|Institution:||University of Illinois – Urbana-Champaign|
|Full text PDF:||http://hdl.handle.net/2142/44166|
Hyperthermia has been proven to be an effective way of enhancing radiotherapy and chemotherapy, but monitoring the temperature accurately and noninvasively is imperative for controlling the exposures. Ultrasound thermometry techniques have been proposed, such as tracking echo shifts or correlating the changes in backscattered energy (CBE) with temperature. 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 CBE with temperature has been hypothesized to be from the changes in scattering properties of local aqueous and lipid scatterers. A new mechanism is hypothesized to be responsible for much of the observed CBE versus temperature rise, i.e., changes in signal coherence. To test this hypothesis, simulations were conducted in software phantoms and the CBE was calculated versus changes in SOS, which are typically associated with changes in temperature. The simulations were carried out with a linear array having 128 elements and center frequency of 5.5 MHz. Experiments were carried out by scanning physical phantoms containing randomly spaced glass beads with a Sonix RP scanner at every 0.5 ??C from 37 ??C to 48 ??C. Shifts in the backscattered signal caused by changes of SOS with temperature were compensated using 2D motion compensation techniques. Each pixel in the CBE image underwent either a monotonic increase (up to 7.1 dB) or a monotonic decrease (down to -4.6 dB) with increasing temperature. Similar CBE curves were also produced at a fixed temperature by shifting the elevation image plane location or by shifting the focus of the linear array probe. Therefore, using CBE curves to monitor temperature elevation may not be robust against tissue motion. Furthermore, the production of CBE curves versus temperature did not require the presence of lipid and aqueous scatterers.