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Khan S, Neuhaus K, Thaware O, Ni S, Ju MJ, Redd T, Huang D, Jian Y. Corneal imaging with blue-light optical coherence microscopy. BIOMEDICAL OPTICS EXPRESS 2022; 13:5004-5014. [PMID: 36187260 PMCID: PMC9484440 DOI: 10.1364/boe.465707] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/03/2022] [Revised: 08/17/2022] [Accepted: 08/17/2022] [Indexed: 06/16/2023]
Abstract
Corneal imaging is important for the diagnostic and therapeutic evaluation of many eye diseases. Optical coherence tomography (OCT) is extensively used in ocular imaging due to its non-invasive and high-resolution volumetric imaging characteristics. Optical coherence microscopy (OCM) is a technical variation of OCT that can image the cornea with cellular resolution. Here, we demonstrate a blue-light OCM as a low-cost and easily reproducible system to visualize corneal cellular structures such as epithelial cells, endothelial cells, keratocytes, and collagen bundles within stromal lamellae. Our blue-light OCM system achieved an axial resolution of 12 µm in tissue over a 1.2 mm imaging depth, and a lateral resolution of 1.6 µm over a field of view of 750 µm × 750 µm.
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Affiliation(s)
- Shanjida Khan
- Casey Eye Institute, Oregon Health & Science University, Portland, OR 97239, USA
- Department of Biomedical Engineering, Oregon Health & Science University, Portland, OR 97239, USA
| | - Kai Neuhaus
- Casey Eye Institute, Oregon Health & Science University, Portland, OR 97239, USA
| | - Omkar Thaware
- Casey Eye Institute, Oregon Health & Science University, Portland, OR 97239, USA
- Department of Biomedical Engineering, Oregon Health & Science University, Portland, OR 97239, USA
| | - Shuibin Ni
- Casey Eye Institute, Oregon Health & Science University, Portland, OR 97239, USA
- Department of Biomedical Engineering, Oregon Health & Science University, Portland, OR 97239, USA
| | - Myeong Jin Ju
- Department of Ophthalmology and Visual
Sciences, University of British Columbia,
Vancouver, BC, Canada
- School of Biomedical Engineering,
University of British Columbia, Vancouver,
BC, Canada
| | - Travis Redd
- Casey Eye Institute, Oregon Health & Science University, Portland, OR 97239, USA
| | - David Huang
- Casey Eye Institute, Oregon Health & Science University, Portland, OR 97239, USA
- Department of Biomedical Engineering, Oregon Health & Science University, Portland, OR 97239, USA
| | - Yifan Jian
- Casey Eye Institute, Oregon Health & Science University, Portland, OR 97239, USA
- Department of Biomedical Engineering, Oregon Health & Science University, Portland, OR 97239, USA
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Germann JA, Martínez-Enríquez E, Martínez-García MC, Kochevar IE, Marcos S. Corneal Collagen Ordering After In Vivo Rose Bengal and Riboflavin Cross-Linking. Invest Ophthalmol Vis Sci 2020; 61:28. [PMID: 32186674 PMCID: PMC7401826 DOI: 10.1167/iovs.61.3.28] [Citation(s) in RCA: 12] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023] Open
Abstract
Purpose Photoactivated cornea collagen cross-linking (CXL) increases corneal stiffness by initiating formation of covalent bonds between stromal proteins. Because CXL depends on diffusion to distribute the photoinitiator, a gradient of CXL efficiency with depth is expected that may affect the degree of stromal collagen organization. We used second harmonic generation (SHG) microscopy to investigate the differences in stromal collagen organization in rabbit eyes after corneal CXL in vivo as a function of depth and time after surgery. Methods Rabbit corneas were treated in vivo with either riboflavin/UV radiation (UVX) or Rose Bengal/green light (RGX) and evaluated 1 and 2 months after CXL. Collagen fibers were imaged with a custom-built SHG scanning microscope through the central cornea (350 µm depth, 225 × 225 µm en face images). The order coefficient (OC), a metric for collagen organization, and total SHG signal were computed for each depth and compared between treatments. Results OC values of CXL-treated corneas were larger than untreated corneas by 27% and 20% after 1 month and 38% and 33% after 2 months for the RGX and UVX, respectively. RGX OC values were larger than UVX OC values by 3% and 5% at 1 and 2 months. The SHG signal was higher in CXL corneas than untreated corneas, both at 1 and 2 months after surgery, by 18% and 26% and 1% and 10% for RGX and UVX, respectively. Conclusions Increased OC corresponded with increased collagen fiber organization in CXL corneas. Changes in collagen organization parallel reported temporal changes in cornea stiffness after CXL and also, surprisingly, are detected deeper in the stroma than the regions stiffened by collagen cross-links.
