Abstract
Purpose: To measure temperature change and magnetization transfer ratio (MTR) simultaneously during high-intensity focused ultrasound (HIFU) treatment. Materials and Methods: This study proposed an inter-leaved dual gradient-echo technique to monitor the heat and tissue damage brought to the heated tissue. The technique was applied to tissue samples to test its efficacy. Results: Ex vivo experiments on the porcine muscle demonstrated that both temperature changes and MTR exhibited high consistency in localizing the heated regions. As the heat dissipated after the treatment, the temperature of the heated regions decreased rapidly but MTR continued to be elevated. Moreover, thermal dose (TD) maps derived from the temperature curves demonstrated a sharp margin in the heated regions, but MTR maps may show a spatial gradient of tissue damage, suggesting complimentary information provided by these two measures. Conclusion: In a protocol of spot-by-spot heating over a large volume of tissue, MTR provides additional values to mark the locations of previously heated regions. By continuously recording the locations of heated spots, MTR maps could help plan the next target spots appropriately, potentially improving the efficiency of HIFU treatment and reducing undesirable damage to the normal tissue. © 2009 Wiley-Liss, Inc.