Overall William R, Nishimura Dwight G, Hu Bob S
Magnetic Resonance Systems Research Laboratory, Department of Electrical Engineering, Stanford University, Stanford, California 94305-9510, USA.
Magn Reson Med. 2002 Nov;48(5):890-8. doi: 10.1002/mrm.10285.
A new method of encoding flow velocity as image phase in a refocused steady-state free precession (SSFP) sequence, called steady-state phase contrast (SSPC), can be used to generate velocity images rapidly while retaining high signal. Magnitude images with refocused-SSFP contrast are simultaneously acquired. This technique is compared with the standard method of RF-spoiled phase contrast (PC), and is found to have more than double the phase-signal to phase-noise ratio (PNR) when compared with standard PC at reasonable repetition intervals (TRs). As TR decreases, this advantage increases exponentially, facilitating rapid scans with high PNR efficiency. Rapid switching between the two necessary steady states can be accomplished by the insertion of a single TR interval with no flow-encoding gradient. The technique is implemented in a 2DFT sequence and validated in a phantom study. Preliminary results indicate that further TR reduction may be necessary for high-quality cardiac images; however, images in more stationary structures, such as the descending aorta and carotid bifurcation, exhibit good signal-to-noise ratio (SNR) and PNR. Comparisons with standard-PC images verify the PNR advantage predicted by theory.
一种在重聚焦稳态自由进动（SSFP）序列中将流速编码为图像相位的新方法，称为稳态相位对比（SSPC），可用于快速生成流速图像，同时保持高信号强度。同时采集具有重聚焦SSFP对比度的幅度图像。将该技术与射频扰相相位对比（PC）的标准方法进行比较，发现在合理的重复间隔（TR）下，与标准PC相比，其相位信号与相位噪声比（PNR）增加了一倍多。随着TR的减小，这一优势呈指数增长，有利于以高PNR效率进行快速扫描。通过插入一个没有流动编码梯度的单个TR间隔，可以在两个必要的稳态之间快速切换。该技术在二维傅里叶变换（2DFT）序列中实现，并在体模研究中得到验证。初步结果表明，对于高质量的心脏图像，可能需要进一步降低TR；然而，在更稳定的结构中，如下降主动脉和颈动脉分叉处的图像，显示出良好的信噪比（SNR）和PNR。与标准PC图像的比较证实了理论预测的PNR优势。
