Analysis of FDG uptake with hybrid PET using standardised uptake values

The standardised uptake value (SUV) has been used as an index of glucose metabolism to classify malignant tumours. To date, calculation of SUVs has been restricted to dedicated PET. The aim of this study was to investigate the feasibility of SUV calculation with attenuation-corrected hybrid PET, applying a singles count rate-related calibration method. Calibration factors for hybrid PET at different singles count rates were determined by phantom studies. SUVs were determined for hot spheres in a phantom study as well as for 68 malignant lesions in 56 patients. Recovery coefficients calculated for hot spheres were applied to SUVs of malignant lesions to correct for partial volume and recovery effects. At a sphere-to-background ratio of 10:1, SUVs of spheres with diameters from 34 to 16 mm varied from 5.0 to 1.5 for hybrid PET, and from 8.0 to 4.3 for dedicated PET. SUVs of malignant lesions calculated by hybrid and dedicated PET showed a strong correlation (r=0.95, P<0.001), with a mean percentage difference of 36%. SUVs calculated by hybrid PET were significantly lower than SUVs calculated by dedicated PET (6.2+/-4.3 vs 8.5+/-5.3, P<0.001). Application of recovery coefficients revealed an SUV of 12.2+/-7.3 for hybrid PET versus 10.8+/-6.3 for dedicated PET, with a significant reduction in the mean percentage difference (22%, P<0.01). In conclusion, singles count rate-related calibration factors allow calculation of SUVs with hybrid PET for lesions with a diameter larger than 15 mm. Correction for partial volume and recovery effects is needed to improve the agreement of SUVs of lesions determined by hybrid PET and dedicated PET.