Diffusion-Weighted MRI—The Way Forward for MRI in Myeloma?

Multiple myeloma and other plasma cell disorders infiltrate the bone marrow in different patterns. While some patients show a homogeneous distribution of the clonal plasma cells others present with focal accumulations, commonly called focal lesions. Novel imaging techniques can provide information on these infiltration patterns and, due to their low invasiveness, can be performed repeatedly and therefore be used for monitoring. Conventional magnetic resonance imaging (MRI) has a high sensitivity for bone marrow assessment but cannot safely differentiate between active and inactive lesions. Therefore, positron emission tomography, especially combined with computed tomography (PET/CT), has been more widely used, at least for the monitoring of treatment response. Comparative, but mostly retrospective studies, have shown that functional MRI techniques, namely diffusion-weighted imaging (DWI), which assesses the movement of water molecules, can evaluate tissue cellularity with high sensitivity, which challenges the dominance of PET/CT in treatment response assessment. This review will discuss the benefits and challenges of DWI and compare it to other available imaging techniques used in patients with monoclonal plasma cell disorders.