Phase-contrast Magnetic Resonance Angiography Research Articles

Principles Behind 4D Time-Resolved MRA/Dynamic MRA in Neurovascular Imaging

The abstract summarizes the evolution and role of dynamic magnetic resonance angiography (MRA) in neurovascular imaging. It highlights the historical context of neuroimaging, including the development of non-invasive techniques such as MRA. Different sequences of MRA, including time of flight (TOF), phase-contrast, contrast-enhanced, time-resolved, and dynamic MRA, are discussed, emphasizing their unique capabilities and clinical applications. Dynamic MRA, a four-dimensional imaging technique, offers high temporal and spatial resolution without ionizing radiation exposure, making it valuable for diagnosing cerebrovascular conditions like aneurysms, arteriovenous malformations (AVMs), dural arteriovenous fistulas (DAVF), steno-occlusive extracranial vascular disease, spinal vascular disease, neurovascular conflict, head and neck tumors, and cerebral venous sinus thrombosis (CVT). Comparative analyses with other imaging modalities, such as digital subtraction angiography (DSA), computed tomographic venography (CTV), and MR-based images, are presented, highlighting the diagnostic strengths and limitations of each technique. While DSA remains the gold standard, dynamic MRA shows promise as a non-invasive alternative with broad clinical utility. However, further large-scale prospective studies are needed to validate its diagnostic accuracy and establish its role in clinical practice.

Cerebrovascular Imaging at 7T: A New High

In this article, we will review the current techniques used in clinical cerebrovascular imaging, including time-of-flight MR Angiography (TOF-MRA), magnetization prepared rapid gradient echo (MPRAGE) MRA, phase-contrast MRA (PC-MRA), vessel wall MRI (VW-MRI) and MR venography (MRV). We will also discuss current problems and obstacles encountered at 7T vascular imaging.

Are hemodynamics responsible for inflammatory changes in venous vessel walls? A quantitative study of wall-enhancing intracranial arteriovenous malformation draining veins.

Signal enhancement of vascular walls on vessel wall MRI might be a biomarker for inflammation. It has been theorized that contrast enhancement on vessel wall imaging (VWI) in draining veins of intracranial arteriovenous malformations (AVMs) may be associated with disease progression and development of venous stenosis. The aim of this study was to investigate the relationship between vessel wall enhancement and hemodynamic stressors along AVM draining veins. Eight AVM patients with 15 draining veins visualized on VWI were included. Based on MR venography data, patient-specific 3D surface models of the venous anatomy distal to the nidus were segmented. The enhanced vascular wall regions were manually extracted and mapped onto the venous surface models after registration of image data. Using image-based blood flow simulations applying patient-specific boundary conditions based on phase-contrast quantitative MR angiography, hemodynamics were investigated in the enhanced vasculature. For the shear-related parameters, time-averaged wall shear stress (TAWSS), oscillatory shear index (OSI), and relative residence time (RRT) were calculated. Velocity, oscillatory velocity index (OVI), and vorticity were extracted for the intraluminal flow-related hemodynamics. Visual observations demonstrated overlap of enhancement with local lower shear stresses resulting from decreased velocities. Thus, higher RRT values were measured in the enhanced areas. Furthermore, nonenhancing draining veins showed on average slightly higher flow velocities and TAWSS. Significant decreases of 55% (p = 0.03) for TAWSS and of 24% (p = 0.03) for vorticity were identified in enhanced areas compared with near distal and proximal domains. Velocity magnitude in the enhanced region showed a nonsignificant decrease of 14% (p = 0.06). Furthermore, increases were present in the OSI (32%, p = 0.3), RRT (25%, p = 0.15), and OVI (26%, p = 0.3) in enhanced vessel sections, although the differences were not significant. This novel multimodal investigation of hemodynamics in AVM draining veins allows for precise prediction of occurring shear- and flow-related phenomena in enhanced vessel walls. These findings may suggest low shear to be a local predisposing factor for venous stenosis in AVMs.

Left atrium 4D-flow segmentation with high-resolution contrast-enhanced magnetic resonance angiography.

