Estimation of Blood Velocity with High Frequency Ultrasound

Estimation of low velocities in small vessels is a challenge with current ultrasound systems. In order to establish the feasibility of mapping flow with high frequency ultrasound, we present the results of in vitro and in vivo ultrasound velocity estimation. We evaluate the performance of an infinite impulse response (IIR) clutter rejection filter and the wideband maximum likelihood (WMLE) velocity estimation strategy with a transducer center frequency of 38 MHz. Using the short transmitted pulse and the narrow lateral beam width obtained using this frequency, we show that velocities below 1 mm/s can be estimated reliably, and vessels as small as 40 µm distinguished from stationary tissue. Using this experimental methodology and these signal processing strategies, blood flow and wall motion can be assessed in vivo in small vessels near the transducer. This provides the opportunity to study physiologic phenomena on a very small scale. Clinical applications include the assessment of flow in the skin and lymphatic system and within anterior structures of the eye. In previous work, we have established the performance of the WMLE for a transducer center frequency below 7 MHz and vessels with a diameter of 2 mm or above. In order to extend this work to a higher center frequency, with the goals of detecting lower velocity flow and smaller vessels, this paper is organized as follows. First, an in vitro flow phantom with known experimental ...(this text has been cut automatically)