The influence of respiratory motion on the cumulative SUV-volume histogram and fractal analyses of intratumoral heterogeneity in PET/CT imaging

Objective The purpose of this study was to investigate the influence of respiratory motion on the evaluation of the intratumoral heterogeneity of FDG uptake using cumulative SUV-volume histogram (CSH) and fractal analyses. Methods We used an NEMA IEC body phantom with a homogeneous hot sphere phantom (HO) and two heterogeneous hot sphere phantoms (HE1 and HE2). The background radioactivity of 18 F in the NEMA phantom was 5.3 kBq/mL. The ratio of radioactivity was 4:2:1 for the HO and the outer rims of the HE1 and HE2 phantoms, the inner cores of the HE1 and HE2 phantoms, and background, respectively. Respiratory motion was simulated using a motion table with an amplitude of 2 cm. PET/CT data were acquired using Biograph mCT in motionless and moving conditions. The PET images were analyzed by both CSH and fractal analyses. The area under the CSH (AUC-CSH) and the fractal dimension (FD) was used as quantitative metrics. Results In motionless conditions, the AUC-CSHs of the HO (0.80), HE1 (0.75) and HE2 (0.65) phantoms were different. They did not differ in moving conditions (HO, 0.63; HE1, 0.65; HE2, 0.60). The FD of the HO phantom (0.77) was smaller than the FDs of the HE1 (1.71) and HE2 (1.98) phantoms in motionless conditions; however, the FDs of the HO (1.99) and HE1 (2.19) phantoms were not different from each other and were smaller than that of the HE2 (3.73) phantom in moving conditions. Conclusion Respiratory motion affected the results of the CSH and fractal analyses for the evaluation of the heterogeneity of the PET/CT images. The influence of respiratory motion was considered to vary depending on the object size.