High resolution PET imaging of tumour using (18)FDG

A high resolution positron emission tomography (PET) scanner based on multiwire chamber detectors has been used to study murine tumours of about I cm diameter. Using a fully three-dimensional (3D) reconstruction algorithm the image resolution was 2.7 mm in all three planes. The ability of this high resolution PET device to delineate regional function within small rumours was demonstrated on a series of mice with tumour xenografts. Varying degrees of necrosis were induced in the rumours by photodynamic therapy, and PET scans were obtained 24 h later following iv injection of 20 MBq 18-fluorodeoxyglucose (FDG). Immediately after the scan the rumours were excised, their FDG uptake assayed by sodium iodide (NaI) well counter, and multiple sections prepared for histological assessment. The pattern of FDG uptake correlated with the distribution of viable residual tumour identified by histological measurement, even in cases where a layer of only 10-20 cells remained. Uptake determined on the 3D PET image, P, showed a high correlation with the true uptake, T, determined by well counter (P=1.38T-1.3; r=0.98). It is concluded that this type of PET scanner is able to delineate accurately and quantify tracer uptake in small rumours.