Empirical correction method for spatial averaging effect in ultrasonic device calibration: Enhancing the precision-sensitivity trade-off

The calibration of ultrasound diagnostic equipment is essential to ensure their effectiveness and safety. Calibrating acoustic fields using hydrophones involves the measurement of the maximum pressure point. Since the signal at the hydrophone output is proportional to the average pressure incident on its surface, when the active area of the hydrophone is larger than the area of the ultrasonic beam at the focus, the lower acoustic pressures surrounding the point of maximum pressure will cause an underestimation of this value. This phenomenon is referred as the spatial averaging effect. The main limitation in the use of smaller hydrophones is the inherent reduction in sensitivity. The International Electrotechnical Commission standards provide methods to correct for the spatial averaging effect when the ratio of the - 6 dB beam width to the hydrophone diameter (Rbh) is higher than 1.5. In this study, a novel method is presented for spatial averaging correction, developed using computational simulation. It consists of an empirical correction factor and allows extending corrections for Rbh values as low as 0.35, with errors below 3%, addressing the compromise between precision and sensitivity of the hydrophone. This method also generalizes to ultrasonic probes with varying characteristics.