SWI is a relatively new MR technique which allows the visualisation of magnetic susceptibility changes caused by various substances,
including iron.
Given that iron plays an important role in numerous conditions,
the clinical application of SWI are vast.
The combination of magnitude and phase data results in an enhanced contrast magnitude image,
which is more sensitive to magnetic susceptibility changes than T2* gradient echo (GE) sequence images.
The abnormality of importance on SWI is blooming; a susceptibility artefact encountered in the presence of paramagnetic substances.
The use of the term is in reference to the fact that lesions appear larger than they are.
Fig. 1: T2* GE (a) and SWI (b) images of the same patient at the same level demonstrating the superiority of SWI which is two-fold; a greater number of foci of blooming signal loss reflecting greater sensitivity, and a higher degree of blooming signal loss reflecting greater contrast.
Fig. 2: SWI images of a 56-year-old female with a right caudate head haemorrhage and multiple cerebral microhaemorrhages predominantly involving the basal ganglia. This figure illustrates the different forms data can be presented from an SWI sequence, including the magnitude image (a), the phase image (b), the SWI image (c) and the minimum intensity projection (mIP) image (d).
Fig. 3: Utility of mIP images. Note the ease of detection of numerous microhaemorrhages on the mIP images (a-b) when compared to the SWI images (c-d) of the same patient at the same level.