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Background: Multislice proton magnetic resonance spectroscopic imaging (1H-MRSI) permits the simultaneous acquisition of N-acetylaspartate (NA), choline (Cho), creatine/phosphocreatine (Cre), and lactate (Lac) signal intensities from four 15-mm slices divided into 0.84-ml single-volume elements. NA is inferred to be a neuron-specific molecule, whereas Cho mainly reflects glycerophosphocholine and phosphocholine, compounds involved in phospholipid metabolism. Objective: To assess whether 1H-MRSI could detect a regional pattern of cortical and subcortical involvement in the brain of Alzheimer's disease (AD) patients. Methods: 1H-MRSI was performed in 15 patients with probable AD and 15 age-matched healthy controls. Regions of interest (ROIs) were selected from frontal (FC), temporal (TC), parietal (PC), occipital, and insular cortices, subcortical white matter (WM), and thalamus. Results: In AD patients, we found a significant reduction of NA/Cre in the FC, TC, and PC and a significant reduction of Cho/Cre in the WM. Conclusions: This 1H-MRSI study of AD patients shows a regional pattern of neuronal damage in the associative cortices, as revealed by significant reduction of NA/Cre in the FC, TC, and PC, and regional derangement of phospholipid metabolism, as revealed by significant reduction of Cho/Cre in the WM.NEUROLOGY 1996;47: 696-704

✓ The authors measured cerebral glucose metabolism (CMRglu) using [18F]fluoro-2-deoxyglucose (FDG) positron emission tomography (PET) in patients with brain tumors to evaluate the effect of exogenous corticosteroids (in this instance, dexamethasone) on glucose metabolism. Fifty-six FDG-PET studies obtained in 45 patients with unilateral supratentorial brain tumors were analyzed. Patients with brain tumors were divided into three groups: 1) patients with cushingoid symptoms, who had been treated with combinations of radiotherapy and chemotherapy taking oral dexamethasone; 2) patients not taking dexamethasone but treated with radiotherapy; and 3) patients not taking dexamethasone who had not been treated with radiotherapy. Serial FDG-PET scans were obtained in eight of the cushingoid patients. Glucose metabolism was measured in the contralateral cerebral and ipsilateral cerebellar hemispheres in patients and compared to measurements taken from 19 normal volunteers. The authors found that in the cushingoid brain tumor patients there was a marked reduction in CMRglucompared to normal volunteers and other brain tumor patients (Kruskal—Wallis test; p 0.001). In the majority of patients who had serial FDG-PET scans, there was a decline in glucose metabolism over time and in one patient, in whom dexamethasone was reduced in dosage, there was a subsequent increase in CMRglu. The authors conclude that there is a generalized reduction in CMRgluin brain tumor patients taking dexamethasone compared to other brain tumor patients and normal volunteers, and that this effect is independent of radiotherapy, concurrent anticonvulsant medication, and transhemispheric functional disconnection (transhemispheric diaschisis).

Objective To determine if the transneuronal cerebellar hemispheric metabolic asymmetry seen in crossed cerebellar diaschisis, and readily detected with positron emission tomography (PET), is associated with alterations in metabolite signal intensities on [1H]MR spectroscopic (MRS) imaging when compared with the normal pattern and distribution of cerebellar metabolites. Materials and methods The pattern and distribution of metabolites [N-acetyl-aspartate (NAA), choline-containing compounds, creatine, phosphocreatine, and lactate] in the cerebellum, using [1H]MRS imaging, were studied in a patient with documented long-standing (3 years duration) crossed cerebellar diaschisis and seven normal subjects. Cerebellar diaschisis was detected with fluorodeoxyglucose-PET imaging. Single slice [1H]MRS imaging was carried out at 1.5 T. Results There was a marked reduction in NAA signal intensity in the diaschitic cerebellar hemisphere but minimal reduction in choline and creatine signal intensities. The decrease in NAA signal intensity was most marked in the middle cerebellar peduncle and white matter of the diaschitic cerebellar hemisphere. In the normal subjects and in the uninvolved cerebellar hemisphere of the patient the NAA signal intensity was more prominent in the white matter than the cerebellar cortex. Conclusion Our data indicate (a) transneuronal metabolic effects can be detected with [1H]MRS imaging and (b) there is a differential distribution of metabolite signal intensities in the cerebellum with NAA signal intensity predominantly localized to axons of the cerebellar fiber tracts rather than neuronal cell bodies in the cortex and the converse is true for choline and creatinine signal intensities.

Exposure to 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) can cause an acute chemical toxicity resulting in a parkinsonian state in humans and nonhuman primates. We wished to assess whether the toxicity from MPTP is associated with changes on magnetic resonance images of brain structures containing dopamine neuronal processes or with disrupture of the blood-brain barrier. Normal rhesus monkeys and monkeys at various times after being subjected to unilateral intracarotid injection of MPTP (0.4 mg/kg) were studied with magnetic resonance imaging using T1- and T2-weighted spin-echo and gradient-echo sequences. Disrupture of the blood-brain barrier was assessed also with magnetic resonance imaging after administration of gadolinium-diethylenetriamine pentaacetic acid. Parkinsonian symptoms contralateral to the infused carotid usually appeared within 1 day after MPTP exposure, reaching their peak severity by 7 days, when all monkeys showed clear clinical abnormalities. Magnetic resonance imaging changes developed in concomitance with the clinical signs and were characterized by increased signal intensity on T2-weighted images as well as decreased intensity on T1-weighted images of the ipsilateral caudate and putamen. T2 hyperintensity was also present just dorsal to the pars compacta of the substantia nigra, in the region of the proximal nigrostriatal tract. All magnetic resonance imaging changes dissipated in the next 2 weeks. There were no abnormalities at any time in the globus pallidus, nucleus accumbens, and other structures innervated by the mesocorticolimbic dopamine system. After MPTP exposure, there was no evidence of blood-brain barrier disrupture, suggesting that vasogenic edema was an unlikely factor in the production of the observed abnormalities.(ABSTRACT TRUNCATED AT 250 WORDS)

