From the Guidelines
The SWI sequence is a T2 gradient echo sequence with added susceptibility weighting, making it a sensitive technique for detecting microbleeds, iron deposits, and calcifications in the brain*. This is based on the study by 1, which highlights the benefits of SWI in improving visualization of cortical veins and detecting microbleeds. The study notes that SWI was originally developed to improve visualization of cortical veins but has also become a valuable tool for detecting microbleeds, with higher field strength, longer TE, lower read out bandwidth, and asymmetric centering of the echo increasing its sensitivity.
Some key features of the SWI sequence include:
- Higher field strength, which increases sensitivity to detection of microbleeds
- Longer TE, which increases the conspicuity of microbleeds
- Lower read out bandwidth, which increases sensitivity to detection of microbleeds
- Asymmetric centering of the echo, which increases sensitivity to detection of microbleeds
- Small voxel sizes, which decrease partial volume averaging of small microbleeds and increase conspicuity, but also decrease image signal to noise (SNR)
The study by 1 also notes that the image geometry parameter that varies most from protocol to protocol in determining voxel size is slice thickness, with thinner slices increasing resolution but decreasing SNR. The two major hardware features that improve SNR are field strength and receiver RF coil type, with multi-channel arrays having greater SNR than single-channel volume coils.
Overall, the SWI sequence is a valuable tool for detecting microbleeds, iron deposits, and calcifications in the brain, and its sensitivity can be increased with higher field strength, longer TE, lower read out bandwidth, and asymmetric centering of the echo, as noted in the study by 1.
From the Research
SWI Sequence
- The Susceptibility-Weighted Imaging (SWI) sequence is a type of MRI sequence that is sensitive to magnetic susceptibility differences in tissues 2.
- SWI is particularly useful in detecting hemorrhage, as it can reveal a "blooming" effect of hemosiderin deposition, which is a protein that stores iron and is often present in hemorrhagic lesions 2.
- In the context of cerebral cavernous malformations, SWI can help identify the presence of hemorrhage and distinguish it from other types of lesions 2.
- The use of SWI in neuroimaging has become essential in the management of patients with acute ischemic stroke, as it can help identify the underlying cause of the stroke and guide treatment decisions 3.
Clinical Applications
- SWI is commonly used in the diagnosis and management of hemorrhagic stroke, as it can help identify the location and extent of hemorrhage 4.
- In patients with cerebral cavernous malformations, SWI can help identify associated developmental venous anomalies, which can increase the risk of hemorrhage 2, 5.
- The use of SWI in combination with other neuroimaging modalities, such as CT and MRI, can provide a more comprehensive understanding of the underlying pathology and guide treatment decisions 4, 6.