Faculty Bibliography

PRIMARY OBJECTIVE: To investigate the relationship between the number of dilated Virchow-Robin spaces (VRS) and neurocognitive findings in patients with traumatic brain injury (TBI). RESEARCH DESIGN: Thirty-eight patients with TBI and 21 controls were studied. METHODS AND PROCEDURES: Fifteen patients underwent MRI within a mean interval of 5.4 (range 1-12) days from the brain injury and 23 after an average period of 5.5 (range 0.2-31) years. All subjects were examined with a battery of 13 neuropsychological tests (NP). MAIN OUTCOMES AND RESULTS: The average number of VRS was significantly higher in patients than in controls. There were no significant differences between patients and controls in terms of NP tests. The number of VRS showed a significant inverse correlation with processing speed and a positive correlation with visual perceptual of attention only in patients studied within a short delay of trauma. CONCLUSIONS: VRS are not directly associated to neurocognitive findings, suggesting that they may represent a result of the shear-strain injury

The point spread function (PSF) of Hadamard encoding deviates from its ideal profile due to practical (as opposed to intrinsic) reasons. Finite radiofrequency (RF) pulse length and gradient strength cause slice profile imperfections that lead to cross-talk ('voxel bleed') as large as 17% for a 1-KHz bandwidth, 5.12-ms RF pulse under 3 mT/m. This could adversely affect localization and quantification, and consequently clinical usefulness. A simple modification of the Hadamard RF pulse synthesis that exploits its unique ability to encode noncontiguous slices is proposed and shown to markedly improve the PSF. Computer simulation, in vitro and in vivo experiments confirm the theoretical derivation of voxel bleed reduction from approximately 17% to below 5% per Hadamard-encoded direction

A new strategy to yield information from the maximum number of voxels, each at the optimum signal-to-noise ratio (SNR) per unit time, in MR spectroscopic imaging (MRSI) is introduced. In the past, maximum acquisition duty-cycle was obtained by multiplexing in time several single slices each repetition time (TR), while optimal SNR was achieved by encoding the entire volume of interest (VOI) each TR. We show that optimal SNR and acquisition efficiency can both be achieved simultaneously by multiplexing in space and time several slabs of several slices, each. Since coverage of common VOIs in 3D proton MRSI in the human brain typically requires eight or more slices, at 3 T or higher magnetic fields, two or more slabs can fit into the optimum TR (approximately 1.6 s). Since typically four or less slices would then fit into each slab, Hadamard encoding is favored in that direction for slice profile reasons. It is demonstrated that per fixed examination length, the new method gives, at 3 T, twice as many voxels, each of the same SNR and size, compared with current 3D chemical shift imaging techniques. It is shown that this gain will increase for more extensive spatial coverage or higher fields

BACKGROUND AND PURPOSE: Glial cancer cells can be found well beyond the MR imaging T2 signal-intensity hyperintensity. To quantify the extent of the diffuse microstructural tissue damage possibly due to the presence of these satellite tumor cells, we investigated the relationships between global metabolic and microstructural abnormalities in the normal-appearing brain regions of patients with newly diagnosed glioma. MATERIAL AND METHODS: Ten patients (6 men, 4 women) with radiologically suspected untreated supratentorial glial tumors and 9 healthy controls (5 men, 4 women) were studied with T1- and T2-weighted MR imaging, diffusion-weighted echo-planar MR imaging, and whole-brain N-acetylaspartate (WBNAA) proton MR spectroscopy. The relationship between the WBNAA concentration, the mean diffusivity (MD), and fractional anisotropy (FA) values in a large contralateral normal-appearing white matter (NAWM) brain region was investigated with the Spearman rank correlation test. RESULTS: WBNAA values were significantly lower (P < .001) in patients (9.7 +/- 1.7 mmol/L) than controls (13.1 +/- 1.1 mmol/L). MD values were higher (P = .0001) in patients (0.95 +/- 0.07 mm(2)s(-1)) than in controls (0.61 +/- 0.04 mm(2)s(-1)). FA values did not differ between patients (0.42 +/- 0.08) and controls (0.43 +/- 0.041). A strong inverse correlation between WBNAA and MD (r = -0.88, P = .0008) was found in the patients but not in controls (r = 0.012, P = .975). CONCLUSION: The correlation between the WBNAA and MD in the contralateral NAWM suggests that the microstructural damage possibly related to the presence of infiltrative tumor cells contributes to WBNAA decline in these patients