PURPOSE: To correlate the findings on diffusion-weighted magnetic resonance (MR) images with the cytologic and histologic findings in ischemic tissue. MATERIALS AND METHODS: A photochemical model of cerebral infarction in rats was studied with diffusion- and T2-weighted MR imaging. The development of lesions was followed from 20 minutes to 5 days after the onset of ischemia. Apparent water diffusion coefficient (ADC) maps were calculated and correlated with light and electron microscopic findings. RESULTS: T2-weighted images clearly showed vasogenic edema but did not enable distinction between areas with cellular damage and the surrounding edematous regions. In contrast, the ADC, which was elevated in nonischemic edematous regions, was diminished in areas with histologic evidence of ischemic damage or necrosis. In the core of the infarct, the ADC became elevated when electron microscopy revealed cellular lysis. CONCLUSION: Diffusion-weighted images may help ascertain the extent of cellular damage and deat...

To present the imaging, metabolic, and clinical data obtained in five patients with juvenile pilocytic astrocytomas (JPAs) and discuss the paradoxical neuroimaging findings.Five patients with JPAs who had undergone structural imaging and fluorine-18 fluorodeoxyglucose (FDG) positron emission tomography (PET) were studied. Normalized glucose utilization rates (GURs) in the tumor were compared with GURs in histopathologically verified low-grade astrocytomas and high-grade tumors.All JPAs enhanced markedly after administration of contrast medium. Their glucose metabolism was significantly (P.001) higher than that of low-grade astrocytomas and was similar to that of anaplastic astrocytomas. All patients with JPAs were in stable condition and showed no evidence of disease progression despite contrast enhancement and high tumoral glucose metabolism.The paradoxical FDG PET findings and enhancement at structural imaging might reflect the unusual vascularity of pilocytic tumors, and the increased GUR might be related to expression of the glucose transporter.

Nuclear magnetic relaxation times T1 and T2 were measured in ferritin solutions at field strengths from 0.04 to 1.5 T. T1 was relatively constant, but 1/T2 increased linearly with field strength, in agreement with earlier MRI observations in the monkey brain. This finding supports the theory that ferritin is responsible for T2 shortening in brain nuclei containing iron. The linear dependence of 1/T2 on magnetic field is unique and not explained by present theories of the magnetic properties of ferritin.

As a preliminary to positron emission tomography (PET) studies of excitatory amino acid neurotransmission, N-methyl-d-aspartate (NMDA)-sensitive glutamate receptors of mice and rats were labelled in vivo with [3H]fluorothienylcycloexylpiperidine (FTCP), which binds to the phencyclidine site of the NMDA receptor. After intravenous injection, the half-life of clearance of authentic FTCP from blood was 4.2 min in mice, 12 min in rats and 45 min in a rhesus monkey. In rodent brain, the specific binding of [3H]FTCP, 10 min after intravenous injection, was 10–20% of the total binding and no regional differences were observed. However, if animals were treated with NMDA intraperitoneally (0.68 mmol/kg), 10 min before injection of [3H]FTCP, a three- to five-fold increase in specific binding was observed in hippocampus, cerebral cortex and striatum but not in cerebellum. Thus, specific binding of [3H]FTCP in vivo revealed the physiological status of the NMDA receptor: in fact, preliminary PET studies with [18F]FTCP in monkeys indicated increased binding after activation of NMDA receptors. These data suggest that PET with [18F]FTCP can be a tool to evaluate physiological or pathological modifications of the function of NMDA receptors.

We studied 45 patients who had autonomic failure with computed tomography, magnetic resonance imaging and positron emission tomography with [18F]fluorodeoxyglucose to characterize the neuroimaging features of multiple system atrophy and pure autonomic failure and determine the utility of these techniques in distinguishing multiple system atrophy from pure autonomic failure. There were 30 patients with multiple system atrophy and 15 with pure autonomic failure. In the multiple system atrophy group, eight patients had mainly cerebellar signs, seven extrapyramidal and 15 had combinations of cerebellar and extrapyramidal signs. Cerebellar atrophy on computerized tomography and magnetic resonance imaging, signal hypointensity in the posterolateral putamen on magnetic resonance imaging and a generalized reduction in glucose utilization rate with positron emission tomography with [18F]fluorodeoxyglucose, were the main findings and were seen only in the patients with multiple system atrophy. Decreased glucose utilization (hypometabolism) was most prominent in the cerebellum, brainstem, striatum and frontal and motor cortices. These results indicate clear differences, using neuroimaging studies, between multiple system atrophy and pure autonomic failure.

