1
|
Redaelli E, Nana M, Calvo B, Rodríguez Matas JF, Luraghi G, Rozema J, Grasa J. Improving early detection of keratoconus by Non Contact Tonometry. A computational study and new biomarkers proposal. J Mech Behav Biomed Mater 2024; 152:106413. [PMID: 38281439 DOI: 10.1016/j.jmbbm.2024.106413] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/16/2023] [Revised: 01/08/2024] [Accepted: 01/17/2024] [Indexed: 01/30/2024]
Abstract
Keratoconus is a progressive ocular disorder affecting the corneal tissue, leading to irregular astigmatism and decreased visual acuity. The architectural organization of corneal tissue is altered in keratoconus, however, data from ex vivo testing of biomechanical properties of keratoconic corneas are limited and it is unclear how their results relate to true mechanical properties in vivo. This study explores the mechanical properties of keratoconic corneas through numerical simulations of non-contact tonometry (NCT) reproducing the clinical test of the Corvis ST device. Three sensitivity analyses were conducted to assess the impact of corneal material properties, size, and location of the pathological area on NCT results. Additionally, novel asymmetry-based indices were proposed to better characterize corneal deformations and improve the diagnosis of keratoconus. Our results show that the weakening of corneal material properties leads to increased deformation amplitude and altered biomechanical response. Furthermore, asymmetry indices offer valuable information for locating the pathological tissue. These findings suggest that adjusting the Corvis ST operation, such as a camera rotation, could enhance keratoconus detection and provide insights into the relative position of the affected area. Future research could explore the application of these indices in detecting early-stage keratoconus and assessing the fellow eye's risk for developing the pathology.
Collapse
Affiliation(s)
- Elena Redaelli
- Aragón Institute of Engineering Research (I3A), Universidad de Zaragoza, Zaragoza, Spain.
| | - Michael Nana
- LaBS, Department of Chemistry, Materials and Chemical Engineering "Giulio Natta", Politecnico di Milano, Milan, Italy
| | - Begoña Calvo
- Aragón Institute of Engineering Research (I3A), Universidad de Zaragoza, Zaragoza, Spain; Centro de Investigación Biomecánica en Red en Bioingeniería, Biomateriales y Nanomedicina (CIBER-BBN), Zaragoza, Spain
| | - José Félix Rodríguez Matas
- LaBS, Department of Chemistry, Materials and Chemical Engineering "Giulio Natta", Politecnico di Milano, Milan, Italy
| | - Giulia Luraghi
- LaBS, Department of Chemistry, Materials and Chemical Engineering "Giulio Natta", Politecnico di Milano, Milan, Italy
| | - Jos Rozema
- Visual Optics Lab Antwerp (VOLANTIS), Faculty of Medicine & Health Sciences, University of Antwerp, Antwerp, Belgium; Department of Ophthalmology, Antwerp University Hospital, Edegem, Belgium
| | - Jorge Grasa
- Aragón Institute of Engineering Research (I3A), Universidad de Zaragoza, Zaragoza, Spain; Centro de Investigación Biomecánica en Red en Bioingeniería, Biomateriales y Nanomedicina (CIBER-BBN), Zaragoza, Spain
| |
Collapse
|
2
|
Shih HJ, Cheng SC, Shih PJ. Experimental evaluation of corneal stress-optic coefficients using a pair of force test. J Mech Behav Biomed Mater 2024; 152:106454. [PMID: 38354567 DOI: 10.1016/j.jmbbm.2024.106454] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/10/2023] [Revised: 01/04/2024] [Accepted: 01/31/2024] [Indexed: 02/16/2024]
Abstract
BACKGROUND Topography and tomography are valuable techniques for measuring the corneal shape, but they cannot directly assess its internal mechanical stresses. And nonuniform corneal stress plays a crucial biomechanical role in the progression of diseases and postoperative changes. Given the cornea's inherent transparency, analyzing corneal stresses using the photoelasticity method is highly advantageous. However, quantification of photoelasticity faces challenges in obtaining the stress-optic coefficient due to wrinkles caused by the non-spherical geometry during tensional experiments. OBJECTIVE In this study, we propose an innovative experimental setup aimed at generating a gradient field of simple shear stress and achieving surface flatness during corneal stretching experiments, enabling the acquisition of the stress-optic coefficient through comparison with numerical results. METHODS Our designed setup applies fluid pressure and force couples on the cornea. The internal fluid pressure maintains the corneal shape, preventing wrinkles, while the force couples create a stress field leading to isochromatic fringes. RESULTS We successfully measured the stress-optic coefficients of the porcine anisotropic cornea in ex-vivo as 1.87 × 10-9 (horizontal) and 1.97 × 10-9 (vertical) (m2/N). Each isochromatic fringe order represents a shear stress range of 6.05 × 104 Pa under a low tension. CONCLUSIONS This study establishes a significant connection between corneal photoelastic patterns and the quantification of corneal stress by enabling direct measurement through advanced photoelastic visualization technology for clinical applications.
Collapse
Affiliation(s)
- Hua-Ju Shih
- Institute of Applied Mechanics, National Taiwan University, Taipei, Taiwan
| | - Shan-Chien Cheng
- Department of Mechanical Engineering, National Taiwan University, Taipei, Taiwan
| | - Po-Jen Shih
- Department of Biomedical Engineering, National Taiwan University, Taipei, Taiwan.
