Briggs R W, Liebig T, Ballinger J R, Ros P R
Department of Radiology, University of Florida College of Medicine, Gainesville 32610.
Magn Reson Imaging. 1993;11(5):635-44. doi: 10.1016/0730-725x(93)90005-x.
The individual components of two commercially available barium sulfate (BaSO4) suspensions, Liquid HD and E-Z-paque (E-Z-EM Inc., Westbury, NY), were investigated to determine their contribution to relaxation. Longitudinal and transverse relaxation times of suspensions and solutions of the different BaSO4 particles and the vehicle used to keep them in suspension were measured separately at 2.0 T. A multiple echo Carr-Purcell-Meiboom-Gill (CPMG) pulse sequence was used for T2 determinations with different values of the echo spacing 2 tau. Longer values of 2 tau resulted in significant shortening of the calculated T2 relaxation times, indicating that the major mechanism leading to signal loss in BaSO4 suspensions is the diffusion of water molecules through susceptibility gradients in the vicinity of suspended particles. At higher BaSO4 concentrations, decreased water proton density also produces significant signal loss. Viscosity has little effect on the relaxation. A combination of larger and smaller BaSO4 particle sizes was found to be more effective than smaller sizes only in enhancing signal decay.
对两种市售硫酸钡（BaSO4）混悬液——Liquid HD和E-Z-paque（E-Z-EM公司，纽约州韦斯特伯里）的各个成分进行了研究，以确定它们对弛豫的影响。分别在2.0 T场强下测量了不同BaSO4颗粒混悬液及用于保持其混悬状态的溶媒的纵向和横向弛豫时间。采用多重回波Carr-Purcell-Meiboom-Gill（CPMG）脉冲序列，通过不同的回波间隔2τ值测定T2。2τ值越大，计算得到的T2弛豫时间显著缩短，这表明导致BaSO4混悬液信号丢失的主要机制是水分子通过悬浮颗粒附近的磁化率梯度扩散。在较高的BaSO4浓度下，水质子密度降低也会导致显著的信号丢失。粘度对弛豫影响很小。结果发现，大小颗粒混合的BaSO4比仅含小颗粒的BaSO4在增强信号衰减方面更有效。
