Susceptibility-weighted imaging (SWI) is a new neuroimaging technique which uses magnetic susceptibility differences in tissue to generate a unique contrast, different from that of spin density, T1, T2, and T2*. SWI consists of using both magnitude and phase images from a high-resolution, three-dimensional fully velocity-compensated gradient echo sequence. Phase mask is created from the MR phase images, and multiplying these with the magnitude images increases the conspicuity of the smaller veins and other sources of susceptibility effects, which is depicted using minimal intensity projection (minIP). The phase images are useful in differentiating between diamagnetic and paramagnetic susceptibility effects of calcium and blood, respectively. This unique MR sequence will help in detecting occult low flow vascular lesions, calcification and cerebral microbleed in various pathologic conditions and aids in characterizing tumors and degenerative diseases of the brain. This sequence also can be used to visualize normal brain structures with conspicuity.. Using phase as an iron marker may be useful for studying absorption of iron in diseases such as Parkinson’s, Huntington’s, neurodegeneration with brain iron accumulation, Alzheimer’s, and MS and other iron-related diseases.

The use of SWI in MS has gained increasing attention in the last couple of years. Although, the use of SWI in MS is in infancy, the detection of the vein abnormalities and areas of iron deposition in the brain are two main topics of interests.