Bone imaging in infections: artefacts from spectral overlap between a Tc-99m tracer and In-111 leukocytes

In three patients with skeletal infectious disease, scintigrams with a Tc-99m bone-seeker and In-111-tagged leukocytes, made within 24 hr of each other, showed striking similarities. In two cases, the findings from the In-111 WBC images were ultimately determined to be artefacts due to Tc-99m crosstalk within the 173-keV photopeak of In-111. In the second case, the error was traced to failure to use a pure In-111 source for energy calibration: the camera had been peaked on the radiation from the patient himself, who had had an earlier Tc-99m bone scan.