MTT and Blood-Brain Barrier Disruption within Asymptomatic Vascular WM Lesions

BACKGROUND AND PURPOSE

White matter lesions of presumed ischemic origin are associated with progressive cognitive impairment and impaired BBB function. Studying the longitudinal effects of white matter lesion biomarkers that measure changes in perfusion and BBB patency within white matter lesions is required for long-term studies of lesion progression. We studied perfusion and BBB disruption within white matter lesions in asymptomatic subjects.

MATERIALS AND METHODS

Anatomic imaging was followed by consecutive dynamic contrast-enhanced and DSC imaging. White matter lesions in 21 asymptomatic individuals were determined using a Subject-Specific Sparse Dictionary Learning algorithm with manual correction. Perfusion-related parameters including CBF, MTT, the BBB leakage parameter, and volume transfer constant were determined.

RESULTS

MTT was significantly prolonged (7.88 [SD, 1.03] seconds) within white matter lesions compared with normal-appearing white (7.29 [SD, 1.14] seconds) and gray matter (6.67 [SD, 1.35] seconds). The volume transfer constant, measured by dynamic contrast-enhanced imaging, was significantly elevated (0.013 [SD, 0.017] minutes-1) in white matter lesions compared with normal-appearing white matter (0.007 [SD, 0.011] minutes-1). BBB disruption within white matter lesions was detected relative to normal white and gray matter using the DSC-BBB leakage parameter method so that increasing BBB disruption correlated with increasing white matter lesion volume (Spearman correlation coefficient = 0.44; P < .046).

CONCLUSIONS

A dual-contrast-injection MR imaging protocol combined with a 3D automated segmentation analysis pipeline was used to assess BBB disruption in white matter lesions on the basis of quantitative perfusion measures including the volume transfer constant (dynamic contrast-enhanced imaging), the BBB leakage parameter (DSC), and MTT (DSC). This protocol was able to detect early pathologic changes in otherwise healthy individuals.

Cerebral Ketones Detected by 3T MR Spectroscopy in Patients with High-Grade Glioma on an Atkins-Based Diet

BACKGROUND AND PURPOSE

Ketogenic diets are being explored as a possible treatment for several neurological diseases, but the physiologic impact on the brain is unknown. The objective of this study was to evaluate the feasibility of 3T MR spectroscopy to monitor brain ketone levels in patients with high-grade gliomas who were on a ketogenic diet (a modified Atkins diet) for 8 weeks.

MATERIALS AND METHODS

Paired pre- and post-ketogenic diet MR spectroscopy data from both the lesion and contralateral hemisphere were analyzed using LCModel software in 10 patients.

RESULTS

At baseline, the ketone bodies acetone and β-hydroxybutyrate were nearly undetectable, but by week 8, they increased in the lesion for both acetone (0.06 ± 0.03 ≥ 0.27 ± 0.06 IU, P = .005) and β-hydroxybutyrate (0.07 ± 0.07 ≥ 0.79 ± 0.32 IU, P = .046). In the contralateral brain, acetone was also significantly increased (0.041 ± 0.01 ≥ 0.16 ± 0.04 IU, P = .004), but not β-hydroxybutyrate. Acetone was detected in 9/10 patients at week 8, and β-hydroxybutyrate, in 5/10. Acetone concentrations in the contralateral brain correlated strongly with higher urine ketones (r = 0.87, P = .001) and lower fasting glucose (r = -0.67, P = .03). Acetoacetate was largely undetectable. Small-but-statistically significant decreases in NAA were also observed in the contralateral hemisphere at 8 weeks.

CONCLUSIONS

This study suggests that 3T MR spectroscopy is feasible for detecting small cerebral metabolic changes associated with a ketogenic diet, provided that appropriate methodology is used.

7T Brain MRS in HIV Infection: Correlation with Cognitive Impairment and Performance on Neuropsychological Tests

BACKGROUND AND PURPOSE

Validated neuroimaging markers of HIV-associated neurocognitive disorder in patients on antiretroviral therapy are urgently needed for clinical trials. The purpose of this study was to explore the relationship between cognitive impairment and brain metabolism in older subjects with HIV infection. It was hypothesized that MR spectroscopy measurements related to neuronal health and function (particularly N-acetylaspartate and glutamate) would be lower in HIV-positive subjects with worse cognitive performance.

MATERIALS AND METHODS

Forty-five HIV-positive patients (mean age, 58.9 ± 5.3 years; 33 men) underwent detailed neuropsychological testing and brain MR spectroscopy at 7T. Twenty-four subjects were classified as having asymptomatic cognitive impairment, and 21 were classified as having symptomatic cognitive impairment. Single-voxel proton MR spectra were acquired from 5 brain regions and quantified using LCModel software. Brain metabolites and neuropsychological test results were compared using nonparametric statistics and Pearson correlation coefficients.

RESULTS

Differences in brain metabolites were found between symptomatic and asymptomatic subjects, with the main findings being lower measures of N-acetylaspartate in the frontal white matter, posterior cingulate cortex, and precuneus. In the precuneus, glutamate was also lower in the symptomatic group. In the frontal white matter, precuneus, and posterior cingulate cortex, NAA and glutamate measurements showed significant positive correlation with better performance on neuropsychological tests.

CONCLUSIONS

Compared with asymptomatic subjects, symptomatic HIV-positive subjects had lower levels of NAA and glutamate, most notably in the frontal white matter, which also correlated with performance on neuropsychological tests. High-field MR spectroscopy offers insight into the pathophysiology associated with cognitive impairment in HIV and may be useful as a quantitative outcome measure in future treatment trials.

Decoupling of N-acetyl-aspartate and glutamate within the dorsolateral prefrontal cortex in schizophrenia

Aberrant function of glutamatergic pathways is likely to underlie the pathology of schizophrenia. Evidence of oxidative stress in the disease pathology has also been reported. N-Acetylaspartate (NAA) is metabolically linked to both cascades and may be a key marker in exploring the interconnection of glutamatergic pathways and oxidative stress. Several studies have reported positive correlation between the levels of NAA and Glx (the sum of glutamate and glutamine) in several brain regions in healthy subjects, by using proton magnetic resonance spectroscopy ([(1)H]MRS). Interestingly, one research group recently reported decoupling of the relationship between NAA and Glx in the hippocampus of patients with schizophrenia. Here we report levels of NAA and Glx measured using [(1)H]MRS, relative to the level of creatine (Cr) as an internal control. The dorsolateral prefrontal cortex (DLPFC) and anterior cingulate cortex (ACC) in 25 patients with schizophrenia and 17 matched healthy controls were studied. In DLPFC, NAA/Cr and Glx/Cr were significantly positively correlated in healthy controls after correction for the effect of age and smoking status and after correction for multiple comparisons (r= 0.627, P= 0.017). However, in patients with schizophrenia, the positive correlation between NAA/Cr and Glx/Cr was not observed even after correcting for these two variables (r= -0.330, P= 0.124). Positive correlation between NAA/Cr and Glx/Cr was not observed in the ACC in both groups. Decoupling of NAA and Glx in the DLPFC may reflect the interconnection of glutamatergic pathways and oxidative stress in the pathology of schizophrenia, and may possibly be a biomarker of the disease.

Parallel reconstruction in accelerated multivoxel MR spectroscopy

PURPOSE

To develop the simultaneous acquisition of multiple voxels in localized MR spectroscopy (MRS) using sensitivity encoding, allowing reduced total scan time compared to conventional sequential single voxel (SV) acquisition methods.

METHODS

Dual volume localization was used to simultaneously excite voxels in both hemispheres. Receiver coil sensitivity profiles were used to unfold the data. To demonstrate the method, MRS voxels in the left and right hippocampus were measured at 3 tesla (T) and the left and right motor cortices at 7T. Spectra were compared to conventional SV acquisitions. Spectra were also recorded from the lesion and contralateral hemisphere of a patient with a low-grade oligodendroglioma at 7T.

RESULTS

It was possible to generate signal in two voxels simultaneously and separate the signal originating from the different locations, with spectral results almost identical to those observed using conventional single voxel methods. The method results in an increased chemical shift displacement artifact, which might be improved by advanced pulse designs, and a noise increase due to the unfolding g-factor, which was larger at 3T than 7T.

CONCLUSION

The simultaneous acquisition of voxels for MRS is possible by using modulated slice-selective pulses and receive coil sensitivity profiles to unfold the resulting signals.

