冠状动脉粥样硬化斑块磁共振成像研究进展

当前直接显示冠状动脉管壁和粥样斑块为磁共振成像(MRI)研究的热点之一,这是因为不引起冠状动脉管腔50%以上狭窄程度的粥样硬化斑块常为具有破裂倾向的易损斑块,斑块破裂随后血栓形成是导致心肌梗死的主要原因。无创性、高分辨率MRI具有显示冠状动脉粥样硬化斑块、判定斑块成分的潜力。本综述总结冠脉斑块MR成像原理,描述现有MRI技术下斑块的信号特点,并讨论MR在斑块成像的新对比剂、靶向分子成像等方面的研究进展。     

Characterization and molecular detection of atherothrombosis by magnetic resonance--potential tools for individual risk assessment and diagnostics

This review focuses on recent non-invasive or minimally invasive magnetic resonance (MR) approaches to study atherothrombosis. The potential benefits of combining diverse metabolic information obtained by the variety of MR techniques from tissues in vivo and ex vivo and from body fluids in vitro are also briefly discussed. A well established methodology is available for lipoprotein subclass quantification from plasma by 1H MR spectroscopy providing information for assessing the long-term risk of atherosclerosis. Multi-contrast MR imaging in vivo relying on endogenous contrast allows partial characterization of components in atherothrombotic plaques. The use of exogenous contrast agents in MR angiography enhances blood-tissue contrast and provides functional information on plaque metabolism, improving plaque characterization and assessment of plaque vulnerability by MR imaging. Recent applications of molecular targeted MR imaging have revealed novel opportunities for specific early detection of atherothrombotic processes, such as angiogenesis and accumulation of macrophages. Currently, MR imaging and spectroscopy can produce such metabolic in vivo and in vitro information that in combination could facilitate the screening, identification and follow-up of cardiovascularly vulnerable patients in research settings. The recent developments imply that in the near future MR techniques will be part of clinical protocols for individual diagnostics in atherothrombosis.     

易损斑块磁共振成像：共识与挑战

研究显示,黑血管壁成像技术能够较为准确地识别和定量分析动脉粥样硬化易损斑块的特征,尤其在颈动脉血管床。采用磁共振技术早期识别易损斑块的重要特征将有助于预防心血管事件的发生。因此,有必要对该技术进行临床推广应用。然而,目前广泛推广磁共振斑块成像技术亦存在一定的挑战性,如应用该技术在冠状动脉等其他血管床仍具有一定的局限性,以及如何权衡效益/费用比等等。本文重点描述应用磁共振斑块成像技术的共识性观点和所面临的挑战。     

重视MRI对易损斑块的研究

研究已表明,易损斑块是导致急性冠脉综合征（ACS）和脑卒中的主要原因。利用简便、准确、无创的诊断技术对易损斑块进行早期检测以及对其致病机制进行研究,是当前心脑血管疾病研究的热点和难点。近年来,随着磁共振软、硬件技术的发展,MRI可以直接观察血管管壁情况,对斑块的大小、体积及斑块成分提供较为准确的信息,广泛应用于动脉粥样硬化斑块的检测和预后评估。本组专题围绕易损斑块的定义和诊断标准、影像学检查方法、MRI检测易损斑块的优势与不足、以及MRI评价易损斑块的临床新进展等内容进行全面系统地阐述,同时,并对MRI检测易损斑块的发展方向及其面临的挑战进行展望。     

