EPI7005_2 Essay Example | Topics and Well Written Essays - 2500 words

EPI7005_2 - Essay ExampleSuch inhomogeneties may be a egress in some imperfection within the magnet or magnetic susceptibility spatial interpretation of the object that is being imaged (Christ, 2000, p. 78). The spatial variation is conventionalismly referred to as susceptibility artifacts. EPI applied in nearly of protocols used in diffusion weighted acquisition uses a homogenous static field. Such a field does not normally hold for magnetic resonance imaging head. The distortion that comes out of this is significant enough to rase exceed ten millimeters. Such artifacts come in the way of perfect diffusion images alignment with morphologic MRI and are considered obstacles to the head MRI joint analysis of structure and connectivity. Some of the methods used for field of magnetic susceptibility distortions include the use of a filed map. However, such methods of applying field maps are not received and accurate hence, they do not result in reliable EPI alignment with struct ural images that correspond to it. The T2-weighted structural image approach that relies on EPI baseline image and still gives account of the susceptibility artifacts is the recommended approach (Edelman and Schmitt, 1994, p. 610). How accurate the reconstruction of the image is depends on the rotates resonance frequency (rf) which is formed normally through with(predicate) a spatial linear gradient superposition and an external filed that is homogenous and strong. The above conditions have to trifle 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 nonrepresentational distortions process will be witnessed from the MRI image (Reinsberg, Doran, Charles-Edwards, and Leach, 2005). When the spin is increased, it leads to t he production of MRI signals whose intensity is comparatively low while areas having high magnetic susceptibility experiencing total signal loss (Zhou and Gullapalli, 2006). Question 1A several(prenominal) parameters have to be reduced in order to optimize EPI image, and they include A. Reducing the time of ricochet correspond length the longer the length of the echo train, the more time is required by the spin to gather phase error and the greater the distortion witnessed. One of the ways of minimizing the total time of train length is by minimizing the echo spacing. The less the time is taken by the frequency gradient in taste the signal, the less the distortion will be witnessed as shown in figure 1. The period for sampling is normally during the flat readout gradient portion unless there is ramp sampling. In FSE, the less the ESP or the echo spacing is, the less the blurring of the image gets. In EPI, minimizing the echo spacing also results in a reduction in the blurring and geometric distortion. Figure 2. The sampling time and the read encoding gradient during normal gradient performance (McMahon, 2012) As the segmentation degree increases, the echo number acquired per rf excitation decreases. This in turn minimizes the geometric distortion as the phase error time of accumulation is reduced. Figure 3 below demonstrates the reduction in