Ferumoxytol-enhanced MRI in the peripheral vasculature.

Ferumoxytol is a promising non-gadolinium-based contrast agent with numerous varied magnetic resonance imaging applications. Previous reviews of vascular applications have focused primarily on cardiac and aortic applications. After considering safety concerns and technical issues, the objective of this paper is to explore peripheral applications for ferumoxytol-enhanced magnetic resonance angiography (MRA) and venography (MRV) in the upper and lower extremities. Separate searches for each of the following keywords were performed in pubmed: "ferumoxytol," "ultrasmall superparamagnetic iron oxide," and "USPIO." All studies pertaining to MRA or MRV in humans are included in this review. Case-based examples of various peripheral applications are used to supplement a relatively scant literature in this space. Ferumoxytol's unique properties including high T1 relaxivity and prolonged intravascular half-life make it the optimal vascular imaging contrast agent on the market and one whose vast potential has only begun to be tapped.

Survey of the American Society of Neuroradiology Membership on the Use and Value of Intracranial Vessel Wall MRI.

BACKGROUND AND PURPOSE: Intracranial vessel wall MR imaging is an emerging technique for intracranial vasculopathy assessment. Our aim was to investigate intracranial vessel wall MR imaging use by the American Society of Neuroradiology (ASNR) members at their home institutions, including indications and barriers to implementation. MATERIALS AND METHODS: The ASNR Vessel Wall Imaging Study Group survey on vessel wall MR imaging use, frequency, applications, MR imaging systems and field strength used, protocol development approaches, vendor engagement, reasons for not using vessel wall MR imaging, ordering-provider interest, and impact on clinical care, was distributed to the ASNR membership between April 2 and August 30, 2019. RESULTS: There were 532 responses; 79 were excluded due to nonresponse and 42 due to redundant institutional responses, leaving 411 responses. Fifty-two percent indicated that their institution performs vessel wall MR imaging, with 71.5% performed at least 1-2 times/month, most frequently on 3T MR imaging, and 87.7% using 3D sequences. Protocols most commonly included were T1-weighted pre- and postcontrast and TOF-MRA; 60.6% had limited contributions from vendors or were still in protocol development. Vasculopathy differentiation (94.4%), cryptogenic stroke (41.3%), aneurysm (38.0%), and atherosclerosis (37.6%) evaluation were the most common indications. For those not performing vessel wall MR imaging, interpretation (53.1%) or technical (46.4%) expertise, knowledge of applications (50.5%), or limitations of clinician (56.7%) or radiologist (49.0%) interest were the most common reasons. If technical/expertise obstacles were overcome, 56.4% of those not performing vessel wall MR imaging indicated that they would perform it. Ordering providers most frequently inquiring about vessel wall MR imaging were from stroke neurology (56.5%) and neurosurgery (25.1%), while 34.3% indicated that no providers had inquired. CONCLUSIONS: More than 50% of neuroradiology groups use vessel wall MR imaging for intracranial vasculopathy characterization and differentiation, emphasizing the need for additional technical and educational support, especially as clinical vessel wall MR imaging implementation continues to grow.

Survey of the American Society of Neuroradiology Membership on the Use and Value of Extracranial Carotid Vessel Wall MRI.

