Non-mono-exponential attenuation of water and N-acetyl aspartate signals due to diffusion in brain tissue
Non-mono-exponential attenuation of water and N-acetyl aspartate signals due to diffusion in brain tissue
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DOI：
10.1006/jmre.1997.1313
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发表时间：
1998-03-01
影响因子：
2.2
通讯作者：
Cohen, Y
中科院分区：
文献类型：
--
作者：
Assaf, Y;Cohen, Y
用大范围的b值(水和N-乙酰天冬氨酸分别高达28.3×10(6)和35.8×10(6)S厘米(-2))测量了水和N-乙酰天冬氨酸分子在离体脑组织中的扩散，在固定的扩散时间(t(D))测量了水和N-乙酰天冬氨酸分子扩散引起的信号衰减。这些测量将回声时间(TE)设置为70ms，重复几次扩散时间，范围从35到305ms，信号衰减被拟合为单指数、双指数和三指数函数，以获得这些分子在每个扩散时间的表观扩散系数(ADC)。从这些实验中得到以下观察和结论：(1)在所考察的整个b值范围内，水和NaA的信号扩散衰减不是单指数的，所提取的ADC取决于扩散时间：(2)在水的情况下，实验数据最好用三指数函数来拟合，而对于b值高达1×10(6)的S厘米(-2)，双指数函数似乎既能再现实验数据，又能再现三指数函数；(3)如果只拟合b值的低范围(高达0.5×10~(6)S cm~(-2))，水的信号衰减是单指数的，对t(D)不敏感：(4)水的ADC随TO的增加而减少，但快扩散分量的相对布居增加，使得在t(D)为305ms时几乎只有一个布居；(5)水的主要快扩散分量仅表现出非常有限的限制；(6)NAA信号衰减是双指数的，对低b值范围的分析只给出了单指数衰减，但获得的ADC对扩散时间很敏感：(7)用双指数函数拟合数据得到的ADC随着扩散时间的增加而减小，(8)慢扩散分量的相对布居随着t(D)的增加而减少；(9)NAA的快扩散成分和慢扩散成分都受到非渗透屏障的限制，用爱因斯坦方程计算了7-8微米和1微米的两个隔室，推测这两个隔室代表了胞体和轴突内的NAA。讨论了扩散实验中使用的b值的范围对结果的影响，并用来调和在不同实验中得到的关于脑组织中水扩散的一些明显差异。讨论了NAA扩散实验探测细胞结构的潜力。(C)1998年学术出版社。
Diffusion measurements were performed on water and N-acetyl aspartate (NAA) molecules in excised brain tissue using a wide range of b-values (up to 28.3 x 10(6) and 35.8 x 10(6) s cm(-2) for water and NAA, respectively), The attenuation of the signals of water and NAA due to diffusion was measured at fixed diffusion times (t(D)). These measurements, in which the echo time (TE) was set to 70 ms, were repeated for several diffusion times ranging from 35 to 305 ms, Signal attenuations were fitted to mono-, bi-, and triexponential functions to obtain the apparent diffusion coefficients (ADCs) of these molecules at each diffusion time. From these experiments the following observations and conclusions were made: (1) Signal attenuation of water and NAA due to diffusion over the entire range of b values examined is not monoexponential and the extracted ADCs depend on the diffusion time; (2) In the case of water the experimental data are best fitted by a triexponential function, while for b values up to 1 x 10(6) s cm(-2), a biexponential function seems to reproduce the experimental data as well as the triexponential function; (3) If only the low range of b values are fitted (up to 0.5 x 10(6) s cm(-2)) signal attenuation of water is monoexponential and insensitive to t(D); (4) Water ADCs decreased with the increase in to but the relative population of the fast diffusing component increases such that at a t(D) of 305 ms there is nearly a single population; (5) The major fast diffusion component of the water shows only very limited restriction; (6) NAA signal attenuation is biexponential and analysis of the low b-value range gives only monoexponential decay, but the obtained ADC is sensitive to the diffusion time; (7) The ADCs obtained from fitting the data with a biexponential function decrease as diffusion time increases; (8) The relative population of the slow-diffusing component decreases with increasing t(D); (9) Both the fast and the slow diffusing components of NAA show a considerable restriction by what seems to be a nonpermeable barrier from which two compartments, one of 7-8 mu m and one of similar to 1 mu m, were calculated using the Einstein equation, It is suggested that the two compartments represent the NAA in cell bodies and in the intra-axonal space. The effect of the range of the b value used in the diffusion experiments on the results is discussed and used to reconcile some of the apparent discrepancies obtained in different experiments concerning water diffusion in brain tissue. The potential of NAA diffusion experiments to probe cellular structure is discussed. (C) 1998 Academic Press.