Combined PET/MRI system in Head and Neck Cancer: Initial Experience

The recently introduced whole-body PET/MRI systems combine the unique metabolic imaging capabilities of positron emission tomography (PET) and the excellent soft tissue contrast of magnetic resonance imaging (MRI). The aim of this pilot study was to evaluate the feasibility of PET/MRI for initial staging of head and neck cancer.
Materials and Methods:Ten male patients aged (age 52 to 78 years, median age 62.8 y) with histologically proven squamous cell carcinoma of the head and neck region were examined using both a stand-alone PET scanner and a wholebody
PET/MRI scanner. Scanning started 60 minutes after intravenous administration of 350 MBq [18-F]-2-fluoro-2-deoxy-D-glucose (FDG) for the body trunk to exclude distant metastases. PET/MRI of the head and neck region followed immediately the first scan. The study was approved by the local ethics committee. A four-point-scale was used for qualitative evaluation of PET image quality. Furthermore, the signal-to-noise ratio (SNR) of the tumor and of both cerebellar hemispheres were determined for both PET data sets and used for semiquantitative comparison of image quality. Results were compared using the Wilcoxon matched-pair test.Results:The primary tumor was detected by PET/MRI in all 10 patients, by PET in 9 out of 10 cases, and by MRI in 9 out of 10 cases. Seven patients had lymph nodes suspect for metastatic disease. In two patients, lymph nodes considered suspect using MRI showed no pathological FDG uptake. In contrast, a single patient had lymph nodes considered suspect by PET but not by MRI. Visual evaluation of PET images showed consistent results (including regional contrast) for both scanners. There were no statistically significant differences regarding SNR between conventional PET and PET/MRI for the tumor and for both cerebellar hemispheres (p > 0.05).
Conclusion: PET/MRI of head and neck cancer is feasible with a whole-body PET/MRI scanner with excellent image quality and - fusion. While previously available PET/MRI systems were largely restricted to brain examinations, whole-body PET/MRI scanners allow comprehensive tumor staging. Further patients will be examined to evaluate the clinical role of PET/MRI in head and neck cancer.