A case series of multiple myeloma PET/MR scans.

1324 Objectives: Plasma cell dyscrasias span a range of diseases from monoclonal gammopathy of undetermined significance (MGUS) to multiple myeloma (MM) based on a combination of clinical, laboratory and imaging findings with early diagnosis key to successful treatment of disease. Multiple imaging modalities including CT, PET/CT and MR are all currently used in the diagnosis and management of MM. A newer imaging technique PET/MR, combines the sensitivity of MR imaging with the physiologic imaging of PET; with only a few institutions currently using the technique. MR has proven useful in disease management by detecting bone marrow involvement before lytic changes are seen on CT and is the best technique for detecting diffuse bone marrow involvement. Furthermore, it can be problematic identifying focal lesions on PET/CT in patients with diffuse bone marrow hyperplasia without CT correlate; MR can be useful in detecting these focal lesions. Combining FDG-PET and MR, two common imaging modalities each having their own unique role in detecting active MM, is predicted to have a greater benefit for detecting active lesions and influencing treatment options and prognosis. Methods: Patients undergoing FDG-PET/MR were scanned using the GE Signa PET/MR. They were scanned 60 minutes after the injection of FDG. Images are obtained from the skull vertex through the mid-thigh. MR sequences obtained include axial T1, axial T2 FS, and axial DWI/ADC. Coronal and sagittal T1 and T2 reformatted images are also created. Dixon sequences were utilized for attenuation correction. 5 bed positions are used with total imaging time approximately 40 minutes. Results: 5 MM PET-MRs have been performed since August 2019. Greater than 50% (3/5) have proven clinical utility. 2 (40%) of the exams were negative for active lesions by both PET and MR criteria. A single exam (20%) showed diffuse marrow involvement on MR without FDG uptake as well as a focal lesion in the pelvis. 2 (40%) had comparison PET/CTs in which the PET/CT was negative or inconclusive. The inconclusive PET/CT showed skeletal FDG uptake in 3 separate areas all without CT correlate. The PET/MR on this patient had a MR correlate for 2 of these areas and subsequent biopsy of one of these lesions was positive for plasma cell proliferation confirming the diagnosis of MM. The final patient who presented with a negative PET/CT was discovered to have an active rib lesion adjacent to the left kidney on both the MR and PET images. This lesion was obscured by adjacent renal uptake on prior PET but the increased conspicuity of the lesion on MR allowed for diagnosis. Conclusions: PET/MR for multiple myeloma is a novel imaging modality for the diagnosis of MM. While our institution has performed only 5 examinations to date, PET/MR has proven clinical utility in over half of the cases indicating that PET/MR can be a useful tool for assessing active MM. This is likely due to the increased soft tissue contrast and sensitivity that MR provides in addition to the physiologic imaging of PET. $$graphic_F58024F3-2EA5-44A8-8A36-42ADAA951319$$