In vivo verification of the acoustic model used to predict temperature elevations for MRI guided ultrasound surgery

Previous studies have shown that larger focal volumes created by phased-arrays result in lower overall treatment times when multiple sonications are required to necrose large tissue volumes. To fully utilize and optimize complex phased arrays, accurate theoretical models are required for prediction of the temperature elevation in vivo. So far, numerical simulation models have been shown to be relatively accurate for predicting coagulated tissue volumes (C. Damiano et al., 1995). However, there have not been studies investigating the accuracy of the actual temperature elevations in vivo. In the current experiment, an 8 element sector-vortex array has been constructed and tested in rabbit thigh in vivo. Temperature sensitive MRI imaging sequences were used to monitor the temperature elevations. A comparison of the theoretically calculated temperature elevations with the temperature elevations as monitored with the MRI resulted in a discrepancy. The theoretical temperature elevation for a single focus pattern was 2.7/spl plusmn/19% times higher than the measured, while for a mode 4 sonication, the theoretical value was only 1.1/spl plusmn/21% higher than the measured. These results indicate that the theoretical model used to predict temperature elevations in vivo neglects some phenomenon that is dependent on focal volume.