In vivo image-guided MR thermometry during laser ablation: Experience in kidney and liver

This works aims at assessing the thermal outcome of laser-based hyperthermia on living animals. Temperature evolution in target organs were monitored by means of non-invasive and contactless magnetic resonance (MR) images and fiber optic based-thermometers. Through MR-guidance, an expert interventional radiologist inserted MR-compatible fiber optic laser applicator and the thermometers through percutaneous procedure into kidney and liver. MR compatible, custom-made needle-like probes relying on fiber Bragg grating (FBG) technology were use to ease the percutaneous insertion of the thermometers into the organs. The thermal dependence of proton resonance frequency (PRF) of tissue water protons was used to obtain the MR thermal mapping; phase imaging method allowed the analysis of the thermal evolution. A respiratory-gated sequence was used to synchronize the images acquisition with the breathing frequency of the animal. The thermal maps provided by MR images were compared with the thermal trends measured by FBGs. Results showed that the temperature evolution measured by the FBGs at a specific distance from laser applicator tip was in accordance with the data provided by MR images, in both organs. Especially in liver, FBGs were subjected to the breathing movements (maximum error of 7 °C). Regarding MR thermometry, it was also subjected to some artifacts, mostly due to: 1) cavitation-induced phase shift in the images, and 2) breathing movements (temperature changes up to 10 °C). In conclusion, even though MR imaging is particularly useful for clinical applications, improvements still should be implemented in terms of motion compensation. The introduction of sensors in clinical practice can allows a safer evaluation of the temperature distribution, hence, of the induced thermal damage.