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• Higher field strength MRI may improve image quality and diagnostic accuracy. • There are few direct comparisons of 1.5 and 3 T MRI. • Theoretical doubling of the signal-to-noise ratio in practice was only 25 %. • Objective evidence of improved routine clinical diagnosis is lacking. • Other aspects of technology improved images more than field strength.

Magnetic resonance imaging (MRI) is widely used in brain imaging research (neuroimaging) to explore structural and functional changes across dispersed neural networks visible only via multisubject experiments. Multicenter investigations are an effective way to increase recruitment rates. This article describes image-based power calculations for a two-group, cross-sectional design specified by the mean effect size and its standard error, sample size, false discovery rate (FDR), and size of the network (i.e., proportion of image locations) that truly demonstrates an effect. Minimum sample size (for fixed effect size) and the minimum effect size (for fixed sample size) are calculated by specifying the acceptable power threshold. Within-center variance was estimated in five participating centers by repeat MRI scanning of 12 healthy participants from whom distributions of gray matter were estimated. The effect on outcome measures when varying FDR and the proportion of true positives is presented. Their spatial patterns reflect within-center variance, which is consistent across centers. Sample sizes 3-6 times larger are needed when detecting effects in subcortical regions compared to the neocortex. Hypothesized multicenter studies of patients with first episode psychosis and control participants were simulated with varying proportions of the cohort recruited at each center. There is little penalty to sample size for recruitment at five centers compared to the center with the lowest variance alone. At 80% power 80 participants per group are required to observe differences in gray matter in high variance regions.

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Calibration experiments precede multicenter trials to identify potential sources of variance and bias. In support of future imaging studies of mental health disorders and their treatment, the Neuro/PsyGRID consortium commissioned a calibration experiment to acquire functional and structural MRI from twelve healthy volunteers attending five centers on two occasions. Measures were derived of task activation from a working memory paradigm, fractal scaling (Hurst exponent) from resting fMRI, and grey matter distributions from T(1) -weighted sequences. At each intracerebral voxel a fixed-effects analysis of variance estimated components of variance corresponding to factors of center, subject, occasion, and within-occasion order, and interactions of center-by-occasion, subject-by-occasion, and center-by-subject, the latter (since there is no intervention) a surrogate of the expected variance of the treatment effect standard error across centers. A rank order test of between-center differences was indicative of crossover or noncrossover subject-by-center interactions. In general, factors of center, subject and error variance constituted>90% of the total variance, whereas occasion, order, and all interactions were generally <5%. Subject was the primary source of variance (70%-80%) for grey-matter, with error variance the dominant component for fMRI-derived measures. Spatially, variance was broadly homogenous with the exception of fractal scaling measures which delineated white matter, related to the flip angle of the EPI sequence. Maps of P values for the associated F-tests were also derived. Rank tests were highly significant indicating the order of measures across centers was preserved. In summary, center effects should be modeled at the voxel-level using existing and long-standing statistical recommendations.

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Objective: Both brain and body temperature rise after stroke but the cause of each is uncertain.We investigated the relationship between circulating markers of inflammation with brain and body temperature after stroke. Methods:We recruited patients with acute ischemic stroke and measured brain temperature at hospital admission and 5 days after stroke with multivoxel magnetic resonance spectroscopic imaging in normal brain and the acute ischemic lesion (defined by diffusion-weighted imaging [DWI]). We measured body temperature with digital aural thermometers 4-hourly and drew blood daily to measure interleukin-6, C-reactive protein, and fibrinogen, for 5 days after stroke. Results:In 44 stroke patients, the mean temperature in DWI-ischemic brain soon after admission was 38.4°C (95% confidence interval [CI] 38.2-38.6), in DWI-normal brain was 37.7°C (95% CI 37.6-37.7), and mean body temperature was 36.6°C (95% CI 36.3-37.0). Higher mean levels of interleukin-6, C-reactive protein, and fibrinogen were associated with higher temperature in DWInormal brain at admission and 5 days, and higher overall mean body temperature, but only with higher temperature in DWI-ischemic brain on admission.Conclusions: Systemic inflammation after stroke is associated with elevated temperature in normal brain and the body but not with later ischemic brain temperature. Elevated brain temperature is a potential mechanism for the poorer outcome observed in stroke patients with higher levels of circulating inflammatory markers. Neurology ® 2012;79:152-158 GLOSSARY CI ϭ confidence interval; DVT ϭ deep venous thrombosis; DWI ϭ diffusion-weighted imaging; FLAIR ϭ fluid-attenuated inversion recovery; FOV ϭ field of view; 1 H MRSI ϭ proton magnetic resonance spectroscopy imaging; IL-6 ϭ interleukin-6; IQR ϭ interquartile range; MR ϭ magnetic resonance; MRS ϭ magnetic resonance spectroscopy; NIHSS ϭ NIH Stroke Scale; PRESS ϭ point resolved spectroscopy.After ischemic stroke, the temperature in areas of brain affected by ischemia is higher than in unaffected brain and the rest of the body.1 Investigators have proposed clinical trials of therapeutic hypothermia, in patients with ischemic stroke, 2 based on the observations that hypothermia more than halves the size of cerebral infarcts in animal models, 3 and in stroke patients higher body temperature is associated with poorer outcome. 4 The processes that determine brain temperature after human ischemic stroke are uncertain. Animal studies suggest that in health, brain temperature is a balance between heat-generating metabolic processes and cooling by cerebral blood flow, 5 though in disease other mechanisms may be important. We have shown previously that there may be dissociation between metabolic activity and heat generation in ischemic brain.

In reference to Rudick and Miller's editorial, "Multiple sclerosis or multiple possibilities: The continuing problem of misdiagnosis," Dr. Deisenhammer calls attention to the importance of CSF oligoclonal band analysis in difficult diagnostic cases. The authors agree but point out reasons for caution. Drs. Kano et al. ask whether lesion location had an effect on brain or body temperature in the study by Whiteley et al., "Do acute phase markers explain body temperature and brain temperature after ischemic stroke?"