Correlation of cine MR velocity measurements in the internal carotid artery with collateral flow in the circle of willis: Preliminary study

The velocity-phase relationship intrinsic to phase-contrast magnetic resonance (MR) angiography permits the quantitative and qualitative assessment of blood flow. The ability to measure velocity and vessel cross-sectional area allows noninvasive assessment of volume flow rate (VFR) in the internal carotid artery (ICA). Phase-contrast techniques also demonstrate flow direction. Using two-dimensional cine phase-contrast angiography, the authors evaluated VFR in the ICA and collateral flow about the circle of Willis in 15 patients with ischemic neurologic symptoms. The VFR in each carotid artery was correlated with the degree of stenosis and presence or absence of abnormal circle of Willis collateral flow. There was a correlation between a decrease in VFR and abnormal circle of Willis collateral flow. In addition, a correlation between severe stenosis and a decrease in VFR was found. In patients with ischemic neurologic symptoms without severe stenosis (<70% diameter stenosis), no decrease in VFR was seen. It is hoped that flow quantification and directional flow imaging with phase-contrast angiography will help further characterize carotid artery occlusive disease by enabling assessment of VFR changes associated with ischemic neurologic symptoms. This study also supports the hypothesis that two mechanisms-hemodynamic and embolic-play a role in ischemic neurologic symptoms.     

Carotid plaque formation and its evaluation with angiography,ultrasound, and MR angiography

The accurate assessment of carotid artery disease is an important challenge for magnetic resonance (MR) angiography. Studies indicate that the detection and grading of stenosis and the evaluation of plaque morphology are all important steps in the clinical assessment of atherosclerosis. The prevalence of significant carotid artery stenosis in the elderly population and even in patients with symptoms of carotid artery disease is low; clinical risk seems to correlate more closely with plaque morphology and surface characterization than with the degree of stenosis. This highlights the importance of MR angiography and ultrasound, which can help characterize plaque morphology in addition to showing the degree of stenosis. The authors review the present understanding of plaque formation, comparisons of plaque imaging with conventional angiography, ultrasound, and MR angiography, and recent progress in MR angiography techniques. Several studies, including the North American Symptomatic Carotid Endarterectomy Trial and the European Carotid Surgery Trial, are discussed regarding the current objectives of carotid artery imaging. The sensitivity and specificity of plaque detection and morphologic evaluation continue to improve.     

Carotid and vertebral artery blood flow in left- and right-handed healthy subjects measured with MR velocity mapping

The goal of the study was to establish normal carotid artery flow rates in left-handed and right-handed individuals as a standard against which patients with carotid artery disease could be compared. Antegrade and retrograde flow were measured in the ascending aorta, in the right and left common, internal, and external carotid arteries, and in the vertebral arteries of 12 healthy subjects. Five subjects were right-handed, five left-handed, and two ambidextrous. Measured flow rates were as follows: common carotid arteries, 360–557 mL/min (mean [± standard deviation], 465 mL/min ± 52); internal carotid arteries, 132–367 mL/min (mean, 265 mL/min ± 60); external carotid arteries, 113–309 mL/min (mean, 186 mL/min ± 51); vertebral arteries from 133–308 mL/min (mean, 244 mL/min ± 43); and cerebral circulation, 546–931 mL/min (mean, 774 mL/min ± 134). All right-handed subjects had higher flow rates in the left internal carotid artery than in the right, and all left-handed subjects had higher flow rates in the right internal carotid artery (P =.007). There were no significant differences in left and right common carotid artery flow rates between left- and right-handed subjects. The standard deviation of a single measurement was 5%. The flow rates were similar to those obtained previously with other techniques and could be used as a normal standard.     

