4D phase contrast flow imaging for in-stent flow visualization and assessment of stent patency in peripheral vascular stents - A phantom study

Purpose

4D phase contrast flow imaging is increasingly used to study the hemodynamics in various vascular territories and pathologies. The aim of this study was to assess the feasibility and validity of MRI based 4D phase contrast flow imaging for the evaluation of in-stent blood flow in 17 commonly used peripheral stents.

Materials and methods

17 different peripheral stents were implanted into a MR compatible flow phantom. In-stent visibility, maximal velocity and flow visualization were assessed and estimates of in-stent patency obtained from 4D phase contrast flow data sets were compared to a conventional 3D contrast-enhanced magnetic resonance angiography (CE-MRA) as well as 2D PC flow measurements.

Results

In all but 3 of the tested stents time-resolved 3D particle traces could be visualized inside the stent lumen. Quality of 4D flow visualization and CE-MRA images depended on stent type and stent orientation relative to the magnetic field. Compared to the visible lumen area determined by 3D CE-MRA, estimates of lumen patency derived from 4D flow measurements were significantly higher and less dependent on stent type. A higher number of stents could be assessed for in-stent patency by 4D phase contrast flow imaging (n = 14) than by 2D phase contrast flow imaging (n = 10).

Conclusions

4D phase contrast flow imaging in peripheral vascular stents is feasible and appears advantageous over conventional 3D contrast-enhanced MR angiography and 2D phase contrast flow imaging. It allows for in-stent flow visualization and flow quantification with varying quality depending on stent type.     

MRI和MRA对烟雾病的诊断价值

目的：评价ＭＲＩ和ＭＲ血管成像（ＭＲＡ）在烟雾病中的诊断价值。材料与方法：回顾性分析２３例烟雾病患者的ＭＲＩ和ＭＲＡ资料，ＭＲＡ采用三维时间飞跃法。结果：２３例患者ＭＲＡ图像均有不同程度的颈内动脉分叉处的血管狭窄／闭塞，１８例基底节区异常网状的血管和１４例软脑膜侧支循环血管显示清晰。ＭＲＩ上显示了所有患者的脑实质改变和１５例颈内动脉分叉处的血管狭窄／闭塞改变，所有患者根据其ＭＲ上脑血管的改变均可做出正确的诊断。结论：ＭＲＡ结合ＭＲＩ能对烟雾病患者做出正确的诊断和较准确的分期，同时可用于烟雾病患者的随访检查和术后复查。     

冠心病患者血管内皮功能与颈总动脉内中膜厚度的相关性研究

 目的研究冠心病患者颈动脉内-中膜厚度、血管弹性与肱动脉血管内皮功能.方法将研究对象分为3组,Ⅰ组为30名健康人,Ⅱ组为心绞痛型冠心病患者30例,Ⅲ组为冠心病心肌梗死患者30例,用高频超声测量颈动脉内-中膜厚度、收缩期颈动脉内径(DS)、舒张期颈动脉内径(DC),计算颈总动脉壁弹性的相关参数:可扩张度(DC)、顺应性(CC);观察受检者的肱动脉充血反应性扩张(DTRH)和含服硝酸甘油后血管内径的变化(DTNG),并进行对比分析.结果冠心病心肌梗死患者颈动脉内-中膜厚度较心绞痛型冠心病患者、正常对照组增厚(P＜0.01),血管弹性与血管内皮功能明显减低(P＜0.01),心绞痛型冠心病患者较正常对照组血管内皮功能明显减低(P＜0.01),血管内皮功能与颈动脉内-中膜厚度之间有较大相关性,呈负相关,与颈总动脉壁可扩张度、顺应性有较大相关性,呈正相关.结论冠心病患者肱动脉依赖性血管内皮细胞功能减退早于颈动脉内-中膜厚度变化,可与颈总动脉内中膜厚度、血管弹性一起作为监测冠心病病情发展变化及判断预后的客观指标.     

Arterial flow characteristics in the presence of vascular disease and implications for fast spin echo-based noncontrast MR angiography

Purpose:

To investigate arterial flow characteristics in the setting of vascular disease, and examine their effect on the performance of fast spin‐echo (FSE)‐based noncontrast MR angiography (NC‐MRA).

Materials and Methods:

Seventeen patients were recruited from among those scheduled for routine contrast‐enhanced MR angiography (CE‐MRA) of the lower extremities at 1.5 Tesla. The research portion of the exam was performed before the clinically‐indicated protocol and included phase‐contrast imaging at multiple levels in the legs and FSE‐based NC‐MRA in the calf and thigh, using a three‐dimensional ECG‐gated technique that exploits differences in arterial flow velocity between diastole and systole.

