Background: Technetium-99m radioisotope is the backbone of any nuclear medicine institute. It is well known that various 99mTclabeled radiopharmaceuticals may get absorbed into the plastic syringes. The consequences of this adsorption are inadequate or inconsistent absorbed dose which produces the inappropriate diagnostic response in patients. The aim of our study was to investigate the true activity administrated to patients and also compare the results of residual activities of the same dose by using different volumes of syringes.
Methods: A total 946 measurements were analyzed in which patients were injected with either 3 or 5 ml syringes and 99mTc was labeled with different pharmaceuticals, i.e., mercaptoacetyltriglycine-3, methoxy-iso-butyl isonitrile, methylenediphosphonic acid (MDP), and technetium pertechnitate. Residual activity was measured for every patient.
Results: The 3 ml syringes have less average retention rate for any radiopharmaceutical as compared to 5 ml syringes. Residual activity for MDP is lower when compared to other radiopharmaceutical for both volumes of syringes. Maximum residual activity for 5 ml syringes happens to be 3.42% of dispensed activity, while for 3 ml syringes it is 2.74% of dispensed activity. The mean effective activities were within the recommended range of EANM and PNRA guidelines.
Conclusion: For all radiopharmaceuticals and both syringes, average residual activity remained well under 1.5% of the activity drawn into syringes, which is insignificant when compared to previous reported results and may not alter the resultant image quality to a larger extent. In hospital, practices should be encouraged to reduce the residual activity as low as possible.
Key words: Tc99m labelled radiopharmaceutical, Residual activity, Nuclear medicine imaging
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