Blood flow modeling in carotid arteries with computational fluid dynamics and MR imaging

RATIONALE AND OBJECTIVES: The authors' goal was to develop a noninvasive method for detailed assessment of blood flow patterns from direct in vivo measurements of vessel anatomy and flow rates. MATERIALS AND METHODS: The authors developed a method to construct realistic patient-specific finite element models of blood flow in carotid arteries. Anatomic models are reconstructed from contrast material-enhanced magnetic resonance (MR) angiographic images with a tubular deformable model along each arterial branch. A surface-merging algorithm is used to create a watertight model of the carotid bifurcation for subsequent finite element grid generation, and a fully implicit scheme is used to solve the incompressible Navier-Stokes equations on unstructured grids. Physiologic boundary conditions are derived from cine phase-contrast MR flow velocity measurements at two locations below and above the bifurcation. Vessel wall compliance is incorporated by means of fluid-solid interaction algorithms. RESULTS: The method was tested on imaging data from a healthy subject and a patient with mild stenosis. Finite element grids were successfully generated, and pulsatile blood flow calculations were performed. Computed and measured velocity profiles show good agreement. Flow patterns and wall shear stress distributions were visualized. CONCLUSIONS: Patient-specific computational fluid dynamics modeling based on MR images can be performed robustly and efficiently. Preliminary validation studies in a physical flow-through model suggest that the model is accurate. This method can be used to characterize blood flow patterns in healthy and diseased arteries and may eventually help physicians to supplement imaging-based diagnosis and predict and evaluate the outcome of interventional procedures.     

Carotid magnetic resonance angiography: improved image quality with dual 3-inch surface coils

Magnetic resonance angiography (MRA) hs inherent artifacts due to variation in velocity and direction of flowing blood in the carotid bulb and regions of stenosis. We examined the efficiency of dual 3-inch surface coils to delineate carotid artery flow better. Carotid MRA was performed on ten healthy volunteers and six patients, on a 1.5 T system. A special adapter was constructed to use with 3-inch (receive-only) coils, which were placed over the carotid bifurcations. Routine anterior neck coils were also used. Contiguous axial two-dimensional (45/8.7, 1.5 mm, flip angle 60°) time-of-flight sequences were used. Image matrix was 256×256 with two signals averaged and acquisition time 6–10 min. These images were postprocessed and reformatted into angiographic views using a maximum intensity projection algorithm. Computer simulation of carotid artery blood flow through-out the cardiac cycle based on vessel contours derived from digital subtraction angiography was carried out by finite element analysis. Improved definition of vessel margin, particularly at the carotid bifurcation, and substantially increased signal-to-background ratio of flowing blood were obtained with 3-inchcoils. Apparent loss of signal in the carotid bulb was diminished. In one patient, contiguous flow throughout a high-grade stenosis was well defined, with the surface coil method, while drop-off of signal was observed with routine neck coil imaging.     

Redistribution of cerebropetal blood flow in patients with carotid artery stenosis measured non-invasively with fast cine phase contrast MR angiography

The purpose was to evaluate the blood flow redistribution in the neck vessels of patients with internal carotid artery (ICA) stenosis. Eighty-six patients with ICA stenosis underwent contrast-enhanced magnetic resonance angiography (CEMRA) and fast 2D phase contrast (2D-PC) sequence to measure the mean blood flow (MBF) of ICA, basilar artery (BA) and middle cerebral artery (MCA). CEMRA revealed 53 severe stenoses, 45 moderate stenoses and 3 occluded vessels. Patients with a unilateral severe ICA stenosis had a significantly reduced MBF of the ICA compared to the control group; the MBF reduction of the severely stenosed ICA was less conspicuous if associated with a controlateral severe stenosis. The MBF of the BA increased significantly in the presence of the bilateral severe ICA stenosis and in the ICA occlusion. The MBF of the MCA was unchanged in the presence of various degrees of ICA stenosis. Measurement of MBF with fast PC MRA permits cerebropethal blood flow assessment and gives additional information in grading ICA stenosis. The reduced MBF of a severe ICA stenosis has to be considered with caution since it depends also on the status of the controlateral ICA and may be considered a confident parameter only in case of unilateral carotid stenosis.     

