*2.1. Patients and Lesions*

We retrospectively reviewed the images of DTC patients who underwent 18F-FDG PET in our center from 23 October 2017 to 29 July 2020. The inclusion criteria were as follows: (1) diagnosis of DTC was confirmed by histopathological analysis; (2) patients had received comprehensive treatment (including total or subtotal thyroidectomy, 131I ablation therapy, or/and thyroid hormone replacement/suppression therapy); (3) patients had one or more of the following high-risk features of recurrence or cervical lymph node metastasis: (1) positive serum Tg and negative 131I-WBS, (2) rising anti-thyroglobulin antibodies (TgAb) after radioactive iodine ablation, (3) suspected widespread metastases throughout the body,

eligible for 18F-FDG PET examination according to the available guidelines at that time; (4) patients accepted 18F-FDG PET/CT and subsequent PET/MR examination; (5) patients were available for follow-up including postoperative pathology/fine-needle aspiration biopsy (FNAB) or regular ultrasonography and Tg/TgAb level monitor every 3–6 months. This retrospective study was approved by the Ethics Committee of Union Hospital, Tongji Medical College, Huazhong University of Science and Technology. All patients signed an informed consent before undergoing 18F-FDG PET/MR imaging.

The local thyroid region lesions and cervical lymph nodes included in the present study were involved according to the following criteria: (1) the lesion was diagnosed by pathology after reoperation or FNAB; (2) the lesion was monitored regularly by imaging including neck ultrasonography, 131I-WBS, CT, and/or MRI, for at least 6 months.
