms obtained by PWUM and those obtained by tonometry in all subjects (0.94 < r < 0.98). A significant bias of 4.7 mmHg was found between PWUM and tonometry. PWUM is a highly translational method that can be easily integrated in clinical ultrasound imaging systems. It provides an estimate of the pulse pressure waveform at the imaged location, and may offer therefore the possibility to estimate the pulse pressure at different arterial sites. Future developments include the validation of the method against invasive estimates on patients, as well as its application to other large arteries.
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Affiliation(s)
- J Vappou
- Ultrasound and Elasticity Imaging Laboratory, Columbia University, New York, NY, USA
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Konofagou E. WE-B-220-01: Ultrasound-Guided Techniques for HIFU Monitoring. Med Phys 2011. [DOI: 10.1118/1.3613307] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022] Open
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Vlachos F, Tung YS, Konofagou EE. Permeability assessment of the focused ultrasound-induced blood-brain barrier opening using dynamic contrast-enhanced MRI. Phys Med Biol 2010; 55:5451-66. [PMID: 20736501 DOI: 10.1088/0031-9155/55/18/012] [Citation(s) in RCA: 67] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
Focused ultrasound (FUS) in conjunction with microbubbles has been shown to successfully open the blood-brain barrier (BBB) in the mouse brain. In this study, we compute the BBB permeability after opening in vivo. The spatial permeability of the BBB-opened region was assessed using dynamic contrast-enhanced MRI (DCE-MRI). The DCE-MR images were post-processed using the general kinetic model (GKM) and the reference region model (RRM). Permeability maps were generated and the K(trans) values were calculated for a predefined volume of interest in the sonicated and the control area for each mouse. The results demonstrated that K(trans) in the BBB-opened region (0.02 +/- 0.0123 for GKM and 0.03 +/- 0.0167 min(-1) for RRM) was at least two orders of magnitude higher when compared to the contra-lateral (control) side (0 and 8.5 x 10(-4) +/- 12 x 10(-4) min(-1), respectively). The permeability values obtained with the two models showed statistically significant agreement and excellent correlation (R(2) = 0.97). At histological examination, it was concluded that no macroscopic damage was induced. This study thus constitutes the first permeability assessment of FUS-induced BBB opening using DCE-MRI, supporting the fact that the aforementioned technique may constitute a safe, non-invasive and efficacious drug delivery method.
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Affiliation(s)
- F Vlachos
- Department of Biomedical Engineering, Columbia University, New York, NY 10027, USA
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Maleke C, Konofagou EE. Harmonic motion imaging for focused ultrasound (HMIFU): a fully integrated technique for sonication and monitoring of thermal ablation in tissues. Phys Med Biol 2008; 53:1773-93. [PMID: 18367802 DOI: 10.1088/0031-9155/53/6/018] [Citation(s) in RCA: 74] [Impact Index Per Article: 4.6] [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
FUS (focused ultrasound), or HIFU (high-intensity-focused ultrasound) therapy, a minimally or non-invasive procedure that uses ultrasound to generate thermal necrosis, has been proven successful in several clinical applications. This paper discusses a method for monitoring thermal treatment at different sonication durations (10 s, 20 s and 30 s) using the amplitude-modulated (AM) harmonic motion imaging for focused ultrasound (HMIFU) technique in bovine liver samples in vitro. The feasibility of HMI for characterizing mechanical tissue properties has previously been demonstrated. Here, a confocal transducer, combining a 4.68 MHz therapy (FUS) and a 7.5 MHz diagnostic (pulse-echo) transducer, was used. The therapy transducer was driven by a low-frequency AM continuous signal at 25 Hz, producing a stable harmonic radiation force oscillating at the modulation frequency. A pulser/receiver was used to drive the pulse-echo transducer at a pulse repetition frequency (PRF) of 5.4 kHz. Radio-frequency (RF) signals were acquired using a standard pulse-echo technique. The temperature near the ablation region was simultaneously monitored. Both RF signals and temperature measurements were obtained before, during and after sonication. The resulting axial tissue displacement was estimated using one-dimensional cross correlation. When temperature at the focal zone was above 48 degrees C during heating, the coagulation necrosis occurred and tissue damage was irreversible. The HMI displacement profiles in relation to the temperature and sonication durations were analyzed. At the beginning of heating, the temperature at the focus increased sharply, while the tissue stiffness decreased resulting in higher HMI displacements. This was confirmed by an increase of 0.8 microm degrees C(-1)(r=0.93, p<.005). After sustained heating, the tissue became irreversibly stiffer, followed by an associated decrease in the HMI displacement (-0.79 microm degrees C(-1), r=-0.92, p<0.001). Repeated experiments showed a reproducible pattern of the HMI displacement changes with a temperature at a slope equal to 0.8+/-0.11 and -0.79+/-0.14 microm degrees C(-1), prior to and after lesion formation in seven bovine liver samples, respectively. This technique was thus capable of following the protein-denatured lesion formation based on the variation of the HMI displacements. This method could, therefore, be applied for real-time monitoring of temperature-related stiffness changes of tissues during FUS, HIFU or other thermal therapies.