| |
Collapse
|
3
|
Shih PJ, Shih HJ, Wang IJ, Chang SW. The extraction and application of antisymmetric characteristics of the cornea during air-puff perturbations. Comput Biol Med 2024; 168:107804. [PMID: 38070205 DOI: 10.1016/j.compbiomed.2023.107804] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/28/2023] [Revised: 11/04/2023] [Accepted: 11/29/2023] [Indexed: 01/10/2024]
Abstract
BACKGROUND A non-contact tonometer is used to measure intraocular pressure, and studies have primarily relied on apex displacements to assess corneal properties. However, previous studies have overlooked the asymmetric characteristics of lateral corneal perturbations, leading to a gap in understanding of the lateral mechanical properties and its application. METHOD To investigate these lateral perturbations, we designed an experiment to sequentially record the corneal profiles when two consecutive air-puffs were applied at the center of the same cornea within a short period. Moreover, we used modal decomposition to decompose anterior surface profiles into symmetric and antisymmetric modes to comprehensively analyze the asymmetric characteristics. To extract mechanical properties, we utilized high-pass frequency analysis (>250 Hz) to filter out noise and errors. RESULTS Symmetric modes between the two consecutive air-puffs exhibited major similarities during vibration; however, antisymmetric modes exhibited minor differences in lateral perturbations of asymmetric vibration. The antisymmetric modes might be related to air-puff misalignment and mechanical properties. Through applying frequency analysis, the mechanical properties could be proven at high frequencies and misalignment shown at low frequencies. Furthermore, we compared the corneal vibration profiles of 259 healthy participants and 50 patients with keratoconus. Their properties showed that the antisymmetric modes of the keratoconus group exhibited a completely opposite direction of deformation compared to that in the healthy group. CONCLUSIONS Our proposed algorithm not only extracts antisymmetric characteristics but also offers valuable insights into decompose misalignment and mechanical properties of healthy and keratoconus corneas, presenting a new perspective for corneal biomechanics.
Collapse
Affiliation(s)
- Po-Jen Shih
- Department of Biomedical Engineering, National Taiwan University, Taipei, Taiwan.
| | - Hua-Ju Shih
- Department of Otolaryngology, National Taiwan University Hospital, Taipei, Taiwan
| | - I-Jong Wang
- Department of Ophthalmology, National Taiwan University Hospital, Taipei, Taiwan
| | - Shu-Wen Chang
- Department of Ophthalmology, Far Eastern Memorial Hospital, New Taipei City, Taiwan.
| |
Collapse
|
4
|
Urizar MP, Gambra E, de Castro A, de la Peña Á, Pascual D, Cetinkaya O, Marcos S, Curatolo A. Long-range frequency-domain optical delay line based on a spinning tilted mirror for low-cost ocular biometry. BIOMEDICAL OPTICS EXPRESS 2023; 14:6521-6541. [PMID: 38420323 PMCID: PMC10898555 DOI: 10.1364/boe.501889] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 08/02/2023] [Revised: 10/25/2023] [Accepted: 10/27/2023] [Indexed: 03/02/2024]
Abstract
Optical biometers are routinely used to measure intraocular distances in ophthalmic applications such as cataract surgery planning or myopia monitoring. However, due to their high cost and reduced transportability, access to them for screening and surgical planning is still limited in low-resource and remote settings. To increase patients' access to optical biometry we propose a novel low-cost frequency-domain optical delay line (FD-ODL) based on an inexpensive stepper motor spinning a tilted mirror, for integration into a time-domain (TD)-biometer, amenable to a compact footprint. In the proposed FD-ODL, the axial scan range and the A-scan rate are decoupled from one another, as the former only depends on the spinning mirror tilt angle, while the A-scan rate only depends on the motor shaft rotational speed. We characterized the scanning performance and specifications for two spinning mirror tilt angles, and compared them to those of the standard, more expensive FD-ODL implementation, employing a galvanometric scanner for group delay generation. A prototype of the low-cost FD-ODL with a 1.5 deg tilt angle, resulting in an axial scan range of 6.61 mm and an A-scan rate of 10 Hz was experimentally implemented and integrated in a dual sample beam optical low-coherence reflectometry (OLCR) setup with a detour unit to replicate the measurement window around the anterior segment and the retina. The intraocular distances of a model eye were measured with the proposed low-cost biometer and found to be in good agreement with those acquired by a custom swept-source optical coherence tomography (SS-OCT) system and two commercial biometers, validating our novel design.
Collapse
Affiliation(s)
- María Pilar Urizar
- 2EyesVision S.L., Madrid, Spain
- Instituto de Óptica ‘Daza de Valdés’, Consejo Superior de Investigaciones Científicas (IO, CSIC), Madrid, Spain
| | | | - Alberto de Castro
- Instituto de Óptica ‘Daza de Valdés’, Consejo Superior de Investigaciones Científicas (IO, CSIC), Madrid, Spain
| | - Álvaro de la Peña
- Instituto de Óptica ‘Daza de Valdés’, Consejo Superior de Investigaciones Científicas (IO, CSIC), Madrid, Spain
| | - Daniel Pascual
- Instituto de Óptica ‘Daza de Valdés’, Consejo Superior de Investigaciones Científicas (IO, CSIC), Madrid, Spain
| | - Onur Cetinkaya
- International Centre for Translational Eye Research (ICTER), and Institute of Physical Chemistry, Polish Academy of Sciences (IPC-PAS), Warsaw, Poland
| | - Susana Marcos
- Instituto de Óptica ‘Daza de Valdés’, Consejo Superior de Investigaciones Científicas (IO, CSIC), Madrid, Spain
- The Institute of Optics and Flaum Eye Institute, Center for Visual Sciences, University of Rochester, New York, USA
| | - Andrea Curatolo
- Instituto de Óptica ‘Daza de Valdés’, Consejo Superior de Investigaciones Científicas (IO, CSIC), Madrid, Spain
- International Centre for Translational Eye Research (ICTER), and Institute of Physical Chemistry, Polish Academy of Sciences (IPC-PAS), Warsaw, Poland
| |
Collapse
|
5
|
Frigelli M, Büchler P, Kling S. Optomechanical assessment of photorefractive corneal cross-linking via optical coherence elastography. Front Bioeng Biotechnol 2023; 11:1272097. [PMID: 38026898 PMCID: PMC10680454 DOI: 10.3389/fbioe.2023.1272097] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/03/2023] [Accepted: 10/20/2023] [Indexed: 12/01/2023] Open
Abstract