Atrial fibrillation (AF) leads to intracardiac thrombus and an associated risk of stroke. Phase-contrast cardiovascular magnetic resonance (CMR) with flow-encoding in all three spatial directions (4D-flow) provides a time-resolved 3D volume image with 3D blood velocity, which brings individual hemodynamic information affecting thrombus formation. As the resolution and contrast of 4D-flow are limited, we proposed a semi-automated 4D-flow segmentation method for the left atrium (LA) using a standard-of-care contrast-enhanced magnetic resonance angiography (CE-MRA) and registration technique. LA of 54 patients with AF were segmented from 4D-flow taken in sinus rhythm using two segmentation methods. (1) Phase-contrast magnetic resonance angiography (PC-MRA) was calculated from 4D-flow, and LA was segmented slice-by-slice manually. (2) LA and other structures were segmented from CE-MRA and transformed into 4D-flow coordinates by registration with the mutual information method. Overlap of volume was tested by the Dice similarity coefficient (DSC) and the average symmetric surface distance (ASSD). Mean velocity and stasis were calculated to compare the functional property of LA from two segmentation methods. LA volumes from segmentation on CE-MRA were strongly correlated with PC-MRA volume, although mean CE-MRA volumes were about 10% larger. The proposed registration scheme resulted in visually successful registration in 76% of cases after two rounds of registration. The mean of DSC of the registered cases was 0.770 ± 0.045, and the mean of ASSD was 2.704 mm ± 0.668 mm. Mean velocity had no significant difference between the two segmentation methods, and mean stasis had a 3.3% difference. The proposed CE-MRA segmentation and registration method can generate segmentation for 4D-flow images. This method will facilitate 4D-flow analysis for AF patients by making segmentation easier and overcoming the limit of resolution.

The influence of contralateral circulation on computational fluid dynamics of intracranial arteries: simulated versus measured flow velocities

BackgroundThis study aimed to retrospectively evaluate the influence of contralateral anterior circulation on computational fluid dynamics (CFD) of intracranial arteries, by comparing the CFD values of flow velocities in unilateral anterior circulation with the measured values from phase-contrast magnetic resonance angiography (PC-MRA).MethodsWe analyzed 21 unilateral anterior circulation models without proximal stenosis from 15 patients who performed both time-of-flight MRA (TOF-MRA) and PC-MRA. CFD was performed with the inflow boundary condition of a pulsatile flow of the internal carotid artery (ICA) obtained from PC-MRA. The outflow boundary condition was given as atmospheric pressure. Simulated flow velocities of the middle cerebral artery (MCA) and anterior cerebral artery (ACA) from CFD were compared with the measured values from PC-MRA.ResultsThe velocities of MCA were shown to be more accurately simulated on CFD than those of ACA (Spearman correlation coefficient 0.773 and 0.282, respectively). In four models with severe stenosis or occlusion of the contralateral ICA, the CFD values of ACA velocities were significantly lower (< 50%) than those measured with PC-MRA. ACA velocities were relatively accurately simulated in the models including similar diameters of both ACAs.ConclusionIt may be necessary to consider the flow condition of the contralateral anterior circulation in CFD of intracranial arteries, especially in the ACA.Relevance statementIncorporating the flow conditions of the contralateral circulation is of clinical importance for an accurate prediction of a rupture risk in Acom aneurysms as the bidirectional flow and accurate velocity of both ACAs can significantly impact the CFD results.Key points• CFD simulations using unilateral vascular models were relatively accurate for MCA.• Contralateral ICA steno-occlusion resulted in an underestimation of CFD velocity in ACA.• Contralateral flow may need to be considered in CFD simulations of ACA.Graphical

Coupling synthetic and real-world data for a deep learning-based segmentation process of 4D flow MRI