Various MRS application tools for Alzheimer disease and mild cognitive impairment

MR spectroscopy is a noninvasive technique that allows the detection of several naturally occurring compounds (metabolites) from well-defined regions of interest within the human brain. Alzheimer disease, a progressive neurodegenerative disorder, is the most common cause of dementia in the elderly. During the past 20 years, multiple studies have been performed on MR spectroscopy in patients with both mild cognitive impairment and Alzheimer disease. Generally, MR spectroscopy studies have found decreased N-acetylaspartate and increased myo-inositol in both patients with mild cognitive impairment and Alzheimer disease, with greater changes in Alzheimer disease than in mild cognitive impairment. This review summarizes the information content of proton brain MR spectroscopy and its related technical aspects, as well as applications of MR spectroscopy to mild cognitive impairment and Alzheimer disease. While MR spectroscopy may have some value in the differential diagnosis of dementias and assessing prognosis, more likely its role in the near future will be predominantly as a tool for monitoring disease response or progression in treatment trials. More work is needed to evaluate the role of MR spectroscopy as a biomarker in Alzheimer disease and its relationship to other imaging modalities.

Characterization of peripheral nerve sheath tumors with 3T proton MR spectroscopy

BACKGROUND AND PURPOSE

The characterization of peripheral nerve sheath tumors is challenging. The purpose here was to investigate the diagnostic value of quantitative proton MR spectroscopy at 3T for the characterization of peripheral nerve sheath tumors as benign or malignant, compared with PET.

MATERIALS AND METHODS

Twenty participants with 24 peripheral nerve sheath tumors underwent MR spectroscopy by use of a point-resolved sequence (TE, 135 ms). Six voxels were placed in 4 histologically proven malignant peripheral nerve sheath tumors and 22 voxels in 20 benign peripheral nerve sheath tumors (9 histologically proven, 11 with documented stability). The presence or absence of a trimethylamine signal was evaluated, the trimethylamine concentration estimated by use of phantom replacement methodology, and the trimethylamine fraction relative to Cr measured. MR spectroscopy results for benign and malignant peripheral nerve sheath tumors were compared by use of a Mann-Whitney test, and concordance or discordance with PET findings was recorded.

RESULTS

In all malignant tumors and in 9 of 18 benign peripheral nerve sheath tumors, a trimethylamine peak was detected, offering the presence of trimethylamine as a sensitive (100%), but not specific (50%), marker of malignant disease. Trimethylamine concentrations (2.2 ± 2.8 vs 6.6 ± 5.8 institutional units; P < .049) and the trimethylamine fraction (27 ± 42 vs 88 ± 22%; P < .012) were lower in benign than malignant peripheral nerve sheath tumors. A trimethylamine fraction threshold of 50% resulted in 100% sensitivity (95% CI, 58.0%-100%) and 72.2% (95% CI, 59.5%-75%) specificity for distinguishing benign from malignant disease. MR spectroscopy and PET results were concordant in 12 of 16 cases, (2 false-positive results for MR spectroscopy and PET each).

CONCLUSIONS

Quantitative measurement of trimethylamine concentration by use of MR spectroscopy is feasible in peripheral nerve sheath tumors and shows promise as a method for the differentiation of benign and malignant lesions. Trimethylamine presence within a peripheral nerve sheath tumor is a sensitive marker of malignant disease, but quantitative measurement of trimethylamine content is required to improve specificity.

Cerebral abnormalities in adults with ataxia-telangiectasia

Ataxia-telangiectasia, an autosomal recessive disorder caused by defect of the ataxia-telangiectasia mutated gene, is characterized by progressive neurologic impairment with cerebellar atrophy, ocular and cutaneous telangiectasia, immunodeficiency, heightened sensitivity to ionizing radiation and susceptibility to developing lymphoreticular malignancy. Supratentorial brain abnormalities have been reported only rarely. In this study, brain MRI was performed in 10 adults with ataxia-telangiectasia having stable neurologic impairment. Intracerebral telangiectasia with multiple punctate hemosiderin deposits were identified in 60% of subjects. These lesions were apparently asymptomatic. They are similar in appearance to radiation-induced telangiectasia and to cryptogenic vascular malformations. Also noted, in the 2 oldest subjects, was extensive white matter T2 hyperintensity, and in 1 of these a space-occupying fluid collection consistent with transudative capillary leak and edema as evidenced by reduced levels of metabolites on MR spectroscopic imaging. Asymptomatic supratentorial vascular abnormalities appear to be common in adults with ataxia-telangiectasia.

Imaging characteristics of oligodendrogliomas that predict grade

BACKGROUND AND PURPOSE

Oligodendrogliomas are tumors that have variable WHO grades depending on anaplasia and astrocytic components and their treatment may differ accordingly. Our aim was to retrospectively evaluate imaging features of oligodendrogliomas that predict tumor grade.

MATERIALS AND METHODS

The imaging studies of 75 patients with oligodendrogliomas were retrospectively reviewed and compared with the histologic grade. The presence and degree of enhancement and calcification were evaluated subjectively. rCBV and ADC maps were measured. Logistic linear regression models were used to determine the relationship between imaging factors and tumor grade.

RESULTS

Thirty of 75 (40%) tumors enhanced, including 9 of 46 (19.6%) grade II and 21 of 29 (72.4%) grade III tumors (P < .001). Grade III tumors showed lower ADC values compared with grade II tumors (odds ratio of a tumor being grade III rather than grade II = 0.07; 95% CI, 0.02-0.25; P = .001). An optimal ADC cutoff of 925 10(-6) mm(2)/s was established, which yielded a specificity of 89.1%, sensitivity of 62.1%, and accuracy of 78.7%. There was no statistically significant association between tumor grade and the presence of calcification and perfusion values. Multivariable prediction rules were applied for ADC < 925 10(-6) mm(2)/s, the presence of enhancement, and the presence of calcification. If either ADC < 925 10(-6) mm(2)/s or enhancement was present, it yielded 93.1% sensitivity, 73.9% specificity, and 81.3% accuracy. The most accurate (82.2%) predictive rule was seen when either ADC < 925 10(-6) mm(2)/s or enhancement and calcification were present.

CONCLUSIONS

Models based on contrast enhancement, calcification, and ADC values can assist in predicting the grade of oligodendrogliomas and help direct biopsy sites, raise suspicion of sampling error, and predict prognosis.

Cerebral blood flow alterations in pain-processing regions of patients with fibromyalgia using perfusion MR imaging

BACKGROUND AND PURPOSE

Widespread pain sensitivity in patients with FM suggests a CNS processing problem. The purpose of this study was to assess alterations in perfusion as measured by DSC in a number of brain regions implicated in pain processing between patients with FM and healthy controls.

MATERIALS AND METHODS

Twenty-one patients with FM and 27 healthy controls underwent conventional MR imaging and DSC. For DSC, 12 regions of interest were placed in brain regions previously implicated in pain processing. rCBF values were calculated for each region of interest. Subjects answered mood/pain coping questionnaires and underwent clinical/experimental pain assessment.

RESULTS

There were significant correlations between the thalamic rCBF values and the pain-control beliefs of FM subjects. The strength of the relationship between clinical pain measures and thalamic rCBF values increased after adjusting for pain-control beliefs. There was a significantly different distribution pattern of rCBF values across various brain regions between the FM group and the healthy controls. There was a lower degree of correlation in the FM group between the thalamic rCBF values and the other brain regions relative to the healthy controls.

CONCLUSIONS

Significant correlations were found between thalamic rCBF values and pain belief values. These data suggest that there are baseline alterations of brain perfusion in patients with FM. rCBF values of the thalami exhibited lower correlations with respect to other brain regions thought to be involved in pain processing compared with those in healthy controls.

Magnetic resonance perfusion imaging in acute middle cerebral artery stroke: comparison of blood volume and bolus peak arrival time

Ten patients with a diagnosis of acute middle cerebral artery stroke were evaluated using perfusion magnetic resonance imaging (MRI) during bolus injection of gadolinium diethylenetriaminepentaacetic acid (GdDTPA), MR angiography, and conventional MRI. Scans were performed within 24 hours of symptoms, onset, and 5 of the 10 patients had follow-up MR scans 3 or more days later to determine radiological outcome. Perfusion data were analyzed in terms of relative regional cerebral blood volume (rCBV) and bolus peak arrival times (BAT). Although relative rCBV values overall showed no significant changes compared with contralateral regions of interest, BAT was significantly increased in both infarct and peri-infarct regions. Areas of abnormal BAT significantly exceeded areas of T(2) hyperintensity in acute studies; follow-up images indicated that the size of infarction increased to include some regions with previously abnormal BAT. BAT appears to be a more sensitive parameter for the detection of abnormal cerebral perfusion than rCBV. Used in conjunction with other MR methods, perfusion MR imaging may allow visualization of ischemic tissue at risk of infarction in acute stroke.