Although a variety of methods have been proposed to provide automated adjustment of shim homogeneity, these methods typically fail or require large numbers of iterations in vivo when applied to regions with poor homogeneity, such as the temporal lobe. These limitations are largely due to 1) the limited accuracy of single evolution time measurements when full B0 mapping studies are used, and 2) inaccuracies arising from projection-based methods when the projections pass through regions where the inhomogeneity exceeds the order of the fitted parameters. To overcome these limitations we developed a novel B0 mapping method using multiple evolution times with a novel unwrapping scheme in combination with a user-defined ROI selection tool. We used these methods at 4T on 10 control subjects to obtain high-resolution spectroscopic images of glutamate from the bilateral hippocampi

PURPOSE: To quantify, with three-dimensional proton magnetic resonance (MR) spectroscopy, metabolic characteristics of normal-appearing white matter and nonenhancing lesions in patients with relapsing-remitting multiple sclerosis (MS). MATERIALS AND METHODS: Institutional review board approval and informed patient consent were obtained. Nine patients with relapsing-remitting MS (six women, three men) and nine age-matched control subjects (seven women, two men) were studied with T1- and T2-weighted MR imaging and three-dimensional proton MR spectroscopy at spatial resolution less than a cubic centimeter. Absolute N-acetylaspartate (NAA), creatine (Cr), and choline (Cho) levels were obtained from 171 voxels: 66 from lesions on T2-weighted MR images (43 hypointense and 23 isointense on T1-weighted MR images), 31 from normal-appearing white matter, and 74 from analogous normal white matter regions on images in control subjects. RESULTS: Mean NAA level in hypointense lesions (5.30 mmol/L +/- 2.27 [standard deviation]) was significantly lower (P < or = .05) than that in isointense lesions (7.82 mmol/L +/- 2.28), normal-appearing white matter (7.37 mmol/L +/- 1.71), and normal white matter in control subjects (8.89 mmol/L +/- 1.54). Cho (1.79 mmol/L +/- 0.65) and Cr (5.64 mmol/L +/- 1.50) levels in isointense lesions were indistinguishable from those in normal-appearing white matter (1.74 mmol/L +/- 0.46 and 4.99 mmol/L +/- 0.97, respectively) but were significantly higher (Cho, 20%; Cr, 24%) than those in normal white matter in control subjects (1.44 mmol/L +/- 0.40 and 4.30 mmol/L +/- 1.32, respectively). NAA, Cho, and Cr levels in normal-appearing white matter were significantly different than those in normal white matter in control subjects (NAA, 20% lower; Cho, 14% higher; and Cr, 17% higher). CONCLUSION: Abnormal metabolic activity persists in all MS tissue types. Increased Cr and Cho levels suggest (a) ongoing gliosis and attempted remyelination in isointense lesions on T1-weighted MR images and (b) membrane turnover (de- and remyelination), in addition to increased cellularity (gliosis, inflammation) in normal-appearing white matter

BACKGROUND AND PURPOSE: Recent animal and human studies have shown an increased frequency of enlarged, high-convexity Virchow-Robin spaces (VRS) in several neurologic diseases, suggesting their role as neuroradiologic markers of inflammatory changes. The aim of this study was to determine the prevalence of high-convexity dilated VRS in mild traumatic brain injury (TBI). METHODS: T2-weighted, T1-weighted, fluid-attenuated inversion recovery, and T2*-weighted gradient-echo brain MR images were acquired in 24 patients with TBI (10 women, 14 men; mean age, 33.6; range, 18.1-50.8 years) and 17 age- and sex-matched healthy control subjects (nine women, eight men; mean age, 32.8; range, 18.4-47.8 years). The mean interval after TBI was 3.6 days (range, 1-9 days) in 15 patients and 3.7 years (range, 0.6-13.4 years) in nine patients. Axial T2-weighted images were used to identify dilated VRS and to measure CSF volume; T1-weighted images were used to measure brain volume. Dilated VRS were identified as punctuate areas with CSF-like signal intensity in the high-convexity white matter. RESULTS: Mean (+/- standard deviation) number of VRS was significantly higher in patients (7.1 +/- 4.6) than in controls (2.4 +/- 2.9, P < .0003). In controls, VRS were associated with age (R = 0.69, P < .001) whereas in patients, they neither correlated with brain and CSF volumes nor with age and the elapsed time from injury. CONCLUSION: Our results suggest that the increased number of dilated VRS is a radiologic marker of mild head injury that is readily detectable on T2-weighted images. Because their number does not vary with time from injury, VRS probably reflect early and permanent brain changes