Background and objectivePhase contrast magnetic resonance imaging (4D flow MRI) is an imaging technique able to provide blood velocity in vivo and morphological information. This capability has been used to study mainly the hemodynamics of large vessels, such as the thoracic aorta. However, the segmentation of 4D flow MRI data is a complex and time-consuming task. In recent years, neural networks have shown great accuracy in segmentation tasks if large datasets are provided. Unfortunately, in the context of 4D flow MRI, the availability of these data is limited due to its recent adoption in clinical settings. In this study, we propose a pipeline for generating synthetic thoracic aorta phase contrast magnetic resonance angiography (PCMRA) to expand the limited dataset of patient-specific PCMRA images, ultimately improving the accuracy of the neural network segmentation even with a small real dataset. MethodsThe pipeline involves several steps. First, a statistical shape model is used to synthesize new artificial geometries to improve data numerosity and variability. Secondly, computational fluid dynamics simulations are employed to simulate the velocity fields and, finally, after a downsampling and a signal-to-noise and velocity limit adjustment in both frequency and spatial domains, volumes are obtained using the PCMRA formula. These synthesized volumes are used in combination with real-world data to train a 3D U-Net neural network. Different settings of real and synthetic data are tested. ResultsIncorporating synthetic data into the training set significantly improved the segmentation performance compared to using only real data. The experiments with synthetic data achieved a DICE score (DS) value of 0.83 and a better target reconstruction with respect to the case with only real data (DS = 0.65). ConclusionThe proposed pipeline demonstrated the ability to increase the dataset in terms of numerosity and variability and to improve the segmentation accuracy for the thoracic aorta using PCMRA.

Venous 3D Phase Contrast Magnetic Resonance Angiography Increases Diagnostic Certainty in Children with Ventriculoperitoneal Shunt and Suspected Shunt Failure

BackgroundClinical symptoms in children with suspected malfunction of ventriculoperitoneal shunt may not be specific and difficult to interpret. The presence or absence of ventricular enlargement on magnetic resonance imaging (MRI) does not reliably predict raised intracranial pressure (ICP) in these patients. Therefore, the aim was to investigate the diagnostic utility of 3D venous phase-contrast MR angiography (vPCA) in these patients.MaterialsThe MR studies of two groups of patients at two different examination dates were retrospectively analyzed; one group without clinical symptoms on both examinations and one with symptoms of shunt dysfunction on one examination receiving surgery. Both MRI examinations had to have been performed including axial T2 weighted (T2-w) images and 3D vPCA. Two (neuro)radiologists evaluated T2-w images alone and in combination with 3D vPCA in terms of suspected elevated ICP. Interrater reliability, sensitivity and specificity were assessed.ResultsCompression of venous sinuses was seen significantly more often in patients with shunt failure (p = 0.00003). Consequently, evaluation of 3D vPCA and T2-w images increases sensitivity to 0.92/1.0 compared to T2-w images alone with 0.69/0.77, the interrater agreement for the diagnosis of shunt failure rises from κ = 0.71 to κ = 0.837. Concerning imaging markers, three groups could be identified in children with shunt failure.ConclusionIn accordance with the literature, the results show that ventricular morphology alone is an unreliable marker for elevated ICP in children with shunt malfunction. The findings confirmed 3D vPCA as a valuable supplemental diagnostic tool improving diagnostic certainty for children with unchanged ventricular size in cases of shunt failure.

Cerebrovascular segmentation in phase-contrast magnetic resonance angiography by a Radon projection composition network.

Cerebrovascular segmentation based on phase-contrast magnetic resonance angiography (PC-MRA) provides patient-specific intracranial vascular structures for neurosurgery planning. However, the vascular complex topology and spatial sparsity make the task challenging. Inspired by the computed tomography reconstruction, this paper proposes a Radon Projection Composition Network (RPC-Net) for cerebrovascular segmentation in PC-MRA, aiming to enhance distribution probability of vessels and fully obtain the vascular topological information. Multi-directional Radon projections of the images are introduced and a two-stream network is used to learn the features of the 3D images and projections. The projection domain features are remapped to the 3D image domain by filtered back-projection transform to obtain the image-projection joint features for predicting vessel voxels. A four-fold cross-validation experiment was performed on a local dataset containing 128 PC-MRA scans. The average Dice similarity coefficient, precision and recall of the RPC-Net achieved 86.12%, 85.91% and 86.50%, respectively, while the average completeness and validity of the vessel structure were 85.50% and 92.38%, respectively. The proposed method outperformed the existing methods, especially with significant improvement on the extraction of small and low-intensity vessels. Moreover, the applicability of the segmentation for electrode trajectory planning was also validated. The results demonstrate that the RPC-Net realizes an accurate and complete cerebrovascular segmentation and has potential applications in assisting neurosurgery preoperative planning.