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Lee SL, Chen YF, Dong CY. Second harmonic generation imaging reveals asymmetry in the rotational helicity of collagen lamellae in chicken corneas. BIOMEDICAL OPTICS EXPRESS 2019; 10:5223-5234. [PMID: 31646043 PMCID: PMC6788602 DOI: 10.1364/boe.10.005223] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/15/2019] [Revised: 09/04/2019] [Accepted: 09/05/2019] [Indexed: 05/03/2023]
Abstract
High tensile strength and optical clarity are unique properties of the cornea. These features are dictated by the three-dimensional architecture of corneal lamellae. Therefore, understanding the microscopic details of the cornea's structural organization may contribute to the development of artificial cornea for the treatment of corneal diseases. In this study, the combination of forward second harmonic generation (SHG) microcopy and fast Fourier-transform based image analysis was used to characterize the depth-dependent superstructure of chicken corneal stroma. Our results show that from the surface, adjacent lamellae of anterior chicken cornea lamella rotate in a counterclockwise direction, and the same rotational helicity is observed in left and right corneas. Furthermore, the overall average rotational pitch of lamellae is 0.92 ± 0.11 degree/µm which persists for 176 ± 14 µm in the anterior stroma. As depth further increased, the rate of lamellar rotation decreases. Upon reaching posterior stroma, lamellar orientation remains constant. Throughout the stroma, collagen lamellae in chicken rotate a total of 169 ± 21 degrees. The lack of lamellar rotation in posterior stroma suggests that packing efficiency cannot be used to explain the helicity of depth-dependent rotation of anterior stroma. In addition, although the right cornea has a higher rotational pitch (0.95 ± 11 vs 0.90 ± 10 degrees/µm) and thinner anterior stroma (173 ± 13 vs 179 ± 14 µm) than the left cornea, the two effects cancel each other out and result in similar total angular rotation of anterior stroma (161 ± 23 and 165 degrees ± 21). Finally, our observation of a total angular rotation of 169 ± 21 degrees shows that within experimental error, chicken cornea lamellae rotate around 180 degrees or half of a complete turn. Additional studies are needed to arrive at an explanation of chicken superstructure in three dimensions.
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Affiliation(s)
- Sheng-Lin Lee
- Department of Physics, National Taiwan University, Taipei 106, Taiwan, China
| | - Yang-Fang Chen
- Department of Physics, National Taiwan University, Taipei 106, Taiwan, China
| | - Chen-Yuan Dong
- Department of Physics, National Taiwan University, Taipei 106, Taiwan, China
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Ávila FJ, Artal P, Bueno JM. Quantitative Discrimination of Healthy and Diseased Corneas With Second Harmonic Generation Microscopy. Transl Vis Sci Technol 2019; 8:51. [PMID: 31293806 PMCID: PMC6601709 DOI: 10.1167/tvst.8.3.51] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/17/2018] [Accepted: 04/30/2019] [Indexed: 12/20/2022] Open
Abstract
Purpose To analyze the spatial organization of pathological corneas with second harmonic generation (SHG) imaging and to provide a proof of concept to objectively distinguish these from the healthy corneas. Methods A custom-built SHG microscope was used to image the anterior stroma of ex vivo corneas, both control and affected by some representative pathologies. The structure tensor (ST) was employed as a metric to explore and quantify the alterations in the spatial distribution of the collagen lamellae. Results The collagen arrangement differed between healthy and pathological samples. The former showed a regular distribution and a low structural dispersion (SD < 40°) within the stroma with a well-defined dominant orientation. This regular arrangement drastically turns into a disorganized pattern in pathological corneas (SD > 40°). Conclusions The combination of SHG imaging and the ST allows obtaining quantitative information to differentiate the stromal collagen organization in healthy and diseased corneas. This approach represents a feasible and powerful technique with potential applications in clinical corneal diagnoses. Translational Relevance The ST applied to SHG microscopy images of the corneal stroma provides an experimental objective score to differentiate control from pathological or damaged corneas. Future implementations of this technique in clinical environments might might be a promising tool in Ophthalmology, not only to diagnose and monitor corneal diseases, but also to follow-up surgical outcome.