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Affiliation(s)
- C Maleke
- Department of Biomedical Engineering, Columbia University, New York, NY, USA.
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Choi JJ, Pernot M, Brown TR, Small SA, Konofagou EE. Spatio-temporal analysis of molecular delivery through the blood-brain barrier using focused ultrasound. Phys Med Biol 2007; 52:5509-30. [PMID: 17804879 DOI: 10.1088/0031-9155/52/18/004] [Citation(s) in RCA: 91] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
The deposition of gadolinium through ultrasound-induced blood-brain barrier (BBB) openings in the murine hippocampus was investigated. First, wave propagation simulations through the intact mouse skull revealed minimal beam distortion while thermal deposition simulations, at the same sonication parameters used to induce BBB opening in vivo, revealed temperature increases lower than 0.5 degrees C. The simulation results were validated experimentally in ex vivo skulls (m = 6) and in vitro tissue specimens. Then, in vivo mice (n = 9) were injected with microbubbles (Optison; 25-50 microl) and sonicated (frequency: 1.525 MHz, pressure amplitudes: 0.5-1.1 MPa, burst duration: 20 ms, duty cycle: 20%, durations: 2-4 shots, 30 s per shot, 30 s interval) at the left hippocampus, through intact skin and skull. Sequential, high-resolution, T1-weighted MRI (9.4 Tesla, in-plane resolution: 75 microm, scan time: 45-180 min) with gadolinium (Omniscan; 0.5 ml) injected intraperitoneally revealed a threshold of the BBB opening at 0.67 MPa and BBB closing within 28 h from opening. The contrast-enhancement area and gadolinium deposition path were monitored over time and the influence of vessel density, size and location was determined. Sonicated arteries, or their immediate surroundings, depicted greater contrast enhancement than sonicated homogeneous brain tissue regions. In conclusion, gadolinium was delivered through a transiently opened BBB and contained to a specific brain region (i.e., the hippocampus) using a single-element focused ultrasound transducer. It was also found that the amount of gadolinium deposited in the hippocampal region increased with the acoustic pressure and that the spatial distribution of the BBB opening was determined not only by the ultrasound beam, but also by the vasculature of the targeted brain region.
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Affiliation(s)
- J J Choi
- Department of Biomedical Engineering, Columbia University, New York, USA
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Zervantonakis IK, Fung-Kee-Fung SD, Lee WN, Konofagou EE. A novel, view-independent method for strain mapping in myocardial elastography: eliminating angle and centroid dependence. Phys Med Biol 2007; 52:4063-80. [PMID: 17664595 DOI: 10.1088/0031-9155/52/14/004] [Citation(s) in RCA: 48] [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] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
Robust indices of regional and global cardiac function are a key factor in detection and treatment of heart disease as well as understanding of the fundamental mechanisms of a healthy heart. Myocardial elastography provides a noninvasive method for imaging and measuring displacement and strain of the myocardium for the early detection of cardiovascular disease. However, two-dimensional in-plane axial and lateral strains measured depend on the sonographic view used. This becomes especially critical in a clinical setting and may induce large variations in the measured strains, potentially leading to false diagnoses. A novel method in myocardial elastography is proposed for eliminating this view dependence by deriving the polar, principal and classified principal strains. The performance of the proposed methodology is assessed by employing 3D finite-element left-ventricular models of a control and an ischemic canine heart. Although polar strains are angle-independent, they are sensitive to the selected reference coordinate system, which requires the definition of a centroid of the left ventricle (LV). In contrast, principal strains derived through eigenvalue decomposition exhibit the inherent characteristic of coordinate system independence, offering view (i.e., angle and centroid)-independent strain measurements. Classified principal strains are obtained by assigning the principal components in the physical ventricular coordinate system. An extensive strain analysis illustrates the improvement in interpretation and visualization of the full-field myocardial deformation by using the classified principal strains, clearly depicting the ischemic and non-ischemic regions. Strain maps, independent of sonographic views and imaging planes, that can be used to accurately detect regional contractile dysfunction are demonstrated.
