Biomedical subjects

G Di Chiro

Publications and source records attributed to G Di Chiro.

At least 19 recordsLinked to original sources

PubMed1998

Decreased brain glucose utilization in patients with Cushing's disease.

UNLABELLED: 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. METHODS: 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. RESULTS: 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. CONCLUSION: 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.

Brain↗

PubMed1997

Increased choline signal coinciding with malignant degeneration of cerebral gliomas: a serial proton magnetic resonance spectroscopy imaging study.

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.

Adult↗

PubMed1996

The relation between brain iron and NMR relaxation times: an in vitro study.

T1 and T2 relaxation times and iron concentrations were measured in 24 specimens of gray matter from fresh human and monkey brains at magnetic fields from 0.05 to 1.5 Tesla. Three different effects were found that correlate with iron content: a T1-shortening that falls off somewhat at high fields, a T2-shortening that is field-independent and thus important at low fields, and a contribution to 1/T2 that increases linearly with field strength. This linear field dependence has been seen only in ferritin and other ferric oxyhydroxide particles. Our results are in agreement with in vivo MRI studies and are generally consistent with values for ferritin solution, except for differences such as clustering of ferritin in tissue. A cerebral cavernous hemangioma specimen showed similar T2-shortening, but with a 2.7 times larger magnitude, attributed to larger clusters of hemosiderin in macrophages. The dependence on interecho time 2 tau was measured in three brains; 1/T2 increased significantly for tau up to 32 ms, as expected from the size of the ferritin clusters. These findings support the theory that ferritin iron is the primary determinant of MRI contrast in normal gray matter.

Adult↗

PubMed1996

High temporal resolution diffusion MRI of global cerebral ischemia and reperfusion.

Although brain ischemia has been extensively studied using diffusion-weighted magnetic resonance imaging, most studies performed so far have not had adequate time resolution to follow the temporal changes in the water apparent diffusion coefficient (ADC) in hyperacute ischemia. Using diffusion echo planar imaging, we obtained ADC maps (calculated from measurements made with 8 b-values) with a time resolution of 43 s in a feline model of global brain ischemia and reperfusion. Different protocols were performed: 10-min hypoperfusion, 10- and 22-min ischemia followed by reperfusion, and cardiac arrest. ADC values were obtained from white matter of the internal capsule and from the thalamus. Cortical gray matter measurements were not deemed reliable due to the close proximity of CSF in the cortical sulci. Following occlusion, the ADC declined in the thalamus to < 2 SD of its normal baseline value within 1.5-2.5 min. This decay was exponential with a time constant (tau +/- SD) of 6.0 +/- 2.6 min; no further decrease in the ADC was observed 10 min following ischemia. Following reperfusion, in animals that showed ADC recovery, the ADC began increasing immediately, returning to its preischemic value in approximately 15 min. No significant ADC changes were observed during hypoperfusion. Following cardiac arrest, the decay of ADC was more rapid in the thalamus (tau = 2.6 +/- 0.6 min) than in white matter (tau = 6.6 +/- 1.8 min). We observed that the ADC at 40 min after cardiac arrest was similar to the ADC at 10 min after ischemia. Given that all animals subjected to 10-min ischemic episodes showed ADC recovery with reperfusion, doubt is cast on whether it is possible to define a threshold value of the ADC below which brain tissue is irreversibly damaged. Finally, despite variability in the time constants of the ADC decay induced by ischemia, the ADC values at 10 min were very similar in all the animals. This suggests that when blood flow is diminished sufficiently to induce an ADC reduction, differences in perfusion affect the rapidity of the decrease but not the final asymptotic value reached.

Animals↗

PubMed1996

Diffusion tensor MR imaging of the human brain.

