Diffusion tensor-based imaging reveals occult abnormalities in adrenomyeloneuropathy.

"Pure" adrenomyeloneuropathy (AMN) is the noninflammatory myeloneuropathic variant of X-linked adrenoleukodystrophy, where the disease process appears to be restricted to spinal cord tracts and peripheral nerves. The absence of obvious brain involvement makes it distinct from the inflammatory cerebral phenotypes of X-linked adrenoleukodystrophy. However, some pure AMN patients later experience development of cerebral demyelination, but little is known about the extent of brain involvement in pure AMN patients who have normal brain magnetic resonance imaging. We used diffusion tensor imaging to investigate possible occult cerebral abnormalities in such pure AMN patients. Fractional anisotropy and trace were studied in three-dimensional reconstructions of white matter tracts commonly involved in cerebral phenotypes of X-linked adrenoleukodystrophy. Results demonstrated reduced fractional anisotropy and increased trace in bilateral corticospinal tracts and genu of corpus callosum (p < 0.05). Diffusion tensor imaging-based three-dimensional fiber tracking showed occult tract-specific cerebral microstructural abnormalities in pure AMN patients who had a normal conventional brain magnetic resonance image. Corticospinal tract abnormalities could reflect a centripetal extension of spinal cord long-tract distal axonopathy. Accompanying abnormalities in genu of corpus callosum indicate that the disease pathology in pure AMN may not be limited to spinal cord long tracts alone, although the involvement of the latter is most prominent and severe.

Routine clinical brain MRI sequences for use at 3.0 Tesla.

PURPOSE: To establish image parameters for some routine clinical brain MRI pulse sequences at 3.0 T with the goal of maintaining, as much as possible, the well-characterized 1.5-T image contrast characteristics for daily clinical diagnosis, while benefiting from the increased signal to noise at higher field. MATERIALS AND METHODS: A total of 10 healthy subjects were scanned on 1.5-T and 3.0-T systems for T(1) and T(2) relaxation time measurements of major gray and white matter structures. The relaxation times were subsequently used to determine 3.0-T acquisition parameters for spin-echo (SE), T(1)-weighted, fast spin echo (FSE) or turbo spin echo (TSE), T(2)-weighted, and fluid-attenuated inversion recovery (FLAIR) pulse sequences that give image characteristics comparable to 1.5 T, to facilitate routine clinical diagnostics. Application of the routine clinical sequences was performed in 10 subjects, five normal subjects and five patients with various pathologies. RESULTS: T(1) and T(2) relaxation times were, respectively, 14% to 30% longer and 12% to 19% shorter at 3.0 T when compared to the values at 1.5 T, depending on the region evaluated. When using appropriate parameters, routine clinical images acquired at 3.0 T showed similar image characteristics to those obtained at 1.5 T, but with higher signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR), which can be used to reduce the number of averages and scan times. Recommended imaging parameters for these sequences are provided. CONCLUSION: When parameters are adjusted for changes in relaxation rates, routine clinical scans at 3.0 T can provide similar image appearance as 1.5 T, but with superior image quality and/or increased speed.

DTI tractography based parcellation of white matter: application to the mid-sagittal morphology of corpus callosum.

Morphology of the corpus callosum (CC) at the mid-sagittal level has been a target of extensive studies. However, the lack of internal structures and its polymorphism make it a challenging task to quantitatively analyze shape differences among subjects. In this paper, diffusion tensor Imaging (DTI) and tract tracing technique were applied to incorporate cortical connectivity information to the morphological study. The CC was parcellated into six major subdivisions based on trajectories to different cortical areas. This subdivision was performed for eight normal subjects and one stroke patient. The parcellated CCs of the normal subjects were normalized for morphological analysis. When comparing the stroke patient to the normal population, we detected significant atrophy in the motor and sensory areas of the patient CC, in line with the clinical deficits. This approach provides a new tool to investigate callosal morphology and functional relationships.

Macroscopic orientation component analysis of brain white matter and thalamus based on diffusion tensor imaging.

Diffusion tensor imaging (DTI) can delineate white matter architecture based on fiber orientation. The purpose of this paper is to use the orientation information contained in DTI to study axonal organization of the brain both macroscopically and quantitatively. After performing gray/white matter segmentation using a fractional anisotropy threshold, the white matter can be further decomposed into components composed of tracts oriented along three orthogonal anatomic axes (right-left, superior-inferior, and anterior-posterior). For each component, the volume and MR parameters were quantified. To characterize the axonal architecture of the brain, this technique was applied to the entire brain using a Talairach-based brain parcellation method and to the thalamus by manual segmentation. Reproducibility of this analysis tool was examined by repeating the measurements in the same subject, and individual differences were appreciated from the data acquired in 11 healthy volunteers. Based on the results from these preliminary data sets, this new analysis technique is expected to be an effective tool for macroscopic white matter characterization.

High-resolution diffusion tensor imaging of the brain stem at 3 T.

