Preliminary Clinical Results for ¹⁸F-FDGPET/MR Compared with PET/CT in Patients with Suspected Recurrent or Metastatic Differentiated Thyroid Cancer

Purpose: To compare the diagnostic performance of ¹⁸F-FDG-PET/MR and PET/CT in patients with elevated thyroglobulin levels or a clinical suspicion of recurrent or metastatic differentiated thyroid cancer (DTC).

Methods: This prospective study included 35 thyroidectomized and remnant-ablated DTC patients (mean age = 51 ± 15.7 years) with signs of tumor recurrence/metastases. The datasets (whole-body PET/CT, whole-body PET/MRI) were rated by two readers regarding lesion conspicuity and diagnostic confidence. The Sensitivity, specificity, positive (PPV) and negative predictive values (NPV) for lesions in the local residual and lymph nodes in the neck, lungs, bones and other distant sites were calculated. The standard of reference included pathology and/or follow-up > 6 months.

Results: A total of 111 metastatic lesions were present in 21/35 patients; 10 patients had local recurrences or lymph node metastases in the neck, 7 had both local and distant recurrent disease, 2 had bone metastases only, and 2 had pulmonary metastases only. Reader confidence for the two examinations was similar (ICC = 0.889) with an excellent Inter-reader agreement for lesions (weighted kappa = 0.834 for PET/MRI and 0.818 for PET/CT) . In the patient-per-patient analysis, sensitivity and specificity of both tests were similar (p > 0.05). In the lesion-per-lesion analysis, the sensitivity of PET/MR and PET/CT for bone metastases, pulmonary metastases, local recurrences or lymphnode metastases in the neck, and all lesions together was 0.920 and 0.718 (p = 0.016), 0.841 and 0.923 (p = 0.031), 0.878 and 0.829 (p = 0.453), and 0.891 and 0.809 (p = 0.039) respectively. The corresponding specificity was 0.943 and 0.991 (p = 0.016), 0.933 and 0.976 (p = 0.125), 0.991 and 0.979 (p = 0.625), 0.966 and 0.983 (p = 0.008) respectively.

Conclusions: Diagnostic performance on a patient-per-patient basis, reader confidence and inter-reader agreement were similar with PET/MR and PET/CT. PET/CT had a significantly higher sensitivity but similar specificity to PET/MR for pulmonary metastases, while ¹⁸F-FDG PET/MR may be of great value in identifying bone metastases. Keywords: Positron emission tomography computed tomography; Magnetic resonance imaging; Metastases; Differentiated thyroid carcinoma