Scintigraphy performed with Tc-99m labeled RBCs

Tc-99m labeled RBCs - with radiolabelling technique in vivo or in vitro of red cells ³ - is one of the technetium radiopharmaceuticals used in the non-invasive assessment of gastrointestinal (GI) bleeding ², characterized by high sensitivity (93%) and specificity (95%) ⁴. It is capable, in fact, of targeting intestinal hemorrhages of a few milliliters immediately after the injection of the radioactive tracer or in the following 12-24 hours (diluition principle) ^5,6.

Characteristics

• photon energy: 140 KeV

• physical half-life: 6 hours

• biological half-life: 

• normal distribution: heart, vessels, spleen

• miscellaneous facts:

  • threshold for detection is 0.05-0.1 mL/min

  • angiography threshold is 0.5-1 mL/min

  • the criteria for positive scan are qualitative type: hot spot appears and conforms to intestinal anatomy, abnormal activity increases over time, activity moves antegrade or retrograde through bowel

Uses, doses and timings

• GI bleeding

• adult dose: 925 MBq (25 mCi) IV

• timing: immediate/angioscintigraphic phase (1 sec frames x 60 sec); 1 min frames x 60-90 min; delayed imaging if necessary (6-8-24 hrs).