The clinical relevance of distortion correction in presurgical fMRI at 7 T

Abstract

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.

Whole-slice mapping of GABA and GABA+ at 7T via adiabatic MEGA-editing, real-time instability correction, and concentric circle readout

“…1253, several optimizations to the EPI navigator protocol used on 3T had to be made to exploit the potential of vNavs at 7T. As Nyquist N/2-ghosting artifacts were significantly worse at 7T (Beisteiner et al, 2011), a local phase correction (Feiweier et al, 2011;Lima Cardoso et al, 2018) was implemented. Fat artifacts were eliminated by using water-selective excitation, which allowed shorter TRs compared to dedicated fat suppression pulses.…”

Get real: Orbitofrontal cortex mediates the ability to sense reality in early adolescents

“…Thanks to the distortion correction of vulnerable brain regions on the single‐subject level, this additional unwarping step not only improves the coregistration between structural and functional images, but it also reduces the distortion variability across subjects during spatial normalization to a common space (Hutton et al, ). This solution has been successfully used in several recent studies in adults including task (Daw, Gershman, Seymour, Dayan, & Dolan, ) and resting‐state (Togo et al, ) experimental paradigms, as well as in presurgical planning (Cardoso et al, ) and in children (Wozniak et al, ).…”

Phase Unwrapping with a Rapid Opensource Minimum Spanning TreE AlgOrithm (ROMEO)

“…Human measurements were approved by the Ethics Committee of the Medical University of Vienna and all participants provided written informed consent. All human data sets were acquired from healthy volunteers except for five 7 T EPI time series (57 volumes) from a prior study (20), which were collected from four patients with brain tumours and one patient with a developmental venous anomaly.…”