Machbarkeitsstudie zur nicht-invasiven, CT-basierten Thermometrie während der perkutanen Radiofrequenzablation von Leberparenchym im In-vivo-Schweinemodell
- Feasibility study of the non-invasive, CT-based thermometry during percutaneous hepatic radiofrequency ablation in an in vivo porcine model
Rösch, Eva Michaela Simone; Mahnken, Andreas H. (Thesis advisor)
Aachen : Publikationsserver der RWTH Aachen University (2012)
Dissertation / PhD Thesis
Aachen, Techn. Hochsch., Diss., 2012
The aim of this study is to evaluate the feasibility of the CT-based non-invasive thermometry during percutaneous hepatic RF ablation in an in vivo porcine model. It should be proved that an increase of the temperature in the liver parenchyma leads to a change of the CT value. Percutaneous hepatic RF ablation was performed in four female pigs. Parallel to the used bipolar needle-shaped RF applicator (CelonLabPower) with an active tip of 30 mm (Celon ProSurge T30) optical temperature probes (SFF-2m) were inserted into the liver with a fixed distance of 5, 10, 15 mm and in two pigs also with a distance of 20 mm to the RF applicator. After starting the RF ablation performed with a generator output of 20 W, unenhanced sequential CT scans of the liver were acquired using the following scan protocol: 140 kV tube voltage, 300 mAs/rotation tube current time product, collimation 24 x 1.2 mm, rotation time 0.5 s (SOMATOM Definition). After acquisition of the raw data, axial image data were reconstructed with a slice thickness of 1.2 mm and the convolution kernel B30s using the conventional as well as the extended CT scale. Temperature was recorded continuously by the temperature probes. For analysing the CT scans a circular 0.5 cm² region of interest (ROI) was manually placed around the tips of the temperature probes to measure local CT values. For statistical analysis mean value and standard deviation of the measured temperature change and of the change of the CT value were calculated for each animal and each temperature probe and compared descriptively. Some CT values of the four animals were investigated for the same temperature and also compared descriptively. Additionally, regression analysis was performed to analyse the relationship between local temperature changes and the measured averaged CT value. A p-value < 0.05 was considered statistically significant (SAS Software 9.1.3). Descriptive analysis showed an inverse relationship between the measured temperature and the averaged CT value for all animals. The measured averaged temperature decreased with increasing distance to the RF applicator. In addition, the averaged CT value rose with increasing distance to the RF applicator. Comparing the CT values for the same temperature descriptively, interindividual differences were found. Performing regression analysis a significant influence of the temperature on the CT value was proved. With an exception of two temperature probes, negative regression coefficients were measured for the relationship between local temperature and averaged CT value. Negative regression coefficients varied between - 0.053 HU/°C (p = 0.4987) and - 0.671 HU/°C (p < 0.0001). There was no difference between the results using the conventional or the extended CT scale. The results of the study show that the CT-based non-invasive thermometry during percutaneous hepatic RF ablation is feasible in an in vivo porcine model. Using multislice CT during RF ablation, local temperature changes can be detected by a change of the CT value, so that in using the CT value temperature can be determined in vivo non-invasively. In conclusion, the results of this study may provide a base for a CT-based non-invasive thermometry during hyperthermal ablation therapies. However, artefacts by motion and metal hamper a precise CT-based temperature monitoring. Furthermore, the development of a more accurate and robust software-based method for a standardised analysis of the image data is required, so that the CT-based non-invasive thermometry can find its way into the clinical routine.