Impact of CT-Based and MRI-Based Attenuation Correction Methods on ¹⁸ F-FDG PET Quantification Using PET Phantoms

Purpose:: Integrated PET/MRI imaging system has been widely used in clinical and research applications since it can simultaneously provide functional and structural information. Accurate attenuation correction (AC) is an important challenge that PET/MRI must overcome to obtain correct quantification results and clinical diagnosis. This study aimed to determine the relationship between the radioactivity concentrations produced by computed tomography AC (CTAC) and that produced by magmetic resonance AC (MRAC) and investigate the possibility of comparing the acquired results from different integrated imaging systems. Methods:: This study used the American College of Radiology (ACR), the International Electrotechnical Commission (IEC), and striatal phantom to simulate the attenuation of organs (lung, abdomen, and head). All phantoms were injected with 18 F-FDG and underwent a PET/CT scan under GE Discovery STE and a PET/MRI scan under GE SIGNA. The built-in AC method was adopted for both scanners. Regions-of-interest (ROIs) were manually drawn, and mean activity concentrations in each ROI were calculated. Relative percent difference and linear correlation were used to compare the obtained results from CTAC and MRAC. Result:: Strong correlation were found in ACR phantom (CMRAC = 0.77 × CCTAC – 76.26 with R2 = 0.96), IEC phantom (CMRAC = 1.73 × CCTAC – 588.03 with R2 = 0.98), and striatal phantom (CMRAC = 0.75 × CCTAC – 830.61 with R2 = 0.99). Conclusion:: Quantification results of MRAC were strongly correlated with those of CTAC. Results acquired from different integrated imaging systems can be compared using a linear equation.