Background: Birefringent crystals such as cholesterol and monosodium urate have recently been identified as possible pharmacologic targets for the treatment of coronary artery disease. The size of these crystals can be very small (on the order of 1 µm), making them difficult to identify. To image these microscopic crystals and enhance contrast, we modified existing micro optical coherence tomography system so that it was capable of obtaining polarization-sensitive images (PS-µOCT).
A spectrometer-based PS-µOCT system was developed using a 270 nm wide broadband light source centered at 765 nm. Light was polarized using a polarizer and coupled to a SMF. The polarized light after SMF was divided into reference and sample arms using a beam splitter. Images of orthogonal polarization states were acquired sequentially by inserting and removing a quarter wave plate in the reference arm. The orthogonal PS- µOCT image components were used to generate birefringent images of the tissue.
The axial resolution of the PS-µOCT system was 1.9 mm and the lateral resolution was 2 microns and the SNR was 92 dB. PS-µOCT was able to clearly identify isolated cholesterol and uric acid crystals. When used to image cadaver coronary arteries, the PS-µOCT images of crystals had up to 11 dB improved contrast compared to images obtained with a standard µOCT system.
Results show that the use of PS-µOCT improves image contrast for isolated crystals and crystals within coronary atherosclerotic plaque and suggest that it could be useful for understanding their roles in the development and progression of coronary artery disease.
Gargi Sharma, Kanwarpal Singh, Kensuke Nishimiya, Joseph A. Gardecki, and Guillermo J. Tearney, "Contrast enhancement of microscopic birefringent crystals using polarization sensitive micro-optical coherence tomography (Conference Presentation)," Proc. SPIE 10471, Diagnostic and Therapeutic Applications of Light in Cardiology 2018, 104710X (Presented at SPIE BiOS: January 28, 2018; Published: 14 March 2018); https://doi.org/10.1117/12.2295819.5751475920001.
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