Advanced functional flow index imaging using planewave excitation: Phantom study

In conventional ultrasound imaging, the quantitative information of vascular hemodynamics, e.g., resistive index (RI) and pulsatility index (PI), is provided by a spectral Doppler mode. However, achieving the Doppler indices with spectral Doppler imaging is time consuming and has limitation on accuracy when scanning various vascular regions. In this paper, a new functional flow index imaging (FFII) method with plane wave excitation is proposed. In the proposed FFII method, by transmitting a plane wave, sufficient temporal samples on a two-dimensional plane can be obtained during one cardiac cycle. To measure functional indices, the velocity of blood flow is calculated via an auto-correlation method. Then, the RI and PI values are extracted from the estimated blood velocities. In FFII, the measured RI and PI values are visualized as a two-dimensional pseudo color image. To evaluate the performance of the proposed method, pre-beamformed radio-frequency data from a flow phantom were acquired using a commercial ultrasound scanner with a research package. The mean RI and PI values from the proposed method were compared with those from the conventional spectral Doppler method. The maximum error was less than 3%. These results indicate that the proposed FFII method can provide a two-dimensional functional index image with a high frame rate.