Contrast-Enhanced PET/MR Imaging Versus Contrast-Enhanced PET/CT in Head and Neck Cancer: How Much MR Information Is Needed?

Abstract

Considering PET/MR imaging as a whole-body staging tool, scan time restrictions in a single body area are mandatory for the costeffective clinical operation of an integrated multimodality scanner setting. It has to be considered that 18 F-FDG already acts as a contrast agent and that under certain circumstances MR contrast may not yield additional clinically relevant information. The concept of the present study was to understand which portions of the imaging information enhance the sensitivity and specificity of the hybrid examination and which portions are redundant. Methods: One hundred fifty consecutive patients referred for primary staging or restaging of head and neck cancer underwent sequential wholebody 18 F-FDG PET with CT-based attenuation correction, contrast-enhanced (ce) CT, and conventional diagnostic MR imaging of the head and neck in a trimodality PET/CT-MR system. Assessed were image quality, lesion conspicuity, diagnostic confidence, and the benefit of additional coronal and sagittal imaging planes in cePET/CT, PET/MR imaging with only T2-weighted fat-suppressed images (T2w PET/MR imaging), and cePET/MR imaging. Results: In 85 patients with at least 1 PET-positive lesion, 162 lesions were evaluated. Similar robustness was found for CT and MR image quality. T2w PET/MR imaging performed similarly to (metastatic lymph nodes) or better than (primary tumors) cePET/CT in the morphologic characterization of PET-positive lesions and permitted the diagnosis of necrotic or cystic lymph node metastasis without application of intravenous contrast medium. CePET/MR imaging yielded a higher diagnostic confidence for accurate lesion conspicuity (especially in the nasopharynx and in the larynx), infiltration of adjacent structures, and perineural spread. Conclusion: The results of the present study provide evidence that PET/MR imaging can serve as a legitimate alternative to PET/CT in the clinical workup of patients with head and neck cancers. Intravenous MR contrast medium may be applied only if the exact tumor extent or infiltration of crucial structures is of concern (i.e., preoperatively) or if perineural spread is anticipated. In early assessment of the response to therapy, in follow-up examinations, or in a whole-body protocol for non-head and neck tumors, T2w PET/MR imaging may be sufficient for coverage of the head and neck. The additional MR scanning time may instead be used for advanced MR techniques to increase the specificity of the hybrid imaging examination. Int egrated PET/CT has been established as an important diagnostic technique for staging and therapy assessment in advanced head and neck cancers. 18 F-FDG PET/CT has a higher sensitivity than CT or MR imaging for the detection of small lymph nodes (1). Also, in therapy assessment PET/CT has been shown to differentiate early responders from nonresponders (2). However, 18 F-FDG is known not to be specific to cancer cells, and inflammatory or physiologic uptake has to be considered as a differential diagnosis. Furthermore, cystic lymph node alte...

FDG Whole-Body PET/MRI in Oncology: a Systematic Review

“…Sensitivity and NPV of PET/MRI has been reported to be 92.2 and 95.1 %, higher than those of PET/CT (sensitivity 67.8 % and NPV 82.2 %, respectively). Non-enhanced fast T1 weighted MR imaging showed superiority to low-dose CT in terms of conspicuity rating in liver lesions [36]. Benign lesions of liver as well as metastatic lesions were better characterized by PET/MRI than PET/CT [46] (Fig.…”

“…CT scans have limitation for evaluating oral cavity lesion when metallic and/or dental artifact exists. One study showed that most artifacts are noted in the suprahyoid region in CT and infrahyoid region in MRI [36]. PET/CT and PET/MRI would be considered as alternative diagnostic modality of HN cancer according to the location of primary tumor (Fig.…”

Combined Evaluation of FDG-PET/CT and CT Imaging Characteristics of Cervical Lymph Nodes to Increase the Interpretation Accuracy for Nodal Metastatic Involvement in Head and Neck Cancer

“…However, concerns remain regarding the non-specific nature of FDG uptake, which results in false positive readings. Recent publications comparing hybrid PET/magnetic resonance imaging (PET/MR) and PET/CT demonstrated equivalent or slight superiority of PET/MR in the imaging workup of patients with head and neck cancer, however additional data is needed to establish the role of PET/MR as preferred imaging modality or problem solving tool [12,13].…”

PET/MRI and PET/CT: is there room for both at the top of the food chain?

“…The remaining 13 publications report some evidence that PET/ MRI is superior to PET/CT for characterizing primary tumours, e.g. primary bone tumours [11][12][13] or oesophageal carcinoma [14], but do not demonstrate significant advantages of whole-body MRI over whole-body PET/CT for N or M staging [15][16][17][18][19][20][21][22][23][24].…”

“…The remaining 13 publications report some evidence that PET/ MRI is superior to PET/CT for characterizing primary tumours, e.g. primary bone tumours [11][12][13] or oesophageal carcinoma [14], but do not demonstrate significant advantages of whole-body MRI over whole-body PET/CT for N or M staging [15][16][17][18][19][20][21][22][23][24].The introduction of PET/MRI was heralded as a technological breakthrough, and many expected a subsequent clinical revolution, with the newer modality vying to supersede PET/CT atop the diagnostic food chain just as the Burmese python is supplanting the American alligator in the Florida Everglades. However, none of the above-mentioned papers offers a definitive answer as to whether or not integrated and simultaneous PET/MR imaging is clinically more accurate than sequentially performed whole-body PET/CT and MRI dedicated to one body region registered in retrospect.…”