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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 30–60 s 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°C, 17.5 ml/100 g/min, and 46.3 W/kg, respectively. The most frequent artifact was in the range 0–0.2°C and the mean artifact was 0.6°C. Less than 15% of the artifacts were above 1°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.
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