Breast MRI : no time like the present

Abstract

Breast imaging – as a radiological subspecialty – is perhaps the epitome of how the practice of radiology has changed through the decades. Imaging of the breast is an exciting and challenging combination of multimodality image acquisition, interpretation, biopsy procedures, clinical, radiological and radiopathological correlation. The breast radiologist is an integral part of the multidisciplinary team guiding patients on this most personal journey from diagnosis to an end-goal of survivorship and quality-adjusted life-years gained. Breast magnetic resonance imaging (MRI) was introduced to the breast imaging community in the 1990s and has since then become a validated tool for the diagnostic evaluation of the breast. Compared to conventional imaging modalities, namely mammography and ultrasound, MRI has been proven to have a very high cancer detection sensitivity ranging between 93-100% albeit with a low specificity ranging between 37-97%. In simplest terms, the physiological explanation for the high sensitivity of MRI for cancer detection is that contrast-enhanced MRI is extremely sensitive for tumour angiogenesis. The vessels formed by tumour angiogenesis are abnormal and more ‘leaky’ than native vessels. The increased enhancement of cancers relative to normal breast tissue may result from both an increased supply of contrast agent (gadolinium) through this proliferation of blood vessels and their increased permeability. Hence, breast MRI utilizes the dynamic (with time) contrast-enhancement (DCE) characteristics of lesions. Several sets of imaging are acquired at different time points. The increased leakiness of the abnormal vasculature results in earlier wash-out of contrast from malignant lesions when compared to normal breast parenchyma. The varying cyclical vascularity of the premenopausal breast actually determines the opportune timing (day 10 – 16 of menstrual cycle) of imaging examination. Features such as restricted diffusivity and corresponding apparent diffusion coefficients of lesions can further differentiate benign from more suspicious findings. [excerpt]