Multiexponential attenuation of the CPMG spin echoes due to a geometrical confinement
- 作者：D.S. Grebenkov
- 关键词：Magnetic resonance ; Multi-echo ; CPMG ; Restricted diffusion ; Confined media ; Multiexponential behavior
- 刊名：Journal of Magnetic Resonance
- 出版年：2006
- 期刊代码：126_10907807
- 类别：ch
- 出版时间：May 2006
- 卷：180
- 期：1
- 页码：118-126
- 文件大小：249 K
摘要
The CPMG multi-echo technique is often used to investigate the translational motion of diffusing nuclei in a confining medium. Henceforth, periodically repeated RF pulses with a diffusion-sensitizing gradient yield a formation of spin echoes of gradually decreasing amplitudes. The parameters of their exponential fits may characterize the structure of porous materials or biological tissue. In this paper, a multiexponential character of the CPMG measurements is rigorously demonstrated, once a geometrical confinement is present. Based on the multiple propagator approach, we derived a spectral representation for the echo amplitudes under external magnetic field of an arbitrary gradient profile. The multiple relaxation times and their spectral weights were found in a general form. The study of simple restrictive media allowed to obtain a quantitative condition under which the multiexponential attenuation is reduced to a monoexponential one.