Vidorreta Marta, Balteau Evelyne, Wang Ze, De Vita Enrico, Pastor María A, Thomas David L, Detre John A, Fernández-Seara María A
Neuroimaging Laboratory, CIMA, University of Navarra, Pamplona, Navarra, Spain.
NMR Biomed. 2014 Nov;27(11):1387-96. doi: 10.1002/nbm.3201. Epub 2014 Sep 26.
Recent technical developments have significantly increased the signal-to-noise ratio (SNR) of arterial spin labeled (ASL) perfusion MRI. Despite this, typical ASL acquisitions still employ large voxel sizes. The purpose of this work was to implement and evaluate two ASL sequences optimized for whole-brain high-resolution perfusion imaging, combining pseudo-continuous ASL (pCASL), background suppression (BS) and 3D segmented readouts, with different in-plane k-space trajectories. Identical labeling and BS pulses were implemented for both sequences. Two segmented 3D readout schemes with different in-plane trajectories were compared: Cartesian (3D GRASE) and spiral (3D RARE Stack-Of-Spirals). High-resolution perfusion images (2 × 2 × 4 mm(3) ) were acquired in 15 young healthy volunteers with the two ASL sequences at 3 T. The quality of the perfusion maps was evaluated in terms of SNR and gray-to-white matter contrast. Point-spread-function simulations were carried out to assess the impact of readout differences on the effective resolution. The combination of pCASL, in-plane segmented 3D readouts and BS provided high-SNR high-resolution ASL perfusion images of the whole brain. Although both sequences produced excellent image quality, the 3D RARE Stack-Of-Spirals readout yielded higher temporal and spatial SNR than 3D GRASE (spatial SNR = 8.5 ± 2.8 and 3.7 ± 1.4; temporal SNR = 27.4 ± 12.5 and 15.6 ± 7.6, respectively) and decreased through-plane blurring due to its inherent oversampling of the central k-space region, its reduced effective TE and shorter total readout time, at the expense of a slight increase in the effective in-plane voxel size.
近期的技术发展显著提高了动脉自旋标记(ASL)灌注磁共振成像的信噪比(SNR)。尽管如此,典型的ASL采集仍采用较大的体素尺寸。本研究的目的是实现并评估两种针对全脑高分辨率灌注成像优化的ASL序列,将伪连续ASL(pCASL)、背景抑制(BS)和3D分段读出相结合,并采用不同的面内k空间轨迹。两种序列均采用相同的标记和BS脉冲。比较了两种具有不同面内轨迹的分段3D读出方案:笛卡尔(3D GRASE)和螺旋(3D RARE Stack-Of-Spirals)。在3T条件下,使用这两种ASL序列对15名年轻健康志愿者进行了高分辨率灌注成像(2×2×4 mm³)。根据SNR和灰质与白质对比度评估灌注图的质量。进行了点扩散函数模拟,以评估读出差异对有效分辨率的影响。pCASL、面内分段3D读出和BS的组合提供了全脑高SNR高分辨率的ASL灌注图像。尽管两种序列都产生了优异的图像质量,但3D RARE Stack-Of-Spirals读出的时间和空间SNR均高于3D GRASE(空间SNR分别为8.5±2.8和3.7±1.4;时间SNR分别为27.4±12.5和15.6±7.6),并且由于其对中心k空间区域的固有过采样、有效TE的降低和总读出时间的缩短,减少了层面内模糊,代价是面内有效体素尺寸略有增加。