Characterization of experimental ischemic brain edema utilizing proton nuclear magnetic resonance imaging

Correlations between T1 and T2 relaxation times and water and electrolyte content in the normal and ischemic rat and gerbil brains were studied by means of both nuclear magnetic resonance (NMR) spectroscopic and imaging methods. In the spectroscopic experiment on excised rat brains, T1 was linearly dependent on tissue water content and T2 was prolonged in edematous tissue to a greater extent than expected by an increase in water content, showing that T2 possesses a greater sensitivity for edema identification and localization. Changes in Na+ and K+ content of the tissue mattered little in the prolongation of relaxation times. Serial NMR imaging of gerbil brains insulted with permanent hemispheric ischemia offered early lesion detection in T1- and especially T2-weighted images (detection as soon as 30 min after insult). The progressive nature of lesions was also imaged. Calculated T1 and T2 relaxation times in regions of interest correlated excellently with tissue water content (r = 0.892 and 0.744 for T1 and T2, respectively). As a result, detection of cerebral ischemia utilizing NMR imaging was strongly dependent on a change in tissue water content. The different nature of T1 and T2 relaxation times was also observed.     

High-field-strength magnetic resonance imaging and SPECT of multiple system atrophy]

Two cases of multiple system atrophy (MSA) showing similar abnormalities by magnetic resonance (MR) imaging and SPECT are reported. The clinical diagnoses of the two cases were striatonigral degeneration (SND) and sporadic olivopontocerebellar atrophy (OPCA). In addition, one case of sporadic OPCA without parkinsonism was used for comparison. The MR images were obtained using a 1.5-T MR system and included spin-echo transverse sections with T1-weighted images (TR = 450 ms and TE = 15 ms) and T2-weighted images (TR = 2500 ms and TE = 90 ms). The T1-weighted images demonstrated atrophy of cerebellum and pons, with increased signal intensity in the bilateral putamen. The T2-weighted images demonstrated decreased signal intensity in the putamen, as reported recently. SPECT demonstrated reduced uptake in the celleberum, basal ganglia and frontal lobe cortex. The putaminal changes evident on T1-weighted images may have resulted from deposition of pigments such as neuromelanin and lipofuscin, related to parkinsonism. Both T1- and T2-weighted MRI seem to be useful clinical diagnosis of MSA.     

Diagnostic value of fluid attenuated inversion recovery versus T2-weighted image in diffuse axonal injury

BACKGROUND: At present, the most common examination modality for diffuse axonal injury (DAI) is CT or MRI. However, both methods exhibit low sensitivity in the diagnosis of DAI lesions.OBJECTIVE: To investigate the value of fluid attenuated inversion recovery (FLAIR) in the clinical diagnosis of DAI, and to compare with T2-weighted images.DESIGN, TIME AND SETTING: This prospective study was based on imaging analysis, and wasperformed in the First Affiliated Hospital of Chongqing Medical University (Chongqing, China) between October 2002 and April 2004.PARTICIPANTS: Sixty-three patients with craniocerebral injury were admitted to the Department of Neurosurgery at the First Affiliated Hospital of Chongqing Medical University, including 50 males and 13females. The patients were included in the experiment and were divided into DAI (n=24) and non-DAl (n=39)groups, according to the emergent CT findings and clinical manifestations.METHODS: Both groups underwent MR examinations, including axial and sagittal T1 weighted images (TR=450 ms, TE = 8-9 ms), T2-weighted images (TR = 3600 ms, TE = 100 ms), and FLAIR (TR = 10 000 ms,TI = 2500 ms, TE = 40 ms), 8-mm thick and 2-mm wide, using a GE Sigma MRI device.MAIN OUTCOME MEASURES: The DAI diagnostic rate and lesion-detecting rate of T2-weighted images and FLAIR were determined.RESULTS: All 63 patients were included in the final analysis. The DAI diagnosis rates of FLAIR and T2-weighted images were 88% (21/24) and 62% (15/24), respectively, of which the difference was statistically significant (P < 0.05). T2-weighted images and FLAIR detected lesions located in the gray matter-white matter junction in parasagittal areas, the corpus callosum, deep periventricular white matter,basal ganglia, internal capsule, hippocampus, cerebellum, and brain stem, with a detailed amount of 123 and 256, respectively. FLAIR was significantly greater than T2-weighted images (P < 0.01 ).CONCLUSION: FLAIR is superior to T2-weighted images for improving the DAI diagnostic rate and lesion-detecting rate, as well as revealing the extent and severity of DAI.     