Purpose: Corneal cross-linking (CXL) has recently been used with promising results to positively affect corneal refractive power in the treatment of hyperopia and mild myopia. However, understanding and predicting the optomechanical changes induced by this procedure are challenging. Methods: We applied ambient pressure modulation based optical coherence elastography (OCE) to quantify the refractive and mechanical effects of patterned CXL and their relationship to energy delivered during the treatment on porcine corneas. Three different patterned treatments were performed, designed according to Zernike polynomial functions (circle, astigmatism, coma). In addition, three different irradiation protocols were analyzed: standard Dresden CXL (fluence of 5.4 J/cm2), accelerated CXL (fluence of 5.4 J/cm2), and high-fluence CXL (fluence of 16.2 J/cm2). The axial strain distribution in the stroma induced by ocular inflation (Δp = 30 mmHg) was quantified, maps of the anterior sagittal curvature were constructed and cylindrical refraction was assessed. Results: Thirty minutes after CXL, there was a statistically significant increase in axial strain amplitude (p < 0.050) and a reduction in sagittal curvature (p < 0.050) in the regions treated with all irradiation patterns compared to the non-irradiated ones. Thirty-6 hours later, the non-irradiated regions showed compressive strains, while the axial strain in the CXL-treated regions was close to zero, and the reduction in sagittal curvature observed 30 minutes after the treatment was maintained. The Dresden CXL and accelerated CXL produced comparable amounts of stiffening and refractive changes (p = 0.856), while high-fluence CXL produced the strongest response in terms of axial strain (6.9‰ ± 1.9‰) and refractive correction (3.4 ± 0.9 D). Tripling the energy administered during CXL resulted in a 2.4-fold increase in the resulting refractive correction. Conclusion: OCE showed that refractive changes and alterations in corneal biomechanics are directly related. A patient-specific selection of both, the administered UV fluence and the irradiation pattern during CXL is promising to allow customized photorefractive corrections in the future.
Collapse
Affiliation(s)
- Matteo Frigelli
- Computational Bioengineering Group, ARTORG Center for Biomedical Engineering Research, University of Bern, Bern, Switzerland
| | - Philippe Büchler
- Computational Bioengineering Group, ARTORG Center for Biomedical Engineering Research, University of Bern, Bern, Switzerland
| | - Sabine Kling
- Computational Bioengineering Group, ARTORG Center for Biomedical Engineering Research, University of Bern, Bern, Switzerland
- Institute for Biomedical Engineering, ITET Department, ETH Zürich, Zürich, Switzerland
| |
Collapse
|
6
|
Urizar MP, Gambra E, de Castro A, de la Peña Á, Cetinkaya O, Marcos S, Curatolo A. Optical beam scanner with reconfigurable non-mechanical control of beam position, angle, and focus for low-cost whole-eye OCT imaging. BIOMEDICAL OPTICS EXPRESS 2023; 14:4468-4484. [PMID: 37791284 PMCID: PMC10545213 DOI: 10.1364/boe.493917] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/28/2023] [Revised: 06/23/2023] [Accepted: 06/30/2023] [Indexed: 10/05/2023]
Abstract
Whole-eye optical coherence tomography (OCT) imaging is a promising tool in ocular biometry for cataract surgery planning, glaucoma diagnostics and myopia progression studies. However, conventional OCT systems are set up to perform either anterior or posterior eye segment scans and cannot easily switch between the two scan configurations without adding or exchanging optical components to account for the refraction of the eye's optics. Even in state-of-the-art whole-eye OCT systems, the scan configurations are pre-selected and cannot be dynamically reconfigured. In this work, we present the design, optimization and experimental validation of a reconfigurable and low-cost optical beam scanner based on three electro-tunable lenses, capable of non-mechanically controlling the beam position, angle and focus. We derive the analytical theory behind its control. We demonstrate its use in performing alternate anterior and posterior segment imaging by seamlessly switching between a telecentric focused beam scan to an angular collimated beam scan. We characterize the corresponding beam profiles and record whole-eye OCT images in a model eye and in an ex vivo rabbit eye, observing features comparable to those obtained with conventional anterior and posterior OCT scanners. The proposed beam scanner reduces the complexity and cost of other whole-eye scanners and is well suited for 2-D ocular biometry. Additionally, with the added versatility of seamless scan reconfiguration, its use can be easily expanded to other ophthalmic applications and beyond.
Collapse
Affiliation(s)
- María Pilar Urizar
- 2EyesVision S.L., Madrid, Spain
- Instituto de Óptica “Daza de Valdés”, Consejo Superior de Investigaciones Científicas (IO, CSIC), Spain
| | | | - Alberto de Castro
- Instituto de Óptica “Daza de Valdés”, Consejo Superior de Investigaciones Científicas (IO, CSIC), Spain
| | - Álvaro de la Peña
- Instituto de Óptica “Daza de Valdés”, Consejo Superior de Investigaciones Científicas (IO, CSIC), Spain
| | - Onur Cetinkaya
- International Centre for Translational Eye Research (ICTER), Institute of Physical Chemistry, Polish Academy of Sciences (IPC-PAS), Warsaw, Poland
| | - Susana Marcos
- Instituto de Óptica “Daza de Valdés”, Consejo Superior de Investigaciones Científicas (IO, CSIC), Spain
- The Institute of Optics and Flaum Eye Institute, Center for Visual Sciences, University of Rochester, New York, USA
| | - Andrea Curatolo
- Instituto de Óptica “Daza de Valdés”, Consejo Superior de Investigaciones Científicas (IO, CSIC), Spain
- International Centre for Translational Eye Research (ICTER), Institute of Physical Chemistry, Polish Academy of Sciences (IPC-PAS), Warsaw, Poland
| |
Collapse
|
7
|
de la Hoz A, Martinez-Enriquez E, Marcos S. Estimation of Crystalline Lens Material Properties From Patient Accommodation Data and Finite Element Models. Invest Ophthalmol Vis Sci 2023; 64:31. [PMID: 37639248 PMCID: PMC10461688 DOI: 10.1167/iovs.64.11.31] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/04/2023] [Accepted: 08/03/2023] [Indexed: 08/29/2023] Open
Abstract
Purpose The mechanical properties of the crystalline lens are related to its optical function of accommodation, and their changes with age are one of the potential causes for presbyopia. We estimated the mechanical parameters of the crystalline lens using quantitative optical coherence tomography (OCT) imaging and wavefront sensing data from accommodating participants and computer modeling. Methods Full-lens shape data (from quantitative swept-source OCT and eigenlens representation) and optical power data (from Hartmann-Shack wavefront sensor) were obtained from 11 participants (22-30 years old) for relaxed accommodation at infinity and -4.5 D accommodative demand. Finite element models of lens, capsular bag, zonulae, and ciliary body were constructed using measured lens geometry and literature data, assuming a 60-mN radial force. An inverse modeling scheme was used to determine the shear moduli of the nucleus and cortex of the lens, such that the simulated deformed (maximally stretched) lens matched the participant's lens at -4.5 D. Results The shear moduli of the nucleus and cortex were 1.62 ± 1.32 and 8.18 ± 5.63 kPa, on average, respectively. The shear modulus of the nucleus was lower than that of the cortex for all participants evaluated. The average of the two moduli per participant was statistically significantly correlated with age (R2 = 0.76, P = 0.0049). Conclusions In vivo imaging and mechanical modeling of the crystalline lens allow estimations of the crystalline lens' mechanical properties. Differences between nuclear and cortical moduli and their dependency with age appear to be critical in accommodative function and likely in its impairment in presbyopia.
