The broad, long-term objective of the proposed research is to develop an integrated system for monitoring and guidance of noninvasive and minimally-invasive thermotherapy devices. We consider the use of pulsed high intensity focused ultrasound (pHIFU) in single-shot mode and raster scanned mode to form volumetric lesions. Noninvasive estimation of tissue temperature in response to the application of therapeutic and sub-therapeutic pHIFU shots is a key to the wide spread acceptance of these devices in the clinic. Pulse-echo ultrasound has been shown to be suitable, in principle, as an image guidance modality with temperature imaging capability. However, noninvasive temperature imaging using pulse-echo ultrasound still suffers from limitations that hindered its adoption in clinical systems. This application addresses these limitations by proposing to develop an integrated imaging system with a variety of imaging modes designed to capture all the spatial and temporal dynamics of tissue deformations, whether native (e.g. due to breathing and cardiac cycle) or source induced. For a pHIFU source with single shots heating mm-size volumes, the mechanical stresses on the tissue due to radiation force effects may require M-mode imaging with high pulse repetition frequency (PRF) to capture the full dynamics of tissue deformation in response to therapeutic and subtherapeutic pulses. In raster-scan mode with relatively large heterogeneous heating field may require a number of A-lines to be acquired at high PRF to capture transient 2D tissue deformations in response to the pulsed source. For both of these modes, we propose new data acquisition protocols mixing full frame 2D RF data collection with M-mode for single-shot pHIFU and M2D-mode for raster-scan volumetric heating mode. By M2D-mode imaging we mean the collection of limited number of neighboring A-lines at the highest possible PRF. This will allow for simultaneous capture of tissue deformations with simultaneously high resolution in space and time to capture the dynamics of the complex temperature field. If successful, this research will lead to a robust real-time temperature imaging using diagnostic pulse-echo ultrasound. This will have significant impact on the clinical acceptance of pHIFU as a cost-effective and reliable modality for delivering thermal therapy to tumors and other tissue abnormalities.
Robust temperature imaging is considered an """"""""enabling technology"""""""" for minimally-invasive and noninvasive thermal therapy. Diagnostic pulse-echo ultrasound has the potential for imaging temperature changes in response to heating devices, but suffers from significant limitations that hindered its clinical acceptance. The proposed research addresses these limitations from the system and signal processing design perspectives. If successful, robust real-time temperature estimation for monitoring and guidance of thermal therapy will be developed and be ready for in vivo testing.
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