Optimized pulsing of high-intensity focused ultrasound for enhanced therapeutic window

University of Minnesota. M.S. thesis. March 2010. Major: Biomedical engineering. Advisor:Emad Ebbini. 1 computer file (PDF)); v, 37 pages. Ill. (some col.)High intensity focused ultrasound (HIFU) provides a unique modality to perform non-invasive surgeries. The thermal ablation technique relies on focusing the non-ionizing acoustic wave within soft tissues to produce a small lesion. HIFU operations are typically attempted by continuous-wave (CW) applications of the beam intervened by wait periods to allow surrounding tissue to cool down. Large contiguous lesions are produced by raster-scanning the beam over the volume of the tumor; a procedure that requires up to three hours for a 2-cm diameter tumor. This is one of the main limitations of HIFU thermal therapy. As part of the ongoing research to accelerate the procedure, we investigate the role of pulsed-HIFU (pHIFU) parameters in the enhancement of the therapeutic gain within the HIFU focus. A therapeutic gain is observed when high duty cycle pHIFU is pulsed at the mechanical resonance of the medium. Up to 50% increase in temperature was measured in lab-prepared tissue mimicking phantoms. The therapeutic gain achieved by pHIFU over cwHIFU is attractive as no modifications on the currently used applicators are required