Emerging Colors for Optical Coherence Tomography

Optical Coherence Tomography (OCT) is a depth-resolved, interferometric technique that enables micron resolution, label-free imaging in vivo. OCT is a standard of care in ophthalmology, but has also had an impact in cardiology as well as a number of emerging areas. In OCT, a broadband spectrum facilitates optical depth sectioning by providing a coherence gate. At the same time, this broadband spectrum also provides the ability to decode tissue chromophore content from the differential signal attenuation versus depth. Typically, OCT is performed between 700 nm and 1600 nm. In this thesis, new and emerging OCT “colors,” or wavelength ranges, are investigated through a series of demonstrative studies in mice and rats. The introduction describes relevant considerations for selecting the appropriate OCT color. In the visible light range (Chapter 2), which benefits from high hemoglobin absorption, a novel way of estimating vessel hemoglobin and saturation was proposed. In the 1300 nm optical window (Chapter 3), light-blood cell interaction was investigated in the retina to understand the contrast mechanisms of OCT angiography in the retina. Finally, two emerging colors for OCT were investigated in vivo. In the 1700 nm optical window (Chapter 4), benefitting from minimal overall ballistic light attenuation, cellular resolution deep brain imaging was achieved. In the 2200 nm optical window (Chapter 5), benefitting from even lower scattering and low attenuation in water-scarce tissues, non-invasive in vivo imaging of the brain was achieved for the first time. Conclusions are summarized and future directions are discussed in Chapter 6