Quantitative MR thermometry based on phase-drift correction PRF shift method at 0.35 T

Abstract

BackgroundNoninvasive magnetic resonance thermometry (MRT) at low-field using proton resonance frequency shift (PRFS) is a promising technique for monitoring ablation temperature, since low-field MR scanners with open-configuration are more suitable for interventional procedures than closed systems. In this study, phase-drift correction PRFS with first-order polynomial fitting method was proposed to investigate the feasibility and accuracy of quantitative MR thermography during hyperthermia procedures in a 0.35 T open MR scanner.MethodsUnheated phantom and ex vivo porcine liver experiments were performed to evaluate the optimal polynomial order for phase-drift correction PRFS. The temperature estimation approach was tested in brain temperature experiments of three healthy volunteers at room temperature, and in ex vivo porcine liver microwave ablation experiments. The output power of the microwave generator was set at 40 W for 330 s. In the unheated experiments, the temperature root mean square error (RMSE) in the inner region of interest was calculated to assess the best-fitting order for polynomial fit. For ablation experiments, relative temperature difference profile measured by the phase-drift correction PRFS was compared with the temperature changes recorded by fiber optic temperature probe around the microwave ablation antenna within the target thermal region.ResultsThe phase-drift correction PRFS using first-order polynomial fitting could achieve the smallest temperature RMSE in unheated phantom, ex vivo porcine liver and in vivo human brain experiments. In the ex vivo porcine liver microwave ablation procedure, the temperature error between MRT and fiber optic probe of all but six temperature points were less than 2 °C. Overall, the RMSE of all temperature points was 1.49 °C.ConclusionsBoth in vivo and ex vivo experiments showed that MR thermometry based on the phase-drift correction PRFS with first-order polynomial fitting could be applied to monitor temperature changes during microwave ablation in a low-field open-configuration whole-body MR scanner.

Practical implementation of robust MR-thermometry during clinical MR-guided microwave ablations in the liver at 1.5 T

“…Field drifts are most likely responsible for consistent underestimation of lesion sizes listed in Table 1. This phenomenon has been widely reported on in the literature [12,[29][30][31][32] and several methods have been proposed to mitigate it for improved accuracy of PRFS [33,34]. Real-time corrections for field drifts at the ablation site are currently being investigated by our group.…”

Contactless Thermometry by MRI and MRS: Advanced Methods for Thermotherapy and Biomaterials

“…Open-configuration MR scanners are characterized by lower fields (<1 T) and also involve a lower purchase price and reduced operational cost compared with high-field instruments. Therefore, Chen et al showed by in vitro experiments with phantoms and porcine liver that MRT based on drift-correction phase PRFS with first-order polynomial fitting can be applied to monitor temperature changes during MW ablation in a low-field (0.35 T) configuration whole-body MR scanner designed for applications in humans (Chen et al, 2018). However, work on high-field PRFS (cited above) consistently indicated that discrepancies between PRFS and fiber optic probe-measured temperatures are on the order of %1 C, whereas errors may increase to about 2 C for fields as low as 0.35 T (Chen et al, 2018).…”

“…Therefore, Chen et al showed by in vitro experiments with phantoms and porcine liver that MRT based on drift-correction phase PRFS with first-order polynomial fitting can be applied to monitor temperature changes during MW ablation in a low-field (0.35 T) configuration whole-body MR scanner designed for applications in humans (Chen et al, 2018). However, work on high-field PRFS (cited above) consistently indicated that discrepancies between PRFS and fiber optic probe-measured temperatures are on the order of %1 C, whereas errors may increase to about 2 C for fields as low as 0.35 T (Chen et al, 2018). Phase PRFS tests in vivo on volunteers showed that drift correction had a marked effect on the stability of temperature measurements in the human brain, setting the stage for future clinical tests involving MW hyperthermia.…”

Organic Fluorine Compounds and Their Uses as Molecular MR‐Based Temperature Sensors

“…For several thermometry studies, magnetic resonance (MR)-based analysis (spectroscopy and imaging) is a valuable analytical tool among other things for biological objects. [1][2][3] Furthermore, knowledge of in vivo temperature changes is important in clinical diagnostic, therapy (such as hypothermia [4,5] or hyperthermia [6] ) or investigation of implants distortions. [7] Conventional thermometers cannot be used for temperature measurements in strong magnetic fields.…”

“…Whether solids, liquids or gases, knowledge of the local temperature or the temperature distribution can lead to the optimization of processes and structures or improve the diagnosis and therapy of diseases (theranostics). For several thermometry studies, magnetic resonance (MR)‐based analysis (spectroscopy and imaging) is a valuable analytical tool among other things for biological objects [1–3] . Furthermore, knowledge of in vivo temperature changes is important in clinical diagnostic, therapy (such as hypothermia [4,5] or hyperthermia [6] ) or investigation of implants distortions [7] .…”