Results:

Vascular occlusions were associated with reduced systolic velocity, a delayed systolic peak, and, in two middle‐aged patients, an increase in diastolic velocity. Elevated systolic and diastolic velocities were observed in a subject with a nonhealing ulcer. NC‐MRA allowed visualization of arteries with systolic velocities as low as 3 cm/s, and exhibited comparable depiction to CE‐MRA for diastolic velocities as high as 6 cm/s. At the highest diastolic velocities observed (15 cm/s) arterial depiction was severely degraded.

Conclusion:

FSE‐based NC‐MRA as presently implemented performs successfully over a wide range of flow patterns, but does not accommodate extremely low systolic velocities or very high diastolic velocities. J. Magn. Reson. Imaging 2011;. © 2011 Wiley Periodicals, Inc.     

儿童烟雾病MRI与MRA诊断

目的 探讨MRI、MRA对儿童烟雾病(Moyamoya)的诊断价值。资料与方法 分析11例3．5～14岁烟雾病患儿的MRI和MRA表现。MRI至少包括横断面TlWI、T2WI；MRA采用3D TOF法，2例行增强MRA。结果 MRI习显不颈内动脉(ICA)末段、大脑前动脉(ACA)、大脑中动脉(MCA)、基底动脉(BA)末段、大脑后动脉(PCA)血管流空影纤细或缺失(11／11)，脑实质内代偿扩张的穿动脉流空影(11／11)，以两侧基底节丘脑区明显；MCA、PCA周围细小血管流空影(11／11)；伴脑梗死9例、脑萎缩3例；FLMR可显示软脑膜血管代偿扩张(3／5)。MRA对血管狭窄或闭塞范围、程度显示更直观，且能显示眼动脉、颈外动脉(ECA)分支、PCA等扩张，但由于失相位和饱和效应，导致对血管狭窄或闭塞过高评价，细小血管不能充分显示，增强MRA有助于显示颅底血管网。结论 MRI可提示本病诊断，MRA结合MRI可明确诊断。     

Evaluation of flow characteristics of soft-tissue vascular malformations using technetium-99m labelled red blood cells

The estimation of intralesional haemodynamics is crucial in determining appropriate treatment for soft-tissue vascular malformations. The aim of this study was to develop a method to evaluate the flow characteristics of soft-tissue vascular malformations using technetium-99m labelled red blood cells (^99mTc-RBCs). Seventy-nine soft-tissue vascular malformations, including 20 arteriovenous malformations and 59 venous malformations, in 57 patients were examined. Following the intravenous injection of ^99mTc-RBCs, dynamic imaging was performed for 30 min with the lesion in the field of view (^99mTc-RBC flow study). A time-activity curve was generated for the lesion, and the lesion was categorized as a high-flow or low-flow lesion by visual inspection of the curve. In low-flow lesions, mean vascular transit time (MTT) was calculated by curve fitting based on a two-compartment model. Twenty-nine lesions in 19 patients were examined twice, and reproducibility was assessed. In 23 venous malformations in 16 patients, ^99mTc-Sn colloid was percutaneously injected into the intravascular space of the lesion, and dynamic data of 5-min duration were acquired (direct puncture scintigraphy). MTT was estimated from the washout curve and compared with MTT estimated by ^99mTc-RBC flow study. ^99mTc-RBC flow study classified all 20 arteriovenous malformations as high-flow lesions and all 59 venous malformations as low-flow lesions. In the low-flow lesions, MTT estimated by ^99mTc-RBC flow study ranged from 61.2 to 2174.9 s. In the reproducibility study, complete concordance in classification and high correlation in MTT were shown between the first and second examinations. MTT estimated by ^99mTc-RBC flow study was significantly correlated with that estimated by direct puncture scintigraphy. In summary, ^99mTc-RBC flow study provides a quantitative indicator of intralesional haemodynamics in low-flow lesions in addition to accurate distinction between high-flow and low-flow lesions. The results of this study suggest the feasibility of detailed evaluation of flow characteristics in soft-tissue vascular malformations using ^99mTc-RBCs. Received 3 November and in revised form 13 December 1998     

Time-resolved 3D MR velocity mapping at 3T: improved navigator-gated assessment of vascular anatomy and blood flow

