Susceptibility-weighted imaging (SWI) and SWAN
are two different commercialized 3D gradient-echo MR
techniques provided by different MR vendors. SWAN is a
product of the GE Healthcare and SWI belong to Siemens.
These two sequence are highly sensitive in detecting blood
degradation products, calcifications and iron deposits. SWI
sequence is a single-TE 3D T2* gradient-echo scan. The
core of the SWI is a complex reconstruction algorithm,
which utilizes both magnitude and local phase information extracted from the raw acquisition data. Subjected to
a long TE, tissues with different magnetic susceptibility
will become out of phase. SWI use the phase difference
information to emphasize the susceptibility between tissue
via phase mask, which is designed to enhance the contrast
in original magnitude image.