Collapse
Affiliation(s)
- Andres de la Hoz
- Instituto de Óptica “Daza de Valdés,” Consejo Superior de Investigaciones Científicas (IO, CSIC), Madrid, Spain
| | - Eduardo Martinez-Enriquez
- Instituto de Óptica “Daza de Valdés,” Consejo Superior de Investigaciones Científicas (IO, CSIC), Madrid, Spain
| | - Susana Marcos
- Center for Visual Science, The Institute of Optics, Flaum Eye Institute, University of Rochester, New York, United States
| |
Collapse
|
8
|
Li X, Luo S, Wang Z, Miao Y, Zhu M, Zheng X, Luo G, Bao F, Chen S, Wang J. Dynamic topography analysis of the cornea and its application to the diagnosis of keratoconus. Comput Biol Med 2023; 158:106800. [PMID: 36966554 DOI: 10.1016/j.compbiomed.2023.106800] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/10/2023] [Revised: 03/02/2023] [Accepted: 03/20/2023] [Indexed: 03/31/2023]
Abstract
PROPOSE To establish a dynamic topography analysis method which simulates the dynamic biomechanical response of the cornea and reveals the variations of such response within the corneal surface, and thereafter to propose and clinically evaluate new parameters for the definite diagnosis of keratoconus. METHODS 58 normal (Normal) and 56 keratoconus (KC) subjects were retrospectively included. Personalized corneal air-puff model was established using corneal topography data by Pentacam for each subject, and the dynamic deformation under air-puff loading was simulated using finite element method, which then enabled calculations of corneal biomechanical parameters of the entire corneal surface along any meridian. Variations in these parameters across different meridians and between different groups were explored by two-way repeated measurement analysis of variance. New dynamic topography parameters were proposed as the range of the calculated biomechanical parameters within the entire corneal surface, and the AUC of ROC curve was used to compare the diagnostic efficiency of newly proposed and existing parameters. RESULTS Corneal biomechanical parameters measured in different meridians varied significantly which were more pronounced in KC group due to its irregularity in corneal morphology. Considering such between-meridian variations thus led to improved diagnostic efficiency of KC as presented by the proposed dynamic topography parameter rIR with an AUC of 0.992 (sensitivity: 91.1%, specificity: 100%), significantly better than the current topography and biomechanical parameters. CONCLUSIONS The diagnosis of keratoconus may be affected by the significant variations of corneal biomechanical parameters due to corneal morphology irregularity. By considering such variations, the current study established the dynamic topography analysis process which benefits from the high accuracy of (static) corneal topography measurement while improving its diagnosis capacity. The proposed dynamic topography parameters, especially the rIR parameter, showed comparable or better diagnostic efficiency for KC than existing topography and biomechanical parameters, which can be of great clinical significance for clinics without access to instrument for biomechanical evaluations.
Collapse
|
9
|
de Castro A, Martínez-Enríquez E, Marcos S. Effect of fixational eye movements in corneal topography measurements with optical coherence tomography. BIOMEDICAL OPTICS EXPRESS 2023; 14:2138-2152. [PMID: 37206127 PMCID: PMC10191639 DOI: 10.1364/boe.486460] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/26/2023] [Revised: 03/24/2023] [Accepted: 03/25/2023] [Indexed: 05/21/2023]
Abstract
There is an increasing interest in applying optical coherence tomography (OCT) to quantify the topography of ocular structures. However, in its most usual configuration, OCT data is acquired sequentially while a beam is scanned through the region of interest, and the presence of fixational eye movements can affect the accuracy of the technique. Several scan patterns and motion correction algorithms have been proposed to minimize this effect, but there is no consensus on the ideal parameters to obtain a correct topography. We have acquired corneal OCT images with raster and radial patterns, and modeled the data acquisition in the presence of eye movements. The simulations replicate the experimental variability in shape (radius of curvature and Zernike polynomials), corneal power, astigmatism, and calculated wavefront aberrations. The variability of the Zernike modes is highly dependent on the scan pattern, with higher variability in the direction of the slow scan axis. The model can be a useful tool to design motion correction algorithms and to determine the variability with different scan patterns.