Il metabolismo del glucosio di cinquanta pazienti con glioma cerebrale è stato valutato con la Spettroscopia del protone RM localizzata (H-SRM) e la Tomografia ad Emissione di Positroni con 18 Fluoro-deoxyglucosio (PET-FDG). I segnali RM di lattato, colina, creatina e NAA sono stati acquisiti da un volume scelto nella lesione e da un volume di controllo nell'emisfero controlaterale, e analizzati nel contesto delle caratteristiche patologiche e metaboliche del tumore. Un segnale del lattato è stato rilevato nel 70% dei pazienti con lesioni ipermetaboliche (e alto grado di malignità) e nel 30% con lesioni ipometaboliche (e basso grado di malignità). La possibile correlazione tra velocità di consumo del glucosio e accumulo di lattato è discussa. Un'elevazione del segnale RM per la colina e una riduzione del segnale per NAA e creatina sono stati riscontrati nella maggioranza dei gliomi cerebrali esaminati.

Twenty cases of surgically verified pituitary microadenoma (17 with Cushing disease and three with acromegaly) were studied with positron emission tomography (PET) with use of fluorine-18-2-fluorodeoxyglucose (FDG). The diagnostic results were compared with those of other modalities, namely, computed tomography (CT), magnetic resonance (MR) imaging, and, in the cases of Cushing disease, simultaneous bilateral inferior petrosal sinus sampling (SIPS). The PET results showed 12 positive readings and one questionable reading, compared with seven positive readings and one questionable reading for CT (18 cases studied) and 13 positive and two questionable MR imaging readings. PET complemented MR imaging, in the sense that five of the positive PET readings were negative or questionable at MR imaging. PET studies of 20 healthy control subjects showed no false-positive cases, whereas other studies of healthy subjects with contrast material-enhanced CT and MR imaging have yielded, respectively, 20% and 15% positive readings, with findings suggestive of silent or occult adenomas.

Motion of the cerebrospinal fluid (CSF) in and around the brain and spinal cord was examined in healthy subjects and in a number of patients with abnormalities of the CSF circulation. The pulsatile motion of the CSF was determined by spin echo phase (velocity) imaging, sometimes in combination with gradient echo phase contrast cine. Differences in flow patterns across CSF spaces were observed: flow reversal in the cerebellomedullary cistern and lumbar area relative to cervical CSF, and in the posterior versus the anterior subarachnoid space in the spinal canal. Flow communication was demonstrated in known communicating cysts or cavities. Differences in flow were also noted across spinal narrowing or block, and across the walls of a variety of cystic lesions in the brain and spinal cord. MR phase imaging of CSF flow provides pathophysiological information of potential clinical importance for the assessment of diseases affecting the CSF circulation.

Udgivelsesdato: 1999-Jul We tested the hypothesis that N-methylspiperone binding to dopamine D2 receptors must be reduced when L-dopa therapy of parkinsonism augments the binding of dopamine to the receptors and improves the clinical state expressed by the Hoehn & Yahr stage. A patient with MPTP-induced parkinsonism underwent two positron emission tomographic studies of the D2-like dopamine receptors with N-[11C]methylspiperone (NMSP). The first study took place 3 days after cessation of the L-dopa medication, the second 5 days after its resumption. Noticeable clinical deterioration occurred during both studies, consistent with significant dopamine receptor blockade by NMSP and elevated NMSP binding in both scans. The dopa treatment did not reduce the NMSP binding. On the contrary, the rate of binding of NMSP (k3) was increased on-dopa, compared to off-dopa. The increase was consistent with the slightly greater dopamine receptor density estimated after resumption of the dopa therapy. The NMSP binding to serotonin receptors suggested lower synaptic serotonin on-dopa than off-dopa. The results are consistent with negative correlation between the Hoehn & Yahr stage and the amount of dopamine bound to dopamine D2 receptors. Low synaptic serotonin may explain the depression seen in some patients on dopa for Parkinson's disease.

The impact of image segmentation on 0.84-ml nominal voxel volume proton spectroscopic imaging in normal brain and in age-related cortical atrophy was investigated. Segmentation improved the gray matter-white matter (GM-WM) contrast for N-acetyl aspartate (NAA)/creatine (Cr) and choline (Cho)/Cr in normal brain, and for NAA/Cho and NAA/Cr in atrophic brain. NAA(GM/WM) (approximately 0.7), Cho(GM/WM) (approximately 0.8), and Cr(GM/WM) (approximately 1.3) in normal brain obtained with segmentation agreed with values obtained with quantitative magnetic resonance spectroscopy. Age-related cortical atrophy led to decreased cortical GM NAA/Cho and NAA/Cr; no changes were evident in WM or in NAA(GM/WM), Cho(GM/WM), or Cr(GM/WM). GM/WM metabolite analysis may be of limited use in conditions in which parallel metabolite changes occur in WM and GM.

Glucocorticoid hormones affect glucose use in different tissues, and the results of several experimental studies have suggested that glucocorticoids have a central action on cerebral metabolism. PET, using the radiotracer 18F-fluorodeoxyglucose (FDG), permits the measurement of cerebral glucose metabolism.To investigate whether cerebral glucose metabolism would be altered in patients with increased plasma glucocorticoid levels, we analyzed the FDG PET studies that were done on 13 patients with Cushing's disease and compared the results with those obtained in 13 age-matched normal control subjects. A second FDG PET scan was performed on 4 patients after surgical removal of the pituitary adenoma.Patients with Cushing's disease had a significant reduction in cerebral glucose metabolism compared with normal controls. In the patients on whom a second PET scan was performed, there was a trend toward increased glucose metabolism on the second scan when comparing pre- and postsurgery values for each patient.We suggest that the decreased cerebral glucose metabolism we observed in Cushing's disease is attributable to increased glucocorticoid levels, and we speculate that abnormal cerebral glucose metabolism might contribute to the cognitive and psychiatric abnormalities that are frequently observed in patients with Cushing's disease.