Extracranial carotid MR imaging at 3T

Some controversy exists over the accuracy and optimal parameters for carotid CE MR angiography at 1.5T. Spatial resolution remains more important than does temporal resolution to address the key question of vessel stenosis, based upon a review of the available literature that compares CE MR angiography with DSA. Specifically, CE MR angiograms with 0.9- to 1.2-mm resolution in all three planes before interpolation have a high reported sensitivity and specificity compared with DSA. To achieve this type of spatial resolution, cover the entire course of the carotid arteries from the aortic arch through the skull base, and achieve an absence of venous signal usually requires an elliptic-centric phase encoding CE MR angiogram that lasts for 50 to 60 seconds without the use of parallel imaging techniques. This near-millimeter resolution requires an accurate timing of the gadolinium bolus arrival to maximize intra-arterial SNR and to minimize venous contamination. Parallel imaging techniques can decrease the imaging time, but at a cost of some SNR. Initial experience with eight-channel or higher neurovascular coils at 3T indicates an increase in SNR/CNR compared with 1.5T. This should allow more consistent submillimeter-resolution carotid CE MR angiography with adequate SNR to maintain good IQ in a wide variety of clinical patients. Although a definite, prospective comparison of various CE MR angiography techniques,including a 20- to 30-second scan with 1.2- to 1.4-mm(3) voxel resolution and 50- to 60-second scan with 0.9- to 1.1-mm(3) voxel resolution at 1.5T, as well as 0.5- to 0.6-mm(3) voxel resolution with scan time of 50 to 60 seconds at 3T versus rotational DSA does not exist, the expectation is that the higher resolution and increased SNR that has resulted from 3T carotid CE MR angiography will have high sensitivity and specificity in detecting severe carotid stenosis. The most exciting application of 3T for carotid artery imaging may not be the higher resolution CE MR angiogram, however. Early work has demonstrated the potential of 3T, combined with sensitive surface coils, to depict carotid plaque with sufficient SNR to identify important plaque components consistently in most patients. This could help move MR imaging of the carotid arteries away from a strict evaluation of luminal narrowing to a focused evaluation of plaque morphology. Much work needs to be done. Although there is a growing body of literature to support the contention that plaque morphology is a predictor of subsequent thrombo-embolic disease, the natural history of these various plaque components in a large number of patients needs to be elucidated. If plaque characterization proves to be an independent risk factor that predicts stroke, more aggressive clinical treatment option strategies may be devised for patients who are at the highest risk. Currently, plaque characterization at 3T requires a different set of coils compared with the global assessment of the entire course of the carotid arteries. Future generations of 16- to 32-channel carotid coils should be able to combine the best features of current 4- to 8-channel surface carotid coils and neurovascular coils. These will enable a comprehensive evaluation of the entire course of the carotid artery and detailed carotid bifurcation plaque characterization at 3T within a clinically acceptable 1-hour time frame. This comprehensive carotid artery evaluation with 3T MR imaging would be far superior to that which is possible with US or CT.     

MR与CT对实验性动脉粥样硬化斑块检出的比较研究

目的研究MR及CT检测动脉粥样硬化斑块的能力并进行比较。方法以成年新西兰大白兔为实验动物,破坏腹主动脉内膜加高脂饮食造型成功后12周分别进行MR及CT检查。MR检查包括T1WI、T2WI、PDWI、TOF序列。结果经病理证实动物模型制作成功。MR图像T1WI、T2WI、PDWI表现为管壁增厚,斑块可呈等信号、高信号或低信号,与病理切片对照发现MR可以检测斑块及其成分;与CT比较,MR具有较高的准确性。结论MR可以较为准确地对斑块进行定位及定性。     

Three-dimensional volumetric analysis of atherosclerotic plaques: a magnetic resonance imaging-based study of patients with moderate stenosis carotid artery disease

Atherosclerotic plaque burden has a strong correlation with plaque vulnerability. Three-dimensional (3D) volumetric assessment of atherosclerotic plaques has been suggested as an accurate method of quantifying plaque burden but has not been performed. In this study we use high-resolution magnetic resonance (MR) imaging to compare 3D volume differences of asymptomatic and acutely symptomatic carotid plaques (i.e. had cerebrovascular ischaemic symptoms within the previous 72 h of MR imaging). One hundred patients (46 acutely symptomatic and 54 asymptomatic) with atherosclerotic carotid artery disease underwent carotid MR imaging. Manual segmentation of plaque components was done to delineate lipid, fibrous tissue and plaque haemorrhage (PH). 3D-volume reconstruction of plaque components was done and used for comparison. Acutely symptomatic plaques had a lower normalized wall index and normalized volume index than the asymptomatic group (P = 0.04 and 0.01 respectively). Median percentage lipid volume was higher for asymptomatic plaques (28 vs. 5%, P = 0.004). However, the median percentage volume and prevalence of PH was higher in the acutely symptomatic group (P = 0.01 and 0.02 respectively). Acutely symptomatic plaques have less lipid content immediately after the acute event than asymptomatic plaques. This is most likely because of the escape of lipid-rich atheromatous debris into the blood stream at the time of plaque rupture. Due to this paradox, “high” lipid content of a plaque may not be a reliable feature of estimating its vulnerability immediately following the acute event. PH, which is prevalent and consistent in such plaques, may be a better indicator of plaque vulnerability during that period.     

