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Biomedical subjects

S Grafton

Publications and source records attributed to S Grafton.

7 recordsLinked to original sources
PubMed1995

Ventroposterior medial pallidotomy in patients with advanced Parkinson's disease.

In a preliminary study, the effects of ventroposterior medial pallidotomy were evaluated in five patients with advanced Parkinson's disease in whom medical therapy had failed. The mean age was 67.0 +/- 5.6 years, and the mean Hoehn and Yahr stage when "off" was 3.9 +/- 1.3. Three patients received unilateral pallidotomies; two of these received another pallidotomy after 8 weeks. Two other patients received staged bilateral pallidotomies. No significant differences in overall function could be seen before and after the first surgical procedure. All three patients with peak-dose dyskinesias or dystonia had marked contralateral reduction in these symptoms. Ventroposterior medial pallidotomy can ameliorate peak-dose dyskinesias in patients with advanced Parkinson's disease. Overall function improvement is not remarkable.

Aged↗
PubMed1992

Bilateral fetal grafts for Parkinson's disease: 22 months' results.

Five patients with severe Parkinson's disease underwent bilateral multiple graft implants of nondissociated fetal mesodiencephalic tissues. Graft implantation was performed in China following CT-guided stereotactic placement of a novel delivery system. Follow-up has demonstrated substantially reduced levodopa requirements and clinical improvements of motor, postural functions and reduction of freezing and on-off phenomenon. PET utilizing [18F]-dopa, at 14 months in the first case, suggested graft-induced restoration of dopaminergic transmission in the striatum.

Brain Tissue Transplantation↗
PubMed1991

Relating structure to function in vivo with tomographic imaging.

For the normal physiological responses of the brain or the pathophysiological changes that accompany disease states to be evaluated, it is necessary to compare data sets between different imaging modalities for individual subjects. Similarly, it is important to compare data between individuals both within and across imaging modalities for individual subjects. In a collaborative project with a number of university groups we have developed a system that allows for the within-subject alignment and registration of three-dimensional data sets obtained from different modalities for the same individual. This analysis takes into account the error induced by image acquisition, registration and alignment with regard to scaling, translation and rotation. A more difficult problem is the between-subject warping of individual brain anatomy to match that of another individual or of an idealized model. If the principles of morphometrics and homologous landmarks are applied, three-dimensional brain warping can provide this type of between-subject comparison. The results of accomplishing these two tasks is a system that allows data obtained in a given individual to be compared across structure and function, as obtained from magnetic resonance imaging (MRI) and from positron emission tomography (PET), respectively. It also allows comparison of the resultant information with averaged between-subject data from populations of normal individuals or patients with specific neurological disorders. This system provides the means by which to compare quantitative data between individuals in an objective and automated fashion.

Algorithms↗
PubMed1991

Kinetics and modeling of L-6-[18F]fluoro-dopa in human positron emission tomographic studies.

Kinetics of L-3,4-dihydroxy-6-[18F]fluorophenylalanine (FDOPA) in striatum and cerebellum were measured in 10 normal human subjects with positron emission tomography (PET) from 0 to 120 min after an intravenous bolus injection of the tracer. The time course of the arterial plasma concentrations of the tracer and its metabolites was also assayed biochemically. FDOPA compartmental models that are based on biochemical information were investigated for their consistency with the measured striatal and cerebellar tissue kinetics. A modeling approach was also developed for separating plasma FDOPA and metabolite time-activity curves from the measured total 18F time-activity curve in plasma. Results showed that a model consisting of three separate compartments for tissue FDOPA, tissue 6-[18F]fluorodopamine (FDA) and its metabolites, and tissue L-3,4-dihydroxy-6-[18F]fluoro-3-O-methylphenylalanine (3-OMFD) could describe adequately the striatal kinetics in humans. Based on this model, the FDOPA transport constant across the blood-brain barrier (BBB) (K1), the FDOPA decarboxylation rate constant (k3), and the turn-over rate constant of FDA and its metabolites (k4) could be estimated by model fitting to the tissue kinetics and were found for the normal subjects to be 0.031 +/- 0.006 ml/min/g (mean +/- SD), 0.041 +/- 0.015/min, and 0.004 +/- 0.002/min, respectively. About 50% of the FDOPA that crossed the BBB from plasma to striatum was decarboxylated. The decarboxylation constant with respect to plasma FDOPA (K3) was 0.015 +/- 0.003 ml/min/g. The BBB transport corresponded to a permeability-surface area product of 0.032 ml/min/g for FDOPA. For 3-OMFD, the BBB transport was 1.7 times faster. The effects of tissue heterogeneity on the FDOPA kinetics and on the estimated model parameters were also investigated. The usefulness and implications of these findings for interpretation of PET FDOPA studies are discussed.

Adult↗
PubMed1991

Modelling approach for separating blood time-activity curves in positron emission tomographic studies.

A modelling approach is developed to generate the full time course of an injected radiotracer and its labelled metabolites in plasma/blood, based on measurements of the total radioactivities in withdrawn plasma/blood samples. A compartmental model is used to describe the conversion of an injected tracer to its metabolites in the body. The model equation is formulated with the total radioactivity concentration curve as the input function. The utility and characteristics of the approach in quantitative positron emission tomographic (PET) studies are shown with two examples. In the first example, using the tracer 6-[18F]fluoro-L-dopa (FDOPA), the approach is shown to derive the full time course of plasma FDOPA and its metabolites. In the second example of dynamic 15O oxygen PET, the approach is used to solve a deconvolution problem to give separated time-activity curves of 15O oxygen and 15O water in blood. The modelling approach improves the separation of blood/plasma time-activity curves and leads to better quantitative interpretation of PET results.

Dihydroxyphenylalanine↗
PubMed1990

Thallium-201 SPECT imaging of brain tumors: methods and results.

Recent studies suggest that thallium-201 (201Tl) planar scans of brain tumors more accurately reflect viable tumor burden than CT, MRI, or radionuclide studies with other single-photon emitting compounds. We have previously reported the utility of 201Tl SPECT index in distinguishing low- from high-grade gliomas elsewhere. Here we describe the technical considerations of deriving a simple 201Tl index, based on uptake in the tumor normalized to homologous contralateral tissue, from SPECT images of brain tumors. We evaluated the importance of consistently correcting for tissue attenuation, as it may achieve better lesion discrimination on qualitative inspection, and the methodologic limitations imposed by partial volume effects at the limits of resolution.

Astrocytoma↗