High-Resolution Magnetic Resonance Angiography of the Mouse Brain: Application to Murine Focal Cerebral Ischemia Models

Three-dimensional time-of-flight high-resolution magnetic resonance angiography was applied to visualize the cerebral vasculature of the mouse brain. In normal mice, angiograms of good quality, showing the essential details of the arterial cerebrovascular anatomy, could be obtained in only 2.5 min without the use of contrast agents. Signals from slowly flowing blood, e.g., in veins, could also be detected after administration of a blood pool contrast agent. The technique was applied to mouse models of permanent and transient brain ischemia, involving the occlusion of the middle cerebral artery. High-resolution magnetic resonance angiography proved to be a very useful tool for verifying the success of the occlusion in these models.     

In vivo comparison of three ultrasound vector velocity techniques to MR phase contrast angiography

The objective of this paper is to validate angle independent vector velocity methods for blood velocity estimation. Conventional Doppler ultrasound (US) only estimates the blood velocity along the US beam direction where the estimate is angle corrected assuming laminar flow parallel to vessel boundaries. This results in incorrect blood velocity estimates, when angle of insonation approaches 90° or when blood flow is non-laminar. Three angle independent vector velocity methods are evaluated in this paper: directional beamforming (DB), synthetic aperture flow imaging (STA) and transverse oscillation (TO). The performances of the three methods were investigated by measuring the stroke volume in the right common carotid artery of 11 healthy volunteers with magnetic resonance phase contrast angiography (MRA) as reference. The correlation with confidence intervals (CI) between the three vector velocity methods and MRA were: DB vs. MRA: R = 0.84 (p < 0.01, 95% CI: 0.49–0.96); STA vs. MRA: R = 0.71 (p < 0.05, 95% CI: 0.19–0.92) and TO vs. MRA: R = 0.91 (p < 0.01, 95% CI: 0.69–0.98). No significant differences were observed for any of the three comparisons (DB vs. MRA: p = 0.65; STA vs. MRA: p = 0.24; TO vs. MRA: p = 0.36). Bland–Altman plots were additionally constructed, and mean differences with limits of agreements (LoA) for the three comparisons were: DB vs. MRA = 0.17 ml (95% CI: −0.61–0.95) with LoA = −2.11–2.44 ml; STA vs. MRA = −0.55 ml (95% CI: −1.54–0.43) with LoA = −3.42–2.32 ml; TO vs. MRA = 0.24 ml (95% CI: −0.32–0.81) with LoA = −1.41–1.90 ml. According to the results, reliable volume flow estimates can be obtained with all three methods. The three US vector velocity techniques can yield quantitative insight into flow dynamics and visualize complex flow patterns, which potentially can give the clinician a novel tool for cardiovascular disease assessment.     

Combining magnetic resonance measurements with numerical simulations – Extracting blood flow physiology information relevant to the investigation of intracranial aneurysms in the circle of Willis

Cerebral aneurysms in the region of the circle of Willis have an incidence of 3–6% in western populations and involve the risk of rupture with subsequent subarachnoidal bleeding. The patient specific blood flow patterns are of substantial importance for understanding the pathogenesis of the lesions and may eventually contribute to deciding on the most efficient treatment procedure for a specific patient.A non-invasive method for performing in vivo measurements on blood velocity is 4D phase-contrast magnetic resonance angiography (PC-MRA), on the basis of which a flow field with all its parameters can be simulated. We are using this approach to investigate the hemodynamic parameters in the circle of Willis and, by analyzing the values at common locations of aneurysms, trying to find potential parameters to predict the development of aneurysms. Methodologically, we are acquiring the artery geometry with 3D-time-of-flight magnetic resonance (TOF) measurements and the blood velocity in the feeding arteries with 4D PC-MRA measurements in a healthy volunteer. These measurements are combined with computational fluid dynamics (CFD) to describe detailed hemodynamic patterns within the circle of Willis.     

Magnetic resonance measurement of blood flow in peripheral vessels after acute exercise

Velocity-encoded Cine magnetic resonance imaging (MRI) was used to measure blood flow in the anterior tibial artery (AT), posterior tibial artery (PT), and popliteal artery of adult human subjects (mean age 29 yr) before and after 90 s of ankle dorsiflexion exercise. Before exercise, mean flow, peak systolic velocity, and end-diastolic velocity in AT were 8.1 ± 1.6 (SE, n = 6) ml/min, 26.9 ± 2.6 cm/s, and −0.6 ± 0.4 cm/s, respectively. After exercise, mean flow and peak systolic velocity in AT increased by 19-fold and 3-fold, respectively, and end-diastolic velocity increased to 8.7 ± 1.1 cm/s. Flow in popliteal artery above its bifurcation was similar to the sum of flows in AT and PT, both before and after exercise. Flow in AT declined exponentially after exercise with a mean half-time of 4 min. The results demonstrate the utility of MR phase-encoded flow-velocity measurements for physiological studies of peripheral vascular dynamics after exercise.     

