Spiral Sequence System Development and It''s Application in fMRI

• Main Authors: Tun-Wei Hsu, 許敦韋
• Other Authors: Chung-Ming Chen
• Format: Others
• Language: zh-TW
• Published: 2003
• Online Access: http://ndltd.ncl.edu.tw/handle/36080800594610150303

碩士 === 國立臺灣大學 === 醫學工程學研究所 === 91 === Functional MRI (fMRI) reveals the dynamic signal changes to the neuronal activity. It provides such information non-invasively by mapping changes in MR signal that are blood oxygenation level dependent (BOLD). However, the susceptibility-induced signal loss occurs at the inferior temporal, inferior frontal and ventral frontal areas near air/tissue interfaces. The signal loss seriously limits neuroscientists from studying some important cognitive processes, such as memory, emotion, language and attention. Strong challenges are presented to MR data acquisition methods to detect fMRI signal with sensitivity and reliability. According to the shortcomings, spiral pulse sequence was proposed to reduce the susceptibility artifact. In 2000, Bornert et al. proposed reverse spiral could improve TR efficiency、temporal resolution and enhance contrast and in 2001, Glover et al. proposed Spiral-In and Spiral-In/Out could solve susceptibility artifacts. In this study, spiral pulse sequence and image reconstruction methods were developed in Bruker MEDSPEC 3T MR machine of National Taiwan University. In spiral sequence development, a spiral trajectory design algorithm was proposed that was fast converged at the second order and the exact solution of the spiral trajectory. In sequence implementation, we built up traditional spiral trajectory and took the gradient and slew-rate limitation in consideration. The efforts on parameter selection were also included in this study. In image reconstruction, comparison was made between different reconstruction methods on spiral signal. We adapted the optimal MNLS iterative reconstruction method as well as developed a graphic-user-interface-based image reconstruction tool. In the future, we plan to measure the spiral trajectory and optimize the spiral parameters. At the last, developing Spiral-In and Spiral-In/Out sequences will be constructed and utilized to improve fMRI susceptibility artifacts and SNR enhancement.