Faculty Bibliography

PURPOSE: To elucidate the natural history of visualized MR abnormalities in patients with multiple sclerosis using proton spectroscopy. METHODS: MR imaging and proton spectroscopy (1H spectroscopy) were performed on 16 patients with clinically definite multiple sclerosis. All patients received gadopentetate dimeglumine (Gd-DTPA). RESULTS: Decreased levels of N-acetylaspartate (NAA) were demonstrated in 17 out of 21 lesions. No correlation was found between decreased NAA and Gd-DTPA enhancement. In five out of seven enhancing lesions, abnormal 1H spectra with extra peaks (termed marker peaks) at 2.1-2.6 ppm (ranging in absolute concentration from 10-50 mM protons) were observed. In nine out of 14 unenhancing lesions, no elevated marker peaks were observed. In the five other unenhancing lesions, the levels of these marker peaks were generally lower than the enhancing group. No correlation was found between the NAA levels and the levels of the marker peaks. We suggest two distinct biochemical processes: 1) decreased NAA reflecting neuronal cell loss, and 2) elevated marker peaks reflecting ongoing demyelination. CONCLUSIONS: Based upon these observations we infer that 1) the majority of enhancing lesions are demyelinating with extra peaks at 2.1-2.6 ppm representing a marker of this process, 2) enhancing lesions without this marker most likely represent edematous regions without significant demyelination, and 3) demyelination may be long in duration compared with transient blood-brain barrier disruption manifested by Gd-DTPA enhancement. Our results suggest that 1H spectroscopy has the ability to further categorize MR-demonstrated enhancing and unenhancing lesions in patients with multiple sclerosis and that it may be more sensitive than contrast enhancement in revealing the true time course of demyelination

We studied the spectroscopic appearance of radiation-induced myelinolysis in cats to understand the characteristics of proton MR spectroscopy of demyelinating disorders. Eight cats received 5,000 rads to a 1.5 x 1.5 cm area of the right cerebral hemisphere. Eight to 9 months after irradiation, a gross area of abnormal postcontrast enhancement and/or high MR signal intensity was detected in the irradiated hemisphere of six of the eight cats. Proton spectra of a 1.0 cm3 voxel in the affected region demonstrated depressed N-acetyl aspartate/creatine-phosphocreatine and N-acetyl aspartate/choline-containing compound peak ratios compared with the contralateral non-irradiated brain in all cats. Elevated amino acid resonances in the 2.0-2.5 ppm range were not consistently seen in irradiated zones of the brain with pathologic findings of demyelination. In vivo proton MR spectroscopy may show differences between irradiated brain and nonirradiated brain even when histopathologic lesions are not apparent yet

Magnetization transfer imaging (MTI) was initially performed in normal guinea pigs and human volunteers. A magnetization transfer ratio (MTR) was calculated in the normal white matter and was found to be 42%-44%, with less than 2.5% variation, which indicates the high reproducibility of the measurement. MTI was then applied to an animal model of white matter disease, acute experimental allergic encephalomyelitis (EAE). In this model of EAE, pathologically proved lesions were edematous with essentially no demyelination. MTRs decreased slightly but significantly (5%-8%) compared with the MTRs of the same tissue region measured before the onset of the lesion [corrected]. Fifteen patients with multiple sclerosis (MS) also underwent MTI. In the 15 patients with MS, all lesions (209 plaques) had a significantly decreased MTR (average, 26%). The authors believe that demyelination produced the lower MTR, and, thus, lesions varied in transfer ratio on the basis of the extent of myelin loss. In patients with MS, particularly those with chronic and/or progressive MS, the MTR of the normal-appearing white matter was significantly decreased. The data suggest that calculated MTR obtained with in vivo MTI may enable differentiation of edema from demyelination, and that MTI can demonstrate white matter abnormalities that cannot be seen with standard spin-echo or gradient-echo magnetic resonance imaging

The role of individual structures within the diencephalon for memory functioning is unknown. We present anatomic localization of lesions and a longitudinal neuropsychological profile of a young man who had a bilateral diencephalic stroke in the interpeduncular profundus arterial territory. MRI localized the lesions to the mamillothalamic tracts and inferior thalamic peduncle. The amnesia was characterized by severe impairment in explicit recall of new facts and events, while word-completion priming and remote memory were intact. We suggest that the memory deficit results from a disconnection of the diencephalon from the medial temporal region

Cerebral vasculitis is an unusual disorder with numerous causes. One such entity, noninfectious granulomatous angiitis of the nervous system (GANS), is an extremely rare disease with a predilection for leptomeningeal and parenchymal arteries and veins. Isolated involvement of the central nervous system is characteristic of GANS, which has also been referred to as primary angiitis of the central nervous system (PACNS). The results of magnetic resonance (MR) imaging and angiography in seven patients with presumed PACNS were retrospectively analyzed and correlated. MR images were positive in every case. Characteristically, lesions were multiple, bilateral, and supratentorial. Both gray- and white-matter infarcts were identified in four of seven patients; infarcts were most common in the deep white matter. PACNS can also appear as primary parenchymal hemorrhage or simulate low-grade glioma. All lesions identified on MR images were associated with positive angiographic findings of cerebral vasculitis in the corresponding vascular distribution. However, for 12 of 33 vascular distributions with angiographic evidence of cerebral vasculitis, no lesions were identified on MR images. These correlative observations suggest that some patients with proved PACNS may have normal MR imaging results

