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MR imaging of temperature rise in ultrasound fields of diagnostic relevance.

Shaw, A; Clemence, M* (2003) MR imaging of temperature rise in ultrasound fields of diagnostic relevance. NPL Report. CAIR 7

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Abstract

The generation of heat within tissue due to exposure to ultrasound fields at diagnostic levels is a recognised safety concern. Due to the rapid development of ultrasound equipment and the large number of routine scans performed clinically, there is a need for rapid and accurate evaluation of the temperature rise caused by these spatially complex, time varying fields. While the use of directly applied thermal probes allows accurate point measurements to be made, the visualisation of complex three dimensional temperature distributions is exceedingly time consuming and the presence of the thermal probe can potentially affect the amount of heating. Magnetic Resonance Imaging (MRI) has the potential to provide a non-invasive temperature measurement system both in phantoms and in vivo.
To date, MRI has been used for the monitoring of thermal effects, both in vivo and in vitro, mainly in the areas related to thermal ablative therapies. As a result, much of the work has concentrated on large tissue temperature increases and rapid imaging with relatively coarse resolution. In contrast, the metrological requirements for fields of diagnostic relevance are rather different: a temperature rise of only 4 ºC is considered potentially hazardous if maintained for five minutes or more and the focal region may be 2 mm or less in diameter; consequently, it is necessary to measure the small temperature increases with high spatial resolution.
This report describes the development of an MRI protocol for determining the temperature distribution generated by an ultrasound transducer in a tissue-mimicking phantom with a resolution of approximately 0.5 mm and 0.2ºC in less than 20 seconds. The results are compared with measurements using thin-film thermocouples.

Item Type: Report/Guide (NPL Report)
NPL Report No.: CAIR 7
Subjects: Acoustics
Acoustics > Ultrasound
Last Modified: 02 Feb 2018 13:16
URI: http://eprintspublications.npl.co.uk/id/eprint/2862

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