Evaluation of partial volume corrections for (R)-[C-11]PK11195 studies

Introduction: Partial volume effects may affect quantification of position emission tomography (PET) scans. The purpose of the present study was to evaluate several partial volume correction (PVC) Methods: in relation to the analysis of (R)-[C-11]PK11195 studies in healthy subjects and in subjects with mild cognitive impairment (MCI) and Alzheimer's disease (AD). Methods: Young (n = 12; age 28 ± 9 yr) and elderly (n = 18; 69 ± 7 yr) healthy subjects, together with MCI (n = 9; 73 ± 6 yr) and probable AD (n = 15; 69 ± 7 yr) patients, were included. Subjects underwent a 60 minutes dynamic brain scan following bolus injection of 400 ± 60 MBq of (R)-[C-11]PK11195. A metabolite corrected plasma input function was derived using continuous online and discrete manual arterial blood sampling. Eight PVC Methods: were tested [1], including Methods: by Meltzer [2], M?ller-Gartner [3], Rousset [4] and Alfano [5]. Regions of interest (ROI) were defined on a co-registered MRI scans for the following structures: thalamus and orbital frontal, medial inferior, temporal and parietal cortex. MRI segmentation was used to restrict ROI to grey matter and to apply PVC. Binding potential (BP) and volume of distribution (VD) were determined using a two-tissue reversible plasma input compartment model, both with and without fixing K1/k2 to the value for whole cortex (BPfixed, VDfixed and BPunfixed, VDunfixed). In addition, BP was obtained using the simplified reference tissue model (BPsrtm) with whole cerebellum as reference tissue [6]. Results: and discussion: Different ROI showed similar trends. Therefore, only thalamus Results: are presented. PVC increased VDfixed, VDunfixed, BPfixed and BPsrtm, but not BPunfixed (Fig. 1A). Changes in BP and VD values for young, elderly, MCI and AD subjects were similar, although occasionally a smaller increase in BP or VD was seen in MCI and AD patients. More importantly, PVC changed the K1/k2 ratio (Fig. 1B), resulting in changes in BPsrtm and BPfixed but not BPunfixed values. Therefore changed BPsrtm and BPfixed values were considered unphysiological. In addition, PVC reduced BP and VD precision and did not improve discrimination between subject groups. Simulations confirmed clinical Results:. Therefore, PVC cannot be recommended for (R)-[C-11]PK11195 studies.