Assessment of thermal index compliance in clinical ultrasound examinations

Abstract

Introduction: The thermal index (TI) is critical for monitoring potential heating risks in ultrasound examinations. This study aims to analyse adherence to TI guidelines in clinical ultrasound exams, focusing on the thermal index for soft tissue (TIS) and thermal index for bone at the focus (TIB). Methods: Clinical ultrasound images over a five working day period from a single NHS University Hospital Trust were analysed using a custom MATLAB script. TI values were extracted from DICOM headers, supplemented by optical character recognition for missing values. Time at each TI value (image interval) was measured assuming a constant TI between consecutive images. TI values and corresponding image intervals were compared to TI guidelines provided by the British Medical Ultrasound Society (BMUS). Results: Analysis included 627 obstetric and 1023 non-obstetric examinations, comprising 4643 obstetric and 19,228 non-obstetric image intervals. TIS values across all examinations and image intervals adhered to recommended BMUS limits; however, breaches of the guidelines were observed for TIB. In obstetrics, 44 image intervals across 47 examinations exceeded the TIB limits (1.01% of TIB image intervals and 7.02% of examinations). For non-obstetrics, two image intervals across two examinations exceeded the TIB limits (0.02% of intervals and 0.44% of examinations). Conclusion: The majority of ultrasound examinations considered for this analysis demonstrated compliance with BMUS guidelines for TI, except for a small fraction which showed breaches in the obstetric thermal index for bone at the focus limits. All breaches were associated with the use of pulsed-wave Doppler.