Biodistribution and radiation dosimetry of stabilized ^99mTc- exametazime-labeled leukocytes in normal subjects

Labeling leukocytes with ^99mTc-exametazime is a validated technique for imaging infection and inflammation. A new radiolabeling technique has recently been described that enables leukocyte labeling with a more stable form of ^99mTc-exametazime. A normal value study of stabilized ^99mTc- exametazime-labeled leukocytes has been performed, including biodistribution and dosimetry estimates in normal subjects. Methods: Ten volunteers were injected with stabilized ^99mTc-exametazime-labeled autologous leukocytes to study labeled 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 calculations were obtained from the blood samples and imaging data as well as urine and stool collection up to 36 h after injection. Results: Cell-labeling efficiency of 87.5% (+) 5.1% was achieved, which is similar to or better than that reported with the standard preparation of ^99mTc-exametazime. In vivo stability of the radiolabeled leukocytes was also similar to in vitro results with stabilized ^99mTc-exametazime and better than previously reported in vivo stability for nonstabilized ^99mTc- exametazime-labeled leukocytes. Organ dosimetry and radiation absorbed doses were similar with a whole-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 with the leukocytes labeled with the nonstabilized preparation of ^99mTc-exametazime. There are advantages in more cost- effective preparation of the stabilized ^99mTc-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 compared with previous estimates using nonstabilized ^99mTc-exametazime-labeled leukocytes.