Collapse
Affiliation(s)
- Alberto de Castro
- Instituto de Óptica, Consejo Superior de Investigaciones Científicas, Madrid, Madrid, Spain
| | | | - Susana Marcos
- Instituto de Óptica, Consejo Superior de Investigaciones Científicas, Madrid, Madrid, Spain
- Center for Visual Science, The Institute of Optics, Flaum Eye Institute, University of Rochester, Rochester, NY, USA
| |
Collapse
|
10
|
Lan G, Twa MD, Song C, Feng J, Huang Y, Xu J, Qin J, An L, Wei X. In vivo corneal elastography: A topical review of challenges and opportunities. Comput Struct Biotechnol J 2023; 21:2664-2687. [PMID: 37181662 PMCID: PMC10173410 DOI: 10.1016/j.csbj.2023.04.009] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/14/2023] [Revised: 04/07/2023] [Accepted: 04/12/2023] [Indexed: 05/16/2023] Open
Abstract
Clinical measurement of corneal biomechanics can aid in the early diagnosis, progression tracking, and treatment evaluation of ocular diseases. Over the past two decades, interdisciplinary collaborations between investigators in optical engineering, analytical biomechanical modeling, and clinical research has expanded our knowledge of corneal biomechanics. These advances have led to innovations in testing methods (ex vivo, and recently, in vivo) across multiple spatial and strain scales. However, in vivo measurement of corneal biomechanics remains a long-standing challenge and is currently an active area of research. Here, we review the existing and emerging approaches for in vivo corneal biomechanics evaluation, which include corneal applanation methods, such as ocular response analyzer (ORA) and corneal visualization Scheimpflug technology (Corvis ST), Brillouin microscopy, and elastography methods, and the emerging field of optical coherence elastography (OCE). We describe the fundamental concepts, analytical methods, and current clinical status for each of these methods. Finally, we discuss open questions for the current state of in vivo biomechanics assessment techniques and requirements for wider use that will further broaden our understanding of corneal biomechanics for the detection and management of ocular diseases, and improve the safety and efficacy of future clinical practice.
Collapse
Affiliation(s)
- Gongpu Lan
- Guangdong-Hong Kong-Macao Intelligent Micro-Nano Optoelectronic Technology Joint Laboratory, School of Physics and Optoelectronic Engineering, Foshan University, Foshan, Guangdong 528000, China
- Weiren Meditech Co., Ltd., Foshan, Guangdong 528000, China
| | - Michael D Twa
- College of Optometry, University of Houston, Houston, TX 77204, United States
| | - Chengjin Song
- Guangdong-Hong Kong-Macao Intelligent Micro-Nano Optoelectronic Technology Joint Laboratory, School of Physics and Optoelectronic Engineering, Foshan University, Foshan, Guangdong 528000, China
| | - JinPing Feng
- Institute of Engineering and Technology, Hubei University of Science and Technology, Xianning, Hubei 437100, China
| | - Yanping Huang
- Guangdong-Hong Kong-Macao Intelligent Micro-Nano Optoelectronic Technology Joint Laboratory, School of Physics and Optoelectronic Engineering, Foshan University, Foshan, Guangdong 528000, China
- Weiren Meditech Co., Ltd., Foshan, Guangdong 528000, China
| | - Jingjiang Xu
- Guangdong-Hong Kong-Macao Intelligent Micro-Nano Optoelectronic Technology Joint Laboratory, School of Physics and Optoelectronic Engineering, Foshan University, Foshan, Guangdong 528000, China
- Weiren Meditech Co., Ltd., Foshan, Guangdong 528000, China
| | - Jia Qin
- Weiren Meditech Co., Ltd., Foshan, Guangdong 528000, China
| | - Lin An
- Weiren Meditech Co., Ltd., Foshan, Guangdong 528000, China
| | - Xunbin Wei
- Biomedical Engineering Department, Peking University, Beijing 100081, China
- International Cancer Institute, Peking University, Beijing 100191, China
- Institute of Medical Technology, Peking University Health Science Center, Beijing 100191, China
| |
Collapse
|
11
|
Wang B, Yang L, Cheng J, Wang J, Mei Y. In-vivo high-speed biomechanical imaging of the cornea using Corvis ST and digital image correlation. Comput Biol Med 2023; 153:106540. [PMID: 36646022 DOI: 10.1016/j.compbiomed.2023.106540] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/10/2022] [Revised: 12/16/2022] [Accepted: 01/10/2023] [Indexed: 01/12/2023]
Abstract
In-vivo corneal biomechanical characterization has gained significant clinical relevance in ophthalmology, especially in the early diagnosis of eye disorders and diseases (e.g. keratoconus). In clinical medicine, the air-puff-based tonometers such as Ocular Response Analyzer (ORA) and Corvis ST have been used in the in-vivo biomechanical testing. In the test, the high-speed dynamic deformation of the cornea under air-puff excitation is analyzed to identify the abnormities in the morphological and biomechanical properties of the cornea. While most existing measurements reflect the overall corneal biomechanical properties, in-vivo high-speed strain and strain rate fields at the tissue level have not been assessed. In this study, 20 subjects were classified into two different groups: the normal (NORM, N = 10) group and the keratoconus (KC, N = 10) group. Image sequences of the horizontal cross-section of the human cornea under air puff were captured by the Corvis ST tonometer. The macroscale mechanical response of the cornea was determined through image analysis. The high-speed evolution of full-field corneal displacement, strain, velocity, and strain rate was reconstructed using the incremental digital image correlation (DIC) approach. Differences in the parameters between the NORM and KC groups were statistically analyzed and compared. Statistical results indicated that compared with the NORM group, the KC corneas absorbed more energy (KC: 8.98 ± 2.76 mN mm; NORM: 4.79 ± 0.62 mN mm; p-value <0.001) with smaller tangent stiffness (KC: 22.49 ± 2.62 mN/mm; NORM: 24.52 ± 3.20 mN/mm; p-value = 0.15) and larger maximum deflection (KC: 0.99 ± 0.07 mN/mm; NORM: 0.92 ± 0.06 mN/mm; p-value <0.05) on the macro scale. Further, we also observed that The maximum displacement (KC: 1.17 ± 0.06 mm; NORM: 1.06 ± 0.07 mm; p-value <0.005), velocity (KC: 236 ± 29 mm/s; NORM: 203 ± 17 mm/s; p-value <0.01), shear strain (KC: 24.43 ± 2.59%; NORM: 20.26 ± 1.54%; p-value <0.001), and shear strain rate (KC: 69.74 ± 11.99 s-1; NORM: 54.84 ± 3.03 s-1; p-value <0.005) in the KC group significantly increased at the tissue level. This is the first time that the incremental DIC method was applied to the in-vivo high-speed corneal deformation measurement in combination with the Corvis ST tonometer. Through the image registration using incremental DIC analysis, spatiotemporal dynamic strain/strain rate maps of the cornea can be estimated at the tissue level. This is constructive for the clinical recognition and diagnosis of keratoconus at a more underlying level.