Proton MRS in a case of intracerebellar epidermoid]

We report a case of epidermoid, in which proton MR spectroscopy(MRS) provided additional information to MRI. The tumor revealed high signal intensity on T2-weighted images(WI) and low signal intensity on T1 WI. No enhancement was observed. Proton MRS was acquired with the Proton Regional Imaging of Metabolites(PRIME) method(TR/TE/measurements = 2,000 ms/136,272 ms/128 times). Proton MRS revealed lactate(Lac) peak at 1.33 ppm as negative peak at TE 136 ms and positive peak at TE 272 ms. N-acetylaspartate(NAA), creatine/phosphocreatine(Cr) and choline-containing compounds(Cho) were not visible. Lac peak without other peaks such as NAA, Cr, Cho is a unique finding of proton MRS for epidermoid and this could be useful in the differential diagnosis.     

Deep white matter hyperintensity in occipital lobe on T2 weighted magnetic resonance imaging

Magnetic resonance imaging (MRI) was performed in 270 patients with various neurologic complaints (1-15 Y) with a 0.5 tesla superconducting imaging system (MRT-50 A, Toshiba Co.) using a field echo sequence (TR/TE: 300 ms/14 ms) and a spine echo sequence (TR/TE: 2,000 ms/100 ms or 2,000 ms/120 ms, and 2,000 ms/30 ms). The slice thickness was 10 mm. Hyperintensity areas on T2-weighted images were noted at the occipital lobe in 33 patients (12.2%). Twenty-seven of them had hyperintensity within the deep white matter, which revealed iso- or hypointensity on T1-weighted images. The diagnosis for the 27 patients included medulloblastoma after multidisciplinary therapy (1), congenital heart disease (1), neurofibromatosis (1), tuberous sclerosis (1), congenital muscular dystrophy (1), congenital myotonic dystrophy (2), febrile convulsion (2), autism (3), epilepsy (9) and unknown causes (6). Because the hyperintensity areas are age-dependent, they may result from delayed myelination in the central nervous system.     

Visualization of the IXth to XIIth Cranial Nerves Using 3-Dimensional Constructive Interference in Steady State, 3-Dimensional Magnetization-Prepared Rapid Gradient Echo and T2-Weighted 2-Dimensional Turbo Spin Echo Magnetic Resonance Imaging Sequences

OBJECTIVE: The purpose of this study was to evaluate the visibility of the IXth to XIIth cranial nerves using different magnetic resonance sequences. Thirty healthy volunteers underwent magnetic resonance imaging at 1.5 T using 3-dimensional constructive interference in steady state (CISS) sequence (TR = 17 ms, TE = 8.08 ms, alpha = 70 degrees), 3-dimensional magnetization-prepared rapid gradient echo (MP-RAGE) sequence (TR = 11.08 ms, TE = 4.3 ms, alpha = 15 degrees), and T2-weighted (w) 2-dimensional turbo spin echo (TSE) sequence (TR = 4000 ms, TE = 102 ms, alpha = 180 degrees, slice thickness = 2 mm). Visibility of the IXth to XIIth cranial nerves in each sequence was evaluated by consensus of 2 radiologists using an evaluation scale from 1 (excellently visible) to 5 (not visible). A correlation with anatomic specimens was made. The 3-dimensional CISS sequence provides best resolution of the IXth to XIIth cranial nerves and their relation to surrounding structures. Additional information is given by the 3-dimensional MP-RAGE when nerves are surrounded by soft tissues. Using the T2w 2-dimensional TSE sequence, even whole nerves cannot be visualized due to intersection gap and partial volume effects. However, even in 3-dimensional high-resolution sequences, segments of nerves are not always visualized. A combination of 3-dimensional CISS and 3-dimensional MP-RAGE proved to be useful to visualize the IXth to XIIth cranial nerves, whereas the 2-dimensional technique failed. Further investigations using 3-dimensional MP-RAGE with contrast medium should be performed in the case of abnormality.     

