Technetium[99mTc]Pyrophosphate

Technetium(^99mTc) pyrophosphate (^99mTc-PYP) is a pyrophosphatecomplex with technetium-99m indicated for bone, cardiac,and blood pool imaging. The primary current clinical usesare for cardiac and blood pool imaging.
For cardiac imaging, the complex is prepared by addingsodium pertechnetate (^99mTc) to the shielded vial containingsodium pyrophosphate and stannous fluoride. Radiolabelingrequires an incubation of 30 to 60 seconds, and the recommendedshelf life is 6 hours. For blood pool imaging, thevial is reconstituted with normal saline (0.9% NaCl) andused within the next 30 minutes without further processing.The unlabeled pyrophosphate/stannous fluoride solution isadministered to the patient intravenously 15 to 60 minutesprior to sodium pertechnetate (^99mTc) for in vivo labeling ofRBCs.
The recommended dose for cardiac imaging is anintravenous injection of 10 to 15 mCi (370–555 MBq) oftechnetium (^99mTc) pyrophosphate within 24 to 144 hoursafter the onset of symptoms. The mechanism of radiotraceraccumulation in damaged myocardium is unclear, but it isassumed that the radiotracer may bind to an ongoing calcificationprocess that occurs in the damaged cells. Forblood pool imaging (gated cardiac blood pool or gastrointestinal[GI] bleeding), the stannous salt is administeredand allowed to accumulate by binding to hemoglobin inthe RBCs. Then, 20 to 30 mCi (740–1,110 MBq) ofsodium pertechnetate (^99mTc) is administered. Thepertechnetate ion also penetrates the RBC, but encountersthe stannous salt for in vivo reduction and entrapmentwithin the RBCs.