Collapse
Affiliation(s)
- Bo Wang
- State Key Laboratory of Structural Analysis for Industrial Equipment, Department of Engineering Mechanics, Dalian University of Technology, Dalian, 116023, PR China; International Research Center for Computational Mechanics, Dalian University of Technology, Dalian, 116023, PR China; Ningbo Institute of Dalian University of Technology, Ningbo, 315016, PR China; DUT-BSU Joint Institute, Dalian University of Technology, 116023, PR China
| | - Lanting Yang
- Eye Hospital, Wenzhou Medical University, Wenzhou, China; The Institution of Ocular Biomechanics, Wenzhou Medical University, Wenzhou, China
| | - Jiaxuan Cheng
- Eye Hospital, Wenzhou Medical University, Wenzhou, China; The Institution of Ocular Biomechanics, Wenzhou Medical University, Wenzhou, China
| | - Junjie Wang
- Eye Hospital, Wenzhou Medical University, Wenzhou, China; The Institution of Ocular Biomechanics, Wenzhou Medical University, Wenzhou, China.
| | - Yue Mei
- State Key Laboratory of Structural Analysis for Industrial Equipment, Department of Engineering Mechanics, Dalian University of Technology, Dalian, 116023, PR China; International Research Center for Computational Mechanics, Dalian University of Technology, Dalian, 116023, PR China; Ningbo Institute of Dalian University of Technology, Ningbo, 315016, PR China; DUT-BSU Joint Institute, Dalian University of Technology, 116023, PR China.
| |
Collapse
|
12
|
Martínez-Enríquez E, Curatolo A, de Castro A, Birkenfeld JS, González AM, Mohamed A, Ruggeri M, Manns F, Fernando Z, Marcos S. Estimation of the full shape of the crystalline lens in-vivo from OCT images using eigenlenses. BIOMEDICAL OPTICS EXPRESS 2023; 14:608-626. [PMID: 36874490 PMCID: PMC9979676 DOI: 10.1364/boe.477557] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/06/2022] [Revised: 11/29/2022] [Accepted: 11/29/2022] [Indexed: 06/18/2023]
Abstract
Quantifying the full 3-D shape of the human crystalline lens is important for improving intraocular lens power or sizing calculations in treatments of cataract and presbyopia. In a previous work we described a novel method for the representation of the full shape of the ex vivo crystalline lens called eigenlenses, which proved more compact and accurate than compared state-of-the art methods of crystalline lens shape quantification. Here we demonstrate the use of eigenlenses to estimate the full shape of the crystalline lens in vivo from optical coherence tomography images, where only the information visible through the pupil is available. We compare the performance of eigenlenses with previous methods of full crystalline lens shape estimation, and demonstrate an improvement in repeatability, robustness and use of computational resources. We found that eigenlenses can be used to describe efficiently the crystalline lens full shape changes with accommodation and refractive error.
Collapse
Affiliation(s)
| | - Andrea Curatolo
- Instituto de Óptica, Consejo Superior de Investigaciones Científicas, Madrid, Madrid, Spain
- Institute of Physical Chemistry, Polish Academy of Sciences (IChF-PAN), Warsaw, Poland
- International Centre for Translational Eye Research (ICTER), Warsaw, Poland
| | - Alberto de Castro
- Instituto de Óptica, Consejo Superior de Investigaciones Científicas, Madrid, Madrid, Spain
| | - Judith S. Birkenfeld
- Instituto de Óptica, Consejo Superior de Investigaciones Científicas, Madrid, Madrid, Spain
| | - Ana M. González
- Instituto de Óptica, Consejo Superior de Investigaciones Científicas, Madrid, Madrid, Spain
| | - Ashik Mohamed
- Ophthalmic Biophysics, LV Prasad Eye Institute, Hyderabad, Telangana, India
- Brien Holden Vision Institute, Sydney, NSW, Australia
| | - Marco Ruggeri
- Ophthalmic Biophysics Center, Bascom Palmer Eye Institute, University of Miami School of Medicine, Miami, FL, USA
- Department of Biomedical Engineering, University of Miami College of Engineering, Coral Gables, FL, USA
| | - Fabrice Manns
- Ophthalmic Biophysics Center, Bascom Palmer Eye Institute, University of Miami School of Medicine, Miami, FL, USA
- Department of Biomedical Engineering, University of Miami College of Engineering, Coral Gables, FL, USA
| | - Zvietcovich Fernando
- Instituto de Óptica, Consejo Superior de Investigaciones Científicas, Madrid, Madrid, Spain
| | - Susana Marcos
- Instituto de Óptica, Consejo Superior de Investigaciones Científicas, Madrid, Madrid, Spain
- Center for Visual Science. The Institute of Optics. Flaum Eye Institute, University of Rochester, Rochester, NY, USA
| |
Collapse
|
13
|
Co-axial acoustic-based optical coherence vibrometry probe for the quantification of resonance frequency modes in ocular tissue. Sci Rep 2022; 12:18834. [PMID: 36336702 PMCID: PMC9637745 DOI: 10.1038/s41598-022-21978-8] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/27/2022] [Accepted: 10/07/2022] [Indexed: 11/08/2022] Open
Abstract
We present a co-axial acoustic-based optical coherence vibrometry probe (CoA-OCV) for vibro-acoustic resonance quantification in biological tissues. Sample vibrations were stimulated via a loudspeaker, and pre-compensation was used to calibrate the acoustic spectrum. Sample vibrations were measured via phase-sensitive swept-source optical coherence tomography (OCT). Resonance frequencies of corneal phantoms were measured at varying intraocular pressures (IOP), and dependencies on Young´s Modulus (E), phantom thickness and IOP were observed. Cycling IOP revealed hysteresis. For E = 0.3 MPa, resonance frequencies increased with IOP at a rate of 3.9, 3.7 and 3.5 Hz/mmHg for varied thicknesses and 1.7, 2.5 and 2.8 Hz/mmHg for E = 0.16 MPa. Resonance frequencies increased with thickness at a rate of 0.25 Hz/µm for E = 0.3 MPa, and 0.40 Hz/µm for E = 0.16 MPa. E showed the most predominant impact in the shift of the resonance frequencies. Full width at half maximum (FWHM) of the resonance modes increased with increasing thickness and decreased with increasing E. Only thickness and E contributed to the variance of FWHM. In rabbit corneas, resonance frequencies of 360-460 Hz were observed. The results of the current study demonstrate the feasibility of CoA-OCV for use in future OCT-V studies.
