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A FAST AND EFFICIENT Same day Tc-99m Sulfur Colloid bone marrow and Indium leukocyte imaging PROTOCOL for suspected bone infection.

Lette, J, Cerino M, Eybalin MC, Levasseur A.

Maisonneuve Hospital, Montreal, QC, Canada.

Indium labelled leukocytes concentrate in both bone marrow and infection, hence the use of combined Tc-99m Sulfur Colloid and In-111 leukocyte imaging for the detection of osteomyelitis. Imaging hands and feet are no exception: we have observed cases of atypically located marrow activity, both in the initial active and in the later healing regenerative phases of osteomyelitis.

Combined Tc-99m Sulfur Colloid and In-111 leukocyte image acquisition protocols vary. Some authors carry out the Tc-99m and In-111 acquisitions on different days which is time consuming for the technical staff and complicated for the patient. Others perform In-111 imaging followed by Tc-99m sulfur colloid injection and a dual isotope acquisition using a medium energy collimator with10% windows around the 140 ke V, 174 ke V and 247 ke V photopeaks, which in our experience can lead to false negative studies for infection because of the downscatter of In-111 activity into the 140 ke V Tc-99m window resulting in the overestimation of marrow activity, especially in the hands and feet where the foci of marrow and infection are small and the count rate low.

Objective: to develop a quicker and more efficient method for combined same day Tc-99m sulfur colloid and Indium leukocyte imaging..

Methods:

The following imaging protocol eliminates diagnostic uncertainty related to downscatter:

1-     Blood is withdrawn and the leukocytes labelled with In-111, followed immediately by

2-    a 10 mCi injection of Tc-99m of sulfur colloid, followed 15 minutes later by the (uncontaminated) Tc-99m bone marrow imaging using an all purpose collimator and an acquisition window centered on 140 ke V.

3-     The labelled leukocytes are then reinjected and images acquired at 4 and 24 hours using a medium energy collimator centered on 174 ke V and 247 ke V.

Cases will be presented depicting our method.

In conclusion, we describe a faster and more efficient method for combined same day Tc-99m sulfur colloid and Indium leukocyte bone imaging which, contrary to the simultaneous acquisition technique, does not compromise neither the specificity of the test for the detection of bone marrow nor its sensitivity for the detection of infection.