Recent developments and new perspectives on imaging of atherosclerotic plaque: role of anatomical,cellular and molecular MRI Part I and II

Atherosclerotic plaque disruption accounts for the major part of cardiovascular mortality and the risk of disruption appears to depend on plaque composition. Carotid plaques in patients, scheduled for endarterectomy, have been successfully characterised with MRI. MRI has the advantage of combining information about morphology and function. Unfortunately, the tortuosity and size of the coronary arteries, and the respiratory and cardiac motion hinder the in vivo characterisation of human coronary plaque. In addition to plaque composition several molecular markers of the different processes involved in atherosclerosis, such as integrins, matrix metalloproteinases and fibrin seem to correlate with risk of plaque rupture and clinical outcome. These molecular markers can be targeted with antibodies coupled to carriers, which are loaded with gadolinium for detection (molecular MRI). Several cellular/molecular MRI studies in animal models and some in human patients have been conducted with varying levels of success. The advent of clinical high field magnets, the development of contrast agent carriers with high relaxivity and the development of relatively new MR contrast techniques are promising in the field of plaque imaging. Future MRI studies will have to focus on the molecular target of the atherosclerotic process, which has the highest prognostic value with regard to acute coronary syndromes and on the most suitable contrast agent to visualize that target.     

Recent developments and new perspectives on imaging of atherosclerotic plaque: role of anatomical,cellular and molecular MRI part III

Atherosclerotic plaque disruption accounts for the major part of cardiovascular mortality and the risk of disruption appears to depend on plaque composition. Carotid plaques in patients, scheduled for endarterectomy, have been successfully characterised with MRI. MRI has the advantage of combining information about morphology and function. Unfortunately, the tortuosity and size of the coronary arteries, and the respiratory and cardiac motion hinder the in vivo characterisation of human coronary plaque. In addition to plaque composition several molecular markers of the different processes involved in atherosclerosis, such as integrins, matrix metalloproteinases and fibrin seem to correlate with risk of plaque rupture and clinical outcome. These molecular markers can be targeted with antibodies coupled to carriers, which are loaded with gadolinium for detection (molecular MRI). Several cellular/molecular MRI studies in animal models and some in human patients have been conducted with varying levels of success. The advent of clinical high field magnets, the development of contrast agent carriers with high relaxivity and the development of relatively new MR contrast techniques appear to be promising in the field of plaque imaging. Future MRI studies will have to focus on the molecular target of the atherosclerotic process, which has the highest prognostic value with regard to acute coronary syndromes and on the most suitable contrast agent to visualize that target.     

Molecular MRI of Atherosclerosis Burden

Atherosclerosis is a systemic vascular disease predominantly affecting the intima of central and peripheral arteries. Its complications, myocardial infarction and stroke, remain the leading cause of morbidity and mortality in the Western world and developing countries. Angiographic imaging methods are the current gold standard for the clinical graduation of coronary and carotid artery disease and the guidance of treatment. These techniques are however limited to the assessment of the extent of luminal narrowing. MRI is a noninvasive modality, which allows the direct evaluation of the thin arterial vessel wall with excellent soft tissue contrast and high spatial resolution. Targeted MR contrast agents enable the evaluation of specific cellular and subcellular markers on a molecular level. This review will introduce and discuss novel molecular MR imaging techniques for the assessment of plaque and inflammatory burden in the context of atherosclerosis. Both measures can provide additional information beyond the assessment of luminal stenosis alone.     

High-Resolution magnetic resonance imaging of normal and atherosclerotic human coronary arteries ex vivo: discrimination of plaque tissue components.