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Affiliation(s)
- I K Zervantonakis
- Department of Biomedical Engineering, Columbia University, New York, NY, USA
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Konofagou EE, Ottensmeyer M, Agabian S, Dawson SL, Hynynen K. Estimating localized oscillatory tissue motion for assessment of the underlying mechanical modulus. Ultrasonics 2004; 42:951-956. [PMID: 15047412 DOI: 10.1016/j.ultras.2003.12.001] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/24/2023]
Abstract
The technique of harmonic motion imaging (HMI) uses the localized stimulus of the oscillatory ultrasonic radiation force as produced by two overlapping beams of distinct frequencies, and estimates the resulting harmonic displacement in the tissue in order to assess its underlying mechanical properties. In this paper, we studied the relationship between measured displacement and stiffness in gels and tissues in vitro. Two focused ultrasound transducers with a 100 mm focal length were used at frequencies of 3.7500 MHz and either 3.7502 (or 3.7508 MHz), respectively, in order to produce an oscillatory motion at 200 Hz in the gel or tissue. A 1.1 MHz diagnostic transducer (Imasonics, Inc.) was also focused at 100 mm and acquired 5 ms RF signals (pulse repetition frequency (PRF)=3.5 kHz) at 100 MHz sampling frequency during radiation force application. First, three 50x50 mm(2) acrylamide gels were prepared at concentrations of 4%, 8% and 16%. The resulting displacement was estimated using crosscorrelation techniques between successively acquired RF signals with a 2 mm window and 80% window overlap at 1260 W/cm(2). A normal 1-D indentation instrument (TeMPeST) applied oscillatory loads at 0.1-200 Hz with a 5 mm-diameter flat indenter. Then, 12 displacement measurements in 6 porcine muscle specimens (two measurements/case, as above) were made in vitro, before and after ablation which was performed for 10 s at 1260 W/cm(2). In all gel cases, the harmonic displacement was found to linearly increase with intensity and exponentially decrease with gel concentration. The TeMPeST measurements showed that the elastic moduli for the 4%, 8% and 16% gels equaled 3.93+/-0.06, 17.1+/-0.2 and 75+/-2 kPa, respectively, demonstrating that the HMI displacement estimate depends directly on the gel stiffness. Finally, in the tissues samples, the mean displacement amplitude showed a twofold decrease between non-ablated and ablated tissue, demonstrating a correspondence between the HMI response and an increase in stiffness measured with the TeMPeST instrument.
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Affiliation(s)
- E E Konofagou
- Department of Biomedical Engineering, Columbia University, New York, NY 10027, USA.
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Abstract
In the past decade, an important field that has emerged as complementary to ultrasonic imaging is that of elasticity imaging. The term encompasses a variety of techniques that can depict a mechanical response or property of tissues. In ultrasound, its premise is built on two important facts: (a) that significant differences between mechanical properties of several tissue components exist and (b) that the information contained in the coherent scattering, or speckle, is sufficient to depict these differences following an external or internal mechanical stimulus. Parameters, such as velocity of vibration, displacement, strain, strain rate, velocity of wave propagation and elastic modulus, have all been demonstrated feasible in their estimation and have resulted in the accurate depiction of stiffer tissue masses, such as tumors, high-intensity focused ultrasound (HIFU) lesions and atherosclerotic plaques. More recently, through the development of ultrafast algorithms tailored to suitable hardware as well as the familiarity of the physician with the sensitivity of the methods used, one elasticity imaging technique in particular, elastography, has been shown applicable in a typical clinical ultrasound setting. In other words, elastograms can currently be obtained at quasi real-time (approximately at a frame rate of 8 frames/s) and with the use of a hand-held transducer (as opposed to the previously used frame-suspended setup) during and simultaneously with an ultrasound exam of, e.g., the breast or the prostate. The higher frame rate available with certain clinical ultrasound scanners has also resulted in the successful application of elasticity imaging techniques on the myocardium and monitoring its deformation over several cardiac cycles for the detection of ischemic regions. As a result, elasticity imaging with its ever increasing number of applications and demonstrated applicability in a typical, clinical ultrasound setting promises to make an important contribution to the ultrasound practice as we know it.
