Beauchamp N J, Ulug A M, Passe T J, van Zijl P C
Russell H. Morgan Department of Radiology and Radiological Science, The Johns Hopkins Hospital, Baltimore, MD 21287, USA.
Radiographics. 1998 Sep-Oct;18(5):1269-83; discussion 1283-5. doi: 10.1148/radiographics.18.5.9747619.
Magnetic resonance (MR) diffusion imaging allows detection of cerebral ischemia within minutes of onset, and the temporal evolution of diffusion characteristics enables differentiation of acute from chronic stroke. T2-weighted MR imaging demonstrates infarcted tissue but fails to demonstrate acutely ischemic regions. Furthermore, the similar signal intensity characteristics of acute and chronic stroke on T2-weighted images limit the ability to determine the acuteness of an infarct. Diffusion imaging thus has tremendous potential for helping direct the treatment of acute ischemic stroke. Controversy exists over the pathophysiology of underlying changes in diffusion and the reversibility of changes after reperfusion in humans. There is also a lack of reproducibility in the time course of diffusion changes between research centers. Use of optimal diffusion imaging strategies results in increased conspicuity of ischemic regions and increased reproducibility of diffusion constants between research centers. An understanding of the principles of diffusion imaging and current controversies in the field is necessary for optimal application of this technique in the evaluation and treatment of cerebral ischemia.
磁共振（MR）扩散成像能够在发病数分钟内检测出脑缺血，并且扩散特征的时间演变有助于区分急性和慢性卒中。T2加权磁共振成像可显示梗死组织，但无法显示急性缺血区域。此外，急性和慢性卒中在T2加权图像上相似的信号强度特征限制了确定梗死急性程度的能力。因此，扩散成像在指导急性缺血性卒中治疗方面具有巨大潜力。关于人类扩散潜在变化的病理生理学以及再灌注后变化的可逆性存在争议。研究中心之间扩散变化的时间进程也缺乏可重复性。使用最佳扩散成像策略可提高缺血区域的清晰度，并增加研究中心之间扩散常数的可重复性。为了在脑缺血的评估和治疗中最佳应用该技术，了解扩散成像原理和该领域当前的争议是必要的。
