ABSTRACT
OCT performs cross-sectional imaging by measuring the magnitude and echo time delay of light. A crosssectional image is acquired by performing successive rapid axial measurements of echo time delay and scanning the incident optical beam transversely, as shown in Figure 2.1. The result is a two-dimensional data set that represents the optical back-reflection or backscattering in a cross-sectional plane through the material or tissue. OCT was first demonstrated by Huang et al. in 19911. In this study, imaging was performed ex vivo in the human retina and in atherosclerotic plaque as examples of imaging in nominally transparent tissues as well as in highly optically scattering tissues. Figures 2.2 and 2.3 show ex vivo OCT images of the human coronary artery and retina with corresponding histology from reference 1. OCT imaging was performed at a wavelength of 830 nm with 17 µm axial resolution in air, corresponding to 15 µm in tissue. The image is displayed using a log false color scale with a signal level ranging between 4×10−10 and 10−6, or between –94 dB and –60 dB of the incident light intensity. The OCT image of the coronary artery shows fibrocalcific plaque on the right three-quarters of the specimen and fibroatheromatous plaque on the left side. The plaque scatters light and therefore attenuates the OCT beam, limiting the image penetration depth. The OCT image of the retina shows the contour of the optic disc as well as retinal vasculature near the disc region. The retinal nerve fiber layer can also be visualized emanating
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Figure 2.1 OCT is analogous to ultrasound, except that it measures the magnitude and echo time delay of light rather than sound. Axial scans (A-scans) measure the back-reflection or backscattering versus depth. Cross-sectional images are generated by performing a series of axial scans at different transverse positions to generate a two-dimensional data set (Bscan) which is displayed as a gray-scale or false color image
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Figure 2.2 OCT image of a human artery ex vivo. OCT imaging was performed at 830 nm wavelength with 17 µm axial resolution in air, corresponding to 15 µm in tissue. The image is displayed using a log false color scale with a signal level ranging between 4 × 10−10 and 10−6, or between –94 dB and –60 dB of the incident light intensity. The OCT image of the coronary artery shows fibrocalcific plaque on the right three-quarters and fibroatheromatous plaque on the left side of the specimen. The fatty calcified plaque scatters light and therefore attenuates the OCT beam, limiting the depth of the image penetration. (From reference 1, with permission)
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Figure 2.3 OCT image of the human retina ex vivo. OCT imaging was performed at 830 nm wavelength with 17µm axial resolution in air, corresponding to 15 µm in tissue. The OCT image of the retina shows the contour of the optic disc as well as retinal vasculature near the disc region. The retinal nerve fiber layer is also visualized. This image was obtained ex vivo and postmortem retinal detachment with subretinal fluid accumulation are evident. (From reference 1, with permission)
from the optic nerve head. This image was obtained ex vivo, and postmortem retinal detachment with subretinal fluid accumulation are evident.
