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Biomedical subjects

M E Raichle

Publications and source records attributed to M E Raichle.

At least 127 records · Page 7Linked to original sources
PubMed1985

The role of cerebral cortex in the generation of voluntary saccades: a positron emission tomographic study.

The purpose of this study was to define the location and behavior of cerebral structures within the normal human brain that participate in the generation of voluntary saccadic eye movements. Changes in regional cerebral blood flow (rCBF) during task performance were assumed to reflect like changes in regional neuronal activity induced by the task. The locations of all rCBF changes were described in stereotaxic coordinates. Cerebral blood flow (CBF) was measured with positron emission tomography (PET) and bolus intravenous injection of H2(15)O. The use of H2(15)O with PET allowed six, seven-slice measurements of brain blood flow to be made in rapid sequence for each subject, without removing the subject from the tomograph between scans. Nine paid normal volunteers were studied. The paradigm included three saccadic eye-movement (SEM) conditions, one finger-movement condition and two control conditions (initial and final). The three SEM conditions allowed comparisons to be drawn between targeted versus untargeted SEMs, auditorily cued versus visually cued SEMs, and stochastic versus rhythmic SEMs. All tasks were simple and deterministic in that each movement exactly mirrored the preceding movement: finger flexion then extension, saccade-left then saccade-right. Saccadic eye movements were associated with rCBF increases within the frontal eye fields, the supplementary motor area, and the cerebellum. Finger movements were associated with rCBF changes within the sensorimotor hand areas, the supplementary motor area, and the cerebellum. The frontal eye fields were discrete cortical regions consistently active during the generation of voluntary SEMs and uninfluenced by target presence, type of cue, or task complexity, indicating a predominantly motor function. The supplementary motor area (SMA) was consistently active during all motor tasks and was uninfluenced by the degree of task complexity or stochasticity. A role for SMA in establishing "motor set" during both simple and complex motor tasks is suggested. An anterior-posterior somatotopy was found for SMA-eye (anterior) versus SMA-hand (posterior). Lateral occipital visual association cortex activation was present only during targeted saccadic conditions.(ABSTRACT TRUNCATED AT 400 WORDS)

Adult↗
PubMed1985

Positron emission tomography in the newborn: effect of seizure on regional cerebral blood flow in an asphyxiated infant.

Regional cerebral blood flow (CBF) was measured by positron emission tomography (PET) with 15O-labeled water in an asphyxiated infant during a seizure. After intrauterine asphyxia, the infant had a syndrome characteristic of hypoxic-ischemic encephalopathy. During a PET scan on the second postnatal day, the infant had a focal seizure with deviation of eyes to the right and clonic jerking of the right arm. Regional blood flow was highest, about 80 ml/100 g/min, in the left temporal-parietal frontal region of the left hemisphere, the site of origin of the seizure; blood flow in the same region on the other side was about 57 ml/100 g/min. These observations extend to the newborn previous demonstrations in older patients of a focal increase of CBF at the cerebral site of origin of a focal seizure.

Asphyxia Neonatorum↗
PubMed1985

Regional blood flow in hemiparkinsonism.

Positron emission tomography was used to measure global and local blood flow in 11 patients with hemiparkinsonism (before and after an acute oral dose of L-dopa) and in 26 normal subjects. Global hemispheric blood flow was not significantly different between the patients [45 +/- 11 ml/(min X 100 g)] and the controls [49 +/- 8 ml/(min X 100 g)]. After L-dopa, the patients' mean global hemispheric flow did not change. Measurements of local blood flow from specific, anatomically defined cortical and basal ganglia regions were performed using a newly developed stereotactic localization technique. Before L-dopa, mesocortical blood flow contralateral to the patients' symptoms was significantly less than controls (p less than 0.003), suggesting a specific abnormality in the cortical dopaminergic projection from the ventral tegmental area. In addition, right and left pallidal blood flow were significantly less tightly coupled in patients than controls (p = 0.0312). After L-dopa, the mesocortical blood flow remained below normal, whereas pallidal blood flow was no longer significantly different from controls (p greater than 0.05).

Adult↗
PubMed1985

Regional cerebral blood flow and metabolism in reversible ischemia due to vasospasm. Determination by positron emission tomography.

Regional cerebral blood flow (rCBF) and regional cerebral metabolic rate of oxygen (rCMRO2) were measured by positron emission tomography (PET) in four patients with subarachnoid hemorrhage and hemiparesis due to cerebral vasospasm. With resolution of the vasospasm, two patients recovered and two remained hemiparetic. Contralateral to the hemiparesis, rCBF was slightly higher in the two patients who eventually recovered (15.0 and 16.2 ml/100 gm/min) than in the two who remained hemiparetic (12.0 and 11.7 ml/100 gm/min). The rCMRO2 measurements showed similar differences, with values of 1.34 and 2.60 ml/100 gm/min in the patients who recovered, and 0.72 and 1.66 ml/100 gm/min in those who did not. These preliminary findings indicate that with PET studies it may be possible to prospectively differentiate patients with neurological deficits due to reversible ischemia from patients with irreversible infarction.

Adult↗
PubMed1985

Brain oxygen utilization measured with oxygen-15 radiotracers and positron emission tomography: generation of metabolic images.

We recently described a PET method for the measurement of local brain tissue oxygen extraction (E) and the local cerebral metabolic rate for oxygen (CMRO2) using 15O-labeled radiotracers. The equation for the calculation of E from measured PET data is mathematically complex and its direct application in the generation of PET images of either E or the CMRO2 on a pixel-by-pixel basis is computationally burdensome. We describe a simplification of this equation which permits the efficient generation of quantitative images.

Brain↗
PubMed1984

Pet scan controversy.