PURPOSE: To evaluate an improved image acquisition and data-processing strategy for assessing aortic vascular geometry and 3D blood flow at 3T. MATERIALS AND METHODS: In a study with five normal volunteers and seven patients with known aortic pathology, prospectively ECG-gated cine three-dimensional (3D) MR velocity mapping with improved navigator gating, real-time adaptive k-space ordering and dynamic adjustment of the navigator acceptance criteria was performed. In addition to morphological information and three-directional blood flow velocities, phase-contrast (PC)-MRA images were derived from the same data set, which permitted 3D isosurface rendering of vascular boundaries in combination with visualization of blood-flow patterns. RESULTS: Analysis of navigator performance and image quality revealed improved scan efficiencies of 63.6%+/-10.5% and temporal resolution (<50 msec) compared to previous implementations. Semiquantitative evaluation of image quality by three independent observers demonstrated excellent general image appearance with moderate blurring and minor ghosting artifacts. Results from volunteer and patient examinations illustrate the potential of the improved image acquisition and data-processing strategy for identifying normal and pathological blood-flow characteristics. CONCLUSION: Navigator-gated time-resolved 3D MR velocity mapping at 3T in combination with advanced data processing is a powerful tool for performing detailed assessments of global and local blood-flow characteristics in the aorta to describe or exclude vascular alterations.     

Quantitative assessment of left ventricular function in humans at 7 T

The purpose of this study was to determine the ability of 7 T cardiac magnetic resonance imaging (MRI) to quantitatively assess left ventricular volumes, mass, and function from cine short‐axis series and left ventricular diastolic filling from velocity‐encoded MRI in 10 healthy volunteers. As comparative “gold standard,” the corresponding measures obtained at 1.5 T were taken. Left ventricular volumes, function, and mass were obtained by manual image segmentation. Trans‐mitral flow graphs were obtained from 2D one‐directional through‐plane velocity‐encoded MRI planned at the mitral valve in end‐systole. Imaging at 7 T MRI was successful in 80% of the examinations. Assessment of left ventricular volumes, function, and mass at 7 T showed good agreement with 1.5 T (no significant differences between variables describing volumes, function, and mass with intraclass correlation coefficients ranging from 0.77 to 0.96). Trans‐mitral stroke volume and the ratio between early and atrial peak filling rate showed strong agreement at both field strengths (no significant differences between stroke volumes and filling ratios with intraclass correlation coefficients 0.92 for stroke volumes and 0.77 for peak filling ratios). In conclusion, this study shows that assessing left ventricular volumes, function, and flow is feasible at 7 T MRI and that standardized MRI protocols provide similar quantitative results when compared with 1.5 T MRI. Magn Reson Med, 2010. © 2010 Wiley‐Liss, Inc.     

MRI measurement of wall shear stress vectors in bifurcation models and comparison with CFD predictions.

Steady fluid flow was studied in a simple bifurcation model and in a physiologically realistic model of the human carotid bifurcation. Wall shear stress (WSS) vectors were calculated from phase-contrast (PC) magnetic resonance imaging (MRI) measurements of the velocity field. Velocity measurements in the inflow regions were also used as boundary conditions for computational fluid dynamics (CFD) calculations of WSS, which were compared with those derived from MRI alone. In regions of well-behaved flow, MRI and CFD estimates of WSS were in good general agreement. In regions of disturbed flow, for example near the bifurcation, the quality of the MRI measurements was sufficient for reliable calculation of WSS vectors when a sensitive surface coil was used. The combination of MRI and CFD would seem to be a powerful technique for the investigation of flow phenomena.     

原发性高血压病患者血管内皮功能检测的临床意义

目的：探讨原发性高血压病患者血管内皮功能改变的临床意义。方法：选择原发性高血压病患者按病情分为三组。通过反应性充血后肱动脉内径变化及冷加压后冠状动脉内径变化评估血管内皮功能。结果：与正常对照组相比，原发性高血压病患者内皮依赖性舒张功能明显受损，冠状动脉和肱动脉内径变化率均减低，并随着病情加重，内皮功能损害更严重。肱动脉内皮功能变化与冠状动脉内皮功能变化高度相关。结论：血管内皮功能的变化可以反应高血压患者病情的不同程度，肱动脉内皮功能的检测可以问接地反映冠状动脉的内皮功能。     

烟雾病的磁共振诊断和临床分析

目的探讨烟雾病MRI、MRA的诊断特征。方法回顾分析17例10～49岁烟雾病患者的MRI和MRA表现。MRI至少包括横断面T1WI、T2WI;4例行增强T1WI,2例行增强MRA,5例行快速自旋回波液体衰减反转恢复(FLAIR)检查;16例行MRA,采用三维时间飞跃法(3DTOF)。结果MRI可显示颈内动脉(ICA)末段、大脑前动脉(ACA)、大脑中动脉(MCA)、大脑后动脉(PCA)血管流空影纤细或缺失(17/17);脑实质内或脑池内代偿扩张的烟雾血管(17/17);脑梗死5例、陈旧性出血灶4例,单侧侧脑室扩张2例。MRA对血管狭窄或闭塞范围、程度显示更直观,且能显示颈外动脉分支、大脑后动脉分支侧枝循环。2例显示常春藤征(ivysign)和柔脑膜高信号征。结论MRI可提示烟雾病诊断,结合MRA可明确诊断。     

