Are Gadolinium-Enhanced MR Sequences Needed in Simultaneous 18F-FDG-PET/MRI for Tumor Delineation in Head and Neck Cancer?

Abstract

Background and purpose: PET/MRI with ¹⁸F-FDG has demonstrated the advantages of simultaneous PET and MR imaging in head and neck cancer imaging, MRI allowing excellent soft-tissue contrast, while PET provides metabolic information. The aim of this study was to evaluate the added value of gadolinium contrast-enhanced sequences in the tumor delineation of head and neck cancers on ¹⁸F-FDG-PET/MR imaging.

Materials and methods: Consecutive patients who underwent simultaneous head and neck ¹⁸F-FDG-PET/MR imaging staging or restaging followed by surgery were retrospectively included. Local tumor invasion and lymph node extension were assessed in 45 head and neck anatomic regions using ¹⁸F-FDG-PET/MR imaging by 2 rater groups (each one including a radiologist and a nuclear medicine physician). Two reading sessions were performed, one without contrast-enhanced sequences (using only T1WI, T2WI, and PET images) and a second with additional T1WI postcontrast sequences. The results were compared with the detailed histopathologic analysis, used as reference standard. The κ concordance coefficient between the reading sessions and sensitivity and specificity for each region were calculated.

Results: Thirty patients were included. There was excellent agreement between the contrast-free and postgadolinium reading sessions in delineating precise tumor extension in the 45 anatomic regions studied (Cohen κ = 0.96, 95% CI = [0.94-0.97], P < .001). The diagnostic accuracy did not differ between contrast-free and postgadolinium reading sessions, being 0.97 for both groups and both reading sessions. For the 2 rater groups, there was good sensitivity for both contrast-free (0.83 and 0.85) and postgadolinium reading sessions (0.88 and 0.90, respectively). Moreover, there was excellent specificity (0.98) for both groups and reading sessions.

Conclusions: Gadolinium chelate contrast administration showed no added value for accurate characterization of head and neck primary tumor extension and could possibly be avoided in the PET/MR imaging head and neck workflow.

FIG 1.

Initial staging of a right maxillary squamous cell carcinoma in an 84-year-old woman. A, Axial T1-weighted spin-echo (SE) sequence. B, Axial T1-weighted fat-saturated sequence. C, Fusion between axial T1WSE sequence. C, 3D T1-weighted fat-saturated SE postcontrast sequence, axial plane. D, Fusion between axial T1-weighted SE sequence and ¹⁸F-FDG-PET. Both T1-weighted FDG-PET/MR imaging with and without gadolinium showed right hard palate invasion. The anterior tumor margin (arrow) was difficult to define on both contrast-free and postcontrast T1WI (B and D). PET imaging allowed clarification of the lesion margins (A and C).

FIG 2.

Initial staging of right adenoid cystic carcinoma of a minor salivary gland (palate) in a 55-year-old man. A, Axial FDG-PET. B, Axial T2-weighted spin-echo (SE) sequence. C, Axial T1-weighted SE sequence. D, 3D T1-weighted fat-saturated SE postcontrast sequence. On both T1-weighted and T2-weighted MR imaging (B and C), thickening of the trigeminal nerve is present, with a loss of signal of the fatty tissue in the pterygopalatine fossa, strongly suggestive of perineural spread of the tumor. On the T1-weighted postgadolinium sequence (D), high enhancement of the trigeminal nerve is visible (arrow). There is no significant perineural ¹⁸F-FDG uptake (A); only slight uptake is discernable when guided by MR imaging findings.

FIG 3.

Local extension of a mandibular gingiva tumor in a 71-year-old woman. A, Axial contrast-free T1-weighted. B, Axial ¹⁸F-FDG-PET image. C, 3D T1-weighted spin-echo (SE) contrast-enhanced sequence, axial plane. D, Fusion between axial T1-weighted and ¹⁸F-FDG-PET. Both contrast-free and gadolinium-enhanced T1W MR imaging showed right vestibular invasion. Although bone invasion remained doubtful because of dental artifacts on MR alone, high FDG uptake includes a portion of the mandibular bone with margins that are clearly visible on the fusion images between PET and T1-weighted MRI, demonstrating bone involvement (arrow), which was pathologically confirmed.