Biomedical subjects

A Luxen

Publications and source records attributed to A Luxen.

At least 55 records · Page 3Linked to original sources

PubMed1995

Basal ganglia and frontal lobe glucose metabolism. A reproducibility positron emission tomography study.

Positron emission tomography (PET) with 18F-fluoro-2-deoxy-D-glucose (FDG) is frequently used to study the metabolic correlates of movement and mental disorders. These studies generally focus on changes in the frontal cortex and the basal ganglia. The reproducibility of glucose metabolism estimates in these structures was tested in 13 normal subjects studied at rest using a standard and simple protocol. A reproducible dorsoventral metabolic gradient was demonstrated in the frontal cortex. Such a gradient was not present in the basal ganglia when the upper region of interest in the caudate nucleus, where the lower metabolic rate of glucose was probably attributable to partial volume effects, was not considered. Absolute values of glucose metabolic rates varied by 6.4 to 12.5% in the frontal cortex and by 6.8 to 14.7% in the basal ganglia. Variations in normalized values in the basal ganglia ranged from 4.0 to 8.6%. The number of subjects required to detect statistical differences in group comparison or in test-retest studies was calculated for different anticipated levels of change. With the variability detected in this experiment, less than 10 subjects were expected to be sufficient to detect a 15% change in most regions and in both types of studies.

Adult↗

PubMed1995

Changes in metabolism of cerebral glucose after stereotactic leukotomy for refractory obsessive-compulsive disorder: a case report.

Brain glucose metabolism was investigated with PET and [18F]fluorodeoxyglucose, before and after a bifrontal stereotactic leukotomy in a 37 year old woman with refractory obsessive-compulsive disorder. A bilateral decrease in glucose metabolism was found in the orbital frontal cortex after psychosurgery. Glucose metabolism was decreased to a lesser degree in Brodmann's area 25, in the thalamus, and in the caudate nucleus. Clinical improvement in obsessive-compulsive disorder after stereotactic tractotomy seems to be associated with metabolic changes in the brain, in particular, in the orbital part of the frontal lobe.

Adult↗

PubMed1995

Diagnostic yield of stereotactic brain biopsy guided by positron emission tomography with [18F]fluorodeoxyglucose.

The aim of the present study was to determine whether routine integration of positron emission tomography (PET) with 18F-labeled fluorodeoxyglucose (FDG) in the planning of stereotactic brain biopsy increases the technique's diagnostic yield. Forty-three patients underwent combined FDG-PET- and computerized tomography (CT)-guided stereotactic biopsy of intracranial lesions according to a previously described technique. In 36 patients, an area of abnormal FDG uptake was used to guide at least one stereotactic biopsy trajectory. A total of 90 stereotactic trajectories were performed; among them, 55 were based on FDG-PET-defined targets and 35 were based on CT-defined targets. Histological diagnosis was obtained in all patients, but six of the 90 trajectories were nondiagnostic; all six were based on targets defined by CT only. Differences between the diagnostic yield of trajectories based on FDG-PET-defined targets and those based on CT-defined targets were statistically significant in patients with contrast-enhanced lesions, but not in patients with nonenhancing lesions. These results support the view the FDG-PET may contribute to the successful management of brain tumor patients requiring stereotactic biopsy. Because no significant increase in discomfort or morbidity related to the technique was found, it is suggested that the development of similar techniques integrating PET data in the planning of stereotactic biopsy should be considered by centers performing stereotactic surgery and having access to PET technology.

Adolescent↗

PubMed1994

Acute effect of carmustine on glucose metabolism in brain and glioblastoma.

