Influence of time of flight and point spread function on PET / CT image quality and standard uptake value: A phantom study

Objectives: To explore the influence of time of flight (TOF) and point spread function (PSF) on PET / CT image quality and standard uptake value (SUV) based on a phantom study .

Methods: PET / CT imaging were performed using Jaszack model and IEC model respectively, conventional clinical imaging protocol (3min / bed) was used for three consecutive imaging. The ordered subsets expectation maximum(OSEM), OSEM + TOF, OSEM + PSF and OSEM + TOF + PSF were used to reconstruct the raw data respectively. The differences of image resolution, image uniformity, contrast, signal to noise ratio(SNR) and SUV between different reconstruction algorithms were compared.

Results: Compared with OSEM, the contrast of Jaszack model was significantly better in OSEM + TOF and OSEM + TOF + PSF than that in OSEM (t = 14.438, 15.485, P < 0.05). There was no significant difference between OSEM + PSF and OSEM (t = 2.287, P = 0.071); The maximum and minimum uniformity percentages were significantly lower in OSEM + PSF than in OSEM (t = -6.935, - 39.672, P < 0.001), and the maximum uniformity percentages of OSEM + TOF were significantly higher than OSEM (t = 3.295, P = 0.011); In IEC phantom imaging, the SNR and SUVmax of OSEM + PSF and OSEM + TOF + PSF were higher than those of OSEM (t = 4.047, 5.983, 3.178, 3.639, P < 0.05), but there was no significant difference between OSEM + TOF and OSEM (t = 0.868, 0.769, P > 0.05). Among the four reconstruction methods, the SNR and Suvmen increased with the increase of the sphere diameter (r = 0.913 to 0.963, P < 0.05), and SUVmax had no significant correlation with the sphere diameter (r = 0.496 to 0.754, P > 0.05). Comparing the resolution ability of different reconstruction methods of Jaszczak model imaging to different hot columns, the minimum hot column diameter that can be resolved by OSEM and OSEM + PSF reconstruction images is 6.4mm, and the minimum hot column diameter that can be resolved by OSEM + TOF and OSEM + TOF + PSF reconstruction images is 4.8mm.

Conclusions: Under specific acquisition and reconstruction conditions, TOF mainly improves image resolution and contrast, PSF mainly improves image uniformity and SNR. The combination of the two method can obtain better image quality and significantly improve the standard uptake value of hot lesions.