Trends in diagnostic ultrasound exposure

Trends in exposure for diagnostic ultrasonic equipment and a contemporary survey of exposure values are presented. It is demonstrated that both time-averaged intensities and peak pressures have increased steadily over the last two decades. Currently available diagnostic equipment generates pulses for which the average worst-case rarefaction pressure, p-, is about 2 MPa in water, irrespective of the mode of operation. Overall the highest values of p- are found in short-focus beams. Average spatial-peak time-averaged intensities, I(SPTA), are greatest for pulsed Doppler operation at a little over 1 W cm-2. M-mode and colour Doppler operation have average values of I(SPTA) of about 100 mW cm-2 and imaging operates at about an order of magnitude lower again. Vaginal transducers differ little in operational exposure from other transducers. Exposure measurement on colour Doppler systems demands a knowledge of the effect of scanner controls on the field, and some details are given.