POSITRON EMISSION TOMOGRAPHY IN PRIMARY BRAIN-TUMORS USING COBALT-55

Primary brain tumours are usually assessed by computed tomography (CT) and magnetic resonance imaging (MRI), sometimes in conjunction with p ositron emission tomography (PET). We used cobalt-55 (Co-55) as a calc ium (Ga) tracer to visualize decaying tumour tissue, based on the fact that Ca-influx is essential in both cell death and leukocyte activati on. Net Co-55 uptake may be the result of cell decay, leukocyte infilt ration, (re)perfusion and the pharmacological profile of Co-55. Three patients with primary malignant brain tumours (first presentation) wer e studied with CT, MRI and Go-PET after the intravenous administration of 0.5 mCi Co-55. Histopathological diagnosis was obtained by biopsy or resection. Go-PET demonstrated each of the brain tumours and showed good topographical agreement with CT and MRI. Go-PET provided additio nal detail as to the site and size of the necrotic core and the peri-n ecrotic rim of decaying tumour. The Co-55 uptake indices varied betwee n 2.6 and 5.3. Co-55 demonstrated uptake in decaying tissue, irrespect ive of the integrity of the blood-brain barrier. Neither necrotic nor viable tumour tissue showed affinity for Co-55. Since Co-55 is readily applicable to both PET and single photon emission tomography (SPET), differences in the uptake mechanism and functional significance of the Co-55 tracer are discussed in relation to Tl-201 SPET. We present a ( limited) pilot series of three patients to forward the claim of this n ew functional technique in nuclear neurology.