非对比增强MR血管成像技术发展及应用

近年来,随着MR设备的发展和新序列的开发,非对比增强MR血管成像(NCE-MRA)技术发展迅速,除传统的时间飞跃法和相位对比法外,许多新方法已可用于全身各部位血管成像。NCE-MRA包括血流依赖和非血流依赖两大类成像技术,这些技术联合应用于不同的成像序列。为了提高对NCE-MRA技术的认识,促进该类技术的开发应用,对多种NCE-MRA方法的成像机制、优缺点和临床应用作一综述。     

提高支架再狭窄探测的血池对比剂增强、高分辨率、稳态MR血管成像

目的本研究的目的是与首过MR血管成像(FP-MRA)对比,评估用高分辨率、稳态的、血池对比剂增强MR血管成像是否能改善支架内病变的显示。用动脉数字减影血管造影(DSA)作为参考标准。方法20例股浅动脉支架置入术后的病人在接受再次干预前进行了MRA检查。股浅动脉的     

3TMR重复动静脉标记技术的非增强肾血管成像与增强MR血管成像的对比研究:用于肾功能正常者

<正>摘要目的研究采用重复动静脉标记(RAVEL)技术行非对比增强MR血管成像(NC-MRA)评估肾动脉的可行性,并与对比增强MR血管成像(CE-MRA)进行比较。方法 在     

三维对比增强MR血管成像在头颈部的临床应用

目的:探讨三维对比增强MR血管成像(3DCE-MRA)在头颈部的临床应用价值。材料和方法:应用3D小角度激发快速梯度回波序列,对76例临床疑头颈部血管疾病患者进行3DCE-MRA检查。结果:76例3DCE-MRA均获成功,3DCE-MRA图像明确显示了病变部位及范围。结论:3DCE-MRA快速、准确,有利于头颈部血管疾病的诊断和治疗。     

三维对比增强MR血管成像在颈部血管病变中的应用

目的探讨三维对比增强MR颈部血管成像（3D—CE—MRA）的方法及临床应用价值。方法对87例患者行颈部血管3D—CE-MRA检查,双日检查者采用testbolus＋3D—CE—MRA扫描,共检查49例患者,单日检查者采用carebolus＋3D—CE—MRA扫描,共检查38例患者,评价图像质量并分析病变血管情况．结果87例患者采用两种方法扫描图像质量无明显差异,均能满足临床诊断需要,3D—CE—MRA图像清楚显示了血管病变部何肢性质。结论3D—CE—MRA是无创、安全、便捷、可靠的颈部血管病变的检查方法,可以代替诊断性的DSA。     

采用高速采集技术的腹部MR对比增强血管成像

目的证实高速采集技术[净加速因子(Rnet)≥10]可用于生成三维亚秒计时影像和具有高空间分辨率的诊断质量的单次分割剂量的肾脏对比增强MR血管成像影像。材料与方法所有研究均经机构审查委员会批准,符     

先天性心脏病:应用血管内血池对比剂的心血管MR成像

目的比较先天性心脏病(CHD)MR血管成像(MRA)检查的两种方法,即采用血池对比剂的对比剂特异性反转恢复稳态自由进动(inversion-recovery steady state freeprecession,IRSSFP)MRA和采用联合血管内对比剂     

对比增强MR血管成像对阴部附属动脉的术前检出及定位

目的评价对比剂增强MR血管成像对前列腺癌病人阴部附属动脉(accessory pudendal artery,APA)术前检出和定位的诊断价值。材料与方法这项前瞻性研究得到机构审查委员会的批准,并获得知情同意书。2007年7月—2010     

在动脉粥样硬化兔模型中应用特异性弹性蛋白对比剂的延迟增强MR成像与未增强的黑血MR成像技术对比研究血管重塑及斑块不稳定性

正目的在动脉粥样硬化兔模型中,比较应用特异性弹性蛋白对比剂行延迟增强(DE)MR成像与未增强的黑血(BB)MR成像技术对血管壁轮廓的显示,用于评估血管重     

三维对比增强MR血管造影技术及临床应用

目的探讨三维对比增强MR血管造影(3DCE-MRA)技术及其临床应用价值。资料与方法应用3D小角度激发快速梯度回波序列(3D FLASH),对32例临床疑血管疾病患者行3DCE-MRA,重建方法为最大密度投影(MIP)及多平面重建(MPR),并对两种方法进行评价。结果32例3DCE-MRA均获成功,其中26例经手术病理或DSA证实,3DCE-MRA图像明确显示了病变部位及范围;在显示血管病变方面,MIP及MPR各有其优势。结论3DCE-MRA快速、安全、有效,有利于血管疾病的检出,可以为临床提供更丰富的信息。     

Catheter angiography, MR angiography, and MR perfusion in posterior reversible encephalopathy syndrome

