Fast Imaging Techniques (MRI) - Essay Example

Download file to see previous pages Consequently, the shortened duration of flat top reduces both ESP and the geometric distortion of the image (Jezzard and Balaban, 1995, p.71). Another consequence of increasing the receiver bandwidth is faster imaging. Although increasing the receiver bandwidth allows faster imaging, it may also significantly reduce the SNR, and this often leads to more noise outside the spectrum (Parrish, 2000, p.927). For example, as the bandwidth range is gradually increased, the system may begin to sample more inherent noise together with the generated echo signal, thereby resulting in the fall of SNR. There are a number of ways that can generally be used to help recover the signals lost as a result of a wider bandwidth during the optimization of image. Some of the choices include acquisition of more signal averages and improving the receiver coil technology. The first option is, however, counter-productive because it may increase the amount of time needed to perform the overall scan while the second option if often preferred because it helps maintain the original objective of choosing EPI. Lastly, with regard to the required T2 weighted image, increasing the receiver bandwidth may reduce the effects of chemical shift artefacts on the image. According to Ra and Rim (1993, p.145), this is because higher receiver bandwidth results in a wide range of resonant frequencies on which the distortion is spread in order to cover a smaller pixel range and minimize the geometric distortion. 2. Discuss the advantages and disadvantages of using segmentation in EPI. Segmentation is a new concept that has significantly made it possible to use EPI on most of the conventional imaging systems where constraints related to signal to noise would have otherwise prevented EPI. Segmenting EPI is increasingly becoming more important to a number of its properties that ensure improved image quality as compared to the conventional single shot EPI. For example, one of the potential benefits of segmentation is that it allows EPI to be able to effectively run on the conventional systems where single short EPI can not be used. This is because segmentation ensures less stress is placed on the gradients as opposed to single short EPI and is therefore critically important in situations where by the available SNR and hardware makes it difficult to acquire all the necessary k-space data before the elimination of the MR signal by the traverse relaxation (McRobbie et al., 2003, p.75). Another important advantage of segmented EPI is that it helps reduce the magnetic susceptibility of various artefacts. This is because phase errors often have less time to build up when segmented EPI as compared to single shot EPI. The shortening of echo train length also allows segmented EPI to be less prone to the effects of artefact variations. Segmentation can also be used to help reduce imaging distortion and enable higher image resolution as compared to single shot EPI. The other key benefit of segmentation of EPI is the fact that it can be used to increase resolution. This is particularly attributed to the fact that segmented EPI have relatively short echo train length, thereby leading to increased spatial resolution. On the other hand, normal single shot EPI usually have lower spatial ...Download file to see next pagesRead More