Sir Peter Mansfield Magnetic Resonance Centre, School of Physics and Astronomy, University of Nottingham, University Park, Nottingham, UK.
Neuroimage. 2010 Nov 1;53(2):515-25. doi: 10.1016/j.neuroimage.2010.06.070. Epub 2010 Jul 6.
Optimisation and comparison of the performance of three different methods for calculating three-dimensional susceptibility maps of the whole brain from gradient-echo (phase and modulus) image data acquired at 7 T is described. The methods studied are a multiple-orientation method in which image data acquired with the head at several different angles to the main field are combined and two methods which use data acquired at a single orientation: the first of these is based on exclusion of some k-space data from the calculation (through thresholding of the dipolar field kernel), while the second incorporates a regularisation method that is based on using information from the modulus images. The methods were initially optimised via analysis of data from a phantom containing different compartments of known susceptibility. As part of this work, a novel high-pass filtering methodology was introduced to remove background fields from field maps based on phase data. The optimised methods were successfully applied to high-resolution (0.7 mm isotropic) whole-brain modulus and phase data acquired in vivo from five healthy male subjects, 25-30 years of age. The multiple-orientation method yielded high quality susceptibility maps, out-performing the single-orientation methods. Venous blood vessels as well as the substantia nigra and globus pallidus brain regions showed particularly high positive susceptibility offsets relative to surrounding tissue, consistent with high deoxyhemoglobin and non-heme iron content, respectively. To compare the performance of the different methods, regions of interest were drawn in deep grey matter structures and in cortical grey and white matter. The threshold-based approach was fast and simple to use, but underestimated susceptibility differences and showed significant artefacts due to noise amplification in difficult regions of k-space. The regularised single-orientation method yielded contrast dependent on the choice of spatial priors, but demonstrated the potential to yield susceptibility maps of a similar quality to those calculated using data acquired at multiple orientations to the field.
描述了从在 7T 采集的梯度回波（相位和模）图像数据中计算整个大脑三维磁化率图的三种不同方法的性能优化和比较。研究的方法是一种多方向方法，其中将头部置于与主磁场几个不同角度的位置采集的图像数据组合在一起，以及两种仅在一个方向上使用数据的方法：第一种方法基于从计算中排除一些 k 空间数据（通过对偶极场核进行阈值处理），而第二种方法则结合了一种基于从模量图像中获取信息的正则化方法。这些方法最初通过分析包含已知磁化率的不同隔室的体模数据进行了优化。作为这项工作的一部分，引入了一种新的高通滤波方法，该方法基于相位数据从磁场图中去除背景场。优化后的方法成功应用于从 5 名年龄在 25-30 岁的健康男性体内采集的高分辨率（0.7mm 各向同性）全脑模量和相位数据。多方向方法产生了高质量的磁化率图，优于单方向方法。与周围组织相比，静脉血管以及黑质和苍白球脑区表现出特别高的正磁化率偏移，分别与高脱氧血红蛋白和非血红素铁含量一致。为了比较不同方法的性能，在深部灰质结构以及皮质灰质和白质中绘制了感兴趣区域。基于阈值的方法快速且易于使用，但低估了磁化率差异，并由于在 k 空间困难区域的噪声放大而显示出明显的伪影。正则化单方向方法产生了依赖于空间先验选择的对比度，但显示出了产生与使用多方向采集数据计算的磁化率图质量相似的潜力。
