The output of pulse-echo ultrasound equipment: a survey of powers, pressures and intensities

A survey of the powers, pressures and intensities generated by ultrasonic pulse-echo equipment in clinical use has been carried out. Three conventional B-scanners, four linear-array scanners and four mechanically sectored scanners were included in the study. Measurements were made on a total of 22 transducers covering the nominal frequency range 2.25-7.5 MHz. On those instruments where an output power control was provided, two measurements were made: one at the maximum available power and a second at a lower power. On arrays with a variable transmit focus control, measurements were made at all available focus settings. In all, measurements were made on 38 separate focused pulsed ultrasonic fields. The measurements were carried out using a calibrated ultrasonic force balance, and a calibrated polyvinylidene difluoride (PVdF) membrane hydrophone. A very wide range of maximum powers, pressures and intensities were found. Powers from 0.5-80 mW were measured; spatial-average temporal-peak positive pressures at the transducer varied between 30 kPa and 1.15 MPa, and spatial-peak pulse-average intensities were in the range 3.6 X 10(3)-1.1 X 10(7) Wm-2.