LAUSR

S usceptibility-weighted imaging (SWI) generates a unique contrast, which is different from those of spin density, T1, T2, and T2 * , based on magnetic susceptibility differences of tissues. 1 SWI provides a new source of contrast in MRI by harnessing magnetic susceptibility differences of various compounds including deoxygenated blood, blood products, iron and calcium. 1,2 The susceptibility effect is most pronounced in non-refocused gradient echo (GRE) methods which use long echo times (TE), short fl ip angles, and high fi eld strengths. SWI relies on GRE sequences, but since it uses fi ltered-phase information in each voxel by a high-resolution, long TE, fl ow-compensated, 3D GRE imaging technique, its sensitivity for susceptibility is greater than those of conventional T2 * weighted GRE sequences. 2,3 SWI relies on a fully velocity-compensated, high-resolution, three-dimensional gradient-echo sequence and characterizes brain tissue using magnitude and phase images sep-arately or in combination. 2 On SWI, the magnitude and phase MR data are combined to create a phase mask. These are multi-plied with the original magnitude images, and a fi nal magnitude SWI dataset is produced. Both magnitude and phase information are essential for proper tissue characterization, and are combined to create an SWI image. Eventually, these images are further processed with a minimum intensity projection algo-rithm (minIP) to create 3 – 10 mm thick high signal to noise minIP slabs. These minIP images show the continuity of tortu-ous veins across the slices while suppressing the signal from the brain tissue. 1,2