BACKGROUND AND PURPOSE: Extracranial vessel wall MRI (EC-VWI) contributes to vasculopathy characterization. This survey study investigated EC-VWI adoption by American Society of Neuroradiology (ASNR) members and indications and barriers to implementation. MATERIALS AND METHODS: The ASNR Vessel Wall Imaging Study Group survey on EC-VWI use, frequency, applications, MR imaging systems and field strength used, protocol development approaches, vendor engagement, reasons for not using EC-VWI, ordering provider interest, and impact on clinical care was distributed to the ASNR membership between April 2, 2019, to August 30, 2019. RESULTS: There were 532 responses; 79 were excluded due to minimal, incomplete response and 42 due to redundant institutional responses, leaving 411 responses. Twenty-six percent indicated that their institution performed EC-VWI, with 66.3% performing it ≤1-2 times per month, most frequently on 3T MR imaging, with most using combined 3D and 2D protocols. Protocols most commonly included pre- and postcontrast T1-weighted imaging, TOF-MRA, and contrast-enhanced MRA. Inflammatory vasculopathy (63.3%), plaque vulnerability assessments (61.1%), intraplaque hemorrhage (61.1%), and dissection-detection/characterization (51.1%) were the most frequent applications. For those not performing EC-VWI, the reasons were a lack of ordering provider interest (63.9%), lack of radiologist time/interest (47.5%) or technical support (41.4%) for protocol development, and limited interpretation experience (44.9%) and knowledge of clinical applications (43.7%). Reasons given by 46.9% were that no providers approached radiology with interest in EC-VWI. If barriers were overcome, 51.1% of those not performing EC-VWI indicated they would perform it, and 40.6% were unsure; 48.6% did not think that EC-VWI had impacted patient management at their institution. CONCLUSIONS: Only 26% of neuroradiology groups performed EC-VWI, most commonly due to limited clinician interest. Improved provider and radiologist education, protocols, processing techniques, technical support, and validation trials could increase adoption.

A Volumetric Metric for Monitoring Intracranial Aneurysms: Repeatability and Growth Criteria in a Longitudinal MR Imaging Study.

BACKGROUND AND PURPOSE: The reliability of contrast-enhanced MRA in monitoring serial volumetric changes of unruptured intracranial aneurysms has not been established. We aimed to determine the coefficient of variance of contrast-enhanced MRA in measuring aneurysm volumes, thus establishing criteria for aneurysm growth and permitting identification of variables predictive of growth. MATERIALS AND METHODS: Aneurysm volumes were measured from serial contrast-enhanced MRA studies of patients with untreated intracranial aneurysms who underwent >2 sequential MR imaging evaluations. After coregistering all sequential studies in 3D space for each aneurysm and signal intensity normalization, aneurysm volume was determined across all time points. A linear mixed effects model was built to estimate the coefficient of variance of the measurement as well as to determine predictive variables. Growth was defined as relative growth exceeding 2 times the measurement coefficient of variance (sudden growth, as 4 times the coefficient of variance). RESULTS: A total of 95 patients with 112 aneurysms were included (5.9 scans during 4.0 years on average, 616 scan measurements in total). The coefficient of variance was 5.5% of the aneurysm volume, and the relative growth rate was dependent on the location: anterior cerebral artery, 4.52% per year; vertebral artery, 2.46% per year; middle cerebral artery, 2.74% per year; basilar artery, 2.36% per year; internal carotid artery, 1.14% per year. Thirty-six of 112 (32%) aneurysms were characterized as growing, and 11/36 of them had an episode of sudden growth. CONCLUSIONS: Volume measurement of unruptured intracranial aneurysms by contrast-enhanced MRA seems a reliable metric for tracking the growth trajectory of aneurysms. Furthermore, the aneurysm growth rate differs among different locations.

Roadmap Consensus on Carotid Artery Plaque Imaging and Impact on Therapy Strategies and Guidelines: An International, Multispecialty, Expert Review and Position Statement.

Current guidelines for primary and secondary prevention of stroke in patients with carotid atherosclerosis are based on the quantification of the degree of stenosis and symptom status. Recent publications have demonstrated that plaque morphology and composition, independent of the degree of stenosis, are important in the risk stratification of carotid atherosclerotic disease. This finding raises the question as to whether current guidelines are adequate or if they should be updated with new evidence, including imaging for plaque phenotyping, risk stratification, and clinical decision-making in addition to the degree of stenosis. To further this discussion, this roadmap consensus article defines the limits of luminal imaging and highlights the current evidence supporting the role of plaque imaging. Furthermore, we identify gaps in current knowledge and suggest steps to generate high-quality evidence, to add relevant information to guidelines currently based on the quantification of stenosis.

