This study presents an echo-stretching-based ultrasound technique for estimating temperature rise during hyperthermia therapy, eliminating the need for low-pass filtering and gradient computation used in conventional methods. The algorithm was evaluated using multiphysics simulations for thermal gradient of 0-0.1 °C using consecutive frames, and 0-6 °C using initial frame as reference. Inadequate up-sampling of radio frequency (RF) beamformed data resulted in spikes in the temperature estimates on echo stretching, which was reduced using adaptive up-sampling and median filtering. The average temperature estimation error relative to the peak temperature rise was less than 5% for 6 °C temperature gradient using 10λ sliding window, where, λ is the wavelength of ultrasound excitation in soft tissue. Window length of 40λ could resolve temperature gradient < 0.1 °C at the cost of spatial resolution. Axial resolution of 2.5 to 5 mm was achieved in hyperthermia temperature rise of 6 °C. Temperature estimation deteriorated with decline in signal to noise ratio (SNR) and depth. Experimental verification of echo stretching algorithm is tissue mimicking phantom and ex-vivo bovine tissues subjected to microwave hyperthermia at 434 MHz for 6 minutes using water loaded microstrip patch antenna indicated estimation error < 5 and 20% in phantoms and heterogeneous ex-vivo tissues, respectively. It is concluded that temperature rise estimated using the echo stretching of ultrasound RF data could be used for microwave hyperthermia treatment monitoring.
Ramu et al. (Thu,) studied this question.