University of Leeds and Department of Medical Physics and Engineering, Leeds Teaching Hospitals NHS Trust, 1st Floor, Bexley Wing, St James's University Hospital, Leeds, LS9 7TF, UK.
J Cardiovasc Magn Reson. 2012 Sep 20;14(1):66. doi: 10.1186/1532-429X-14-66.
This is the second of two reviews that is intended to cover the essential aspects of cardiovascular magnetic resonance (CMR) physics in a way that is understandable and relevant to clinicians using CMR in their daily practice. Starting with the basic pulse sequences and contrast mechanisms described in part I, it briefly discusses further approaches to accelerate image acquisition. It then continues by showing in detail how the contrast behaviour of black blood fast spin echo and bright blood cine gradient echo techniques can be modified by adding rf preparation pulses to derive a number of more specialised pulse sequences. The simplest examples described include T2-weighted oedema imaging, fat suppression and myocardial tagging cine pulse sequences. Two further important derivatives of the gradient echo pulse sequence, obtained by adding preparation pulses, are used in combination with the administration of a gadolinium-based contrast agent for myocardial perfusion imaging and the assessment of myocardial tissue viability using a late gadolinium enhancement (LGE) technique. These two imaging techniques are discussed in more detail, outlining the basic principles of each pulse sequence, the practical steps required to achieve the best results in a clinical setting and, in the case of perfusion, explaining some of the factors that influence current approaches to perfusion image analysis. The key principles of contrast-enhanced magnetic resonance angiography (CE-MRA) are also explained in detail, especially focusing on timing of the acquisition following contrast agent bolus administration, and current approaches to achieving time resolved MRA. Alternative MRA techniques that do not require the use of an endogenous contrast agent are summarised, and the specialised pulse sequence used to image the coronary arteries, using respiratory navigator gating, is described in detail. The article concludes by explaining the principle behind phase contrast imaging techniques which create images that represent the phase of the MR signal rather than the magnitude. It is shown how this principle can be used to generate velocity maps by designing gradient waveforms that give rise to a relative phase change that is proportional to velocity. Choice of velocity encoding range and key pitfalls in the use of this technique are discussed.
这是两篇综述中的第二篇，旨在以一种易于理解且与临床医生在日常实践中使用 CMR 相关的方式，涵盖心血管磁共振（CMR）物理学的基本方面。从第一部分中描述的基本脉冲序列和对比机制开始，它简要讨论了进一步加速图像采集的方法。然后，它继续详细展示如何通过向快速自旋回波和亮血电影梯度回波技术添加射频准备脉冲来修改黑血对比行为，以衍生出许多更专业的脉冲序列。描述的最简单示例包括 T2 加权水肿成像、脂肪抑制和心肌标记电影脉冲序列。梯度回波脉冲序列的另外两个重要衍生，通过添加准备脉冲获得，与钆基造影剂的给药结合使用，用于心肌灌注成像和使用晚期钆增强（LGE）技术评估心肌组织活力。更详细地讨论了这两种成像技术，概述了每个脉冲序列的基本原理、在临床环境中获得最佳结果所需的实际步骤，以及在灌注的情况下，解释了影响灌注图像分析当前方法的一些因素。还详细解释了对比增强磁共振血管造影（CE-MRA）的关键原理，特别是重点介绍了在对比剂团注给药后采集的时间，以及实现时间分辨 MRA 的当前方法。概述了不需要使用内源性对比剂的替代 MRA 技术，并详细描述了使用呼吸导航门控来成像冠状动脉的特殊脉冲序列。文章最后解释了相位对比成像技术背后的原理，该技术生成的图像代表 MR 信号的相位而不是幅度。展示了如何通过设计产生与速度成正比的相对相位变化的梯度波形来使用该原理生成速度图。讨论了速度编码范围的选择和使用该技术的关键陷阱。
