Magnetic Susceptibility Technology - Essay Example

However, its behavior will still resemble that of off-resonance fat. Several methods have been used in the correction of geometric distortions in MRI diffusion-weighted normally resulting from static magnetic field inhomogeneities. Such inhomogeneities may be a result in some imperfection within the magnet or magnetic susceptibility spatial variation of the object that is being imaged (Christ, 2000, p. 78). The spatial variation is normally referred to as susceptibility artifacts. EPI applied in most protocols used in diffusion-weighted acquisition uses a homogenous static field. Such a field does not normally hold for MRI head. The distortion that comes out of this is significant enough to even exceed ten millimeters. Such artifacts come in the way of accurate diffusion image alignment with structural MRI and are considered obstacles to the head MRI joint analysis of structure and connectivity. Some of the methods used for the correction of magnetic susceptibility distortions include the use of a filed map. However, such methods of applying field maps are not reliable and accurate; hence, they do not result in reliable EPI alignment with structural images that correspond to it. The T2-weighted structural image approach that relies on EPI baseline image and still gives an account of the susceptibility artifacts is the recommended approach (Edelman and Schmitt, 1994, p. 610).
How accurate the reconstruction of the image depends on the spin’s resonance frequency (rf) which is formed normally through a spatial linear-gradient superposition and an external field that is homogenous and strong. The above conditions have to meet failure to which the anatomical structures relative positions will end up being misrepresented in the MRI image reconstruction. A good example of this is a case in which a spin is presented to a magnetic field that is not the same as the expected value resulting from the magnetic susceptibility. In this case, the geometric distortions process will be witnessed from the MRI image (Reinsberg, Doran, Charles-Edwards, and Leach, 2005).