SWI sequence (MRI)

Susceptibility-Weighted Imaging (Susceptibility-Weighted Imaging, SWI) is an MRI imaging technique used in medical diagnostics, specifically in the area of venous vessels.

Historical

The underlying principle was first published in 1997[^1] and comprehensively described in 2001[^2].

Background

The SWI sequence is based on the physical property of magnetic susceptibility. SWI is a magnetic resonance imaging technique. It uses flow-compensated, high-resolution 3D gradient echo sequences (GRE-sequence) in single and multi-echo techniques utilizing the different magnetic susceptibilities of various tissues. These differences lead to a phase difference and cause a signal loss. No contrast agent is used. By combining the signal and phase images, an enhanced contrast image is generated, which can display venous blood, (brain) hemorrhages, and iron deposits such as hemosiderin. Imaging of venous blood with SWI is referred to as blood-oxygen-level-dependent imaging (BOLD). Venous (deoxygenated) blood is less diamagnetic than arterial (oxygenated) blood. Therefore, the technique was originally referred to as BOLD, but later replaced by the more general term susceptibility-weighted imaging. The term BOLD venography is sometimes still in use today. Due to the BOLD effect, the venous vascular system can be well visualized with SWI.

Application

SWI sequences can be used, for example, in patients with traumatic brain injury, in high-resolution brain venographies, and other clinical applications.

Imaging