Magnetic Resonance Phase Contrast Angiography Research Articles

Common Carotid Artery Volume Flow: A Comparison Study between Ultrasound Vector Flow Imaging and Phase Contrast Magnetic Resonance Imaging.

Volume flow estimation in the common carotid artery (CCA) can assess the absolute hemodynamic effect of a carotid stenosis. The aim of this study was to compare a commercial vector flow imaging (VFI) setup against the reference method magnetic resonance phase contrast angiography (MRA) for volume flow estimation in the CCA. Ten healthy volunteers were scanned with VFI and MRA over the CCA. VFI had an improved precision of 19.2% compared to MRA of 31.9% (p = 0.061). VFI estimated significantly lower volume flow than MRA (mean difference: 63.2 mL/min, p = 0.017), whilst the correlation between VFI and MRA was strong (R2 = 0.81, p < 0.0001). A Bland–Altman plot indicated a systematic bias. After bias correction, the percentage error was reduced from 41.0% to 25.2%. This study indicated that a VFI setup for volume flow estimation is precise and strongly correlated to MRA volume flow estimation, and after correcting for the systematic bias, VFI and MRA become interchangeable.

Cardiovascular effects of two adenosine constant rate infusions in anaesthetized dogs

ObjectiveAdenosine induces vasodilatation. The aim of this study was to investigate cardiovascular effects of two adenosine constant rate infusion (CRI) doses in dogs. Study designExperimental, longitudinal repeated measure design. AnimalsTen healthy purpose-bred Beagle dogs. MethodsEach dog was sedated with butorphanol. Anaesthesia was induced with propofol intravenously and maintained with sevoflurane (inspired oxygen fraction = 47–55%). Controlled mechanical ventilation was used to maintain normocapnia. Two doses of adenosine were administered as CRIs to each dog: 140 μg kg–1 minute–1 (A140) followed by 280 μg kg–1 minute–1 (A280). Pulse rate, invasive arterial pressure and stroke volume (by magnetic resonance phase contrast angiography) were measured at baseline, 3 minutes after starting adenosine and 3 and 10 minutes after discontinuing adenosine. Cardiac output, cardiac index and approximated systemic vascular resistances (approximate SVR) were calculated. Additionally, arterial blood gases, co-oximetry, electrolytes, glucose and lactate were measured and oxygen content and delivery calculated. One-way repeated measures analysis of variance (p < 0.05) was used for data analysis. ResultsA140 and A280 resulted in a significant decrease in arterial blood pressure [systolic (p = 0.008), mean (p = 0.003), and diastolic arterial pressure (p = 0.004)] and approximate SVR (p = 0.008) compared with baseline. No significant changes were detected for the other variables. All values returned to baseline within 3 minutes after adenosine discontinuation. Conclusions and clinical relevanceAdenosine CRI decreases arterial pressure by vasodilatation in healthy dogs. No additional effects were observed with the higher dose. The effects in compromised dogs remain to be investigated.

A Comparison Study of Vector Velocity, Spectral Doppler and Magnetic Resonance of Blood Flow in the Common Carotid Artery

Magnetic resonance phase contrast angiography (MRA) is the gold standard for blood flow evaluation. Spectral Doppler ultrasound (SDU) is the first clinical choice, although the method is angle dependent. Vector flow imaging (VFI) is an angle-independent ultrasound method. The aim of the study was to compare VFI- and SDU-estimated peak systolic velocities (PSV) of the common carotid artery (CCA) with PSV obtained by MRA. Furthermore, intra- and inter-observer agreement was determined. MRA estimates were significantly different from SDU estimates (left CCA: p < 0.001, right CCA: p < 0.001), but not from VFI estimates (left CCA: p = 0.28, right CCA: p = 0.18). VFI measured lower PSV in both CCAs compared with SDU (p < 0.001) with improved precision (VFI: left: 24%, right: 18%; SDU: left 38%, right: 23%). Intra- and inter-observer agreement was almost perfect for VFI and SDU (inter-observer correlation coefficient: VFI 0.88, SDU 0.91; intra-observer correlation coefficient: VFI 0.96, SDU 0.97). VFI is more accurate than SDU in evaluating PSV compared with MRA.