Diffusion tensor imaging with 1.8-mm isotropic resolution was performed to delineate structures of the brain stem. High-resolution single-shot imaging was achieved by the combination of a high-field magnet (3T) and the SENSitivity Encoding (or SENSE) parallel imaging technique. Various structures in the brain stem, such as the inferior olivary nuclei, deep cerebellar nuclei, some cranial nerves, and white matter tracts were identified, which have been difficult to appreciate by conventional MR techniques.

Metabolites in ventricular cerebrospinal fluid detected by proton magnetic resonance spectroscopic imaging.

Normally, ventricular cerebrospinal fluid (CSF) contains low levels of all metabolite signals on proton magnetic resonance spectroscopic imaging (MRSI). We present here three cases (two with seizure disorders, one with a central nervous system lymphoma) who presented with unusually elevated CSF signals on MRSI. Based on chemical shifts and in vitro studies (in one case), the signals were assigned to propan-1,2-diol (PD), acetone, and lactate, respectively. These compounds were either exclusively, or more readily, detected in CSF than in brain. Proton MRSI conveniently screens both brain and CSF for abnormal metabolism simultaneously.

Asymmetry and gender effect in functionally lateralized cortical regions: a proton MRS imaging study.

PURPOSE: to compare metabolite concentrations and ratios in gray matter regions known for their anatomical/functional asymmetry and evaluate gender effect. MATERIALS AND METHODS: Proton MRS imaging was performed at 1.5 T with TR/TE 2300/280 msec in 20 healthy right-handed subjects (mean age 29.6 +/- 5.3 years, 10 men). Concentrations of N-acetyl aspartate (NAA), choline (Cho), and creatine (Cr), and the peak area ratios NAA/Cho, NAA/Cr, and Cho/Cr were evaluated in hippocampal and parahippocampal gyri, thalamus, insula, Broca's and Wernicke's areas (and corresponding contralateral areas), primary and secondary visual areas, temporal, inferior parietal, cingulate, supplemental motor, dorsolateral prefrontal, and sensorimotor areas. Linear mixed-effects regression models were used for statistical analyses. RESULTS: NAA concentration and NAA/Cho were higher in the left thalamus by 21.9% and 20%, respectively (both P < 0.001). NAA concentration was 13% higher in the region contralateral to Wernicke's area (P < 0.02). No gender differences were found. CONCLUSION: Metabolite concentrations and ratios were symmetric and gender independent in most brain regions, however small hemispheric side differences in the thalamus and in Wernicke's area were found.

Fiber tract-based atlas of human white matter anatomy.

Two- and three-dimensional (3D) white matter atlases were created on the basis of high-spatial-resolution diffusion tensor magnetic resonance (MR) imaging and 3D tract reconstruction. The 3D trajectories of 17 prominent white matter tracts could be reconstructed and depicted. Tracts were superimposed on coregistered anatomic MR images to parcel the white matter. These parcellation maps were then compared with coregistered diffusion tensor imaging color maps to assign visible structures. The results showed (a). which anatomic structures can be identified on diffusion tensor images and (b). where these anatomic units are located at each section level and orientation. The atlas may prove useful for educational and clinical purposes.

Neuroimaging in spasticity and movement disorders.

Advances in neuroimaging provide unique opportunities to evaluate brain structure, biochemistry, and function. Although a number of imaging techniques have been used in newborns, cranial ultrasonography in premature infants and nuclear magnetic resonance modalities, including magnetic resonance imaging and diffusion-weighted imaging, in high-risk term infants are of foremost benefit. Interpretation is based on knowledge of characteristic imaging findings in specific childhood neurologic disorders and an understanding of differential diagnosis in cerebral palsy syndromes, such as spastic diplegia and various subtypes of extrapyramidal cerebral palsy. This review focuses on imaging studies that can be effectively used in at-risk infants and in children with spasticity and movement disorders to refine diagnosis and guide therapeutic interventions.

Proton MR spectroscopic imaging in Pelizaeus-Merzbacher disease.

BACKGROUND AND PURPOSE: Pelizeaus-Merzbacher disease (PMD) is a clinically and molecularly heterogeneous disorder linked to deletion, mutations, or duplication of the proteolipid protein (PLP1) gene locus at Xq22. The current study was conducted to characterize the results of proton MR spectroscopic (MRS) imaging in PMD. METHODS: Three boys with PMD (one with the severe connatal form and two with a more mild clinical phenotype [spastic paraplegia type 2]). and three age-matched healthy control subjects (age range, 2-7 years) underwent MR and MRS imaging. All imaging was performed at 1.5 T. For MRS imaging, oblique-axial sections (thickness, 15 mm; intersection gap, 2.5 mm) were recorded parallel to the anterior commissure-posterior commissure line (TR/TE/NEX, 2300/272/1) with lipid and water suppression. Ratios of metabolite peak areas were calculated, and spectra were bilaterally evaluated. RESULTS: Diffuse or focal reductions in N-acetylaspartate were observed in the affected white matter in all three cases. These reductions seemed to be consistent with axonal damage. In addition, mild increases in choline and creatine levels were observed; these may have been due to astrocytic changes. CONCLUSION: Proton MRS imaging may be helpful in evaluating regional pathophysiologic abnormalities in PMD and in distinguishing PMD from other leukodystrophies, which exhibit different metabolic profiles.