Sequential dose injections. A new technique for technetium-99m colloid gastrointestinal bleeding studies

For Tc-99m colloid bleeding studies to be positive, the patient must be actively bleeding while the colloid is circulating in the blood pool. A simple technique of sequential dose injections (SDI) is presented where five injections of 2 mCi each are made at 5-minute intervals. Image acquisition is performed after each injection. This technique results in an increase in the effective plasma residence time of the colloidal particles from 10-15 minutes to 35-40 minutes. A case report is presented in which the bleeding site was identified only after the fifth serial injection of a fractionated dose of Tc-99m microaggregated albumin colloid.