Original Article   

The Quarterly Journal of Nuclear Medicine and Molecular Imaging 2022 Sep 19

DOI: 10.23736/S1824-4785.22.03409-4

Copyright © 2022 EDIZIONI MINERVA MEDICA

language: English

Total variation regularized expectation maximization reconstruction improves 68Ga-FAPI-04 PET/CT image quality as compared to ordered subset expectation maximization reconstruction

Hanxiang LIU ^{1, 2, 3}, Lin LIU ^{1, 2, 3}, Shijie XU ⁴, Zhonglin LU ⁵, Greta S. MOK ⁵, Yingwei WANG ^{1, 2, 3}, Yi TAO ^{1, 2, 3}, Yue CHEN ^{1, 2, 3} ✉

¹ Department of Nuclear Medicine, The Affiliated Hospital of Southwest Medical University, Luzhou, Sichuan, PR China; ² Nuclear Medicine and Molecular Imaging Key Laboratory of Sichuan Province, Luzhou, Sichuan, PR China; ³ Academician (Expert) Workstation of Sichuan Province, PR China; ⁴ United Imaging Healthcare, Shanghai, PR China; ⁵ Biomedical Imaging Laboratory (BIG), Department of Electrical and Computer Engineering, Faculty of Science and Technology, University of Macau, Macau SAR, PR China

BACKGROUND: This study aimed to investigate improvements in 68Ga-FAPI PET/CT image quality due to using total variation regularized expectation maximization (TVR-EM) and ordered subset expectation maximization (OS-EM) reconstruction.
METHODS: Data from a total of 24 patients were retrospectively analyzed in this study. Positron emission tomography (PET) images were reconstructed using OS-EM and TVR-EM for 2 and 3 minutes-per-bed (min/bed) acquisition. The SUVmean of a region-of-interest on the liver, image noise, signal-to-noise ratios (SNR), the SUVmax of the lesions and the tumour-to-background ratios (TBR) were measured and compared between the 2 methods. Subjective image qualities were evaluated by two experienced radiologists using a 5-point score scale (5-excellent, 1-poor).
RESULTS: In total, 132 lesions were analyzed. The image noise in TVR-EM reconstruction groups was lower than in the OS-EM groups (all p < 0.05). The SNR, SUVmax of lesions and the TBR were higher for the TVR-EM reconstruction groups compared to OS-EM groups (all p < 0.05). Also, the SUVmax of the lesions in the TVR-EM groups increased by at least 12% compared to OS-EM 3 min/bed group. The SUVmax for small (<10 mm) and large lesions (> 10 mm) in the TVR-EM 2 min/bed group were significantly larger compared to the OS-EM 3 min/bed groups (all p <0.05). The highest image quality score resulted from the TVR-EM 3 min/bed group with a penalization factor of 0.25 (3.92 ± 0.19).
CONCLUSIONS: TVR-EM reduces image noise and improved the SNR, SUVmax and TBR of the lesions. It also enables fast acquisition without compromising image quality compared to standard OS-EM.

KEY WORDS: Total variation regularized expectation maximization; Ordered subset expectation maximization; Image reconstruction; PET/CT; FAPI