A preliminary study of brain macrovascular reactivity in impaired glucose tolerance and type-2 diabetes: Quantitative internal carotid artery blood flow using magnetic resonance phase contrast angiography.

The aims of this study were (1) to examine cerebrovascular autoregulation in subjects with impaired glucose tolerance and type 2 diabetes and (2) to clarify whether cardiovascular autonomic nerve function is associated with abnormal cerebrovascular autoregulation. Totally, 46 subjects were recruited (12 = impaired glucose tolerance, 17 = type 2 diabetes and 17 = healthy volunteers). Arterial blood flow was assessed within the internal carotid artery at baseline and 20 min after intravenous pharmacological stress (1 g acetazolamide), using quantitative magnetic resonance phase-contrast angiography. Internal carotid artery vascular reactivity and pulsatility index was determined. All subjects underwent baroreceptor reflex sensitivity assessment. Subjects with impaired glucose tolerance and type 2 diabetes had significantly lower internal carotid artery vascular reactivity [40.2%(19.8) and 41.5%(18.7)], respectively, compared with healthy volunteers [57.0%(14.2); analysis of variance, p = 0.02]. There was no significant difference in internal carotid artery vascular reactivity between type 2 diabetes and impaired glucose tolerance groups (p = 0.84). There was a significant positive correlation between baroreceptor reflex sensitivity (low frequency:high frequency) with cardiac rhythm variability (ρ = 0.47, p = 0.04) and PI (ρ = 0.46, p = 0.04). We have demonstrated significant cerebrovascular haemodynamic abnormalities in subjects with type 2 diabetes and impaired glucose tolerance. This was associated with greater sympathovagal imbalance. This may provide an important mechanistic explanation for increased risk of cerebrovascular disease in diabetes. It also highlights that these abnormalities may already be present in prediabetes.

Computational Fluid Dynamics and Its Impact on Flow Measurements Using Phase-Contrast MR-Angiography

Rationale and Objectives: Computational fluid dynamic (CFD) simulations are discussed with respect to their potential for quality assurance of flow quantification using commercial software for the evaluation of magnetic resonance phase contrast angiography (PCA) data. Materials and Methods: Magnetic resonance phase contrast angiography data was evaluated with the Nova software. CFD simulations were performed on that part of the vessel system where the flow behavior was unexpected or non-reliable. The CFD simulations were performed with in-house written software. Results: The numerical CFD calculations demonstrated that under reasonable boundary conditions, defined by the PCA velocity values, the flow behavior within the critical parts of the vessel system can be correctly reproduced. Conclusion: CFD simulations are an important extension to commercial flow quantification tools with regard to quality assurance.

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.

In vivo validation of a blood vector velocity estimator with MR angiography

Conventional Doppler methods for blood velocity estimation only estimate the velocity component along the ultrasound beam direction. This implies that a Doppler angle under examination close to 90 degrees results in unreliable information about the true blood direction and blood velocity. The novel method transverse oscillation (TO), which combines estimates of the axial and the transverse velocity components in the scan plane, makes it possible to estimate the vector velocity of the blood regardless of the Doppler angle. The present study evaluates the TO method with magnetic resonance phase contrast angiography (MRA) by comparing in vivo measurements of stroke volume. Eleven healthy volunteers were included in this prospective study. From the obtained data sets recorded with the 2 modalities, vector velocity sequences were constructed and stroke volume calculated. Angle of insonation was approximately 90 degrees for TO measurements. The correlation between the stroke volume estimated by TO and MRA was 0.91 (p < 0.01) with the equation for the line of regression: MRA = 1.1.TO-0.4. A Bland-Altman plot was additionally constructed where the mean difference was 0.2 ml with limits of agreement at -1.4 ml and 1.9 ml. The results indicate that reliable vector velocity estimates can be obtained in vivo using the presented angle-independent 2-D vector velocity method. The TO method can be a useful alternative to conventional Doppler systems by avoiding the angle artifact, thus giving quantitative velocity information.

