Analysis of effective radiating area, power, intensity, and field characteristics of ultrasound transducers

Abstract

Objective: To characterize the ultrasound fields produced by a cohort of transducers from a single manufacturer via hydrophone and Schlieren technology.

Design: Descriptive study.

Setting: Measurement laboratory.

Participants: Seven same-model ultrasound transducers from a single manufacturer.

Interventions: Not applicable.

Main outcome measures: Effective radiating area (ERA), total power, spatial average intensity (SAI), beam nonuniformity ratio (BNR), and Schlieren beam widths at 1.0 and 3.3 MHz.

Results: Values for ERA (1.0 MHz range, 3.62-4.38 cm(2); 3.3 MHz range, 3.74-4.76 cm(2)), total power (1.0 MHz range, 5.0-5.6 W; 3.3 MHz range, 4.7-5.7 W), SAI (1.0 MHz range, 1.2-1.4 W/cm(2); 3.3 MHz range, 1.0-1.5 W/cm(2)), and BNR (1.0 MHz range, 2.79-5.85; 3.3 MHz range, 2.51-4.56) fell within manufacturer's specifications and U.S. Food and Drug Administration (FDA) regulations. Schlieren analysis showed significantly larger beam widths at 3.3 MHz compared with 1.0 MHz and a large degree of variability in the ultrasound fields generated by the different transducers. There were no significant correlations between beam widths and ERA values.

Conclusions: ERA and total power values in a test cohort exist within a range that met FDA regulations. Individual variability in ERA and total power resulted in 50% variability in SAI. This variability may help explain previous reports of heating differences between transducers.