应用图像后处理技术测量和分析人体颈动脉分叉血管几何学指标

目的 初步应用MR血管影像结合计算机三维图像后处理技术测量和分析在体颈动脉分叉的几何学属性指标,探讨不同年龄组该段血管形态的差异.方法 搜集2005年至2007年经超声检查或DSA检查证实为颈动脉分叉正常或狭窄率小于30%的受检者57例,分为≤40岁组27例和>40岁组30例,行颈动脉1VIR增强血管成像(CEMRA)检查,扫描所得减影图像经计算机图像后处理重建三维血管图像并测量颈动脉分叉的各项几何学指标.采用嵌套设计方差分析方法分析两组的各项测量指标的差异是否有统计学意义.结果 >40岁组和≤40岁组的颈动脉分叉几何学指标分别为:分叉角:70.268°±16.050°和58.857°±13.294°,颈内动脉(ICA)角:36.893°±11.837°和30.275°±9.533°,ICA非平面角:6.453°±5.009°和6.263°±4.250°,颈总动脉(CCA)曲率:0.023±0.011和0.014±0.005,ICA曲率:0.070±0.042和0.046±0.022,ICA/CCA直径比:0.693±0.132和0.728±0.106,颈外动脉(ECA)/CCA直径比:0.750±0.123和0.809±0.122,ECA/ICA直径比:1.103±0.201和1.127±0.195;分叉面积比:1.057±0.281和1.291±0.252.>40岁组和≤40岁组的分叉角、ICA角、CCA曲率、ICA曲率、ECA/CCA直径比和分叉面积比的差异有统计学意义(F值分别为17.16、11.74、23.02、13.38、6.54、22.80,P值均<0.05).结论 应用MR血管成像结合图像后处理方法实现了在体颈动脉分叉的三维立体重组和其各项几何学指标的测量,为进一步分析血管几何形态与血流动力学状态的关系以及其与动脉粥样硬化病变的发生与发展提供了一种崭新而简便易行的技术.     

High-resolution carotid artery MRA. Comparison with fast dynamic acquistion and duplex ultrasound scanning

Purpose:
To determine whether the diagnostic accuracy of contrast-enhanced MR angiography (CE-MRA) of the carotid arteries is improved by using a slow-injection, high-resolution technique. Material and Methods:
In 22 patients suspected to have internal carotid artery (ICA) stenosis at duplex ultrasound scanning (DUS), CE-MRA was performed both with a fast, dynamic (8 s/phase) and with a slower, high-resolution technique (scan time 2:20 min). Results:
There was conformity between the CE-MRA techniques regarding the degree of stenosis in 34/40 extracranial ICAs. In 3/6 discrepant cases, short occlusions were seen with the fast dynamic technique, whereas both the high-resolution CE-MRA technique and DUS showed patent vessels. There was an overall tendency toward higher stenosis grading with the dynamic technique. Overlying veins could be removed on a workstation in all high-resolution examinations. Conclusion:
The high-resolution carotid CE-MRA technique proposed herein seems to improve the diagnostic accuracy, at least for differentiation between high-grade stenoses and occlusions.     

MR flow quantification using race: Clinical application to the carotid arteries

Real time MR flow quantification was performed with real time acquisition and evaluation of motion (RACE) in a rigid phantom under steady flow conditions and in the common carotid arteries of 43 subjects aged 24–78 years. Hemodynamic information included the intraluminal velocity distribution during the complete cardiac cycle, the distensibility of the arterial wall, and age-dependent changes of the flow curves. Systolic peak velocities of 51 ± 33 cm/s and time-averaged volume flow rates of 4.3 ± 2.0 ml/s were measured in healthy subjects. Flow rates below 3.0 ml/s and the observation of abnormal flow patterns indicated stenoses greater than 70% in the region of the bifurcation (sensitivity: 83.3%; specificity: 93.7%; accuracy: 71.4%). Improvements may be achieved from a combination with MR angiography, providing both functional and morphologic vascular information noninvasively within one observer-independent examination. MR imaging, therefore, has a strong potential for the diagnosis of critical stenoses in symptomatic patients.     

