Catheter induced temperature artifacts in ultrasound hyperthermia

Abstract

Temperature artifacts were evaluated at 72 different sensor locations in 10 different tumour sites heated by use of planar ultrasound transducers operated at 1 and 3 MHz. Thermometry was carried out by single- and multisensor thermocouple probes inserted into 19- and 16-gauge polyurethane catheters, respectively. Nearly all catheters were oriented approximately perpendicular to the ultrasound beam. The artifacts were determined by backward extrapolation of the thermal decay 30-60s after the power was turned off. The effective blood flow and specific absorption rate (SAR) at the sensor locations were determined from the rate of decay and the steady-state temperature. The sample mean steady-state temperature, effective blood flow, and SAR were 41.4 degrees C, 17.5 ml/100 g/min, and 46.3 W/kg, respectively. The most frequent artifact was in the range 0-0.2 degrees C and the mean artifact was 0.6 degrees C. Less than 15% of the artifacts were above 1 degree C. The magnitude of the artifact correlates with the SAR of ultrasonic power, the effective blood flow rate, and the steady-state temperature. These results indicate that the artifact produced at 1 MHz by a multisensor, Teflon-sheathed thermocouple inserted into a 16-gauge polyurethane catheter is 1.7 +/- 0.4 degrees at an SAR of 100 W/kg.