Equivalence of arterial and venous blood for ¹¹CO₂-metabolite analysis following intravenous administration of ¹¹C-acetate and ¹¹C-palmitate

Objectives Sampling of arterial blood for metabolite correction is often required to define a true radiotracer input function in quantitative modeling of PET data. However, arterial puncture for blood sampling is often undesirable. To establish whether venous blood could substitute for arterial blood in quantitative PET studies with ¹¹C-acetate and ¹¹C-palmitate, we compared the results of ¹¹CO₂-metabolite analyses performed on simultaneously collected arterial and venous blood samples.

Methods Paired arterial and peripheral venous blood samples were drawn from anesthetized pigs at 1, 3, 6, 8, 10, 15, 20, 25 and 30 minutes after i.v. administration of ¹¹C-acetate and ¹¹C-palmitate. Blood radioactivity present as ¹¹CO₂ was determined using a validated method. Briefly, total blood ¹¹C-radioactivity was counted in alkalinized ¹¹C-blood, and non-¹¹CO₂ radioactivity was counted after the ¹¹C-blood was acidified and bubbled with air for 10-minutes to quantitatively remove ¹¹CO₂.

Results For both ¹¹C-acetate and ¹¹C-palmitate, a total of 34-pairs of arterial and venous samples were analyzed from four resting-state pigs. Over the 1-30 minute period, the fraction of total blood ¹¹C present as ¹¹CO₂ rose from 4% to 64% for acetate, and 0% to 24% for palmitate. An excellent correlation was found between concurrent arterial and venous ¹¹CO₂ levels. For the ¹¹C-acetate study, the regression equation derived to estimate the venous ¹¹CO₂ from the arterial values was: y = 0.9943x + 0.0042 (R²=0.97, p<0.001), and for the ¹¹C-palmitate: y = 0.8847x + 0.0118, (R²=0.91, p<0.001).

Conclusions Venous ¹¹CO₂ values appear suitable as substitutes for arterial blood samples in ¹¹CO₂ metabolite analysis after administration of ¹¹C-acetate or ¹¹C-palmitate