Optimization of pulse transmission in a high-frequency ultrasound imaging system

The effect of cables that connect the transducer and an imaging system can no longer be ignored when the ultrasound frequency is higher than 20MHz. The length of transmission line between transducer and electronic system critically affects the amplitude and bandwidth of pulse transmission. We report an evaluation method for assessing the effects of the cables and results obtained from this method. A time domain PSpice simulation model including high frequency impulse generator and receiver, a transducer simulated with a Mason model and a lossy transmission line has been developed. The model allows the simulation of the echo pulse shape at the input of the receiver. The investigation is carried out with a transducer of center frequency 45MHz and 48% bandwidth. The effect of cable length on the amplitude, space pulse length and bandwidth of received pulse is studied. Moreover, the effect of impedance tuning is also studied between the system and transducer when the cable is not used. Both experimental and simulation results show that the system performance is optimized by a cable length of 60cm to achieve higher sensitivity. If a suitable impedance matching method is applied between the system and the transducer without the cable connected, the system performance in sensitivity would be better than that with a cable connected. However, the results also show that achieving a highest sensitivity would increase pulse length. The results show that optimizing high frequency pulse transmission with high sensitivity and acceptable pulse shape, the pulser and receiver should be placed as close as possible to transducer with suitable impedance matching. The results also suggest the shorted pulse length could occur at a certain cable length but the result is also dependent on the original pulse shape.