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

EPI7005_2 - Essay Example Such inhomogeneties 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 of 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 images alignment with structural MRI and are considered obstacles to the head MRI joint analysis of structure and connectivity. Some of the methods used for 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 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 spin’s resonance frequency (rf) which is formed normally through a spatial linear gradient superposition and an external filed 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). When the spin is increased, it leads to the production of MRI signals whose intensity is relatively low while areas having high magneti c susceptibility experiencing total signal loss (Zhou and Gullapalli, 2006). Question 1A Several parameters have to be reduced in order to optimize EPI image, and they include: A. Reducing the time of echo train 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 sampling 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

Was Henry David Thoeau a true transcendentalist Essay

Was Henry David Thoeau a true transcendentalist - Essay Example Through many of his works, more specifically Walden, Thoreau divulged into the concept of living without the dependency of material goods and completely giving up ideas of religion and spirituality, as these two things only existed to impede on the happiness of human beings. By living a life of simplicity, a life that was without such an attachment to materialism, and by understanding that spirituality is within a person and not without them, then a person could discover true human happiness. Unfortunately, in a world that depends so much on the quality and quantity of what they have externally, paying very little attention to what is available internally, true human happiness was often easier discussed than it was obtained. The factor that truly make Thoreau a transcendentalist is that he actually did what he had to in an effort to obtain true happiness. Instead of simply preaching to others that all it takes is for someone to live a simple life without all of the material possessio ns and to live without a need for religion and spirituality, Thoreau actually set out to live a life just like that. In his book, Walden, Thoreau details his life after he built a small cabin on the shore of Walden Pond, Massachusetts (Thoreau).