Whenever a linear gradient is activated, concomitant magnetic fields with non-linear spatial dependence result. This is a consequence of Maxwell's equations, i.e., within the imaging volume the magnetic field must have zero divergence, and has negligible curl. The concomitant, or Maxwell field has been described in the MRI literature for over 10 years. In this paper, we theoretically and experimentally show the existence of two additional lowest-order terms in the concomitant field, which we call cross-terms. The concomitant gradient cross-terms only arise when the longitudinal gradient Gz is simultaneously active with a transverse gradient (Gx or Gy). The effect of all of the concomitant gradient terms on phase contrast imaging is examined in detail. Several methods for reducing or eliminating phase errors arising from the concomitant magnetic field are described. The feasibility of a joint pulse sequence-reconstruction method, which requires no increase in minimum TE, is demonstrated. Since the lowest-order terms of the concomitant field are proportional to G2/B0, the importance of concomitant gradient terms is expected to increase given the current interest in systems with stronger gradients and/or weaker main magnetic fields.

Background:In the midbrain of patients with Parkinson disease (PD), there is a selective loss of

No abstract

In general, multiple components such as water direct saturation (DS), magnetization transfer (MT), chemical exchange saturation transfer (CEST) and aliphatic nuclear overhauser effect (NOE) contribute to Z-spectrum. The conventional CEST quantification method based on asymmetrical analysis may lead to quantification errors due to the semi-solid MT asymmetry and the aliphatic NOE effect located on single side of the Z-spectrum. Fitting individual contributors to the Z-spectrum may improve the quantification of each component. In this study, we aim to characterize the multiple exchangeable components from an intracranial tumor model using a simplified Z-spectral fitting method. In this method, the Z-spectrum acquired at low saturation RF amplitude (50 Hz) was modeled as the summation of five Lorentzian functions that correspond to NOE, MT effect, bulk water, amide proton transfer (APT) effect and a CEST peak located at +2ppm, called CEST@2ppm. With the pixel-wise fitting, the regional variation of these five components in the brain tumor and the normal brain tissue were quantified and summarized. Increased APT effect, decreased NOE and reduced CEST@2ppm were observed in the brain tumor compared to the normal brain tissue. Additionally, the CEST@2ppm decreased with tumor progression. The CEST@2ppm was found to correlate with the creatine concentration quantified with proton magnetic resonance spectroscopy (1H-MRS). Based on the correlation curve, the creatine contribution to the CEST@2ppm was quantified. The CEST@2ppm signal could be a novel imaging surrogate for in vivo creatine, the important bioenergetics marker. Given its noninvasive nature, this CEST MRI method may have broad applications in cancer bioenergetics.

Objective-To investigate microstructure of white matter fiber tracts in pediatric bipolar disorder (PBD) and attention deficit hyperactivity disorder (ADHD).Methods-A diffusion tensor imaging (DTI) study was conducted at 3 Tesla on age and IQ-matched children and adolescents with PBD (n=13), ADHD (n=13), and healthy controls (HC) (n=15). Three DTI parameters, fractional anisotropy (FA), apparent diffusion coefficient (ADC), and regional fiber coherence index (r-FCI), were examined in eight fiber tracts: Anterior corona radiata (ACR); anterior limb of the internal capsule (ALIC); superior region of the internal capsule (SRI); posterior limb of the internal capsule (PLIC); superior longitudinal fasciculus (SLF); inferior longitudinal fasciculus (ILF); cingulum (CG); splenium (SP).Results-Significantly lower FA was observed in ACR in both PBD and ADHD relative to HC. In addition, FA and r-FCI values were significantly lower in ADHD relative to PBD and HC in both the ALIC and the SRI. Further, ADC was significantly greater in ADHD relative to both the PBD and HC in ACR, ALIC, PLIC, SRI, CG, ILF, and SLF. Publisher's Disclaimer: This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. Conclusions-Decreased FA in ACR implies an impaired fiber density or reduced myelination in both PBD and ADHD in this prefrontal tract. These abnormalities, together with the reduced fiber coherence, extended to cortico-bulbar tracts in ADHD. Increased ADC across multiple white matter tracts in ADHD indicates extensive cellular abnormalities with less diffusion restriction in ADHD relative to PBD. NIH Public Access

