Linear array transducers generally have lower intensities than sector because of the broader beam area. Fetal Heart Monitors have the lowest pressure amplitudes and peak intensities. The highest recorded value are equivalent to the median values for imaging. This doppler mode is continuous and the acoustic dwell time is very long. Physical Therapy 1 msec. . .
Beams are unfocused.
In a comparison between physical therapy equipment and pulsed doppler equipment operating at its highest output, it was found that the highest peak pressures were reached at the focus of the pulsed Doppler beam, and that the acoustic power was equivalent for pulsed Doppler operating at the highest output and physical therapy machines. It is noted that physical therapy machines are required to have the output automatically stop after a certain time period. Such controls are built into therapy machines. The pulse energy however is much higher reaching a maximum of 90 mJ per pulse and the center frequency is much lower than that for imaging. Exposure Values for Medical Devices.