Identification of vascular structures as a major source of signal contrast in high resolution 2D and 3D functional activation imaging of the motor cortex at l.5T preliminary results

We have measured the T₂* signal response associated with cortical activation due to finger motion at 1.5 Tesla. Both thin slice 2D and 3D images show signal intensity changes which vary from 2% to 32% depending on volunteer, echo time, slice thickness, and in-plane resolution. The largest signal change occurred for the thinnest slices and highest resolution (2 mm³). This is consistent with reducing partial volume effects and a simple difference in phase between the intravascular signal and surrounding parenchyma. No inflow enhancement was seen on the 2D or 3D scans, confirming the nature of the signal difference for this approach was due to local field in-homogeneity effects. Using 3D imaging, multiple effects can be seen simultaneously. With a 3D MRA method, it was possible to locate the vessel that was the source of the T₂* behavior; it was in each case a vein on the surface of the cortical parenchyma.     

Magnetic resonance in the assessment of renal function

The kidneys are the most important organs to maintain homeostasis. In the assessment of renal functional disorders laboratory tests offer only indirect hints on location of the disease; radionuclide nephrography is hampered by low spatial resolution and radiologic methods provide only limited quantitative information. The MRI technique with fast pulse sequences and renally eliminated contrast agent has the capability of combining both anatomic and functional information. This article gives an overview on functional MRI of the kidneys with its possibilities and limitations. The clinical application of functional MRI allows a better understanding of some pathologic conditions such as urinary tract obstruction, renal insufficiency, effects of extracorporeal shock wave lithotripsy, different states of hydration, effects of drugs, vascular disorders, and effects of transplantation. Received 12 May 1997; Accepted 17 July 1997     

Proton magnetic resonance imaging for assessment of lung function and respiratory dynamics

Since many pulmonary diseases present with a variable regional involvement, modalities for assessment of regional lung function gained increasing attention over the last years. Together with lung perfusion and gas exchange, ventilation, as a result of the interaction of the respiratory pump and the lungs, is an indispensable component of lung function. So far, this complex mechanism is still mainly assessed indirectly and globally. A differentiation between the individual determining factors of ventilation would be crucial for precise diagnostics and adequate treatment. By dynamic imaging of the respiratory pump, the mechanical components of ventilation can be assessed regionally. Amongst imaging modalities applicable to this topic, magnetic resonance imaging (MRI), as a tool not relying on ionising radiation, is the most attractive. Recent advances in MRI technology have made it possible to assess diaphragmatic and chest wall motion, static and dynamic lung volumes, as well as regional lung function. Even though existing studies show large heterogeneity in design and applied methods, it becomes evident that MRI is capable to visualise pulmonary function as well as diaphragmatic and thoracic wall movement, providing new insights into lung physiology. Partly contradictory results and conclusions are most likely caused by technical limitations, limited number of studies and small sample size. Existing studies mainly evaluate possible imaging techniques and concentrate on normal physiology. The few studies in patients with lung cancer and emphysema already give a promising outlook for these techniques from which an increasing impact on improved and quantitative disease characterization as well as better patient management can be expected.     

Left ventricular diastolic function assessment from three-dimensional three-directional velocity-encoded MRI with retrospective valve tracking

Purpose

To compare parameters describing left ventricular (LV) diastolic function obtained with three‐dimensional (3D) three‐directional velocity‐encoded (VE) MRI with retrospective valve tracking and two‐dimensional (2D) one‐directional VE MRI in patients with ischemic heart failure. Second, to compare classification of LV diastolic function, and in particular for discriminating restrictive filling patterns, with both MRI techniques versus Doppler echocardiography.

Materials and Methods

The 3D and 2D VE MRI early (E) and atrial (A) peak flow rate indices, determined from transmitral waveform analyses, were compared. Also, net forward flow volume per cycle and transmitral regurgitation fraction were determined. Agreement in classifying diastolic filling patterns between 3D and 2D VE MRI versus Doppler echocardiography was evaluated using kappa statistics.

