Baete S H, De Deene Y, Masschaele B, De Neve W
Department of Radiotherapy, Ghent University Hospital, De Pintelaan 185, 9000 Gent, Belgium.
J Magn Reson. 2008 Aug;193(2):286-96. doi: 10.1016/j.jmr.2008.05.010. Epub 2008 May 20.
The spin-spin relaxation rate R2 (=1/T2) in hydrogel foams measured by use of a multiple spin echo sequence is found to be dependent on the echo time spacing. This property, referred to as R2-dispersion, originates to a large extent from molecular self-diffusion of water within internal field gradients that result from magnetic susceptibility differences between the gel and air phase. Another contribution to the R2 relaxation rate is surface relaxation. Numerical simulations are performed to investigate the relation between the foam microstructure (the mean air bubble radius and standard deviation of the air bubble radius) and foam composition properties (such as magnetic susceptibilities, diffusion coefficient and surface relaxivity) at one hand and the R2-dispersion at the other hand. The simulated R2-dispersions of gel foam are in agreement with the measured R2-dispersions. By correlating the R2-dispersion parameters and simulated microstructure properties a semi-empirical relationship is obtained that enables the mean air bubble size to be derived from measured R2-dispersion curves. The R2-derived mean air bubble size of a hydrogel foam is in agreement with the bubble size measured with X-ray micro-CT. This illustrates the feasibility of using 1H R2-dispersion measurements to determine the size of air bubbles in hydrogel foams and of alveoli in lung tissue.
通过使用多自旋回波序列测量发现，水凝胶泡沫中的自旋 - 自旋弛豫率R2（=1/T2）取决于回波时间间隔。这种特性，即所谓的R2色散，在很大程度上源于凝胶和空气相之间的磁化率差异所导致的内部场梯度内水分子的自扩散。对R2弛豫率的另一个贡献是表面弛豫。进行了数值模拟，一方面研究泡沫微观结构（平均气泡半径和气泡半径的标准偏差）和泡沫组成特性（如磁化率、扩散系数和表面弛豫率）之间的关系，另一方面研究R2色散之间的关系。凝胶泡沫的模拟R2色散与测量的R2色散一致。通过关联R2色散参数和模拟的微观结构特性，得到了一个半经验关系，该关系能够从测量的R2色散曲线中推导出平均气泡尺寸。水凝胶泡沫的R2推导平均气泡尺寸与用X射线显微CT测量的气泡尺寸一致。这说明了使用1H R2色散测量来确定水凝胶泡沫中的气泡尺寸以及肺组织中肺泡尺寸的可行性。
