Lenz G W, Haacke E M, Masaryk T J, Laub G
Department of Radiology, University Hospitals of Cleveland, Ohio.
Radiology. 1988 Mar;166(3):875-82. doi: 10.1148/radiology.166.3.3340788.
Magnetic resonance (MR) angiography is a noninvasive method of obtaining images without contrast agents. Recent developments in sequence design have allowed images of moving spins to be obtained without a loss of signal by rephasing the spins with three or four gradient pulses to compensate for constant velocity or acceleration, respectively. At longer echo times (TE), this approach allowed for low readout gradients and high signal-to-noise ratios. Angiograms with a resolution of 300 micron were obtained. With additional sequences that allow some dephasing but minimal signal loss, separate images of arteries and veins were obtained. Phase information was used to estimate flow velocity. Application of the rephasing scheme to gradient-echo sequences allowed for ungated, fast MR angiograms. Acceleration correction was important for long TE sequences, but velocity-corrected, gradient-echo sequences with a very short TE were comparable to velocity- and acceleration-corrected, gradient-echo sequences with slightly longer TEs. With ungated three-dimensional, gradient-echo sequences, susceptibility artifacts were minimized and excellent contrast-to-noise ratios were obtained.
磁共振（MR）血管造影是一种无需使用造影剂即可获取图像的非侵入性方法。序列设计的最新进展使得通过分别用三个或四个梯度脉冲对自旋进行重新相位编码以补偿恒定速度或加速度，从而在不失信号的情况下获得移动自旋的图像。在较长的回波时间（TE）下，这种方法允许采用低读出梯度和高信噪比。获得了分辨率为300微米的血管造影片。通过允许一些去相位但信号损失最小的附加序列，获得了动脉和静脉的单独图像。相位信息用于估计流速。将重新相位编码方案应用于梯度回波序列可实现非门控快速MR血管造影。加速度校正对于长TE序列很重要，但具有非常短TE的速度校正梯度回波序列与具有稍长TE的速度和加速度校正梯度回波序列相当。使用非门控三维梯度回波序列时，磁敏感伪影最小化，并获得了出色的对比度噪声比。
