Susceptibility-Weighted Imaging and Quantitative Susceptibility Mapping

For many years, gradient echo (GRE) imaging has played a major role in helping to create rapid, high-resolution, high-contrast, large flip angle T1-weighted images for both very short and longer echo times. Clinically, it has been used more with smaller flip angles to highlight T2* effects in order to look for blood products such as those that occur in hemorrhage. About 15 years ago, another form of gradient echo imaging referred to as susceptibility-weighted imaging (SWI) came onto the scene and offered to enhance the contrast even further by using the phase information. This has been very successful in revealing small hemorrhages in the form of microbleeds but still suffers from some forms of blooming artifact and orientation or geometry dependence of the magnetic fields coming from the objects of interest. More recently, an inversion process to create magnetic source images from phase images has made it possible to perform quantitative susceptibility mapping (QSM). In this article, we will discuss the current state-of-the-art imaging with SWI and QSM in measuring iron content and oxygen saturation in vivo.