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Affiliation(s)
- Francisco J Ávila
- Laboratorio de Óptica, Instituto Universitario de Investigación en Óptica y Nanofísica, Universidad de Murcia, Murcia, Spain
| | - Pablo Artal
- Laboratorio de Óptica, Instituto Universitario de Investigación en Óptica y Nanofísica, Universidad de Murcia, Murcia, Spain
| | - Juan M Bueno
- Laboratorio de Óptica, Instituto Universitario de Investigación en Óptica y Nanofísica, Universidad de Murcia, Murcia, Spain
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Kim H, Jang J, Park J, Lee KP, Lee S, Lee DM, Kim KH, Kim HK, Cho DW. Shear-induced alignment of collagen fibrils using 3D cell printing for corneal stroma tissue engineering. Biofabrication 2019; 11:035017. [PMID: 30995622 DOI: 10.1088/1758-5090/ab1a8b] [Citation(s) in RCA: 89] [Impact Index Per Article: 17.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023]
Abstract
The microenvironments of tissues or organs are complex architectures comprised of structural proteins including collagen. Particularly, the cornea is organized in a lattice pattern of collagen fibrils which play a significant role in its transparency. This paper introduces a transparent bioengineered corneal structure for transplantation. The structure is fabricated by inducing shear stress to a corneal stroma-derived decellularized extracellular matrix bioink based on a 3D cell printing technique. The printed structure recapitulates the native macrostructure of the cornea with aligned collagen fibrils which results in the construction of a highly matured and transparent cornea stroma analog. The level of shear stress, controlled by the various size of the printing nozzle, manipulates the arrangement of the fibrillar structure. With proper parameter selection, the printed cornea exhibits high cellular alignment capability, indicating a tissue-specific structural organization of collagen fibrils. In addition, this structural regulation enhances critical cellular events in the assembly of collagen over time. Interestingly, the collagen fibrils that remodeled along with the printing path create a lattice pattern similar to the structure of native human cornea after 4 weeks in vivo. Taken together, these results establish the possibilities and versatility of fabricating aligned collagen fibrils; this represents significant advances in corneal tissue engineering.
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Affiliation(s)
- Hyeonji Kim
- Department of Mechanical Engineering, Pohang University of Science and Technology, 77 Cheongam-ro, Pohang, Gyeongbuk, 37673, Republic of Korea
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Quantitative Analysis of the Corneal Collagen Distribution after In Vivo Cross-Linking with Second Harmonic Microscopy. BIOMED RESEARCH INTERNATIONAL 2019; 2019:3860498. [PMID: 30756083 PMCID: PMC6348900 DOI: 10.1155/2019/3860498] [Citation(s) in RCA: 16] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 07/24/2018] [Revised: 10/24/2018] [Accepted: 12/04/2018] [Indexed: 12/14/2022]
Abstract
Corneal cross-linking (CXL) is a surgical procedure able to modify corneal biomechanics and stabilize keratoconus progression. Although it is known that CXL produces changes in corneal collagen distribution, these are still a topic of discussion. Here we quantitatively compare the corneal stroma architecture between two animal models four weeks after in vivo conventional CXL treatment, with second harmonic generation (SHG) imaging microscopy and the structure tensor (ST). The healing stage and the stroma recovery were also analyzed by means of histological sections. Results show that the CXL effects depend on the initial arrangement of the corneal collagen. While the treatment increases the order in corneas with a low level of initial organization, corneas presenting a fairly regular pattern are hardly affected. Histological samples showed active keratocytes in anterior and middle stroma, what means that the recovery is still in progress. The combination of SHG imaging and the ST is able to objectively discriminate the changes suffered by the collagen arrangement after the CXL treatment, whose effectiveness depends on the initial organization of the collagen fibers within the corneal stroma.
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Germann JA, Martinez-Enriquez E, Marcos S. Quantization of collagen organization in the stroma with a new order coefficient. BIOMEDICAL OPTICS EXPRESS 2018; 9:173-189. [PMID: 29359095 PMCID: PMC5772573 DOI: 10.1364/boe.9.000173] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/26/2017] [Revised: 11/20/2017] [Accepted: 11/21/2017] [Indexed: 05/20/2023]
Abstract
Many optical and biomechanical properties of the cornea, specifically the transparency of the stroma and its stiffness, can be traced to the degree of order and direction of the constituent collagen fibers. To measure the degree of order inside the cornea, a new metric, the order coefficient, was introduced to quantify the organization of the collagen fibers from images of the stroma produced with a custom-developed second harmonic generation microscope. The order coefficient method gave a quantitative assessment of the differences in stromal collagen arrangement across the cornea depths and between untreated stroma and cross-linked stroma.
