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Item type:Publication, In vivo assessment of corneal biomechanics under a localized cross-linking treatment using confocal air-coupled optical coherence elastography(Optica Publishing Group (formerly OSA), 2022-05-01)The localized application of the riboflavin/UV-A collagen cross-linking (UV-CXL) corneal treatment has been proposed to concentrate the stiffening process only in the compromised regions of the cornea by limiting the epithelium removal and irradiation area. However, current clinical screening devices dedicated to measuring corneal biomechanics cannot provide maps nor spatial-dependent changes of elasticity in corneas when treated locally with UV-CXL. In this study, we leverage our previously reported confocal air-coupled ultrasonic optical coherence elastography (ACUS-OCE) probe to study local changes of corneal elasticity in three cases: untreated, half-CXL-treated, and full-CXL-treated in vivo rabbit corneas (n = 8). We found a significant increase of the shear modulus in the half-treated (>450%) and full-treated (>650%) corneal regions when compared to the non-treated cases. Therefore, the ACUS-OCE technology possesses a great potential in detecting spatially-dependent mechanical properties of the cornea at multiple meridians and generating elastography maps that are clinically relevant for patient-specific treatment planning and monitoring of UV-CXL procedures. - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Viscoelastic characterization of in vivo human dermis using high-frequency ultrasonic crawling wave elastography(Institute of Electrical and Electronics Engineers Inc., 2022-01-01)High-frequency (center frequency of 18MHz) ultrasound was combined with crawling wave elastography to characterize skin viscoelastic properties in two anatomical sites (i.e., thigh and forearm) in humans in the range of 200-400 Hz. The Voigt model was used to obtain shear elasticity and shear viscosity estimates. The forearm's mean shear elasticity and shear viscosity were 6 kPa and 5.5 Pa.s, respectively, exhibiting significantly higher values than in the thigh (3.4 kPa and 3.2 Pa.s, respectively, p < 0.05). These results suggest that skin viscoelastic properties can be estimated in vivo using high-frequency crawling wave elastography and show translation potential for future application in the clinical screening of skin disorders. - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Multiple optical elastography techniques reveal the regulation of corneal stiffness by collagen XII(Association for Research in Vision and Ophthalmology Inc., 2022-11-01)PURPOSE. Collagen XII plays a role in regulating the structure and mechanical properties of the cornea. In this work, several optical elastography techniques were used to investigate the effect of collagen XII deficiency on the stiffness of the murine cornea. METHODS. A three-prong optical elastography approach was used to investigate the mechanical properties of the cornea. Brillouin microscopy, air-coupled ultrasonic optical coherence elastography (OCE) and heartbeat OCE were used to assess the mechanical properties of wild type (WT) and collagen XII–deficient (Col12a1–/–) murine corneas. The Brillouin frequency shift, elastic wave speed, and compressive strain were all measured as a function of intraocular pressure (IOP). RESULTS. All three optical elastography modalities measured a significantly decreased stiffness in the Col12a1–/– compared to the WT (P < 0.01 for all three modalities). The optical coherence elastography techniques showed that mean stiffness increased as a function of IOP; however, Brillouin microscopy showed no discernable trend in Brillouin frequency shift as a function of IOP. CONCLUSIONS. Our approach suggests that the absence of collagen XII significantly softens the cornea. Although both optical coherence elastography techniques showed an expected increase in corneal stiffness as a function of IOP, Brillouin microscopy did not show such a relationship, suggesting that the Brillouin longitudinal modulus may not be affected by changes in IOP. Future work will focus on multimodal biomechanical models, evaluating the effects of other collagen types on corneal stiffness, and in vivo measurements. - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Optical coherence elastography measures the biomechanical properties of the ex vivo porcine cornea after LASIK(SPIE, 2024-01-01)Significance: The biomechanical impact of refractive surgery has long been an area of investigation. Changes to the cornea structure cause alterations to its mechanical integrity, but few studies have examined its specific mechanical impact. Aim: To quantify how the biomechanical properties of the cornea are altered by laser assisted in situ keratomileusis (LASIK) using optical coherence elastography (OCE) in ex vivo porcine corneas. Approach: Three