THEORY OF NMR SIGNAL BEHAVIOR IN MAGNETICALLY INHOMOGENEOUS TISSUES - THE STATIC DEPHASING REGIME
THEORY OF NMR SIGNAL BEHAVIOR IN MAGNETICALLY INHOMOGENEOUS TISSUES - THE STATIC DEPHASING REGIME
复制标题
DOI：
10.1002/mrm.1910320610
复制
发表时间：
1994-12-01
影响因子：
3.3
通讯作者：
HAACKE, EM
中科院分区：
文献类型：
--
作者：
YABLONSKIY, DA;HAACKE, EM
本文研究了静磁场不均匀条件下生物组织中核磁共振信号行为的理论。我们已经开发了一种方法，分析描述的核磁共振信号在静态减相状态，扩散现象可能被忽略。该方法已被应用于评估血管网络（应用于功能成像）、骨髓（用于两种特定的小梁结构，不对称和柱状）和铁氧体造影剂存在下的核磁共振信号。所有研究的系统都有一些共同的行为。如果回波时间TE小于给定系统的已知特征时间t(c)，则信号呈指数衰减，其参数依赖于TE的二次函数。它等价于R2*弛豫速率它是TE的线性函数。在相反的情况下，当TE大于t(c)时，核磁共振信号遵循简单的指数衰减，弛豫速率不依赖于回波时间。对于这个时间间隔，R2*是a)产生磁场的物体占据的体积分数sigma， b)磁场b -o或仅仅是物体对铁氧体粒子的磁矩，以及c)物体与介质之间的磁化率差Delta chi的线性函数。
This paper is devoted to a theory of the NMR signal behavior in biological tissues in the presence of static magnetic field inhomogeneities. We have developed an approach that analytically describes the NMR signal in the static dephasing regime where diffusion phenomena may be ignored. This approach has been applied to evaluate the NMR signal in the presence of a blood vessel network (with an application to functional imaging), bone marrow (for two specific trabecular structures, asymmetrical and columnar) and a ferrite contrast agent. All investigated systems have some common behavior. If the echo time TE is less than a known characteristic time t(c) for a given system, then the signal decays exponentially with an argument which depends quadratically on TE. This is equivalent to an R2* relaxation rate which is a linear function of TE. In the opposite case, when TE is greater than t(c), the NMR signal follows a simple exponential decay and the relaxation rate does not depend on the echo time. For this time interval, R2* is a linear function of a) volume fraction sigma occupied by the field-creating objects, b) magnetic field B-o or just the objects' magnetic moment for ferrite particles, and c) susceptibility difference Delta chi between the objects and the medium.