Collapse
|
14
|
Vinas-Pena M, Feng X, Li GY, Yun SH. In situ measurement of the stiffness increase in the posterior sclera after UV-riboflavin crosslinking by optical coherence elastography. BIOMEDICAL OPTICS EXPRESS 2022; 13:5434-5446. [PMID: 36425630 PMCID: PMC9664890 DOI: 10.1364/boe.463600] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/10/2022] [Revised: 08/08/2022] [Accepted: 08/09/2022] [Indexed: 06/16/2023]
Abstract
Scleral crosslinking may provide a way to prevent or treat myopia by stiffening scleral tissues. The ability to measure the stiffness of scleral tissues in situ pre and post scleral crosslinking would be useful but has not been established. Here, we tested the feasibility of optical coherence elastography (OCE) to measure shear modulus of scleral tissues and evaluate the impact of crosslinking on different posterior scleral regions using ex vivo porcine eyes as a model. From measured elastic wave speeds at 6 - 16 kHz, we obtained out-of-plane shear modulus value of 0.71 ± 0.12 MPa (n = 20) for normal porcine scleral tissues. After riboflavin-assisted UV crosslinking, the shear modulus increased to 1.50 ± 0.39 MPa (n = 20). This 2-fold change was consistent with the increase of static Young's modulus from 5.5 ± 1.1 MPa to 9.3 ± 1.9 MPa after crosslinking, which we measured using conventional uniaxial extensometry on tissue stripes. OCE revealed regional stiffness differences across the temporal, nasal, and deeper posterior sclera. Our results show the potential of OCE as a noninvasive tool to evaluate the effect of scleral crosslinking.
Collapse
|
15
|
Li W, Feng J, Wang Y, Shi Q, Ma G, Aglyamov S, Larin KV, Lan G, Twa M. Micron-scale hysteresis measurement using dynamic optical coherence elastography. BIOMEDICAL OPTICS EXPRESS 2022; 13:3021-3041. [PMID: 35774312 PMCID: PMC9203113 DOI: 10.1364/boe.457617] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/04/2022] [Revised: 04/11/2022] [Accepted: 04/14/2022] [Indexed: 05/28/2023]
Abstract
We present a novel optical coherence elastography (OCE) method to characterize mechanical hysteresis of soft tissues based on transient (milliseconds), low-pressure (<20 Pa) non-contact microliter air-pulse stimulation and micrometer-scale sample displacements. The energy dissipation rate (sample hysteresis) was quantified for soft-tissue phantoms (0.8% to 2.0% agar) and beef shank samples under different loading forces and displacement amplitudes. Sample hysteresis was defined as the loss ratio (hysteresis loop area divided by the total loading energy). The loss ratio was primarily driven by the sample unloading response which decreased as loading energy increased. Samples were distinguishable based on their loss ratio responses as a function loading energy or displacement amplitude. Finite element analysis and mechanical testing methods were used to validate these observations. We further performed the OCE measurements on a beef shank tissue sample to distinguish the muscle and connective tissue components based on the displacement and hysteresis features. This novel, noninvasive OCE approach has the potential to differentiate soft tissues by quantifying their viscoelasticity using micron-scale transient tissue displacement dynamics. Focal tissue hysteresis measurements could provide additional clinically useful metrics for guiding disease diagnosis and tissue treatment responses.
