Temperature measurements in high thermal gradients: II. Analysis of conduction effects.

Measurement errors associated with thermal conduction along a temperature probe in regions of high thermal gradients are examined. An analysis of a conducting probe inserted into an insulating catheter for the purpose of temperature mapping gives a means for estimating the effects of thermal smearing on the measured distribution. A comparison is made between the theory and an experimental test case (flow cell-thermal step gradient). Also, an iterative algorithm is developed to correct thermally smeared temperature distributions in order to reconstruct the desired unsmeared distributions. The algorithm is checked for self consistency in the flow cell experiment and is applied to in vivo data obtained during interstitial microwave heating in normal dog brain. Data from flow cell measurements are used to make relative comparisons of the probe conduction artifact for several different temperature probes (2 thermocouple needle probes, a thermistor needle probe and an optical probe) and assorted teflon catheters (16, 18 and 20 ga).