Hydrophone Spatial Averaging Correction for Acoustic Exposure Measurements From Arrays-Part II: Validation for ARFI and Pulsed Doppler Waveforms

• Published in: IEEE transactions on ultrasonics, ferroelectrics, and frequency control ferroelectrics, and frequency control, 2021-03, Vol.68 (3), p.376-388
• Main Authors: Wear, Keith A., Shah, Anant, Ivory, Aoife M., Baker, Christian
• Format: Article
• Language: English
• Subjects: Acoustic measurement; Acoustic measurements; Acoustic output measurement; Acoustics; Arrays; Elastic waves; Empirical analysis; exposimetry; Filtration; Frequency measurement; hydrophone; Hydrophones; Linear arrays; Membranes; Parameter estimation; Phased arrays; Power harmonic filters; Sensitivity; Sonar equipment; Sound waves; spatial averaging; Transducers; Waveforms
• ISSN: 0885-3010; 1525-8955
• DOI: 10.1109/TUFFC.2020.3037999

This article reports the experimental validation of a method for correcting underestimates of peak compressional pressure ( {p}_{c}{)} , peak rarefactional pressure ( {p}_{r}{)} , and pulse intensity integral ( pii ) due to hydrophone spatial averaging effects that occur during output measurement of clinical linear and phased arrays. Pressure parameters ( {p}_{c} , {p}_{r} , and pii ), which are used to compute acoustic exposure safety indexes, such as mechanical index (MI) and thermal index (TI), are often not corrected for spatial averaging because a standardized method for doing so does not exist for linear and phased arrays. In a companion article (Part I), a novel, analytic, inverse-filter method was derived to correct for spatial averaging for linear or nonlinear pressure waves from linear and phased arrays. In the present article (Part II), the inverse filter is validated on measurements of acoustic radiation force impulse (ARFI) and pulsed Doppler waveforms. Empirical formulas are provided to enable researchers to predict and correct hydrophone spatial averaging errors for membrane-hydrophone-based acoustic output measurements. For example, for a 400- \mu \text{m} membrane hydrophone, inverse filtering reduced errors (means ± standard errors for 15 linear array/hydrophone pairs) from about 34% ( {p}_{c}{)} , 22% ( {p}_{r}{)} , and 45% ( pii ) down to within 5% for all three parameters. Inverse filtering for spatial averaging effects significantly improves the accuracy of estimates of acoustic pressure parameters for ARFI and pulsed Doppler signals.