Cancer Screening Using ¹⁸F-FDG PET/MRI in Asymptomatic Subjects: A Multicenter Retrospective Study

Introduction: Cancer is a leading cause of death worldwide. The diagnosing and treating of the tumor at its early stage is the best way to improve prognosis. The advantages of positron emission tomography/magnetic resonance imaging (PET/MRI) are better soft-tissue contrast, low-dose radiation, simultaneous acquisition of functional MRI and PET data, allowing multi-parametric tumor evaluation. However, PET/MRI as a whole-body cancer screening method has not been studied on a large population of healthy subjects. We collected data of two PET/MRI scanners at different centers and investigated the clinical values of PET/MRI for cancer screening in a large cohort of asymptomatic subjects.

Methods: Two imaging diagnostic centers in east China, located in Shanghai and Hangzhou, were enrolled in this study. Screening modalities included were whole-body FDG-PET/MRI and lung computed tomography (CT) with different vendors. ¹⁸F-FDG PET/MRI in Shanghai and Hangzhou were performed on a whole-body PET/MRI scanner (Biograph mMR, Siemens Healthcare, Erlangen, Germany) and a whole-body PET/MRI scanner (TOF PET/MR, GE SIGNA, WI, USA) respectively with 5 bed positions. PET data acquisition started 40-45 min after the injection of ¹⁸F-FDG (3.7 MBq/Kg). The MRI protocols included whole-body (WB) T1WI, WB T2WI, WB DWI(b=800), brain T2 FLAIR, and spinal T2 TSE. The local ethics committee has approved this study. Written, informed consent was obtained from all subjects. Individuals who took FDG PET/MRI examination from January 1^st 2017 to December 31^st 2018 in the two centers were retrospectively selected after excluding individuals with a history of malignant tumors or incomplete data. Subjects who had no positive findings in the following 12 months or longer were considered as cancer negative.

Results: In the 3010 subjects in Shanghai center, PET/MRI with lung CT detected 83 suspicious lesions, 69 of them(36 cases of the early stage of lung cancer can only found by CT but not PET/MRI) were diagnosed as malignant tumors (true positive) and 14 of them were benign (false positive) (Figure 1). The cancer type distribution of the subjects is shown in Table 1. 5 malignant tumors were missed but detected by other modalities (false negative). The false-positive cases and false-negative cases are summarized in Table 2 and Table 3 respectively. While among the total 1080 subjects in Hangzhou center, 28 of them were found with suspicious lesions, 21 of them(11 cases of early stage of lung cancer can only found by CT) were diagnosed as malignant tumors and 7 of them were benign(Figure 2).1 malignant tumor was missed but detected by other modalities. When considering the two centers together,4090 subjects in total were enrolled, the detection rates of the complete screening program and PET/MRI-only screening were 2.71% and 1.57%, respectively.The sensitivity,specificity,PPV and NPV of PET/MRI screening program were 93.75%, 99.47%, 81.08% and 99.85%,respectively.The statistical results of multicenter is shown in Table 4. Discussions:To the best of our knowledge, this is the first study on evaluating the clinical values of FDG PET/MRI for cancer screening in different centers in a large cohort of asymptomatic volunteers. In this study, the cancer detection rate of PET/MRI with lung CT was 2.71%, which is much higher than the rate of PET/CT ranging from 0.9% to 1.3% in previous studies. It should be noted that most of the malignant cases were lung cancer, for which CT has a very high detecting accuracy. Therefore, a supplementary CT examination is necessary for PET/MRI screening.

Conclusions: Based on the findings in this study, we suggest that FDG PET/MRI might be an effective cancer screening modality, especially in combination with lung CT.

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