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

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 7 T 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 5.1 mm 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 7 T

Risonanza magnetica a 7 Tesla: una tecnologia avanzata per l'imaging del cervello

Negli ultimi anni lo sviluppo di nuove tecnologie sta determinando un progresso nel campo dell’imaging cerebrale. Una delle tecnologie più avanzate in questo ambito è la risonanza magnetica a 7 Tesla (MRI) che, grazie alla maggiore risoluzione spettrale e spaziale, permette un più elevato rapporto tra segnale e rumore, garantendo una migliore caratterizzazione dei tessuti cerebrali; ciò sia dal punto di vista anatomico che delle possibili alterazioni patologiche. Questo elaborato vuole offrire una panoramica sulle caratteristiche, i vantaggi, gli svantaggi nonché alcune applicazioni pratiche di questa nuova tipologia di risonanza magnetica, che, stando ai risultati ottenuti, si configura come un promettente strumento per la diagnosi ed il monitoraggio delle patologie cerebrali.In recent years, the development of new technologies has been leading to progress in the field of brain imaging. One of the most advanced technologies in this area is the 7 Tesla magnetic resonance imaging (MRI), which, thanks to its higher spectral and spatial resolution, allows for a higher signal-to-noise ratio, ensuring better characterization of brain tissues, both from an anatomical and pathological perspective. This paper aims to provide an overview of the characteristics, advantages, disadvantages, as well as some practical applications of this new type of MRI, which, according to the results obtained, appears to be a promising tool for the diagnosis and monitoring of brain pahologies

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

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 7 T 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 5.1 mm 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 7 T