One-dimensional NMR thermal mapping of focused ultrasound surgery

The aim of this study was to evaluate a technique for real-time monitoring of tissue temperature and tracking of the heat source during minimally invasive thermal interventions such as focused ultrasound surgery. A temperature-sensitive NMR line scan pulse sequence was directed interactively from a workstation during the application of focused ultrasound to samples of excised bovine skeletal muscle. The NMR signal along a sensitive line was monitored during and after heating by means of a scrolling display on the workstation. The temperature sensitivity was found to be approximately 2 degrees C with a time resolution of 300 ms along a line intersecting the ultrasonic focal point. Experimental temperature rises determined from the NMR signal showed close agreement with theoretical temperature behavior derived from the heat equation. Temperature quantitation capabilities were lost upon onset of thermal denaturation and coagulation. This technique could serve as a noninvasive guide in tracking the heat source and in monitoring thermal dose during focused ultrasound surgery and other minimally invasive thermal interventions.