BACKGROUND: Noninvasive detection of plaque lipid and calcium in human atherosclerosis may have clinical utility, because the presence of each may be associated with increased risk of plaque disruption. Magnetic resonance imaging (MRI) has the potential to detect both plaque lipid and calcium. However, no previous studies have: 1) used an MR coil with sufficient resolution to image the components of human coronary arteries, 2) evaluated the utility of a combination of different MR contrast weightings in discriminating plaque components in human coronary arteries, or 3) used sensitive and specific histological stains for lipid and calcium to determine their MR image characteristics in human atherosclerosis. METHODS: Using a custom-made surface coil on a whole-body, 1.5T MRI scanner, high resolution MR images were obtained from 22 nonatherosclerotic and atherosclerotic human coronary artery segments and then compared with histological sections stained for neutral lipid, calcium, and ribrous and cellular components. RESULTS: With a multicontrast protocol using T1-, proton density-, and T2-weighted images, statistically significant differences were found among MR image contrast values for regions identified by histological stains as containing lipid only, calcium only, mixed lipid and calcium, or fibrous tissue. All four of these histologically defined region types could be differentiated from one another by a multicontrast MRI protocol. Of the 22 segments, 10 (45%) contained areas with combined plaque lipid and calcium; calcium would not have been recognized histologically in these regions without the use of a specific calcium stain. CONCLUSIONS: These results demonstrate that multicontrast MRI can produce remarkably high-resolution images and can discriminate between clinically relevant components of the atherosclerotic vessel wall.     

心血管磁共振成像临床应用和新进展

近年来由于MRI的进展,现已成为医学成像技术的主要组成部分,心血管MRI已广泛、有效地应用于心脏、大血管、内脏和外周血管成像及诊治工作.本文简要叙述心血管MRI临床应用概况,如对胸主动脉疾患、缺血性心脏病、心肌病、心脏肿瘤、先心病、心包疾患和心脏瓣膜病的诊断评价等.重点讨论一些新进展,如MR心肌灌注成像和心肌存活的评价;MR冠脉造影和斑块成像;深静脉血栓和肺栓塞的MR诊断以及MR血管造影对腹主-髂股-下肢动脉狭窄性病变的诊断及效果分析.     

Comparison of 3D-diffusion-prepared segmented steady-state free precession and 2D fast spin echo imaging of femoral artery atherosclerosis

Magnetic resonance (MR) imaging is a promising modality for the in vivo detection and characterization of atherosclerotic lesions in peripheral arteries. 2D imaging techniques for evaluation of peripheral artery disease (PAD) suffer from poor spatial coverage and have long scan times. The purpose of this study was to compare a diffusion prepared dark blood 3D steady state free precession (3D-DP-SSFP) sequence for evaluating atherosclerotic plaque burden in inguinal and thigh segments of the femoral artery and comparing the results obtained with 2D turbo spin echo (2D-TSE) techniques. A further goal of the study was to examine the inter observer reproducibility of MR plaque burden measures using the 3D DP-SSFP technique. Results of the study indicated higher signal to noise ratios for the 3D-DP-SSFP technique and higher CNR (better vessel-wall delineation) compared to the 2D-TSE technique. Furthermore, a good correlation between 3D-DP-SSFP and 2D-TSE techniques for the inguinal segment but poorer correlation for the thigh segment was observed. Inter-observer reproducibility for the 3D plaque burden measures was excellent. 3D-DP-SSFP may be a useful and reproducible technique for evaluating atherosclerosis in peripheral arteries.     

Functional MR imaging of the uterus

Recent developments in MR imaging techniques have enabled the functional assessment of the uterus. Cine MR imaging is a useful tool for evaluating uterine kinematic functions derived from myometrial contractility, and for investigating the alteration of uterine contractility in a variety of conditions and gynecologic disorders. Diffusion-weighted imaging can demonstrate abnormal signal in pathologic foci based on differences in molecular diffusion, and could provide useful information in evaluating malignant conditions. Dynamic contrast-enhanced MR imaging has the potential to improve tumor detection and local staging, and quantitative information may be useful for both monitoring therapeutic effects and predicting outcome. These state-of-the-art functional MR imaging techniques are beneficial for elucidating various uterine conditions when used appropriately, and the findings further provide the basis of future MR imaging investigations.     

Molecular PET and CT Imaging of Inflammation and Metabolism in Atherosclerosis

The molecular and biological processes that take place in atherosclerotic plaque play an important role in determining the pathologic progression of the plaque. Current imaging techniques primarily inform about plaque structure and thus fail to assess the functional aspects of atherosclerosis. Accordingly, imaging of plaque biology might provide important incremental information about the underlying disease process. An emerging body of work shows that molecular imaging with fluorodeoxyglucose—positron emission tomography (PET) can provide information about plaque biology. This review provides an overview of the development of vascular PET imaging, with an evaluation of current and potential future uses of this imaging modality.     

