Positron emission tomography (PET) has been widely used in the study of neurological and psychiatric disorders. It has been used most extensively in research to determine pathophysiology as well as prognostic and diagnostic information and response to various interventions in different disorders. PET imaging has also been used in the clinical setting, although its use has been primarily to help differentiate or diagnose specific disorders. With the continued development of a large array of radiopharmaceuticals that can evaluate all the components of different neurotransmitter systems (such as serotonin and dopamine), PET imaging will continue to play a key role in research and clinical applications for neurological and psychiatric disorders. © 2012 Wiley Periodicals, Inc. Int J Imaging Syst Technol, 22, 2–17, 2012
Microvascular functional MR angiography using ultra-high-field 7 T MRI was used to visualize specific arterial changes in response to stimulation, and the results were compared to conventional blood oxygen level-dependent (BOLD) functional magnetic resonance imaging (fMRI). To demonstrate the potential of this new method, we conducted a visual experiment with 14 healthy subjects using optimized acquisition parameters and a dedicated radio frequency coil for 7 T MRI. The signal intensity change in the blood vessels supplying to the visual cortex, specifically the calcarine arteries, was clearly observed during stimulation. The signal changes were increased gradually up to as high as 12% as the vessel segments approach to the visual cortex where neuronal activity was believed to be occurred. The activation foci were not identical to those obtained by conventional fMRI, as expected, but they were closely related and confined to the visual cortical areas, when compared to fMRI responses. Therefore, fMRA technique using ultra-high-field 7 T MRI could provide the direct observation of microvascular changes in the arterial input vessels in relation to neuronal activity. © 2012 Wiley Periodicals, Inc. Int J Imaging Syst Technol, 22, 18–22, 2012
Balanced steady-state free precession (bSSFP) has been proposed as an alternative method to acquire the blood oxygenation level dependent contrast. Particularly, pass-band bSSFP functional magnetic resonance imaging (fMRI) is believed to utilize the T2 sensitivity of bSSFP in a relatively wide and flat off-resonance frequency band of the bSSFP profile. The method has a potential to provide higher signal to noise ratio (SNR) efficiency with reduced imaging artifacts compared to conventional approaches. Previous experimental results suggested that the level of the functional contrast and its characteristics are significantly influenced by the sequence parameters. However, few of these contrast characteristics have been investigated systematically. In this study, a computer simulation was performed to investigate the sources of functional contrast and the influence of scan parameters on the functional contrast to elucidate the contrast characteristics of pass-band bSSFP fMRI. Experiments were performed to validate the simulation results. © 2012 Wiley Periodicals, Inc. Int J Imaging Syst Technol, 22, 23–32, 2012
Spatiotemporal data coherence widely exists in fMRI data and can be potentially used to increase brain activation detection. To assess this possibility, a two-stage fMRI data analysis method was presented in this work. Standard voxelwise general linear model (GLM) was used to first exclude voxels with low correlation to the functional design, and an intervoxel coherence map (ICM) was then calculated voxel by voxel to locate brain regions, which were most consistently activated during the functional experiment. Population inference about the detected effects was provided through random effect analysis or permutation testing. Evaluations using synthetic data and scene-encoding memory task fMRI data both showed enhanced activation detection performance for the proposed method when compared with standard GLM. © 2012 Wiley Periodicals, Inc. Int J Imaging Syst Technol, 22, 33–36, 2012
Magnetic resonance imaging (MRI) investigations of resting-state functional connectivity (RSFC) typically use blood oxygen level-dependent (BOLD)-weighted imaging because of its ability to provide whole-brain coverage and high temporal resolution. Single-shot 3D gradient- and spin-echo (GRASE) arterial spin labeling (ASL) offers a number of potential advantages for RSFC measurements, such as a more direct quantitative correlate of neural activity and lower variability across subjects; however, current sequences are usually not suitable for whole-brain acquisitions because of T2 decay during the long echo train. In this study, we proposed a k-space sharing 3D GRASE ASL sequence to achieve whole-brain coverage, applied it to measure RSFC on a group of healthy subjects, and compared it with BOLD data. Similar RSFC networks were estimated using both techniques, providing corroboration of the capability of our method for RSFC analysis. Furthermore, ASL data enable calculation of mean cerebral blood flow (CBF) values within the RSFC networks, thus assigning them biologically meaningful values. The inherently quantitative nature of CBF measurements should provide a more stable and interpretable biomarker in comparison to BOLD and may, therefore, be particularly useful for applications such as longitudinal studies of RSFC. © 2012 Wiley Periodicals, Inc. Int J Imaging Syst Technol, 22, 37–43, 2012
The addition of a pair of magnetic field gradient pulses had initially enabled the measurement of spin motion to nuclear magnetic resonance (NMR) experiments. In the adaptation of diffusion weighted (DW)-NMR techniques to magnetic resonance imaging (MRI), the taxonomy of mathematical models is divided in two categories: model matching and spectral methods. In this review, the methods are summarized starting from early DW NMR models followed up with their adaptation to DW MRI. Finally, a newly introduced Fourier analysis based unifying theory, so-called Complete Fourier Direct MRI, is included to explain the mechanisms of existing methods. © 2012 Wiley Periodicals, Inc. Int J Imaging Syst Technol, 22, 44–52, 2012
