Abstract
Introduction: Really injected radioactivity of a radiopharmaceutical is lower than the radioactivity of the syringe prepared for application - disintegration of the radionuclide and residual activity in the syringe take part. Careful application, the low residual activity is a part of it, is a one prerequisite of well performed examination.
Goal: To measure the residual activity under the conditions of our department. Method: We measured 48 syringes after the injection of 99mTc-HDP with a specific activity of 926.0 to 1050.6 MBq/ml (median (Me) 984.0 MBq/ml).
We put the syringe together with a needle into the plastic vial immediately after the injection and perform the measurement in the dose calibrator. Applications were done during 6 days, 8 injections per day, each day by a different staff member.
Results: Residual activity was 17.25 to 95.15 MBq (Me 72.90 MBq), i.e. 2.73 to 14.35 % (Me 8.34 %) of prepared activity. It is 0.02 to 0.10 ml (Me 0,07 ml) converted to the volume.
Values of the measured residual activity do not correlate with the volume of radiopharmaceutical prepared for the application (p=0.08). There are also differences of measured values of residual activity among individual staff members (minima 17.25 to 53.48 MBq (2.73 to 5.45 %); maxima 77.46 to 99.15 MBq (9.25 to 14.35 %).
Conclusion: Really injected radioactivity of 99mTc-HDP was mostly about 8 % lower comparing to radioactivity prepared for application. Difference among individual injections are up to 12 %, there are also differences among individual staff members.
The optimal technique for minimal residual activity comprises: withdraw a small volume of blood after injection and inject back again; always carefully press the piston of the syringe to the end of the syringe cylinder; to aspire back to the syringe immediately after injection and thus to prevent the leakage of radioactivity into the environment.