Current Development of Molecular Coronary Plaque Imaging using Magnetic Resonance Imaging towards Clinical Application

Cardiovascular disease (CVD) remains the leading cause of death in Western countries despite improvements in prevention, diagnosis and treatment. Atherosclerosis is a chronic inflammatory disease that remains clinically silent for many decades. Sudden rupture of “high-risk/vulnerable” plaques has been shown to be responsible for the majority of acute cardiovascular events, including myocardial infarction and stroke. Therefore, early detection of biological processes associated with atherosclerosis progression and plaque instability may improve diagnosis and treatment and help to better monitor the effectiveness of therapeutic interventions. Molecular magnetic resonance imaging (MRI) is a promising tool to detect molecular and cellular changes in the carotid, aortic and coronary vessel wall including endothelial dysfunction, inflammation, vascular remodelling, enzymatic activity, intraplaque haemorrhage and fibrin deposition and thus may allow early detection of unstable lesions and improve the prediction of future coronary events. Evaluation of atherosclerosis at both, the preclinical and clinical level includes non-contrast-enhanced (NCE) and contrast-enhanced (CE) MRI with and without the use of MR contrast agents. To increase the biological information obtained by MRI a variety of targeted-specific molecular probes have been developed for the non-invasive visualization of particular biological processes at the molecular and cellular level. This review will discuss the recent advances in molecular MRI of atherosclerosis, covering both pulse sequence development and also the design of novel contrast agents, for imaging atherosclerotic disease in vivo.     

颈动脉粥样硬化斑块MR成像的研究

目的 探讨多对比加权的MRI序列对颈动脉粥样硬化斑块检出并定性分析的价值。方法 采用采用1．5T磁共振仪、多对比加权序列3D—TOF、FSEPDWI、FSE—DIRT．WI、FSE—DIRPDWI、FSE—DIRT2WI对24例动脉粥样硬化的患者的35个颈动脉斑块进行MRI成像．分析斑块信号特征。结果 35个粥粥样斑块中18个斑块在所有序列上信号单一均匀；17个斑块在一个或多个序列上信号混杂，其中9个斑块含有脂质核心信号；9个斑块含钙化信号；1个表现为血管腔内血栓形成管腔闭塞。10个斑块可见厚纤维帽信号；23个表现为薄纤维帽信号特征；2个斑块表面不光滑。结论 采用多对比加权的MRI序列可以检出颈动脉粥样硬化斑块．并在一定程度上可对其进行成分分析。     

易损斑块的影像学检查方法

目前动脉粥样硬化斑块的影像学检查方法主要包括无创性（如多普勒超声、CT和MRI）和有创性（如DSA、血管内超声、血管内MRI）检查,每种检查方法各有优缺点,无创影像学评估易损斑块的比较研究有利于优化影像学检查技术。多种方法的联合应用,可以大大提高诊断准确率。     

Novel techniques for MR imaging of pulmonary airspaces

Hyperpolarized gas- and molecular oxygen-enhanced MR imaging are two new techniques for high-resolution MR imaging of pulmonary airspaces. Both techniques produce excellent images in a safe, reproducible, and technically feasible manner. Because morphologic and functional information is obtained, and radiation is not used, these techniques may prove ideal for serially evaluating patients with a variety of lung diseases that affect pulmonary ventilation, such as cystic fibrosis, emphysema, asthma, or bronchiolitis obliterans syndrome in lung transplant recipients. At present, the greatest clinical experience is with hyperpolarized He-3-enhanced MR imaging. This technique is limited, however, by the limited availability of He-3, by its polarization requirements, and by the need to tune the MR system to the resonant frequency of the gas. There is less clinical experience with oxygen-enhanced MR imaging. Although this technique produces images with more inherent noise than hyperpolarized He-3 imaging, this problem can be overcome by signal averaging. Oxygen-enhanced imaging has the major advantages of lower cost and ready availability. For oxygen-enhanced imaging, the MR imaging system does not need to be readjusted; imaging is performed at the conventional hydrogen proton frequency.