Value of 18F-FDG Hybrid PET/MR in Differentiated Thyroid Cancer Patients with Negative 131I Whole-Body Scan and Elevated Thyroglobulin Levels

Abstract

Purpose: To evaluate the diagnostic performance of ¹⁸F-FDG PET/MR in detecting recurrent or metastatic disease in patients with differentiated thyroid cancer (DTC) who have increased thyroglobulin (Tg) levels but a negative ¹³¹I whole-body scan (WBS). The relationship between ¹⁸F-FDG PET/MR and serum Tg levels was explored. We also evaluated the therapeutic impact of PET/MR on patient clinical management.

Patients and methods: Twenty-nine DTC patients with a negative ¹³¹I-WBS of the last post-therapeutic and increased Tg levels under thyroid-stimulating hormone suppression treatment who underwent ¹⁸F-FDG PET/MR examination were retrospectively analyzed.

Results: Of those 29 patients, ¹⁸F-FDG PET/MR findings were true positive, true negative, false positive, and false negative in 18, 7, 2, and 2 patients, respectively. The overall sensitivity, specificity, and accuracy were 90.0%, 77.8%, and 86.2%, respectively. We noticed significant differences in serum Tg levels between the PET/MR-positive and PET/MR-negative patient groups (P=0.049). Receiver operating characteristic curve analysis showed that a Tg level of 2.4 ng/mL was the optimal cut-off value for predicting PET/MR results. The sensitivity, specificity, and accuracy of PET/MR were higher in patients with Tg levels greater than 2.4 ng/mL than in patients with lower levels. By detecting recurrent or metastatic disease, ¹⁸F-FDG PET/MR altered the clinical management in 7 patients (24.1%) of the overall population.

Conclusion: ¹⁸F-FDG PET/MR has high diagnostic accuracy for detecting recurrent or metastatic diseases in DTC patients and is useful for clinical management.

Keywords: 18F-FDG; PET/MR; differentiated thyroid cancer; thyroglobulin.

Figure 1

A 43-year-old female patient with a history of papillary thyroid carcinoma who underwent thyroidectomy and RAI therapy. Her serum Tg level was 38.72 ng/mL. The images ((A) maximal intensity projection; (C and F) PET/MR fusion; (D) PET image; arrows) showed cervical lymph nodes with increased FDG uptake (SUVmax, 15.6). Cervical lymph nodes can be identified the MRI ((B and E) axial T2-weighted with fat suppression, arrows). The patient underwent neck surgery, and pathology results confirmed lymph node metastasis. The serum Tg levels decreased in the later follow-up.

Figure 2

A 60-year-old male patient with a history of papillary thyroid carcinoma who underwent thyroidectomy and RAI therapy. The patient presented with a serum Tg level of 10.68 ng/mL. Maximal intensity projection ((A) arrow, thin arrow, curved arrow) showed multiple lesions with elevated activity in the neck and chest. The MRI axial image of the neck ((B) T2-weighted with fat suppression, arrow) revealed a 1.3cm lesion with an SUVmax of 5.5 on the corresponding fusion image ((C) arrow). The selected axial images ((D) MRI T2-weighted with fat suppression; (E) fusion image; thin arrows) show the left supraclavicular node with elevated focal activity and an SUVmax of 6.9. The images ((F) MRI T1-weighted sequence; (G) fusion image; curved arrows) show the mediastinum lesion with increased FDG uptake (SUVmax, 4.2). Recurrent disease was confirmed by pathology results. The serum Tg levels decreased in the later follow-up.

Figure 3

Distribution of serum Tg levels in patients according to positive and negative ¹⁸F-FDG PET/MR findings.

Figure 4

Receiver operating characteristic curve analysis demonstrates Tg cut-off value (2.4 ng/mL, arrow) under TSH suppression therapy.