  Functional behavior of breast cancer - representing underlying biology - can
be analyzed using MRI. The most widely used breast MR imaging protocol is
dynamic contrast-enhanced T1-weighted imaging. The cancer enhances on dynamic
contrast-enhanced MR imaging because the contrast agent leaks from the leaky
vessels into the interstitial space. The contrast agent subsequently leaks back
into the vascular space, creating a washout effect. The normal parenchymal
tissue of the breast can also enhance after contrast injection. This
enhancement generally increases over time. Typically, a radiologist assesses
this background parenchymal enhancement (BPE) using the Breast Imaging
Reporting and Data System (BI-RADS). According to the BI-RADS, BPE refers to
the volume of enhancement and the intensity of enhancement and is divided in
four incremental categories: minimal, mild, moderate, and marked.
  Researchers have developed semi-automatic and automatic methods to extract
properties of BPE from MR images. For clarity, in this syllabus the BI-RADS
definition will be referred to as BPE, whereas the computer-extracted
properties will not. Both BPE and computer-extracted parenchymal enhancement
properties have been linked to screening and diagnosis, hormone status and age,
risk of development of breast cancer, response monitoring, and prognosis.
