¹⁸F-FDG PET/MRI in patients suffering from lymphoma: how much MRI information is really needed?

To evaluate and compare the diagnostic potential of different reading protocols, entailing non-enhanced/contrast-enhanced and diffusion-weighted ¹⁸F-FDG PET/MR imaging for lesion detection and determination of the tumor stage in lymphoma patients.

A total of 101 ¹⁸F-FDG PET/MRI datasets including a (1) transverse T2-w HASTE and ¹⁸F-FDG PET (PET/MRI₁), (2) with an additional contrast enhanced VIBE (PET/MRI₂), and (3) with additional diffusion-weighted imaging (PET/MRI₃) were evaluated. Scans were performed for initial staging, restaging during treatment, or at the end of treatment and under surveillance with suspicion for tumor relapse. In all datasets lymphoma manifestations as well as tumor stage in analogy to the revised criteria of the Ann Arbor staging system were determined. Furthermore, potential changes in therapy compared to the reference standard were evaluated. Hitherto performed PET/CT and all available follow-up and prior examinations as well as histopathology served as reference standard.

PET/MRI₁ correctly identified 53/55 patients with active lymphoma and 190/205 lesions. Respective values were 55/55, 202/205 for PET/MRI₂ and 55/55, 205/205 for PET/MRI₃. PET/MRI₁ determined correct tumor stage in 88 out of 101 examinations, and corresponding results for PET/MRI₂ were 95 out of 101 and 96 out of 101 in PET/MRI₃. Relating to the reference standard changes in treatment would occur in 11% based on PET/MRI₁, in 6% based on PET/MRI₂, and in 3% based on PET/MRI₃.

The additional application of contrast-enhanced and diffusion-weighted imaging to ¹⁸F-FDG PET/MRI resulted in higher diagnostic competence, particularly for initial staging and correct classification of the disease extent with potential impact on patient and therapy management.