TEMPERATURE AND SAR MEASUREMENTS IN DEEP-BODY HYPERTHERMIA WITH THERMOCOUPLE THERMOMETRY

Multisensor (7-14) thermocouple thermometry is used at our department for temperature measurement with our 'Coaxial TEM' regional hypertherm ia system. A special design of the thermometry system with high resolu tion (0.005-degrees-C) and fast data-acquisition (all channels within 320 ms) together with a pulsed power technique allows assessment of sp ecific absorption rate (SAR) information in patients along catheter tr acks. A disadvantage of thermocouple thermometry, EM interference, is almost entirely eliminated by application of absorbing ferrite beads a round the probe leads. We investigated the effect of remaining disturb ance on the temperature decay after power-off, both experimentally in phantoms and in the clinic, and with numerical simulations. Probe and tissue characteristics influence the response time tau(dist) of the de cay of the disturbance. In our clinical practice a normal pulse sequen ce is 50 s power-on, 10 s power-off: a response time longer than the p ower-off time results in a deflection of the temperature course at the start. Based on analysis of temperature decays correction of temperat ure is possible. A double-pulse technique is introduced to provide an initial correction of temperature, and fast information about accuracy . Sometimes disturbance with a relatively long response time occurs, p robably due to a bad contact between probe, catheter and/or tissue. Th ermocouple thermometry proved to be suitable to measure the SAR along a catheter track. This is used to optimize the SAR distribution by pat ient positioning before treatment. A clinical example illustrates this .