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Stanciu SG, Ávila FJ, Hristu R, Bueno JM. A Study on Image Quality in Polarization-Resolved Second Harmonic Generation Microscopy. Sci Rep 2017; 7:15476. [PMID: 29133836 PMCID: PMC5684207 DOI: 10.1038/s41598-017-15257-0] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/05/2017] [Accepted: 10/24/2017] [Indexed: 01/21/2023] Open
Abstract
Second harmonic generation (SHG) microscopy represents a very powerful tool for tissue characterization. Polarization-resolved SHG (PSHG) microscopy extends the potential of SHG, by exploiting the dependence of SHG signals on the polarization state of the excitation beam. Among others, this dependence translates to the fact that SHG images collected under different polarization configurations exhibit distinct characteristics in terms of content and appearance. These characteristics hold deep implications over image quality, as perceived by human observers or by image analysis methods custom designed to automatically extract a quality factor from digital images. Our work addresses this subject, by investigating how basic image properties and the outputs of no-reference image quality assessment methods correlate to human expert opinion in the case of PSHG micrographs. Our evaluation framework is based on SHG imaging of collagen-based ocular tissues under different linear and elliptical polarization states of the incident light.
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Affiliation(s)
- Stefan G Stanciu
- Center for Microscopy-Microanalysis and Information Processing, University Politehnica of Bucharest, Bucharest, Romania.
| | | | - Radu Hristu
- Center for Microscopy-Microanalysis and Information Processing, University Politehnica of Bucharest, Bucharest, Romania
| | - Juan M Bueno
- Laboratorio de Óptica, Universidad de Murcia, Murcia, Spain.
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Bueno JM, Ávila FJ, Artal P. Comparison of second harmonic microscopy images of collagen-based ocular tissues with 800 and 1045 nm. BIOMEDICAL OPTICS EXPRESS 2017; 8:5065-5074. [PMID: 29188103 PMCID: PMC5695953 DOI: 10.1364/boe.8.005065] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/21/2017] [Revised: 10/11/2017] [Accepted: 10/17/2017] [Indexed: 06/07/2023]
Abstract
Second harmonic generation (SHG) imaging is a well-suited multiphoton technique allowing visualization of biological tissues mainly composed of collagen with submicron resolution. Despite its inherent confocal properties, imaging of deeper layers within thick samples has still some limitations. Although the use of longer wavelengths might help to overcome this, the dependence between SHG signals and wavelength is still under discussion. We report here on the dependence with wavelength of SHG signals from collagen-based ocular tissues. The quality of SHG images for two commonly used excitation wavelengths (800 and 1045 nm) is studied. The analysis of the collagen structural information reveals that the information provided by both wavelengths is similar. It was also found that, independently of the depth location, 1045-nm SHG images presented always lower signal levels than those acquired with 800 nm. However, the contrast of the former images was higher, what may improve the visualization of certain features of interest.
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Ávila FJ, Del Barco O, Bueno JM. Polarization response of second-harmonic images for different collagen spatial distributions. JOURNAL OF BIOMEDICAL OPTICS 2016; 21:66015. [PMID: 27330006 DOI: 10.1117/1.jbo.21.6.066015] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/22/2016] [Accepted: 06/01/2016] [Indexed: 05/11/2023]
Abstract
The response to polarization of second-harmonic generation (SHG) microscopy images of samples with different collagen distributions (quasialigned, partially organized, and nonorganized) has been analyzed. A linear decay relationship between the external arrangement and polarization sensitivity was found. SHG signal from nonorganized samples presented a large structural dispersion and a weak dependence with incident polarization. Polarization dependence is also associated with the internal organization of the collagen fibers, directly related to the ratio of hyperpolarizabilities ρ. This parameter can experimentally be computed from the modulation of the SHG signal. The results show that both external and internal collagen structures are closely related. This provides a tool to obtain information of internal properties from the polarimetric response of the external spatial distribution of collagen, which might be useful in clinical diagnosis of pathologies related to changes in collagen structure.