Explore the source record for details and available documents.

Tomography, Emission-Computed↗
PubMed1984

A quantitative model for the in vivo assessment of drug binding sites with positron emission tomography.

We propose an in vivo method for use with positron emission tomography (PET) that results in a quantitative characterization of neuroleptic binding sites using radiolabeled spiperone. The data are analyzed using a mathematical model that describes transport, nonspecific binding, and specific binding in the brain. The model demonstrates that the receptor quantities Bmax (i.e., the number of binding sites) and KD-1 (i.e., the binding affinity) are not separably ascertainable with tracer methodology in human subjects. We have, therefore, introduced a new term, the binding potential, equivalent to the product BmaxKD-1, which reflects the capacity of a given tissue, or region of a tissue, for ligand-binding site interaction. The procedure for obtaining these measurements is illustrated with data from sequential PET scans of baboons after intravenous injection of carrier-added [18F]spiperone. From these data we estimate the brain tissue nonspecific binding of spiperone to be in the range of 94.2 to 95.3%, and the regional brain spiperone permeability (measured as the permeability-surface area product) to be in the range of 0.025 to 0.036 cm3/(s X ml). The binding potential of the striatum ranged from 17.4 to 21.6; these in vivo estimates compare favorably to in vitro values in the literature. To our knowledge this represents the first direct evidence that PET can be used to characterize quantitatively, locally and in vivo, drug binding sites in brain. The ability to make such measurements with PET should permit the detailed investigation of diseases thought to result from disorders of receptor function.

Animals↗
PubMed1984

Pure hemidystonia with basal ganglion abnormalities on positron emission tomography.

We present a patient with hemidystonia and an abnormality of the contralateral basal ganglion seen only with positron emission tomography. A 50-year-old sinistral man suffered minor trauma to the right side of his head and neck. Within 20 minutes he developed paroxysmal intermittent dystonic posturing of his right face, forearm, hand, and foot, with weaker contractions of the left foot, lasting several seconds and recurring every few minutes. Neurological findings between spells were normal. The following were also normal: electrolyte, calcium, magnesium, and arterial blood gas levels, and findings of drug screen, cerebrospinal fluid examination, electroencephalography with nasopharyngeal leads, computed tomographic scanning (initially and four weeks later), and cerebral angiography. Positron emission tomographic scanning revealed abnormalities in the left basal ganglion region, including decreased oxygen metabolism, decreased oxygen extraction, increased blood volume, and increased blood flow.

Basal Ganglia↗
PubMed1984

Physiological responses to focal cerebral ischemia in humans.

Positron emission tomography (PET) was used to investigate the regional hemodynamic and metabolic changes that accompany focal reductions in cerebral blood flow to ischemic but uninfarcted regions of the brain. Studies were performed on 7 patients chosen from a larger group of subjects with transient ischemic attacks and normal computed tomographic findings, specifically because their PET studies showed decreased blood flow to the symptomatic hemisphere rather than symmetrical flow to the two hemispheres. In regions with decreased blood flow, the cerebral metabolic rate for oxygen was also decreased, but to a lesser degree. Cerebral blood volume, vascular mean transit time, and fractional extraction of oxygen from blood were all increased. These findings indicate that cerebral oxygen metabolism was maintained in the face of decreased blood flow by local compensatory mechanisms that included dilation of intraparenchymal blood vessels and increased transfer of oxygen from blood to tissue. Such knowledge of the physiological characteristics of ischemic, uninfarcted brain is important if PET is to be used clinically to differentiate reversible cerebral ischemia from irreversible infarction.

Aged↗
PubMed1984

Cerebral blood volume, blood flow, and oxygen metabolism in cerebral ischaemia and subarachnoid haemorrhage: an in-vivo study using positron emission tomography.

A characteristic sequence of metabolic and haemodynamic changes has been shown to occur in the brain as cerebral perfusion pressure is reduced in experimental animals. Increased cerebral blood volume (CBV) occurs initially, followed by a fall in blood flow (CBF) and, finally, a fall in oxygen metabolism (CMRO2). By measuring CBV, CBF, and CMRO2 with positron emission tomography in patients with vasospasm associated with subarachnoid haemorrhage and in patients with arteriosclerotic occlusion or stenosis of extraparenchymal cerebral arteries, we have demonstrated the presence of similar changes distal to such lesions in man. These findings suggest the presence of a local decrease in perfusion pressure. This study demonstrates the utility of positron emission tomography in the assessment of cerebral circulation and metabolism in man. Measurements of regional CBV must be included for a complete assessment of the dynamics of the cerebral circulation.

Blood Volume↗
PubMed1984

A noninvasive approach to quantitative functional brain mapping with H2 (15)O and positron emission tomography.

Positron emission tomographic (PET) measurements of regional cerebral blood flow (rCBF) with intravenously administered 15O-labeled water and an adaptation of the Kety autoradiographic model are well suited to the study of functional-anatomical correlations within the human brain. This model requires arterial blood sampling to determine rCBF from the regional tissue radiotracer concentration (Cr) recorded by the tomograph. Based upon the well-defined, nearly linear relation between Cr and rCBF inherent in the model, we have developed a method for estimating changes in rCBF from changes in Cr without calculating true rCBF and thus without arterial sampling. This study demonstrates that quantitative functional brain mapping does not require the determination of rCBF from Cr when regional neuronal activation is expressed as the change in rCBF from an initial, resting-state measurement. Patterned-flash visual stimulation was used to produce a wide range of increases in rCBF within the striate cortex. Changes in occipital rCBF were found to be accurately estimated directly from Cr over a series of 56 measurements on eight subjects. This adaptation of the PET/autoradiographic method serves to simplify its application and to make it more acceptable to the subject.

Adult↗