Technetium (99mTc) Pentetate
Technetium ("mTc) Pyrophosphate. Technetium (99mTc) pyrophosphate (99mTc-PYP)20 is a pyrophosphate complex with technetium-99m indicated for bone, cardiac, and blood pool imaging. The primary current clinical uses are for cardiac and blood pool imaging.
For cardiac imaging, the complex is prepared by adding sodium pertechnetate (99mTc) to the shielded vial containing sodium pyrophosphate and stannous fluoride. Radiolabeling requires an incubation of 30 to 60 seconds, and the recommended shelf life is 6 hours. For blood pool imaging, the vial is reconstituted with normal saline (0.9% NaCl) and used within the next 30 minutes without further processing. The unlabeled pyrophosphate/stannous fluoride solution is administered to the patient intravenously 15 to 60 minutes prior to sodium pertechnetate (99mTc) for in vivo labeling of RBCs.
The recommended dose for cardiac imaging is an intravenous injection of 10 to 15 mCi (370-555 MBq) of technetium (99mTc) pyrophosphate within 24 to 144 hours after the onset of symptoms. The mechanism of radiotracer accumulation in damaged myocardium is unclear, but it is assumed that the radiotracer may bind to an ongoing calcification process that occurs in the damaged cells. For blood pool imaging (gated cardiac blood pool or gastrointestinal [GI] bleeding), the stannous salt is administered and allowed to accumulate by binding to hemoglobin in the RBCs. Then, 20 to 30 mCi (740-1,110 MBq) of sodium pertechnetate (99mTc) is administered. The pertechnetate ion also penetrates the RBC, but encounters the stannous salt for in vivo reduction and entrapment within the RBCs.
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