期刊
JOURNAL OF MAGNETIC RESONANCE
卷 151, 期 1, 页码 107-117出版社
ACADEMIC PRESS INC
DOI: 10.1006/jmre.2001.2363
关键词
magnetic resonance; MRI; fMRI; susceptibility; blood; bone
资金
- NCI NIH HHS [R24 CA83060] Funding Source: Medline
A theory of the NMR signal dephasing due to the presence of tissue-specific magnetic field inhomogeneities is developed for a two-compartment model. Randomly distributed magnetized objects of finite size embedded in a given media are modeled by ellipsoids of revolution (prolate and oblate spheroids). The model can be applied for describing blood vessels in a tissue, red blood cells in the blood, marrow within trabecular bones, etc. The time dependence of the dephasing function connected with the spins inside of the objects, s(i), is shown to be expressed by Fresnel functions and creates a powder-type signal in the frequency domain. The short-time regime of the dephasing function for spins outside the objects, s(e), is always characterized by Gaussian time dependence, s(e) similar to exp[ - zetak(t/t(c))(2)], with zeta being a volume fraction occupied by the objects, t(c) being a characteristic dephasing time, and the coefficient k depending on the ellipsoid's shape through the aspect ratio of its axes (a/c), The long-time asymptotic behavior of s(e) is always quasispherical-linear exponential in time, s(e) similar to exp(-zeta Ct/t(c)), with the same spherical decay rate for any ellipsoidal shape. For long prolate spheroids (a/c) << 1, there exists an intermediate characteristic regime with a linear exponential time behavior and an aspect-ratio-dependent decay rate smaller than (zetaC/t(c)). (C) 2001 Academic Press.
作者
我是这篇论文的作者
点击您的名字以认领此论文并将其添加到您的个人资料中。
推荐
暂无数据