PURPOSE: To assess intrinsic properties of water diffusion in normal human brain by using quantitative parameters derived from the diffusion tensor, D, which are insensitive to patient orientation. MATERIALS AND METHODS: Maps of the principal diffusivities of D, of Trace(D), and of diffusion anisotropy indices were calculated in eight healthy adults from 31 multisection, interleaved echo-planar diffusion-weighted images acquired in about 25 minutes. RESULTS: No statistically significant differences in Trace(D) (approximately 2,100 x 10(-6) mm2/sec) were found within normal brain parenchyma, except in the cortex, where Trace(D) was higher. Diffusion anisotropy varied widely among different white matter regions, reflecting differences in fiber-tract architecture. In the corpus callosum and pyramidal tracts, the ratio of parallel to perpendicular diffusivities was approximately threefold higher than previously reported, and diffusion appeared cylindrically symmetric. However, in other white matter regions, particularly in the centrum semiovale, diffusion anisotropy was low, and cylindrical symmetry was not observed. Maps of parameters derived from D were also used to segment tissues based on their diffusion properties. CONCLUSION: A quantitative characterization of water diffusion in anisotropic, heterogeneously oriented tissues is clinically feasible. This should improve the neuroradiologic assessment of a variety of gray and white matter disorders.

Adult↗

PubMed1996

Cortical and subcortical chemical pathology in Alzheimer's disease as assessed by multislice proton magnetic resonance spectroscopic imaging.

BACKGROUND: Multislide 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.

Aged↗

PubMed1996

Gloves and memos.

Explore the source record for details and available documents.

Gloves, Surgical↗

PubMed1995

Magnetic resonance imaging of brain iron in health and disease.

Brain iron is a major contributor to magnetic resonance imaging (MRI) contrast in normal gray matter, and its role in the pathogenesis of different neurological disorders has also become apparent. Non-heme brain iron is present in the brain mainly in the form of ferritin. The unique magnetic properties of ferritin determine different signal changes on both T1- and T2-weighted images, and the T2 relaxation rates have a linear dependence on applied field strength. This finding is typical for ferric oxyhydroxide cores. The resulting T2-shortening also depends on echo-spacing used in the imaging sequence as well as on the water diffusion coefficient and the size of the ferritin cluster. Quantitation of non-heme brain iron by MRI aids in the diagnosis and monitoring of different neurological diseases.

Brain↗

PubMed1995

Response of non-Hodgkin lymphoma to radiation therapy: early and long-term assessment with H-1 MR spectroscopic imaging.

PURPOSE: To determine whether proton magnetic resonance (MR) spectroscopic imaging is a sensitive technique for defining tumor extent and assessing response of cerebral lymphoma to therapy. MATERIALS AND METHODS: Four hydrogen-1 MR spectroscopic imaging studies were performed in a patient with non-Hodgkin lymphoma (NHL) before, during, and after radiation therapy and at follow-up at 33 months after diagnosis of the recurrence of disease. The patient had a single, large lesion in the brain and underwent hyperfractionated radiation therapy for 4 weeks. A series of MR images was also obtained. RESULTS: The pretreatment study showed a lesion with a distinct spectral pattern: marked elevation of choline and lipids and great reduction of creatine and N-acetylaspartate. During and after treatment, H-1 MR spectroscopic images depicted a progressive reduction of the abnormal choline and lipid signals. Thirty-three months after treatment, multiple-section H-1 MR spectroscopic images showed normal spectral patterns in all sections examined. CONCLUSION: H-1 MR spectroscopy may contribute to the neuroradiologic evaluation of NHL and, in particular, may be useful in monitoring therapeutic response.

Aspartic Acid↗

PubMed1995

Brain regional distribution pattern of metabolite signal intensities in young adults by proton magnetic resonance spectroscopic imaging.

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.

Adult↗

PubMed1995

Proton magnetic resonance spectroscopic imaging in childhood ataxia with diffuse central nervous system hypomyelination.

The spatial distribution of metabolite signal intensities can be measured within entire sections of the brain by proton magnetic resonance spectroscopic imaging (1H-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-slice 1H-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 no 1H-MRSI abnormalities in the gray matter. 1H-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.

Aspartic Acid↗

PubMed1995

Decreased cerebral glucose metabolism in patients with brain tumors: an effect of corticosteroids.

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 CMRglu compared 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 CMRglu in 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).

Adult↗

PubMed1995

Correlative morphologic and functional imaging for diagnosis, staging and follow up in AIDS: an overview.

