Feasibility Assessment and Analysis of Thermal Sensitivity of CT-Thermometry During Microwave Ablation of Ex Vivo Porcine Kidneys

The aim of the present study was to assess the feasibility of thermometry based on Computed Tomography (CT) images during Microwave Ablation (MWA) at 2.45GHz in ex vivo porcine kidneys. Under MW radiation, a water molecule flips back and forth 2•109-5•109 times a second depending on the frequency of the microwave. This biomolecular interaction induces a tissue temperature increment and cellular death via coagulation necrosis. The thermal sensitivity was investigated at two CT scan settings. Four fresh pig kidneys were treated using two antennae at 65W and for 4 minutes, and they were scanned before the treatment and 24 times during the MWA (each 10 s). During the heating the temperature trend was measured in two points by two thermocouples located at different distances from the antennae, from 10mm to 30mm. The relationship between the CT number and the increase of tissue temperature was obtained by using a linear regression analysis. Lastly, the thermal sensitivity of the technique, showing the change of the CT number for unit of temperature increase, was estimated as the slope of the best fitting line. The CT number shows an inverse linear relationship with tissue temperature with a thermal sensitivity of about -0.34 HU.°C-1. This result agree with data reported in literature on other organs. The scan settings have a negligible influence on thermal sensitivity; on the other hand at higher kVp and mAs the performances are better in terms of measurement dispersion. Our promising results foster further investigation around this technique, which is particularly attractive because with a non-invasive approach may provide a three-dimensional temperature distribution within the organ.