Konstandin Simon, Krämer Philipp, Günther Matthias, Schad Lothar R
Computer Assisted Clinical Medicine, Medical Faculty Mannheim, Heidelberg University, Theodor-Kutzer-Ufer 1-3, 68167 Mannheim, Germany; MR-Imaging and Spectroscopy, Faculty 01 (Physics/Electrical Engineering), University of Bremen, NW 1 Otto-Hahn-Allee 1, 28359 Bremen, Germany.
Computer Assisted Clinical Medicine, Medical Faculty Mannheim, Heidelberg University, Theodor-Kutzer-Ufer 1-3, 68167 Mannheim, Germany.
Magn Reson Imaging. 2015 Apr;33(3):319-27. doi: 10.1016/j.mri.2014.12.007. Epub 2014 Dec 16.
A method for uniform k-space sampling of 3D ultra-short echo time (UTE) techniques with anisotropic resolution in one direction is introduced to increase signal-to-noise ratio (SNR). State-of-the-art acquisition schemes for sodium MRI with radial (projection reconstruction) and twisting (twisted projection imaging (TPI)) trajectories are investigated regarding SNR efficiency, blurring behavior under T2(⁎) decay, and measurement time in case of anisotropic field-of-view and resolution. 3D radial and twisting trajectories are redistributed in k-space for UTE sodium MRI with homogeneous noise distribution and optimal SNR efficiency, if T2(⁎) decay can be neglected. Simulations based on Voronoi tessellations and phantom simulations/measurements were performed to calculate SNR efficiency. Point-spread functions were simulated to demonstrate the influence of T2(⁎) decay on SNR and resolution. Phantom simulations/measurements and in vivo measurements confirm the SNR gain obtained by simulations based on Voronoi cells. An increase in SNR of up to 21% at an anisotropy factor of 10 could be theoretically achieved by TPI with projection adaption compared to the same sequence but without redistribution of projections in k-space. Sodium MRI with anisotropic resolution and uniform k-space sampling is demonstrated by in vivo measurements of human intervertebral disks and heart at 3 T. The SNR gain can be invested in a measurement time reduction of up to 32%, which is important especially for sodium MRI.
介绍了一种用于三维超短回波时间（UTE）技术的均匀k空间采样方法，该方法在一个方向上具有各向异性分辨率，以提高信噪比（SNR）。针对钠MRI的现有采集方案，研究了其采用径向（投影重建）和扭曲（扭曲投影成像（TPI））轨迹时的SNR效率、T2（⁎）衰减下的模糊行为以及在各向异性视野和分辨率情况下的测量时间。对于UTE钠MRI，如果可以忽略T2（⁎）衰减，可在k空间中重新分布三维径向和扭曲轨迹，以实现均匀的噪声分布和最佳的SNR效率。基于Voronoi镶嵌的模拟以及体模模拟/测量用于计算SNR效率。模拟点扩散函数以证明T2（⁎）衰减对SNR和分辨率的影响。体模模拟/测量和体内测量证实了基于Voronoi单元的模拟所获得的SNR增益。与相同序列但在k空间中不重新分布投影相比，通过具有投影自适应的TPI理论上在各向异性因子为10时可实现高达21%的SNR增加。在3T下对人体椎间盘和心脏进行体内测量，展示了具有各向异性分辨率和均匀k空间采样的钠MRI。SNR增益可用于将测量时间减少多达32%，这对于钠MRI尤其重要。
