Measured acoustic intensities for clinical diagnostic ultrasound transducers and correlation with thermal index

Objectives To investigate if the thermal index for bone (TIB) displayed on screen is an adequate predictor for the derated spatial‐peak temporal‐average (ISPTA.3) and spatial‐peak pulse‐average (ISPPA.3) acoustic intensities in a selection of clinical diagnostic ultrasound machines and transducers. Methods We calibrated five clinical diagnostic ultrasound scanners and 10 transducers, using two‐dimensional grayscale, color Doppler and pulsed‐wave Doppler, both close to and far from the transducer, with a TIB between 0.1 and 4.0, recording 103 unique measurements. Acoustic measurements were performed in a bespoke three‐axis computer‐controlled scanning tank, using a 200‐μm‐diameter calibrated needle hydrophone. Results There was significant but poor correlation between the acoustic intensities and the on‐screen TIB. At a TIB of 0.1, the ISPTA.3 range was 0.51–50.49 mW/cm2 and the ISPPA.3 range was 0.01–207.29 W/cm2. At a TIB of 1.1, the ISPTA.3 range was 19.02–309.44 mW/cm2 and the ISPPA.3 range was 3.87–51.89 W/cm2. Conclusions TIB is a poor predictor for ISPTA.3 and ISPPA.3 and for the potential bioeffects of clinical diagnostic ultrasound scanners.