The spatial distribution of metabolite signal intensities can be measured within entire sections of the brain by proton magnetic resonance spectroscopic imaging (1) H-MRSI). A group of six patients (4 unrelated girls and 2 brothers from 5 families) with childhood ataxia with diffuse CNS hypomyelination (CACH) underwent long-echo-time, single-slice1 H-MRSI. Relative to controls, there was a decrease in the signal intensity of N-acetylaspartate, choline, and creatine throughout the white matter in all six patients. We identified lactate signals in white matter in three of them with advanced disease. The degree of white matter involvement was not homogeneous over the entire patient group, but did correlate with clinical presentation. Deep and posterior white matter tended to be more involved. There were no1 H-MRSI abnormalities in the gray matter.1 H-MRSI findings suggest that this syndrome is secondary to a metabolic defect causing hypomyelination, axonal degeneration, and, in the most compromised cases, accumulation of lactate. This study shows that CACH is not limited to girls. NEUROLOGY 1995;45: 1526-1532

A young patient with pleomorphic xanthoastrocytoma (PXA), a usually benign cerebral tumor, had two recurrences in a short time period. The clinical, pathological and neuroradiological features, including PET with [18F]-fluorodeoxyglucose (FDG), are presented. The PET-FDG study revealed the recurrent tumor to be hypermetabolic. The diagnosis was confirmed histopathologically. As the clinical outcome of patients harboring PXA is not easy to predict because of possible recurrence and/or transformation into more aggressive gliomas, we discuss the predictive indicators of more aggressive clinical behavior.

Proton magnetic resonance spectroscopy (1H-MRS) is evolving from single-volume localized acquisitions to multiple-volume acquisitions using magnetic resonance spectroscopic imaging (1H-MRSI). The normal regional patterns of 1H-MRSI-detectable metabolite signal intensities have yet to be established. We studied 13 healthy young adults with a multiple-section 1H-MRSI technique. The metabolite signals measured were N-acetylaspartate (NA), choline-containing compounds (CHO), creatine-phosphocreatine (CRE), and lactate. Ten neuroanatomic regions (nine bilateral) were identified in gray matter, white matter, and basal nuclei. Analysis of the data led to the following conclusions: (1) NA and CHO signals from centrum semiovale (CSO) can be used as a normalizing factor to reduce intersubject variability due to external causes; (2) in normal human brain, there is no left versus right asymmetry in the regions studied; (3) statistically significant patterns of signal distribution of NA, CHO, and CRE can be identified in normal human brain; and (4) CSO-normalized metabolite signal intensities and metabolite ratios complement each other for the detection of significant regional differences.

The objective of this study was to evaluate whether water apparent diffusion coefficient (ADC) measurements provide more specific information than T2-weighted MRI about brain parenchyma lesions secondary to prolonged complex partial seizure. We measured the ADC in the brain of rats exhibiting prolonged complex partial seizures induced by an intraperitoneal injection of kainic acid (KA). The animals were imaged with diffusion and T2-weighted MRI at 2 T from 3 h to 9 days after the KA injection. In the piriform cortex and amygdala, the T2-weighted MRI signal intensity appeared to be uniformly increased from 24 to 72 h after KA injection, and to return to normal by 9 days after. In the same regions between 24 and 72 h, the ADC first decreased and then increased. The ADC changes were consistent with the known histopathological alterations. In this complex partial seizure model, the ADC measurement provides more specific information than T2-weighted MRI about the histopathological evolution of the lesions.

To determine if the transneuronal cerebellar hemispheric metabolic asymmetry seen in crossed cerebellar diaschisis, and readily detected with positron emission tomography (PET), is associated with alterations in metabolite signal intensities on [1H]MR spectroscopic (MRS) imaging when compared with the normal pattern and distribution of cerebellar metabolites.The pattern and distribution of metabolites [N-acetyl-aspartate (NAA), choline-containing compounds, creatine, phosphocreatine, and lactate] in the cerebellum, using [1H]MRS imaging, were studied in a patient with documented long-standing (3 years duration) crossed cerebellar diaschisis and seven normal subjects. Cerebellar diaschisis was detected with fluorodeoxyglucose-PET imaging. Single slice [1H]MRS imaging was carried out at 1.5 T.There was a marked reduction in NAA signal intensity in the diaschitic cerebellar hemisphere but minimal reduction in choline and creatine signal intensities. The decrease in NAA signal intensity was most marked in the middle cerebellar peduncle and white matter of the diaschitic cerebellar hemisphere. In the normal subjects and in the uninvolved cerebellar hemisphere of the patient the NAA signal intensity was more prominent in the white matter than the cerebellar cortex.Our data indicate (a) transneuronal metabolic effects can be detected with [1H]MRS imaging and (b) there is a differential distribution of metabolite signal intensities in the cerebellum with NAA signal intensity predominantly localized to axons of the cerebellar fiber tracts rather than neuronal cell bodies in the cortex and the converse is true for choline and creatinine signal intensities.