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Affiliation(s)
- E E Konofagou
- Department of Biomedical Engineering, Columbia University, 1210 Amsterdam Avenue, 351 Engineering Terrace, Mail Code 8, New York, NY 10027, USA.
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Abstract
Similar to other therapeutic methods, ultrasound surgery requires an imaging modality to monitor the extent of tissue damage during treatment. In this paper, we have considered the method of ultrasound-stimulated acoustic emission (USAE) that uses two ultrasonic beams at high frequency (1.7 MHz) (same as that used for ablation) to locally excite the tissue by generating a low-frequency (1-50 kHz) radiation force. Recording of the tissue response at several locations yields an image. The amplitude of the tissue response depends on the mechanical and acoustic tissue properties, namely its stiffness and absorption. These two properties were initially hypothesized to have counteractive effects on the response amplitude, i.e., the amplitude should increase with absorption and decrease with stiffness. To check this hypothesis as well as the degree to which these properties influence the response, finite-element simulations of a uniform lesion formed inside a homogeneous medium were used. The results show that, as expected, the displacement amplitude decreased with increasing lesion stiffness at lower frequencies (except at resonance) while, contrary to our initial hypothesis, it increased with stiffness at relatively higher frequencies (>22 kHz). At resonance, a frequency upshift occurred with increasing stiffness but was found to be highly spatially variant and system dependent, i.e., not yielding a uniform lesion response when imaged. On the other hand, the absorption increase led to a uniform linear increase of the mechanical response amplitude of the lesion. Therefore, at higher frequencies, increase of the two parameters had a synergistic effect on the tissue response to the applied radiation force. This study showed that relatively higher frequencies constitute the optimal range in the use of USAE for coagulation monitoring. A preliminary experimental verification in vitro is also provided.
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Affiliation(s)
- E Konofagou
- Department of Radiology, Brigham and Women's Hospital, Harvard Medical School, Boston, MA, USA
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Abstract
In the field of elastography, biological tissues are conveniently assumed to be purely elastic solids. However, several tissues, including brain, cartilage and edematous soft tissues, have long been known to be poroelastic. The objective of this study is to show the feasibility of imaging the poroelastic properties of tissue-like materials. A poroelastic material is a material saturated with fluid that flows relative to a deforming solid matrix. In this paper, we describe a method for estimating the poroelastic attributes of tissues. It has been analytically shown that during stress relaxation of a poroelastic material (i.e., sustained application of a constant applied strain over time), the lateral-to-axial strain ratio decreases exponentially with time toward the Poisson's ratio of the solid matrix. The time constant of this variation depends on the elastic modulus of the solid matrix, its permeability and its dimension along the direction of fluid flow. Recently, we described an elastographic method that can be used to map axial and lateral tissue strains. In this study, we use the same method in a stress relaxation case to measure the time-dependent lateral-to-axial strain ratio in poroelastic materials. The resulting time-sequenced images (poroelastograms) depict the spatial distribution of the fluid within the solid at each time instant, and help to differentiate poroelastic materials of distinct Poisson's ratios and permeabilities of the solid matrix. Results are shown from finite-element simulations.
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Affiliation(s)
- E E Konofagou
- Ultrasonics Laboratory, Department of Radiology, University of Texas Medical School-Houston, Houston, TX, USA.
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Abstract
This paper presents the tradeoffs in elastographic imaging. Elastography is viewed as a new imaging modality and presented in terms of three fundamental concepts that constitute the basis for the elastographic imaging process. These are the tissue elastic deformation process, the statistical analysis of strain estimation and the image characterization. The first concept involves the use of the contrast transfer efficiency (CTE) that describes the mapping of a distribution of local tissue elastic moduli into a distribution of local longitudinal tissue strains. The second concept defines the elastographic system and the relationship between ultrasonic and signal processing parameters. This process is described in terms of a stochastic framework (the strain filter) that provides upper and practical performance bounds and their dependence on the various system parameters. Finally, the output image, the elastogram, is characterized by its image parameters, such as signal-to-noise ratio, contrast-to-noise ratio, dynamic range and resolution. Finite-element simulations are used to generate examples of elastograms that are confirmed by the theoretical prediction tools.
