Time-Resolved Lower Extremity MR Angiography using HighlY Constrained Back PRojec

描述(由申请人提供)：我们建议使用我们最近构思的HYPR方法来开发一种易于实施的、时间分辨率的、多站、对比度增强的外围MR血管成像协议，该协议提供高空间分辨率的血管成像，其时间分辨率显著高于目前的MR技术。HYPR方法通过仅使用满足奈奎斯特准则所需的径向k空间线总数的非常小的子集来产生时间帧，从而允许极大地改进径向k空间采集中的时间分辨率。通过将未过滤的反向投影数据约束到已知存在对象(在这种情况下为血管)的区域，改进了通常由使用严重减少的投影数量来构建图像而产生的条纹伪影。为了确定血管的位置，使用来自多个时间帧的数据产生血管地图或合成图像。这是可能的，因为每个时间帧的数据是从以略微不同的角度获取的径向k空间线产生的。合成图像中的高信噪比决定了各个时间帧中的SNR，与仅基于欠采样的加速方法相比，提供了更好的图像质量。初步模拟表明，即使使用大于100%的欠采样因子，也可以获得良好的图像质量。为了实现我们的目标，我们建议开发三种MRA技术-3D混合HYPR、3D HYPR技巧和3D HYPR VIPR，并使用一系列模拟、体模和志愿者研究来评估和优化这些技术的性能。在此之后，最成功的HYPR外周血管方案将在一组患者中与传统的x射线DSA进行比较。我们的中心假设是，HYPR将能够获得非常高的时间分辨率、对比度增强的多站外周MR血管成像，其中空间分辨率、信噪比和图像质量保持在高水平。

DESCRIPTION (provided by applicant): We propose to use our recently-conceived HYPR method to develop an easy-to-implement, time-resolved, multi-station, contrast-enhanced peripheral MR angiography protocol that provides high spatial resolution angiograms with dramatically higher temporal resolution than is possible with current MR techniques. The HYPR method permits great improvements to temporal resolution in radial k-space acquisitions by producing time frames using only a very small subset of the total number of radial k-space lines necessary to satisfy the Nyquist criterion. Streak artifacts that would ordinarily result from constructing images using a severely reduced number of projections are ameliorated by constraining unfiltered back projected data to regions in which objects, in this case vessels, are known to exist. In order to determine the location of the vessels, a vessel map, or composite image, is produced using data from multiple time frames. This is possible because the data for each of the time frames is produced from radial k-space lines that are acquired at slightly different angles. The high SNR in the composite images dictates the SNR in the individual time frames, providing improved image quality relative to accelerated methods that are based solely on undersampling. Preliminary simulations suggest that good image quality may be achieved even when undersampling factors greater than 100 are used. In order to achieve our goal, we propose to develop three MRA techniques - 3D hybrid HYPR, 3D HYPR TRICKs, and 3D HYPR VIPR - and to evaluate and optimize the performance of these techniques using a series of simulation, phantom, and volunteer studies. Following this, the most successful HYPR peripheral vascular protocol will be compared with conventional x-ray DSA in a cohort of patients. Our central hypothesis is that HYPR will permit acquisition of very high temporal resolution contrast-enhanced multi-station peripheral MR angiograms, in which spatial resolution, SNR, and image quality are maintained at high levels.