Effects of atrial natriuretic peptide on ischemic brain edema in rats evaluated by proton magnetic resonance method.

We examined the effect of atrial natriuretic peptide on cerebral edema in 96 rats. Forty-four rats were given 30 (n = 11), 120 (n = 26), or 150 (n = 7) micrograms/kg of the peptide intravenously over 24 hours after occlusion of the left middle cerebral artery to induce cerebral ischemia. We then measured the brain water content, the brain sodium and potassium contents, the in vitro proton nuclear magnetic resonance longitudinal (T1) and transverse (T2) relaxation times, and the area of the edematous regions. Compared with saline treatment (n = 39), peptide treatment decreased the brain water content in a dose-dependent manner and decreased the brain sodium content significantly (p less than 0.05). Peptide treatment also suppressed the lengthening of both T1 and T2 in edematous tissue (p less than 0.05 and p less than 0.01, respectively) and reduced the area of the edematous regions observed by magnetic resonance imaging (p less than 0.01). Atrial natriuretic peptide appears to have a pharmacological effect on ischemic brain edema, possibly by suppressing the elevation of water content through regulation of electrolyte transport in the brain.     

Dynamic contrast-enhanced susceptibility-weighted perfusion MRI (DSC-MRI) in a glioma model of the rat brain using a conventional receive-only surface coil with a inner diameter of 47 mm at a clinical 1.5 T scanner

Magnetic resonance (MR) imaging in animal models is usually performed in expensive dedicated small bore animal scanners of limited availability. In the present study a standard clinical 1.5 T MR scanner was used for morphometric and dynamic contrast-enhanced susceptibility-weighted MR imaging (DSC-MRI) of a glioma model of the rat brain. Ten male Wistar rats were examined with coronal T2-weighted, and T1-weighted images (matrix 128 x 128, FOV 64 mm) after implantation of an intracerebral tumor xenografts (C6) using a conventional surface coil. For DSC-MRI a T2*-weighted sequence (TR/TE=30/14 ms, matrix 64 x 64, FOV 90 mm; slice thickness of 1.5mm) was performed. Regions of interest were defined within the tumor and the non-affected contralateral hemisphere and the mean transit time (MTT) was determined. Tumor dimensions in MR predicted well its real size as proven by histology. The MTT of contrast agent passing through the brain was significantly decelerated in the tumor compared to the unaffected hemisphere (p<0.001, paired t-test), which is most likely due to the leakage of contrast agent through the disrupted blood brain barrier. This setup offers advanced MR imaging of small animals without the need for dedicated animal scanners or dedicated custom-made coils.     

Proton NMR relaxation times in ischemic brain edema

The state of water in cerebral ischemia was studied by using the proton nuclear magnetic resonance (1H-NMR) method. Cerebral ischemia was induced experimentally in Mongolian gerbils by unilateral ligation of the common carotid artery. Longitudinal (T1) and transverse (T2) relaxation times of the ischemic brain were measured with a pulse FT-NMR spectrometer and the water content was determined by the wet/dry method. Quantitative analysis of the relaxation times was performed sequentially during the initial 7 hours following ligation and the data were compared with those of brain edema previously reported by S. Naruse in the rat. Characteristic findings in brain ischemia include prolongation of the slow component of T2 and increase in the water content. A quantitative comparison of relaxation rate and water content demonstrates that ischemic brain edema in Mongolian gerbils is different from cytotoxic and vasogenic types of brain edema. When R2 (1/T2) was plotted against the water content, the slope value of ischemia in the gerbil was between the slope values of the TET intoxication and cold injury induced edemas reported previously. From these results, it might be said that ischemic brain edema includes both the cytotoxic and vasogenic types of brain edema. Glycerol was demonstrated to affect brain ischemia by decreasing the water content and by shortening the slow component of T2. By analysis of the relaxation times and water content, we examined the pathophysiological characteristics of water molecules in ischemic brain tissue.     

