Six DWI questions you always wanted to know but were afraid to ask: clinical relevance for breast diffusion MRI.

Diffusion MRI (often called diffusion-weighted imaging or DWI) has enjoyed a tremendous growth since its introduction in the mid-1980s, especially to investigate neurological disorders and in oncology. At a time when standardization and quality control appear as critical as ever to support widespread utilization, our aim was to address common fundamental questions that arise regarding results obtained with DWI. We focus on six questions taking breast DWI as an example, as breast DWI is increasingly used in clinical practice, but most of our conclusions would apply to DWI in general. We show especially that noise can act in a pernicious way specific to DWI. Ignoring such noise effects could lead to incorrect data interpretations or conclusions, of which authors and readers may be genuinely unaware. While addressing these six questions, we give practical examples of how noise effects can be understood, corrected when possible, or taken to our advantage. Key Points • Ignoring noise effects in DWI could lead to incorrect data interpretations or conclusions, of which authors and readers may be genuinely unaware. • In vivo apparent diffusion coefficient (ADC) decreases with b value, which must therefore be reported along with ADC. • Synthesized DWI boosts contrast at the expense of accurate diffusion/microstructure characterization.