BACKGROUND: Adjuvant chemotherapy benefits a minority of patients with recurrent glioblastoma; a critical question therefore is how to select such responders. Metabolic reaction of the tumor, studied by positron emission tomography (PET) with [18F]-fluoro-2-deoxy-D-glucose (FDG), may be a suitable test of tumor responsiveness. In an effort to evaluate their prognostic value, the early effects of carmustine on brain and recurrent glioblastoma glucose metabolism were studied. METHODS: Positron emission tomography with [18F]fluoro-2-deoxy-D-glucose was used to study 10 patients with recurrent glioblastoma before and 24 hours after a first dose of carmustine (120 mg/m2). Absolute quantification of glucose metabolism was obtained, and metabolic changes were analyzed and confronted with survival duration. RESULTS: The mean ratios of pre- to postchemotherapy values were 0.98 +/- 0.06 (range, 0.90-1.06) for the cortex and 0.97 +/- 0.06 (range, 0.89-1.09) for the white matter. There was no statistical difference between pre- and post-chemotherapy metabolism. In the glioblastoma, individual ratios of pre- to postchemotherapy values were considerably more scattered than in the nonneoplastic tissues, ranging from 0.76 to 1.51. A significant positive correlation (P < 0.002) was found between post- to pre-chemotherapy ratios of glucose metabolism and survival length. CONCLUSIONS: In patients with recurrent glioblastoma, the first administration of carmustine produces no acute change of glucose metabolism in the noninvolved cerebral tissues. Acute changes of glucose metabolism in tumor tissue in response to this treatment varied, and a hypermetabolic reaction possibly predicts longer survival.

Adult↗

PubMed1994

Frontal and parietal metabolic disturbances in unipolar depression.

The authors investigated brain glucose utilization using positron emission tomography (PET) in 12 normal volunteers and 12 unipolar unmedicated depressed patients (six endogenous; six nonendogenous) following injection of [18F]fluoro-deoxyglucose (FDG). Compared by analyses of variance, absolute and relative regional glucose metabolic rates appeared different in depressed patients and control subjects, especially in parietal and frontal lobes. In patients with unipolar depression, metabolic rates were increased in the orbital part of the frontal lobe and decreased in a frontal dorsolateral area. The metabolic supero-basal gradient calculated in the frontal cortex was significantly lower in depressed patients than in normal subjects. Decreased glucose metabolism was also observed in the parietal cortex of depressed patients. No differences in glucose metabolic rates have been detected between endogenous and nonendogenous patients. No correlation has been found between the metabolic data and the Hamilton Rating Scale.

Adult↗

PubMed1994

Effect of catechol-O-methyl transferase inhibition on peripheral and central metabolism of 6-[18F]fluoro-L-dopa.

In the presence of carbidopa, L-3,4-dihydroxy-6-[18F]fluorophenylalanine ([18F]fluoro-DOPA) is mainly metabolized by catechol-O-methyl transferase. We studied the effects of entacapone, a peripheral catechol-O-methyl transferase inhibitor, on striatal [18F]fluoro-DOPA uptake in rats. Rats were pretreated with carbidopa, entacapone or both before high specific activity (> 2 Ci/mmol) [18F]fluoro-DOPA administration. Entacapone alone antagonized the appearance of methylated metabolites in plasma, striatum and cerebellum but did not increase striatal [18F]fluoro-DOPA availability. Entacapone added to carbidopa significantly increased the striatum/cerebellum total radioactivity ratio (1.4 versus 1.2 in rats with carbidopa, 1.0 in controls) but significant levels of methylated metabolites were found in the brain. Entacapone added to carbidopa might increase the striatum/cerebellum total radioactivity ratio in humans undergoing [18F]fluoro-DOPA positron emission tomography (PET) studies. However, the appearance of methylated metabolites in the brain could hamper quantification of the PET data.

Animals↗

PubMed1994

Multicompartmental study of fluorine-18 altanserin binding to brain 5HT2 receptors in humans using positron emission tomography.

