Introduction

Characterization of renal masses mainly relies on the presence or absence of enhancement on contrast-enhanced computed tomography (CT) or magnetic resonance (MR) imaging. With MRI, enhancement can be assessed by measuring signal intensity changes or visually without or with image subtraction. There is a growing interest in the application of diffusion-weighted MRI (DWI) in body imaging for multiple reasons: DWI can provide structural and functional information without any intravenous (IV) contrast administration, thus it is easy to implement and repeat, and is very attractive in patients at risk for nephrogenic systemic fibrosis (NSF).

The signal and contrast in DWI are based on the thermally driven random motion of water and microcapillary perfusion in tissues, and are usually quantified by calculating the apparent diffusion coefficient (ADC). The ADC is dependent on different factors such as molecular architecture, interactions, and temperature in free fluid. The protons' motion is hindered or restricted by different components such as cell membranes, cellular density, or macromolecules in tissues. This is manifested by an ADC that is reduced from the bulk value. In general, the clinical implications of ADC change depend upon the tissue under investigation; an anomalous rise in ADC can indicate increased edema, cystic changes, and necrosis; while an anomalous reduction in ADC might indicate ischemia, infection, or tumor. As such, diffusion measures should be taken in context with other imaging sequences to ensure an accurate diagnosis.