Clinical results of carotid artery stenting with a nitinol self-expanding stent (SMART stent)

Our objective was to assess the technical feasibility and the clinical results of internal carotid artery (ICA) stenting using a nitinol self-expanding stent (SMART stent). In 13 patients 13 high-grade stenoses of the internal carotid artery were treated via an implantation of a SMART stent. In all cases a predilation of the stenosis and a postdilation within the stent were performed. Follow-up examinations were carried out in all patients after a period of 6 months. In each case the implantation of the stent was performed without technical complications. In 12 of 13 cases the stent was placed in the patients' internal carotid artery, in 1 case from the internal to the common carotid artery (CCA). The average degree of stenosis of 78% (70-95%) was reduced to an average of 2.8% (0-21%). The 6-month follow-up angiography showed an average degree of restenosis of 11.8% (0-29%) in 8 of 13 patients. Duplex sonography in the remaining 5 patients demonstrated patent stents. One patient showed brief neurological symptoms during the intervention. No further complications occurred during follow-up time. Treatment of internal carotid artery stenosis with the SMART stent seems technically feasible, safe, and promises long-term patency.     

Contrast-enhanced MR angiography of the supra-aortic vessels in 24 seconds: a feasibility study

A contrast-enhanced, gradient-echo 3D pulse sequence providing angiographic information in 24 s was tested in five healthy subjects and used prospectively in 21 patients for the investigation of the cervical arteries. Indications included suspected stenosis of the carotid (in 13), or vertebral arteries (in 1), carotid dissection (3), variants of the branches of the aortic arch (2) and extracranial carotid aneurysms (2). The results in all patients were compared with those of intra-arterial digital subtraction angiography (DSA). In patients with carotid stenosis, they were also compared with high-resolution 3D time-of-flight (TOF) MR angiography (MRA). Good quality MR angiograms of the neck vessels were obtained with the fast 3D sequence in 20 of the 21 patients. One claustrophobic patient was unable to co-operate. The degree of internal carotid artery (ICA) stenosis was graded correctly (compared to DSA) in 21 of 24 cases (87.5 %). Two mild stenoses were overestimated as moderate using the fast MR sequence and one high-grade stenosis was misdiagnosed as a complete occlusion. Carotid dissection was confirmed in one case and correctly excluded in two. Four extracranial ICA aneurysms in two patients, arterial variants and stenosis of the origin of the vertebral artery were correctly diagnosed using the contrast-enhanced MR angiogram. Three-dimensional TOF MRA was unsuccessful due to motion artefacts in half of the cases of ICA stenosis. Received: 6 August 1998 Accepted: 21 December 1998     

Striatocapsular infarction: MRI and MR angiography

We present a case of left striatocapsular infarction manifest clinically as a transient right hemiparesis. MRI showed a left striatocapsular infarct. Striatocapsular infarction, unlike lacunar infarction, is often associated with occlusive disease of the carotid artery. In order to screen the carotid vessels, cervical MR angiography (MRA) was performed during the same examination, demonstrating a left internal carotid artery occlusion, confirmed by contrast arteriography. MRA, a noninvasive modality, can be a useful adjunct to MRI, when diagnostic information concerning the cervical carotid artery is needed.     

Carotid stent delivery in an XMR suite: immediate assessment of the physiologic impact of extracranial revascularization

BACKGROUND AND PURPOSE: Patients undergoing stent placement as treatment for severe stenosis of the internal carotid artery (ICA) were assessed with MR imaging in a combined MR-radiographic (XMR) angiography suite. MR imaging was performed before and immediately following conventional radiography-guided stent placement. Changes in MR imaging measurable properties, including flow and perfusion, resulting from stent placement were evaluated. PATIENTS AND TECHNIQUES: MR imaging analysis was performed for 12 patients with >70% stenosis of the ICA before and after conventional radiography-guided deployment of a carotid stent. MR imaging acquisitions included angiography, quantitative flow analysis, perfusion, diffusion, and turbo-fluid-attenuated inversion recovery (FLAIR). These acquisitions were all performed immediately before and following stent placement by using conventional techniques. RESULTS: MR angiography proved sufficient for identifying the target lesion and permitting targeted flow analysis. MR flow analysis demonstrated a marked increase in flow in the treated carotid artery (+2.2 +/- 1.2 mL/s) and little change in other extracranial arteries. MR perfusion imaging showed no significant differences in relative cerebral blood volume between hemispheres before or after treatment, but there was a modest decrease in mean transit time and time to peak evident in the treated hemisphere after stent placement. Diffusion imaging did not demonstrate any ischemic foci resulting from carotid stent treatment. Hyperintensity of the CSF was noted on turbo-FLAIR acquisitions in the ipsilateral hemisphere following stent placement in 75% of patients. CONCLUSION: MR imaging reliably reflects the state of the carotid artery and provides a means of monitoring and quantifying the effects of revascularization.     