Serotoninergic type 2 (5HT2) receptors have been implicated in the regulation of many brain functions in humans and may play a role in several neurological and psychiatric diseases. Fluorine-18 altanserin has been proposed as a new radiotracer for the study of 5HT2 receptors by PET because of its high affinity for 5HT2 receptors (Ki: 0.13 nM) and its good specificity in in vitro studies. Dynamic PET studies were carried out in 12 healthy volunteers after intravenous injection of 0.1 mCi/kg [18F]altanserin. Ninety minutes after injection, we observed mainly cortical binding. Basal ganglia and cerebellum showed very low uptake and the frontal cortex to cerebellum ratio was about 3. To evaluate the quantitative distribution of this ligand in the brain, we used two different methods of data analysis: a four-compartment model was used to achieve quantitative evaluation of rate constants (K1 and k2 through k6) by non-linear regression, and a multiple-time graphical analysis technique for reversible binding was employed for the measurement of k1/k2 and k3/k4 ratios. Using both methods, we found significant differences in binding capacity (estimated by k3/k4 = Bmax/Kd) between regions, the values increasing as follows: occipital, limbic, parietal, frontal and temporal cortex. After correction of values obtained by the graphical method for the existence of non-specific binding, results generated by the two methods were consistent.

Adult↗

PubMed1994

Temporal glucose metabolism in borderline personality disorder.

The pathophysiology of borderline personality disorder (BPD) is obscure. Underlying organic factors such as epilepsy are suspected because clinical characteristics of the syndrome are similar to some manifestations of patients with complex partial seizures (CPS). Positron emission tomography (PET) with 18F-fluorodeoxyglucose (FDG) reveals hypometabolism in the area surrounding epileptic foci. To test the epilepsy hypothesis in BPD, we have explored 10 patients with BPD and compared them with 15 control subjects using PET with FDG. We conclude that PET provides no metabolic indication of temporal lobe epilepsy in BPD.

Adult↗

PubMed1994

Carbon-11-methionine and fluorine-18-FDG PET study in brain hematoma.

Three patients were examined using PET with L-methyl-11C-methionine (11C-methionine) and 2-18F-fluoro-2-deoxy-D-glucose (FDG) 20 to 32 days after the occurrence of nontumoral brain hematomas. PET revealed high uptake of 11C-methionine in the area surrounding the hematoma in all three patients. In two patients, discrete spots of moderate uptake of FDG were found at the periphery of a hypometabolic area. PET studies were repeated in two patients 76 and 103 days after the bleeding, respectively, and showed a dramatic decrease in 11C-methionine uptake around the hematoma. The spots of FDG uptake disappeared on the repeated late scans. We hypothesize that the subacute gliotic reaction surrounding brain hematomas is responsible for increased uptake of 11C-methionine and for the presence of spots of FDG uptake. PET studies with 11C-methionine and FDG performed 20 to 32 days after the initial symptom are not helpful in the differentiation between neoplastic and non-neoplastic origins of an intracerebral hemorrhage since tracer uptake at the periphery of the lesion may be increased in both.

Acute Disease↗

PubMed1994

[Cerebral lesions following convulsive partial status epilepticus. Clinical, neuroradiologic and PET study of a case].

An 11-year-old girl developed signs of intracranial hypertension after status epilepticus with convulsive movements of her right upper limb. Computerized tomography revealed left hemispheric hypodensity with mass effect, attributed to vasogenic edema. Intracranial hypertension was controlled under intracranial pressure monitoring and clinical status slowly improved. The patient was aphasic and right hemiplegic when she recovered consciousness but she remarkably recovered from her neurological deficits during the following two years despite neuroradiological evolution demonstrating extensive destruction of the left cortex and white matter. Two positron emission tomography (PET) scans were performed respectively six weeks and eight months after status epilepticus, and both demonstrated profound left hemispheric hypometabolism except in the lenticular nucleus and a restricted area of motor/premotor cortex. On the other hand, glucose metabolism in the right hemisphere was heterogeneously increased on the second PET when compared with the first PET. We concluded that, in this case, clinical recovery might have implicated functional reorganization arising from the intact hemisphere.

Aphasia↗

PubMed1993

Reversible striatal hypermetabolism in a case of Sydenham's chorea.