Collapse
Affiliation(s)
- Wenjie Li
- Foshan University, School of Mechatronic Engineering and Automation, Foshan, Guangdong, 528000, China
- Contributed equally
| | - Jinping Feng
- Hubei University of Science and Technology, Institute of Engineering and Technology, Xianning, Hubei, 437100, China
- Contributed equally
| | - Yicheng Wang
- Foshan University, School of Mechatronic Engineering and Automation, Foshan, Guangdong, 528000, China
| | - Qun Shi
- Foshan University, School of Mechatronic Engineering and Automation, Foshan, Guangdong, 528000, China
| | - Guoqin Ma
- Foshan University, School of Mechatronic Engineering and Automation, Foshan, Guangdong, 528000, China
| | - Salavat Aglyamov
- University of Houston, Mechanical Engineering, Houston, TX 77204, USA
| | - Kirill V Larin
- University of Houston, Biomedical Engineering, Houston, TX 77204, USA
| | - Gongpu Lan
- Foshan University, School of Physics and Optoelectronic Engineering, Guangdong-Hong Kong-Macao Joint Laboratory for Intelligent Micro-Nano Optoelectronic Technology, Foshan, Guangdong 528000, China
- Innovation and Entrepreneurship Team of Guangdong Pearl River Talents Program, Weiren Meditech Co., Ltd., Foshan, Guangdong, 528000, China
| | - Michael Twa
- University of Houston, College of Optometry, Houston, TX 77204, USA
| |
Collapse
|
16
|
Bronte-Ciriza D, Birkenfeld JS, de la Hoz A, Curatolo A, Germann JA, Villegas L, Varea A, Martínez-Enríquez E, Marcos S. Estimation of scleral mechanical properties from air-puff optical coherence tomography. BIOMEDICAL OPTICS EXPRESS 2021; 12:6341-6359. [PMID: 34745741 PMCID: PMC8548012 DOI: 10.1364/boe.437981] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/16/2021] [Revised: 08/15/2021] [Accepted: 08/15/2021] [Indexed: 05/11/2023]
Abstract
We introduce a method to estimate the biomechanical properties of the porcine sclera in intact eye globes ex vivo, using optical coherence tomography that is coupled with an air-puff excitation source, and inverse optimization techniques based on finite element modeling. Air-puff induced tissue deformation was determined at seven different locations on the ocular globe, and the maximum apex deformation, the deformation velocity, and the arc-length during deformation were quantified. In the sclera, the experimental maximum deformation amplitude and the corresponding arc length were dependent on the location of air-puff excitation. The normalized temporal deformation profile of the sclera was distinct from that in the cornea, but similar in all tested scleral locations, suggesting that this profile is independent of variations in scleral thickness. Inverse optimization techniques showed that the estimated scleral elastic modulus ranged from 1.84 ± 0.30 MPa (equatorial inferior) to 6.04 ± 2.11 MPa (equatorial temporal). The use of scleral air-puff imaging holds promise for non-invasively investigating the structural changes in the sclera associated with myopia and glaucoma, and for monitoring potential modulation of scleral stiffness in disease or treatment.
Collapse
Affiliation(s)
- David Bronte-Ciriza
- Instituto de Óptica "Daza de Valdés", Consejo Superior de Investigaciones Científicas (IO-CSIC), Madrid, Spain
- CNR - IPCF, Istituto per i Processi Chimico-Fisici, Messina, Italy
- Co-first authors
| | - Judith S Birkenfeld
- Instituto de Óptica "Daza de Valdés", Consejo Superior de Investigaciones Científicas (IO-CSIC), Madrid, Spain
- Co-first authors
| | - Andrés de la Hoz
- Instituto de Óptica "Daza de Valdés", Consejo Superior de Investigaciones Científicas (IO-CSIC), Madrid, Spain
| | - Andrea Curatolo
- Instituto de Óptica "Daza de Valdés", Consejo Superior de Investigaciones Científicas (IO-CSIC), Madrid, Spain
- International Centre for Translational Eye Research, Warsaw, Poland
- Institute of Physical Chemistry, Polish Academy of Sciences, Warsaw, Poland
| | - James A Germann
- Instituto de Óptica "Daza de Valdés", Consejo Superior de Investigaciones Científicas (IO-CSIC), Madrid, Spain
| | - Lupe Villegas
- Instituto de Óptica "Daza de Valdés", Consejo Superior de Investigaciones Científicas (IO-CSIC), Madrid, Spain
| | - Alejandra Varea
- Instituto de Óptica "Daza de Valdés", Consejo Superior de Investigaciones Científicas (IO-CSIC), Madrid, Spain
| | - Eduardo Martínez-Enríquez
- Instituto de Óptica "Daza de Valdés", Consejo Superior de Investigaciones Científicas (IO-CSIC), Madrid, Spain
| | - Susana Marcos
- Instituto de Óptica "Daza de Valdés", Consejo Superior de Investigaciones Científicas (IO-CSIC), Madrid, Spain
- Center for Visual Science, The Institute of Optics, Flaum Eye Institute, University of Rochester, NY 14642, USA
| |
Collapse
|
17
|
|
18
|
Nair A, Singh M, Aglyamov S, Larin KV. Heartbeat optical coherence elastography: corneal biomechanics in vivo. JOURNAL OF BIOMEDICAL OPTICS 2021; 26:JBO-200338LR. [PMID: 33624461 PMCID: PMC7901857 DOI: 10.1117/1.jbo.26.2.020502] [Citation(s) in RCA: 13] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/14/2020] [Accepted: 01/19/2021] [Indexed: 05/02/2023]
Abstract
SIGNIFICANCE Mechanical assessment of the cornea can provide important structural and functional information regarding its health. Current clinically available tools are limited in their efficacy at measuring corneal mechanical properties. Elastography allows for the direct estimation of mechanical properties of tissues in vivo but is generally performed using external excitation force. AIM To show that heartbeat optical coherence elastography (Hb-OCE) can be used to assess the mechanical properties of the cornea in vivo. APPROACH Hb-OCE was utilized to detect Hb-induced deformations in the rabbit cornea in vivo without the need for external excitation. Furthermore, we demonstrate how this technique can distinguish corneal stiffness between untreated (UT) and crosslinked (CXL) tissue. RESULTS Our results demonstrate that stiffness changes in the cornea can be detected using only the Hb-induced deformations in the cornea. Additionally, we demonstrate a statistically significant difference in strain between the UT and CXL corneas. CONCLUSIONS Hb-OCE may be an effective tool for assessing the mechanical properties of the cornea in vivo without the need for external excitation. This tool may be effective for clinical assessment of corneal mechanical properties because it only requires optical coherence tomography imaging and data processing.
Collapse
Affiliation(s)
- Achuth Nair
- University of Houston, Department of Biomedical Engineering, Houston, Texas, United States
| | - Manmohan Singh
- University of Houston, Department of Biomedical Engineering, Houston, Texas, United States
| | - Salavat Aglyamov
- University of Houston, Department of Mechanical Engineering, Houston, Texas, United States
| | - Kirill V. Larin
- University of Houston, Department of Biomedical Engineering, Houston, Texas, United States
- Address all correspondence to Kirill V. Larin,
| |
Collapse
|