OBJECT: Diffuse axonal injury (DAI) is a major complication of traumatic brain injury (TBI) that leads to functional and psychological deficits. Although DAI is frequently underdiagnosed by conventional imaging modalities, it can be demonstrated using diffusion tensor imaging. The aim of this study was to assess the presence and extent of DAI in patients with mild TBI. METHODS: Forty-six patients with mild TBI and 29 healthy volunteers underwent a magnetic resonance (MR) imaging protocol including: dual-spin echo, fluid-attenuated inversion recovery, T2-weighted gradient echo, and diffusion tensor imaging sequences. In 20 of the patients, MR imaging was performed at a mean of 4.05 days after injury. In the remaining 26, MR imaging was performed at a mean of 5.7 years after injury. In each case, mean diffusivity and fractional anisotropy were measured using both whole-brain histograms and regions of interest analysis. No differences in any of the histogram-derived measures were found between patients and control volunteers. Compared with controls, a significant reduction of fractional anisotropy was observed in patients' corpus callosum, internal capsule, and centrum semiovale, and there were significant increases of mean diffusivity in the corpus callosum and internal capsule. Neither histogram-derived nor regional diffusion tensor imaging metrics differed between the two groups. CONCLUSIONS: Although mean diffusivity and fractional anisotropy abnormalities in these patients with TBI were too subtle to be detected with the whole-brain histogram analysis, they are present in brain areas that are frequent sites of DAI. Because diffusion tensor imaging changes are present at both early and late time points following injury, they may represent an early indicator and a prognostic measure of subsequent brain damage.

On October 9-11, 2003, the third meeting of the White Matter Study Group of the International Society for Magnetic Resonance in Medicine was held in Venice, Italy. This article is the report of the meeting on how to use MRI in the diagnostic workup of multiple sclerosis (MS) and allied white matter disorders, and to define the nature and the extent of MS pathology in vivo. Both of these steps are central to the design of future treatment strategies aimed at limiting the functional consequences of the most disabling aspects of this disease

BACKGROUND AND PURPOSE: Because of their invasive nature, high-grade glial tumors are uniformly fatal. The purpose of this study was to quantify MR imaging-occult, glial tumor infiltration beyond its radiologic margin through its consequent neuronal cell damage, assessed by the global concentration decline of the neuronal marker N-acetylaspartate (NAA). METHODS: Seventeen patients (10 men; median age, 39 years; age range, 23-79 years) with radiologically suspected (later pathologically confirmed) supratentorial glial neoplasms, and 17 age- and sex-matched controls were studied. Their whole-brain NAA (WBNAA) amounts were obtained with proton MR spectroscopy: for patients on the day of surgery (n = 17), 1 day postsurgery (n = 15), and once for each control. To convert into concentrations, suitable for intersubject comparison, patients' global NAA amounts were divided by their brain volumes segmented from MR imaging. Least squares regression was used to analyze the data. RESULTS: Pre- and postoperative WBNAA (mean +/- SD) of 9.2 +/- 2.1 and 9.7 +/- 1.8 mmol/L, respectively, in patients were indistinguishable (P = .369) but significantly lower than in controls (12.5 +/- 1.4 mmol/L). Mean resected tumor size (n = 15) was approximately 3% of total brain volume. CONCLUSION: The average 26% WBNAA deficit in the patients, which persisted following surgical resection, cannot be explained merely by depletion within the approximately 3% MR imaging-visible tumor volume or an age-dependent effect. Although there could be several possible causes of such widespread decline--perineuronal satellitosis, neuronal deafferentation, Wallerian and retrograde degeneration, vasogenic edema, functional diaschisis, secondary vascular changes--most are a direct or indirect reflection of extensive, MR imaging-occult, microscopic tumor cell infiltration, diffusely throughout the otherwise 'normal-appearing' brain