Hydrophone Spatial Averaging Correction for High-Frequency Arrays

Abstract

A hydrophone spatial averaging correction algorithm, previously validated in the 5–8 MHz range [1, 2], was tested at higher frequencies using two high-frequency linear arrays: L12-5 (9 MHz; F/1.6) and L22-14 (15 MHz; F/3). Seven hydrophones (with capsule, needle, and membrane designs and sensitive element diameters ( <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$d_{g}$</tex> ) ranging from 85 to 1000 µm) were used, one at a time, to measure the beams at the focal point. Spatial averaging errors were characterized by percent change in parameter (peak compressional pressure <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$p_{c}$</tex> , peak rarefactional pressure <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$P_{r}$</tex> , pulse intensity integral pii, and spatial-peak temporal average intensity Ispta) measurement for every 100 µm of hydrophone sensitive element diameter. The spatial averaging correction algorithm reduced errors in measurements of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$p_{c}$</tex> from 11%±2 % to 3 %±2 % per 100 µm, measurements of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$P_{r}$</tex> from 7%±1% to 0%±4% per 100 µm and measurements of intensities from 12%±1% to 0%±2% per 100 µm. The spatial averaging correction was effective up to at least 15 MHz and resulted in significant reduction in errors of measurements for acoustic pressures and intensities from clinical high-frequency linear arrays.