CD4 and infection: SPECT/CT imaging relies on the use of autologous radiolabeled leucocytes (111In-oxine or 99mTc-hexamethyl propylene amine oxime) that accumulate in a time-dependent fashion in late images versus earlier images [33], whereas PET/CT is generally performed using a single acquisition time point (generally at 1 h) after the administration of 18F-FDG, which is actively incorporated in vivo by the activated leucocytes, monocyte macrophages, and CD4+ T-lymphocytes accumulating at the sites of infection.