Minimal hepatic encephalopathy in children: evaluation with proton MR spectroscopy

BACKGROUND AND PURPOSE

Minimal hepatic encephalopathy (MHE) in children is difficult to evaluate because of lack of standardized neuropsychological tests for all age ranges. The purpose of this retrospective study of children with clinically suspected MHE was to investigate relationships between brain MR spectroscopy metabolites and biochemical markers of encephalopathy as well as measures of liver disease severity.

MATERIALS AND METHODS

A total of 12 children (age range, 9-19 years; 8 female) with clinically suspected MHE were studied by short TE brain MR spectroscopy on a 1.5T magnet. We estimated gray matter (GM) and white matter (WM) metabolite concentrations using "LCModel" software. Regional metabolite concentrations were examined for correlation with various parameters, including plasma ammonia, the ratio of branched-chain to aromatic amino acids (BCAA/AAA), model for end stage liver disease/pediatric end stage liver disease (MELD/PELD) and Child-Pugh scores, bilirubin, albumin, and platelet counts.

RESULTS

Myo-inositol (mIns) levels correlated with BCAA/AAA ratios (r = 0.86; P = .002 for GM and r = 0.77; P = .01 for WM). WM choline (Cho) levels and GM mIns levels showed significant negative correlation with ammonia levels (r = -0.58; P = .04 and r = -0.65; P = .02, respectively). A positive significant correlation trend was present for GM glutamine/glutamate (Glx) and ammonia levels (r = 0.66; P = .05). There was no correlation of brain MR spectroscopy parameters and severity of liver disease.

CONCLUSIONS

Brain MR spectroscopy metabolites in children with suspected MHE show significant correlations with plasma ammonia levels and BCAA/AAA. As in adults, brain MR spectroscopy in children may be helpful in establishing a diagnosis of MHE.

Minimal hepatic encephalopathy in children: evaluation with proton MR spectroscopy

BACKGROUND AND PURPOSE

Minimal hepatic encephalopathy (MHE) in children is difficult to evaluate because of lack of standardized neuropsychological tests for all age ranges. The purpose of this retrospective study of children with clinically suspected MHE was to investigate relationships between brain MR spectroscopy metabolites and biochemical markers of encephalopathy as well as measures of liver disease severity.

MATERIALS AND METHODS

A total of 12 children (age range, 9-19 years; 8 female) with clinically suspected MHE were studied by short TE brain MR spectroscopy on a 1.5T magnet. We estimated gray matter (GM) and white matter (WM) metabolite concentrations using "LCModel" software. Regional metabolite concentrations were examined for correlation with various parameters, including plasma ammonia, the ratio of branched-chain to aromatic amino acids (BCAA/AAA), model for end stage liver disease/pediatric end stage liver disease (MELD/PELD) and Child-Pugh scores, bilirubin, albumin, and platelet counts.

RESULTS

Myo-inositol (mIns) levels correlated with BCAA/AAA ratios (r = 0.86; P = .002 for GM and r = 0.77; P = .01 for WM). WM choline (Cho) levels and GM mIns levels showed significant negative correlation with ammonia levels (r = -0.58; P = .04 and r = -0.65; P = .02, respectively). A positive significant correlation trend was present for GM glutamine/glutamate (Glx) and ammonia levels (r = 0.66; P = .05). There was no correlation of brain MR spectroscopy parameters and severity of liver disease.

CONCLUSIONS

Brain MR spectroscopy metabolites in children with suspected MHE show significant correlations with plasma ammonia levels and BCAA/AAA. As in adults, brain MR spectroscopy in children may be helpful in establishing a diagnosis of MHE.

Crossed cerebellar diaschisis in acute stroke detected by dynamic susceptibility contrast MR perfusion imaging

BACKGROUND AND PURPOSE

Crossed cerebellar diaschisis (CCD), the decrease in blood flow and metabolism in the cerebellar hemisphere contralateral to a supratentorial stroke, is frequently reported on positron-emission tomography (PET) and single-photon emission CT (SPECT) but is rarely described with MR perfusion techniques. This study was undertaken to determine the frequency of CCD observed in acute stroke by retrospective review of a research data base of patients with acute stroke evaluated by diffusion-weighted (DWI) and dynamic contrast susceptibility perfusion MR imaging (PWI).

MATERIALS AND METHODS

PWI scans of 301 consecutive patients with acute stroke and positive DWI abnormality from a research data base were reviewed. Contralateral cerebellar hypoperfusion was identified by inspection of time-to-peak (TTP) maps for asymmetry with an absence of cerebellar abnormalities on T2-weighted scans, DWI, or disease of the vertebrobasilar system on MR angiography. In a subset of the cases, quantitative analysis of perfusion scans was performed using an arterial input function and singular value decomposition (SVD) to generate cerebral blood flow (CBF) maps.

RESULTS

A total of 47 of 301 cases (15.61%) met the criteria of CCD by asymmetry of cerebellar perfusion on TTP maps. On quantitative analysis, there was corresponding reduction of CBF by 22.75 +/- 10.94% (range, 7.45% to 52.13%) of the unaffected cerebellar hemisphere).

CONCLUSIONS

MR perfusion techniques can be used to detect CCD, though the frequency presented in this series is lower than that commonly reported in the PET/SPECT literature. Nevertheless, with its role in acute stroke and noninvasive nature, MR perfusion may be a viable alternative to PET or SPECT to study the phenomenon and clinical consequences of supratentorial stroke with CCD.

Classification of childhood white matter disorders using proton MR spectroscopic imaging

BACKGROUND AND PURPOSE

Childhood white matter disorders often show similar MR imaging signal-intensity changes, despite different underlying pathophysiologies. The purpose of this study was to determine if proton MR spectroscopic imaging ((1)H-MRSI) may help identify tissue pathophysiology in patients with leukoencephalopathies.

MATERIALS AND METHODS

Seventy patients (mean age, 6; range, 0.66-17 years) were prospectively examined by (1)H-MRSI; a diagnosis of leukoencephalopathy due to known genetic defects leading to lack of formation, breakdown of myelin, or loss of white matter tissue attenuation (rarefaction) was made in 47 patients. The diagnosis remained undefined (UL) in 23 patients. Patients with definite diagnoses were assigned (on the basis of known pathophysiology) to 3 groups corresponding to hypomyelination, white matter rarefaction, and demyelination. Choline (Cho), creatine (Cr), and N-acetylaspartate (NAA) signals from 6 white matter regions and their intra- and intervoxel (relative to gray matter) ratios were measured. Analysis of variance was performed by diagnosis and by pathophysiology group. Stepwise linear discriminant analysis was performed to construct a model to predict pathophysiology on the basis of (1)H-MRSI, and was applied to the UL group.

RESULTS

Analysis of variance by diagnosis showed 3 main metabolic patterns. Analysis of variance by pathophysiology showed significant differences for Cho/NAA (P < .001), Cho/Cr (P < .004), and NAA/Cr (P < .002). Accuracy of the linear discriminant analysis model was 75%, with Cho/Cr and NAA/Cr being the best parameters for classification. On the basis of the linear discriminant analysis model, 61% of the subjects in the UL group were classified as hypomyelinating.

CONCLUSION

(1)H-MRSI provides information on tissue pathophysiology and may, therefore, be a valuable tool in the evaluation of patients with leukoencephalopathies.

Can proton MR spectroscopic and perfusion imaging differentiate between neoplastic and nonneoplastic brain lesions in adults?

BACKGROUND AND PURPOSE

Noninvasive diagnosis of brain lesions is important for the correct choice of treatment. Our aims were to investigate whether 1) proton MR spectroscopic imaging ((1)H-MRSI) can aid in differentiating between tumors and nonneoplastic brain lesions, and 2) perfusion MR imaging can improve the classification.