Mr angiography artifact due to metal joint of ventriculoperitoneal shunt mimicking severe carotid stenosis

An artifact due to the metal joint of a ventriculoperitoneal shunt resulted in a diagnosis of severe internal carotid artery stenosis at magnetic resonance angiography. Conventional x-ray angiography showed the presence of the metal joint and revealed that the artery was not stenotic.     

Therapeutic Occlusion of an Internal Carotid Artery with a High-Grade Stenosis Using Guglielmi Detachable Coils

We present a patient with a symptomatic, high-grade stenosis of the internal carotid artery (ICA) and contraindication for open surgery. Endovascular treatment was attempted, but stent placement was not possible. In view of good collateral flow to the related hemisphere, embolization of the stenosis of the ICA with Guglielmi detachable coils (GDCs) was performed to occlude the vessel. No complications occurred during the procedure or in the 1-year follow-up period. In cases where open surgery or endovascular treatment of a stenosis of the ICA are contraindicated or not possible, therapeutic occlusion of the stenotic ICA could be an alternative treatment option in patients with good collateral flow.     

颈动脉粥样斑块3T MR高分辨成像和MRA诊断

目的:应用3.0T MR高分辨管壁成像和MR血管造影在体显示颈动脉粥样斑块,探讨MR对颈动脉斑块的诊断价值。方法:经彩超检查证实的症状性颈动脉狭窄37例,所有病例行管腔MRA和管壁高分辨MR检查,MR检查序列包括3DTOF、DIR T1WI、T2WI、PDWI和MRA。其中,17例检查前1周内行CT血管造影检查,9例患者检查后1周内行颈动脉内膜剥脱术。根据颈动脉内膜剥脱术手术部位,将获得的病理标本与MR图像逐层对照,研究斑块脂质成分、纤维成分和纤维帽、斑块钙化、出血和脂质坏死池等MR表现,探讨斑块变性的MR表现及其病理基础。结果:37个病例共发现52条颈动脉分叉处斑块,其中,管腔轻度狭窄24条(46.1%),中度狭窄19条(36.5%),重度狭窄7条(13.5%),闭塞2条(3.9%)。斑块钙化21条(40.4%)、无钙化斑块31条(59.6%);31条软斑块中纤维成分为主斑块8条(15.6%),有明显脂质核心斑块23条(44.2%);其中,伴斑块出血5条(10%)、脂质坏死核心3条(6%),纤维帽撕裂(溃疡或纤维帽撕裂)3条(6%)。相对于胸锁乳突肌,脂质坏死池在TOF、T1WI、PDWI、T2WI均呈显著高信号,钙化在各序列均呈低信号。斑块内出血的信号与出血的时间有关,新鲜出血各序列表现为点、结节或片状高信号,亚急性出血或者陈旧出血的信号与出血时间长短有关。结论:颈动脉MRA和管壁高分辨成像是评估颈动脉斑块风险性的有效手段,无创性MRA可以显示颈动脉斑块的狭窄程度;管壁高分辨成像可以直接显示斑块纤维帽、斑块内结构和成分,预测斑块脱落的风险性。     

