327 research outputs found
Visualizing choriocapillaris using swept source optical coherence tomography angiography with various probe beam sizes
Imaging choriocapillaris (CC) is a long-term challenge for commercial OCT angiography (OCTA) systems due to limited transverse resolution. Effects of transverse resolution on the visualization of a CC microvascular network are explored and demonstrated in this paper. We use three probe beams with sizes of ~1.12 mm, ~2.51 mm and ~3.50 mm at the pupil plane, which deliver an estimated transverse resolution at the retina of 17.5 µm, 8.8 µm and 7.0 µm, respectively, to investigate the ability of OCTA to resolve the CC capillary vessels. The complex optical microangiography algorithm is applied to extract blood flow in the CC slab. Mean retinal pigment epithelium (RPE) to CC (RPE-CC) distance, mean CC inter-vascular spacing and the magnitude in the radially-averaged power spectrum are quantified. We demonstrate that a clearer CC lobular capillary network is resolved in the angiograms provided by a larger beam size. The image contrast of the CC angiogram with a large beam size of 3.50 mm is 114% higher than that with a small beam size of 1.12 mm. While the measurements of the mean RPE-CC distance and CC inter-vascular spacing are almost consistent regardless of the beam sizes, they are more reliable and stable with the larger beam size of 3.50 mm. We conclude that the beam size is a key parameter for CC angiography if the purpose of the investigation is to visualize the individual CC capillaries.</p
Possible depth-resolved reconstruction of shear moduli in the cornea following collagen crosslinking (CXL) with optical coherence tomography and elastography
Collagen crosslinking of the cornea (CXL) is commonly employed to prevent or
treat keratoconus. Although the change of corneal stiffness induced by CXL
surgery can be monitored with non-contact dynamic Optical Coherence
Elastography (OCE) by tracking mechanical wave propagation, the depth
dependence of this change is still unclear if the cornea is not crosslinked
through the whole depth. Here we propose to combine phase-decorrelation
measurement applied to OCT structural images and acoustic micro-tapping
(AT) OCE to explore possible depth reconstruction of stiffness within
crosslinked corneas in an ex vivo human cornea sample. The analysis of
experimental OCT images is used to define the penetration depth of CXL into the
cornea, which varies from 100 in the periphery to 150
in the central area and exhibits a sharp transition between areas. This
information was used in a two-layer analytical model to quantify the stiffness
of the treated layer. We also discuss how the elastic moduli of partially
CXL-treated cornea layers reconstructed from OCE measurements reflect the
effective mechanical stiffness of the entire cornea to properly quantify
surgical outcome.Comment: Main: 10 Pages, 6 Figures Supplemental: 12 Pages, 3 Figure
Possible depth-resolved reconstruction of shear moduli in the cornea following collagen crosslinking (CXL) with optical coherence tomography and elastography
Corneal collagen crosslinking (CXL) is commonly used to prevent or treat
keratoconus. Although changes in corneal stiffness induced by CXL surgery can
be monitored with non-contact dynamic optical coherence elastography (OCE) by
tracking mechanical wave propagation, depth dependent changes are still unclear
if the cornea is not crosslinked through the whole depth. Here,
phase-decorrelation measurements on optical coherence tomography (OCT)
structural images are combined with acoustic micro-tapping (AT) OCE to
explore possible reconstruction of depth-dependent stiffness within crosslinked
corneas in an ex vivo human cornea sample. Experimental OCT images are analyzed
to define the penetration depth of CXL into the cornea. In a representative ex
vivo human cornea sample, crosslinking depth varied from in the
periphery to in the cornea center and exhibited a sharp
in-depth transition between crosslinked and untreated areas. This information
was used in an analytical two-layer guided wave propagation model to quantify
the stiffness of the treated layer. We also discuss how the elastic moduli of
partially CXL-treated cornea layers reflect the effective engineering stiffness
of the entire cornea to properly quantify corneal deformation.Comment: Submitted to Biomedical Optics Express on June 13th 2023, Manuscript
ID: 497970 - Under Review. Manuscript, 10 pages / 6 figures / 2 tables.
Supplementary, 7 pages / 4 figure
Shear wave pulse compression for dynamic elastography using phase-sensitive optical coherence tomography
Assessing the biomechanical properties of soft tissue provides clinically valuable information to supplement conventional structural imaging. In the previous studies, we introduced a dynamic elastography technique based on phase-sensitive optical coherence tomography (PhS-OCT) to characterize submillimetric structures such as skin layers or ocular tissues. Here, we propose to implement a pulse compression technique for shear wave elastography. We performed shear wave pulse compression in tissue-mimicking phantoms. Using a mechanical actuator to generate broadband frequency-modulated vibrations (1 to 5Â kHz), induced displacements were detected at an equivalent frame rate of 47Â kHz using a PhS-OCT. The recorded signal was digitally compressed to a broadband pulse. Stiffness maps were then reconstructed from spatially localized estimates of the local shear wave speed. We demonstrate that a simple pulse compression scheme can increase shear wave detection signal-to-noise ratio ([Formula: see text] gain) and reduce artifacts in reconstructing stiffness maps of heterogeneous media
Quantitative Assessment of Anterior Segment Inflammation in a Rat Model of Uveitis Using Spectral- Domain Optical Coherence Tomography
Citation: Pepple KL, Choi WJ, Wilson L, Van Gelder RN, Wang RK. Quantitative assessment of anterior segment inflammation in a rat model of uveitis using spectral-domain optical coherence tomography. Invest Ophthalmol Vis Sci. 2016;57:3567-3575. DOI:10.1167/iovs.16-19276 PURPOSE. To develop anterior segment spectral-domain optical coherence tomography (SD-OCT) and quantitative image analysis for use in experimental uveitis in rats. METHODS. Acute anterior uveitis was generated in Lewis rats. A spectral domain anterior segment OCT system was used to image the anterior chamber (AC) and ciliary body at baseline and during peak inflammation 2 days later. Customized MatLab image analysis algorithms were developed to segment the AC, count AC cells, calculate central corneal thickness (CCT), segment the ciliary body and zonules, and quantify the level of ciliary body inflammation with the ciliary body index (CBI). Images obtained at baseline and during peak inflammation were compared. Finally, longitudinal imaging and image analysis was performed over the 2-week course of inflammation. RESULTS. Spectral-domain optical coherence tomography identifies structural features of inflammation. Anterior chamber cell counts at peak inflammation obtained by automated image analysis and human grading were highly correlated (r ¼ 0.961), and correlated well with the histologic score of inflammation (r ¼ 0.895). Inflamed eyes showed a significant increase in average CCT (27 lm, P ¼ 0.02) and an increase in average CBI (P < 0.0001). Longitudinal imaging and quantitative image analysis identified a significant change in AC cell and CBI on day 2 with spontaneous resolution of inflammation by day 14. CONCLUSIONS. Spectral-domain optical coherence tomography provides high-resolution images of the structural changes associated with anterior uveitis in rats. Anterior chamber cell count and CBI determined by semi-automated image analysis strongly correlates with inflammation, and can be used to quantify inflammation longitudinally in single animals
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