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.     

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.     

Pulsatile flow artifacts in two-dimensional time-of-flight MR angiography: Initial studies in elastic models of human carotid arteries

Initial experimental and numerical analysis of artifacts due to pulsatile flow in two-dimensional time-of-flight (2D-TOF) magnetic resonance (MR) angiography are presented. The experimental studies used elastic models of the carotid artery bifurcation cast from fresh cadavers and accurately reproducing the twisting and tapering of the human blood vessels, allowing direct comparison of images with and without flow. Prominent image artifacts, including periodic ghosts and signal loss, were produced by pulsatile flow even though flow-compensated gradient waveforms were used. The dependence of artifacts due to partial saturation on pulse sequence parameters (TR and flip angle) was investigated theoretically for a simple pulsatile velocity profile and compared with experimental results from a model of a normal carotid artery. Signal reduction was observed proximal and distal to the stenosis in a model with a 70% internal carotid artery (ICA) stenosis and a model with 90% stenoses in both the ICA and the external carotid artery. Although this study deals exclusively with 2D-TOF imaging, the methods can also be applied to evaluate other MR angiography techniques.     

Flow velocity quantification in human coronary arteries with fast,breath-hold MR angiography

Measurement of coronary artery flow velocities has, until now, largely required the use of invasive technologies. The authors have implemented a breath-hold magnetic resonance (MR) angiography technique for depicting the coronary arteries and for quantifying flow velocities. The method was tested in flow phantoms and then applied to a series of subjects: 11 subjects were studied at rest, and four were studied before and during pharmacologic stress induced by intravenous adenosine. Flow velocities at rest in the midportion of the right coronary artery were 9.9 cm/sec ± 3.5 (n = 12); in the proximal left anterior descending coronary artery, they were significantly higher, measuring 20.5 cm/sec ± 5.2 (n = 6). With adenosine, flow velocities typically increased at least fourfold. The authors conclude that noninvasive measurement of coronary artery flow velocities is feasible with MR angiography; this method may prove useful for determining the physiologic significance of coronary artery stenosis.     

MR characterization of blood flow in native and grafted internal mammary arteries

In the postoperative patient with anginal symptoms, differentiation between bypass graft compromise and nonischemic causes has until now been accomplished only by means of x-ray angiography. A noninvasive test is clearly desirable. The authors used a cine phase-contrast (PC) magnetic resonance (MR) imaging technique to characterize blood flow in native and grafted internal mammary arteries (IMAs). Ten volunteers and 15 patients who had recently undergone IMA coronary artery bypass grafting were imaged. Cine PC MR imaging was performed in the transaxial plane at the level of the pulmonary artery bifurcation. Flow in both IMAs was quantified and expressed as a percentage of cardiac output measured in the ascending aorta. In the 15 patients, flow analysis was performed in both the native and grafted IMAs. In the volunteers, IMA blood flow ranged from 2.1% to 4.3% of cardiac output on the left (mean, 3.5%) and 2.1% to 5.1% (mean, 3.5%) on the right. There was considerable intersubject variability, with coefficients of variation of 10.7% for the left and 12.3% for the right IMA. Intrasubject variability was limited, with estimated common standard deviations of 0.45% of cardiac output (range, 0.2%–1.1%) for the left and 0.39% (range, 0.1%–0.6%) for the right IMA. Flow in grafted IMAs was identified in 13 of 15 patients. In one of two patients without demonstrable IMA graft flow, cardiac catheterization confirmed lack of flow. IMA graft flow varied from 28 to 164 mL/min (mean, 80.3 mL/min). This study shows the feasibility of using cine PC MR imaging as a quantitative method of evaluating blood flow in IMA coronary artery bypass grafts.     

Cerebrovascular occlusive complications in osteopetrosis major

Summary We report the case of a 16-year-old patient with osteopetrosis major, complaining of transient sensory and motor disturbances in the left upper limb and diziness on changing the position of his head. Selective angiography of the cerebral vessels showed severe narrowing of the internal carotid artery within the petrous carotid canal and in its supraclinoid portion. The cervical vertebral arteries showed multiple stenosis within the vertebral canal. These findings are explained by narrowing of the basal foramina by the osteopetrotic bone.     

