Susceptibility Weighted Imaging (SWI)*
We have developed a new type of contrast in MRI different from spin density, T1, or T2 imaging. This new method exploits the susceptibility differences between tissues. We refer to this method as Susceptibility Weighted Imaging*. SWI uses a fully velocity compensated, three dimensional, rf spoiled, high-resolution, 3D gradient echo scan. Signal from substances with different susceptibilities than their neighboring tissues (such as venous blood, or hemorrhage, for example) will become out of phase with adjacent tissues at sufficiently long echo times. If the size of the source is smaller than a voxel then the signal from this substance will beat against that of its neighbor creating a powerful partial volume effect. SWI can be run on any manufacturer’s machine at field strengths of 1.0T, 1.5T, 3.0T and higher.
What is Susceptibility Weighted Imaging and How Can it Help?
SWI is a unique combination of the following features:
- High resolution 3D gradient echo imaging
- Full flow compensation in all three directions
- Thin slices to avoid signal losses
- Filtering of phase images to reduce unwanted field effects
- Creating a phase mask image
- Operating on the magnitude image with the phase mask
- Taking a minimum intensity projection over neighboring slices
This special data acquisition and image processing produces an enhanced contrast magnitude image which is exquisitely sensitive to venous blood, hemorrhage and iron storage. SWI offers you the potential for:
- Better diagnosis of disease
- Better follow up for longitudinal studies
- An opportunity to be involved in the clinical evaluation of a new concept
- An opportunity to open new doors in clinical MRI
*The mechanisms behind susceptibility weighted imaging are protected via US Patent 6,501,272 B1 issued 31 December, 2002. Dr. E. Mark Haacke is the primary inventor of SWI along with his fellow co-inventors both Dr. Juergen Reichenbach and Dr. Yi Wang. Dr. Haacke also has another patent on both data collection and processing aspects of SWI via US Patent 6,658,280 B1 issued 2 December 2003.
Enhanced Detection of Tumors
The development of susceptibility weighted imaging (SWI) has opened the door for improved contrast and improved detection of hemorrhage in tumors. Part of the characterization of tumors lies in understanding the angiographic behavior of lesions both from the perspective of angiogenesis and micro - hemorrhages. Aggressive tumors tend to have rapidly growing vasculature and many microhemorrhages. Hence, our ability to detect these changes in the tumor could lead to a better determination of the tumor status. The enhanced sensitivity of SWI to venous blood and blood products due to their differences in susceptibility compared to normal tissue leads to better contrast in detecting tumor boundaries and tumor hemorrhage.
Small Vessel Imaging
Imagine the ability to image vessels smaller than a voxel, as small as deep white matter vessels. With SWI this is now possible for venous blood. Using 1.5T systems you can visualize veins on the order of a few hundred microns with 1 mm3 resolution in imaging times of roughly 5 to 10 minutes. Using 3.0T systems, imaging time can be reduced or resolution increased.