Visualizing Cerebral Small Vessel Degeneration During Aging and Diseases Using Magnetic Resonance Imaging.

Cerebral small vessel disease is a major contributor to brain disorders in older adults. It is associated with a much higher risk of stroke and dementia. Due to a lack of clinical and fluid biomarkers, diagnosing and grading small vessel disease are highly dependent on magnetic resonance imaging. In the past, researchers mostly used brain parenchymal imaging markers to represent small vessel damage, but the relationships between these surrogate markers and small vessel pathologies are complex. Recent progress in high-resolution magnetic resonance imaging methods, including time-of-flight MR angiography, phase-contrast MR angiography, black blood vessel wall imaging, susceptibility-weighted imaging, and contrast-enhanced methods, allow for direct visualization of cerebral small vessel structures. They could be powerful tools for understanding aging-related small vessel degeneration and improving disease diagnosis and treatment. This article will review progress in these imaging techniques and their application in aging and disease studies. Some challenges and future directions are also discussed. EVIDENCE LEVEL: 4. TECHNICAL EFFICACY: 3.

Intracranial arterial flow velocity mapping in quantitative time-of-flight MR angiography using deep machine learning

PurposeTo evaluate the application of deep machine learning (DML) to 3D quantitative time-of-flight (qTOF) magnetic resonance angiography (MRA) to measure blood flow velocity within the intracranial arteries. Materials and methodsIntracranial qTOF MRA was acquired in 15 subjects at 3 T. Blood flow velocity quantitation with qTOF MRA was done using a non-DML computer-vision procedure, and using convolutional DML neural networks. 3D phase contrast (PC) MRA was used as the comparator. Using PC velocity measures as the output target and qTOF two-echo source image data as inputs, DML neural networks were trained to predict component blood flow velocities. Total velocities and peak intracranial arterial blood flow velocities were computed from component velocities. ResultsCompared to non-DML image analysis, DML-based analysis of qTOF MRA image data improved agreement with PC for mean component velocity (intraclass correlation coefficient (ICC) = 0.966 versus 0.939), mean total velocity (ICC = 0.835 versus 0.723), and peak velocity (ICC = 0.816 versus 0.597), as well as narrowed the 95% Bland-Altman limits of agreement for mean component velocity ([−5.16, +4.31]cm/s versus [−6.86, +6.53]cm/s), mean total velocity ([−6.78,+3.59]cm/s versus [−9.39, +7.09]cm/s) and peak velocity ([−13.5,+10.2]cm/s versus [−21.3, +10.2]cm/s). Compared to non-DML analysis, DML image analysis reduced the root-mean-square deviation from PC velocity measures by 28%–36%, and shortened calculation times by 35-fold. ConclusionThe application of DML image analysis to intracranial qTOF MRA for velocity quantitation markedly shortened calculation times, substantially improved the agreement of component, total, and peak arterial blood flow velocities, and provided excellent agreement of hemodynamic measures with respect to 3D PC.

