Time-spatial ultrasound induced temperature evaluation on perfused phantoms

Abstract

Ultrasound usage as a hyperthermia therapeutic procedure still requires more research on spatial-temporal temperature propagation characterization over tissues and on non-invasive temperature monitoring techniques. Present work compares how temperature is propagated inside tissue phantoms without and with blood vessels. The artificial vessels simulated common carotid and right hepatic arteries pulsatile blood flow. Phantoms were heated by a therapeutic ultrasound (TU) device emitting continuously and temperature was monitored by thermocouples at some specific spatial points and evaluated by analysis of imaging ultrasound (IU) transducer's signals at those points. Experiments show that the existence of a blood vessel at the TU's axial line reduces the tissue temperature raise at that point in more than 50% in comparison with the non-perfused phantoms' behavior. As furthest spatial points are considered the effect of blood vessel is less noticeable. Thus the use of TU in vascularized tissues requires longer therapeutic sessions or higher TU intensities according to the location of the treatment area. Non-invasive temperature evaluation was performed using computed temporal echo-shifts (TES) proving that, besides the influence of a blood vessel on the overall model performance, TES are still a reliable noninvasive method of monitoring temperature in perfused tissues.