The in vitro behavior of various states of hemoglobin was examined over a wide range of concentrations. Solutions of increasing concentrations of oxyhemoglobin displayed significant increases in T1 and T2 relaxation rates that were insensitive to pH values between 6.0 and 6.9. Bovine serum albumin, which displayed a relaxation behavior nearly identical to that of oxyhemoglobin, was used to normalize for the protein concentration of the deoxyhemoglobin and methemoglobin samples. Concentrated protein solutions with increasing proportions of deoxyhemoglobin yielded little change in the T1 relaxation rate. In these samples, however, the T2 relaxation rate displayed a parabolic dependence on the concentration of intracellular deoxyhemoglobin paralleling the inhomogeneity of the sample; this was not observed with extracellular deoxyhemoglobin. Similar T2 relaxation behavior was observed for intracellular methemoglobin, except that the magnitude of the T2 shortening was smaller than that for deoxyhemoglobin. The magnitude of the T2 shortening was pH dependent, roughly paralleling the change in the equilibrium between the high-spin acid form of methemoglobin and the low-spin basic form of methemoglobin. Marked increase in the T1 relaxation rate is observed with increasing concentrations of methemoglobin, again with greater relaxation enhancement at lower pH. The results of our study emphasize the importance of normalizing for protein concentration when assessing the effects of paramagnetic forms of hemoglobin

A modified fat-suppression pulse sequence (consisting of combined frequency-selective fat presaturation followed by a spin-echo acquisition when fat and water magnetization vectors have opposite phase) was used to optimize the conspicuity of intravenous enhancement by gadopentetate dimeglumine on magnetic resonance images in 10 patients previously operated on for lumbar discogenic disease as well as in two patients with herniated disks who had not previously undergone surgery. This technique produced the greatest degree of fat suppression in the phantom study. In six of the patients who had previously undergone surgery, epidural enhancement was more obvious on the fat-suppressed images than on conventional spin-echo images, while in four patients, enhancement was equivalent. The herniated disks in two patients not previously operated on were not enhanced with either technique. Contrast enhancement was universally distinguishable from fat signal and from nonenhancing water-containing tissue on the fat-suppressed images obtained after contrast material administration. This technique may reduce the need for precontrast imaging. Furthermore, postoperative enhancement of nerve roots was more obvious on fat-suppressed images in seven of eight patients. This finding might represent previously undiagnosed degrees of arachnoidal inflammation, which may be a factor in the failed back syndrome

One form of retinopathy associated with diabetes is a proliferative small vessel process thought to be mediated by biochemical, hemodynamic, and endocrinologic factors. The authors conducted a prospective study to determine whether patients with diabetes who had proliferative retinopathy had evidence of intracranial microangiopathy visible at magnetic resonance (MR) imaging. Twenty-five patients under 40 years of age with proliferative retinopathy and insulin-dependent diabetes mellitus and 10 age-matched control subjects were studied with MR imaging. Axial images were reviewed by two neuroradiologists for the presence of white matter foci of high signal intensity. No patients demonstrated evidence of these foci. There was no evidence of ischemic foci in any of the patients (all patients were neurologically asymptomatic). The vasculopathy associated with proliferative retinopathy does not appear to affect the intracranial circulation to the extent detectable with MR imaging. The presence of white matter foci of high signal intensity or ischemic changes in the brains of insulin-dependent diabetic patients under 40 years of age should not be attributed to diabetic vasculopathy. Other causes should be considered

Conventional two-dimensional Fourier transform (2DFT) MR evaluation of osteophytic disease of the cervical neural foramina is limited by section thickness, signal-to-noise problems, and CSF flow artifacts. We evaluated the role of thin-section, high-resolution, gradient-refocused three-dimensional Fourier transform (3DFT) MR imaging in assessing degenerative foraminal narrowing in the cervical spine. Contiguous 1.5-mm axial 3DFT gradient-recalled acquisition in the steady state MR images of 120 neural foramina at 60 disk levels were evaluated blindly and independently by three neuroradiologists. High-resolution axial CT was used as the gold standard in all patients. 3DFT MR was found to agree with CT in the detection of neural foraminal narrowing and in the determination of the cause of the narrowing in approximately 76% of neural foramina. The accuracy for the assessment of neural foraminal narrowing on 3DFT MR ranged from 73% to 82% when a 5 degrees-flip-angle, high-intensity CSF technique was used. When using the 30 degrees-flip-angle, low-intensity CSF technique, the accuracy ranged from 66% to 86%. When the cause of narrowing was evaluated, the 5 degrees and 30 degrees studies agreed with CT in 70-92% and 48-88% of the levels, respectively. When lesions were missed on MR, it was usually because of osteophytic disease. The interobserver concordance of MR and CT interpretations was higher for detecting the presence of narrowing than its cause. This MR technique is a useful method in the evaluation of foraminal stenosis since contrast between disk, cord, osteophyte, and CSF is high without the need for intrathecal injections.(ABSTRACT TRUNCATED AT 250 WORDS)