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  • Calculation for ejection fraction
  • Tc99m labeled RBCs
  • (ED counts – ES counts)/(ED counts – background counts)
  • If the background has increased counts (free Tc) such as in vascular structures like the spleen, the denominator gets smaller and EF is falsely elevated

In vivo

Inject stannous pyrophosphate then Tc pertechnetate 15 min later
60-80% labeling efficiency

Modified in vitro

Inject stannous pyrophosphate, draw blood, label and reinject
90% labeling efficiency

In vitro

Blood is drawn, mixed with stannous pyrophosphate, labeled and reinjected
95-98% labeling efficiency
UltraTag kit takes longer and costs more