A discussion of procedures for ultrasonic intensity and power calculations from miniature hydrophone measurements.

In this paper, some of the fundamental procedures for evaluating medical ultrasound fields using miniature hydrophones are discussed. Examples are considered for both static (fixed beam) and real-time (moving beam) ultrasound systems. Intensity and power quantities are calculated from hydrophone measurements using definitions contained in current standards, and where reasonable some simplified computational procedures are introduced. Assumptions implicit in common expressions for spatial average-temporal average intensity and ultrasonic power are identified, and in some cases illustrations of calculations using idealized pressure waveforms and beam shapes are given and compared with more exact results. Also, the adequacy of present guidelines for choosing the hydrophone size is evaluated using a simple time domain approach. This material is presented to augment and help clarify descriptions of procedures contained in existing standards, and to provide a basis for pursuing some of the more difficult problems associated with hydrophone measurements.