An in vitro investigation of transverse flow estimation

Abstract

Conventional ultrasound scanners are restricted to display the blood velocity component in the ultrasound beam direction. By introducing a laterally oscillating field, signals are created from which the transverse velocity component can be estimated. This paper presents velocity and volume flow estimates obtained from flow phantom and in-vivo measurements at 90° relative to the ultrasound beam axis. The flow phantom experiment setup consists of a SMI140 flow phantom connected to a CompuFlow 1000 programmable flow pump, which generates a flow similarly to that in the femoral artery. A B-K medical 8804 linear array transducer with 128 elements and a center frequency of 7 MHz is emitting 8 cycle ultrasound pulses with a pulse repetition frequency of 7 kHz in a direction perpendicular to the flow direction in the phantom. The transducer is connected to the experimental ultrasound scanner RASMUS, and 1.4 seconds of data is acquired. Using 2 parallel receive beamformers a transverse oscillation is introduced with an oscillation period 1.2 mm. The velocity estimation is performed using an extended autocorrelation algorithm. The volume flow can be estimated with a relative standard deviation of 13.0% and a relative mean bias of 3.4%. The in-vivo experiment is performed on the common carotid artery of a healthy 25 year old male. The same transducer and setup is used as in the flow phantom experiment, and the data is acquired using the RASMUS scanner. The peak velocity of the carotid flow is estimated to 1.2 m/s and the volume flow to 290 ml/min. This is within normal physiological range.