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The Theoretical Study of Using the EPI to Improve Susceptibility-weighted Imaging

Author: WenLiang
Tutor: HongYang
School: China Medical University
Course: Biomedical Engineering
Keywords: Magnetic resonance imaging Magnetic susceptibility weighted imaging Gradient echo - echo planar sequence
CLC: R445.2
Type: Master's thesis
Year: 2010
Downloads: 33
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Abstract


The purpose of the magnetic susceptibility weighted imaging (susceptibility weighted imaging, SWI) is a recent development of a new magnetic resonance imaging techniques. It is based on the different tissue of the human body is the role of the external magnetic field having a different magnetic susceptibility characteristics, using T2 *-weighted 3D gradient echo sequence (GRE), simultaneously in the same parts of the phase images and amplitude images, the phase image phase mask, made after a high-pass filter then multiplied phase mask and amplitude images, the SWI images with high resolution and high contrast. Provides an excellent means of imaging the brain veins and iron deposition associated lesions, with good prospects in the area of ??clinical diagnosis. SWI imaging slow, and therefore can only be used for brain imaging, which greatly limits the development of SWI. This project is to start from the point of view of the sequence improved, the the clinical imaging fastest echo-planar imaging (echo planer imaging, EPI) in combination with SWI theoretically prove its feasibility, in order to shorten the time of SWI imaging for a kinds of practical methods. Materials and Methods In this study, starting from the analysis of the imaging characteristics of SWI, its imaging characteristics are summarized in the following five aspects are: 3D imaging, GRE sequence, T2 *-weighted, phase and amplitude diagram used in combination, as well as the organization The Magnetic Susceptibility sensitive. Five characteristics from three demonstration EPI sequence can be used to improve the SWI: EPI sequence sensitive to magnetic susceptibility;, EPI sequence T2 *-weighted;, EPI sequence encoding a frequency. After determine the EPI sequence can be used to improve the SWI imaging, the need for existing EPI sequence classification and filtering. The the existing EPI sequence can be divided in accordance with the preparation pulse SE-EPI, GRE-EPI and IR-EPI three; K space filling mode can be divided into the original EPI, BEST sequence, the involute sequence three kinds. , SE-EPI sequence and IR-EPI sequence as insensitive to the magnetic susceptibility is not suitable for improving the SWI imaging, non-adoption. Therefore, the retention of the original form of a pulse of the GRE sequences, and combine to form several different GRE-EPI sequence with the different K-space filling mode EPI. This analysis of several different GRE-EPI sequence timing diagram and K space filling mode selected BEST sequence combined GRE-EPI sequence to improve the SWI. Original 3D GRE sequences and the GRE-EPI sequence into the image quality of the image from the imaging time, and the signal-to-noise ratio, spatial resolution and contrast the contrast to noise ratio of these four aspects. In contrast to the process, the first derivation of existing formulas, and assuming the use of the same instrument, in the formula under conditions of exclusion of factors of external environmental factors and equipment to approximate, the approximation formula retain only associated with the imaging sequence Some of the factors. Commonly used in clinical SWI imaging parameter and individual associated with the performance of the instrument, the physical quantity substituting into the approximation formula and to draw 3D GRE sequences and various GRE-EPI sequence relationship of contrast in the image quality between the different conditions. The results are on the imaging time, GRE-EPI sequence mostly in about 30s, while 3D GRE sequences majority reached about 500s; in the signal to noise ratio, due to the different organizations have different signal-to-noise ratio, the selected two brain Ministry's major organizations: the gray matter (GM) and white quality (WM), they are in different field strength of the signal-to-noise ratio were comparing the relative signal-to-noise ratio of the 3D GRE sequences between 0.78 to 1.05, while the GRE-EPI sequences of signal-to-noise ratio larger range from 0.71 to 1.4; set or selected for each set of parameters of the imaging range and the imaging matrix is ??determined and therefore the spatial resolution of the two sequences is the same for the same set of parameters ; and GM / WM contrast to noise ratio, 3D GRE sequence and GRE-EPI sequence were 0.01 to 0.15 and from 0.66 to 1.44. Discussion is seen, under conditions of the same spatial resolution, with the 3D GRE sequence comparison, GRE-EPI sequence can greatly shorten the imaging time; GRE-EPI sequence of the signal-to-noise ratio is generally higher than the 3D GRE sequence; while in contrast signal-to-noise ratio, GRE-EPI sequence than 3D GRE sequence. Therefore, the use of EPI sequence improved SWI imaging is feasible in theory.

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CLC: > Medicine, health > Clinical > Diagnostics > Diagnostic Imaging > Magnetic resonance imaging
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