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Introduction A main obstacle that impedes standardized clinical and research applications of arterial spin labeling (ASL), is the substantial differences between the commercial implementations of ASL from major MRI vendors. In this study, we compare a single identical 2D gradient-echo EPI pseudo-continuous ASL (PCASL) sequence implemented on 3T scanners from three vendors (General Electric Healthcare, Philips Healthcare and Siemens Healthcare) within the same center and with the same subjects. Material and methods Fourteen healthy volunteers (50% male, age 26.4 ± 4.7 years) were scanned twice on each scanner in an interleaved manner within 3 h. Because of differences in gradient and coil specifications, two separate studies were performed with slightly different sequence parameters, with one scanner used across both studies for comparison. Reproducibility was evaluated by means of quantitative cerebral blood flow (CBF) agreement and inter-session variation, both on a region-of-interest (ROI) and voxel level. In addition, a qualitative similarity comparison of the CBF maps was performed by three experienced neuro-radiologists. Results There were no CBF differences between vendors in study 1 ( p > 0.1), but there were CBF differences of 2–19% between vendors in study 2 ( p < 0.001 in most gray matter ROIs) and 10–22% difference in CBF values obtained with the same vendor between studies ( p < 0.001 in most gray matter ROIs). The inter-vendor inter-session variation was not significantly larger than the intra-vendor variation in all ( p > 0.1) but one of the ROIs ( p < 0.001). Conclusion This study demonstrates the possibility to acquire comparable cerebral CBF maps on scanners of different vendors. Small differences in sequence parameters can have a larger effect on the reproducibility of ASL than hardware or software differences between vendors. These results suggest that researchers should strive to employ identical labeling and readout strategies in multi-center ASL studies. [ABSTRACT FROM AUTHOR]

Abstract: The intra-class class correlation coefficient (ICC) is a prominent statistic to measure test–retest reliability of fMRI data. It can be used to address the question of whether regions of high group activation in a first scan session will show preserved subject differentiability in a second session. With this purpose, we present a method that extends voxel-wise ICC analysis. We show that voxels with high group activation have more probability of being reliable, if a subsequent session is performed, than typical voxels across the brain or across white matter. We also find that the existence of some voxels with high ICC but low group activation can be explained by stable signals across sessions that poorly fit the HRF model. At a region of interest level, we show that our voxel-wise ICC calculation is more robust than previous implementations under variations of smoothing and cluster size. The method also allows formal comparisons between the reliabilities of given brain regions; aimed at establishing which ROIs discriminate best between individuals. The method is applied to an auditory and a verbal working memory task. A reliability toolbox for SPM5 is provided at http://brainmap.co.uk. [Copyright &y& Elsevier]

Abstract: The stimulant drug methylphenidate (MPH) and the non-stimulant drug atomoxetine (ATX) are both widely used for the treatment of attention deficit/hyperactivity disorder (ADHD), but their differential effects on human brain function are poorly understood. PET and blood oxygen level dependent (BOLD) fMRI have been used to study the effects of MPH and BOLD fMRI is beginning to be used to delineate the effects of MPH and ATX in the context of cognitive tasks. The BOLD signal is a proxy for neuronal activity and is dependent on three physiological parameters: regional cerebral blood flow (rCBF), cerebral metabolic rate of oxygen and cerebral blood volume. To identify areas sensitive to MPH and ATX and assist interpretation of BOLD studies in healthy volunteers and ADHD patients, it is therefore of interest to characterize the effects of these drugs on rCBF. In this study, we used arterial spin labeling (ASL) MRI to measure rCBF non-invasively in healthy volunteers after administration of MPH, ATX or placebo. We employed multi-class pattern recognition (PR) to discriminate the neuronal effects of the drugs, which accurately discriminated all drug conditions from one another and provided activity patterns that precisely localized discriminating brain regions. We showed common and differential effects in cortical and subcortical brain regions. The clearest differential effects were observed in four regions: (i) in the caudate body where MPH but not ATX increased rCBF, (ii) in the midbrain/substantia nigra and (iii) thalamus where MPH increased and ATX decreased rCBF plus (iv) a large region of cerebellar cortex where ATX increased rCBF relative to MPH. Our results demonstrate that combining ASL and PR yields a sensitive method for detecting the effects of these drugs and provides insights into the regional distribution of brain networks potentially modulated by these compounds. [Copyright &y& Elsevier]

Abstract: The neurobiological basis for attention deficit hyperactivity disorder (ADHD) has not yet been fully established, although there is a growing body of evidence pointing to functional and structural abnormalities involving the basal ganglia, cerebellum, and regions of frontal grey matter. The purpose of this study was to investigate regional cerebral perfusion in adults with ADHD and age-matched control subjects, and to assess the perfusion response to stimulant treatment in the ADHD group using a non-invasive magnetic resonance perfusion imaging technique. Whole-brain cerebral perfusion images were acquired from nine right-handed male patients with ADHD and eleven age-matched control subjects using a continuous arterial spin labelling (CASL) technique. The ADHD group was assessed once on their normal treatment and once after withdrawing from treatment for at least one week. An automated voxel-based analysis was used to identify regions where the cerebral perfusion differed significantly between the ADHD and control groups, and where the perfusion altered significantly with stimulant treatment. Regional cerebral perfusion was increased in the ADHD group in the left caudate nucleus, frontal and parietal regions. Psychomotor stimulant treatment acted to normalise perfusion in frontal cortex and the caudate nucleus with additional decreases in parietal and parahippocampal regions. These findings highlight the potential sensitivity of non-invasive perfusion MRI techniques like CASL in the evaluation of perfusion differences due to illness and medication treatment, and provide further evidence that persistence of ADHD symptomatology into adulthood is accompanied by abnormalities in frontal and striatal brain regions. [Copyright &y& Elsevier]