Regional cerebral perfusion was assessed in six patients with asymmetric Parkinson's disease (PD) of mild to moderate severity and in six matched normal subjects using 99mTc-bicisate single photon emission computed tomography (SPECT). Regional activity was normalized to whole-brain activity. Each subject was studied twice, separated by 15.2 +/- 9.2 and 18.0 +/- 4.8 days in normals and PD patients, respectively. There was low intrasubject scan-rescan variability in normals, with all regions showing an average intrasubject difference in repeat studies of3%. In PD patients after chronic oral antiparkinsonian drugs had been withdrawn, as compared with normal subjects, there was increased perfusion in the caudate and lenticular nuclei contralateral to the worst affected extremities. This increased basal ganglia perfusion was attenuated by chronic oral therapy. The clinical relevance of these changes is indicated by the high positive correlation between various measures of clinical PD severity and the lenticular perfusion. These differences in basal ganglia perfusion measured with 99mTc-bicisate SPECT in mild to moderate, asymmetric PD may be secondary to increased metabolic demand resulting from alterations of synaptic activity.

PURPOSE: To correlate the findings of gadolinium-diethylenetriaminepentaacetic acid (Gd-DTPA)-enhanced MR imaging with positron emission tomography (PET) in the evaluation of central nervous system neoplasia. MATERIALS AND METHODS: Thirty-six lesions identified on noncontrast MR in 35 patients with biopsy-proved intracranial tumors were imaged with both T1-weighted Gd-DTPA MR at 1.5 T and [18F]2-fluoro-2-deoxyglucose (FDG) positron emission tomography (PET). Eighteen women and 17 men with a mean age of 47.1 years (range 22-72) were studied. The degrees of Gd-DTPA enhancement and FDG uptake were rated separately, and then all scans were reviewed together. FDG uptake was graded 1-5. RESULTS: Of the 35 lesions rated, 30 had Gd-DTPA enhancement and 28 of these were hypermetabolic (FDG accumulation greater than white matter) on PET (93% concordance). Twenty-six of 32 neoplastic lesions had Gd-DTPA enhancement. Twenty-four of these enhancing tumors were hypermetabolic. Only one lesion was completely missed on PET but identified on routine spin echo MR. CONCLUSION: Gd-DTPA MR and FDG-PET are complementary and there is a high concordance of Gd-DTPA-enhancing tumours displaying FDG hypermetabolism. Although FDG hypermetabolism and Gd-DTPA enhancement are usually suggestive of high-grade malignancy, anaplastic astrocytomas may not enhance with Gd-DTPA and can be hypometabolic. In addition, benign intracranial tumors (two cases of meningioma) and radiation necrosis can be associated with both FDG uptake and Gd-DTPA enhancement.

Brain tumor metabolism was studied with hydrogen-1 magnetic resonance spectroscopy and positron emission tomography with fluorine-18 fluorodeoxyglucose in 50 patients. N-acetylaspartate (NAA) was generally decreased in tumors and radiation necrosis but was somewhat preserved at neoplasm margins. Choline was increased in most solid tumors. Solid high-grade gliomas had higher normalized choline values than did solid low-grade gliomas (P < .02), but the normalized choline value was not a discriminator of tumor grade, since necrotic high-grade lesions had reduced choline values. Serial studies in one case showed an increase in choline as the glioma underwent malignant degeneration. Choline values were lower in chronic radiation necrosis than in solid anaplastic tumors (P < .001). In two cases studied before and after treatment, clinical improvement and a reduction in choline followed therapy. Lactate is more likely to be found in high-grade gliomas, but its presence is not a reliable indicator of malignancy.

Five patients with eighth nerve, one with ninth nerve and one with cervical neuromas were studied with PET and [18F] fluorodeoxyglucose (FDG). Four of the patients had had surgery prior to the PET study, and six patients had subsequent surgery. All tumors were well-visualized on the PET images. Only one patient with bilateral acoustic neuroma exhibited tumor recurrence or growth after the PET study; these two lesions showed the highest FDG uptakes in the PET studies (tumor-to-cerebellum ratio of 0.93-0.98). All other tumors were relatively hypometabolic (tumor-cerebellum ratios of 0.43-0.65) and showed no tumor growth or recurrence during follow-up periods ranging from 5 to 8 yr. These results suggest that PET-FDG may be of value in the evaluation of cranial and spinal schwannomas.

As a preliminary to positron emission tomography (PET) studies of excitatory amino acid neurotransmission, N-methyl-D-aspartate (NMDA)-sensitive glutamate receptors of mice and rats were labelled in vivo with [3H]fluorothienylcyclohexylpiperidine [corrected] (FTCP), which binds to the phencyclidine site of the NMDA receptor. After intravenous injection, the half-life of clearance of authentic FTCP from blood was 4.2 min in mice, 12 min in rats and 45 min in a rhesus monkey. In rodent brain, the specific binding of [3H]FTCP, 10 min after intravenous injection, was 10-20% of the total binding and no regional differences were observed. However, if animals were treated with NMDA intraperitoneally (0.68 mmol/kg), 10 min before injection of [3H]FTCP, a three- to five-fold increase in specific binding was observed in hippocampus, cerebral cortex and striatum but not in cerebellum. Thus, specific binding of [3H]FTCP in vivo revealed the physiological status of the NMDA receptor; in fact, preliminary PET studies with [18F]FTCP in monkeys indicated increased binding after activation of NMDA receptors. These data suggest that PET with [18F]FTCP can be a tool to evaluate physiological or pathological modifications of the function of NMDA receptors.

