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Biomedical subjects

R S Frackowiak

Publications and source records attributed to R S Frackowiak.

At least 253 records · Page 14Linked to original sources
PubMed1990

[Functional metabolic neuroimaging by positron-emission tomography in man].

Positron emission tomography allows an in vivo assessment of various physiological and biochemical processes, for example cerebral blood flow, metabolism, or interactions between ligands and receptors. Data quantification and interpretation rest on models describing in a simple way the behavior of the labelled molecules. The general principles are common, but each model has limitations. The different methods are first validated in and applied to normal populations under resting conditions. New techniques for rapid assessments of blood flow and metabolism make it possible to measure cerebral activation after sensori-motor, mental or pharmacological stimulation. This should allow the study of recovery or plasticity of the lesioned brain, after a stroke for example. PET measurements of cerebral blood flow, oxygen consumption and extraction, and cerebral blood volume are particularly well suited to investigate the physiopathology of cerebrovascular diseases. Remote metabolic disturbances give information on interregional cerebral connections, and on clinico-metabolic correlations. In epilepsy, PET is useful in localizing the epileptogenic focus in partial epilepsy: it is hypometabolic interictally. The meaning of the hypometabolism has still to be established. New information about the neurochemistry of the epileptogenic focus should become available from studies of benzodiazepine, excitatory amino acid or opiate systems, for example. PET has already enabled pathophysiological hypotheses to be tested in status epilepticus. Disturbances of metabolism and neurotransmission systems have been observed at various stages and in various types of neurodegenerative diseases. The modifications are not only an early reflection of anatomopathological lesions, but could give more direct information on the pathogenesis or symptomatology of these diseases and hence lead to new therapeutic endeavours, such as appropriate replacement therapy analogous by to dopatherapy in Parkinson's disease.

Aging↗
PubMed1989

The colour centre in the cerebral cortex of man.

Anatomical and physiological studies have shown that there is an area specialized for the processing of colour (area V4) in the prestriate cortex of macaque monkey brain. Earlier this century, suggestive clinical evidence for a colour centre in the brain of man was dismissed because of the association of other visual defects with the defects in colour vision. However, since the demonstration of functional specialization in the macaque cortex, the question of a colour centre in man has been reinvestigated, based on patients with similar lesions in the visual cortex. In order to study the colour centre in normal human subjects, we used the technique of positron emission tomography (PET), which measures increases in blood flow resulting from increased activity in the cerebral cortex. A comparison of the results of PET scans of subjects viewing multi-coloured and black-and-white displays has identified a region of normal human cerebral cortex specialized for colour vision.

Cerebral Cortex↗
PubMed1989

PET scanning.

Explore the source record for details and available documents.

Brain↗
PubMed1989

The C15O2 build-up technique to measure regional cerebral blood flow and volume of distribution of water.

A new method to measure regional CBF (rCBF) and volume of distribution of water is presented. It centres on recording the tissue build-up and retention of 15O-labelled water during the continuous inhalation of 15O-labelled carbon dioxide. Simultaneously, the arterial concentration is continuously monitored, and corrections for delay and dispersion in the recorded response are made by curve fitting. The values for the volume of distribution of water obtained in four normal subjects were close to reported in vitro values. Using the same fixed distribution volumes for both build-up and steady-state studies resulted in comparable rCBF values for both techniques.

Adult↗
PubMed1989

Localisation in PET images: direct fitting of the intercommissural (AC-PC) line.

A technique is described for estimating the position of the intercommisural line (AC-PC line) directly from landmarks on positron emission tomographic (PET) images, namely the ventral aspects of the anterior and posterior corpus callosum, the thalamus, and occipital pole. The relationship of this estimate to the true AC-PC line, fitted through the centres of the anterior and posterior commissures, showed minimal vertical and angular displacement when measured on magnetic resonance imaging (MRI) scans. Using regression analysis, the ease and reliability of fitting to these points was found to be high. This directly derived AC-PC line estimate was validated in terms of the assumptions used in the method of Fox et al. The ratio of distance between the AC-PC line and a line passing through the base of the inion (GI line) to total brain height was 0.21, as predicted. The technique has been further validated by localizing focal activation of the sensorimotor cortex. The technique is discussed in terms of absolute limits to localization of structures in the brain using noninvasive tomographic techniques in general and PET in particular.

Brain↗
PubMed1989

PET and movement disorders.

In this paper the use of PET for determining the patterns of disruption of both regional cerebral metabolism, and the pre- and post-synaptic dopaminergic systems, associated with movement disorders is reviewed. That the various akinetic-rigid syndromes result in distinctive PET findings is shown, making functional imaging valuable in their differential diagnosis. PET may also be useful for detecting the presence of sub-clinical disease in Huntington's disease and other inherited movement disorders.

