Influence of OSEM and segmented attenuation correction in the calculation of standardised uptake values for [F-18]FDG PET

Standardised Uptake Values (SUVs) are widely used in positron emission tomo graphy (PET) as a semi-quantitative index of fluorine-18 labelled fluorodeo xyglucose uptake. The objective of this study was to investigate any bias i ntroduced in the calculation of SUVs as a result of employing ordered subse ts-expectation maximisation (OSEM) image reconstruction and segmented atten uation correction (SAC). Variable emission and transmission time durations were investigated. Both a phantom and a clinical evaluation of the bias wer e carried out. The software implemented in the GE Advance PET scanner was u sed. Phantom studies simulating tumour imaging conditions were performed. S ince a variable count rate may influence the results obtained using OSEM, s imilar acquisitions were performed at total count rates of 34 kcps and 12 k cps. Clinical data consisted of 100 patient studies. Emission datasets of 5 and 15 min duration were combined with 15-, 3-, 2- and 1-min transmission datasets for the reconstruction of both phantom and patient studies. Two SU Vs were estimated using the average (SUVavg) and the maximum (SUVmax) count density from regions of interest placed well inside structures of interest . The percentage bias of these SUVs compared with the values obtained using a reference image was calculated. The reference image was considered to be the one produced by filtered backprojection (FBP) image reconstruction wit h measured attenuation correction using the 15-min emission and transmissio n datasets for each phantom and patient study. A bias of 5%-20% was found f or the SUVavg and SUVmax in the case of FBP with SAC using variable transmi ssion times. In the case of OSEM with SAC, the bias increased to 10%-30%. A n overall increase of 5%-10% was observed with the use of SUVmax. The 5-min emission dataset led to an increase in the bias of 25%-100%. with the larg er increase recorded for the SUVmax. The results suggest that OSEM and SAC with 3 and 2 min transmission may be reliably used to reduce the overall da ta acquisition time without compromising the accuracy of SUVs.