BACKGROUND AND PURPOSE:The cause of posterior reversible encephalopathy syndrome (PRES) is unknown. Two primary hypotheses exist: 1) hypertension exceeding auto-regulatory limits leading to forced hyper-perfusion and 2) vasoconstriction and hypo-perfusion leading to ischemia with resultant edema. The purpose of this study was to evaluate the catheter angiography (CA), MR angiography (MRA), and MR perfusion (MRP) features in PRES in order to render further insight into its mechanism of origin.MATERIALS AND METHODS:In 47 patients with PRES, 9 CAs and 43 MRAs were evaluated for evidence of vasculopathy (vasoconstriction and vasodilation), and 15 MRP studies were evaluated for altered relative cerebral blood volume (rCBV) in PRES lesions and regions. Visualization of vessels on MRA and toxicity blood pressures were compared with the extent of hemispheric vasogenic edema.RESULTS:Vasculopathy was present in 8 of 9 patients on CA (direct correlation to MRA in 3/6 patients). At MRA, moderate to severe vessel irregularity consistent with vasoconstriction and vasodilation was present in 30 of 43 patients and vessel pruning or irregularity in 7 patients, with follow-up MRA demonstrating reversal of vasoconstriction or vasodilation in 9 of 11 patients. Vasogenic edema was less in patients with hypertension compared with patients who were normotensive. Preserved normal length of the posterior cerebral artery (PCA) was commonly seen in patients with severe hypertension despite diffuse or focal vasoconstriction or vasodilation. In these patients, lengthier visualization of the distal PCA correlated with a lower grade of hemispheric edema (P = .002). Cortical rCBV was significantly reduced in 51 of 59 PRES lesions and regions compared with a healthy reference cortex (average 61% of reference cortex) with mild decrease in the remainder.CONCLUSION:Vasculopathy was a common finding on CA and MRA in our patients with PRES, and MRP demonstrated reduced cortical rCBV in PRES lesions. Vasogenic edema was reduced in patients with hypertension, and superior distal PCA visualization correlated with reduced hemispheric edema in patients with PRES and severe hypertension.

Neurotoxicity with development of posterior reversible encephalopathy syndrome (PRES) is commonly seen in association with cyclosporine and FK-506 immune suppression after transplantation (allogeneic bone marrow transplantation [allo-BMT], solid organ transplantation); preeclampsia and eclampsia; infection, sepsis, and shock; nonspecific medical renal disease; and in autoimmune conditions as well as after high-dose chemotherapy.^1-13 The mechanism behind the development of PRES is yet unproved. Two broad theories have generally been considered.Severe hypertension with autoregulatory failure and hyperperfusion is often cited as the underlying mechanism. Alternatively, vasospasm has been demonstrated (catheter angiography [CA], MR angiography [MRA]), decreased cerebral blood flow noted (MR perfusion [MRP], single-photon emission CT [SPECT]) and the imaging appearance typically resembles a watershed distribution suggesting a mechanism related to brain hypoperfusion.^{1-3,5,9,13-20}Given these opposing views, it was our opinion that parallel observations on CA, MRA, and MRP could render further insight into the state of brain perfusion in PRES. Therefore, the purpose of this study was to retrospectively evaluate the CA, MRA, and MRP features in a large group of patients with PRES.     

Intracranial artery dissections: serial evaluation with MR imaging,MR angiography,and source images of MR angiography

BACKGROUND AND PURPOSE: To assess chronological change in intracranial artery dissections with magnetic resonance imaging (MRI), MR angiography (MRA), and source images of MRA, and to determine whether the source images of MRA provide additional useful information to the combined evaluation of MRI and MRA. MATERIALS AND METHODS: Seven consecutive patients with intracranial artery dissections who were diagnosed by clinical history and conventional angiography were followed sequentially with MRI and MRA (mean follow-up duration, 8.8 months). Two observers independently reviewed the signal intensity of the arterial wall on T1-weighted images, luminal structures on MRA, and source images of MRA. RESULTS: In three (43%) of seven patients, the affected arterial wall had high signal intensity area from 4 to 62 days after onset on T-weighted images. Double lumen on MRA wasobserved only in one patient during the course of the study, whereas a definite low-intensity linear area in the lumen on source images of MRA was seen from 0 to 773 days after onset in all patients. When information from the source images of MRA was added to evaluation with both MRI and MRA, detectability increased to 100% from day 0 to day 3 and 67% from day 4 to day 30. CONCLUSION: The signal intensity of the dissected wall and the luminal structures on MRA and its source images vary according to chronological age. The use of source images from MRA in addition to the combined evaluation of MRI and MRA may provide more accurate diagnosis and follow-up study of intracranial artery dissections.     

