Biomedical subjects

O G Rousset

Publications and source records attributed to O G Rousset.

2 recordsLinked to original sources

PubMed2000

Effect of partial volume correction on estimates of the influx and cerebral metabolism of 6-[(18)F]fluoro-L-dopa studied with PET in normal control and Parkinson's disease subjects.

The poor spatial resolution of positron emission tomography (PET) is a limiting factor in the accurate assay of physiological processes investigated by compartmental modeling of tracer uptake and metabolism in living human brain. The radioactivity concentration in a region-of-interest is consequently altered by loss of signal from that structure and contamination from adjacent brain regions, phenomena known as partial volume effects. We now apply an MRI-based algorithm to compensate for partial volume effects in the special case of compartmental modeling of the cerebral uptake of 6-[(18)F]fluoro-L-dopa (FDOPA), an exogenous substrate of dopa decarboxylase. High-resolution MRI scans were obtained from normal volunteers (n = 4) and patients with Parkinson's disease (n = 4) in order to segment specific brain regions and calculate the partial volume correction factors. Dynamic 2D PET scans were acquired during 90 min following intravenous infusion of FDOPA. After partial volume correction, the apparent net blood-brain clearance of FDOPA (K(i)) was greatly increased in caudate and putamen of normal subjects and in caudate of Parkinson's disease patients. The equilibrium distribution volume of FDOPA (V(D)(e)) in cerebral cortex increased by 35% in all subjects. Using a two-compartment model, the relative activity of dopa decarboxylase with respect to FDOPA (k(D)(3)) in the basal ganglia was increased 2-3 times in normal subjects, to the range obtained previously in brain of living rat. The partial volume correction also increased the magnitude of k(D)(3) in caudate of Parkinson's disease patients, but did not alter k(D)(3) in putamen. A three-compartment model correcting for elimination of decarboxylated metabolites also yielded higher estimates of k(D)(3), but with a penalty in precision of the estimates. Together, these observations suggest that the limited spatial resolution of PET results in substantial underestimation of the true rate of FDOPA uptake and metabolism in vivo, and may also tend to obscure regional heterogeneity in the neurochemical pathology of Parkinson's disease.

Adult↗

PubMed1998

Correction for partial volume effects in PET: principle and validation.

UNLABELLED: The accuracy of PET for measuring regional radiotracer concentrations in the human brain is limited by the finite resolution capability of the scanner and the resulting partial volume effects (PVEs). We designed a new algorithm to correct for PVEs by characterizing the geometric interaction between the PET system and the brain activity distribution. METHODS: The partial volume correction (PVC) algorithm uses high-resolution volumetric MR images correlated with the PET volume. We used a PET simulator to calculate recovery and cross-contamination factors of identified tissue components in the brain model. These geometry-dependent transfer coefficients form a matrix representing the fraction of true activity from each distinct brain region observed in any given set of regions of interest. This matrix can be inverted to correct for PVEs, independent of the tracer concentrations in each tissue component. A sphere phantom was used to validate the simulated point-spread function of the PET scanner. Accuracy and precision of the PVC method were assessed using a human basal ganglia phantom. A constant contrast experiment was performed to explore the recovery capability and statistic error propagation of PVC in various noise conditions. In addition, a dual-isotope experiment was used to evaluate the ability of the PVC algorithm to recover activity concentrations in small structures surrounded by background activity with a different radioactive half-life. This models the time-variable contrast between regions that is often seen in neuroreceptor studies. RESULTS: Data from the three-dimensional brain phantom demonstrated a full recovery capability of PVC with less than 10% root mean-square error in terms of absolute values, which decreased to less than 2% when results from four PET slices were averaged. Inaccuracy in the estimation of 18F tracer half-life in the presence of 11C background activity was in the range of 25%-50% before PVC and 0%-6% after PVC, for resolution varying from 6 to 14 mm FWHM. In terms of noise propagation, the degradation of the coefficient of variation after PVC was found to be easily predictable and typically on the order of 25%. CONCLUSION: The PVC algorithm allows the correction for PVEs simultaneously in all identified brain regions, independent of tracer levels.

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