Positron emission tomography study of regional glucose metabolism in cerebral ischemia--topographic and kinetic aspects.
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Biomedical subjects
K Wienhard
Publications and source records attributed to K Wienhard.
Regional kinetic constants and cerebral metabolic rate for glucose in normal human volunteers determined by dynamic positron emission tomography of [18F]-2-fluoro-2-deoxy-D-glucose.
Using dynamic [18F]fluorodeoxyglucose (FDG) positron emission tomography with a high-resolution, seven-slice positron camera, the kinetic constants of the original three-compartment model of Sokoloff and co-workers (1977) were determined in 43 distinct topographic brain regions of seven healthy male volunteers aged 28-38 years. Regional averages of the cerebral metabolic rate for glucose ( CMRglu ) were calculated both from individually fitted rate constants ( CMRglukinetic ) and from activity maps recorded 30-40 min after FDG injection, employing a four-parameter operational equation with standard rate constants from the literature ( CMRgluautoradiographic ). Metabolic rates and kinetic constants varied significantly among regions and subjects, but not between hemispheres. k1 ranged between 0.0485 +/- 0.00778 min-1 in the oval center and 0.0990 +/- 0.01347 min-1 in the primary visual cortex. k2 ranged from 0.1198 +/- 0.01533 min-1 in the temporal white matter to 0.1472 +/- 0.01817 min-1 in the cerebellar dentate nucleus. k3 was lowest (0.0386 +/- 0.01482 min-1) in temporal white matter and highest (0.0823 +/- 0.02552 min-1) in the caudate nucleus. Maximum likelihood cluster analysis revealed four homogeneous groups of brain regions according to their respective kinetic constants: (1) white matter and mixed brainstem structures; (2) cerebellar gray matter and hippocampal formations; (3) basal ganglia and frontolateral and primary visual cortex; and (4) other cerebral cortex and thalamus. Across the entire brain, k1 and k2 were positively correlated (r = 0.79); k1 and k3 showed some correlation (r = 0.59); but no significant linear association was found between k2 and k3. A strong correlation with CMRglu could be demonstrated for k1 (r = 0.88) and k3 (r = 0.90), but k2 was loosely correlated (r = 0.56). CMRglu kinetic ranged from 17.0 +/- 2.45 mumol/100 g/min in the occipital white matter to 41.1 +/- 5.62 mumol/100 g/min in the frontolateral cortex. In most regions the mean values of CMRglu kinetic did not differ significantly from CMRglu autoradiographic. With few exceptions, however, within-region variance was significantly less for CMRglu kinetic than for CMRglu autoradiographic, suggesting greater individual reliability of results obtained by the kinetic approach.
Adult↗
[Positron emission tomography as a quantitative imaging method for demonstrating regional brain metabolism].
By means of positron emission tomography (PET) the distribution of certain isotopes in transverse sections through the body is visualized and the concentration of labelled tracers in the tissue quantified. Various biochemical and physiological processes in the brain can be followed by positron emitting radionuclides and compounds labelled thereby. Of these methods the measurement of glucose metabolism with 18fluorodeoxyglucose, of oxygen consumption with 15oxygen and of blood flow with 15O-carbon dioxide or 18fluoromethane are of greatest clinical relevance. These techniques demonstrated increases in metabolic rate after functional activation of respective brain regions and revealed local metabolic disturbances after different pathological changes of the central nervous system. With other labelled compounds protein synthesis, distribution of specific receptors, damage of the blood brain barrier, blood volume and regional uptake of drugs can be studied. PET thereby provides an insight in the biochemistry and the function of the brain which is at present not feasible with any other technology.
Adult↗
Hypometabolic cortical lesions in tuberous sclerosis with epilepsy: demonstration by positron emission tomography.
Four patients with a well-established diagnosis of tuberous sclerosis and grand mal type epileptic seizures as their principal clinical symptom were examined by conventional surface electroencephalography (EEG), X-ray computed tomography, and positron emission tomography (PET) using the [18F]-2-fluoro-2-deoxyglucose method. The interictal EEG showed various abnormalities of poor localizing value, but no focal epileptic discharges. X-ray computed tomography demonstrated subependymal calcifications in all cases, although cortical lesions were found only twice. However, in the PET images of each patient one or two localized cortical foci with a metabolic rate for glucose more than 40% lower than in the respective contralateral region were clearly delineated. It may be assumed that those hypometabolic areas represent the epileptogenic cortical tubers, which are characteristic of the disease but usually cannot be detected in vivo by other methods.
Adult↗
Detection of compartmental slippage in noninvasive rCBF measurements.
Noninvasive measurements of regional cerebral blood flow (rCBF), using the Xe-133 clearance technique and a two-compartment open model for data analysis, may produce false numerical results when distinction between compartments is poor. For rapid detection of error conditions of that kind, we propose a three-dimensional graphic display of the quality of fit to the original clearance curve, based on bivariate simulations of clearance constants. This procedure may follow rCBF computation, irrespective of the main algorithm used. The discriminating power of this method is demonstrated in two characteristic routine rCBF measurements by gradual addition of random noise to the original data.
