Positron emission tomography in primary brain tumours using cobalt-55

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