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Affiliation(s)
- T Varghese
- The University of Texas Medical School, Department of Radiology, Houston 77030, USA.
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Abstract
Spectral estimation of tissue strain has been performed previously by using the centroid shift of the power spectrum or by estimating the variation in the mean scatterer spacing in the spectral domain. The centroid shift method illustrates the robustness of the direct, incoherent strain estimator. In this paper, we present a strain estimator that uses spectral cross-correlation of the pre- and postcompression power spectrum. The centroid shift estimator estimates strain from the mean center frequency shift, while the spectral cross-correlation estimates the shift over the entire spectrum. Spectral cross-correlation is shown to be more sensitive to small shifts in the power spectrum and, thus, provides better estimation for smaller strains when compared to the spectral centroid shift. Spectral cross-correlation shares all the advantages gained using the spectral centroid shift, in addition to providing accurate and precise strain estimation for small strains. The variance and noise properties of the spectral strain estimators quantified by their respective strain filters are also presented.
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Affiliation(s)
- T Varghese
- Ultrasonics Laboratory, The University of Texas Medical School, Houston, TX, USA.
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Konofagou EE, Varghese T, Ophir J. Theoretical bounds on the estimation of transverse displacement, transverse strain and Poisson's ratio in elastography. Ultrason Imaging 2000; 22:153-177. [PMID: 11297149 DOI: 10.1177/016173460002200302] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
Abstract
The Cramér-Rao Lower Bounds (CRLB) are derived for the displacement and strain estimation in directions orthogonal to the ultrasonic beam axis, using a previously-described recorrelation method of axial, lateral and elevational motion estimation. We also compare it to the lateral tracking method that involves the sole use of the axial signal in the transverse direction. Our theoretical results, verified with simulations and phantom experiments, show that elastography is capable of measuring axial and transverse strain at up to 10% axially applied compression. Finally, we predict the performance of the estimation of the Poisson's ratio using decoupled axial and lateral estimates that result from the recorrelation method.
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Affiliation(s)
- E E Konofagou
- Department of Radiology, University of Texas Medical School, Houston 77030, USA.
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Abstract
In elastography we have previously developed a tracking and correction method that estimates the axial and lateral strain components along and perpendicular to the compressor/scanning axis following an externally applied compression. However, the resulting motion is a three-dimensional problem. Therefore, in order to fully describe this motion we need to consider a 3D model and estimate all three principal strain components, i.e. axial, lateral and elevational (out-of-plane), for a full 3D tensor description. Since motion is coupled in all three dimensions, the three motion components have to be decoupled prior to their estimation. In this paper, we describe a method that estimates and corrects motion in three dimensions, which is an extension of the 2D motion tracking and correction method discussed before. In a similar way as in the 2D motion estimation, and by assuming that ultrasonic frames are available in more than one parallel elevational plane, we used methods of interpolation and cross-correlation between elevationally displaced RF echo segments to estimate the elevational displacement and strain. In addition, the axial, lateral and elevational displacements were used to estimate all three shear strain components that, together with the normal strain estimates, fully describe the full 3D normal strain tensor resulting from the uniform compression. Results of this method from three-dimensional finite-element simulations are shown.
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Affiliation(s)
- E E Konofagou
- Department of Radiology, The University of Texas Medical School, Houston 77030, USA
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Affiliation(s)
- J Ophir
- Department of Radiology, The University of Texas Medical School, Ultrasonics Laboratory, Houston, Texas 77030, USA.
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Abstract
Like velocity, strain induces a time delay and a time scaling to the received signal. Elastography typically uses time delay techniques to indirectly (i.e. via the displacement estimate) measure tissue strain induced by an applied compression, and considers time scaling as a source of distortion. More recently, we have shown that the time scaling factor can also be spectrally estimated and used as a direct measure of strain. Strain causes a Doppler-like frequency shift and a change in bandwidth of the bandpass power spectrum of the echo signal. Two frequency shift strain estimators are described that have been proven to be more robust but less precise when compared to time delay estimators, both in simulations and experiments. The increased robustness is due to the insensitivity of the spectral techniques to phase decorrelation noise. In this paper we discuss and compare the theoretical and experimental findings obtained with traditional time delay estimators and with the newly proposed spectral methods.
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Affiliation(s)
- E E Konofagou
- Department of Radiology, University of Texas Medical School, Houston 77030, USA.