Quantification of blood flow in the middle cerebral artery with phase-contrast MR imaging

The aim of this study was to assess blood flow in the middle cerebral artery (MCA) according to age, gender, and side. Eighty-eight subjects without carotid obstruction were measured for mean velocity, vessel area, and volume flow rates of both MCA with phase-contrast MR. A high-resolution sequence with a matrix of 300 × 512 and a double oblique localizing strategy was used for measurement. A mean velocity of 33 ± 6.8 cm/s, a mean vessel area of 6.2 ± 1.2 mm² and a mean flow rate of 121 ± 28 ml/min were measured in the MCA. Lower volume flow rates were seen in subjects aged over 50 years (p < 0.01). When comparing women with men, a lower vessel area (p < 0.05) of the MCA was counterbalanced by a higher velocity, resulting in no significant difference of the volume flow rate. No difference occurred between the right and the left side. Flow reduction occurs in the elderly. A lower vessel area of the MCA in women is compensated by a higher velocity. Received: 3 September 1999; Revised: 17 January 2000; Accepted: 23 February 2000     

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.     

Arterial phase carotid and vertebral artery imaging in 3D contrast-enhanced MR angiography by combining fluoroscopic triggering with an elliptical centric acquisition order

Arterial-phase three-dimensional (3D) contrast-enhanced MR angiograms of the carotid and vertebral arteries from their origins through the carotid bifurcations were obtained in 20 patients using acquisition times over 30 sec by using an MR fluoroscopy-triggered pulse sequence with elliptical centric view order. The typical pixel size was 0.8 mm (x) × 1.6 mm (y) × 1.5 mm (z), and 32–48 coronal slices were acquired. The fluoroscopic monitoring of bolus arrival was effective in 18 of the 20 cases; two failures were attributed directly to a poor choice of RF coil. To exploit peak arterial-to-venous contrast, the central 3D views were acquired first in the most compact time period possible for the given TR. For the 18 successfully triggered cases, arterial-phase 3D images were obtained with excellent venous suppression as demonstrated by an average internal jugular vein to common carotid signal enhancement ratio of only 0.05 ± 0.04.     

Selective catheterization of the brachiocephalic arteries via the right brachial artery

Summary Selective intra-arterial digital subtraction angiography of the brachiocephalic arteries using the right brachial artery approach was successfully performed for 169 of 173 patients, 33 of whom were outpatients. Catheterization was unsuccessful for four patients; two of them elderly hypertensive men with tortuous brachial arteries, and two of them middle-aged obese women for whom arterial puncture could not be performed. 4-F modified Simmons type catheters were used in this study. Selective catheterizations of both common carotid arteries were successfully performed in all but one patient, a woman whose aberrant right subclavian artery prevented bilateral common carotid arterial catheterizations. Selective catheterizations of the right vertebral and left subclavian arteries, though relatively difficult, were successfully performed in 84.2% and 93.9% of patients, respectively. The mean examination time for a four-vessel study was 24.3 min. No major complications were encountered. Thus, transbrachial selective catheterization of the brachiocephalic arteries proved to be safe, useful, and relatively easy to perform.     

Blood flow volume quantification of cerebral ischemia: comparison of three noninvasive imaging techniques of carotid and vertebral arteries

OBJECTIVE: Determination of blood flow volume is useful in assessing ischemic cerebrovascular disease. We compared the blood flow volume measurement of three noninvasive imaging techniques, namely color velocity imaging quantification, spectral Doppler imaging quantification, and MR phase-contrast flow quantification, to see how well the flow values determined by each technique agreed with one another. SUBJECTS AND METHODS: Flow volume quantification was tested experimentally using a flow simulator and by the three techniques in the vertebral and internal carotid arteries of 40 patients with histories of cerebral ischemia. In the flow simulation study, the flow values in each technique were compared with the phantom flow by the Wilcoxon's signed rank test. In the patient study, the flow values between each paired technique were compared by paired t test. The significance level was taken at p less than 0.05. RESULTS: Flow volumes were measured by color velocity imaging quantification. MR phase-contrast flow quantification agreed with the phantom flow simulation within the tested range, and spectral Doppler imaging quantification values were significantly overestimated. In patients, a large variation of the blood flow volume was obtained between each technique (p < 0.05). Among them, spectral Doppler imaging quantification showed the highest flow values in the vessels (internal carotid arteries, 312.6 mL/min; vertebral arteries, 112.0 mL/min), followed by color velocity imaging quantification (internal carotid arteries, 216.8 mL/min; vertebral arteries, 58.1 mL/min) and MR phase-contrast flow quantification (internal carotid arteries, 169.1 mL/min; vertebral arteries, 66.5 mL/min). CONCLUSION: Blood flow volume measurements determined by the three noninvasive imaging techniques on the same vessel can differ widely, and spectral Doppler imaging quantification consistently overestimated the flow volume. It is, therefore, essential that the same technique, preferably color velocity imaging quantification or MR phase-contrast flow quantification, be used for clinical follow-up investigations in the future.     

