Noninvasive Temperature Imaging Through Ultrasonic Attenuation

This article deals with a feasibility of imaging the temperature of a specimen of interest in a noninvasive manner by ultrasound technique. A suitable working formula has been deduced to establish as to how ultrasound attenuation of a thermally bad and viscous material changes with the temperature. An experiment on the variation of ultrasound attenuation with the temperature was carried out. Agar hydrogel, a phantom material, mimics acoustic properties of soft tissues e.g. speed and attenuation has been taken as the sample for the proposed experiment. Temperature dependence of ultrasonic attenuation of agar phantom has been suggested as a noninvasive technique for temperature imaging. The attenuation of a tissue mimicking phantom, agar was estimated over a range of temperature of 293 to 316 K for three different agar densities (2%, 3% and 4% by weight). The variation of attenuation with temperature has been found to be a monotonic one in the above range and the curve can be used as a temperature calibration for agar in this temperature range. The concept may be applicable to all the real tissues to measure any temperature rise under in vivo condition during ablation or microwave thermotherapy provided the temperature dependence of ultrasound attenuation of the tissues are known before hand. PACS No: 43.90.+v, 43.58,+z, 05.70.-a, 43.80.-n.