Results

The 3D three‐directional VE MRI with retrospective valve tracking was statistically significantly different from 2D one‐directional VE MRI for net forward flow volume and regurgitation fraction through the mitral valve and all parameters describing the diastolic waveform filling pattern, except for the E deceleration time and E/A filling ratio. Kappa‐agreement between 3D three‐directional VE MRI with retrospective valve tracking and echocardiography for classifying diastolic filling patterns was superior to 2D one‐directional VE MRI and echocardiography (i.e., κ = 0.91 versus κ = 0.79, respectively).

Conclusion

The 3D three‐directional VE MRI with retrospective valve tracking better describes LV diastolic function as compared to 2D one‐directional VE MRI in patients with ischemic heart failure. J. Magn. Reson. Imaging 2011;33:312–319. © 2011 Wiley‐Liss, Inc.     

Time-resolved 3D contrast-enhanced MRA with GRAPPA on a 1.5-T system for imaging of craniocervical vascular disease: initial experience

Introduction: For three-dimensional (3D) imaging with magnetic resonance angiography (MRA) of the cerebral and cervical circulation, both a high temporal and a high spatial resolution with isovolumetric datasets are of interest. In an initial evaluation, we analyzed the potential of contrast-enhanced (CE) time-resolved 3D-MRA as an adjunct for neurovascular MR imaging. Methods: In ten patients with various cerebrovascular disorders and vascularized tumors in the cervical circulation, high-speed MR acquisition using parallel imaging with the GeneRalized Autocalibrating Partially Parallel Acquisitions (GRAPPA) algorithm on a 1.5-T system with a temporal resolution of 1.5 s per dataset and a nearly isovolumetric spatial resolution was applied. The results were assessed and compared with those from conventional MRA and digital subtraction angiography (DSA). Results: CE time-resolved 3D-MRA enabled the visualization and characterization of high-flow arteriovenous shunts in cases of vascular malformations or hypervascularized tumors. In steno-occlusive disease, the method provided valuable additional information about altered vessel perfusion compared to standard MRA techniques such as time-of-flight (TOF) MRA. The use of a nearly isovolumetric voxel size allowed a free-form interrogation of 3D datasets. Its comparatively low spatial resolution was found to be the major limitation. Conclusion: In this preliminary analysis, CE time-resolved 3D-MRA was revealed to be a promising complementary MRA sequence that enabled the visualization of contrast flow dynamics in various types of neurovascular disorders and vascularized cervical tumors.     

MRI estimation of the arterial input function in mice

RATIONAL AND OBJECTIVES: Dynamic contrast-enhanced (DCE) MRI offers the potential to provide quantitative maps of tumor perfusion parameters and is therefore expected to play an important role in the study of cancer in small animal models. Extraction of such information from DCE-MRI data requires a methodology for determination of the arterial input function (AIF) for the target tissues. An MRI based method for observation of the AIF in a mouse model is demonstrated in the present report. MATERIALS AND METHODS: A series of short-axis cardiac images was acquired during the first pass of a bolus of Gadodiamide using a low-resolution, EEG-gated, saturation-recovery gradient echo imaging sequence. The AIF was then extracted from the observed signal intensity changes in the left ventricle (LV) blood pool. RESULTS: The proposed technique provides sufficient temporal and spatial resolution to accurately characterize the AIF of Gadodiamide in mouse models. The AIF was observed in 4 mice and was found to be qualitatively similar to that previously observed in larger animals. However, significant inter-animal variability in the precise form of the AIF was evident. CONCLUSIONS: The proposed method for determination of AIF in mice has been shown to be effective and reliable. The inter-animal variability observed in the present study suggests that the AIF should be measured in each animal undergoing analysis by DCE-MRI.     

Non-invasive assessment of vessel morphology and function in tumors by magnetic resonance imaging

The switch to an angiogenic phenotype is an important precondition for tumor growth, invasion and spread. Since newly formed vessels are characterized by structural, functional and molecular abnormalities, they offer promising targets for tumor diagnosis and therapy. Previous studies indicate that MRI is valuable to assess vessel morphology and function. It can be used to distinguish between benign and malignant lesions and to improve delineation of proliferating areas within heterogeneous tumors. In addition, tracer kinetic analysis of contrast-enhanced image series allows the estimation of well-defined physiological parameters such as blood volume, blood flow and vessel permeability. Frequently, changes of these parameters during cytostatic, anti-angiogenic and radiation therapy precede tumor volume reduction. Moreover, target-specific MRI techniques can be used to elucidate the expression of angiogenic markers at the molecular level. This review summarizes strategies for non-invasive characterization of tumor vascularization by functional and molecular MRI, hereby introducing representative preclinical and clinical applications.