A simulation model for ultrasonic temperature imaging using change in backscattered energy.

Ultrasound backscattered from tissue has previously been shown theoretically and experimentally to change predictably with temperature in the hyperthermia range, i.e., 37 degrees C to 45 degrees C, motivating use of the change in backscattered ultrasonic energy (CBE) for ultrasonic thermometry. Our earlier theoretical model predicts that CBE from an individual scatterer will be monotonic with temperature, with, e.g., positive change for lipid-based scatterers and negative for aqueous-based scatterers. Experimental results have previously confirmed the presence of these positive and negative changes in one-dimensional ultrasonic signals and in two-dimensional images acquired from in vitro bovine, porcine and turkey tissues. In order to investigate CBE for populations of scatterers, we have developed an ultrasonic image simulation model, including temperature dependence for individual scatterers based on predictions from our theoretical model. CBE computed from images simulated for populations of randomly distributed scatterers behaves similarly to experimental results, with monotonic variation for individual pixel measurements and for image regions. Effects on CBE of scatterer type and distribution, size of the image region and signal-to-noise ratio have been examined. This model also provides the basis for future work regarding significant issues relevant to temperature imaging based on ultrasonic CBE such as effects of motion on CBE, limitations of motion-compensation techniques and accuracy of temperature estimation, including tradeoffs between temperature accuracy and available spatial resolution.