Use of Compressed Sensing Accelerated, Low-Velocity Encoded, Isotropic Resolution, Phase Contrast Magnetic Resonance Angiography for SEEG Electrode Implantation

We assessed the feasibility of using compressed sensing accelerated, low-velocity encoded, isotropic resolution phase contrast (CLIP) magnetic resonance angiography (MRA) for avascular trajectory planning of stereoelectroencephalography. Ten healthy subjects (1 woman and 9 men; age, 33.6 ± 9.0 years) and 20 consecutive patients (12 female patients; age, 22 ± 13.6 years) were enrolled in the present study. The healthy subjects underwent CLIP-MRA, and 3 other phase contrast MRA protocols with conventional parallel imaging (PI) acceleration, including low resolution with twofold PI (PI2), high resolution (HR) with fivefold PI (PI5), and HR-PI2. The patients underwent CLIP-MRA and computed tomography angiography (CTA). The image qualities were evaluated. The numbers and locations of trajectory-vessel conflict detected using CLIP-MRA were noted. With similar scan durations, CLIP-MRA achieved higher spatial resolution compared with low resolution with PI2 and detected significantly more branches compared with HR-PI5. With the same spatial resolution, the signal/noise and contrast/noise ratios of CLIP-MRA were higher than those with HR-PI2 with a shorter scan duration. For the 12 adult patients (10 female patients; 28.8 ± 12.7 years), CLIP-MRA had better signal/noise and contrast/noise ratios than CTA. The trajectory had required modification for 14 of the 20 patients (70%), with a proportion of trajectory modification of 10.7% (23 of 215 electrodes). The middle meningeal artery, cortical vessel, and skull vessel were the main vessels with conflict (n= 11, n= 7, and n= 5, respectively). In the present study, CLIP-MRA provided a clear cortical vascular display noninvasively without intravascular contrast and radiation. The middle meningeal artery and diploic and emissary veins were the main conflict vessels and could be clearly displayed using CLIP-MRA but not CTA.

Increase in Cerebral Blood Flow After Catheter Ablation of Atrial Fibrillation.

Recent studies have found that atrial fibrillation (AF) is a risk factor for cognitive impairment. Brain hypoperfusion is hypothesized as an underlying mechanism of cognitive decline in AF patients. This study sought to assess changes in cerebral blood flow (CBF) and brain volume after catheter ablation of AF. Patients undergoing catheter ablation of AF were enrolled in this prospective study. AF patients being treated with pharmaceuticals alone served as a control group. Brain magnetic resonance imaging was performed before and 6months after catheter ablation. CBF was assessed by 2-dimensional phase-contrast magnetic resonance angiography. Brain volume and bilateral hippocampal volume were measured using FreeSurfer software. Of the 57 study patients (age 64 ± 11 years; 45 men; paroxysmal AF: n=22; nonparoxysmal AF: n=35), 48patients were freed from tachyarrhythmia recurrence beyond a 3-month blanking period. Changes in CBF and brain perfusion over 6months were significantly greater in the study patients than control (CBF: 39.26 vs -34.86mL; P = 0.01, ANCOVA; brain perfusion: 3.78 vs -3.02mL/100mL/min; P = 0.009, ANCOVA), while changes in total brain volume and bilateral hippocampal volume were similar between 2 groups (total brain volume: 2.57 vs -2.15mL; P = 0.32, ANCOVA; bilateral hippocampal volume: 0.03 vs 0.04mL; P = 0.8, ANCOVA). Nonparoxysmal AF at baseline was an independent predictor of an increase in CBF of >32.6mL/min. Catheter ablation of AF has favorable effects on CBF, particularly in nonparoxysmal AF. Our results maypartially explain the association between cognitive decline and AF.

Changes in venous drainage after posterior cranial vault distraction and foramen magnum decompression in syndromic craniosynostosis.

