A fast MR-thermometry method for quantitative assessment of temperature increase near an implanted wire

Abstract

Purpose To propose a MR-thermometry method and associated data processing technique to predict the maximal RF-induced temperature increase near an implanted wire for any other MRI sequence. Methods A dynamic single shot echo planar imaging sequence was implemented that interleaves acquisition of several slices every second and an energy deposition module with adjustable parameters. Temperature images were processed in real time and compared to invasive fiber-optic measurements to assess accuracy of the method. The standard deviation of temperature was measured in gel and in vivo in the human brain of a volunteer. Temperature increases were measured for different RF exposure levels in a phantom containing an inserted wire and then a MR-conditional pacemaker lead. These calibration data set were fitted to a semi-empirical model allowing estimation of temperature increase of other acquisition sequences. Results The precision of the measurement obtained after filtering with a 1.6x1.6 mm2 in plane resolution was 0.2°C in gel, as well as in the human brain. A high correspondence was observed with invasive temperature measurements during RF-induced heating (0.5°C RMSE for a 11.5°C temperature increase). Temperature rises of 32.4°C and 6.5°C were reached at the tip of a wire and of a pacemaker lead, respectively. After successful fitting of temperature curves of the calibration data set, temperature rise predicted by the model was in good agreement (around 5% difference) with measured temperature by a fiber optic probe, for three other MRI sequences. Conclusion This method proposes a rapid and reliable quantification of the temperature rise near an implanted wire. Calibration data set and resulting fitting coefficients can be used to estimate temperature increase for any MRI sequence as function of its power and duration.

Radio Frequency Sensing‐Based In Situ Temperature Measurements during Magnetic Resonance Imaging Interventional Procedures

“…We demonstrate a temperature measurement precision comparable to the MRI thermometry sequences. [66][67][68] In contrast to MRI thermometry methods, we measure the temperature using a basic GRE-based MR imaging sequence and eliminating the need for alternating between anatomical and thermometric MRI images. Therefore, the proposed method can measure the temperature continuously with a refresh rate less than 1.8 s, which is 10-30 times faster than the standard thermometric sequences used in the literature, [6,68] and ≈2 times faster than the echo-planar imaging-based fast thermometry methods.…”

“…Therefore, the proposed method can measure the temperature continuously with a refresh rate less than 1.8 s, which is 10-30 times faster than the standard thermometric sequences used in the literature, [6,68] and ≈2 times faster than the echo-planar imaging-based fast thermometry methods. [66,73] Such fast temperature feedback would benefit the interventional MRI procedures and laser ablation procedures inside an MR scanner. During the interventional MRI applications, patients' body should be imaged continuously to guide interventional tools toward the target locations.…”

“…Therefore, the proposed method can measure the temperature continuously with a refresh rate less than 1.8 s, which is 10–30 times faster than the standard thermometric sequences used in the literature, [ 6,68 ] and ≈2 times faster than the echo‐planar imaging‐based fast thermometry methods. [ 66,73 ]…”

“…MRI thermometry has been developed as an in situ temperature monitoring method. [66][67][68][69] Researchers have used MRI thermometry-based temperature feedback to control FUS hyperthermia operations [35,36,70] or to evaluate MRI-guided laser ablation therapies [6,31,71] and MRIguided active catheters. [72,73] While MRI thermometry methods can provide accurate in situ temperature mapping in 3D, they decrease the overall MRI-based visual feedback rate by adding an extra sequence, hindering the real-time MRI feedback.…”

New Insights into MR Safety for Implantable Medical Devices

“… 74 As a result, several studies have been conducted for overcoming this problem. 74 – 80 Pfeil et al proposed the use of proton MRS for thermometry at the tip of pacing leads in a porcine myocardium ex vivo. 76 The measurement was based on the chemical shift difference between protons of water and N-methyl protons of creatine/phosphocreatine (Cr/PCr) and trimethylamine (TMA).…”