Echo planar imaging is a new MRI technique capable of producing images in short periods of time. This type of examination has the time resolution required to study the first passage of contrast medium through an organ. We report observations using this technique in 12 patients with regional variations in perfusion due to cerebral gliomas.

The authors measured in vivo signal intensity on magnetic resonance (MR) images and postmortem iron concentrations in the brains of three young and two old rhesus monkeys. T2-weighted MR imaging was done at 0.5, 1.5, 2.0, and 4.7 T. Relative assessment of iron concentration was made from the optical density of brain sections stained with the Perls' method intensified with diaminobenzidine. MR imaging and optical density measurements were made in the centrum semiovale (white matter) and in four gray matter areas: the insular cortex, caudate nucleus, putamen, and globus pallidus, the latter three of which accumulate significant iron deposits with age. High optical density and decreased signal intensity were found in these areas, and the inverse correlation between gray matter/white matter signal ratio and optical density was in good agreement with the theory of T2 shortening caused by diffusion of water through magnetic inhomogeneities. However, the dependence of T2 shortening on field strength was not quadratic, as expected for paramagnetic iron, but instead showed a marked leveling off at higher field strengths. This magnetic "saturation" is explainable by antiferromagnetism and superparamagnetism of the ferritin core and has been observed in ferritin solutions at low temperatures. Similar observations at body temperature are needed before the iron-ferritin explanation for T2 shortening can be considered proved.

We tested the hypothesis that proton magnetic resonance spectroscopic imaging (1H-MRSI) can be used as a supportive diagnostic tool to differentiate clinically stable brain tumors from those progressing as a result of either low-to-high grade malignant transformation or of post-therapeutic recurrence. Twenty-seven patients with histologically verified cerebral gliomas were studied repeatedly with 1H-MRSI over a period of 3.5 years. At the time of each 1H-MRSI study, clinical examination, MRI, positron emission tomography (PET) with 18F-fluorodeoxyglucose (FDG), and biopsy findings (when available) were used to categorize each patient as being either «stable» or «progressive». Measures of the between-studies percent changes in the choline 1H-MRSI signal intensity, obtained without knowledge of the clinical categorization, segregated the groups with a high degree of statistical significance. All progressive cases showed a between-studies choline signal increase of more than 45%, while all stable cases showed an elevation of less than 35%, no change, or even a decreased signal. We conclude that increased choline coincides with malignant degeneration of cerebral gliomas, and therefore, may possibly be used as a supportive indicator of malignant degeneration of these neoplasms.

✓ The authors tested the hypothesis that proton magnetic resonance spectroscopy (1H-MRS) imaging can be used as a supportive diagnostic tool to differentiate clinically stable brain tumors from those progressing as a result of low- to high-grade malignant transformation or posttherapeutic recurrence. Twenty-seven patients with cerebral gliomas verified on histological examination were studied repeatedly with 1H-MRS imaging over a period of 3.5 years. At the time of each 1H-MRS imaging study, clinical examination, MR imaging, positron emission tomography with 18F-fluorodeoxyglucose, and biopsy findings (when available) were used to categorize each patient as having either stable or progressive disease. Measures of the percentage changes in the choline (Cho) 1H-MRS imaging signal intensity between studies, which were obtained without knowledge of the clinical categorization, allowed the investigators to segregate the groups with a high degree of statistical significance. All progressive cases showed a Cho signal increase between studies of more than 45%, whereas all stable cases showed an elevation of less than 35%, no change, or even a decreased signal. The authors conclude that increased Cho levels coincide with malignant degeneration of cerebral gliomas and therefore may possibly be used as a supportive indicator of progression of these neoplasms.

L'A. se penche sur l'activisme ecologique feministe aux Etats-Unis et en Inde a partir d'un examen critique des formes de savoir « masculinistes ». Elle montre que leurs strategies de creer de nouvelles formes de pratiques de la science produit des formes oppositionnelles d'expertise environnementale, telles que l'« epidemiologie populaire » qui se caraterise par la prise en compte de variables souvent negligees

A unilateral supratentorial lesion may cause hypometabolism in the contralateral cerebellar hemisphere (crossed cerebellar diaschisis). We analyzed glucose metabolism, measured by PET-FDG, in the posterior fossa in 67 patients (78 PET studies) with primary unilateral supratentorial brain tumors selected for visually obvious metabolic asymmetry in the cerebellar hemispheres. We found that glucose utilization was 17% lower in the contralateral cerebellar cortex (compared with the ipsilateral one), consistent with the selection criterion, and 19% lower in the ipsilateral pons, wherein lie the first order synapses of the corticopontocerebellar pathway. This finding helps to validate the prevalent view that cerebellar diaschisis is due to interruption of afferent input from the corticopontocerebellar pathway. However, glucose metabolism in the contralateral dentate nucleus was relatively preserved--only 2% less than the ipsilateral dentate. This "dentate sparing" suggests preservation of afferent input to the largest of the deep cerebellar nuclei from the Purkinje cells in the cortex, despite interruption of the major excitatory input to the Purkinje cells.