We studied a 10-year-old girl with Sydenham's chorea (SC) using positron emission tomography (PET) with fluorodeoxyglucose (FDG). Choreic movements involved the head and the left side of her body. PET showed increased glucose metabolism in the right caudate nucleus and putamen. Three months after complete recovery, striatal glucose metabolism had returned to normal in the caudate nucleus. In the right putamen, glucose metabolism had decreased compared to that in the first study but remained elevated compared to that of normal young adults. We propose that the transient striatal hypermetabolism may have been due to increased afferent inputs to the striatum as a consequence of striatal or subthalamic nucleus dysfunction.

Basal Ganglia↗

PubMed1993

Brain glucose metabolism and dopamine D2 receptor analysis in a patient with hemiparkinsonism-hemiatrophy syndrome.

We report findings on brain glucose metabolism and dopamine D2 receptors generated by positron emission tomography (PET) in a 67-year-old woman with right hemiparkinsonism-hemiatrophy syndrome (HP-HA). PET with [18F]-fluorodeoxyglucose (FDG) showed marked glucose metabolism asymmetry. There were significant reductions in glucose uptake at the level of the basal ganglia and, to lesser extent, in the fronto-parietal cortex contralateral to the clinically involved side. These changes were different from those found in a patient with hemi-Parkinson's disease who was scanned under similar conditions. Because the patient with HP-HA had only minimal response to levodopa therapy, we evaluated post-synaptic dopaminergic structures using PET with [18F]-fluoroethylspiperone (FESP). No striatal binding asymmetry was found in FESP/PET, which suggests a sparing of striatal dopamine D2 receptors. The changes in FDG uptake which we found were in brain areas relevant to the clinical features of HP-HA syndrome. In addition, our study provides evidence that FDG/PET may help to differentiate HP-HA syndrome from hemi-Parkinson's disease. In most instances, since HP-HA is associated with a more benign clinical course than Parkinson's disease, this distinction is of clinical important.

Aged↗

PubMed1993

Direct comparison of [13N]ammonia and [15O]water estimates of perfusion with quantification of regional myocardial blood flow by microspheres.

BACKGROUND: Both [13N]ammonia and [15O]water have been used to quantify myocardial blood flow with positron emission tomography using appropriate tracer kinetic models. A direct comparison of the two tracers with radioactive microspheres has not been performed in the same experimental preparation. METHODS AND RESULTS: The two tracers have been tested for myocardial blood flow quantification in closed-chest dogs with circumflex coronary stenosis or permanent occlusion at rest and during adenosine-induced hyperemia. [13N]ammonia- and [15O]water-derived myocardial blood flow values have been compared with radiolabeled microspheres. Validation studies consisted of simultaneous measurements of blood flow with positron emission tomography and microspheres over a wide range of flow values. Blood pool and regional tissue activity curves were fitted with a three-compartment model for [13N]ammonia with and without arterial metabolite correction and with a single-tissue-compartment model for [15O]water. A correction for finite-resolution effect before the fit was also applied. In large regions of interest (5 cm3), a good correlation between the microsphere method and [13N]ammonia (with metabolite correction) was obtained (y = 3 + 0.78x, r = 0.94). The correlation with microspheres was slightly better with [15O]water (y = -3 + 0.89x, r = 0.97). Similar correlations were achieved in smaller regions of interest (1 cm3) as well as in akinetic segments and in central infarct regions. CONCLUSIONS: Positron emission tomography with appropriate tracer kinetic models using [13N]ammonia and [15O]water provides an accurate quantitative method for measuring regional myocardial blood flow over a wide range of flow values in normally contracting or akinetic canine myocardium in the absence and in the presence of infarction.

Ammonia↗

PubMed1993

Hemibody tremor related to stroke.

