Comparison of ¹⁸F-FDG PET/CT and PET/MRI including diffusion weighted imaging in patients with multiple myelomas

Objectives To assess the potential contribution of the introduction of diffusion-weighted imaging (DWI) in the PET/MRI protocol for multiple myeloma (MM) assessment.

Methods The study includes 24 MM patients (n=15, primary MM; n=9, pre-treated patients). All patients underwent ¹⁸F-FDG PET/CT, followed by PET/MRI including DWI. PET/CT and PET/MRI data were assessed and compared based on qualitative and semi-quantitative (SUV) evaluation. DWI findings were matched to respective PET and static MRI (T1w- and T2w-TIRM-sequences) findings.

Results In total 138 lesions were detected with at least one method. 71 myeloma-indicative focal lesions were detected with PET/CT. The PET part of PET/MRI revealed 63 of the PET/CT-positive lesions (89%). T1w and T2w-TIRM depicted 128 MM lesions, 61 resembled PET/CT findings (61/71; 86%) and 54 matched respective foci in PET/MRI (54/63; 86%). 9 additional lesions were seen in the PET part but not in the MRI part of PET/MRI. Static MRI-sequences demonstrated 67 PET-negative lesions, 63 of which (94%) were seen in patients that had already undergone therapy. DWI demonstrated a total of 111 focal MM lesions, which were all confirmed in static-MR images. 64 lesions correlated anatomically with the lesions that were also visible in PET/CT, while 47 where DWI-positive and PET/CT-negative. DWI failed to depict 20 lesions detected by static MRI-sequences.

Conclusions In our study the use of DWI as part of the PET/MRI protocol did not add significant additional information in addition to well-established T1w/T2w-TIRM sequences in this malignancy. However, the results should be confirmed in larger studies.