OCE techniques, wave-based air-coupled ultrasound (ACUS) OCE, heartbeat (Hb) OCE, and compression OCE were used to measure the mechanical properties of paired porcine corneas, where one eye of the pair was left untreated, and the fellow eye underwent LASIK. Changes in stiffness as a function of intraocular pressure (IOP) before and after LASIK were measured using each technique. Results: ACUS-OCE showed that corneal stiffness changed as a function of IOP for both the untreated and the treated groups. The elastic wave speed after LASIK was lower than before LASIK. Hb-OCE and compression OCE showed regional changes in corneal strain after LASIK, where the absolute strain difference between the cornea anterior and posterior increased after LASIK. Conclusions: The results of this study suggest that LASIK may soften the cornea and that these changes are largely localized to the region where the surgery was performed. - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Whole embryo biomechanics with reverberant optical coherence elastography(Optica Publishing Group (formerly OSA), 2024-05-20)Many morphogenesis processes during embryo development are fundamentally biomechanical processes, and disruption of these events can lead to debilitating congenital abnormalities. Imaging the biomechanical properties of embryos could provide insight into developmental disorders and could open new therapy avenues. However, current methods are invasive and are incapable of producing viscoelasticity maps of live samples in 3D. To overcome these limitations, we propose the use of reverberant shear wave fields in combination with optical coherence tomography (OCT) for high-resolution elastography at different developmental stages of murine embryos. A 1 kHz quasi-harmonic stimulation was applied to induce the diffuse shear field, which leveraged the heterogeneous microstructure and boundaries of the different tissue segments in the embryos. With this approach, we show how the shear wave speed (i.e., stiffness) of the spine, heart, and mid-brain increased as the embryo developed from embryonic day (E) 9.5 to E 11.5 at five separate stages. This noncontact technique is a promising method for imaging the biomechanical properties of different embryo structures during development with important applications for understanding developmental diseases and exploring treatments. - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Revealing regional variations in scleral shear modulus in a rabbit eye model using multi-directional ultrasound optical coherence elastography(Nature Research, 2024-12-01)The mechanical properties of the sclera play a critical role in supporting the ocular structure and maintaining its shape. However, non-invasive measurements to quantify scleral biomechanics remain challenging. Recently introduced multi-directional optical coherence elastography (OCE) combined with an air-coupled ultrasound transducer for excitation of elastic surface waves was used to estimate phase speed and shear modulus in ex vivo rabbit globes (n = 7). The scleral phase speed (12.1 ± 3.2 m/s) was directional-dependent and higher than for corneal tissue (5.9 ± 1.4 m/s). In the tested locations, the sclera proved to be more anisotropic than the cornea by a factor of 11 in the maximum of modified planar anisotropy coefficient. The scleral shear moduli, estimated using a modified Rayleigh-Lamb wave model, showed significantly higher values in the circumferential direction (65.4 ± 31.9 kPa) than in meridional (22.5 ± 7.2 kPa); and in the anterior zone (27.3 ± 9.3 kPa) than in the posterior zone (17.8 ± 7.4 kPa). The multi-directional scanning approach allowed both quantification and radial mapping of estimated parameters within a single measurement. The results indicate that multi-directional OCE provides a valuable non-invasive assessment of scleral tissue properties that may be useful in the development of improved ocular models, the evaluation of potential myopia treatment strategies, and disease characterization and monitoring. - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Revealing Regional Variations in Scleral Shear Modulus in a Rabbit Eye Model Using Multi-Meridian Ultrasound Optical Coherence Elastography(RELX Group (Netherlands), 2023-01-01) - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Estimation of the Full Shape of the Crystalline Lens from OCT: Validation Using Stretched Donor Lenses(Optica Publishing Group (formerly OSA), 2023-08-01)Quantifying human crystalline lens geometry as a function of age and accommodation is important for improved cataract and presbyopia treatments. In previous works we presented eigenlenses as a basis of 3-D functions to represent the full shape of the crystalline lens ex vivo. Also, we presented the application of eigenlenses to estimate the full shape of the lens in vivo from 3-D optical coherence tomography (OCT) images, where