| Summary: | 碩士 === 義守大學 === 電機工程學系碩士在職專班 === 100 === There are three important scanning parameters (i.e. repetition time, echo time and flip angle) that will affect the MR signal intensity and contrast of investigated tissue and organ. SPGR (Spoiled Gradient Recalled echo) and GRASS (Gradient Recalled Acquisition in Steady State) are two of the rapid scanning pulse sequences based on gradient echo technique. However, the image weighting of these two techniques are somewhat different. The purpose of this study is aimed to investigate the variability, correlation and the image weighting scheme between GRASS and SPGR by changing the parameters mentioned above. GE Signa HDxt 1.5T whole body scanner and Fe+3 solutions with various concentrations were used in this study. It is found that the optimal flip angle (i.e. Ernst Angle) of SPGR increases as the concentration of Fe+3 increases. The signal intensity of GRASS increases as the flip angle increases and optimal flip angle of GRASS is 90°increases as the concentration of Fe+3 increases. The signal intensity variations of SPGR are larger than GRASS. It implies that the image contrast of SPGR is larger than that of GRASS. The signal intensity variations for different concentrations of Fe+3 using SPGR are far larger than using GRASS for shorter TR. The signal intensity variations gradually become smaller as TR becomes larger. The larger the concentration of Fe+3 is, the higher the signal intensity of SPGR and GRASS is for any TE. The signal intensity variations for different concentrations of Fe+3 using SPGR are far larger than using GRASS for shorter TE. It is concluded that the signal intensity of GRASS is slightly higher than that of SPGR obtained from same parameter settings, however, the image contrast of SPGR consistently reveals higher than that of GRASS when only one of the three image weighting parameters mentioned above is changed.
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