Blood Flow Field Simulation and Vessel Segmentation in Level Set Frame Work for MR Angiography (Vessel Wall Description and Velocity Boundary Condition)

A novel approach to correct magnetic resonance phase contrast angiography (MR-PCA) based on the coupling computational fluid dynamics (CFD) to vessel segmentation in the level set methodology. MR-PCA data is supplied not only to partial differential equation based fast local level set vessel segmentation as the initial condition, but also to CFD code using level set ghost fluid method as the initial and boundary conditions. These procedures are integrated to provide with the corrected velocity field in the most optimal vessel geometry. The application of this system to both synthetic and clinical data are shown and validity is discussed.

The effect of hyperoxia on cerebral blood flow: a study in healthy volunteers using magnetic resonance phase-contrast angiography

The effect of hyperoxia on cerebral blood flow: a study in healthy volunteers using magnetic resonance phase-contrast angiography

Magnetic Resonance Angiographic Study of Vertebral‐Basilar Flow Voids

In an effort to study the “no flow” void phenomenon as seen on conventional T2‐weighted (TE 80/TR 2500) magnetic resonance spin‐echo images (MRI), 30 vascular patients were studied with both MRI and magnetic resonance phase contrast angiography (MRA). Of the patients with vertebral‐basilar insufficiency, 9 (60%) of 15 had normal‐appearing flow voids in the vertebral and basilar arteries and 6 (40%) of 15 had “no flow” voids. Two of these 6 had either slow flow or normalappearing vertebral‐basilar arteries on MRA while 4 of these 6 had a positive correlation between “no flow” void and arterial occlusion. In the patients with vertebral‐basilar stroke, 3 (20%) of 15 had normal‐appearing flow voids and 12 (80%) of 15 had “no flow” voids. Two of these 12 had either slow flow or normal arteries on MRA while 10 of these 12 had a positive correlation between “no flow” void and arterial occlusion. Eleven of 30 had intraarterial studies and for 9 (82%) of the 11 there was excellent correlation with MRA findings. Fisher exact tests found significant relationships between flow voids and arterial patency in vertebral‐basilar insufficiency (p = 0.01) and in vertebral‐basilar stroke (p = 0.002). That is, MRA was able to delineate patent from slow‐flow or small‐caliber arteries from large‐vessel occlusion in patients with vertebral‐basilar insufficiency or stroke.

Magnetic resonance angiography of abdominal vessels: early experience using the three-dimensional phase-contrast technique

Based on three-dimensional acquisition of three sequences sensitive to one flow-direction, abdominal magnetic resonance phase-contrast angiography (MRA) was performed in 13 volunteers and 20 patients. The subjects received no antiperistaltic medication and were allowed to breath normally during the three acquisition periods of 11 minutes. The frequency of demonstration of the normal aorta, superior mesenteric and right and left renal arteries was 100%/100%/91%/100%, and of the inferior vena cava, splenic, superior mesenteric and portal veins was 92%/67%/92%/100%, respectively, whereas other abdominal vessels were seen less constantly. In renal artery stenosis or occlusion, MRA detected eight out of nine pathological arteries, missed only a minimal stenosis and was never false positive. In all 10 cases of portal hypertension, MRA demonstrated the venous collaterals detected by conventional angiography and in six cases showed more collaterals, particularly paravertebral vessels. A Budd-Chiari syndrome was investigated as well. If the accuracy of MRA can be proved in larger studies, it may become an important diagnostic tool in evaluating abdominal vascular pathology, such as renal artery stenosis or portal hypertension.