Saranathan Manojkumar, Ramanan Venkat, Gulati Rakesh, Venkatesan Ramesh
Department of Electrical Engineering, Indian Institute of Science, Bangalore 560012, Karnataka, India.
Magn Reson Imaging. 2007 Sep;25(7):1039-47. doi: 10.1016/j.mri.2006.12.002. Epub 2007 Jan 18.
This study aimed to investigate the use of anatomically tailored hexagonal sampling for scan-time and error reduction in MRI.
Anatomically tailored hexagonal MRI (ANTHEM), a method that combines hexagonal sampling with specific symmetry in anatomical geometry, is proposed. By using hexagonal sampling, aliasing artifacts are moved to regions where, due to the nature of the anatomy, aliasing is inconsequential. This can be used to either reduce scan time while maintaining spatial resolution or reduce residual errors in speedup techniques like UNFOLD and k-t BLAST/SENSE, which undersample k-space and unwrap fold-over artifacts during reconstruction. Computer simulations as well as phantom and volunteer studies were used to validate the theory. A simplified reconstruction algorithm for hexagonally sampled and subsampled k-space data was also used.
A reduction in sampling density of 13.4% and 25% in each hexagonally sampled dimension was achieved for spherical and conical geometries without aliasing or reduction in spatial resolution. Optimal subsampling schemes that can be utilized by UNFOLD and k-t BLAST/SENSE were derived using hexagonal subsampling, which resulted in maximal, isotropic dispersal of the aliases. In combination with UNFOLD, ANTHEM was shown to move residual aliasing artifacts to the corners of the field of view, yielding reduced artifacts in CINE reconstructions.
ANTHEM was successful in reducing acquisition time in conventional MRI and in reducing errors in UNFOLD imaging.
本研究旨在探讨使用解剖学定制的六边形采样来减少MRI扫描时间和误差。
提出了一种解剖学定制的六边形MRI（ANTHEM）方法，该方法将六边形采样与解剖几何结构中的特定对称性相结合。通过使用六边形采样，混叠伪影被转移到由于解剖结构的性质而混叠无关紧要的区域。这可用于在保持空间分辨率的同时减少扫描时间，或减少加速技术（如UNFOLD和k-t BLAST/SENSE）中的残余误差，这些技术在重建过程中对k空间进行欠采样并展开折叠伪影。使用计算机模拟以及体模和志愿者研究来验证该理论。还使用了一种简化的算法来重建六边形采样和欠采样的k空间数据。
对于球形和锥形几何结构，在每个六边形采样维度上采样密度分别降低了13.4%和25%，且无混叠或空间分辨率降低。利用六边形欠采样推导出了UNFOLD和k-t BLAST/SENSE可使用的最佳欠采样方案，这导致混叠的最大各向同性分散。与UNFOLD相结合，ANTHEM被证明可将残余混叠伪影移动到视野的角落，从而在电影重建中减少伪影。
ANTHEM成功减少了传统MRI中的采集时间，并减少了UNFOLD成像中的误差。
