Presurgical planning with fMRI benefits from increased reliability and the possibility to reduce measurement time introduced by using ultra-high field. Echo-planar imaging suffers, however, from geometric distortions which scale with field strength and potentially give rise to clinically significant displacement of functional activation. We evaluate the effectiveness of a dynamic distortion correction (DDC) method based on unmodified single-echo EPI in the context of simulated presurgical planning fMRI at 7T and compare it with static distortion correction (SDC). The extent of distortion in EPI and activation shifts are investigated in a group of eleven patients with a range of neuropathologies who performed a motor task. The consequences of neglecting to correct images for susceptibility-induced distortions are assessed in a clinical context. It was possible to generate time series of EPI-based field maps which were free of artifacts in the eloquent brain areas relevant to presurgical fMRI, despite the presence of signal dropouts caused by pathologies and post-operative sites. Distortions of up to 5.1mm were observed in the primary motor cortex in raw EPI. These were accurately corrected with DDC and slightly less accurately with SDC. The dynamic nature of distortions in UHF clinical fMRI was demonstrated via investigation of temporal variation in voxel shift maps, confirming the potential inadequacy of SDC based on a single reference field map, particularly in the vicinity of pathologies or in the presence of motion. In two patients, the distortion correction was potentially clinically significant in that it might have affected the localization or interpretation of activation and could thereby have influenced the treatment plan. Distortion correction is shown to be effective and clinically relevant in presurgical planning at 7T.

译文

:使用fMRI进行术前计划得益于更高的可靠性以及使用超高磁场引入的减少测量时间的可能性。然而,回波平面成像受几何失真的影响,几何失真随场强而缩放,并可能在临床上引起功能激活的明显位移。我们在7T模拟的术前计划fMRI的背景下,评估了基于未经修改的单回波EPI的动态失真校正(DDC)方法的有效性,并将其与静态失真校正(SDC)进行了比较。在一组执行运动任务的十一名神经病患者中,研究了EPI畸变和激活转移的程度。在临床环境中评估了忽略针对易感性失真的校正图像的后果。尽管存在由病理和术后部位引起的信号缺失,但有可能生成基于EPI的时间序列的时间序列,该序列在与术前功能磁共振成像相关的雄辩的大脑区域中没有伪影。在原始EPI中的初级运动皮层中观察到高达5.1mm的变形。这些已使用DDC进行了准确校正,而使用SDC进行了一些较不准确。通过研究体素位移图中的时间变化,证实了UHF临床功能磁共振成像中变形的动态性质,证实了基于单个参考场图的SDC的潜在不足,尤其是在病理学附近或存在运动的情况下。在两名患者中,畸变矫正可能在临床上具有重大意义,因为它可能影响了激活的定位或解释,从而影响了治疗计划。畸变矫正在7T的术前计划中被证明是有效的并且在临床上具有相关性。

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