The immunocompromised patient can be affected by different opportunistic infections and tumors, that can involve all organ systems, and particularly, the central nervous system, the respiratory system, the gastrointestinal tract. The extreme variability of AIDS presentations requires a specific preparation and cooperation between the different diagnostic imaging specialists and a close collaboration with the clinicians. With AIDS, different morphologic and functional imaging techniques can be used for detection of disease sites, assessment of the extent of the disease and monitoring of disease changes over time and response to treatment. The complexity of AIDS presentations is such that full integration of the complementary information obtained with different techniques could be most useful. Image registration (coregistration, fusion) indicates approaches where precise spatial cross-references are obtained, in order to combine the information acquired with different imaging modalities, in particular by blending morphologic CT/MRI data with functional SPET/PET data. In this paper, an overview of the developments in the field of "image fusion" follows some comments on the results of morphologic and functional assessment of brain, chest and abdominal diseases in the course of AIDS, as illustrative examples of the potential benefits of multimodality image correlation.

AIDS-Related Opportunistic Infections↗

PubMed1995

PET-FDG of pleomorphic xanthoastrocytoma.

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.

Adult↗

PubMed1994

MRI detects acute degeneration of the nigrostriatal dopamine system after MPTP exposure in hemiparkinsonian monkeys.

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)

1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine↗

PubMed1994

Brain parenchyma apparent diffusion coefficient alterations associated with experimental complex partial status epilepticus.

The objective of this study was to evaluate whether water apparent diffusion coefficient (ADC) measurements provide more specific information than T2-weighted MRI about the evolution of brain parenchyma lesions secondary to prolonged complex partial seizures. We measured the ADC in the brain of rats exhibiting prolonged complex partial seizures induced by intraperitoneal injection of kainic acid (KA). The animals were imaged with diffusion and T2-weighted MRI at 2 T from 3 h up to 9 days after 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 returned to normal by 9 days. In the same regions between 24 and 72 h, the ADC first decreased and then increased. The ADC changes were consistent with the known histopathologic alterations. In this complex partial seizure model, the ADC measurement provides more specific information than T2-weighted MRI about the histopathologic evolution of the lesions. This supports the proposal that diffusion MRI may be valuable for the evaluation of the neuropathologic sequelae in patients with multiple or prolonged seizures.

Animals↗

PubMed1994

Regional cerebral blood flow imaging with 99mTc-bicisate SPECT in asymmetric Parkinson's disease: studies with and without chronic drug therapy.

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 of < 3%. 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.

Adult↗

PubMed1993

6-[18F]fluoro-L-dihydroxyphenylalanine metabolism and positron emission tomography after catechol-O-methyltransferase inhibition in normal and hemiparkinsonian monkeys.

Increased and sustained central delivery of L-dihydroxyphenylalanine (L-DOPA) is a desirable therapeutic strategy in Parkinson's disease. We investigated the effects of peripheral catechol-O-methyltransferase (COMT) inhibition, by the non-toxic drug nitecapone on the metabolism of 6-[18F]fluoro-L-dihydroxyphenylalanine (6FD) and on its positron emission tomography (PET) imaging in non-human primates. Nitecapone produced a dose-dependent inhibition in the formation of 3-O-methyl-6-[18F]fluorodihydroxyphenylalanine (OMFD). This inhibition of OMFD formation was attended by increased production of other metabolites, in particular 6-[18F]fluorodopamine (6FDA), 6-[18F]fluorodihydroxyphenylacetic acid (FDOPAC), 6-[18F]fluorohomovanillic acid (FHVA) and [18F]-sulfated conjugates (FSC). Although nitecapone had no effect on plasma 6FD pharmacokinetics, high-dose nitecapone increased contrast of cerebral 18F uptake and retention between regions with high (striatum) versus sparse (parieto-occipital lobes) dopaminergic innervation. 18F uptake contrast was also improved between structures known to possess an intermediate dopaminergic innervation, including the upper brainstem, frontal and temporal lobes, versus sparsely innervated regions. This increased contrast was secondary to decreased activity in sparsely innervated structures and not to increased activity in highly innervated structures. Contrast was correlated inversely with the plasma OMFD/6FD concentration ratio, OMFD being the main 6FD metabolite which can cross the blood brain barrier. We conclude that nitecapone is an effective inhibitor of COMT in non-human primates. This inhibition results in increased 6FD flux through other catabolic pathways. Because of decreased OMFD formation, however, COMT inhibition improves the specificity of 6FD-PET and facilitates in-vivo detection of a wide range of dopaminergic innervation densities in cerebral structures.

Animals↗