Whole-body diffusion-weighted MRI: a new gold standard for assessing disease burden in patients with multiple myeloma?

Whole body magnetic resonance imaging (MRI) is now recommended for all patients suspected of having asymptomatic myeloma or solitary plasmacytoma, for the detection of disease defining lesions. 1 , 2 Whole body imaging has the potential to easily and painlessly assess the burden of disease throughout the whole marrow at different disease timepoints and may be predictive of disease outcome from diagnosis. 3 , 4 Conventional MRI has previously been shown to be more sensitive and specific than 18 F-fluorodeoxyglucose positron emission tomography–computed tomography (FDG PET–CT) for the detection of small focal lesions and diffuse marrow infiltration. 5 , 6 Until recently, however, only FDG PET–CT offered a quantitative measurement in the form of standard uptake value. With the recent development of whole-body diffusion-weighted MRI (WB-DWI) for myeloma, a non-ionising radiation imaging modality for quantitative assessment of disease burden and therapy response has become available. WB-DWI uses the apparent diffusion coefficient (ADC) measurement to quantify disease. 7 ADC is influenced by tissue microarchitecture but specifically relates to marrow cellularity. 8 The speed, quantitative capabilities and superior sensitivity of WB-DWI compared with conventional MRI sequences 9 have led to its adoption at several leading myeloma centres worldwide. Additional benefits include the assessment of skeletal complications and no intravenous contrast. Despite these advances there has been a lack of data directly comparing WB-DWI and FDG PET–CT to evaluate their relative merits.