Radiolabelling of erythrocytes with ¹⁸FDG : feasibility study

Introduction
The radiolabelling of the erythrocytes is performed to carry out scintigraphies for various indications: ectopic spleen or digestive haemorrhage detection. These preparations are done with ^99mTc but these examinations have shown limitations in sensitivity in case of minor digestive haemorrhages. The use of a PET tracer would allow much better sensitivity and imaging resolution. Thus, we developed the radiolabelling of erythrocytes by ¹⁸F.

Material and method
10 mL of blood were collected from healthy fasting volunteers (n = 3). Blood cells were isolated by 2 cycles of centrifugation. Then, cells were incubated with about 350 MBq of ¹⁸FDG for 20 minutes at 37°C. Free ¹⁸FDG was removed by 1 cycle of centrifugation. Radiolabelling efficiency and free ¹⁸FDG were calculated at the end of labelling. The cell viability was checked by microscopic examination and the stability was assessed 2h after radiolabelling by measuring the free ¹⁸FDG. The dosimetry exposition of the operator was measured for whole body and extremities.

Results and discussion
The mean duration of the process was 80 minutes. The radiolabelling efficiency was 40.6 ± 11% and the free ¹⁸FDG rate was 51.8 ± 5.2%. The cell viability at the end of labelling was > 99% and the ¹⁸FDG release at 2h after labelling was 4.6 ± 0.1%. The dosimetric exposition of the operators for the whole body and the extremities were respectively 13 ± 4.2 µSv and 33.9 ± 13.5 µSv.

The radiolabelling efficiency can be improved by optimization of the labelling conditions (volume of blood withdrawn, labelling activity, incubation duration…). This method allows obtaining a sufficient final activity with respect of the cell integrity and a final suspension cells with a good stability. The dosimetric exposition of the operator is limited and can be reduced by improving the radioprotection of the equipment (centrifuge, heater…). The activity to be injected will be determined by dosimetric characterization.

Conclusion
The radiolabelling of the erythrocytes with ¹⁸FDG allows new diagnosis perspectives for the detection of digestive haemorrhage detection or ectopic spleen when scintigraphy can have a lack of sensitivity and a low imaging resolution.

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