Feasibility assessment of magnetic resonance-thermometry on pancreas undergoing laser ablation: sensitivity analysis of three sequences

Laser ablation (LA) is a minimally invasive technique for the treatment of tumors as an alternative to surgical resection. The light absorbed by tissue is converted into heat, and causes irreversible cell damage when temperatures higher than 60 °C are reached. The knowledge in real time of temperature may be particularly beneficial for adjusting laser settings applied during treatment and to be notified in real time about its end-point. As a consequence, several techniques for temperature monitoring within the tissue have been investigated along the last decades. In the field of LA, particularly attractive are non-invasive methods. Among these techniques, thermometry based on the analysis of Magnetic Resonance Imaging (MR-thermometry) has gaining large acceptance in this field. MR-thermometry allows estimating the temperature variation thanks to the thermal dependence of several MRI parameters, among others the most promising are T1 relaxation time, and proton resonance frequency shift. The aim of this study is to assess the sensitivity of MRI thermometry using three T1-weighted sequences (i.e., Inversion Recovery Turbo-FLASH, IRTF, Saturation Recovery Turbo-FLASH, SRTF, and FLASH) using an 1.5-T MR scanner on healthy swine pancreases undergoing LA. The reference temperature was measured by MRI-compatible fiber optic sensors (fiber Bragg grating sensors). The sensitivity of the proposed techniques was estimated and compared. The thermal sensitivity of the three sequences was -1.47 ± 0.08 °C-1, -0.95 ± 0.05 °C-1, and -0.56 ± 0.04 °C-1 for IRTF, SRTF and FLASH, respectively. Results show that the proposed technique may be adequate for temperature monitoring during LA.