The limited resolution of PET leads to partial volume effect, which consists of "spillover" effects between regions and "tissue-fraction" effects, reflecting underlying tissue heterogeneity [Aston et al 2002]. Spillover effects can be corrected if the point-spread function of the tomograph is known. Addressing the tissue-fraction effect requires coregistered high-resolution MR images. The partial volume correction (PVC) is studied in detail by Aston et al [2002]. One of the international software projects is PVEOut.
In [18F]FDOPA studies PVE leads to severe underestimation of Ki and k3D in certain brain structures, thus obscuring regional heterogeneity in the neurochemical pathology of Parkinson's disease [Rousset et al 2000].
Often K1/k2 in regions of interest is fixed to a value estimated first in the reference region. Because PVE is different between brain structures, this may lead into biases. PVC increased the K1/k2 of cerebral cortex by 35 % in [18F]FDOPA studies [Rousset et al 2000].
However, measured receptor occupancy is independent of partial volume effect [Martinez et al 2001].
Proper PVC is of critical importance in accurate quantitative PET, especially in aging studies, where the apparent reduction in metabolic activity is disappeared after PVC [Giovacchini et al., 2004].
Aston JAD, Cunningham VJ, Asselin M-C, Hammers A, Evans AC, Gunn RN. Positron emission tomography partial volume correction: estimation and algorithms. J Cereb Blood Flow Metab 2002; 22: 1019-1034.
Giovacchini G, Lerner A, Toczek MT, Fraser C, Ma K, DeMar JC, Herscovitch P, Eckelman WC, Rapoport SI, Carson RE. Brain incorporation of 11C-arachidonic acid, blood volume, and blood flow in healthy aging: a study with partial-volume correction. J Nucl Med 2004; 45: 1471-1479.
Martinez D, Hwang D-R, Mawlawi O, Slifstein M, Kent J, Simpson N, Parsey RV, Hashimoto T, Huang Y, Shinn A, Van Heertum R, Abi-Dargham A, Caltabiano S, Malizia A, Cowley H, Mann JJ, Laruelle M. Differential occupancy of somatodendritic and postsynaptic 5HT1A receptors by pindolol: a dose-occupancy study with [11C]WAY 100635 and positron emission tomography in humans. Neuropsychopharmacology 2001; 24:209-229.
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