The authors' objective was to measure the effect of posterior cranial vault distraction (PCVD) plus foramen magnum decompression (FMD) on dural sinus volume and venous flow in patients with syndromic craniosynostosis. The volumes of the sagittal, straight, transverse, and sigmoid sinuses of 5 consecutive patients with syndromic craniosynostosis who underwent PCVD+FMD were calculated in cubic centimeters with T2-weighted volumetric MRI sequences before surgery, immediately after surgery, and after the end of the distraction process. Tridimensional reconstructions of phase-contrast magnetic resonance angiography (PC-MRA) images were obtained with multiplanar reconstruction (MPR). The average total volume of all dural sinuses increased immediately after surgery (from 10.06 cm3 to 12.64 cm3) and continued to increase throughout the 30-day distraction period (from 12.64 cm3 to 14.71 cm3) (p = 0.04), except that the right sigmoid sinus remained stable after the initial increase. The most important increases were observed for the left transverse sinus (+113.2%), right transverse sinus (+104.3%), left sigmoid sinus (+91.3%), and sagittal sinus (+41.8%). Less important modifications were evident for the right sigmoid sinus (+33.7%) and straight sinus (+23.4%). Significant improvements in venous flow were noted on the tridimensional reconstructions of the PC-MRA images. Venous obstruction grading score improved in 4 patients (average [range] 2.4 [ 2-5]) (p = 0.023) and remained stable in 1 patient. All patients had chronic tonsillar herniation (CTH) (mean [range] 16.6 [8-26] mm), and 3 had syringomyelia. CTH showed improvement on the last follow-up MRI evaluation in 4 patients (mean [range] 10.5 [0-25] mm) and worsened from 15 mm to 19 mm in 1 patient. Syringomyelia improved in 2 patients and remained unchanged in 1. This study has provided the first radiological evidence of the impact of craniofacial surgery on dural sinus anatomy and venous drainage. The venous anomalies described in patients with syndromic craniosynostosis are not static, and PCVD+FMD triggers a dynamic process that can lead to significant modifications of intracranial venous drainage. The traction exerted by the distracted bone flap onto the occipitoparietal dura mater adherent to the inner calvaria may account for the enlargement of the dural sinus throughout the distraction period. The impact of these modifications on venous pressure, intracranial pressure, CTH, and hydrocephalus remains to be determined.

Cerebrovascular segmentation in phase-contrast magnetic resonance angiography by multi-feature fusion and vessel completion.

Phase-Contrast Magnetic Resonance Angiography (PC-MRA) is a potential way of cerebrovascular imaging, which can suppress non-vascular tissue while presenting vessels. But PC-MRA will bring much noise and is easy to result in partially broken vessels. Usually, deep learning is an effective way to quantify vessels. However, how to choose an appropriate deep learning model is an important and difficult issue. In this work, we adopted the Dempster-Shafer (DS) evidence theory to fuse multi-feature from different models. Also, the vessel thinning and completion method were proposed to fill in information of broken cerebrovascular in PC-MRA images. For quantitative analysis, we chose Precision (PRE), Recall (REC), and Dice Similarity Coefficient (DSC) as assessment metrics, and established U-Net, V-Net, and Dense-Net. The 22 subjects tested this method. Comparison with different fusion strategies and common deep learning models have confirmed the effectiveness of the proposed method. In addition, we scanned Contrast-Enhanced MRA (CE-MRA) for 12 patients to verify reliability of vessel completion. Experiments show that the completion vessel can improve the matching ratio with CE-MRA, which has clinical potential.

Investigation of Flow Changes in Intracranial Vascular Disease Models Constructed with MRA Images.

This study aimed to develop a magnetic resonance imaging (MRI)-compatible flow delivery system and individualized models of circle of Willis (CoW), which include 50% and 100% blockage in internal carotid artery (ICA50 and ICA100), and 100% blockage in vertebral artery (VA100). Images were obtained using 3D time-of-flight and phase-contrast magnetic resonance angiography (MRA) sequences, and changes in velocity and flow direction at CoW models were analyzed. For the ICA50 and VA100 models, the flow was similar to that of the normal model. For the ICA 50 model, it was found that 50% blockage did not affect cerebral blood flow. For the VA100 model, decreased flow in the posterior cerebral artery and a change to the flow direction in the posterior communicating artery were found. For the ICA100 model, particularly, decreased flow in the ipsilateral middle and anterior cerebral arteries and a change to the flow direction in the ipsilateral anterior cerebral artery of the CoW were found. These results demonstrated that the flow system with various CoW disease models tailored to individual characteristics could be used to predict stroke onset more quickly. For the ICA50 and VA100 models, the possibility of cerebral infarction was significantly lower. On the other hand, for the ICA100 model, there was a high possibility of decreased flow, which could lead to cerebral infarction.

