Breast MRI Physics Essentials: Signal Behavior, Suppression Approaches, and Appearance of Tissue and Implants.

Breast MRI provides the highest sensitivity for breast cancer detection and is widely used for high-risk screening, assessment of disease extent, treatment monitoring, and evaluation of silicone implant integrity. Despite the central role of fat suppression and tissue-specific signal behavior in determining image quality, the underlying physics principles and mechanisms of failure for these techniques are often underrecognized in clinical practice. This review provides a practical primer on MR signal behavior in commonly used T1 and T2weighted breast MRI sequences and outlines the major techniques used to suppress or separate signals from fat, water, and silicone. We summarize the intrinsic MR properties of fibroglandular tissue, fat, saline and silicone implants, highlighting how differences in relaxation times and resonant frequencies shape image contrast. The operational principles, strengths, and limitations of subtraction, chemical shift selective suppression (CHESS) fat suppression, short tau inversion recovery (STIR), hybrid spectral inversion approaches (SPIR and SPAIR), silicone-specific STIR, and chemical shift encoded (CSE) methods are described, with emphasis on characteristic artifacts and strategies for troubleshooting. By integrating key physics concepts with practical examples, this article aims to equip breast imagers and technologists with a clearer understanding of how signal suppression techniques function, why they fail, and how to optimize MR sequence performance and image quality.