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 disorder
