Browsing by Author "Rahmati, Javid J."
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- Characterization of temperature-dependent echo-shifts and backscattered energy induced by thermal ultrasoundPublication . Ruano, M. Graça; Teixeira, C. A.; Rahmati, Javid J.Existence of accurate temporal-spatial temperature models, which would enable non-invasive estimates, will promote ultrasound-based thermal therapy applications. These models should reflect the tissue temperature with a maximum absolute error of 0.5 ºC within 1 cm3. In-vitro experiments have been developed to evaluate the temperature variations induced by standard ultrasound therapeutic device emitting continuously on gel-based phantom and on pork meat tissue using three different emitting intensities (1, 1.5 and 2 W/cm3). Temperature estimates were performed based on raw RF data collected using a second ultrasound transducer (imaging transducer). This second transducer worked in pulse-echo mode, and was placed perpendicularly to the therapeutic transducer. In order to access the quality of the estimates, temperatures were acquired by five and by two thermocouples placed in the gel-based phantom and on the porcine sample, respectively. At every 10 seconds the temperature and one RF-line is stored in a PC for future processing. The possibility to estimate temperature was assessed by considering two RFline features: temporal echo-shifts produced by changes in speed-of-sound and medium expansion/contraction and by changes on the backscattered energy originated by medium inhomogeneities. On one hand, results prove that echo-shifts correlated with temperature in both types of medium (phantom and ex-vivo porcine muscle). On the other hand, analyzing the backscattered energies one may conclude that this measures correlates with temperature in the porcine sample and not on the phantom. This led us to conclude that the developed phantom is not appropriate for studying changes on backscattered energy with temperature. Energy analysis of the porcine sample confirms the non-uniform temperature variation due to the existence of a heterogeneous media with different sound propagation velocities.
- Study of the backscattered ultrasound energy for invasive tissue temperature estimationPublication . Rahmati, Javid J.; Ruano, M. GracaThis experimental work is part of the application of ultrasound for hyperthermia (thermal therapy) aiming at treatment of cancer cells. The analysis of the back-scattered ultrasound energy enables the study of the temperature behavior induced by the ultrasonic signal in the tissues and it is the primary goal of this case study. To carry out this experiment we developed a gel-based phantom which mimics the behavior of human tissues under ultrasound signals. Subsequently, in order to obtain a more human like phantom the experiments were repeated with ex-vivo pork loin. The experiments involved ultrasonic therapeutic and imaging instrumentation connected to a function generator and a signal acquisition system. Experiments were performed considering different energies (0.5, 1, 1.5 and 2 W/cm3) of the therapeutic transducer and two emission frequencies of the image transducer (5 and 7 MHz). Five temperature sensors were used to measure the invasive temperature in the gel-based phantoms and two sensors in the experiments with pork loin. Analyzing the time delays in the echoes of the back-scattered ultrasonic signals of both types of phantoms we verified the relationship between temperature rise and the increase in the speed of propagation of the echoes. The assessment of variations in the back-scattered energy proved its dependency on the temperature applied in pork loin tissue, but no conclusion could be taken in the case of gel-based phantom