Newbould Rexford D, Skare Stefan T, Jochimsen Thies H, Alley Marcus T, Moseley Michael E, Albers Gregory W, Bammer Roland
Lucas MRS/I Center, Department of Radiology, Stanford University, Stanford, California, USA.
Max Planck Institute for Human Cognitive and Brain Sciences, Leipzig, Germany.
Magn Reson Med. 2007 Jul;58(1):70-81. doi: 10.1002/mrm.21255.
Echo-planar imaging (EPI) is the standard technique for dynamic susceptibility-contrast (DSC) perfusion MRI. However, EPI suffers from well-known geometric distortions, which can be reduced by increasing the k-space phase velocity. Moreover, the long echo times (TEs) used in DSC lead to signal saturation of the arterial input signal, and hence to severe quantitation errors in the hemodynamic information. Here, through the use of interleaved shot acquisition and parallel imaging (PI), rapid volumetric EPI is performed using pseudo-single-shot (ss)EPI with the effective T()(2) blur and susceptibility distortions of a multishot EPI sequence. The reduced readout lengths permit multiple echoes to be acquired with temporal resolution and spatial coverage similar to those obtained with a single-echo method. Multiecho readouts allow for unbiased R()(2) mapping to avoid incorrect estimation of tracer concentration due to signal saturation or T(1) shortening effects. Multiecho perfusion measurement also mitigates the signal-to-noise ratio (SNR) reduction that results from utilizing PI. Results from both volunteers and clinical stroke patients are presented. This acquisition scheme can aid most rapid time-series acquisitions. The use of this method for DSC addresses the problem of signal saturation and T(1) contamination while it improves image quality, and is a logical step toward better quantitative MR PWI.
回波平面成像（EPI）是动态磁敏感对比（DSC）灌注磁共振成像的标准技术。然而，EPI存在众所周知的几何畸变问题，可通过提高k空间相位速度来减少。此外，DSC中使用的长回波时间（TE）会导致动脉输入信号的信号饱和，从而导致血流动力学信息出现严重的定量误差。在此，通过使用交错脉冲采集和平行成像（PI），采用伪单激发（ss）EPI进行快速容积EPI，其具有多激发EPI序列的有效T2模糊和磁敏感畸变。缩短的读出长度允许以与单回波方法相似的时间分辨率和空间覆盖范围采集多个回波。多回波读出允许进行无偏R2映射，以避免由于信号饱和或T1缩短效应导致的示踪剂浓度估计错误。多回波灌注测量还减轻了因使用PI而导致的信噪比（SNR）降低。展示了志愿者和临床中风患者的结果。这种采集方案有助于实现最快的时间序列采集。将该方法用于DSC解决了信号饱和和T1污染问题，同时提高了图像质量，是朝着更好的定量磁共振灌注加权成像迈出的合理一步。