In recent years, diffusion-weighted magnetic resonance imaging has attracted considerable attention due to its unique potential to delineate the white matter pathways of the brain. However, methodologies currently available and in common use among neuroscientists and clinicians are typically based on the diffusion tensor model, which has comprehensively been shown to be inadequate to characterize diffusion in brain white matter. This is due to the fact that it is only capable of resolving a single fiber orientation per voxel, causing incorrect fiber orientations, and hence pathways, to be estimated through these voxels. Given that the proportion of affected voxels has been recently estimated at 90%, this is a serious limitation. Furthermore, most implementations use simple “deterministic” streamlines tracking algorithms, which have now been superseded by “probabilistic” approaches. In this study, we present a robust set of tools to perform tractography, using fiber orientations estimated using the validated constrained spherical deconvolution method, coupled with a probabilistic streamlines tracking algorithm. This methodology is shown to provide superior delineations of a number of known white matter tracts, in a manner robust to crossing fiber effects. These tools have been compiled into a software package, called MRtrix, which has been made freely available for use by the scientific community. © 2012 Wiley Periodicals, Inc. Int J Imaging Syst Technol, 22, 53–66, 2012
Cross-relaxation imaging (CRI) provides biomarkers sensitive to the macromolecular content of tissue. Although the CRI parameters are sufficiently precise to exhibit significant correlations with macromolecular content in tissue, their accuracy is hindered by the CRI modeling and measurement variability. In this article, several sources of CRI variability are examined, such as T1 mapping bias, magnetization transfer signal drift, and inaccuracies due to tissue modeling. Simple corrections schemes are proposed to account for these effects and to improve the CRI accuracy. © 2012 Wiley Periodicals, Inc. Int J Imaging Syst Technol, 22, 67–72, 2012
First-episode schizophrenia and chronic schizophrenia have different patterns of cortical gray matter loss, due to differences in the period of illness. Differences in the reduction of cortical thickness between first-episode and chronic schizophrenia has not yet been addressed using a technique of measuring cortical thickness. The goal of this study is to identify differences in cerebral cortical thickness between first-episode schizophrenic patients and matched normal controls as well as between chronic schizophrenic patients and matched normal controls. Thirty-five chronic and 24 first-episode schizophrenic patients were compared with each age- and sex-matched control group, respectively. To measure cortical thickness, we utilized an inner and outer cortical surface reconstruction algorithm. Cortical thickness was directly measured as the distance between the two surfaces. Statistical analysis was performed with diffusion smoothing along cortical manifolds, and surface normalization on a sphere model. There were no significant changes in global mean thickness and cerebral gray matter volume in both first-episode and chronic schizophrenia patients. However, we observed regional thinning of cortical thickness, most significantly in the superior temporal gyrus of first-episode schizophrenic patients. In chronic schizophrenia, larger regions including the prefrontal cortex (PF) were significantly thinned compared to the first-episode group. This suggests that the duration of illness affects cortical thinning in the PF, as well as the extent of cortical thinning. © 2012 Wiley Periodicals, Inc. Int J Imaging Syst Technol, 22, 73–80, 2012
The aim of this article is to report on the importance and challenges of a time-resolved and spatio-temporal analysis of fMRI data from complex cognitive processes and associated disorders using a study on developmental dyscalculia (DD). Participants underwent fMRI while judging the incorrectness of multiplication results, and the data were analyzed using a sequence of methods, each of which progressively provided more a detailed picture of the spatio-temporal aspect of this disease. Healthy subjects and subjects with DD performed alike behaviorally, though they exhibited parietal disparities using traditional “voxel-based” group analyses. Further and more detailed differences, however, surfaced with a “time-resolved” examination of the neural responses during the experiment. While performing intergroup comparisons, a third group of subjects with dyslexia but with no arithmetic difficulties was included to test the specificity of the analysis and strengthen the statistical base with overall 58 subjects. Surprisingly, the analysis showed a functional dissimilarity during an initial reading phase for the group of dyslexic but otherwise normal subjects, with respect to controls, though only numerical digits and no alphabetic characters were presented. Thus, our results suggest that “time-resolved multivariate” analysis of complex experimental paradigms has the ability to yield powerful new clinical insights about abnormal brain function. Similarly, a detailed compilation of aberrations in the functional cascade may have much greater potential to delineate the core processing problems in mental disorders. © 2012 Wiley Periodicals, Inc. Int J Imaging Syst Technol, 22, 81–96, 2012
Genetic imaging techniques allow investigation of the mechanisms by which genetic variants influence brain structure and function. The default mode network (DMN) is characterized by a default state of neuronal activity in the brain that is linked to core processes of human cognition. This study examined the role of catechol-O-methyl transferase (COMT) and brain-derived neurotrophic factor (BDNF) polymorphisms on functional connectivity between brain areas. Twenty-three healthy volunteers underwent a resting-state functional magnetic resonance imaging scan and genotyping of COMT and BDNF single nucleotide polymorphisms (SNPs). A resting-state functional connectivity map was created using the posterior cingulate cortex (PCC) as a seed region. The Val/Val homozygote group of the COMT Val158Met SNP showed significantly greater DMN connectivity in the medial and superior frontal gyri and cerebellum compared with the Met allele carrier group. For the BDNF Val66Met SNP, connectivity between the PCC and precuneus was stronger in the Val/Val homozygote group than in the Met allele carrier group. Different patterns of DMN connectivity related to BDNF and COMT SNPs were observed in this study. These findings suggest interaction between genes and functional connectivity in the brain and indicate that altered functional connectivity may be an endophenotype of cognitive vulnerability. © 2012 Wiley Periodicals, Inc. Int J Imaging Syst Technol, 22, 97–102, 2012