MATERIALS AND METHODS

We retrospectively examined 69 adults with untreated primary brain lesions (brain tumors, n = 36; benign lesions, n = 10; stroke, n = 4; demyelination, n = 10; and stable lesions not confirmed on pathologic examination, n = 9). MR imaging and (1)H-MRSI were performed at 1.5T before biopsy or treatment. Concentrations of N-acetylaspartate (NAA), creatine (Cr), and choline (Cho) in the lesion were expressed as metabolite ratios and were normalized to the contralateral hemisphere. Dynamic susceptibility contrast-enhanced perfusion MR imaging was performed in a subset of patients (n = 32); relative cerebral blood volume (rCBV) was evaluated. Discriminant function analysis was used to identify variables that can predict inclusion in the neoplastic or nonneoplastic lesion groups. Receiver operator characteristic (ROC) analysis was used to compare the discriminatory capability of (1)H-MRSI and perfusion MR imaging.

RESULTS

The discriminant function analysis correctly classified 84.2% of original grouped cases (P < .0001), on the basis of NAA/Cho, Cho(norm), NAA(norm), and NAA/Cr ratios. MRSI and perfusion MR imaging had similar discriminatory capabilities in differentiating tumors from nonneoplastic lesions. With cutoff points of NAA/Cho < or =0.61 and rCBV > or =1.50 (corresponding to diagnosis of the tumors), a sensitivity of 72.2% and specificity of 91.7% in differentiating tumors from nonneoplastic lesions were achieved.

CONCLUSION

These results suggest a promising role for (1)H-MRSI and perfusion MR imaging in the distinction between brain tumors and nonneoplastic lesions in adults.

Proton MR spectroscopic imaging in ataxia-telangiectasia

OBJECT

Ataxia-telangiectasia (A-T) is a recessively inherited neurodegenerative disorder with prominent progressive ataxia and cerebellar degeneration, as well as manifest abnormalities of tone, posture, and movement suggesting extrapyramidal dysfunction. In this study, we tested the hypothesis that regional metabolite levels, as measured by proton magnetic resonance spectroscopic imaging, would be abnormal in patients with A-T in the posterior fossa and basal ganglia, reflecting the underlying neurodegenerative processes in these regions.

METHODS

Spectroscopic images of N-acetyl aspartate (NAA), choline (Cho), and creatine (Cr) were obtained in 8 patients with A-T and 8 age-matched controls. Normalized metabolite levels were compared between A-T patients and control subjects in various regions of interest, including the cerebellum, brainstem, and basal ganglia.

RESULTS

A-T patients were distinguished from controls by the profound loss of all metabolites in the cerebellar vermis (NAA, p < 0.01; Cr and Cho, p < 0.05) and a trend for decreased metabolites within the cerebellar hemispheres. No abnormalities were detected in the basal ganglia.

CONCLUSIONS

Proton MR spectroscopic features in A-T closely correlate with the morphologic neuroimaging findings of posterior fossa atrophy. Although symptoms suggesting extrapyramidal dysfunction are part of the A-T phenotype, these are not associated with altered metabolite levels in the basal ganglia.

Spectroscopic evidence of cerebral axonopathy in patients with "pure" adrenomyeloneuropathy

BACKGROUND

Adrenomyeloneuropathy (AMN) is the adult variant of X-linked adrenoleukodystrophy. The disease pathology is usually limited to spinal cord and peripheral nerves, and when this is the case, it is referred to as "pure" AMN. Histopathology shows cerebral involvement even in pure AMN; however, not much is known about the nature, extent, and clinical relevance of these findings.

OBJECTIVE

To investigate brain involvement in AMN patients with normal MRI, employing multislice MR spectroscopic imaging.

METHODS

Twelve men with pure AMN were compared with 19 age-matched healthy volunteers. Metabolite ratios (N-acetylaspartate [NAA]/choline [Cho], NAA/creatine [Cr], and Cho/Cr) were measured from seven brain regions. Global metabolite ratios were generated as an average of these seven regional ratios. The Expanded Disability Status Scale (EDSS) was used for neurologic evaluation.

RESULTS

The patients with AMN showed reduced global NAA/Cho (AMN 1.40 +/- 0.16 vs controls 1.75 +/- 0.34; p = 0.003)) and global NAA/Cr (AMN 2.32 +/- 0.13 vs controls 2.62 +/- 0.43; p = 0.03). Regionally, NAA/Cho was lowered in the internal capsule (AMN 1.30 +/- 0.20 vs controls 1.69 +/- 0.37; p = 0.002) and in parieto-occipital white matter (AMN 1.45 +/- 0.19 vs controls 1.78 +/- 0.55; p = 0.04). NAA/Cr was lowered in parieto-occipital white matter (AMN 2.34 +/- 0.31 vs controls 2.83 +/- 0.71; p = 0.04). EDSS demonstrated an inverse association with global NAA/Cr (r = -0.65, p = 0.02) and NAA/Cr in centrum semiovale (r = -0.73, p = 0.006) and in parieto-occipital white matter (r = -0.64, p = 0.02). Cho/Cr was not significantly elevated.

CONCLUSIONS

(1)H-MR spectroscopic imaging is able to detect biochemical abnormalities suggestive of axonal damage even in the brains of patients with pure adrenomyeloneuropathy. The axonopathy is most prominent in internal capsule and parieto-occipital white matter and may contribute to clinical disability.

Leukoencephalopathy, cerebral calcifications, and cysts

We describe three cases of the rare syndrome of leukoencephalopathy, brain calcifications, and cysts. Conventional MRI, proton spectroscopy, and diffusion-weighted imaging yielded additional information on the disease. Imaging findings favor increased water content rather than a demyelinating process in the pathophysiology of this disease. Clinical features of Coats disease and consanguinity were also encountered.

Perfusion-weighted MRI as a marker of response to treatment in acute and subacute stroke

We carried out baseline and short-term follow-up MRI, including perfusion-weighted imaging (PWI) and tests of neurologic and cognitive function on 15 consecutive patients with large-vessel ischemic stroke who showed a persistent large perfusion-diffusion mismatch at enrollment up to seven days after the onset of symptoms. Of these, ten underwent induced blood pressure elevation with phenylephrine and oral medications (in eight) or intravenous fluids (in two) with the goal of improving perfusion; five had no such treatment. Significant functional improvement was defined by a reduction of 3 or more points on the NIH stroke scale (NIHSS). Significant improvement in perfusion was defined by a reduction in the volume of hypoperfused brain by 30 cc on PWI using time-to-peak (TTP) maps, without enlargement of the infarct. There was a strong, statistically significant association between improved function and improved perfusion: six (75%) of eight patients who improved in function, but none of the seven who did not, showed a reduction in volume of hypoperfused brain. All six patients who met the perfusion goal, and only two (22%) of nine who did not showed significant functional improvement (Fisher's exact: P < 0.01). There were no differences between patients who improved functionally and those who did not with respect to age, initial volume of abnormality on DWI or PWI, initial NIHSS, or changes on DWI. These findings indicate that reduction in volume of hypoperfused brain on PWI is a marker of response to treatment to improve perfusion even in subacute stroke and that partial reperfusion of regions of salvageable but dysfunctional tissue is a mechanism of improved function associated with induced blood pressure elevation.

A pilot randomized trial of induced blood pressure elevation: effects on function and focal perfusion in acute and subacute stroke

BACKGROUND

Small, unrandomized studies have indicated that pharmacologically induced blood pressure elevation may improve function in ischemic stroke, presumably by improving blood flow to ischemic, but noninfarcted tissue (which may be indicated by diffusion-perfusion mismatch on MRI). We conducted a pilot, randomized trial to evaluate effects of pharmacologically induced blood pressure elevation on function and perfusion in acute stroke.

METHODS

Consecutive series of patients with large diffusion-perfusion mismatch were randomly assigned to induced blood pressure elevation ('treated' patients, n = 9) or conventional management ('untreated' patients, n = 6).

RESULTS

There were no significant differences between groups at baseline. NIH Stroke Scale (NIHSS) scores were lower (better) in treated versus untreated patients at day 3 (mean 5.6 vs. 12.3; p = 0.01) and week 6-8 (mean 2.8 vs. 9.7; p < 0.04). Treated (but not untreated) patients showed significant improvement from day 1 to day 3 in NIHSS score (from mean 10.2 to 5.6; p < 0.002), cognitive score (from mean 58.7 to 27.9% errors; p < 0.002), and volume of hypoperfused tissue (mean 132 to 58 ml; p < 0.02). High Pearson correlations between the mean arterial pressure (MAP) and accuracy on daily cognitive tests indicated that functional changes were due to changes in MAP.

