Vashaee S, Newling B, MacMillan B, Marica F, Li M, Balcom B J
UNB MRI Centre, Department of Physics, University of New Brunswick, Fredericton, New Brunswick E3B 5A3, Canada.
J Magn Reson. 2017 May;278:104-112. doi: 10.1016/j.jmr.2017.03.014. Epub 2017 Mar 27.
Slice-selective pulsed field gradient (PFG) and PFG-T measurements are developed to measure spatially-resolved molecular diffusion and diffusion-T distributions. A spatially selective adiabatic inversion pulse was employed for slice-selection. The slice-selective pulse is able to select a coarse slice, on the order of 1cm, at an arbitrary position in the sample. The new method can be employed to characterize oil-water mixtures in porous media. The new technique has an inherent sensitivity advantage over phase encoding imaging based methods due to signal being localized from a thick slice. The method will be advantageous for magnetic resonance of porous media at low field where sensitivity is problematic. Experimental CPMG data, following PFG diffusion measurement, were compromised by a transient ΔB(t) field offset. The off resonance effects of ΔB(t) were examined by simulation. The ΔB offset artifact in D-T distribution measurements may be avoided by employing real data, instead of magnitude data.
切片选择性脉冲场梯度（PFG）和PFG-T测量技术用于测量空间分辨的分子扩散和扩散-T分布。采用空间选择性绝热反转脉冲进行切片选择。该切片选择脉冲能够在样品中的任意位置选择厚度约为1厘米的粗切片。这种新方法可用于表征多孔介质中的油水混合物。由于信号来自厚切片的局部化，该新技术相对于基于相位编码成像的方法具有固有的灵敏度优势。该方法对于低场下多孔介质的磁共振将是有利的，因为在低场下灵敏度存在问题。在PFG扩散测量之后的实验CPMG数据受到瞬态ΔB(t)场偏移的影响。通过模拟研究了ΔB(t)的失谐效应。在D-T分布测量中，通过使用真实数据而非幅度数据，可以避免ΔB偏移伪影。
