A model of the effects of hydrophone and amplifier frequency response on ultrasound exposure measurements

Because of finite-amplitude effects in water or other low-attenuation media, diagnostic ultrasound pressure pulses can have significant spectral content beyond 50 MHz. To record these pulses accurately, the hydrophone and its preamplifier must have a sufficiently broadband response. To examine how less-than-ideal hydrophones and amplifiers could affect the measurement of pulse parameters, a simulated distorted pressure pulse was analyzed before and after being filtered by hydrophone and amplifier response models (H_h(f ) and H_a(f), respectively). It was found that if errors in the pulse-average intensity were to be below about ±5%, then f_h/f_c should be greater than ≃10 for H_a(f)=1, or f_a/f _c should be greater than ≃8 for H_h (f)=1. However, with both filter functions assigned realistic (i.e. nonunity) forms, an H_h(f) H _a(f) combination can be chosen to allow less restrictive frequency ratios because of the offsetting nature of the two filtering processes