The traveling heads 2.0: Multicenter reproducibility of quantitative imaging methods at 7 Tesla.

OBJECT: This study evaluates inter-site and intra-site reproducibility at ten different 7 T sites for quantitative brain imaging. MATERIAL AND METHODS: Two subjects - termed the "traveling heads" - were imaged at ten different 7 T sites with a harmonized quantitative brain MR imaging protocol. In conjunction with the system calibration, MP2RAGE, QSM, CEST and multi-parametric mapping/relaxometry were examined. RESULTS: Quantitative measurements with MP2RAGE showed very high reproducibility across sites and subjects, and errors were in concordance with previous results and other field strengths. QSM had high inter-site reproducibility for relevant subcortical volumes. CEST imaging revealed systematic differences between the sites, but reproducibility was comparable to results in the literature. Relaxometry had also very high agreement between sites, but due to the high sensitivity, differences caused by different applications of the B1 calibration of the two RF coil types used were observed. CONCLUSION: Our results show that quantitative brain imaging can be performed with high reproducibility at 7 T and with similar reliability as found at 3 T for multicenter studies of the supratentorial brain.

The traveling heads: multicenter brain imaging at 7 Tesla.

OBJECTIVE: This study evaluates the inter-site and intra-site reproducibility of 7 Tesla brain imaging and compares it to literature values for other field strengths. MATERIALS AND METHODS: The same two subjects were imaged at eight different 7 T sites. MP2RAGE, TSE, TOF, SWI, EPI as well as B1 and B0 field maps were analyzed quantitatively to assess inter-site reproducibility. Intra-site reproducibility was measured with rescans at three sites. RESULTS: Quantitative measures of MP2RAGE scans showed high agreement. Inter-site and intra-site reproducibility errors were comparable to 1.5 and 3 T. Other sequences also showed high reproducibility between the sites, but differences were also revealed. The different RF coils used were the main source for systematic differences between the sites. CONCLUSION: Our results show for the first time that multi-center brain imaging studies of the supratentorial brain can be performed at 7 T with high reproducibility and similar reliability as at 3T. This study develops the basis for future large-scale 7 T multi-site studies.

Sensory perceptions of individuals exposed to the static field of a 7T MRI: A controlled blinded study.

PURPOSE: To determine the subjective experience of subjects undergoing 7T magnetic resonance imaging (MRI) compared to a mock scanner with no magnetic field. METHODS AND MATERIALS: In all, 44 healthy subjects were exposed to both the B0 field of a 7T whole-body MRI and a realistic mock scanner with no magnetic field. Subjects were blinded to the actual field strength and no scanning was performed. After exposure, subjects rated their experience of potential sensory perceptions. RESULTS: The most frequently observed side effect was vertigo while entering the gantry, which was reported by 38.6% (n = 17). Other frequent side effects were the appearance of phosphenes (18.2%, n = 8), thermal heat sensation (15.9%), unsteady gait after exposure (13.6%, n = 6), and dizziness (13.6%). All side effects were reported significantly more often after 7T exposure. Nine subjects (20.5%) did not report any sensory perceptions at all, ie, neither in the 7T scanner nor in the mock scanner. CONCLUSION: Light, acute, and transient sensory perceptions can occur in subjects undergoing ultrahighfield MRI, of which vertigo seems to be the most frequently reported. Possible psychological effects might contribute to the emergence of such sensory perceptions, as some subjects also reported them to appear in a realistic mock scanner with no magnetic field.

Efficacy of diphenhydramine in the prevention of vertigo and nausea at 7 T MRI.

PURPOSE: In this study the potential of diphenhydramine in reducing respectively preventing vertigo and nausea induced by the ultra-high static magnetic field at 7 T was evaluated. MATERIALS AND METHODS: In a prospective, double blinded, placebo controlled, cross-over randomized study the sensations of 34 volunteers before, during and after exposure to the static magnetic field with and without drug respectively placebo administration were quantified. Fast table motion was applied to increase the incidence of otherwise sparse reports of field related sensations. RESULTS: The strength of vertigo can be reduced by the application of diphenhydramine. CONCLUSION: Diphenhydramine, even at a low dose, reduces the strength of vertigo at ultra-high static magnetic fields, may be used preventively, and could pave the way to even higher field strength.

Cortical thickness determination of the human brain using high resolution 3T and 7T MRI data.

PURPOSE: The analysis of the human cerebral cortex and the measurement of its thickness based on MRI data can provide insight into normal brain development and neurodegenerative disorders. Accurate and reproducible results of the cortical thickness measurement are desired for sensitive detection. This study compares ultra-high resolution data acquired at 7T with 3T data for determination of the cortical thickness of the human brain. The impact of field strength, resolution, and processing method is evaluated systematically. METHODS: Five subjects were scanned at 3T (1 mm isotropic resolution) and 7T (1 mm and 0.5 mm isotropic resolution) with 3D MP-RAGE and 3D gradient echo methods. The inhomogeneous signal and contrast of the 7T data due to the B1 field was corrected by division of the MP-RAGE with the GE. ARCTIC, utilizing a voxel-based approach, and FreeSurfer, utilizing a surface-based approach, have been used to compute the cortical thickness of the high resolution 3T and 7T data and of the ultra-high resolution 7T data. FreeSurfer is not designed to process data with a spatial resolution other than 1mm and was modified to avoid this limitation. Additionally SPM and FSL have been used to generate segmentations which were further processed with ARCTIC to determine the cortical thickness. RESULTS AND CONCLUSION: At identical resolution, the cortical thickness determination yielded consistent results between 3T and 7T confirming the robustness of the acquisition and processing against potential field strength related effects. However, the ultra-high resolution 7T data resulted in significantly reduced values for the cortical thickness estimation compared to the lower resolution data. The reduction in thickness amounts approximately one sixth to one third, depending on the processing algorithm and software used. This suggests a bias in the gray matter segmentation due to partial volume effects and indicates that true cortical thickness is overestimated by most current MR studies using both a voxel-based or surface-based method and can be more accurately determined with high resolution imaging at 7T.