CONCLUSION

Results warrant a full-scale, double-blind clinical trial to evaluate the efficacy and risk of induced blood pressure elevation in selective patients with acute/subacute stroke.

MRI and proton MRSI in women heterozygous for X-linked adrenoleukodystrophy

OBJECTIVE

To utilize neuroimaging procedures to assess the extent of cerebral involvement in female subjects heterozygous for X-linked adrenoleukodystrophy (X-ALD).

METHODS

Brain MRI studies were performed in 76 female subjects heterozygous for X-ALD (mean age 43 years, range 8 to 75 years). Sixty-five had clinical evidence of spinal cord involvement resembling that in males with adrenomyeloneuropathy (AMN), two had clinical evidence of cerebral involvement, and nine showed no neurologic abnormality. Readers blinded to clinical findings further analyzed abnormal MRI studies. In eight women whose MRI results were normal, four-slice long echo time MRS imaging (MRSI) studies were performed and compared to those of eight age-matched controls.

RESULTS

MRI results were normal in 65 subjects and abnormal in 11. In eight of the latter group, the MRI changes were judged to be due to causes other than X-ALD. Lesions were attributed to X-ALD in the remaining three. Two of these patients had lesions that resembled those in male patients with cerebral X-ALD. In one patient with a mild AMN-like syndrome, brain MRI abnormalities were confined to the corticospinal tract. When compared to those of controls, MRSI studies in eight female patients with normal results on brain MRI showed a significant reduction of N-acetylaspartate/creatine and N-acetylaspartate/choline ratios in the internal capsule and corticospinal projection fibers. The N-acetylaspartate/choline ratio was significantly reduced in the parieto-occipital white matter and the choline/creatine ratio was significantly increased in the frontal white matter.

CONCLUSION

Brain involvement demonstrable by MRI is rare in female subjects heterozygous for X-ALD, including those who have clinical evidence of spinal cord involvement. Nevertheless, N-acetylaspartate levels are reduced in the corticospinal projection fibers in female subjects with normal results on MRI, suggesting axonal dysfunction.

Rapid method for correction of CSF partial volume in quantitative proton MR spectroscopic imaging

Partial volume effects with cerebrospinal fluid (CSF), if uncorrected, can lead to underestimation of metabolite concentrations in quantitative proton magnetic resonance spectroscopic imaging (MRSI) of the brain. A rapid method for the correction of CSF partial volume effects is described based on selective CSF imaging using long echo time (TE) fast spin echo (FSE) magnetic resonance imaging (MRI). In order to achieve maximum suppression of signal from brain parenchyma, the FSE sequence is coupled with an inversion recovery (IR) pulse. Scan time is minimized using single shot (SS) IR-FSE. The method is validated against a current "gold standard" for the determination of CSF volumes, namely, segmented 3D spoiled gradient-echo (SPGR) scans. Excellent agreement in CSF percentage determined by the two methods was found (linear regression analysis: slope = 0.99 +/- 0.02, intercept = 2.08 +/- 0.45; mean +/- standard errors, R = 0.93) in pooled data from four healthy subjects. An example of the use of SS-IR-FSE for partial volume correction in a leukodystrophy patient with T(2) hyperintense lesions is demonstrated. SS-IR-FSE is a simple and rapid method for applying partial volume corrections in quantitative proton MRSI, which may be of particular value in the clinical environment when time constraints do not allow longer, perhaps more accurate segmentation methods to be used.

Subcortical aphasia and neglect in acute stroke: the role of cortical hypoperfusion

We have hypothesized that most cases of aphasia or hemispatial neglect due to acute, subcortical infarct can be accounted for by concurrent cortical hypoperfusion. To test this hypothesis, we demonstrate: (i) that pure subcortical infarctions are associated with cortical hypoperfusion in subjects with aphasia/neglect; (ii) that reversal of cortical hypoperfusion is associated with resolution of the aphasia; and (iii) that aphasia/neglect strongly predicts cortical ischaemia and/or hypoperfusion. We prospectively evaluated a consecutive series of 115 patients who presented within 24 h of onset or progression of stroke symptoms, with MRI sequences including diffusion weighted imaging (DWI) and perfusion weighted imaging (PWI), and detailed testing for aphasia or hemispatial neglect. The association between aphasia or neglect and cortical infarct (or dense ischaemia) on DWI and cortical hypoperfusion indicated by PWI, was evaluated with chi-squared analyses. Fisher exact tests were used for analyses with small samples. Cases of DWI lesion restricted to subcortical white matter and/or grey matter structures (n = 44) were examined for the presence of aphasia or neglect, and for the presence of cortical hypoperfusion. In addition, subjects who received intervention to restore perfusion were evaluated with DWI, PWI, and cognitive tests before and after intervention. Finally, the positive predictive value of the cognitive deficits for identifying cortical abnormalities on DWI and PWI were calculated from all patients. Of the subjects with only subcortical lesions on DWI in this study (n = 44), all those who had aphasia or neglect showed concurrent cortical hypoperfusion. Among the patients who received intervention that successfully restored cortical perfusion, 100% (six out of six) showed immediate resolution of aphasia. In the 115 patients, aphasia and neglect were much more strongly associated with cortical hypoperfusion (chi(2) = 57.3 for aphasia; chi(2) = 28.7 for neglect; d.f. = 1; P < 0.000001 for each), than with cortical infarct/ischaemia on DWI (chi(2) = 8.5 for aphasia; chi(2) = 9.7 for neglect; d.f. = 1; P < 0.005 for each). Aphasia showed a much higher positive predictive value for cortical abnormality on PWI (95%) than on DWI (62%), as did neglect (100% positive predictive value for PWI versus 74% for DWI). From these data we conclude that aphasia and neglect due to acute subcortical stroke can be largely explained by cortical hypoperfusion.

Contrasts in cortical magnesium, phospholipid and energy metabolism between migraine syndromes

BACKGROUND

Previous single voxel (31)P MRS pilot studies of migraine patients have suggested that disordered energy metabolism or Mg(2+) deficiencies may be responsible for hyperexcitability of neuronal tissue in migraine patients. These studies were extended to include multiple brain regions and larger numbers of patients by multislice (31)P MR spectroscopic imaging.

METHODS

Migraine with aura (MWA), migraine without aura (MwoA), and hemiplegic migraine patients were studied between attacks by (31)P MRS imaging using a 3-T scanner.

RESULTS

Results were compared with those in healthy control subjects without headache. In MwoA, consistent increases in phosphodiester concentration [PDE] were measured in most brain regions, with a trend toward increase in [Mg(2+)] in posterior brain. In MWA, phosphocreatine concentration ([PCr]) was decreased to a minor degree in anterior brain regions and a trend toward decreased [Mg(2+)] was observed in posterior slice 1, but no consistent changes were found in phosphomonoester concentration [PME], [PDE], inorganic phosphate concentration ([Pi]), or pH. In hemiplegic migraine patients, [PCr] had a tendency to be lower, and [Mg(2+)] was significantly lower than in the posterior brain regions of control subjects. Trend analysis showed a significant decrease of brain [Mg(2+)] and [PDE] in posterior brain regions with increasing severity of neurologic symptoms.

CONCLUSIONS

Overall, the results support no substantial or consistent abnormalities of energy metabolism, but it is hypothesized that disturbances in magnesium ion homeostasis may contribute to brain cortex hyperexcitability and the pathogenesis of migraine syndromes associated with neurologic symptoms. In contrast, migraine patients without a neurologic aura may exhibit compensatory changes in [Mg(2+)] and membrane phospholipids that counteract cortical excitability.

Proton MR spectroscopic imaging predicts lesion progression on MRI in X-linked adrenoleukodystrophy

BACKGROUND

The phenotypic expression of X-linked adrenoleukodystrophy (X-ALD) ranges from the rapidly progressive childhood cerebral form to the milder adrenomyeloneuropathy in adults. It is not possible to predict phenotype by mutation analysis or biochemical assays. Multislice proton MRS imaging (MRSI) has previously detected more extensive brain abnormalities in X-ALD than conventional MRI, which has been suggested to predict impending demyelination. However, the significance of these changes is unclear.

OBJECTIVE

The purpose of this study was to determine the long-term sensitivity and specificity of MRSI for disease progression in X-ALD.

