Measuring the effect of focal spot size on SD-OCT imaging (2016)

Undergraduate: Eric Boyers

Faculty Advisor: Amy Oldenburg
Department: Physics & Astronomy

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Spectral domain optical coherence tomography (SD-OCT) is an optical interferometry technique that can image the location of reflecting interfaces up to a couple millimeters into a surface with micrometer-scale resolution. OCT typically employs near-infrared light at relatively low intensities making it well suited to studying biological samples. An issue affecting the quality of SD-OCT images is signal roll-off which causes the signal intensity to decrease with increasing depth and limits the effective range of imaging. One contribution to roll-off can be described by the OCT spectrometer¿¿¿s modulation transfer function (MTF). Models of SD-OCT MTF suggest that roll-off should increase with increasing spot size of the beam on the detector. We propose to explore methods of decreasing roll-off by comparing the MTF of an existing OCT spectrometer to that of a newly constructed spectrometer with aberration correcting lenses and a smaller beam spot size. The MTF as a function of depth will be determined by imaging a diffusely reflecting surface at various heights and calculating the ratio of the intensity at each height to the intensity at zero height. These measurements will be repeated for various spectrometer lens types, providing information on how spot size and lens type affect roll-off in SD-OCT systems. This could inform better design of SD-OCT spectrometers and make the technique an even more useful tool in clinical and research settings.