Adaptive optics fundus camera using a liquid crystal phase modulator

We have developed an adaptive optics (AO) fundus camera to obtain high resolution retinal images of eyes. We use a liquid crystal phase modulator to compensate the aberrations of the eye for better resolution and better contrast in the images. The liquid crystal phase modulator has a wider dynamic range to compensate aberrations than most mechanical deformable mirrors and its linear phase generation makes it easy to follow eye movements. The wavefront aberration was measured in real time with a sampling rate of 10 Hz and the closed loop system was operated at around 2 Hz. We developed software tools to align consecutively obtained images. From our experiments with three eyes, the aberrations of normal eyes were reduced to less than 0.1 μm (RMS) in less than three seconds by the liquid crystal phase modulator. We confirmed that this method was adequate for measuring eyes with large aberrations including keratoconic eyes. Finally, using the liquid crystal phase modulator, high resolution images of retinas could be obtained.     

支气管动脉CTA检查在中央型肺癌患者介入术前的指导价值

为探讨支气管动脉CT血管造影(CTA)检查在中央性肺癌患者介入术前的指导价值,本研究选取因反复肺癌咯血于我院行支气管动脉CTA检查的中央性肺癌患者56例,另选取同期正常对照组15例。所有患者均进行支气管动脉栓塞术,比较CTA影像学检查结果。结果显示,左肺癌患者的L支气管动脉显影率、右肺癌患者的R支气管动脉显影率均显著高于对照组,差异均具有统计学意义(P<0.05);左、右肺癌患者的L、R支气管动脉内径均显著高于对照组,差异均具有统计学意义(P<0.05);左肺癌患者的支气管动脉解剖分型以Grade 4型为主,占72.2%;右肺癌患者的支气管动脉解剖分型以Grade 1型为主,占47.4%。共检出咯血动脉76支,其中支气管动脉58支、肺循环动脉10支、多种动脉交通吻合型6支、肋间动脉2支。28例肺癌患者的供血支气管动脉至少有1个弯角≤90°,走行迂曲,CTA可见点或网状肿瘤血管,内肺动脉被包绕,狭窄;部分肺外体循环参与供血的患者,其病灶邻近的胸膜增厚。研究结果显示,支气管动脉CTA检查可有效提供支气管动脉的分支类型、解剖分型及开口部位,能较好地观察肺内疾病的血供来源,为患者介入治疗提供参考。     

基于双源CT血管造影技术评估MMP-9、PAF及Lp-PLA2与冠状动脉斑块性质的关系

冠状动脉粥样硬化性心脏病是威胁健康的常见病之一,本研究选取我院2017年2月~2018年12月确诊的206例冠心病患者,其中急性冠脉综合征(acute coronary syndrome,ACS)患者114例(ACS组)、稳定型心绞痛(stable angina pectoris,SAP)患者92例(SAP组),用双源CT血管造影技术检测患者的斑块性质,并检测了血清明胶酶B(MMP-9)、血小板活化因子(PAF)及脂蛋白相关磷脂酶2(Lp-PLA2)浓度,分析MMP-9、PAF及Lp-PLA2与斑块性质间的关系。结果显示,ACS组患者斑块面积和偏心指数均大于SAP组(P<0.05);ACS组患者血清MMP-9、PAF及Lp-PLA2的水平均高于SAP组(P<0.05);ACS组患者易损斑块的比例明显高于SAP组(P<0.05)。所有易损斑块患者血清MMP-9、PAF及Lp-PLA2的水平均高于稳定斑块的患者,且差异具有统计学意义(P<0.05)。患者冠状动脉斑块偏心指数与血清MMP-9、PAF及Lp-PLA2浓度呈正相关关系(P<0.05)。因此,通过双源CT血管造影技术观察冠状动脉粥样硬化斑块性质,结合血清MMP-9、PAF及Lp-PLA2浓度,可以对患者的病情进行评估。血清MMP-9、PAF及Lp-PLA2浓度与斑块的性质及不稳定性有关,可为预测患者冠状动脉斑块性质提供参考。     

Post-processing central k-space subtraction for high-resolution arterial peripheral MR angiography

Peripheral MR angiography requires high resolution and arterial contrast. Neither can be obtained simultaneously due to the short arterial phase of the contrast agent. To improve temporal resolution, keyhole imaging was developed, which combines high resolution and arterial k-spaces at the time of image acquisition. Here, a related approach is introduced for image post-processing in the Fourier domain. It is demonstrated that simple substitution of the central k-space with low-resolution data leads to severe distortion. Hence, a dedicated calculation scheme is necessary for composite k-space post-processing. A solution is presented for high-resolution arterial peripheral MR angiography that uses subtraction of venous intensities from the central high-resolution k-space. The calculations in the Fourier domain do not require interpolations between the different resolutions. High-resolution steady-state MR angiography, which exhibits contrast-enhanced arteries and veins at an isotropic resolution of 0.65 mm, and standard resolution arterial first-pass MR angiography were combined to obtain images with the resolution of the steady-state images and arterial contrast. Numerical simulations on software phantoms are presented. The operation of the method is demonstrated in five patients.