Innominate artery occlusive disease: sonographic findings

OBJECTIVE: The objective of this study was to report the sonographic abnormalities in a group of patients with angiographically proven innominate artery stenosis and occlusion. MATERIALS AND METHODS: A review of all cerebrovascular sonograms at our institutions was undertaken to identify patients with complete or partial flow reversal in the right vertebral artery and reversal or midsystolic deceleration of flow in any one of the three major segments of the right carotid system (common, internal, or external carotid artery). The distribution and appearance of these abnormalities was evaluated, and the presence or absence of tardus-parvus waveforms was noted in any segment of the right carotid artery. Additionally, a left to right common carotid peak systolic velocity ratio (LCCA/RCCA) was calculated and compared to published normal values. All patients had correlative contrast or MR angiography. Correlation was made between the severity of stenosis as determined by angiographic images and waveform aberrations as well as the more objective LCCA/RCCA ratios. RESULTS: Twelve patients were identified as having the abnormalities described above in the right vertebral and carotid arteries. Doppler waveforms from the right vertebral artery revealed that eight of the 12 patients had complete reversal of flow at rest. Bidirectional flow was found in the remaining four as manifested by the presence of marked midsystolic deceleration. In the carotid arteries, one patient had complete reversal of flow in all segments of the right carotid system. Waveforms with midsystolic deceleration were identified in at least one of the carotid arteries of the remaining 11 patients: common carotid artery (8/11 = 73%), internal carotid artery (10/11 = 91%), external carotid artery (3/11 = 27%). The average LCCA/RCCA was 3.1 with a range of 1.7 to 5.7 (normal = 0.7-1.3). All patients had severe innominate artery disease (from 70% to occlusion) by contrast angiography or MR angiography. There was no correlation between the angiographically determined degree of stenosis and the Doppler findings. CONCLUSION: A distinctive pattern of hemodynamic alterations occurs in the right vertebral and carotid arteries of patients with severe innominate artery disease. Findings include reversed or bidirectional flow in the right vertebral artery, the presence of midsystolic deceleration in any of the branches of the right carotid system, and elevated LCCA/RCCA ratio.     

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.     

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。     

Velocity and flow quantitation in the superior sagittal sinus with ungated and cine (gated) phase-contrast MR imaging

Normal blood flow and velocity in the superior sagittal sinus were measured in 30 patients. A fast two-dimensional ungated phase-contrast (PC) pulse sequence was compared with a peripherally gated cine PC technique for velocity and flow quantitation. The same imaging parameters were used for both methods. Measured values for mean velocity and flow obtained with the two methods were compared by using regression analysis and t testing. For blood flow, the correlation coefficient was 0.976. For velocity measurements, r was 0.950. Mean flow was 285 mL/min ± 19 with the ungated PC method and 281 mL/min ± 19 with the cine PC method. The mean velocities measured with the two methods were 12.94 cm/sec ± 1.1 and 13.59 cm/sec ± 1.1, respectively. There was no significant difference (paired t test) between the methods for mean flow or velocity data. This was true even though flow in the superior sagittal sinus is moderately pulsatile, as shown with the cine PC technique. The ungated PC method provided these data in 13 seconds versus 3.5 minutes for the cine PC method.     

3D MR angiography with ramp-shaped flip-angle distribution

This study addressed the use of 3D MR angiography with flip angles (FAs) linearly varying across the excitation volume in order to diminish spin saturation. The shape of the ramp profile was varied to optimize the method for different regions and pathological alterations. Radio frequency pulses with ramp-shaped excitation profiles were generated flow-compensated 3D-FISP sequence. With the use of ramp-shaped excitation profiles good results were obtained for intracranial arteries as well as for neck arteries (i.e. carotid and vertebral arteries) which were demonstrated in 6 healthy volunteers and in 5 patients with various stenoses and anomalies of the carotid and vertebral arteries. With this technique it was possible to use increased thicknesses of the excitation volume (slab) up to 256 mm. Ramp-shaped excitation pulses with linearly increasing FAs in main flow direction can provide improved contrast of the vessel parts located distally to the entry side of the slab. Although this method has no advantage concerning complex flow or other dephasing effects; its particular effectiveness lies in the reduction of spin saturation. Correspondence to: T. Nägele     

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.     