METHODS

Twenty-five patients with X-ALD were investigated (average age, 15 years; range, 2-43 years) with MRI and proton MRSI at baseline and follow-up MRI over a mean period of 3.5 years. Eight patients had normal MRI findings at baseline and on follow-up (noncerebral group), 11 had abnormal MRI at baseline and no change on follow-up (cerebral nonprogressive group), and 6 had progressive MRI abnormalities (cerebral progressive group). On MRSI, voxels were analyzed in the normal MRI-appearing perilesional white matter, or in the corresponding area in the noncerebral group.

RESULTS

The concentration ratio of N-acetylaspartate (NAA) to choline was the most sensitive indicator of disease progression. The average NAA/choline ratio was 5.99 for the noncerebral group, 5.75 for the cerebral nonprogressive group, and 3.74 for the cerebral progressive group (p = 0.002). At a cut-off point of 5.0, the NAA/choline ratio predicted disease progression in all patients with six cerebral progressive disease (sensitivity 100%). The specificity was 83%, the positive predictive value was 66%, and the negative predictive value was 100%.

CONCLUSIONS

Multislice proton MRS imaging is able to identify impending or beginning degeneration in white matter that still appears normal on conventional MRI. Multislice proton MRSI may be a suitable technique for the prediction of lesion progression on MRI in X-linked adrenoleukodystrophy.

Reperfusion of specific brain regions by raising blood pressure restores selective language functions in subacute stroke

We report a series of six single subject studies examining the effects of pharmacological blood pressure elevation on regional brain perfusion and language function. Previous reports indicate that hypoperfusion of specific brain regions, as delineated by magnetic resonance perfusion weighted imaging (PWI), is associated with disruption of selective lexical functions. On this basis, we hypothesized that reperfusion of the same regions, in the absence of infarct in that region, would restore the associated lexical function. We present five patients with impaired lexical-semantics associated with poor perfusion, but not infarction, of Brodmann's area 22 (BA 22), and one patient with impaired lexical-semantics and a superimposed deficit in retrieving the phonological representations of words, associated with poor perfusion Brodmann's area 37 (BA 37) as well as BA 22. Each patient was treated with induced blood pressure elevation to increase perfusion of the ischemic and dysfunctional tissue. Daily testing of naming and comprehension, with stimulus sets matched for frequency, familiarity, and length, showed improved lexical-semantics in the patients who showed reperfusion of BA 22 and improved oral naming (but not lexical-semantics) in the patient who showed reperfusion of BA 37. These cases illustrate that loss of function with hypoperfusion of a circumscribed area of the brain, and recovery of the same function with improved perfusion of that brain region, can reveal brain/language relationships prior to reorganization after brain injury.

Neuroimaging studies in Rett syndrome

Neuroimaging is a key instrument for determining structural and in vivo functional status of the brain, non-invasively. Multiple approaches can now determine aspects of anatomic and neurochemical changes in brain, and have been utilized effectively in Rett Syndrome patients to understand the biological basis of this neurodevelopmental disorder. Studies performed at our institute include volumetric analyses of MRI, magnetic resonance spectroscopy (MRS), diffusion tensor imaging (DTI), cerebral blood flow measurements with MRI, and positron emission tomography scans (PET). These studies have provided considerable insight into mechanisms underlying the clinical features of this disease. Volumetric analyses suggest that decreased brain volume in RS results from global reductions in both gray and white matter of the brain. A selective vulnerability of the frontal lobes is evidenced by the preferential reduction of blood flow, increased choline and reduced n-acetyl aspartate (NAA) by MRS, and increased glucose uptake in these same regions as shown by ((18)F)-fluorodeoxyglucose (FDG) PET scans. We hypothesize that the increased glucose uptake relates to increased glutamate cycling in synapses. The resulting neuroexcitotoxic injury to the developing brain contributes to the seizures, behavioral disturbance and respiratory irregularities commonly seen in phases 1 and 2 of this disorder.

Hypoperfusion of Wernicke's area predicts severity of semantic deficit in acute stroke

Based on earlier findings that the presence of word comprehension impairment (a deficit in the meaning of words, or lexical semantics) in acute stroke was strongly associated with the presence of hypoperfusion or infarct in Wernicke's area, we tested the hypothesis that the severity of word comprehension impairment was correlated with the magnitude of delay in perfusion of Wernicke's area on magnetic resonance perfusion-weighted imaging. Eighty patients were prospectively studied within 24 hours of onset or progression of acute left hemisphere stroke symptoms, with diffusion-weighted imaging, perfusion-weighted imaging, and detailed language tests. For 50 patients without infarct in Wernicke's area, we found a strong Pearson correlation between the rate of errors on a word comprehension test and the mean number of seconds of delay in time-to-peak concentration of contrast in Wernicke's area, relative to the homologous region on the right. These results add further evidence for the crucial role of Wernicke's area (Brodmann's area 22) in word comprehension and indicate that the magnitude of delay on PWI may be a gross indicator of tissue dysfunction.

Quantitative proton MR spectroscopic imaging of normal human cerebellum and brain stem

Quantitative, multislice proton MR spectroscopic imaging (MRSI) was used to investigate regional metabolite levels and ratios in the normal adult human posterior fossa. Six normal volunteers (36 +/- 3 years, five male, one female) were scanned on a 1.5 T scanner using multislice MRSI at long echo time (TE 280 msec). The entire cerebellum was covered using three oblique-axial slice locations, which also included the pons, mid-brain, insular cortex, and parieto-occipital lobe. Concentrations of N-acetylaspartate (NAA), choline (Cho), and creatine (Cr) were estimated using the phantom replacement technique. Regional variations of the concentrations were assessed using ANOVA (P < 0.05). High-resolution MRSI data was obtained in all subjects and brain regions examined. Metabolite concentrations (mM) (mean +/- SD) were as follows: cerebellar vermis: 2.3 +/- 0.4, 8.8 +/- 1.7 and 7.6 +/- 1.0 for Cho, Cr, and NAA respectively; cerebellar hemisphere: 2.2 +/- 0.6, 8.9 +/- 2.1, 7.5 +/- 0.8; pons 2.2 +/- 0.5, 4.3 +/- 1.1, 8.3 +/- 0.9; insular cortex, 1.8 +/- 0.5, 7.8 +/- 2, 8.0 +/- 1.1, parieto-occipital gray matter, 1.3 +/- 0.3, 5.7 +/- 1.1, 7.2 +/- 0.9, and occipital white matter, 1.4 +/- 0.3, 5.3 +/- 1.3, 7.5 +/- 0.8. Consistent with previous reports, significantly higher levels of Cr were found in the cerebellum compared to parieto-occipital gray and occipital white matter, and pons (P < 0.0001). NAA was essentially uniformly distributed within the regions chosen for analysis, with the highest level in the pons (P < 0.04). Cho was significantly higher in the cerebellum and pons than parieto-occipital gray and occipital white matter (P < 0.002) and was also higher in the pons than in the insular cortex (P < 0.05). Quantitative multislice MRSI of the posterior fossa is feasible and significant regional differences in metabolite concentrations were found.

Proton magnetic resonance spectroscopy of choroid plexus tumors in children

A variety of lesions may present as intraventricular masses in children. We report quantitative proton magnetic resonance spectroscopy (MRS) of two intraventricular tumors of the choroid plexus: choroid plexus carcinoma (CPC) and choroid plexus papilloma (CPP). Both lesions were characterized by high levels of choline-containing compounds and a complete absence of creatine and the neuronal/axonal marker N-acetyl aspartate. The CPC showed higher levels of choline compared to the CPP, and it also had elevated lactate. These preliminary results, if confirmed in a larger cohort of patients, indicate that proton MRS may have a role in the presurgical diagnosis of choroid plexus tumors in children, which may also have important implications for therapy and prognosis.

Quantitative proton MR spectroscopic imaging in acute disseminated encephalomyelitis

Serial MR imaging and quantitative proton MR spectroscopic imaging (MRSI) findings of a 4-year-old boy with acute disseminated encephalomyelitis (ADEM) are reported. Over a 2-month period characterized by an initial illness and two relapses, each with full recovery, MR imaging exhibited the appearance and disappearance of multifocal lesions throughout the CNS that correlated only partly with the neurologic impairment. During one relapse, MRSI revealed low levels of N-acetylaspartate (NAA) within the regions of prolonged T2 signal intensity. All other metabolites were normal. At follow-up, the MR imaging and MRSI abnormalities had fully resolved. MRSI might play an important role in the diagnosis of ADEM, as well as in the elucidation of underlying pathophysiologic processes in this poorly defined disorder of children. This case demonstrates that reduced levels of NAA are not always associated with neuronal loss, irreversible tissue damage, or poor neurologic outcome.