Time-of-flight MR angiography

Time-of-flight effects depend on the displacement of blood with respect to a region of excitation. When combined with static material suppression and projection imaging, time-of-flight effects provide a flexible means of flow sensitization for magnetic resonance (MR) angiography. Bolus tracking, flow enhancement by spin replacement, and selective tagging are three classes of methods being pursued for MR angiography.     

Contrast-enhanced MR angiography

Contrast-enhanced magnetic resonance angiography (CE-MRA) is challenging conventional angiography as the primary diagnostic tool for vascular visualization. This article describes CE-MRA techniques, equipment and many of the applications currently in use, as well as applications under development. The advantages of CE-MRA also are discussed.     

Peripheral MR angiography

Atherosclerotic disease of the lower extremities is a common disorder in western society. Its debilitating nature calls for accurate diagnosis and treatment. The gold standard for diagnosing this disease by depiction of vessel morphology is X-ray angiography (either conventional or digital subtraction angiography). However, the invasive nature of this technique and the possible harmful effects of iodinated contrast agents have led to the idea that non-invasive MR angiography might be a good alternative for acquiring information about vessel morphology. Most extensively studied was time-of-flight MR angiography. Although first results with this technique were encouraging, it is now apparent that time-of-flight MR angiography is hampered by the virtue of which it exists, since blood flow not only generates vessel-to-background contrast, but is also the cause of disturbing artifacts. However, with the introduction of minimally invasive contrast-enhanced MR angiography, using gadolinium chelates to reduce the T1 of blood, image quality has improved dramatically. Moreover, using contrast-enhanced MR angiography, high-resolution three-dimensional data about the entire peripheral vascular tree can be obtained within several minutes, which might make MR angiography a true competitor of X-ray angiography as a diagnostic tool in the clinical work-up of a patient with complaints of peripheral atherosclerosis. The purpose of this article is to explain working mechanisms and usefulness of both time-of-flight and contrast-enhanced MR angiography. Received: 28 August 1998; Revised: 7 December 1998; Accepted: 9 February 1999     

Nonenhanced MR angiography

While nonenhanced magnetic resonance (MR) angiographic methods have been available since the earliest days of MR imaging, prolonged acquisition times and image artifacts have generally limited their use in favor of gadolinium-enhanced MR angiographic techniques. However, the combination of recent technical advances and new concerns about the safety of gadolinium-based contrast agents has spurred a resurgence of interest in methods that do not require exogenous contrast material. After a review of basic considerations in vascular imaging, the established methods for nonenhanced MR angiographic techniques, such as time of flight and phase contrast, are considered and their advantages and disadvantages are discussed. This article then focuses on new techniques that are becoming commercially available, such as electrocardiographically gated partial-Fourier fast spin-echo methods and balanced steady-state free precession imaging both with and without arterial spin labeling. Challenges facing these methods and possible solutions are considered. Since different imaging techniques rely on different mechanisms of image contrast, recommendations are offered for which strategies may work best for specific angiographic applications. Developments on the horizon include techniques that provide time-resolved imaging for assessment of flow dynamics by using nonenhanced approaches.     

Contrast-enhanced MR angiography

Summary Despite many optimizations, the current limitations of plain MR angiography include: saturation that impairs the visualization of veins and arteries with slow flow and spin-dephasing signal voids in locations with turbulent flow. Recently, the use of contrast agents has been proposed to cope with these remaining problems. Because of induced shortening of the T1 of the blood, saturation in the blood vessels is overcome. As a result, arteries and veins are visualized with the same signal intensity, which makes the technique less flow-dependent. In combination with short T1-weighted acquisitions, today CE MRA can be obtained while the patient is holding his breath. This last approach is most promising for abdominal applications since the respiratory motion can be frozen. As these acquisitions also use very short echo times, spin dephasing can be reduced. In conclusion, the use of contrast agents has greatly increased the clinical usefulness of MR angiography.      

Vasovist-enhanced MR angiography

Vasovist (MS-325) is the first intravascular contrast agent approved for use with magnetic resonance angiography in the European Union. Vasovist reversibly binds to albumin, providing extended intravascular enhancement compared to existing extracellular magnetic resonance contrast agents. Prior to approval, Vasovist underwent extensive testing to evaluate the safety and efficacy of the drug; the clinical trials program included blinded, placebo-controlled dose ranging, efficacy in a variety of vascular beds (AIOD, renal, pedal), examination of potential drug interaction with warfarin and comparison with XRA. The clinical trials show that Vasovist-enhanced MR angiography is safe and well-tolerated in patients with vascular disease, effective for the detection of vascular stenosis and aneurysms, significantly more accurate (both more sensitive and specific) than non-contrast MR angiography for the diagnosis of vascular stenoses, and similar to conventional angiography for the overall characterization of vascular disease, without the need for catheterization.