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Temperature elevation measured in a tissue-mimicking phantom for transvaginal ultrasound at clinical settings

Overview The paper reports the results of an audit to assess the potential thermal hazards associated with the clinical use of transvaginal transducers in 17 UK hospitals. A typical scanning protocol incorporating 2D, colour and pulsed Doppler imaging was used.. Greatest temperature rise was 3.6oC and a mean temperature rise of 2.0oC for gynaecology presets and 2.16oC for obstetric presets – all fell within the limits indicated by national and international standards.

The thermal index was shown to greatly underestimate the temperature rise at distances up to 2cm removed from the transducer.


Authors Miloro P, Martin E, Shaw A.


Journal Ultrasound 2017 Feb;25(1):6-15.
Recommendation/Comment Relevant for transvaginal ultrasound scans.
Clinical implication Although temperature rises fell within national and international recommendations, the thermal index significantly unestimated temperature increase up to 2cm distance from transducer.
Link (DOI) https://doi.org/10.1177/1742271X16684529
Ultrasound speciality Quality and safety Issues, physics and US equipment

Original Abstract


This paper reports the results of an audit to assess the possible thermal hazard associated with the clinical use of ultrasound scanners in UK Hospitals for transvaginal ultrasound imaging.


An anatomically relevant phantom composed of a block of agar-based tissue mimicking material with embedded thermal sensors was developed. Seventeen hospitals around the UK were visited and a total of 64 configurations were tested. A representative typical scanning protocol was adopted, which primarily used B-mode with 30 s periods of colour-flow and pulsed Doppler modes for both gynaecology and obstetrics pre-sets.


The results confirmed that the highest temperature increase is always at the surface. The greatest temperature rise measured across all the systems was 3.6℃, with an average of 2.0℃ and 2.16℃ for gynaecology and obstetrics pre-sets, respectively. For some systems, the temperature increased rapidly when selecting one of the Doppler modes, so using them for longer than 30 s will in many cases lead to greater heating. It is also shown that, in agreement with previous studies, the displayed thermal index greatly underestimates the temperature rise, particularly close to the transducer face but even to distances approaching 2 cm.


Overall, the results of the audit for the temperature rise during transvaginal ultrasound at clinical settings fell within the limits indicated by the national and international standards, for the pre-sets tested and following a representative typical scanning protocol. Only selected pre-sets were tested and the scanner outputs were not maximised (for example by using zoom, greater depth or narrow sector angles). Consequently, higher temperatures than those measured can certainly be achieved.


Ultrasound safety; temperature measurement; thermal index; transvaginal ultrasound; ultrasound phantom