Temporal evolution of ischemic damage in rat brain measured by proton nuclear magnetic resonance imaging

We studied the effect of focal cerebral ischemia on the "state" of brain water using proton nuclear magnetic resonance imaging. Focal cerebral ischemia was induced in five halothane-anesthetized rats via tandem occlusion of the left common carotid artery and the left middle cerebral artery. The proton transverse relaxation time, the proton density, and the water diffusion coefficient were measured at various times from the same region of brain tissue from 1.5 to 168 hours after occlusion. Early measurements indicated significant changes in the transverse relaxation time (p = 0.004) and water diffusion coefficient (p = 0.002) of ischemic brain tissue compared with a homologous region from the contralateral hemisphere. However, the transverse relaxation time, proton density, and water diffusion coefficient in ischemic brain tissue showed different temporal evolutions over the study period. Diffusion coefficient weighting was superior to relaxation time and proton density weighting for the visualization of early cerebral ischemia. Our data suggest that nuclear magnetic resonance imaging is sensitive in detecting changes in proton-associated parameters during early cerebral ischemia and confirm significant changes (p less than or equal to 0.01) in the temporal evolution of transverse relaxation times, proton densities, and diffusion coefficients following middle cerebral artery occlusion.     

Quantitative proton magnetic resonance spectroscopy of focal brain lesions

The diagnostic value of single-voxel proton magnetic resonance spectroscopy (2 T, stimulated echo acquisition mode, TR = 6,000 ms, TE = 20 ms, 4-5 mL volumes-of-interest) was assessed for a differentiation of focal brain lesions of unknown etiology in 17 patients 1-14 years of age. Absolute metabolite concentrations were compared with age-matched control subjects and an individual control region. Most of the brain tumors were characterized by strongly reduced total N-acetylaspartyl compounds and marked increases of myo-inositol and choline-containing compounds, consistent with a lack of neuroaxonal tissue and a proliferation of glial cells. Lactate was elevated in only four patients. When using this pattern for a metabolic discrimination of brain tumors from other focal lesions, proton spectroscopy correctly identified 14 of 17 abnormalities, as confirmed by histologic examination after neurosurgical intervention. One false-positive tumor diagnosis was a severe reactive gliosis mimicking a typical tumor spectrum. Two inconclusive cases comprised an astrocytoma with moderately elevated myo-inositol but reduced choline-containing compounds and a patient with an abscess leading to a marked reduction of all metabolites but strong contributions from mobile lipids. In summary, quantitative proton spectroscopy has considerable clinical value for preoperative characterization of focal brain lesions.     

The MR evaluation of normal children and disorders of neuronal migration and myelination

We often experience the case that is difficult to differentiate normal from abnormal myelinating process by CT scan, because the diagnosis of myelinating maturation of the infant during developmental process is confusing. We can understand maturation of myelination adding to the advancement of diagnostic resolution by MR imager. So we obtain more informations about the abnormality of myelination and development of the brain by MR imaging than CT scan. This study demonstrates the ability of MR imaging to show progression of myelination in 10 infants and children. We also reveals the patients with disorders of neuronal migration or myelination during developing process. MR scanning could be obtained by sedation using such as triclofos or chloral hydrate for infant and younger children. It was necessary to use diazepam or pentazocine intravenously for elder children with mental retardation or restlessness. MR scans were performed with Siemens MAGNETOM 1.5 Tesla. T 1-weighted spin echo image (TR 600/TE 15) and T 2-weighted image (TR 3000/TE 90) were obtained for all cases. The ten normal infants and children (7 boys, 3 girls) were aged from 1 month to 4 years. Maturation of white matter generally proceeded from posterior limb of internal capsule to middle cerebellar peduncle, cerebellar white matter, corpus callosum, anterior limb of internal capsule, occipital white matter, centrum semiovale, finally frontal white matter. Myelination was matured during the first two years by T 2-weighted images. Changes caused by brain myelination were seen earlier on T 1-weighted images (7 months after birth) than on T 2-weighted images (one year and 9 months after birth).(ABSTRACT TRUNCATED AT 250 WORDS)     

