susceptibilityweighted

Susceptibility-weighted imaging (SWI) is an MRI technique that enhances contrast by exploiting differences in magnetic susceptibility between tissues. It is particularly sensitive to paramagnetic substances such as deoxyhemoglobin, ferritin, and hemosiderin, as well as to calcium, leading to improved visualization of venous structures, microbleeds, and iron deposition in the brain and other tissues. SWI combines magnitude data from a high-resolution 3D gradient-echo sequence with phase information to produce images that accentuate susceptibility effects. In standard processing, a phase image is high-pass filtered to remove background field variations, then a phase mask is created and multiplied with the magnitude image (often two to four times) to yield the susceptibility-weighted image. Alternative approaches, such as quantitative susceptibility mapping (QSM), can provide absolute susceptibility values.

SWI is widely used in neuroradiology to detect cerebral microbleeds associated with traumatic brain injury, stroke, and cerebral amyloid angiopathy; to visualize venous architecture; and to assess iron accumulation in neurodegenerative diseases such as Parkinson’s disease and multiple sclerosis. It can also aid in identifying calcifications, though differentiation from iron can require additional analysis or QSM.

Limitations include susceptibility and motion artifacts, particularly near air-tissue interfaces such as the paranasal sinuses, and sensitivity to image geometry and scanner parameters. SWI is typically used as a supplemental sequence alongside conventional MRI, rather than a standalone diagnostic tool.