Exploring potential mechanisms responsible for observed changes of ultrasonic backscattered energy with temperature variations.

PURPOSE Previous studies have provided the observation that the ultrasonic backscattered energy from a tissue region will change due to a change of temperature. The mechanism responsible for the changes in backscattered energy (CBE) with temperature has been hypothesized to be from the changes in scattering properties of local aqueous and lipid scatterers. An alternative mechanism is hypothesized here to be capable of producing similar CBE curves, i.e., changes in speckle resulting from changes in summation of scattered wavelets. METHODS Both simulations and experiments were conducted with a 5.5 MHz, 128-element linear array and synthetic and physical phantoms containing randomly spaced scatterers. The speckle pattern resulting from summation of scattered wavelets was changed in simulations and experiments by directly increasing the background sound speed from 1520 to 1540 m/s, and changing the temperature from 37 °C to 48 °C, respectively. Shifts in the backscattered signal were compensated using 2D cross-correlation techniques. RESULTS Excellent agreement between simulations and experiments was observed, with each pixel in the CBE images on average undergoing either a monotonic increase (up to 3.2 dB) or a monotonic decrease (down to -1.9 dB) with increasing sound speed or temperature. Similar CBE curves were also produced by shifting the image plane in the elevational and axial directions even after correcting for apparent motion. CONCLUSIONS CBE curves were produced by changing the sound speed or temperature in tissue mimicking phantoms or by shifting the image plane in the elevational and axial directions and the production of these CBE curves did not require the presence of lipid and aqueous scatterers.