only the central part of the lens -visible through the pupil- is available. The current work presents a validation of the use of eigenlenses to estimate in vivo the full shape of dis-accommodated lenses. We used 14 ex vivo crystalline lenses from donor eyes (11-54 y/o) mounted in a lens stretcher, and measured the geometry and the power of the lenses using a combined OCT and ray tracing aberrometry system. Ex vivo, the full extent of the lens is accessible from OCT because the incident light is not blocked by the iris. We measured in non-stretched (fully accommodated) and stretched (mimicking in vivo dis-accommodated lenses) conditions. Then, we simulated computationally in vivo conditions on the obtained ex vivo lenses geometry (assuming that just the portion of the lens within a given pupil is available), and estimated the full shape using eigenlenses. The mean absolute error (MAE) between estimated and measured lens' diameters and volumes were MAE= 0.26 ± 0.18 mm and MAE= 7.0 ± 4.5 mm3, respectively. Furthermore, we concluded that the estimation error between measured and estimated lenses did not depend on the accommodative state (change in power due to stretching), and thus eigenlenses are also useful for the full shape estimation of in vivo dis-accommodated lenses. - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Eigen Paicas: A 3D Reconstruction of Entire Vessels Using Information of a Single Fragment and a Database(2025-10-01)Traditionally, fragments of ceramic vessels are collected diving an archaeological research project since they provide important pieces of evidence concerning cultural affiliation, dating, and other types of important information. However, complete vessels provide additional data such as food storage capacity and weight. A 3D reconstruction technique for reconstructing complete vessels based on fragments is proposed and applied to paicas, large ceramic containers from the Moche society of northern Peru. A database of profile contours, derived from the 3D models of 23 paicas, was established and used to reconstruct the shape of entire vessels from fragments using Principal Component Analysis (PCA) and the Simplex optimisation algorithm. Preliminary results from a group of four fragments provide good estimations with an average accuracy error of 14% and a precision error equal to 0%.9 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Air-Coupled Ultrasonic Optical Coherence Elastography Reveals Protocol-Dependent Corneal Stiffening in Epi-On and Epi-Off Riboflavin Crosslinking(Association for Research in Vision and Ophthalmology, 2026-07-10)Purpose: To evaluate the biomechanical impact of corneal crosslinking (CXL) when combining three different ultraviolet A (UV-A) riboflavin (RB) photosensitizers and protocols (Dresden protocol [DP] and accelerated protocol [AP]) using air-coupled ultrasonic optical coherence elastography in ex vivo rabbit corneas. Methods: An air-coupled ultrasound excitation optical coherence elastography system was used to excite the corneal apex and generate Lamb wave propagation along 16 corneal cross-sectional meridians. Measurements were conducted on ex vivo rabbit eyes (n = 45) during three treatment phases: Virgin, after 30 minutes of RB soaking, and after UV-A irradiation. The protocols used include the DP (3 mW/cm2, 30 minutes) and two accelerated protocols (AP-1: 9 mW/cm2, 10 minutes; and AP-2: 30 mW/cm2, 3 minutes). Each protocol was tested with three photosensitizers: epithelium-on (TE), and epithelium-off with hyperosmolar (M) and hypo-osmolar solutions (D). Lamb wave speed and average corneal thickness were calculated for each meridian to estimate meridian-dependent corneal shear modulus. Differences were statistically analyzed using linear mixed-effects regression. Results: The DP-D produced the strongest significant corneal stiffness increase (480.5 kPa; P < 0.001) during the UV irradiation phase, and the most pronounced corneal thinning (186 µm; P < 0.001). DP-TE achieved the next strongest stiffening (309.5 kPa) during UV irradiation, with no significant thickness change. All other protocol-photosensitizer combinations did not achieve significant corneal stiffening except for AP-1-D and AP-2-D during the RB soaking phase. Conclusions: Accelerated protocols did not produce significant corneal stiffening for any RB photosensitizer except when using dextran-based D. DP-D and DP-TE produced the greatest balance between shear modulus increase and corneal thickness decrease, suggesting DP-TE as a potential compromise between biomechanical impact, corneal integrity, and faster postoperative recovery. Translational Relevance: This work quantified the impact of clinically used crosslinking photosensitizers and protocols on corneal stiffening using an air-coupled ultrasound excitation optical coherence elastography, which holds promise for clinical assessments in patients.