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Nuclear Medicine, Department of Diagnostic Radiology, Mayo Clinic, Rochester, Minnesota
Correspondence: For correspondence or reprints contact: Joseph C. Hung, PhD, Mayo Clinic, 2000 First Street SW, Rochester, MN 55905.
ABSTRACT
With a stabilizing agent (i.e., methylene blue and sodium phosphate buffer mixture), the in vitro stability of 99mTc-exametazime has been increased to 4–6 hr post reconstitution. However, it is not feasible to use the stabilized 99mTc-exametazime for leukocyte radiolabeling. This is due to the deep blue appearance of the mixture of stabilized 99mTc-exametazime and blood components, which makes it impossible to separate properly the supernatant from the leukocyte button. In our study, we have developed a practical methodology for overcoming this difficulty in order to use stabilized 99mTc-exametazime in leukocyte labeling. Methods: The stabilized 99mTc-exametazime preparation used in our method consisted of 2 ml 7.4–8.0 GBq (200–215 mCi)99mTc and 2 ml methylene blue/phosphate buffer solution. The separated leukocytes from 80-ml fresh venous blood were incubated with three different ages (i.e., 0-, 4-, or 6-hr postreconstitution) of stabilized 99mTc-exametazime (
925 MBq,25 mCi;0.5–1 ml) at room temperature for 15 min. After incubation, 3 ml of 12.6% ACD/NS solution (anticoagulant citrate dextrose, solution A, USP mixed with 0.9% NaCI, v/v) was added to the tube and centrifuged at 160 g for 5 min. Three milliliters of the dark blue supernatant were carefully removed, and the bottom 1 ml portion was resuspended with 9 ml of 12.6% ACD/NS solution. After centrifugation (160 g for 5 min), the supernatant was clear enough to be drawn off without disturbing the radiolabeled leukocyte button. The white cell button was then resuspended in 4 ml of platelet-poor plasma. Results: The overall labeling efficiency (LE) of our new technique was 67.8%–91.9%, with the higher LE associated with fresher stabilized 99mTc-exametazime. During a 6-hr in vitro stability evaluation, radiolabeled leukocytes lost 1.2% ± 0.3% (n = 24), 1.3% ± 0.1 % (n = 16) and 1.8% ± 0.1% (n = 16) each hour of the cell-bound 0-, 4-, and 6-hr-old 99mTc-exametazime, respectively. The 99mTc-exametazime-labeled leukocytes examined by the trypan blue staining technique at 6-hr postradiolabeling yielded nonstained cells indicating viable leukocytes. Conclusion: We concluded that with a small volume of 99mTc-exametazime and double dilution steps with 12.6% ACD/NS solution, stabilized 99mTc-exametazime can be used effectively for leukocyte radiolabeling with a high LE and long in vitro stability.
Key Words: stabilized technetium-99m-exametazime • leukocytes • viability • labeling efficiency • radiolabeled leukocytes • stability
This article has been cited by other articles:
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  J. C. Hung, B. C. Iverson, K. A. Toulouse, and D. W. Mahoney Effects of Methylene Blue Stabilizer on In Vitro Viability and Chemotaxis of 99mTc-Exametazime-Labeled Leukocytes J. Nucl. Med., July 1, 2002; 43(7): 928 - 932. [Abstract] [Full Text] [PDF]
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T. Grüning, W.-G. Franke, P. D. Robins, I. Salazar, L. A. Forstrom, B. P. Mullan, and J. C. Hung Are Leukocytes Labeled with Stabilized 99mTc-HMPAO Becoming Activated During Labeling? J. Nucl. Med., April 1, 2001; 42(4): 685 - 686. [Full Text]
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M. Roca, F. Iglesias, V. García, F. Armero, and M C. Díaz Chemotaxis, Viability, and Labeling Stability of Leukocytes Labeled with 99mTc-Exametazime Stabilized with Methylene Blue J. Nucl. Med., March 1, 2001; 42(3): 505 - 508. [Abstract] [Full Text]
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