Blood flow visualization of left atrial spontaneous echo contrast (SEC) using gradient based optical flow estimation.

Left atrial spontaneous echo contrast (SEC) is a dynamic smoke-like signal caused by an increased ultrasonic backscatter from aggregation of the cellular components of blood in the conditions of blood stases or low-velocity blood flow. SEC can be detected by transesophageal echocardiography (TEE). SEC has been proposed as an important cadioembolic source in patients with nonrheumatic arial fibrillation. Previous clinical investigations have shown that the presence of SEC is associated with a greater incidence of left atrial thrombi. Usually, the blood flow velocity is slower than lower limit of Doppler method in SEC. In order to diagnose SEC quantitatively, blood flow visualization in left atrium was performed using gradient based optical flow estimation. A movie of left atrium (LA) with SEC in a patient with atrial fibrillation was recorded by TEE with the frequency range of 4-7.5 MHz. Serial still frames were made from the movie. The 2-D flow vector map was calculated from consecutive frame images using gradient based optical flow estimation. In the result of 2-D blood flow vector map, the low and swirling flow in LA were successfully visualized.