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  • Susceptibility Weighted Image Processing

    Introduction

    Magnetic susceptibility is dimensionless proportionality constant that indicates the degree of magnetization of a material in response to an applied magnetic field (wikipedia). As the name suggests, Susceptibility Weighted(SW) MR imaging is a method of brain imaging in which the intensity of a particular voxel is proportional to the magnetic susceptibility of the underlying tissue. Because de-oxygenated venous blood is rich in iron content than neighbouring tissues, the magnetic property is also substantially different which is why SW images are used for a good understanding of the distibution of veins in the brain.

    In our experiment full-brain volumetric images (512x512x500) in NIfTI format were recorded with a Philips MR scanner at 3 Tesla using a 3D Presto FFE sequence (0.43x0.43x0.3 mm voxel size). Facial features have been removed from these images for de-identification. Separate phase and magnitude images are provided. The next section gives the details of 2 methods used for processing the SW images thus acquired.

    Susceptibility Weighted Magnitude Image

    Susceptibility Weighted Phase Image

    Method 1

    This image processing method considers both the magnitude volume and the phase volume of SW images. Before the steps of processing are described its worthwhile to take a closer look at what the magnitude volume and phase volume of the MR images actually are(Ying ). Generally complex MR image acquisition can be expressed as:

    \[I = |I|*exp(\phi)\]

    where \(|I|\) is the magnitude part and \(\phi\) is the phase component of the image. The phase image conveys several important information like field inhomogeniety, v