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EPI in MRI - Essay Example

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However, this technique is predisposed to severe artefacts, and as a result, it has proved to be a technically demanding experiment. More often than not, there are a number of…
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Download file to see previous pages Notably, the boundaries existing between fat and compact bone are affected by the rapid de-phasing of the transverse magnetic field as well as distorts the signal. Resultantly, this leads to the wrong positioning of the frequency in the phase direction. K-space line is another parameter that could be optimized so as to change the EPI. A shift in the k-space line from its normal line leads to geometric distortion (Amin & Afzal, 2009, p.232). Such a shift may be resulting from field in-homogeneities. However, this artefact is reduced by spin echo sequences, which do rephrase the spins each time a 180-degree pulse is applied. On the other hand, gradient echo structures of the refocusing of the artefact. Undeniably, EPI makes use of a gradient echo sequence, thus leading to the accumulation of the effect with no radiofrequency (RF) pulse to correct the same. It is worth noting that any accumulation of errors arising from phase encoding will be wrongly registered, thus exposing EPI to this artefact. In the event that the duration of the EPI trajectory if considerably long, the EPI itself gets to be affected even by small field in-homogeneities (Ye et al, 1996, p.219).
Change in the parameter can be so achieved through increasing the bandwidth. Such an action will lead to a reduction in the echo time (TE). So as to realize more ramp sampling, the dwell time can be increased. In optimizing EPI, the frequency of the phase encoding can be increased using a zero filling. The end result of this is an increase in resolution. On the other hand, TE can be increased so as to increase the transverse magnetization, thus giving a greater T2 and T2*. Moreover, a gradient with a relatively high performance can be used in optimising EPI (Ye et al, 1996, p.220).
Bandwidth represents the frequency range resulting from the already read gradient across the field-of-view (FOV). This measure is quite imperative in the determination the ...Download file to see next pagesRead More
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