Quantified flow and angioarchitecture show similar associations with hemorrhagic presentation of brain arteriovenous malformations

IntroductionThe purpose of our study was to elucidate the impact of brain arteriovenous malformation (BAVM) flow and wall shear stress (WSS) on angioarchitecture and to evaluate their association with hemorrhagic presentations. Materials and methodsForty-one patients with BAVMs were evaluated by phase-contrast MR angiography. Volume flow rate and WSS were quantified. Angioarchitectural features such as location, angiogenesis, venous stenosis, venous ectasia, venous phlebitis, venous rerouting, exclusive deep vein and venous sac were evaluated by two neuroradiologists. The correlation between BAVM flow and size was evaluated with Spearman correlation coefficients. Differences of size, flow, and WSS between the hemorrhagic and non-hemorrhagic groups, the seizure and non-seizure groups, and between the different groups based on angioarchitecture were evaluated with Mann-Whitney U tests. Accuracy in predicting hemorrhage was evaluated with receiver operating characteristic curves. ResultBAVM flow was highly correlated with volume (ρ = 0.77). Higher flow was more commonly associated with angiogenesis, venous ectasia, venous rerouting, and venous phlebitis. Flow and angioarchitecture showed similar efficacy in differentiating hemorrhagic from non-hemorrhagic BAVMs. WSS did not demonstrate differences across any clinical groups. ConclusionFlow quantification and angioarchitecture analysis of BAVMs showed similar efficacy as evaluated by associations with hemorrhagic presentation. High flow affects both arterial and venous angioarchitecture, reflecting the nature of low vascular resistance in BAVMs.

Blood Flow Analysis of the Great Saphenous Vein in the Su-Pine Position in Clinical Manifestations of Varicose Veins of Different Severities: Application of Phase-Contrast Magnetic Resonance Imaging Data.

The progression of clinical manifestations of lower-limb varicose veins remains unclear. This study investigated changes in lower-limb venous blood flow using phase-contrast magnetic resonance angiography. Data were collected on veins from 141 legs. We compared legs with and without varicose veins and related symptoms and examined varying levels of varicose vein symptom severity. Legs without varicose veins exhibited a lower absolute stroke volume (ASV, p < 0.01) and mean flux (MF, p = 0.03) for the great saphenous vein (GSV) compared with legs with symptomatic varicose veins. Legs with asymptomatic varicose veins exhibited lower MF for the GSV (p = 0.02) compared with legs with symptomatic varicose veins. Among legs with varicose veins, asymptomatic legs exhibited lower ASV (p = 0.03) and MF (p = 0.046) for the GSV compared with legs that exhibited skin changes or ulcers; however, no significant differences were observed between legs presenting with discomfort or edema and legs with skin changes or ulcers, and between legs presenting with discomfort or edema and asymptomatic legs. In conclusion, in the supine position, increased blood flow rate and blood flow volume in the GSV were associated with symptomatic varicose veins and increased symptom severity.

Intensity of arterial structure acquired by Silent MRA estimates cerebral blood flow

BackgroundCerebral blood flow (CBF) and the morphology of the cerebral arteries are important for characterizing cerebrovascular disease. Silent magnetic resonance angiography (Silent MRA) is a MRA technique focusing on arterial structural delineation. This study was conducted to investigate the correlation between Silent MRA and CBF quantification, which has not yet been reported.MethodsBoth the Silent MRA and time-of-flight magnetic resonance angiography scans were applied in seventeen healthy participants to acquire the arterial structure and to find arterial intensities. Phase-contrast MRA (PC-MRA) was then used to perform the quantitative CBF measurement of 13 cerebral arteries. Due to different dataset baseline signal level of Silent MRA, the signal intensities of the selected 13 cerebral arteries were normalized to the selected ROIs of bilateral internal carotid arteries. The normalized signal intensities were used to determine the relationship between Silent MRA and CBF.ResultsThe image intensity distribution of arterial regions generated by Silent MRA showed similar laminar shape as the phase distribution by PC-MRA (correlation coefficient > 0.62). Moreover, in both the results of individual and group-leveled analysis, the intensity value of arterial regions by Silent MRA showed positively correlation with the CBF by PC-MRA. The coefficient of determination (R2) of individual trends ranged from 0.242 to 0.956, and the R2 of group-leveled result was 0.550.ConclusionsThis study demonstrates that Silent MRA provides valuable CBF information despite arterial structure, rendering it a potential tool for screening for cerebrovascular disease.