Hypertrophic degeneration of the inferior olivary nuclei is the pathologic substrate for palatal myoclonus, but the physiologic correlate of this finding is uncertain. Using the 2-[ 18 F]fluoro-2-deoxy-d-glucose and PET method, we determined the local cerebral metabolic rate of glucose utilization in seven patients with palatal myoclonus (following stroke or infection, or idiopathic), one patient with oculopalatal myoclonus (following a stroke affecting the brainstem), and nine normal subjects. The metabolism of glucose in the medulla of the patients with palatal myoclonus was significantly greater than that of the normal subjects. This may well have been due to increased metabolism of the inferior olivary nuclei. Glucose metabolism in the medulla of the patient with oculopalatal myoclonus was normal. These findings suggest that the inferior olivary nuclei, or a region of the brainstem encompassing the inferior olivary nuclei, are hypermetabolic in palatal myoclonus and may be the generators of the involuntary movements in palatal myoclonus.

The Shy-Drager syndrome (SDS) is a form of progressive autonomic nervous system failure (PAF) with orthostatic hypotension and associated extrapyramidal involvement that is often mistaken for Parkinson disease. SDS includes olivopontocerebellar atrophy and striatonigral degeneration which is attended by PAF. Eight patients with SDS were studied on a 0.5-T superconducting system utilizing T1-weighted inversion recovery (IR) and T2-weighted spin-echo pulse sequences and also on a 1.5-T system using spin-echo sequences. With IR sequences, atrophy of the putamina was demonstrated in patients with SDS that is consistent with findings of neuronal loss in these nuclei reported on postmortem examinations. An abnormal decrease in signal intensity of the putamina, particularly along their lateral and posterior portions, was also detected, predominantly on T2-weighted sequences, and in three cases on T1-weighted spin-echo sequences. Abnormalities were detected on both imagers but were shown with greater clarity on the 1.5-T device. SDS is the first disease in which convincing basal ganglia changes have been shown in vivo exclusively by MR imaging.

Vasogenic cerebral edema was induced cryogenically in rhesus monkeys. Serial scans in both axial and coronal planes were used to study the onset, peak, and regression of edema. Progression of edema, predominantly involving the white matter, was analyzed from the postmortem distribution of a blood/brain barrier indicator (Evans blue) injected at surgery. Specific gravity was measured in fresh, unfixed specimens from both the edematous and normal hemispheres and correlated with corresponding CT attenuation values obtained before death. The drop in specific gravity closely corresponded to the decrease in CT attenuation.

The ACTA-Scanner has virtually unlimited potential in the evalution of any part of the body. The usefulness of the technique has already been shown in the appraisal of pathologies of the brain and cerebrospinal fluid cavities. The orbits and the eyeballs, the facial sinuses, and skull base lesions have also been elucidated. Tumors of the larynx, pharynx, thyroid, and parathyroid; lymphomas; and pathology of the spine and spinal cord are well within the reach of this new diagnostic methodology. Lung pathologies, such as emphysema, pneumonias, neoplasms, infarctions, pleural effusions and granulomatous diseases, and mediastinal pathology represent a challenging complex of lesions to be appraised by ACTA-scanning. For the heart, there is great potential for observing cardiac chamber size, hypertrophy of ventricular or atrial walls, and ventricular or aortic aneurysms, and possibly for recognizing the damaged myocardial tissue immediately after or some time after an infarction. The abdominal pathologies that can be studied are almost uncountable: gastric neoplasms, pancreatic cysts and stones, gallstones, neoplasms of the liver and pancreas, bowel tumors, abdominal aortic aneurysms, renal neoplasms and cysts, atrophy of the kidneys, bladder tumors, uterine tumors, ovarian cysts, and many more. Although bones and joints are adequately demonstrated by conventional x-ray techniques, there is no doubt that as the new technique is developed ACTA-grams will contribute significant information in the transverse plane, as well as in densitometric analyses. The impact of ACTA-scanning will not be limited to the diagnostic area, but will extend, at least indirectly, to general patient management and to some aspects of medical economics as well. Risk-laden, technically complex, and costly diagnostic procedures, sometimes requiring lengthy hospitalization, will in some cases be eliminated. The simple, innocuous, and noninvasive ACTA-scanning can be performed on an outpatient basis. Repeated follow-up examinations should be easily accepted by the patients, considering that this diagnostic test is carried out without discomfort. The entire field of diagnostic radiology is on the verge of revolutionary changes.

✓ Glucose utilization by normal and neoplastic cerebral tissue can be measured in humans using positron emission tomography (PET) with fluorine-18-labeled 2-deoxy-D-glucose (FDG). Malignant gliomas are known to exhibit hypermetabolic glucose consumption compared to normal brain. Barbiturate-sensitive cerebral glucose utilization is coupled to neuronal activity, and lesions lacking neuronal activity should be relatively insensitive to barbiturate suppression of glucose utilization. In a study to examine this phenomenon, three patients with cerebral gliomas underwent FDG-PET while awake and during deep barbiturate coma. Cerebral glucose utilization was measured in normal brain, tumor, and a homologous, non-neoplastic control site in the contralateral hemisphere. A glucose utilization ratio for tumor/control tissue was calculated. The mean reduction of glucose utilization during barbiturate coma was: gray matter 67%, white matter 47%, basal ganglia 66%, thalamus 57%, cerebellar cortex 55%, tumor 32%, and the contralateral control site 64%. The mean tumor glucose utilization ratio was 1.48:1 in the awake state and 2.69:1 during barbiturate coma. The changes in gray matter, basal ganglia, thalamus, cerebellar cortex, and tumor/control tissue ratio were significant (p < 0.05). In one patient, deep tumor invasion not evident on computerized tomography, magnetic resonance imaging, or baseline FDG-PET was apparent during barbiturate-enhanced FDG-PET scanning. The study findings suggest that gliomas resist suppression of glucose utilization by barbiturates; this supports the hypothesis that barbiturates reduce neuronal metabolism by blocking synaptic activity. This differential effect on normal brain and gliomas enhances the capability to assess the extent of neoplastic tissue in brain and may represent the basis for novel therapeutic strategies.

