FMRI Utilizing Blood Oxygenation Sensitive Steady-state Imaging: Techniques and Applications at High Field
| Autor: | Ming-Long Wu, 吳明龍 |
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| Rok vydání: | 2006 |
| Druh dokumentu: | 學位論文 ; thesis |
| Popis: | 94 One major challenge of Blood Oxygenation Sensitive Steady-state (BOSS) fMRI is that the frequency band corresponding to highest functional sensitivity is extremely narrow, leading to substantial loss of functional contrast in the presence of magnetic field drifts. In this thesis, a frequency stabilization scheme was proposed for BOSS fMRI at 3T, where an radio-frequency (RF) pulse with very small flip angle was applied before each image scan, with the initial phase of the excited free induction decay signals extracted to reflect the temporal field drifts. A simple infinite impulse response (IIR) filter was further employed to obtain a low-pass filtered estimate of the central reference frequency for the upcoming scan. Experimental results suggest that the proposed scheme was able to stabilize the central reference frequency settings in accordance with the magnetic drifts, with oscillation amplitudes less than 0.5Hz. Phantom studies show that both the slow drifts and the fast fluctuations were prominently reduced for the dynamic BOSS scans, resulting in less than 5% signal variations. Visual fMRI at sub-millimeter in-plane resolution further demonstrated 10-17% activation signals nicely registered in the microvessels within the sulci. It is concluded that the IIR-filtered frequency stabilization is effective for reliable BOSS fMRI at high fields. |
| Databáze: | Networked Digital Library of Theses & Dissertations |
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