ABSTRACT
INTRODUCTION: Transcranial magnetic resonance-guided focused ultrasound surgery (TcMRgFUS) has the advantage of allowing immediate evaluation of therapeutic effects after each sonication and intraoperative magnetic resonance imaging (MRI) to visualize the lesion. When the image shows that the lesion has missed the planned target and the therapeutic effects are insufficient, the target of the subsequent ablation can be finely adjusted based on the image. The precision of this adjustment is determined by the image quality. However, the current intraoperative image quality with a 3.0T MRI system is insufficient for precisely detecting the lesion. Thus, we developed and validated a method for improving intraoperative image quality. METHODS: Because intraoperative image quality is affected by transmitter gain (TG), we acquired T2-weighted images (T2WIs) with two types of TG: the automatically adjusted TG (auto TG) and the manually adjusted TG (manual TG). To evaluate the character of images with 2 TGs, the actual flip angle (FA), the image uniformity, and the signal-to-noise ratio (SNR) were measured using a phantom. Then, to assess the quality of intraoperative images, T2WIs with both TGs were acquired during TcMRgFUS for 5 patients. The contrast-to-noise ratio (CNR) of the lesion was retrospectively estimated. RESULTS: The images of the phantom with the auto TG showed substantial variations between the preset and actual FAs (p < 0.01), whereas on the images with the manual TG, there were no variations between the two FAs (p > 0.05). The total image uniformity was considerably lower with the manual TG than with the auto TG (p < 0.01), indicating that the image's signal values with the manual TG were more uniform. The manual TG produced significantly higher SNRs than the auto TG (p < 0.01). In the clinical study, the lesions were clearly detected in intraoperative images with the manual TG, but they were difficult to identify in images with the auto TG. The CNR of lesions in images with manual TG was considerably higher than in images with auto TG (p < 0.01). CONCLUSION: Regarding intraoperative T2WIs using a 3.0T MRI system during TcMRgFUS, the manual TG method improved image quality and delineated the ablative lesion more clearly than the current method with auto TG.
Subject(s)
Magnetic Resonance Imaging , Ultrasonic Surgical Procedures , Humans , Retrospective Studies , Magnetic Resonance Imaging/methods , Phantoms, Imaging , Ultrasonic Surgical Procedures/methods , Magnetic Resonance SpectroscopyABSTRACT
Objective To test the central frequency (CF) and transmitter gain(TG) of MRI scanners,and set up their action limits.Methods Three different MRI devices (GE 3.0T HD,GE 1.5T HDi and GE 3.0T 750W) were tested by scanning American College of Radiology (ACR) phantom with the axial T1WI series.In the pre-scanning of T1WI series for the ACR phantom,the CF and TG were recorded.It was tested for eight times when MRI scanners were in good condition.The action limits of CF and TG were calculated based on mean values and standard deviations.Results The mean values of CF for three devices were (127 725 772.38±39.68)Hz,(63 875 740.13± 34.15)Hz,and (127 771 958.38±12.19)Hz,respectively.Their action limits were ≤119.04 Hz,≤68.30 Hz,and ≤36.57 Hz,respectively.The mean values of TG for three devices were (125.25±1.28)dB,(101.75±1.98)dB,and (113.25±0.89)dB,respectively.Their action limits were (125.25±2.56)dB,(101.75±3.96)dB,and (113.25±1.78)dB,respectively.Conclusion The CF and TG for three MRI scanners are all consistent with the action limits in this study.The CF and TG action limits will provide criterions for the clinical quality control.
