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. Copyright © 2016 ISUOG. Published by John Wiley & Sons Ltd.
Keywords: in vitro; intensity measurements; thermal index; ultrasound safety.
Copyright © 2016 ISUOG. Published by John Wiley & Sons Ltd.