Chapter 22 Principles of susceptibility-weighted MRI

Heterogeneous magnetic susceptibility effects between various tissues (gray matter, white matter, and cerebrospinal fluid in the brain, for example) give rise to local variations in the phase of gradient-echo images that form the basis of phase contrast and susceptibility-weighted imaging (SWI). The post-processed SWI images offer a unique contrast based on the tissue susceptibility, which, in turn, depends on the composition and microstructure of the tissue. In this chapter, we discuss the fundamentals of phase, its use to create SWI, data acquisition considerations, data processing steps, pitfalls of using SWI data, and newer imaging and post-processing techniques that can help both speed up data acquisition and improve visualizing the unique susceptibility-based contrast inherent in human tissue. We further extend our discussion into the area of quantitative susceptibility mapping (QSM). QSM provides a means to quantify tissue susceptibility changes that occur in diseases that affect local iron content, such as Parkinson's disease and other neurodegenerative diseases.