Ichikawa T, Araki T
Department of Radiology, Yamanashi Medical University, Japan.
Eur J Radiol. 1999 Mar;29(3):186-210. doi: 10.1016/s0720-048x(98)00176-4.
Recent magnetic resonance (MR) units with a stronger gradient system have allowed various fast MR imaging techniques to develop. These fast scan techniques have easily realized breath-holding acquisition in the liver and the image quality has been greatly improved without sacrificing spatial resolution. The majority of the fast imaging techniques have been devoted to T2-weighted imaging to obtain useful T2-weighted images in the shortest possible time. Among the fast sequences, fast spin-echo (FSE) sequence is the most promising technique and allows high-quality T2-weighted images with reduced motion artifacts. However, FSE sequences using multiple refocused pulses may essentially realize only poor soft-tissue contrast due to magnetization transfer and T2-filtering effects, and therefore, echo-planar (EP) imaging is expected to provide high image contrast. In addition, single-shot EP imaging allows even diffusion-weighted (DW) and perfusion-weighted (PW) imaging in the liver due to its short scanning time. Recent development of fast gadolinium-enhanced 3D MR angiography has also impacted liver imaging. Combined with such gadolinium-enhanced 3D-MRA sequences and zerofilling image interpolation technique, biphasic gadolinium-enhanced 3D-MRA (whole-liver dynamic MR imaging in the arterial phase and MR portography in the portal phase) can be obtained.
近期，具有更强梯度系统的磁共振（MR）设备推动了各种快速MR成像技术的发展。这些快速扫描技术已轻松实现肝脏屏气采集，且在不牺牲空间分辨率的情况下，图像质量得到了极大提升。大多数快速成像技术致力于T2加权成像，以便在尽可能短的时间内获得有用的T2加权图像。在快速序列中，快速自旋回波（FSE）序列是最具前景的技术，可生成减少运动伪影的高质量T2加权图像。然而，由于磁化传递和T2滤波效应，使用多个重聚焦脉冲的FSE序列本质上可能只能实现较差的软组织对比度，因此，回波平面（EP）成像有望提供高图像对比度。此外，单次激发EP成像因其扫描时间短，甚至可用于肝脏弥散加权（DW）和灌注加权（PW）成像。快速钆增强三维MR血管造影术的最新进展也对肝脏成像产生了影响。结合此类钆增强三维MRA序列和零填充图像插值技术，可获得双期钆增强三维MRA（动脉期全肝动态MR成像和门静脉期MR门静脉造影）。