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Abstract
Elastography typically measures and images the normal strain component along the insonification/compression axis, i.e., in the axial direction. We have recently shown that, by using interpolation and cross-correlation methods of transversely displaced RF echo segments, it is possible to measure and image displacement and strain transversely to the beam with good precision. This enables the estimation and imaging of all three principal normal strain components. Generally, motion in a direction other than that in which strain is estimated may result in decorrelation noise, severely corrupting the estimates. Therefore, a correction method is applied to correct the displacement and strain estimates for decorrelating motion. In this paper, we show how corrected displacement estimates can also be used to estimate and image the shear strain components. This may allow us to identify regions of decorrelation noise in the normal strain measurement that are due to shear strain. Shear strain estimates provide supplementary information, which can characterize different tissue elements based on their mobility. In the case of breast lesions, low mobility is related to malignancy. Following an in vivo case, we show with 2D simulations how assessment of tumor mobility can be achieved with shear strain estimation.
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Affiliation(s)
- E E Konofagou
- Department of Radiology, University of Texas Medical School, Houston 77030, USA.
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Abstract
Elastography can produce quality strain images in vitro and in vivo. Standard elastography uses a coherent cross-correlation technique to estimate tissue displacement and tissue strain using a subsequent gradient operator. Although coherent estimation methods generally have the advantage of being highly accurate and precise, even relatively small undesired motions are likely to cause enough signal decorrelation to produce significant degradation of the elastogram. For elastography to become more universally practical in such applications as hand-held, intravascular and abdominal imaging, the limitations associated with coherent strain estimation methods that require tissue and system stability, must be overcome. In this paper, we propose the use of a spectral-shift method that uses a centroid shift estimate to measure local strain directly. Furthermore, we also show theoretically that a spectral bandwidth method can also provide a direct strain estimation. We demonstrate that strain estimation using the spectral-shift technique is moderately less precise, but far more robust than the cross-correlation method. A theoretical analysis, simulations and experimental results are used to illustrate the properties associated with this method.
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Affiliation(s)
- E E Konofagou
- Department of Radiology, The University of Texas Medical School, Houston 77030, USA.
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34
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Ophir J, Alam SK, Garra B, Kallel F, Konofagou E, Krouskop T, Varghese T. Elastography: ultrasonic estimation and imaging of the elastic properties of tissues. Proc Inst Mech Eng H 1999; 213:203-33. [PMID: 10420776 DOI: 10.1243/0954411991534933] [Citation(s) in RCA: 416] [Impact Index Per Article: 16.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
The basic principles of using sonographic techniques for imaging the elastic properties of tissues are described, with particular emphasis on elastography. After some preliminaries that describe some basic tissue stiffness measurements and some contrast transfer limitations of strain images are presented, four types of elastograms are described, which include axial strain, lateral strain, modulus and Poisson's ratio elastograms. The strain filter formalism and its utility in understanding the noise performance of the elastographic process is then given, as well as its use for various image improvements. After discussing some main classes of elastographic artefacts, the paper concludes with recent results of tissue elastography in vitro and in vivo.
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Affiliation(s)
- J Ophir
- Department of Radiology, University of Texas Medical School, Houston 77030, USA
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35
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Abstract
Elastography has been shown to be successful in mapping the relative mechanical attributes of normal as well as abnormal tissues. In this study, the histological characteristics of freshly excised normal canine prostates were used to explain consistently depicted elastographic features. The elastograms of the transverse cross-sections across the urethra demonstrated a consistent symmetry of the gland as well as clear anatomic structures. These include a central portion of the gland surrounding the urethra and a peripheral gland. The central gland was consistently softer than the peripheral gland. At the level of the verumontanum, depicted as a small stiff ridge, the lumen of the urethra was consistently demonstrated as an inverted soft 'u' or 'v' shaped area. The network of branching-fibrous connective tissue septa was depicted by the elastogram as linear features, which converged on the urethra. In the anterior side of the gland, the fibromuscular stroma was seen as a circumscribed hard tissue. In the sagittal view, the elastogram suggested a stiff peripheral zone surrounding a softer central zone, which is traversed by the urethra depicted as soft tissue.
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Affiliation(s)
- F Kallel
- Department of Radiology, University of Texas Medical School, Houston 77030, USA. .
