Clinical applications of neuroimaging with susceptibility‐weighted imaging

Abstract

Susceptibility-weighted imaging (SWI) consists of using both magnitude and phase images from a high-resolution, three-dimensional, fully velocity compensated gradientecho sequence. Postprocessing is applied to the magnitude image by means of a phase mask to increase the conspicuity of the veins and other sources of susceptibility effects. This article gives a background of the SWI technique and describes its role in clinical neuroimaging. SWI is currently being tested in a number of centers worldwide as an emerging technique to improve the diagnosis of neurological trauma, brain neoplasms, and neurovascular diseases because of its ability to reveal vascular abnormalities and microbleeds.

Susceptibility‐weighted imaging to visualize blood products and improve tumor contrast in the study of brain masses

“…3c and d, and in the phase images of Fig. 3e and f. Further details on this effect are provided elsewhere (18,20).…”

“…To avoid aliasing, 40 msec is often used at 1.5T. A more detailed discussion, including the effects on vessels at arbitrary angles or perpendicular to the main field, is provided elsewhere (20). For oxygen-deprived tissue, as Y decreases, the extravascular signal loss increases due to dephasing from the background field.…”

“…For oxygen-deprived tissue, as Y decreases, the extravascular signal loss increases due to dephasing from the background field. When the vessel is only a fraction of the voxel, intravascular cancellation with signal from the parenchyma increases when venous blood volume increases (20,21). In both instances, diseased tissue will have a lower signal than healthy tissue.…”

“…In oxygendeprived tissue, the signal loss for veins occurs at shorter TEs, creating the impression of a shorter T2*. Paramagnetic contrast agents cause increased intravascular signal and signal cancellation, resulting in improved visualization of veins and the ability to resolve smaller veins due to partial volume effects (20,21). The coupling of T1 to T2* is a unique feature of SWI that enhances venous visibility even in the presence of a contrast agent (21).…”

“Brush Sign” on Susceptibility-Weighted MR Imaging Indicates the Severity of Moyamoya Disease

“…Susceptibility-weighted MR imaging is a high spatial resolution 3D gradient-echo MR imaging technique with phase postprocessing that accentuates the paramagnetic properties of blood products such as deoxyhemoglobin, intracellular methemoglobin, and hemosiderin. 10 This technique can show prominent hypointense signals in the draining veins within areas of impaired perfusion. Uncoupling between oxygen supply and demand in hypoperfused tissue may cause a relative increase of deoxyhemoglobin levels and a decrease of oxyhemoglobin in the tissue capillaries and the draining veins.…”