Evaluation of the thermal sensitivity of porcine liver in CT‐guided cryoablation: an initial study

Abstract

Purpose: To evaluate computed tomography (CT)-based thermometry in cryoablation, the thermal sensitivity of an ex-vivo porcine liver was determined in an initial study design. Methods: The CT-guided cryoablation was performed in three porcine liver samples over a period of 10 min. Fiber optic temperature probes were positioned parallel to the shaft of the cryoprobe in an axial slice orientation. During ablation, temperature measurements were performed simultaneously with CT imaging at 5 s intervals. On the CT images, the average CT number was calculated for a region of interest of 3 9 3 pixels just below the tip of each temperature probe. A linear regression analysis was performed using eleven data sets to determine the dependence of the CT number on the temperature. Results: With decreasing temperature, an increasing hypodense area around the tip of the cryoprobe was observed on the CT images and decreasing values of the CT number were determined. Starting at a temperature of À 40°C a linear relation between the CT number and the temperature was determined and a thermal sensitivity of 0.95 HU/°C (R 2 = 0.73) was obtained. The thermal sensitivity was used to calculate color-coded temperature maps. The calculated temperature distribution corresponds quantitatively to the increasing hypodense area. Conclusions: A noninvasive CT-based temperature determination during cryoablation in a normal ex vivo porcine liver is feasible. A thermal sensitivity of 0.95 HU/°C was determined by linear regression analysis. A color-coded map of the temperature distribution was presented.

Improved Thermal Sensitivity Using Virtual Monochromatic Imaging Derived from Photon Counting Detector CT Data Sets: Ex Vivo Results of CT-Guided Cryoablation in Porcine Liver

“…It is not unknown that there is a correlation between temperature and CT attenuation of hepatic tissue. Using a similar experimental setup, Huebner et al reported a thermal sensitivity of 0.95 HU / °C ( R 2 = 0.73) in an ex vivo porcine liver model [ 15 ]. Pohlan et al reported a thermal sensitivity of even 2.11 HU / °C ( R 2 = 0.55) using porcine liver placed on porcine ribs [ 11 ].…”

“…An explanation for the observed deviations might be that Huebner et al used temperatures as low as − 75.4 °C compared to − 41.1 °C in our study and about − 35 °C in Pohlan et al Due to the plateau below − 20 °C, which can also be observed in the study of Huebner et al, the influence of even lower temperatures will most likely attribute to a flattening of the correlation line translating into a reduction thermal sensitivity. Additionally, we used a reference tube voltage of 70 kVp compared to 120 kVp of Huebner et al and Pohlan et al [ 11 , 15 ]. Due to the stagnating CT-values at temperatures below − 20 °C, we decided to separately assess the thermal sensitivity of this range of transition, where we calculated a significantly higher value of 2.2 HU / °C ( R 2 = 0.40) at 120 keV VMI.…”

“…The temperature at the outer margin of the ice ball is 0° Celsius [ 14 ]. The attenuation of the freezing liver tissue decreases with decreasing temperatures and partially shows a linear correlation [ 11 , 15 , 16 ]. Although CT is routinely used in guiding and placing cryoprobes, its use for intraprocedural monitoring and visualization of the ice ball has known limitations [ 14 , 17 , 18 ].…”

Evolution of a theranostic applicator for microwave ablation treatment

“…Ablation was performed at 20 W. Over a period of 16 min, ablation was performed intermittently for 25 s, followed by an interruption of 5 s to perform MR thermometry. Using proton resonance frequency (PRF) thermometry, temperatures were calculated over an ROI of 2 × 2 pixels [23,24]. A comparison of the measured and calculated temperature values showed a slope of m = 1.06 and a correlation coefficient of 1.…”

Thermometry mapping during CT-guided thermal ablations: proof of feasibility and internal validation using spectral CT

“…However, to date the clinical requirements for intraprocedural temperature mapping-specifically the combination of 1-2 mm spatial resolution, <5 °C temperature accuracy and clinically acceptable radiation dose-have been very challenging to achieve. Recent advances in spectral CT, combined with the introduction of advanced reconstruction and postprocessing algorithms to reduce noise without sacrificing quantitative accuracy, offer the opportunity to break this barrier and have renewed the interest in CT-based thermometry for clinical applications (Hübner et al 2020, Heinrich et al 2022, Shapira et al 2022, Liu et al 2023, Wang et al 2023.…”