Hypoplasia of the internal carotid artery: a noninvasive diagnosis

We present the characteristic imaging findings of hypoplasia of the internal carotid artery (ICA) in two cases, one accompanied by an intracranial aneurysm. Finding of a diffuse luminal narrowing of the ICA on MR angiography or digital subtraction angiography (DSA) could wrongly evoke severe acquired diseases such as dissection or atherosclerosis. Absence of associated wall thickening and flow disturbances on color Doppler sonography (CDS) should suggest carotid hypoplasia. Confirmation of the diagnosis is obtained by CT of the skull showing a small carotid canal. Non-invasive procedures are sufficient to differentiate this rare congenital anomaly from acquired string signs. Received: 25 October 1999; Revised: 27 January 2000; Accepted: 30 March 2000     

MR imaging and MR angiography in the evaluation of pulsatile tinnitus.

PURPOSE1) To evaluate the scope of imaging findings seen with spin-echo MR and MR angiography (MRA) in patients with pulsatile tinnitus; 2) to determine whether MRA adds additional imaging information (to that provided by spin-echo MR) necessary for determining the cause of pulsatile tinnitus; and 3) to suggest MR and MRA imaging techniques for evaluation of patients with pulsatile tinnitus.METHODSForty-nine patients with pulsatile tinnitus were evaluated with MR and MRA. Seventeen of these patients had conventional angiography.RESULTSVascular lesions or paraganglioma were demonstrated in 28 patients. Of these 28 lesions, the majority were seen best (46%) or only (36%) on MRA. The spectrum of lesions detected included dural arteriovenous fistula (nine), extracranial arteriovenous fistula (three), paraganglioma (five), jugular bulb variants (three), aberrant internal carotid artery (one), internal carotid artery stenosis (one), tortuous internal carotid artery (one), carotid dissection with pseudoaneurysm (one), stenosis of the transverse sinus (two), and arteriovenous malformation (two).CONCLUSIONSMRA, in conjunction with spin-echo imaging, markedly enhances the ability of MR to diagnose the lesions responsible for pulsatile tinnitus.     

16层螺旋CT颈部血管成像的初步临床应用

目的:探讨颈部血管(颈动脉、椎动脉)16层螺旋CT血管造影成像技术及其临床应用价值。材料和方法:38例临床怀疑颈动脉及椎动脉狭窄者,经16层螺旋CT扫描后,用薄层横断面放大图像(MTI)及最大密度投影(MIP)、多平面重建(MPR)、曲面重建(CPR)等后处理方法,进行管腔及管壁斑块的形态学显示,并用高级血管分析软件测量狭窄段径线、狭窄段长度等作定量分析。结果:38例共计76支颈动脉、76支椎动脉CTA图像中,正常颈动脉血管40支,狭窄血管36支,其中1支颈总动脉中度狭窄者合并有动脉瘤;76支椎动脉中,6支椎动脉狭窄,受压于邻近椎体骨质;38例中有9例行颈动脉DSA检查,18例做了颈动脉多普勒超声(TCD),7例DSA和16例TCD对照结果一致,2例CTA轻度狭窄者TCD显示正常,11例颈动脉斑块均为混合密度斑块。结论:16层螺旋CT颈部血管成像图像质量满意,重建图像质量高,能较准确显示管腔狭窄及管壁斑块形态学改变,满足临床诊断需要,具有很好的临床筛查及实用价值。     

Poststenotic signal attenuation on 3 D phase-contrast MR angiography: a useful finding in haemodynamically significant carotid artery stenosis

We performed blinded visual evaluation of MR angiography (MRA) films in 44 patients with unilateral carotid artery stenosis to determine whether a flow gap and poststenotic signal attenuation on 3 D-PC MRA were useful signs of severe carotid artery stenosis. Although nine patients with a flow gap alone had various degrees of stenosis ranging from 22.2 to 77.3 % without any decrease in regional cerebral blood flow (rCBF), 13 patients with both a flow gap and poststenotic signal attenuation had severe stenoses of 80 % or more, with a definite decrease in baseline rCBF. The presence of both a flow gap and poststenotic signal attenuation on 3 D-PC MRA appeared to be a reliable marker of severe carotid artery stenosis with a decrease in rCBF. Received: 30 April 1999/Accepted: 11 August 2000