Biodistribution and radiation dosimetry of stabilized Tc-99m-exametazime-labeled leukocytes in normal subjects

Labeling leukocytes with Tc-99m-exametazime is a validated technique for im aging infection and inflammation. A new radiolabeling technique has recentl y been described that enables leukocyte labeling with a more stable form of Tc-99m-exametazime. A normal value study of stabilized Tc-99m-exametazime- labeled leukocytes has been performed, including biodistribution and dosime try estimates in normal subjects. Methods: Ten volunteers were injected wit h stabilized Tc-99m-exametazime-labeled autologous leukocytes to study labe led leukocyte kinetics and dosimetry in normal subjects. Serial whole-body imaging and blood sampling were performed up to 24 h after injection. Cell- labeling efficiency and in vivo viability, organ dosimetry, and clearance c alculations were obtained from the blood samples and imaging data as well a s urine and stool collection up to 36 h after injection. Results: Cell-labe ling efficiency of 87.5% +/- 5.1% was achieved, which is similar to or bett er than that reported with the standard preparation of Tc-99m-exametazime. In vivo stability of the radiolabeled leukocytes was also similar to in vit ro results with stabilized Tc-99m-exametazime and better than previously re ported in vivo stability for nonstabilized Tc-99m-exametazime-labeled leuko cytes. Organ dosimetry and radiation absorbed doses were similar with a who le-body absorbed dose of 1.3 x 10(-3) mGy/MBq. Urinary and fecal excretion of activity was minimal, and visual assessment of the images showed little renal parenchymal activity and no bowel activity up to 2 h after injection. Conclusion: Cell labeling and in vivo stability appear improved compared w ith the leukocytes labeled with the nonstabilized preparation of Tc-99m-exa metazime. There are advantages in more cost-effective preparation of the st abilized Tc-99m-exametazime and an extended window for clinical usage, with good visualization of abdominal structures on early images. No significant increase in specific organ and whole-body dosimetry estimates was noted co mpared with previous estimates using nonstabilized Tc-99m-exametazime-label ed leukocytes.