PRESSURE PULSE DISTORTION BY HYDROPHONES DUE TO DIMINISHED LOW-FREQUENCY RESPONSE

In characterizing the bandwidth of measurement devices used in ultraso und exposimetry, attention has been focused on the high frequency resp onse, However, current diagnostic ultrasound measurement standards hav e low frequency specifications for hydrophones and associated amplifie rs, and the response below 1 MHz can be especially significant when me asuring lithotripsy pulses, To model the effects of diminished low fre quency response, simulated diagnostic and lithotripsy pulses were filt ered with a single-pole high-pass filter for a range of -3 dB cutoff f requencies (denoted f(a)). For lithotripsy pulses, it was found that t he pulse quantities peak rarefactional pressure (p(r)) and pulse width (t(w)) were most sensitive to f(a), and to keep errors in p(r) and t( w) below 10%, f(a) should be in the 10-60 kHz range for the pulses exa mined, For the diagnostic case, p(r) was the quantity most significant ly affected, and for an f(a) value approximately one-half the center f requency, p(r) was decreased by more than 30% for a pulse modeled to s how the effects of finite amplitude distortion typical of diagnostic p ulses measured in water, Given this latter result, current hydrophone and amplifier low frequency specifications may need to be reconsidered .