Assessment of Labelling Techniques Used for Gated Heart Pool Scanning (GHPS)
Aims: GHPS SPECT requires good labelling efficiency to optimise image quality and quantitative accuracy. Particularly in patients receiving chemotherapy, image quality can be compromised. The aim of this study was to evaluate the labelling of our standard “in vivtro” method with ex-vivo method.
Methods: Nine patients (19 samples) were used to assess two red cell labelling techniques – the Ultratag and “in-vivtro” techniques. Patients were injected with SnCl2 and 20 minutes later IV access was obtained. A 4mL blood sample was collected and used for Ultratag labelling. Following this 8mL of blood was withdrawn into a syringe containing heparinised saline and 1000MBq of 99mTc04- in 2mL. After 5-10 minutes, 8mL of the blood was reinjected, leaving 2mL for QC. Five minutes post injection (or at equilibrium), a further 5mL whole blood sample was obtained. Each blood sample was centrifuged at 1200rpm for 5 minutes and plasma and whole blood count rates measured in a gamma counter to determine labelling efficiency (% label on RBCs).
Results: The mean labelling efficiencies found were Ultratag (99.2%), in-vivtro sample in syringe(90.2%) and at equilibrium(96.7%). As expected, the Ultratag method had the highest efficiency. However, the efficiency for the in-vivtro technique improved in-vivo. This is likely a result of circulating free 99mTc04- being absorbed by the thyroid and GIT.
Conclusions: The in-vivtro technique while less efficient improves after injection due to physiological extraction of the free 99mTc04- and can be routinely used clinically with acceptable results even in those subjects receiving chemotherapy.