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Ultrasonic heating of mammalian tissues in vivo.

THE thermal effects of ultrasound are of interest not only to physiotherapists but also to oncologists who wish to use local hyperthermia in the treatment of tumours. In order to heat tissue volumes safely and efficiently, it is important to understand the temperature distributions that may be achieved in mammalian tissues in vivo. Despite the widespread usage of ultrasound therapy, published data on ultrasonically induced temperature rises are surprisingly sparse. Many of the measurements that have been reported have been in dog and pig thigh muscle, and interest has been focussed on ultrasonic heating around bone (e.g. Lehmann et al., 1978). In this study, a site in the thigh of young pigs was used for irradiation with 0 75 MHz ultrasound such that no bone lies within the treated volume. This site was used previously for heating studies involving the use of 915 MHz microwaves (Hand et al., 1980). Temperature distributions to a depth of 5 cm in soft tissue are reported. Temperature profiles in depth and time were studied for spatial average intensities of up to 3 0 Wcm-2.