Multi-slice proton MR spectroscopy and diffusion-weighted imaging in methylmalonic acidemia: report of two cases and review of the literature

SUMMARY

Methylmalonic acidemia is an inborn disorder of amino acid metabolism that commonly presents with neurologic deficits. We present the results of multi-slice proton MR spectroscopy and diffusion-weighted imaging of the brain in two patients with methylmalonic acidemia. The findings consisted of restricted diffusion and elevated lactate in the globi pallidi, compatible with acute infarction (patient 1) and elevated lactate in CSF (patient 2).

Single-voxel proton MRS of the human brain at 1.5T and 3.0T

Single-voxel proton spectra of the human brain were recorded in five subjects at both 1.5T and 3.0T using the STEAM pulse sequence. Data acquisition parameters were closely matched between the two field strengths. Spectra were recorded in the white matter of the centrum semiovale and in phantoms. Spectra were compared in terms of resolution and signal-to-noise ratio (SNR), and transverse relaxation times (T(2)) were estimated at both field strengths. Spectra at 3T demonstrated a 20% improvement in sensitivity compared to 1.5T at short echo times (TE = 20 msec), which was lower than the theoretical 100% improvement. Spectra at long echo times (TE = 272 msec) exhibited similar SNR at both field strengths. T(2) relaxation times were almost twofold shorter at the higher field strength. Spectra in phantoms demonstrated significantly improved resolution at 3T compared to 1.5T, but resolution improvements in in vivo spectra were almost completely offset by increased linewidths at higher field.

Diffusion- and perfusion-weighted brain magnetic resonance imaging in patients with neurologic complications after cardiac surgery

BACKGROUND

Neurologic complications after cardiac surgery include stroke, encephalopathy, and persistent cognitive impairments. More precise neuroimaging of patients with these complications may lead to a better understanding of the etiology and treatment of these disorders.

OBJECTIVE

To study the pattern of ischemic changes on diffusion- and perfusion-weighted magnetic resonance imaging (DWI, and MRPI, respectively) in patients with neurologic complications after cardiac surgery.

METHODS

All records were reviewed of our patients undergoing cardiac surgery in the previous year who also underwent postoperative DWI or MRPI. Neurologic symptoms, vascular studies, and the pattern of ischemic changes were recorded. Acute ischemic lesions were classified as having a territorial, watershed, or lacunar pattern of infarction. Patients with multiple territorial infarcts in differing vascular distributions that were not explained by occlusive vascular lesions were classified as having multiple emboli.

RESULTS

Fourteen patients underwent DWI and 4 underwent MRPI. Acute infarcts were found in 10 of 14 patients by DWI as compared with 5 of 12 patients by computed tomography. Eight patients presented with encephalopathy (associated with focal neurologic deficits in 4), 4 with focal deficits alone, and 2 with either fluctuating symptoms or transient ischemic attacks. Among patients with encephalopathy, 7 of 8 had patterns of infarction suggestive of multiple emboli, including 3 of 4 patients with no focal neurologic deficits. Several patients had combined watershed and multiple embolic patterns of ischemia. Findings of MRPI studies were abnormal in 2 of 4 patients, showing diffusion-perfusion mismatch; both patients had either fluctuating deficits or transient ischemic attacks, and their conditions improved with blood pressure manipulation.

CONCLUSIONS

In patients with neurologic symptoms after cardiac surgery, DWI is more sensitive to ischemic change than computed tomographic scanning and can demonstrate patterns of infarction that may help us understand etiology. The most common pattern was multiple embolic infarcts. Preliminary experience with MRPI suggests that some patients have persistent diffusion-perfusion mismatch after surgery and may benefit from therapeutic intervention.

Restoring blood pressure reperfused Wernicke's area and improved language

Longitudinal clinical and imaging data from a patient who sustained a left frontal-temporal stroke with hypoperfusion of the adjacent Wernicke's area are reported. His language deficits were partially ameliorated by pharmacologically increasing his blood pressure, and were exacerbated when blood pressure dropped. There was a striking temporal and statistical correlation between mean arterial pressure and language accuracy. MR perfusion imaging showed that language gains were accompanied by improved perfusion of Wernicke's area when mean arterial pressure was increased.

Broadband proton decoupling for in vivo brain spectroscopy in humans

A new decoupling sequence, PBAR, is described for broadband heteronuclear decoupling in vivo in humans at 1.5T. The sequence uses non-adiabatic, frequency- and amplitude-modulated inversion pulses designed to minimize decoupling sidebands at low applied gammaB(2) RF field levels and to cover only the narrow range of resonance offsets encountered in practice. The offset dependence of the decoupling efficiency of PBAR is demonstrated and compared to the conventional WALTZ-4 sequence. At the same average power levels, PBAR had slightly reduced bandwidth but significantly less intense decoupling sidebands. Applications of PBAR are shown in vivo in the human brain both for (31)P and natural abundance (13)C spectroscopy using volume decoupling coils. The PBAR sequence allows whole brain [(1)H]-[13]C decoupling to be performed at 1.5T with a standard head coil within FDA guidelines for RF power deposition. Magn Reson Med 45:226-232, 2001.

MRI measurement of brain iron in patients with restless legs syndrome

Brain iron insufficiency in the restless legs syndrome (RLS) has been suggested by a prior CSF study. Using a special MRI measurement (R2'), the authors assessed regional brain iron concentrations in 10 subjects (five with RLS, five controls). R2' was significantly decreased in the substantia nigra, and somewhat less significantly in the putamen, both in proportion to RLS severity. The results show the potential utility of this MRI measurement, and also indicate that brain iron insufficiency may occur in patients with RLS in some brain regions.

MR spectroscopy study of dichloroacetate treatment after ischemic stroke

In a double-blind, placebo-controlled study, we used 1H MR spectroscopy to assess the effect of a single infusion of sodium dichloroacetate on lesion lactate 1 to 5 days after ischemic stroke. Apparent trends toward a reduction in lactate/N-acetyl compound ratios were seen at the higher drug doses employed, and in patients treated in the first 2 days following infarction. Use of spectroscopic measures as endpoints is feasible in acute stroke clinical trials.

Diffusion tensor MR imaging of the brain: effect of diffusion weighting on trace and anisotropy measurements

BACKGROUND AND PURPOSE

In human brain, the relationship between MR signal and b value is complicated by cerebral perfusion, restricted diffusion, anisotropy, cellular membrane permeability, and active cellular transport of water molecules. Our purpose was to evaluate the effect of the number and strength of diffusion-sensitizing gradients on measured isotropic apparent diffusion coefficients (ADCi), fractional anisotropy (FA), and their respective SD in different anatomic locations of the brain.

METHODS

Quantitative apparent diffusion coefficients and diffusion anisotropy brain maps were obtained from 10 healthy volunteers by using six different levels of diffusion weighting (b0 = 0, bl = 160, b2 = 320, b3 = 480, b4 = 640, and b5 = 800 s/mm2), applied sequentially in six different directions (Gxx, Gyy, Gzz, Gxy, Gxz, Gyz) and coupled to a single-shot spin-echo echo-planar (2,045/115 [TR/TE]) MR imaging technique. ADCi, FA, eigenvalues (lambda1, lambda2, lamdba3)1 of the principal eigenvectors, and their respective SD were measured from seven different anatomic locations in the brain. Repeated measures analysis of variance was used to evaluate for the existence of significant differences in the average and SD of the calculated ADCi and FA as a function of the number and strength of b values. When a difference existed, the Bonferroni t method was used for paired comparisons of the groups.

RESULTS

The measured ADCi was affected by the number and strength of b values (P < .05). The SD of the ADCi was affected by the strength (P < .05) but not the number of b values (P > .05). The measured FA was unaffected by the number and strength of b values (P > .05). The SD was affected by the number and strength of b values (P < .05).

CONCLUSION

The number and strength of b values do influence measures of diffusion and anisotropy. Attention to the choice of diffusion sensitization parameters is important in decisions regarding clinical feasibility (acquisition time) and normative measures.

