Validation of Theoretical Diffraction Correction Functions for Strongly Focused High Frequency Ultrasonic Transducers

Abstract

Adequate correction for diffraction effects is critical to the measurement of device-independent acoustical parameters. This correction is especially important in situations where strongly focused beams are used in the measurements. Diffraction correction function profiles, for two spherically-focused high frequency transducers (50 MHz, focal distance 5.7 mm, f/number of 1.7 and 29 MHz, focal distance 10.0 mm, f/2), were determined using experimental and theoretical approaches. Experimental measurements are based on established approaches using the power backscattered by an ultrasonic tissue-equivalent calibrating phantom. These results are compared to a recently-published theoretical model. Excellent agreement between the experiment and theory is achieved. No statistically-significant difference in mean backscattered power is found between the experimental and theoretical approaches. The use of a simple normalization procedure (termed ‘diffraction correction’) involving the ratio of the mean power backscattered from the sample to the power for reflection from a plane reflector at the same depth, is shown to introduce significant errors.