Background: Noninvasive magnetic resonance thermometry (MRT) at low-field\nusing proton resonance frequency shift (PRFS) is a promising technique for monitoring\nablation temperature, since low-field MR scanners with open-configuration are more\nsuitable for interventional procedures than closed systems. In this study, phase-drift\ncorrection PRFS with first-order polynomial fitting method was proposed to investigate\nthe feasibility and accuracy of quantitative MR thermography during hyperthermia\nprocedures in a 0.35 T open MR scanner.\nMethods: Unheated phantom and ex vivo porcine liver experiments were performed\nto evaluate the optimal polynomial order for phase-drift correction PRFS. The temperature\nestimation approach was tested in brain temperature experiments of three\nhealthy volunteers at room temperature, and in ex vivo porcine liver microwave ablation\nexperiments. The output power of the microwave generator was set at 40 W for\n330 s. In the unheated experiments, the temperature root mean square error (RMSE) in\nthe inner region of interest was calculated to assess the best-fitting order for polynomial\nfit. For ablation experiments, relative temperature difference profile measured by\nthe phase-drift correction PRFS was compared with the temperature changes recorded\nby fiber optic temperature probe around the microwave ablation antenna within the\ntarget thermal region.\nResults: The phase-drift correction PRFS using first-order polynomial fitting could\nachieve the smallest temperature RMSE in unheated phantom, ex vivo porcine liver\nand in vivo human brain experiments. In the ex vivo porcine liver microwave ablation\nprocedure, the temperature error between MRT and fiber optic probe of all but six\ntemperature points were less than 2 �°C. Overall, the RMSE of all temperature points was\n1.49 �°C.\nConclusions: Both in vivo and ex vivo experiments showed that MR thermometry\nbased on the phase-drift correction PRFS with first-order polynomial fitting could be\napplied to monitor temperature changes during microwave ablation in a low-field\nopen-configuration whole-body MR scanner.
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