A time-of-flight ultrasound system has an angle of 45° between the transducers. Blood flows through a 0.5 cm diameter artery in the arm at a rate of 2 ml/s. It is assumed that the flow profile is uniform, meaning that the blood flows at the same speed at any position in the artery. An ultrasound transducer transmits a 3.0 MHz pulse, which travels at a speed of 1500 m/s through the tissue. The distance between the transducers is 15 cm. Calculate the transmit-receive delay from transducer 1 to 2 when the blood is flowing. How is this different from when the flow rate is zero? Comment briefly on any difficulties in measuring changes in a delay of this size. Assuming laminar flow in the blood vessel, how would the measured delay change? The system is instead used as a continuous wave Doppler flow meter. Calculate the frequency shift that would be measured.
