Fiber Bragg Grating Sensors for Performance Evaluation of Fast Magnetic Resonance Thermometry on Synthetic Phantom.

Martina De Landro,Emiliano Schena,Paola Saccomandi,Bruno Quesson,Jacopo Ianniello,Alexey Wolf,Maxime Yon

doi:10.3390/s20226468

Abstract

The increasing recognition of minimally invasive thermal treatment of tumors motivate the development of accurate thermometry approaches for guaranteeing the therapeutic efficacy and safety. Magnetic Resonance Thermometry Imaging (MRTI) is nowadays considered the gold-standard in thermometry for tumor thermal therapy, and assessment of its performances is required for clinical applications. This study evaluates the accuracy of fast MRTI on a synthetic phantom, using dense ultra-short Fiber Bragg Grating (FBG) array, as a reference. Fast MRTI is achieved with a multi-slice gradient-echo echo-planar imaging (GRE-EPI) sequence, allowing monitoring the temperature increase induced with a 980 nm laser source. The temperature distributions measured with 1 mm-spatial resolution with both FBGs and MRTI were compared. The root mean squared error (RMSE) value obtained by comparing temperature profiles showed a maximum error of 1.2 °C. The Bland-Altman analysis revealed a mean of difference of 0.1 °C and limits of agreement 1.5/−1.3 °C. FBG sensors allowed to extensively assess the performances of the GRE-EPI sequence, in addition to the information on the MRTI precision estimated by considering the signal-to-noise ratio of the images (0.4 °C). Overall, the results obtained for the GRE-EPI fully satisfy the accuracy (~2 °C) required for proper temperature monitoring during thermal therapies.

Highlights

Thermal therapies are used to induce cell coagulative necrosis leading to tissue alterations at both conformational and metabolic levels [1]
Uncertainty values are comprised between 0.2 °C, in the areas not subjected to the laser treatment, and 0.4 °C, close to the laser tip. These results show the dependence of the SNR to the temperature increase due to the T1 increase and the intra-voxel dephasing due to the intra voxel temperature gradients
Uncertainty values are comprised between 0.2 ◦ C, in the areas not subjected to the laser treatment, and 0.4 ◦ C, close to the laser tip

Summary

Introduction

Thermal therapies are used to induce cell coagulative necrosis leading to tissue alterations at both conformational and metabolic levels [1]. To allow optimal therapy outcome with minimally invasive thermal treatments, real-time temperature monitoring of the tissue is of great interest [3]. Commercial systems for radiofrequency ablation and microwave ablation are provided with needles embedding one or a few temperature sensors (e.g., thermocouples), allowing the temperature of the tissues to be measured in contact with the needle [5,6]. These sensors cannot furnish temperature mapping of the tissues surrounding the heating device providing limited information to the surgeon. PRFS method is compatible with all the MR-compatible heating devices [12]

Methods

Discussion

Conclusion