MR perfusion imaging reveals regions of hypoperfusion associated with aphasia and neglect

OBJECTIVE

To evaluate diffusion-weighted imaging (DWI) and MR perfusion imaging (MRPI) as tools for identifying regions of infarct and hypoperfusion associated with aphasia and neglect in hyperacute stroke. Secondary goal: to establish a functional correlate of a radiologically defined "ischemic penumbra."

METHODS

Forty subjects underwent DWI, MRPI, and standardized tests for lexical deficits or hemispatial neglect within 24 hours of stroke onset or progression. Ten patients had repeat DWI, MRPI, and cognitive testing after 3 days (in some cases after reperfusion therapy). Pearson correlations between error rate on cognitive testing and volume of abnormality on DWI versus MRPI were determined at each time period, and regions of hypoperfusion corresponding to specific cognitive deficits were identified.

RESULTS

Error rate was more strongly correlated with volume of hypoperfused tissue on MRPI (r = 0.65 to 0.93; p < 0.01 to p < 0.0003) than with volume of lesion on DWI (r = 0.54 to 0.75; p = 0.14 to p < 0.01) for dominant and nondominant hemisphere stroke, at each time point. Forty-eight percent of aphasic patients and 67% of those with hemispatial neglect had either no infarct or only small subcortical infarct on DWI, but had focal cortical hypoperfusion. Patients who had successful reperfusion therapy showed resolution of the hypoperfused territory beyond the infarction on repeat MRPI and showed resolution of corresponding deficits.

CONCLUSIONS

MRPI shows regions of hypoperfused cortex associated with lexical deficits or hemispatial neglect, even when DWI shows no infarct or only small subcortical infarct. MRPI-DWI mismatch indicates regions of functionally salvageable tissue.

Thalamic involvement in neurofibromatosis type 1: evaluation with proton magnetic resonance spectroscopic imaging

Neurofibromatosis type 1 is a common autosomal dominant disorder associated with learning disabilities. In addition to gliomas and other tumors, T2 hyperintense lesions (unidentified bright objects or UBOs) are frequently found in the globus pallidus, cerebellum, and white matter regions. To better characterize supratentorial UBO functional significance, we studied by quantitative magnetic resonance spectroscopic imaging (MRSI) 9 male subjects with neurofibromatosis type 1 (age, 6-19 years) and 9 age-matched and sex-matched controls. Maps of the anatomical distribution of the metabolites choline (Cho), N-acetylaspartate (NAA), and creatine were calculated in four axial 15-mm slices. Absolute metabolite concentrations within UBOs, unaffected globus pallidus, and thalami demonstrated an age-related pattern, characterized by elevated Cho and relatively preserved NAA in younger subjects (<10 years) and reduced NAA and normal Cho in older subjects. These changes were found in both UBOs and thalami but were only significant for NAA, NAA/creatine, and NAA/Cho in the latter region. Decreases in NAA ratios were most severe in the thalami of subjects with UBOs in the globus pallidus, whereas UBOs showed similar but milder abnormalities than those in the thalamus. We speculate that the MRSI metabolic abnormality may represent a more generalized phenomenon, without a T2 signal counterpart in the affected brain regions. Based on the neuropathological study by DiPaolo and colleagues (1995), we postulate that Cho elevations reflect increased myelin turnover in areas of intramyelinic edema, which is followed by neuropil injury (reduced NAA). Temporal progression and behavioral correlates of these MRSI changes deserve further exploration.

Metabolic heterogeneity at the level of the anterior and posterior commissures

Multislice, 2D proton spectroscopic imaging was performed in six healthy volunteers at long echo time (TE = 280 msec). The center of the most inferior of three slices was placed directly at the level of the line connecting the anterior and posterior commissures. Significant regional variations in metabolite levels were observed. In particular, based on statistical analysis, levels of choline were significantly high in insular cortex, thalamus, and centrum semiovale compared to other brain regions such as parietal or occipital gray and white matter. NAA levels were highest in the centrum semiovale white matter, while creatine levels were relatively constant. Globus pallidus exhibited lower signal intensities and increased linewidths for all metabolites. No spectra could be obtained from the inferior frontal lobe because of field inhomogeneity. These data show that the metabolism, and perhaps the underlying cellular composition, of thalamus and insular cortex appears to be different from other neocortical gray matter. Normal regional variations in the brain spectra should be considered when evaluating pathological conditions.

Diffusion-weighted MRI and proton MR spectroscopic imaging in the study of secondary neuronal injury after intracerebral hemorrhage

BACKGROUND AND PURPOSE

Cerebral ischemia has been proposed as contributing mechanism to secondary neuronal injury after intracerebral hemorrhage (ICH). Possible tools for investigating this hypothesis are diffusion-weighted (DWI) and proton magnetic resonance spectroscopic imaging ((1)H-MRSI). However, magnetic field inhomogeneity induced by paramagnetic blood products may prohibit the application of such techniques on perihematoma tissue. We report on the feasibility of DWI and (1)H-MRSI in the study of human ICH and present preliminary data on their contribution to understanding perihematoma tissue functional and metabolic profiles.

METHODS

Patients with acute supratentorial ICH were prospectively evaluated using DWI and (1)H-MRSI. Obscuration of perihematoma tissue with both sequences was assessed. Obtainable apparent diffusion coefficient (Dav) and lactate spectra in perihematoma brain tissue were recorded and analyzed.

RESULTS

Nine patients with mean age of 63.4 (36 to 87) years were enrolled. Mean time from symptom onset to initial MRI was 3.4 (1 to 9) days; mean hematoma volume was 35.4 (5 to 80) cm(3). Perihematoma diffusion values were attainable in 9 of 9 patients, and (1)H-MRSI measures were obtainable in 5 of 9 cases. Dav in perihematoma regions was 172.5 (120.0 to 302.5)x10(-5) mm(2)/s and 87.6 (76.5 to 102.1)x10(-5) mm(2)/s in contralateral corresponding regions of interest (P=0.002). One patient showed an additional area of reduced Dav with normal T(2) intensity, which suggests ischemia. (1)H-MRSI revealed lactate surrounding the hematoma in 2 patients.

CONCLUSIONS

DWI and (1)H-MRSI can be used in the study of ICH patients. Our preliminary data are inconsistent with ischemia as the primary mechanism for perihematoma tissue injury. Further investigation with advanced MRI techniques will give a clearer understanding of the role that ischemia plays in tissue injury after ICH.

Quantitative 1H MR spectroscopic imaging in early Rett syndrome

OBJECTIVE

To determine cerebral regional concentrations of N-acetyl aspartate (NAA), total choline (Cho), and total creatine (Cr) in Rett syndrome (RS) using 1H magnetic resonance spectroscopic imaging (MRSI).

BACKGROUND

The biochemical defect underlying RS is unknown. Because in vivo MRSI can detect important cerebral metabolites, MRSI has a potential to reveal impairment of regional cerebral metabolism in RS noninvasively.

METHODS

High-resolution, multislice 1H MRSI was carried out in 17 girls with RS. The control group consisted of nine healthy children.

RESULTS

In patients with RS, average Cho concentration was 12% higher (p < 0.005) and average NAA concentration 11% lower (p < 0.0001) compared with the control group. Regional metabolic differences included significantly lower NAA concentration in the frontal gray and white matter, insula, and hippocampus in RS; no difference in regional Cho and Cr concentrations were found. A 20 to 38% higher Cho:NAA ratio in frontal and parietal gray and white matter, insular gray matter, and hippocampus (p < 0.05) and a 14 to 47% lower NAA:Cr ratio in frontal cortical gray matter, parietal and temporal white matter, insula, and putamen (p < 0.05) were found in subjects with RS compared with controls. Patients with seizures had higher average concentrations of Cho, Cr, and NAA compared with those without seizures (8-19%, p < 0.05).

CONCLUSION

Metabolic impairment in RS involves both gray and white matter and particularly involves frontal and parietal lobes and the insular cortex. Loss of NAA most likely reflects reduced neuronal and dendritic tree size; increased Cho concentration may result from gliosis.

Diffusion-negative stroke: a report of two cases

Diffusion-weighted MR imaging is generally thought to be highly sensitive for the diagnosis of acute stroke. We report two cases of hyperacute stroke with absence of changes on diffusion-weighted images within 4 hours of symptom onset. Follow-up studies, performed 4 days later, showed infarction in regions compatible with the clinical presentation and (in one case) with the initial perfusion deficit. These cases indicate that normal findings on diffusion-weighted images in patients with suspected cerebral ischemia do not rule out impending infarction.