Quantitative cardiac blood flow imaging with high frame rate ultrasound

The measurement of blood flow is important for evaluation of cardiac function. Ultrasonic color Doppler imaging is one of the most frequently used methods for the measurement of cardiac blood flow. However, the Doppler method provides only the axial velocity components in the direction of ultrasound propagation. To overcome such a problem, the vector flow mapping method (VFM), which estimates 2-D blood flow velocity by applying the theory of fluid dynamics to the axial velocity field obtained by the color Doppler method. However, the frame rate is limited to less than 30 frames per second (fps), and better temporal resolution is preferable for evaluation of the rapid temporal change in cardiac blood flow. In the present study, echoes from blood cells were visualized by high frame rate ultrasound imaging at a frame rate of 6250 fps. Recently, echo particle image velocimetry (e-PIV) was developed for observation of cardiac blood flow. This method requires intravenous injection of ultrasonic contrast agents. On the other hand, the proposed method does not require contrast agents. Also, echoes from blood cells are visualized at a very high frame rate, and thus, blood flow velocity vectors can be estimated quantitatively by applying motion estimator to visualized echoes.