I. In vivo/in vivo method:
A. Procedure
1. Sn2+, usually as pyrophoshate, given intravenously, ideally 200 ng/ml whole blood
2. 20 min waiting period to permit mixing of the Sn-PYP (often referred to as "cold PYP") in body and diffusion of Sn2+ into RBC.
3. Injection of Tc-99m pertechnetate (usually 2 mCi/m2 of body surface area).
4. 10 min waiting period to permit diffusion of the pertechnetate into RBC's where the radiolabeling takes place.
5. Expected labeling efficiency: 80-85%
B. Advantages/disadvantages
1. Advantages: quick, simple, inexpensive method.
2. Disadvantage: lowest labeling efficiency of all commonly used procedures, but perfectly acceptable for routine work, e.g., MUGAs.
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II. In vivo/in vitro method (in vivtro method)
A. Procedure
1. Sn2+, usually as pyrophoshate, given intravenously, ideally 200 ng/ml whole blood
2. 20 min waiting period to permit mixing of the Sn-PYP in body and diffusion of Sn2+into RBC.
3. Withdrawal of 6-10 ml of blood anticoagulated with heparin or ACD solution into a syringe containing Tc-99m pertechnetate (usually 2 mCi/m2 of body surface area).
4. 10 min waiting period to permit diffusion of the pertechnetate into RBC's and to permit labeling to reach equilibrium.
5. Reinjection of labeled cells into patient.
6. Expected labeling efficiency: 92%
B. Advantages/disadvantages
1. Advantages: quick, simple, inexpensive method; achieves higher labeling efficiency than in vivo/in vivo technique since incubation with RBC is extracorporeal. More suitable for GI Bleeding Studies than previously described technique.
2. Disadvantage: takes extra tech time; potential for breaking sterility; images taken at 24 hr post injection not as good as with packed cell techniques.
III. Modified In vivo/in vitro method (packed cell technique)
A. Procedure
1. Sn2+, usually as pyrophosphate, given intravenously, ideally 200 ng/ml whole blood
2. 20 min waiting period to permit mixing of the Sn-PYP in body and diffusion of Sn2+into RBC.
3. Withdrawal of 6-10 ml of blood anticoagulated with heparin or ACD solution into a vacutainer
4. Centrifugation of the vacutainer in inverted position for 5 min at 3000 rpm.
5. Removal of 1-2 ml of packed cells through a 20 ga or larger needle.
6. Aseptic addition of these tinned, packed cells to a sterile vial containing 35 mCi of Tc-99m pertechnetate.
7. 10 min incubation to permit labeling reaction to go to completion. Expected labeling efficiency: 98-100%
8. Reinjection of Tc-RBC
B. Advantages/disadvantages
1. Advantages: simple, inexpensive method; achieves highest labeling efficiency of all procedures since reaction of Tc with plasma proteins has been eliminated. Ideally suited for GI Bleeding Studies- produces best delayed images.
2. Disadvantage: takes extra tech time; requires clinical centrifuge; potential for breaking sterility.
IV. In vitro/in vitro method (Brookhaven Procedure; packed cell technique)
A. Procedure
1. Withdrawal of 10 ml of blood anticoagulated with heparin into a special vacutainer containing several ug of a stannous compound.
2. 10 min waiting period to permit diffusion of Sn2+ into RBC.
3. Centrifugation of the vacutainer in inverted position for 5 min at 3000 rpm.
4. Removal of 1-2 ml of packed cells through a 20 ga or larger needle.
5. Aseptic addition of these tinned, packed cells to a sterile vial containing 35 mCi of Tc-99m pertechnetate.
6. 10 min incubation to permit labeling reaction to go to completion.
7. Expected labeling efficiency: 98-100%
8. Reinjection of Tc-RBC
B. Advantages/disadvantages
1. Advantages: simple, inexpensive method; like the packed cell technique described above, achieves highest labeling efficiency of all procedures since reaction of Tc with plasma proteins has been eliminated. Ideally suited for GI Bleeding Studies- produces best delayed images. Requires no injection of Sn2+ ion into patient.
2. Disadvantage: takes extra tech time; requires clinical centrifuge; potential for breaking sterility.
