Detection of Breast Malignancy: Different Magnetic Resonance Imaging Modalities

This chapter presents several innovative magnetic resonance imaging techniques employed for the detection of breast malignancy. One of the techniques, ultrasound (US), is an excellent method for assessing palpable abnormalities, differentiating between cystic and solid lesions, and classifying solid masses. It also allows accurate needle placement for biopsy. Ultrasound used as a mammography supplement detects additional cancers, but it also increases the false-positive rate. Furthermore, US is time consuming, and it is difficult to ensure that the entire breast is imaged. Breast dynamic contrast-enhanced-magnetic resonance imaging (DCE-MRI) involves acquisition of a time series of T1-weighted images, during which an intravenous contrast reagent (CR) bolus injection is made. The images are usually acquired with gradient echo pulse sequence, such as spoiled gradient-recalled acquisition at steady state (GRASS) sequence, with short echo time TE (<8 msec), short repetition time TR (<20 msec), and low flip angle (10-30°). Malignant tissues usually show more rapid and larger increases in DCE-MRI signal intensities, followed by faster washout, as compared to benign tissues. Subjective (qualitative) visual assessment of the enhancement time course is used for clinical diagnosis. The most commonly identified enhancement patterns are characterized as persistent (signal intensity rises persistently), plateau (signal intensity remains fairly constant after reaching maximum), and washout (signal intensity immediately decreases after reaching maximum). There are two major classes of DCE-MRI pharmacokinetic models. The first is the heterogeneous class, in which CR and water are not assumed to be always uniformly distributed within each compartment entered. The second is the homogeneous class, in which such assumptions are made.