Quantitative time-of-flight MR angiography for simultaneous luminal and hemodynamic evaluation of the intracranial arteries.

To report a quantitative time-of-flight (qTOF) MRA technique for simultaneous luminal and hemodynamic evaluation of the intracranial arteries. Implemented using a thin overlapping slab 3D stack-of-stars based 3-echo FLASH readout, qTOF was tested in a flow phantom and for imaging the intracranial arteries of 10 human subjects at 3 Tesla. Display of the intracranial arteries with qTOF was compared to resolution-matched and scan time-matched standard Cartesian 3D time-of-flight (TOF) MRA, whereas quantification of mean blood flow velocity with qTOF, done using a computer vision-based inter-echo image analysis procedure, was compared to 3D phase contrast MRA. Arterial-to-background contrast-to-noise ratio was measured, and intraclass correlation coefficient was used to evaluate agreement of flow velocities. For resolution-matched protocols of similar scan time, qTOF portrayed the intracranial arteries with good morphological correlation with standard Cartesian TOF, and both techniques provided superior contrast-to-noise ratio and arterial delineation compared to phase contrast (20.6 ± 3.0 and 37.8 ± 8.7 vs. 11.5 ± 2.2, P < .001, both comparisons). With respect to phase contrast, qTOF showed excellent agreement for measuring mean flow velocity in the flow phantom (intraclass correlation coefficient = 0.981, P < .001) and good agreement in the intracranial arteries (intraclass correlation coefficient = 0.700, P < .001). Stack-of-stars data sampling used with qTOF eliminated oblique in-plane flow misregistration artifacts that were seen with standard Cartesian TOF. qTOF is a new 3D MRA technique for simultaneous luminal and hemodynamic evaluation of the intracranial arteries that provides significantly greater contrast-to-noise ratio efficiency than phase contrast and eliminates misregistration artifacts from oblique in-plane blood flow that occur with standard 3D TOF.

Altered Blood Flow in the Ophthalmic and Internal Carotid Arteries in Patients with Age-Related Macular Degeneration Measured Using Noncontrast MR Angiography at 7T.

Age-related macular degeneration is associated with reduced perfusion of the eye; however, the role of altered blood flow in the upstream ophthalmic or internal carotid arteries is unclear. We used ultra-high-field MR imaging to investigate whether the diameter of and blood flow in the ophthalmic artery and/or the ICA are altered in age-related macular degeneration and whether any blood flow changes are associated with disease progression. Twenty-four patients with age-related macular degeneration and 13 similarly-aged healthy controls participated. TOF and high-resolution dynamic 2D phase-contrast MRA (0.26 × 0.26 × 2mm3, 100-ms effective sampling rate) was acquired at 7T. Vessel diameters were calculated from cross-sectional areas in phase-contrast acquisitions. Blood flow time-series were measured across the cardiac cycle. The ophthalmic artery vessel diameter was found to be significantly smaller in patients with age-related macular degeneration than in controls. Volumetric flow through the ophthalmic artery was significantly lower in patients with late age-related macular degeneration, with a significant trend of decreasing volumetric ophthalmic artery flow rates with increasing disease severity. The resistance index was significantly greater in patients with age-related macular degeneration than in controls in the ophthalmic artery. Flow velocity through the ophthalmic artery and ICA was significantly higher in patients with age-related macular degeneration. Ophthalmic artery blood flow as a percentage of ipsilateral ICA blood flow was nearly double in controls than in patients with age-related macular degeneration. These findings support the hypothesis that vascular changes upstream to the eye are associated with the severity of age-related macular degeneration. Additional investigation into the potential causality of this relationship and whether treatments that improve ocular circulation slow disease progression is warranted.