Adult↗
Computer assisted mapping in quantitative analysis of cerebral positron emission tomograms.
For quantitative analysis of CT of the brain, an interactive FORTRAN program was developed to provide a time saving mapping procedure with high, largely user-independent reproducibility and flexible adaptation to individual anatomical variations. Program scope and functions are demonstrated, and results obtained in a group of seven normal volunteers are presented for positron emission tomography using the [18F]-2-fluoro-2-deoxy-D-glucose (FDG) method. Basically, the procedure is designed as a two step process: first, a region raw contour is defined geometrically on the basis of local Cartesian or polar coordinates relative to the whole brain contour; second, the final region is delimited within the raw region, in the FDG images according to relative local tissue activity. Although all parameters for mapping a brain slice are stored in a standard parameter file ensuring reproducibility and comparability, interactive control of all steps permits user-guided corrections whenever necessary. Numerical results closely correspond to the data obtained in a previous study of normal subjects with individual manual mapping; discrimination between gray and white matter is in good agreement with theoretical predictions. The program can be easily adapted to other CT techniques.
Brain↗
PET, CT, and MR imaging in cerebrovascular disease.
Forty-five patients with cerebrovascular disease (single and multiple infarcts, intracerebral hemorrhages) were examined with X-ray CT, magnetic resonance (MR) imaging, and positron emission tomography (PET). In six patients with acute infarcts repeat measurements with all techniques were performed after 2 weeks. Magnetic resonance and PET were more sensitive in the detection of ischemic lesions than X-ray CT. With PET, functional disturbances could be demonstrated even in two cases where CT and MR were normal, while the latter techniques were superior in exactly localizing a lesion. Changes in lesion appearance with time were observed with all techniques, and the pathophysiologically important phenomena of hyperperfusion or hypermetabolism were documented in four infarcts with PET.
Brain↗
Performance evaluation of the positron scanner ECAT EXACT.
The Cologne Special is a prototype of the ECAT EXACT (model 921), a new generation of Siemens-CTI PET scanners. It consists of three rings of 48 BGO block detectors each, covering an axial field of view of 16.2 cm with a patient port of 56.2 cm diameter. This results in a total of 24 rings with 384 crystals each, giving 47 contiguous image planes in two-dimensional (2D) mode. Total system sensitivity is 216 kcps/microCi/ml for a 20 cm cylinder phantom in 2D. This increases to 1.5 Mcps/microCi/ml in 3D. Data are acquired in the stationary mode only (no wobble motion), resulting in a transaxial spatial resolution of better than 6 mm full width at half-maximum (FWHM) at the center, which degrades to 7.5 mm tangentially and 9.6 mm radially at a radius of 20 cm. Average axial resolution changes from 5.0 mm FWHM at the center to 8.1 mm at R = 20 cm. Count rate performance was investigated at different low energy discriminator settings and found to be linear up to 2.5 microCi/ml with a 20 cm phantom. The magnitude and distribution of scatter were evaluated for both septa-extended and septa-retracted conditions for a range of energy thresholds. Brain, heart, and whole-body studies with the new tomograph demonstrate the versatility of its applications without compromising on physical performance.
Equipment Design↗
The ECAT EXACT HR: performance of a new high resolution positron scanner.
OBJECTIVE: The ECAT EXACT HR is a newly designed CTI-Siemens PET scanner with high spatial resolution. Its physical performance with respect to resolution, count rate efficiency, and scatter was investigated and evaluated with phantom studies. MATERIALS AND METHODS: The new tomograph consists of three rings of 112 BGO block detectors (50 mm x 23 mm x 30 mm deep) each, covering an axial field of view of 15 cm with a patient port of 56 cm diameter. Each block is sawed into an 8 x 7 matrix giving 24 detector rings with 784 crystals each. RESULTS: Total sensitivity for a 20 cm cylinder phantom is 177 kcps/microCi/ml in two-dimensional (2D) mode and increases to 1.46 Mcps/microCi/ml in 3D mode. Count rate performance was investigated for different low energy discriminator thresholds. Smaller detector blocks improve noise equivalent counts by approximately 50% compared with the EXACT system both in 2D and in 3D mode. Scatter fractions vary in 2D from 0.09 to 0.13 for energy thresholds from 450 to 250 keV for line sources in a 20 cm diameter phantom. In 3D mode an increase of scatter by a factor of 3 is observed. Transaxial spatial resolution varies from 3.6 mm full width at half-maximal (FWHM) at the center to 4.5 mm FWHM tangentially and 7.4 mm FWHM radially at R = 20 cm. Average axial resolution changes from 4.0 mm FWHM at center to 6.7 mm FWHM at R = 20 cm. CONCLUSION: Due to its special properties, the EXACT HR can be equally applied to routine clinical brain and whole-body imaging and to noninvasive experimental studies of regional tracer concentrations in medium-sized animals.
Animals↗