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36
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Konofagou E, Ophir J. A new elastographic method for estimation and imaging of lateral displacements, lateral strains, corrected axial strains and Poisson's ratios in tissues. Ultrasound Med Biol 1998; 24:1183-99. [PMID: 9833588 DOI: 10.1016/s0301-5629(98)00109-4] [Citation(s) in RCA: 276] [Impact Index Per Article: 10.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/10/2023]
Abstract
A major disadvantage of the current practice of elastography is that only the axial component of the strain is estimated. The lateral and elevational components are basically disregarded, yet they corrupt the axial strain estimation by inducing decorrelation noise. In this paper, we describe a new weighted interpolation method operating between neighboring RF A-lines for high precision tracking of the lateral displacement. Due to this high lateral-tracking precision, quality lateral elastograms are generated that display the lateral component of the strain tensor. These precision lateral-displacement estimates allow a fine correction for the lateral decorrelation that corrupts the axial estimation. Finally, by dividing the lateral elastogram by the axial elastogram, we are able to produce a new image that displays the distribution of Poisson's ratios in the tissue. Results are presented from finite-element simulations and phantoms as well as in vitro and in vivo experiments.
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Affiliation(s)
- E Konofagou
- Department of Radiology, The University of Texas Medical School, Houston 77030, USA
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37
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Abstract
Elastography is based on the estimation of strain due to applied tissue compression. In conventional elastography, strain is computed from the gradient of the displacement estimates between gated pre- and postcompression echo signals. Gradient-based estimation methods are known to be susceptible to noise. In elastography, in addition to the electronic noise, a principal source of estimation error is the decorrelation of the echo signal as a result of tissue compression (decorrelation noise). Temporal stretching of postcompression signals previously was shown to reduce the decorrelation noise. In this paper, we introduce a novel estimator that uses the stretch factor itself as an estimator of the strain. It uses an iterative algorithm that adaptively maximises the correlation between the pre- and postcompression echo signals by appropriately stretching the latter. We investigate the performance of this adaptive strain estimator using simulated and experimental data. The estimator has exhibited a vastly superior performance compared with the conventional gradient-based estimator.
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Affiliation(s)
- S K Alam
- Ultrasonics Lab., Texas Med. Sch., Houston, TX
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38
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Abstract
In elastography, we want to image the entire range of stiffnesses of the elastic components found in inhomogeneous tissues. In order to achieve this, the elastographic dynamic range should equal the entire stiffness dynamic range in the target. Various sources of noise limit the dynamic range of elastography. The recently-defined strain filter concept offers an analytical and graphical way of observing these limitations. In this paper, we describe a method that achieves the expansion of the elastographic dynamic range. It involves the application of variable strains in combination with selective storage of strain data that have optimal elastographic signal-to-noise ratios. This expands the current dynamic range of elastography by orders of magnitude when compared to single compression elastography. The process is explained theoretically using the strain filter framework, and 1 D as well as 2D tissue simulations are used to corroborate the theory.
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Affiliation(s)
- E E Konofagou
- Department of Radiology, University of Texas Medical School, Houston 77030, USA
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Konofagou E, Dutta P, Ophir J, Céspedes I. Reduction of stress nonuniformities by apodization of compressor displacement in elastography. Ultrasound Med Biol 1996; 22:1229-1236. [PMID: 9123647 DOI: 10.1016/s0301-5629(96)00147-0] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.4] [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
Elastography is a method for imaging the elastic properties of compliant tissues that produces gray-scale strain or elasticity images called elastograms. The method is based on external tissue compression, with ultrasonic detection of local target displacements and subsequent computation of strain profiles along the compression axis. The internal strain variations are a result of the tissue elasticity variations and the applied deformation or compression. A number of mechanical artifacts that appear in elastograms have been identified. One such artifact appears as the result of a nonuniform stress distribution under the compressors used, including darkening (low stress) of the central region and brightening (high stress) of the peripheral regions under the compressor. On an elastogram, these areas may be misinterpreted as being respectively harder and softer than the rest of the target. In this article, a displacement apodization method for the minimization of this artifact is discussed, and its effects are studied using finite element simulations. When the isometric compression of standard elastography was replaced by an apodized displacement profile calculated from reciprocity conditions, a significant improvement in stress uniformity under the compressor was achieved.
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Affiliation(s)
- E Konofagou
- Department of Radiology, University of Texas Medical School, Houston, USA
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