Tc-99m sulfur colloid

Technetium-99m sulfur colloid is one of the technetium radiopharmaceuticals.

Characteristics

• photon energy: 140 keV

• physical half-life: 6 hours

• biological half-life: 2 to 3 minutes

• normal distribution:

  • liver: 85%

  • spleen: 10%

  • bone marrow: 5%

• excretion: hepatic

• target organ: liver, spleen

• pharmacokinetics:

  • rapid extraction by liver, spleen, and bone marrow

  • active bleeding increases in conspicuity as background clears

  • small colloid particles (0.1-1.0 micrometer) extracted by reticuloendothelial system (RES)

  • localization is flow-dependant

  • taken up by Kupffer cells in the liver

• miscellaneous facts

  • colloid shift in severe liver dysfunction

  • all hepatic masses except focal nodular hyperplasia (FNH) are cold

  • technetium-99m sulfur colloids may be prepared from sodium thiosulphate in an acidic medium, or sodium dithionite in a neutral medium via reduction of technetium at an elevated temperature ¹

  • technetium-99m-rhenium-sulphide can also be prepared at an elevated temperature from sodium thiosulphate in the presence of hydrocholic acid and potassium perrhenate ¹

Uses, dosages and timings

Lymphoscintigraphy

• dose: 4-8 injections of 3.7 MBq (100 μCi) injected intradermally

  • encircling the lesion site for a melanoma study

  • in the webs of the fingers and toes for a lymphatic mapping study

• time of imaging: immediately after the last injection

Gastric emptying scan

• adult dose: 37MBq (1 mCi) in meal

  • a meal of chicken liver was the original gold standard, but it is more common to use a scrambled egg, oatmeal, pancake, or an egg sandwich; many things have been used and each facility decides what should be defined as a normal meal for their patients

• pediatric dose: 1.11-1.85 MBq/kg (30-50 μCi/kg), minimum 18.5 MBq (500 μCi)

• time of imaging: immediate

• length of imaging: 2-4 hours

Liver / spleen scan

• adult dose: 148-296 MBq (4-8 mCi) IV

• pediatric dose: 1.11-1.85 MBq/kg (30-50 μCi/kg) minimum 11.1 MBq (300 μCi)

• time of imaging: 20 min

Gastrointestinal tract bleeding

• adult dose: 370 MBq (10 mCi) IV

• time of imaging: immediate (1 sec frames x 60 sec; 1-2 min frames x 20 min)