Neither short-term nor long-term administration of oral choline alters metabolite concentrations in human brain.

BACKGROUND: This study reexamined conflicting proton magnetic resonance spectroscopy (MRS) reports of increased or unaffected choline-containing compounds (Cho) in human brain in response to a single dose of 50 mg/kg choline bitartrate. METHODS: The present work was based on a well-established strategy for quantitative proton MRS (2.0 T, STEAM localization sequence, TR/TE/TM = 6000/20/10 ms, LCModel automated spectral evaluation) that allows the determination of cerebral metabolite concentrations rather than T1-weighted resonance intensity ratios. Moreover, the investigations were extended to a possible long-term effect of oral choline by monitoring the continuous ingestion of 2 x 16 g of lecithin per day for 4 weeks. Six young healthy volunteers participated in each study and metabolite concentrations were determined in standardized locations in gray matter, white matter, cerebellum, and thalamus. RESULTS: Neither for short-term nor for long-term administration of choline do the data reveal statistically significant deviations from the basal concentrations of Cho, total N-acetyl-containing compounds (neuronal markers), total creatine, and myo-inositol (glial marker) in any of the investigated brain regions. CONCLUSIONS: Previous reports of increased Cho are not confirmed.     

High resolution Magnetic Resonance Imaging of the rat spinal cord

Abstract

A two turn saddle shaped surface coil receiver was developed that allowed high resolution magnetic o resonance imaging of the rat spinal cord. This is particularly important in laboratory animals where central nervous system regions of interest are relatively small. A continuous copper wire 1.5 mm in diameter was wound into two turns 28 mm in diameter. The saddle shape of the second turn improved the homogeneity of the signal within the region of interest and maintained sufficient field of view and depth of penetration. The quality factor (Q) for the surface coil was Q= 199 unloaded, and Q=60 loaded. Using this surface coil with a GE CSI II 2.0 Tesla small bore magnet, spin echo T1 (TR= 500 msec, TE=25 msec) and T2 (TR=2000 msec, TE= 100 msec) weighted images were obtained in cross section, using 2 mm slice thickness with 2 excitations per phase encoding step. A sagittal gradient echo (rapid scan, TR=85 msec, TE= 10 msec) was used to document reestablishment of vascular flow following ischemia. Spinal cord ischemia was induced by 14 minute temporary occlusion of spinal cord blood supply. MRI was performed at 18 hours following ischemia. There was a 1.4 fold increase in T2 image intensity in ischemic rat spinal cord (\i = 4), consistent with edema formation, compared to normal rat spinal cord (n = 4). Preliminary studies show that similar high resolution images can be performed on the rat brain. This technique uses standard MRI equipment and the surface coil is made from inexpensive readily available materials. There are various animal models of cerebral and spinal cord injury that would benefit from improved high resolution MRI. This coil design may have application in larger animal models and the clinical setting. [Neurol Res 1996; 18: 471-474]     

