Shields A F, Graham M M, Kozawa S M, Kozell L B, Link J M, Swenson E R, Spence A M, Bassingthwaighte J B, Krohn K A
Department of Medicine, University of Washington, Seattle.
J Nucl Med. 1992 Apr;33(4):581-4.
11CO2 is one of the major metabolites of many [11C]-labeled radiopharmaceuticals, including glucose, thymidine, acetate, amino acids, and fatty acids. Our data contradict the notion that the contribution of labeled CO2 to PET images can be disregarded because of its rapid elimination through the lungs. We have measured the retention and excretion of 11CO2 in dogs after the intravenous injection of labeled CO2/HCO3-, which had been equilibrated ex vivo with blood. Only 58% of the label was exhaled as CO2 over the first 60 min after injection, with the rest retained in the body. The injection of [11C]thymidine labeled in the ring-2 position or [11C]acetate labeled in the carboxylate position resulted in the production of large amounts of labeled CO2 with the exhalation of about 47% and 23%, respectively, of the injected label over 60 min. At 10 min after injection of either [11C]thymidine and [11C] acetate, approximately 60% to 70% of total blood activity was in labeled CO2 or bicarbonate. On the other hand, the use of [1-11C]glucose only resulted in exhalation of 5% of the injected dose and CO2/HCO3- made up less than 10% of blood activity at 10 min. Our results indicate that retention and distribution of labeled CO2 needs to be considered when interpreting PET data obtained from 11C-labeled compounds.
11CO₂是许多[¹¹C]标记放射性药物的主要代谢产物之一，这些放射性药物包括葡萄糖、胸腺嘧啶核苷、乙酸盐、氨基酸和脂肪酸。我们的数据与以下观点相矛盾，即由于标记的CO₂可通过肺部快速排出，因此其对PET图像的贡献可以忽略不计。我们在静脉注射经体外与血液平衡的标记CO₂/HCO₃⁻后，测量了犬体内¹¹CO₂的滞留和排泄情况。注射后最初60分钟内，只有58%的标记物以CO₂形式呼出，其余部分保留在体内。注射2位标记的[¹¹C]胸腺嘧啶核苷或羧基位置标记的[¹¹C]乙酸盐后，会产生大量标记的CO₂，在60分钟内分别呼出约47%和23%的注射标记物。注射[¹¹C]胸腺嘧啶核苷和[¹¹C]乙酸盐后10分钟，总血液活度的约60%至70%存在于标记的CO₂或碳酸氢盐中。另一方面，使用[1-¹¹C]葡萄糖仅导致呼出5%的注射剂量，且在10分钟时CO₂/HCO₃⁻占血液活度不到10%。我们的结果表明，在解释从¹¹C标记化合物获得的PET数据时，需要考虑标记CO₂的滞留和分布情况。