The significance of linear regions of altered signal intensity that appear in sagittal magnetic resonance (MR) images along the length of the spinal cord was investigated. Examinations were performed on ten healthy volunteers and one patient with spinal cord edema. A 0.5-T or a 1.5-T MR system was used. Sampling-related effects (Gibbs phenomenon) at spinal cord edges and cerebrospinal fluid interfaces can lead to different signal patterns within the spinal cord and canal. These artifacts cause problems in interpretation, especially with the use of small object-to-pixel size ratios, by obscuring anatomy and simulating pathologic conditions such as pseudosyringes. Analysis of these intensity variations and of their dependence on sampling may improve the clinical accuracy of MR imaging.

Seventeen patients with intracranial meningiomas were studied with positron emission tomography and fluorine-18-2-fluorodeoxyglucose (PET-FDG) to assess the glucose utilization of these tumors. Four meningiomas followed for 3-5 years after PET-FDG and surgery showed no evidence of recurrence. These tumors had significantly lower glucose utilization rates (1.9 mg/dl/min +/- 1.0) than 11 recurrent or regrowing meningiomas (4.5 mg/dl/min +/- 1.96) (P less than .01). The glucose metabolic rates of meningiomas correlated with tumor growth, as estimated from changes in tumor size on repeated computed tomographic scans. Histopathologically, a syncytial (atypical) meningioma had the highest glucose utilization rate, followed by a papillary meningioma and an angioblastic meningioma. Individual transitional and syncytial (typical) meningiomas showed marked differences in glucose metabolism despite similar microscopic appearance. Glucose utilization rate appears to be at least as reliable as histologic classification and other proposed criteria for predicting the behavior and recurrence of intracranial meningiomas.

Cryptococcus neoformans is an ubiquitous yeast. As a budding type of fungus, it is also known as Torula histolytica and is a common cause of infection of the central nervous system (CNS), particularly in debilitated and immunodeficient patients. We have examined 12 patients with computed tomography who had well documented cryptococcal CNS infection and will review our findings in this paper. Three of these patients had mass lesions, while nine others had a variety of changes such as ventricular dilatation, cortical atrophy, and focal ischemic changes.

In computer assisted tomography, the slice being imaged is not a uniform slab because (1) the X-rays are not parallel, (2) the source and detector may not have equal dimensions, (3) the source collimator may produce a penumbra region on the detector, and (4) in some machines two slices are scanned simultaneously from a common focal spot. One method of measuring slice thickness, uniformity, and overlap is with a phantom containing an aluminum strip at a 45 degree angle. This provides a direct display, in the viewing plane, of the slice profile. Measurements have been made on seven new tomographic scanners, and photographs and plots of slice geometry are presented. It is suggested that slice thickness be defined as the full width at half maximum sensitivity, but that this measure should not necessarily be used as the desirable increment between scans.

As a polychromatic X-ray beam passes through matter, low energy photons are preferentially absorbed, and the (logarithmic) attenuation is no longer a linear function of absorber thickness. This leads to various artifacts in reconstructive tomography. If a water bag is used, the nonlinear attenuation in bone causes a distortion of the bone values and a spill-over inside the skull, or 'pseudo-cortex' artifact. If no water bag is used, there is an additional effect due to the varying thickness of soft tissue which causes a depression of interior values, or 'cupping'. Both artifacts can be remedied by additional prefiltering of the beam and by applying a linearization correction to the detector outputs.

Five patients who had undergone radiation therapy for cerebral tumors and whose conditions were deteriorating were examined by means of positron emission tomography (PET) with [18F] fluorodeoxyglucose. All five cases had similar clinical and computed tomographic findings. Using the PET technique the two cases of radiation necrosis were distinguished from the three recurrent tumors. In the two cases of radiation necrosis the rate of glucose utilization in the lesion was markedly reduced compared with the normal brain parenchyma. In the recurrent gliomas, however, the glucose metabolic rate was elevated. All five diagnoses were confirmed by biopsy or autopsy.

A 64-year-old man had right-sided persistent hemiballismus. Cerebral computed tomography (CT) and 0.5-T magnetic resonance imaging (MRI) showed no abnormalities, but 1.5-T MRI showed decreased signal intensity of the putamina, greater on the left than on the right. The subthalamic area was normal on CT and MRI. Positron emission tomography with 18fluoro2-deoxyglucose showed marked hypometabolism of the left putamen (60% of the right) and hypermetabolism of the left parietal lobe (138% of the right). The decreased metabolism of the left putamen may indicate a reduction in neuronal firing. The pathophysiology of the hemiballismus in this case may be loss of tonic inhibition of the lateral globus pallidus from the putamen, leading in turn to greater inhibition of the subthalamic nucleus, less excitation of the medial globus pallidus, and less inhibition of the thalamus and motor cortex, and thus allowing expression of the ballistic movements.