Modern meningioma imaging techniques.

Steady improvements in imaging modalities have enabled a new realm of capabilities in the identification and assessment of meningiomas. The cross-sectional imaging modalities, MRI and CT, have improved in resolution and fidelity. These modalites now provide not only improved structural information but also insights into functional behavior. MRI has, in particular, proven to have powerful capabilities in evaluating meningiomas because of the ability to assess soft tissue characteristics such as diffusion and vascular supply information, such as perfusion. Recent investigational advances have also been made using a combination of X-ray fluoroscopy for selective catheterization followed by MR perfusion measurement performed with intra-arterial injection of contrast. Together all these modalities provide the radiographer with powerful capabilities for evaluating meningiomas.

Perfusion-CT of developmental venous anomalies: typical and atypical hemodynamic patterns.

This article reports perfusion-CT patterns that can be observed in patients with DVAs. In atypical DVAs, an abnormal venous congestion pattern with increased CBV, CBF and MTT can be observed in the vicinity of a DVA, and needs to be recognized and differentiated from other entities such as cerebral neoplasms or stroke. This pattern might help to stratify risks of associated complications such as hemorrhage.

[State of the art: high resolution MR imaging of carotid atherosclerotic plaque]. / Mise au point sur l'IRM haute résolution de la plaque carotidienne.

A third of cerebrovascular accidents are a complication from carotid artery plaque. In addition to the degree of stenosis, plaque composition and morphology are key elements in determining the probability of complication from the atherosclerotic plaque. High resolution MRI can characterize plaque composition and morphology and therefore help identify unstable plaque. The purpose of this review is to summarize recent concepts on unstable plaque and underlying inflammation. The signal characteristics of the different components of plaque on high resolution MRI then be reviewed. Finally, current morphological and functional criteria for unstable plaque will be discussed.

Multidetector computed tomography for characterization of calcium deposits in reperfused myocardial infarction.

BACKGROUND: Calcium overload is a major cause of reperfusion myocardial injury. Multidetector computed tomography (MDCT) has been previously used in visualizing coronary artery calcium, but not calcium deposits in reperfused infarction. PURPOSE: To assess the ability of MDCT to 1) noninvasively visualize and characterize calcium deposits in reperfused infarcts, and 2) monitor regional wall swelling, regional systolic wall thickening, and infarct resorption. MATERIAL AND METHODS: Reperfused myocardial infarcts were created in seven pigs by 2-hour occlusion of the left anterior descending coronary artery (LAD) after coronary catheterization. A 64-slice MDCT scanner was used for non-contrast images to depict calcium deposits. Furthermore, cine and delayed contrast-enhanced (DE) MDCT imaging were acquired to assess the chronological changes (2-4 hours, 1 week, and 8 weeks) in regional wall swelling, systolic wall thickening, and infarct size. RESULTS: Non-contrast MDCT images depicted calcium deposits as "hot-spots." Attenuation of calcium deposits was greater (89+/-6 Hounsfield units [HU]) than remote myocardium (36+/-3 HU; P<0.05). Calcium deposits were not evident at 2-4 hours and were substantially smaller at 8 weeks compared to 1 week. Correlations were found between the extent of calcium deposits, ejection fraction (R=0.81), and infarction size (R=0.70). Cine MCDT images demonstrated transient wall swelling (edema formation and resorption) at 2-4 hours and differences in regional systolic wall thickening among infarcted, peri-infarcted, and remote myocardium. Calcium-specific von Kossa stain confirmed the presence of calcium deposits in infarcted myocardium. CONCLUSION: 64-slice MDCT has the potential to demonstrate the progression and regression of calcium deposits, interstitial edema, and infarction. The presence of calcium deposits was transient and associated with reperfused recent infarction. The extent of calcium deposits was positively correlated with infarction size and negatively with global left-ventricular function.

Surveillance of Unruptured Intracranial Saccular Aneurysms Using Noncontrast 3D-Black-Blood MRI: Comparison of 3D-TOF and Contrast-Enhanced MRA with 3D-DSA.