White matter hyperintensity in neurologically asymptomatic subjects

Recent advances in magnetic resonance imaging (MRI) technology have had a great impact on the delectability of minute, asymptomatic lesions of the central nervous system. The clinical significance and treatment modes of these lesions, such as white matter hyperintensity (WMH) lesions detected by T2 MRI, remain controversial. To address these problems, we retrospectively evaluated WMH lesions in relation to clinical parameters for 240 neurologically asymptomatic persons who had visited a hospital for a medical check-up of the brain. Proton and T2–weighted MRI were obtained using a 0.5 T superconducting MR imager using the spin echo technique with a repetition time (TR) of 2800 msec. An echo delay times (TE) of 40 msec was used for the proton MRI, and a TE of 100 msec was used for the T2-weighted MRI. The images were visually analyzed according to a four-point grading system. The MRI findings were correlated with clinical parameters including age, gender, presenting symptoms, and hypertension. The overall frequency of WMH increased with age. Grades 2 and 3 of WMH were more frequent in aged persons, whereas the occurrence of grade 1 WMH remained relatively constant across age groups. Based on multiple regression analysis, age was the most significant variable influencing the frequency of WMH, followed by hypertension. These results imply that WMH lesions may simply be a phenomenon of aging, or may be an indicator of prepathologic state in an ischemic brain.     

Proton magnetic resonance spectroscopy of primary pediatric brain tumors: neuropathological correlation

Forty-five children with primary brain tumors were evaluated by in vivo proton magnetic resonance spectroscopy (MRS) with the aim of detecting correlations between the obtained spectra and tumor malignancy and histology. All investigations were performed using a 1.5 T MR scanner (Picker) with point-resolved spectroscopic (PRESS) sequence (TR 1600 ms, TE 270 ms, NEX 256). Spectra were analyzed for N-acetylaspartate (NAA), choline containing-compounds (Cho), creatine and phosphocreatine (Cr) and lactate (Lac). The Cho/NAA ratio was the most useful parameter for differentiating between normal brain, benign and malignant tumors as well as discriminating the three main groups of pediatric brain tumors namely pilocytic astrocytoma, ependymoma and medulloblastoma. Proton MRS appears to be an important noninvasive technique in the differential diagnosis of pediatric brain tumors.     

Clinical utility of diffusion-weighted magnetic resonance imaging in the assessment of ischemic stroke

Diffusion-weighted imaging (DWI) detects small changes in water diffusion that occur in ischemic brain. This study evaluated the clinical usefulness of a phase-navigated spin-echo DWI sequence compared with T2-weighted magnetic resonance imaging (T2W MRI) in patients with cerebral ischemia and assessed apparent diffusion coefficient (ADC) and T2-weighted imaging (T2WI) changes over time. ADC values and T2 ratios of image intensity were measured from the region of ischemia and from the corresponding contralateral brain region. The clinical histories of patients with DWI scans obtained over the course of 1 year were reviewed to ascertain whether DWI aided in clinical diagnosis or management. Of 103 scans obtained a mean of 10.4 days after symptom onset, DWI detected six lesions not seen on T2WI and discriminated two new infarcts from old lesions. DWI was most useful within 48 hours of the ictus. The evolution of ADC values and T2 ratios was evaluated in 26 cases with known symptom onset times. ADC values were low at less than 1 week after stroke onset and became elevated at chronic time points. T2 ratios were near normal acutely, increasing thereafter. DWI was superior to T2W MRI in detecting acute stroke, whereas both techniques assisted in determining lesion age.     

T1 histograms of normal-appearing brain tissue are abnormal in early relapsing-remitting multiple sclerosis

