The Gaussian phase distribution approximation enables analysis of restricted diffusion encoded by general gradient waveforms but fails to account for the diffraction-like features that may occur for simple pore geomet...The Gaussian phase distribution approximation enables analysis of restricted diffusion encoded by general gradient waveforms but fails to account for the diffraction-like features that may occur for simple pore geometries.We investigate the range of validity of the approximation by random walk simulations of restricted diffusion in a cylinder using isotropic diffusion encoding sequences as well as conventional single gradient pulse pairs and oscillating gradient waveforms.The results show that clear deviations from the approximation may be observed at relative signal attenuations below 0.1 for onedimensional sequences with few oscillation periods.Increasing the encoding dimensionality and/or number of oscillations while extending the total duration of the waveform diminishes the non-Gaussian effects while preserving the low apparent diffusivities characteristic of restriction.展开更多
目的探讨三维梯度自旋回波(GRASE)序列在老年患者磁共振胆胰管成像(MRCP)中的应用价值。方法纳入MRCP检查的老年患者63例。同时采集屏气2D-FSE、屏气3D-GRASE和呼吸触发3D-FSE序列。计算图像的信噪比、对比噪声比和对比度,并对图像质量...目的探讨三维梯度自旋回波(GRASE)序列在老年患者磁共振胆胰管成像(MRCP)中的应用价值。方法纳入MRCP检查的老年患者63例。同时采集屏气2D-FSE、屏气3D-GRASE和呼吸触发3D-FSE序列。计算图像的信噪比、对比噪声比和对比度,并对图像质量进行主观评价,包括伪影、背景抑制、总体图像质量和胆胰管各分支的显示情况。组间比较采用单因素ANOVA检验或非参数Kruskal-Wallis检验。结果GRASE序列的伪影评分高于2D-FSE序列,差异具有统计学意义(4.24±0.69 vs 3.76±1.03,P<0.05),但与3D-FSE序列之间差异无统计学意义(P>0.05)。GRASE序列背景抑制的评分高于2D-FSE序列(P<0.05)。在图像的总体质量评分中,GRASE序列略高于3D-FSE序列,差异无统计学意义(4.29±0.83 vs 4.16±0.79,P>0.05),两者均高于2D序列,差异均有统计学意义(P<0.05)。GRASE序列的CNR、CR与3D-FSE序列相近,差异无统计学意义(P>0.05),均高于2D-FSE序列,差异均有统计学意义(P均<0.05)。GRASE序列在胆总管、肝总管、右肝管后支、左肝管内、外支的显示的显示能力与3D-FSE序列无差别。GRASE序列在右肝管前支的显示能力不如3D-FSE序列(P<0.05)。结论GRASE获得胆胰管的图像质量与3D-FSE序列接近,高于2D-FSE序列,为老年人疾病诊断提供影像学依据。展开更多
基金financially supported by the Swedish Research Council(2022-04422_VR)。
文摘The Gaussian phase distribution approximation enables analysis of restricted diffusion encoded by general gradient waveforms but fails to account for the diffraction-like features that may occur for simple pore geometries.We investigate the range of validity of the approximation by random walk simulations of restricted diffusion in a cylinder using isotropic diffusion encoding sequences as well as conventional single gradient pulse pairs and oscillating gradient waveforms.The results show that clear deviations from the approximation may be observed at relative signal attenuations below 0.1 for onedimensional sequences with few oscillation periods.Increasing the encoding dimensionality and/or number of oscillations while extending the total duration of the waveform diminishes the non-Gaussian effects while preserving the low apparent diffusivities characteristic of restriction.
文摘目的探讨三维梯度自旋回波(GRASE)序列在老年患者磁共振胆胰管成像(MRCP)中的应用价值。方法纳入MRCP检查的老年患者63例。同时采集屏气2D-FSE、屏气3D-GRASE和呼吸触发3D-FSE序列。计算图像的信噪比、对比噪声比和对比度,并对图像质量进行主观评价,包括伪影、背景抑制、总体图像质量和胆胰管各分支的显示情况。组间比较采用单因素ANOVA检验或非参数Kruskal-Wallis检验。结果GRASE序列的伪影评分高于2D-FSE序列,差异具有统计学意义(4.24±0.69 vs 3.76±1.03,P<0.05),但与3D-FSE序列之间差异无统计学意义(P>0.05)。GRASE序列背景抑制的评分高于2D-FSE序列(P<0.05)。在图像的总体质量评分中,GRASE序列略高于3D-FSE序列,差异无统计学意义(4.29±0.83 vs 4.16±0.79,P>0.05),两者均高于2D序列,差异均有统计学意义(P<0.05)。GRASE序列的CNR、CR与3D-FSE序列相近,差异无统计学意义(P>0.05),均高于2D-FSE序列,差异均有统计学意义(P均<0.05)。GRASE序列在胆总管、肝总管、右肝管后支、左肝管内、外支的显示的显示能力与3D-FSE序列无差别。GRASE序列在右肝管前支的显示能力不如3D-FSE序列(P<0.05)。结论GRASE获得胆胰管的图像质量与3D-FSE序列接近,高于2D-FSE序列,为老年人疾病诊断提供影像学依据。