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Ávila FJ, Bueno JM. Analysis and quantification of collagen organization with the structure tensor in second harmonic microscopy images of ocular tissues. APPLIED OPTICS 2015; 54:9848-54. [PMID: 26836548 DOI: 10.1364/ao.54.009848] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/20/2023]
Abstract
The important biological role of collagen-based tissues and the changes produced in the fiber distribution under particular situations (surgery, pathology, external damage, etc.) require tools for the analysis of the collagen organization that might potentially help in early diagnoses. Since collagen structures provide efficient second harmonic generation (SHG) signals, SHG microscopy has emerged as a powerful technique to visualize collagen fibers and qualitatively discriminate normal from abnormal tissues. Here we propose a quantitative method based on the structure tensor to quantify the different organization of collagen patterns in SHG images of ocular tissues. Results show that well-organized collagen distributions present a high degree of isotropy (DoI), a dominant orientation (PO), and a low structural dispersion (SD). On the other hand, the PO vanishes when the collagen tissue is not organized as a consequence of an increase in the SD and a decrease in the DoI. The proposed method is also able to discriminate partially organized samples. The combination of SHG microscopy and the structure tensor is a useful method to objectively classify collagen distributions. Clinical applications of this technique could help in the diagnosis and tracking of pathologies related to collagen disorders in connective tissue.
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Lombardo M, Merino D, Loza-Alvarez P, Lombardo G. Translational label-free nonlinear imaging biomarkers to classify the human corneal microstructure. BIOMEDICAL OPTICS EXPRESS 2015; 6:2803-18. [PMID: 26309745 PMCID: PMC4541509 DOI: 10.1364/boe.6.002803] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/27/2015] [Revised: 06/10/2015] [Accepted: 06/12/2015] [Indexed: 05/18/2023]
Abstract
Diseases that affect the cornea can lead to severe vision loss and have tremendous social impact. These diseases are associated to deviations from normal structural order and orientation of collagen fibril bundles. Unfortunately, resolving non-invasively the corneal collagen structure is not possible to date. In this work, polarization sensitive second harmonic generation (pSHG) microscopy is used to obtain information with molecular specificity on microstructure of human corneas. This information is used to develop a set of label-free imaging biomarkers that were generated by means of a novel methodology based on mathematical tensorial calculus. The method is proven to be highly sensitive and robust. The use of these biomarkers permits accurate characterization of the anisotropic, depth-dependent, structural organization of corneal collagen fibril bundles without any a priori information. The method can be valuable to improve understanding of microstructural pathophysiological changes of the human cornea close to in vivo conditions.
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Affiliation(s)
| | - David Merino
- ICFO-Institut de Ciencies Fotoniques, Mediterranean Technology Park, 08860 Barcelona, Spain
| | - Pablo Loza-Alvarez
- ICFO-Institut de Ciencies Fotoniques, Mediterranean Technology Park, 08860 Barcelona, Spain
| | - Giuseppe Lombardo
- CNR-IPCF - Consiglio Nazionale delle Ricerche, Istituto per i Processi Chimico-Fisici, 98158 Messina, Italy
- Vision Engineering Italy srl, 00198 Rome, Italy
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Meyer T, Schmitt M, Dietzek B, Popp J. Accumulating advantages, reducing limitations: multimodal nonlinear imaging in biomedical sciences - the synergy of multiple contrast mechanisms. JOURNAL OF BIOPHOTONICS 2013; 6:887-904. [PMID: 24259267 DOI: 10.1002/jbio.201300176] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/06/2013] [Accepted: 11/06/2013] [Indexed: 05/29/2023]
Abstract
Multimodal nonlinear microscopy has matured during the past decades to one of the key imaging modalities in life science and biomedicine due to its unique capabilities of label-free visualization of tissue structure and chemical composition, high depth penetration, intrinsic 3D sectioning, diffraction limited resolution and low phototoxicity. This review briefly summarizes first recent advances in the field regarding the methodology, e.g., contrast mechanisms and signal characteristics used for contrast generation as well as novel image processing approaches. The second part deals with technologic developments emphasizing improvements in penetration depth, imaging speed, spatial resolution and nonlinear labeling strategies. The third part focuses on recent applications in life science fundamental research and biomedical diagnostics as well as future clinical applications.
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Affiliation(s)
- Tobias Meyer
- Institute of Physical Chemistry and Abbe Center of Photonics, Friedrich-Schiller-University Jena, Helmholtzweg 4, 07743 Jena, Germany
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