Relationship between variations in the circle of Willis and flow rates in internal carotid and basilar arteries determined by means of magnetic resonance imaging with semiautomated lumen segmentation: reference data from 125 healthy volunteers

BACKGROUND AND PURPOSE: Volume flow rates in the feeding arteries of the brain are measured to evaluate blood flow dynamics in vascular disease. Although these flow values are thought to be effected by anatomic variations in the circle of Willis, few reports have described the effect. This study reports on the relationship between variations in the circle of Willis and volume flow rates in the bilateral internal carotid and basilar arteries of normal volunteers. METHODS: We prospectively examined 125 healthy volunteers by MR imaging. Variations in the circle of Willis were classified as "textbook" type, hypoplasia of the precommunicating segment of the anterior cerebral artery (A1), hypoplasia of the precommunicating segment of the posterior cerebral artery (P1), or "other." Volume flow rates were measured by 2D cine phase-contrast MR imaging. Lumen boundaries and volume flow rates were semiautomatically determined by pulsatility-based segmentation. RESULTS: Of the 117 subjects (61 men, 56 women; mean age, 23.6 years) considered suitable for flow measurement, 105 showed textbook type, and 6 each showed A1 hypoplasia and P1 hypoplasia. Total flow rates for the 3 variations were 781 +/- 151 mL/min (mean +/- SD), 744 +/- 119, and 763 +/- 129, respectively. Relative contributions by flow rates of the internal carotid arteries and the basilar artery for the 3 variations were 39.8%:38.9%:21.3%, 31.8%:49.1%:19.0%, and 46.6%:41.6%:11.7%, respectively, showing statistically significant differences. CONCLUSIONS: Variations in the circle of Willis correlate significantly with relative contributions by the flow rates of the bilateral internal carotid and basilar arteries.     

Distribution of cerebral blood flow in the circle of Willis

PURPOSE: To prospectively determine the effect of anatomic variations in the circle of Willis on volume flow in the internal carotid arteries (ICAs) and basilar artery (BA). MATERIALS AND METHODS: Institutional review board approval and informed consent were obtained. Phase-contrast magnetic resonance (MR) angiography was used to measure the volume flow in the BA and ICAs in 208 patients (182 men, 26 women; mean age, 60 years) with symptomatic atherosclerosis or risk factors for atherosclerosis. Patients with steno-occlusive disease were excluded, and flow values were normalized for age. Three-dimensional time-of-flight MR angiograms were used to assess the anatomy of the circle of Willis. Differences in volume flow between a complete circle of Willis, a circle with a missing A1 segment, and a circle with a fetal-type posterior cerebral artery were analyzed (analysis of variance and Scheffe post hoc tests). RESULTS: The ICA volume flow in subjects with a complete configuration of the circle of Willis was 245 mL/min +/- 65 (standard deviation). Flow in the contralateral ICA was significantly increased (P < .01) in subjects with a missing A1 segment (303 mL/min +/- 56) compared with control subjects and compared with flow on the ipsilateral side (214 mL/min +/- 94; P < .01). In subjects with a unilateral or bilateral fetal-type posterior cerebral artery, the ICA volume flow was increased (P < .01) and the BA volume flow was decreased (P < .01) in comparison with the flow in subjects with no fetal-type circle of Willis. CONCLUSION: Large asymmetries in volume flow between the right and left ICAs or decreased volume flow in the BA is not necessarily caused by vascular disease but may be caused by variations in the anatomy of the circle of Willis.     

Submillisievert CT angiography for carotid arteries using wide array CT scanner and latest iterative reconstruction algorithm in comparison with previous generations technologies: Feasibility and diagnostic accuracy

ObjectivesTo assess evaluability and diagnostic accuracy of a low dose CT angiography (CTA) protocol for carotid arteries using latest Iterative Reconstruction (IR) algorithm in comparison with standard 100 kVp protocol using previous generation CT and IR.Materials and methods105 patients, referred for CTA of the carotid arteries were prospectively enrolled in our study and underwent CTA with 80 kVp and latest IR algorithm (group 1). Data were retrospectively compared with 100 consecutive patients with similar examination indications that had previously undergone CTA of carotid arteries with a standard 100 kVp protocol and a first generation IR algorithm (group 2). Image quality was evaluated with a 4-point Likert-scale. For each exam CT number, image noise, signal-to-noise ratio (SNR), contrast-to-noise ratio (CNR) at level of common carotid artery (CCA), internal carotid artery (ICA) and at level of Circle of Willis and Effective Dose (ED) were evaluated. 62 Group 1 patients underwent a clinically indicated DSA and results were compared with CTA.ResultsNo exams reported as not diagnostic. The overall mean CT number value of all arterial segments was above 450 HU in both groups. Significant lower noise, and higher SNR and CNR values were found in group 1 in comparison with group 2 despite the use of 80 kVp. In 62-group 1 patients studied by DSA, CTA showed in a segment-based analysis a sensitivity, negative predictive value and accuracy of 100%, 100% and 99% respectively. Mean ED in group 1 was 0.54 ± 0.1 mSv with a dose reduction up to 86%.ConclusionsCTA for carotid arteries using latest IR algorithm allows to perform exams with submillisievert radiation exposure maintaining good image quality, overall evaluability and diagnostic accuracy.