Prospective evaluation of simultaneous PET/MRI and PET/CT in cervical cancer

Objectives The objective of this study was to compare findings of whole-body FDG-PET/CT to whole-body simultaneously acquired FDG-PET/MRI in patients with cervical cancer.

Methods A prospective institutional study was performed in which whole-body FDG-PET/CT was obtained for routine clinical evaluation and immediately followed by whole-body PET/MRI. We studied 42 patients with cervical cancer: 9 for initial staging, 30 for routine follow-up, 3 to assess tumor response during the course of initial therapy. Patients underwent single FDG injection. Administered activity of FDG ranged from 12.1 to 19.3 mCi (mean, 14.9 mCi). PET/CT was performed on either a Biograph 40 HD or Biograph mCT scanner per our standard clinical procedure after which patients underwent PET/MRI on a Biograph mMR scanner Attenuation correction was performed with a dual-echo VIBE Dixon sequence that separates water and fat with TE1/TE2 = 1.23msec/2.46 msec, TR = 3.6 msec, left-right FOV = 500 mm and anterior-posterior FOV = 300 mm. A high-resolution DWI acquisition was also performed. Additional high resolution small field of view TSE T2 imaging was performed for the pelvis.

Results All sites of metabolically active cervical cancer identified on PET/CT were also identified on PET/MRI. No additional sites of disease were identified on PET/MRI. In 3 of 9 patients with new diagnosis of cervical cancer the PET/MRI significantly clarified the anatomic site of disease visualized on PET/CT. In 2 patients there was inability to distinguish on PET/CT whether tumor was in the ovary versus pelvic lymph node, and this was readily clarified on PET/MRI. For the third patient, PET/MRI clarified omental metastases that were not readily localized on PET/CT. Additionally, localization of the metabolically active disease in the cervix was readily identifiable.

Conclusions Simultaneous PET/MRI is feasible in patients with cervical cancer. PET/MRI findings show all sites of disease seen on PET/CT. PET/MRI has better soft tissue contrast than PET/CT. Radiation dose to patients is less with PET/MRI than with PET/CT.