It is well known that diffusion-induced MR signal loss deviates from monoexponential decay, particularly at high b-values (e.g., >1500 sec/mm 2 for human brain tissues). A number of models have been developed to describe this anomalous diffusion behavior and relate the diffusion measurements to tissue structures. Recently, a new diffusion model was proposed by solving the Bloch-Torrey equation using fractional order calculus with respect to time and space (Magin et al., J Magn Reson 2008;190:255-270; Zhou et al., Proc Int'l Soc Magn Reson Med 2008). Using a spatial Laplacian $ 2b , this model yields a new set of parameters to describe anomalous diffusion: diffusion coefficient D, fractional order derivative in space b, and a spatial parameter m (in units of mm). In this study, we demonstrate that the fractional calculus model can be successfully applied to analyzing diffusion images of healthy human brain tissues in vivo. Five human volunteers were scanned on a commercial 3-T scanner using a customized single-shot echo-planar imaging diffusion sequence with 15 b values ranging from 0 to 4700 sec/mm 2 . The set of images was analyzed using the fractional calculus model, producing spatially resolved maps of D, b, and m. The b and m maps showed notable contrast between white and gray matter. The contrast has been attributed to the varying degree of complexity of the underlying tissue structures and microenvironment. Although the biophysical basis of b and m remains elusive, the potential utility of these parameters to characterize the environment for molecular diffusion, as a complement to apparent diffusion coefficient, may lead to a new way to investigate tissue structural changes in disease progression, intervention, and regression. Magn Reson Med 63:562-569,

Objective: To quantify the effects of traumatic brain injury on integrity of thalamocortical projection fibers and to evaluate whether damage to these fibers accounts for impairments in executive function in chronic traumatic brain injury.Methods: High-resolution (voxel size: 0.78 mm ϫ 0.78 mm ϫ 3 mm 3 ) diffusion tensor MRI of the thalamus was conducted on 24 patients with a history of single, closed-head traumatic brain injury (TBI) (12 each of mild TBI and moderate to severe TBI) and 12 age-and education-matched controls. Detailed neuropsychological testing with an emphasis on executive function was also conducted. Fractional anisotropy was extracted from 12 regions of interest in cortical and corpus callosum structures and 7 subcortical regions of interest (anterior, ventral anterior, ventral lateral, dorsomedial, ventral posterior lateral, ventral posterior medial, and pulvinar thalamic nuclei). Results:Relative to controls, patients with a history of brain injury showed reductions in fractional anisotropy in both the anterior and posterior corona radiata, forceps major, the body of the corpus callosum, and fibers identified from seed voxels in the anterior and ventral anterior thalamic nuclei. Fractional anisotropy from cortico-cortico and corpus callosum regions of interest did not account for significant variance in neuropsychological function. However, fractional anisotropy from the thalamic seed voxels did account for variance in executive function, attention, and memory. Conclusions:The data provide preliminary evidence that traumatic brain injury and resulting diffuse axonal injury results in damage to the thalamic projection fibers and is of clinical relevance to cognition. Neurology ® 2010;74:558 -564 GLOSSARY ACR ϭ anterior corona radiata; AN ϭ anterior thalamic nucleus; bCC ϭ body of the corpus callosum; CST ϭ cortical-spinal tract; DAI ϭ diffuse axonal injury; DM ϭ dorsomedial nucleus; DTI ϭ diffusion tensor imaging; FA ϭ fractional anisotropy; fMaj ϭ forceps major; fMin ϭ forceps minor; FOV ϭ field of view; FSE ϭ fast spin echo; gCC ϭ genu of the corpus callosum; IC ϭ internal capsule; IFOF ϭ inferior frontal occipital fasciculus; LOC ϭ loss of consciousness; miTBI ϭ mild TBI; msTBI ϭ moderate to severe TBI; NEX ϭ number of excitations; PCR ϭ posterior corona radiata; PTA ϭ posttraumatic amnesia; PU ϭ pulvinar; ROI ϭ region of interest; sCC ϭ splenium of the corpus callosum; SLF ϭ superior longitudinal fasciculus; SS ϭ sagittal stratum; TBI ϭ traumatic brain injury; TE ϭ echo time; TR ϭ repetition time; VA ϭ ventral anterior thalamic nucleus; VL ϭ ventral lateral thalamic nucleus; VPL ϭ ventral posterior lateral nucleus; VPM ϭ ventral posterior medial nucleus. Traumatic brain injury (TBI) is a serious public health problem with a high incidence 1-3 which can result in structural damage to the cerebrum including contusions, edema, and diffuse axonal injury (DAI).4 DAI has been demonstrated in all stages and severities [5][6][7] and is often the only significant pathology in milder injury...

The findings revealed volume loss in the right superior temporal gyrus, right middle temporal gyrus, and right anterior cingulate gyrus among antipsychotic-naive first-episode schizophrenia patients. In addition, the functional networks involving the right superior temporal gyrus and middle temporal gyrus were associated with clinical symptom severity. No abnormalities were observed in resting state connectivity with regions of identified gray matter deficits.