Blood Glucose↗
PubMed1988

Cerebral blood flow and metabolism of oxygen and glucose in young autistic adults.

Regional cerebral blood flow, oxygen consumption and glucose consumption were measured by positron emission tomography in six young autistic men. No significant differences were found between patients and normal controls for any of the physiological variables. The results do not substantiate the previous finding of glucose hypermetabolism in autism; the likely reasons for the variance in findings are discussed.

Adult↗
PubMed1988

Acute cerebral ischaemia: concurrent changes in cerebral blood flow, energy metabolites, pH, and lactate measured with hydrogen clearance and 31P and 1H nuclear magnetic resonance spectroscopy. III. Changes following ischaemia.

CBF has been measured with the hydrogen clearance technique in the two cerebral hemispheres of the gerbil under halothane anaesthesia. At the same time, intracellular pH and the concentrations of lactate and high-energy phosphates were measured in the brain using 1H and 31P nuclear magnetic resonance spectroscopy. Flow and metabolism have been followed during either a 15- or a 30-min ischaemic period (induced by bilateral carotid occlusion) and for up to 1 h of recovery. There was no significant difference between the flow characteristics of the two experimental groups. High-energy phosphate levels and pH returned to control within approximately 20 min of the end of the ischaemic period. Lactate clearance, following a 30-min occlusion, was slower than the recovery of pH. The concentration of free ADP, calculated from the creatine kinase equilibrium, was lower during the recovery phase than under control conditions.

Animals↗
PubMed1988

Steele-Richardson-Olszewski syndrome. Brain energy metabolism, blood flow and fluorodopa uptake measured by positron emission tomography.

Brain function was measured in 5 patients with clinically diagnosed Steele-Richardson-Olszewski syndrome using positron emission tomography and tracers of dopamine metabolism, blood flow and oxygen metabolism. A global decrease in blood flow and oxygen utilization compared with normal values was found but the decrease was more marked in the frontal regions. The degree of impairment in oxygen utilization in the frontal region paralleled roughly the duration of the disease. Blood flow was impaired to a greater extent than oxygen utilization, resulting in raised oxygen extraction. This can partially be explained by a lower pCO2 in the patients. Alternatively it may imply involvement of brain vasculature in the pathophysiology of the disease in addition to neuronal degeneration. Striatal dopamine formation and storage, as indicated by L-(18F)fluorodopa uptake, was significantly decreased compared with control values. The severity of this decrease paralleled the degree of reduction in frontal cerebral blood flow. The results suggest that the impairment of cerebral function in Steele-Richardson-Olszewski syndrome is determined to a large extent by brainstem pathology.

Adult↗
PubMed1988

The cerebral metabolism of glucose and oxygen measured with positron tomography in patients with mitochondrial diseases.

Cerebral oxygen and glucose metabolism have been studied in 8 patients with biochemically defined mitochondrial myopathies and 7 normal control subjects using positron emission tomography. Four patients had myopathy alone and 4 had predominantly central nervous system (CNS) disease. Cerebral oxygen and glucose metabolism were measured concurrently in the two groups of patients with 15O, 11C and 18F labelled tracers and positron emission tomography (PET). Patients with major CNS disease showed an uncoupling of glucose and oxygen metabolism when compared with patients without cerebral disease and normal subjects. The mean ratio between oxygen and glucose utilization was 3.8 moles of oxygen per mole of glucose in patients with CNS disease, compared with 5.6 for controls and 6.4 for patients with myopathy alone. The altered stoichiometry in CNS cases indicates aerobic glycolysis to lactate and/or other intermediate metabolites. Patients with major CNS disease showed a 50% reduction in cerebral oxygen utilization compared with cerebrally unaffected patients and normal subjects. These findings indicate that in patients with a mitochondrial encephalopathy the defect identified in skeletal muscle is also expressed in the brain.

Adult↗
PubMed1988

Assessment of cerebral haemodynamic reserve: correlation between PET parameters and CO2 reactivity measured by the intravenous 133 xenon injection technique.

Regional cerebral blood flow (CBF), oxygen utilisation, fractional oxygen extraction (OER) and cerebral blood volume (CBV) were measured by positron emission tomography (PET) in 21 patients with occlusive carotid artery disease. In the same patients, measurements of cerebral CO2 reactivity were performed using the intravenous xenon-133 technique. A significant correlation was found in symptomatic hemispheres between the CBF/CBV ratio and CO2 reactivity. Four patients had significant increases in OER and this was associated with a reduction in CBF/CBV ratio implying exhaustion of haemodynamic reserve. CO2 reactivity was reduced below 1.5% mm Hg in all four cases with raised OER but only in two cases with normal OER. In patients with CO2 reactivities above 1.5% mm Hg, OER was normal in all cases. It is concluded that measurements of CO2 reactivity provide a satisfactory method for assessing cerebral haemodynamic reserve.

Aged↗