BACKGROUND AND PURPOSE: Patients with unruptured intracranial aneurysms routinely undergo surveillance imaging to monitor growth. Angiography is the criterion standard for aneurysm diagnosis, but it is invasive. This study aimed to evaluate the accuracy and reproducibility of a 3D noncontrast black-blood MR imaging technique for unruptured intracranial aneurysm measurement in comparison with 3D-TOF and contrast-enhanced MRA, using 3D rotational angiography as a reference standard. MATERIALS AND METHODS: Sixty-four patients (57.3 ± 10.9 years of age, 41 women) with 68 saccular unruptured intracranial aneurysms were recruited. Patients underwent 3T MR imaging with 3D-TOF-MRA, 3D black-blood MR imaging, and contrast-enhanced MRA, and they underwent 3D rotational angiography within 2 weeks. The neck, width, and height of the unruptured intracranial aneurysms were measured by 2 radiologists independently on 3D rotational angiography and 3 MR imaging sequences. The accuracy and reproducibility were evaluated by Bland-Altman plots, the coefficient of variance, and the intraclass correlation coefficient. RESULTS: 3D black-blood MR imaging demonstrates the best agreement with DSA, with the smallest limits of agreement and measurement error (coefficients of variance range, 5.87%-7.04%). 3D-TOF-MRA had the largest limits of agreement and measurement error (coefficients of variance range, 12.73%-15.78%). The average coefficient of variance was 6.26% for 3D black-blood MR imaging, 7.03% for contrast-enhanced MRA, and 15.54% for TOF-MRA. No bias was found among 3 MR imaging sequences compared with 3D rotational angiography. All 3 MR imaging sequences had excellent interreader agreement (intraclass correlation coefficient, >0.95). 3D black-blood MR imaging performed the best for patients with intraluminal thrombus (n = 10). CONCLUSIONS: 3D black-blood MR imaging achieves better accuracy for aneurysm size measurements compared with 3D-TOF, using 3D rotational angiography as a criterion standard. This noncontrast technique is promising for surveillance of unruptured intracranial aneurysms.

Reduced Jet Velocity in Venous Flow after CSF Drainage: Assessing Hemodynamic Causes of Pulsatile Tinnitus.

BACKGROUND AND PURPOSE: Idiopathic intracranial hypertension is commonly associated with transverse sinus stenosis, a venous cause of pulsatile tinnitus. In patients with idiopathic intracranial hypertension, CSF drainage via lumbar puncture decreases intracranial pressure, which relieves the stenosis, and may provide at least temporary cessation of pulsatile tinnitus. The objective of this study was to evaluate changes in venous blood flow caused by lowered intracranial pressure in patients with pulsatile tinnitus to help identify the cause of pulsatile tinnitus. MATERIALS AND METHODS: Ten patients with suspected transverse sinus stenosis as a venous etiology for pulsatile tinnitus symptoms underwent MR imaging before and after lumbar puncture in the same session. The protocol included flow assessment and rating of pulsatile tinnitus intensity before and after lumbar puncture and MR venography before lumbar puncture. Post-lumbar puncture MR venography was performed in 1 subject. RESULTS: There was a lumbar puncture-induced reduction in venous peak velocity that correlated with the opening pressure (r = -0.72, P = .019) without a concomitant reduction in flow rate. Patients with flow jets had their peak velocity reduced by 0.30 ± 0.18 m/s (P = .002), correlating with a reduction in CSF pressure (r = 0.82, P = .024) and the reduction in subjectively scored pulsatile tinnitus intensity (r = 0.78, P = .023). The post-lumbar puncture MR venography demonstrated alleviation of the stenosis. CONCLUSIONS: Our results show a lumbar puncture-induced reduction in venous peak velocity without a concomitant reduction in flow rate. We hypothesize that the reduction is caused by the expansion of the stenosis after lumbar puncture. Our results further show a correlation between the peak velocity and pulsatile tinnitus intensity, suggesting the flow jet to be instrumental in the development of sound.

