Effect of acoustic output on fetal ultrasound color Doppler performance

Abstract

Increasing transmit acoustic output in color Doppler ultrasound imaging improves the received data temporal signal-to-noise ratio (SNR), but such elevated acoustic pressures increase the potential for inertial cavitation and tissue heating. Safety regulations constrain maximum acoustic output to mitigate bioeffects, but lower output is encouraged following the ALARA (As Low As Reasonably Achievable) principle. In this study, color Doppler imaging with a Siemens ACUSON Sequoia and 10L4 transducer was performed on the placenta umbilical cord insertion site of 10 pregnant volunteers. Flow data were collected at five acoustic output levels and four frequency settings to assess each parameter’s effect. The output Thermal Index (TI) ranged from 0.001 to 0.7 and frequency ranged from 4.0 to 7.3 MHz. Increased temporal SNR in the receive signals at high output levels was linked to lower pulse-to-pulse phase variance and velocity bias. These metrics changed most dramatically across low output levels, before converging towards constant phase variance and velocity bias at high temporal SNR. The output levels approaching stable phase variance and velocity were specific to each volunteer and frequency. This result provides a framework for future automated Doppler ALARA implementations that calculate performance metrics and adjust acoustic power in accordance with ALARA principles.