Background and aim: Although fractional cerebral blood volume (Vb) can easily be included as a separate parameter in full compartmental analysis of PET studies, it is more difficult to account for in simplified analyses. In a previous study a significant change in distribution volume of (R)-[11C]verapamil from morning to afternoon scans was found using Logan analysis, but compartmental analysis revealed that this difference could be attributed solely to differences in Vb . The aim of the present study was to verify whether there is indeed significant daily variation in Vb. Methods: Whole brain grey matter Vb of 73 scans (51 (R)-[11C]PK11195, 12 (R)-[11C]verapamil and 10 [11C]R116301 scans) was related to scan start time retrospectively. (R)-[11C]verapamil and [11C]R116301 scans were part of a test-retest protocol, with the same volunteer being scanned twice on the same day at 10:30 and 15:00 h. All 60 min dynamic scans were acquired in 3D mode following administration of 370 MBq of tracer. A metabolite corrected arterial plasma input function was obtained using continuous arterial sampling together with discrete manual samples. A co-registered segmented T1-weighted MRI scan was used to define whole brain grey matter regions of interest. Data were analysed using single ((R)-[11C]verapamil) or two ((R)-[11C]PK11195, [11C]R116301) tissue compartment models, including Vb as a fit parameter. Differences in Vb between morning and afternoon scans were assessed using two-tailed t-tests. Results: In all scans, whole brain grey matter Vb could be determined with a standard error of less than 10%. A shown in table 1, a significant decrease in blood volume between morning and afternoon scans in the same subject was found for both (R)-[11C]verapamil and [11C]R116301. In addition, a significant difference in Vb between morning and afternoon (R)-[11C]PK11195 scans was found. Conclusion: For all three tracers, a decrease of ∼10% in average Vb was found from morning to afternoon scans. This decrease could not be attributed to blood sampling in the morning scan itself, as the effect was also seen in (R)-[11C]PK11195 scans where subjects underwent only a single scan. As demonstrated previously, a decrease in Vb during the day may lead to erroneous Results: when it is not included as a fit parameter . This effect should be considered especially in challenge studies where successive scans may be acquired during the day.
|Journal||Journal of Cerebral Blood Flow and Metabolism|
|Issue number||SUPPL. 1|
|Publication status||Published - 13 Nov 2007|