Altered hemodynamics in developing embryonic hearts lead to congenital heart diseases, motivating close monitoring of blood flow over several stages of development. Doppler OCT can assess blood flow in tubular hearts where blood velocity increases drastically during the period of cardiac cushion (valve precursors) formation. The blood-induced shear stress undergoes dramatic changes as well, which affects gene expression by the endothelial cells. Previously, we built a high-speed OCT system using an FDML laser (Optores GmbH, Germany) at a sweep rate of 1.68 MHz (axial resolution - 12 μm, sensitivity - 105 dB, phase stability - 96 mrad). The ultra-fast A-line rate of this laser may be used to collect real-time volumetric images of the heart, or can be traded off to obtain dense B-scans for more accurate Doppler measurements with a larger dynamic range using Doppler complex regression. Since we cannot achieve volumetric imaging with dense B-scans, an image-based retrospective gating technique was developed to register the asynchronously acquired dense B-scans to the 4D volumes. The direction of flow was determined by finding the centroid of the Doppler signal from the rearranged B-scans along the heart tube to compute absolute velocity. Subsequently, the cross-section from which the shear stress is calculated was realigned orthogonal to the direction of blood flow to approximate the velocity gradient normal to the wall. In conclusion, our high-speed OCT system will enable semi-automated measurement of the absolute blood velocity, as well as mapping the shear stress exerted on the inner walls of the embryonic hearts.
Sahar Elahi, Shi Gu, Andrew M. Rollins, and Michael W. Jenkins, "Semi-automated measurement of absolute blood velocity and shear stress in developing embryonic hearts using a MHz FDML swept laser source (Conference Presentation)," Proc. SPIE 10472, Diagnosis and Treatment of Diseases in the Breast and Reproductive System IV, 104720R (Presented at SPIE BiOS: January 28, 2018; Published: 14 March 2018); https://doi.org/10.1117/12.2291058.5751468285001.
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