PET/MR v. PET/CT: Former may be more effective for head and neck cancer

A comparison of PET/MR and PET/CT using a trimodality system showed that PET/MR is a worthy alternative, if not superior, to PET/CT when imaging for head and neck tumors, according to a study published Feb. 3 in in the Journal of Nuclear Medicine.

Felix P. Kuhn, MD, from the department of medical radiology at the University Hospital Zurich, Switzerland, and colleagues compared PET/CT and contrast-enhanced PET/MR imaging for the detection of head and neck tumors. Results of the assessment indicated that PET/MR is at least as good, if not better in some cases, as PET/CT for the evaluation of head and neck cancer.

MR was determined to provide a range of clinical utilities, including dynamic contrast enhancement, quantification of cellular density via coefficient maps, arterial spin labeling and intravoxel incoherent motion that reveal the vasculature of tumors.

“This additional information may help to increase the specificity in the characterization of PET-positive lesions,” wrote Kuhn et al. “However, MR imaging using advanced imaging techniques and multiple pulse sequences is time consuming and needs to be limited to a body region of particular interest—for example, the neck—in the framework of an integrated PET/MR examination.”

For this study, 150 subjects underwent sequential FDG PET/CT and MR imaging to evaluate the added utility of MR and contrast enhanced MR to the mix in the case of head and neck cancer. Of these patients, 85 were found to have at least one PET-positive lesion. A total of 162 lesions were evaluated. PET/MR was found to have “similar robustness” when compared to PET/CT. Without the addition of contrast enhancement, PET/MR excelled in characterizing morphology and led to the detection of metastatic lymph node involvement. With the addition of contrast enhancement, PET/MR led to increased diagnostic confidence with regard to assessing the conspicuity of lesions, perineural spread and progression of disease into surrounding structures. 

“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,” wrote the authors. “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.”

The authors added that T2 weighted MR may be all that is needed for early assessment of head and neck tumors. More advanced MR scanning is advised to increase specificity in special cases.