BACKGROUND: Hemibody tremor is an uncommon manifestation of stroke. We describe a case investigated by both brain magnetic resonance imaging and positron emission tomography using [18F]fluorodeoxyglucose. CASE DESCRIPTION: Three months after a pure motor stroke, a 65-year-old man developed a right arm and leg tremor. The tremor was of large amplitude, intermittent at rest; its frequency was 5 to 6 Hz. Neither rigidity nor akinesia was detected, and administration of L-dopa was ineffective. Brain magnetic resonance imaging revealed an ischemic lesion in the left centrum semiovale and a left caudate lacunar infarction. We suspected that the resting unilateral tremor was related to this lacunar lesion. Positron emission tomography demonstrated glucose hypermetabolism in the left sensorimotor cortex. CONCLUSIONS: This case suggests that unilateral tremor may be related to a lacunar stroke in the caudate nucleus and may be accompanied by an increased glucose metabolism in the contralateral sensorimotor cortex.

Aged↗

PubMed1993

Positron emission tomography and histopathology in Creutzfeldt-Jakob disease.

We studied a 62-year-old man with Creutzfeldt-Jakob disease (CJD), using positron emission tomography (PET) and (18F)-2-fluoro-2-deoxy-D-glucose (FDG). Glucose metabolism was heterogeneously decreased throughout the brain. At autopsy, regional distributions of spongiosis, astrogliosis, and neuronal loss correlated with premortem regional metabolic deficits. These results suggest that PET with FDG may provide metabolic regional markers for CJD neuropathology.

Brain↗

PubMed1992

Production of 6-[18F]fluoro-L-dopa and its metabolism in vivo--a critical review.

This report critically appraises methods for the synthesis of 6-[18F]fluoro-L-3,4-dihydroxyphenylalanine (6-FDOPA) that are based on labelling by non-regioselective electrophilic fluorination, regioselective fluorodemetalation or nucleophilic substitution. Recommendations for the standardization of labelling procedures, the optimization of radiochemical yield and the assurance of product quality and safety are given. Studies of the metabolism of 6-FDOPA in vivo are also reviewed to emphasize the importance of the biochemical component of the development of this tracer for positron emission tomography (PET).

Animals↗

PubMed1992

Positron emission tomography-guided stereotactic brain biopsy.

We describe a technique that allows target definition for stereotactic brain biopsy using coordinates calculated on stereotactic positron emission tomographic (PET) images. In this study, PET images were obtained using [18F]-labeled fluorodeoxyglucose, a marker for glucose metabolism. The difference between PET-calculated and actual stereotactic coordinates of simulated targets is within PET spatial resolution. Combined computed tomography- and PET-guided stereotactic biopsies were performed in 11 patients with brain tumors. In this report, we describe two representative patients who underwent stereotactic brain biopsy using the present technique. Because of the complementary role of PET and computed tomography, their integration in multimodality planning might optimize the target selection for stereotactic brain biopsies.

Astrocytoma↗

PubMed1992

The effects of carbidopa administration on 6-[18F]fluoro-L-dopa kinetics in positron emission tomography.

Carbidopa (L-alpha-hydrazino-alpha-methyl-b-(3,4-dihydroxyphenyl) propionic acid is a known inhibitor of aromatic amino acid decarboxylase. In both humans and monkeys, we studied the effects of carbidopa on plasma and brain kinetics of 6-[18F]fluoro-L-DOPA (FDOPA), an analog of L-DOPA used for PET studies of the central dopaminergic system. Pretreatment with carbidopa resulted in increases in the plasma levels of FDOPA and 3-O-methyl-6-[18F]fluoro-L-DOPA (3-OMFD). Total striatal and cerebellar activities measured with PET were also increased. Furthermore, increases observed in the specific striatal activity (striatum minus cerebellum total activity) were correlated with increases in the plasma FDOPA curve. Carbidopa pretreatment did not affect the influx rate constant (K) for FDOPA from plasma to striatum in humans as determined by Patlak graphical analysis. Thus, an increase in measured striatal tomographic activity was secondary to the increase in plasma FDOPA levels rather than as a result of changes in the FDOPA influx rate constant.

Adult↗