OBJECTIVE: To use both whole-brain and normal-appearing brain tissue (NABT) T1 relaxation time histograms to investigate abnormalities in early relapsing-remitting (RR) multiple sclerosis (MS). BACKGROUND: In patients with established MS, both lesions and NABT exhibit an increase in T1 relaxation time. By using T1 histogram analysis, it is hoped that such changes in early disease can be detected. METHOD: Twenty-seven patients and 14 age- and sex-matched controls underwent magnetic resonance imaging (MRI) of the brain, which included the following sequences: 1) proton density (PD)- and T2-weighted fast spin echo (FSE) to measure T2 lesion load, 2) PD- and T1-weighted gradient echos from which T1 relaxation was calculated, and 3) T1-weighted SE imaging pre- and post-triple dose (0.3 mmol/kg) gadolinium (Gd-DTPA) to measure T1 hypointense and gadolinium-enhancing lesion loads, respectively. All patients had RR MS with disease duration <3 years (median 1.7 years). Statistical parametric mapping (SPM) 99 was used to segment brain from cerebrospinal fluid (CSF), and lesions were segmented using a local thresholding technique. RESULTS: Both whole-brain and NABT histograms were abnormal for all six T1 histogram parameters that were measured. For NABT, the mean T1 was 1,027 (+/- 74) ms in patients and 969 (+/- 41) ms in controls (p=0.003). There was little difference between the global and NABT histograms, which indicates that most of the whole-brain histogram abnormality derives from normal-appearing tissues. There was a correlation between the Nine-Hole Peg Test and NABT T1 measures. CONCLUSION: There are widespread abnormalities of NABT in early RR MS, which were sensitively detected by T1 relaxation time histogram analysis. As such, T1 histogram analysis appears promising for studying the natural history of early RR MS, and in the monitoring of response to treatment     

Proton magnetic resonance spectroscopy pattern of progressive multifocal leukoencephalopathy in AIDS

The objective was to determine whether the use of intermediate echo times (135 ms) in proton magnetic resonance spectroscopy (1H-MRS) detects a homogenous pattern in progressive multifocal leukoencephalopathy (PML) in HIV-1 infected people, and to confirm the results of previous studies. Six patients infected with HIV-1, with PML established by biopsy, and six healthy age and sex matched volunteers were evaluated to define their spectroscopic pattern. 1H-MRS spectra performed at 1.5 T were obtained with the STEAM sequence: TE/TM/TR, 20 ms/13.7 ms/2000 ms; 2500 Hz, size 2048 points, 256 acquisitions (STEAM-20) and with the PRESS sequence; TE/TR, 135 ms/2000 ms; 2500 Hz, size 2048 points, 256 acquisitions (PRESS-135). A single voxel was placed on the lesions and on the parieto-occipital white matter of controls. The peaks of N-acetylaspartate (NAA), choline (Cho), myoinositol (mI), lactate, and lipids were considered, and the results were expressed using creatine as reference. Spectra of PML lesions were characterised by significantly reduced NAA, lactate presence, and by significantly increased Cho and lipids compared with control group values. These results indicate that 1H-MRS detects a homogenous pattern in PML lesions. Recent studies, together with this, suggest that 1H-MRS may help in the diagnostic approach to patients with suspected PML lesions associated with AIDS.     

Magnetic resonance imaging (MRI) of pituitary adenomas

MRI of 20 patients, 17-82 years old, with pituitary adenomas confirmed histopathologically, and 30 normal patients without pituitary dysfunction were reviewed. The studies were performed with a 0.5 Tesla MR scanner with a slice thickness of 10 mm. Inversion recovery sequences were employed as T 1-weighted examination, with repetition time (TR) of 2100-2500 msec, an inversion time (TI) of 600 msec and an echo time (TE) of 40 msec. The T 2-weighted examination had a TR of 1800-2500 msec and a TE of 120 msec. T 1-weighted images were obtained in all cases and T 2-weighted images in 14 cases. Spin echo images with a TR of 600-1000 msec and a TE of 40 msec (SE 40/600-1000) were also obtained in 14 cases. On T 1-weighted images, 20 adenomas were classified into six groups, according to their signal intensities; marked low intensity (1), low intensity (1), isointensity (11), high intensity (3), marked high intensity (1) and mixed intensity (3). On T 2-weighted images, 14 adenomas were classified into five groups; low intensity (1), isointensity (2), high intensity (4), marked high intensity (6) and mixed intensity (1). On SE 40/600-1000 images, 14 adenomas were also classified into four groups; low intensity (8), high intensity (2) and mixed intensity (3). Two adenomas with recent intratumoral hemorrhage had marked high intensity on both T1 and T2-weighted images. SE 40/600-1000 images were useful in evaluating the size and the extent of the visual pathway was best appreciated on IR images. Comparison between normal and involved cavernous sinus by adenomas was made.