MR Venous Flow in Sigmoid Sinus Diverticulum.

BACKGROUND AND PURPOSE: Case reports demonstrate that coiling of a sigmoid sinus diverticulum can treat pulsatile tinnitus. We hypothesized that MR imaging 4D flow and computational fluid dynamics would reveal distinct blood flow patterns in the venous outflow tract in these patients. MATERIALS AND METHODS: Patients with pulsatile tinnitus of suspected venous etiology underwent MR imaging at 3T, using venous phase contrast-enhanced MR angiography, 4D flow, and 2D phase contrast. The contrast-enhanced MRA contours were evaluated to determine the presence and extent of a sigmoid sinus diverticulum. Computational fluid dynamics analysis was performed using the 4D flow inlet flow and the luminal contours from contrast-enhanced MRA as boundary conditions. In addition, computational fluid dynamics was performed for the expected post treatment conditions by smoothing the venous geometry to exclude the sigmoid sinus diverticulum from the anatomic boundary conditions. Streamlines were generated from the 4D flow and computational fluid dynamics velocity maps, and flow patterns were examined for the presence of rotational components. RESULTS: Twenty-five patients with pulsatile tinnitus of suspected venous etiology and 10 control subjects were enrolled. Five (20%) of the symptomatic subjects had sigmoid sinus diverticula, all associated with an upstream stenosis. In each of these patients, but none of the controls, a stenosis-related flow jet was directed toward the opening of the sigmoid sinus diverticulum with rotational flow patterns in the sigmoid sinus diverticulum and parent sigmoid sinus on both 4D flow and computational fluid dynamics. CONCLUSIONS: Consistent patterns of blood flow can be visualized in a sigmoid sinus diverticulum and the parent sinus using 4D flow and computational fluid dynamics. Strong components of rotational blood flow were seen in subjects with sigmoid sinus diverticula that were absent in controls.

Clinical Significance of Intraplaque Hemorrhage in Low- and High-Grade Basilar Artery Stenosis on High-Resolution MRI.

BACKGROUND AND PURPOSE: Intraplaque hemorrhage within intracranial atherosclerotic plaques identified by high-resolution MR imaging has been studied as a potential marker of stroke risk. However, previous studies only examined intracranial arteries with high-grade stenosis (degree of stenosis, >50%). This study aimed to ascertain the clinical relevance of intraplaque hemorrhage in patients with low- and high-grade stenotic basilar artery plaques. MATERIALS AND METHODS: Patients with basilar artery stenosis (n = 126; mean age, 62 ± 10 years; 66 symptomatic and 60 asymptomatic) underwent high-resolution MR imaging. The relationship between imaging findings (intraplaque hemorrhage, contrast enhancement, degree of stenosis, minimal lumen area, and plaque burden) and symptoms was analyzed. RESULTS: Intraplaque hemorrhage was identified in 22 patients (17.5%), including 21 (31.8%) symptomatic patients and 1 (1.7%) asymptomatic patient. Multivariate analysis showed that intraplaque hemorrhage was the strongest independent marker of symptomatic status (odds ratio, 27.5; 95% CI, 3.4-221.5; P = .002). Contrast enhancement was also independently associated with symptomatic status (odds ratio, 9.9; 95% CI, 1.5-23.6; P = .016). Stenosis, minimal lumen area, and plaque burden were not correlated with symptoms (P > .05). Intraplaque hemorrhage was present in both low- and high-grade stenotic basilar arteries (11.3% versus 16.3%, P = .63). Diagnostic performance values of intraplaque hemorrhage for patients with acute/subacute symptomatic stroke were the following: specificity, 98.3%; sensitivity, 31.8%; positive predictive value, 95.5%; and negative predictive value, 56.7%. CONCLUSIONS: Intraplaque hemorrhage is present in both low- and high-grade stenotic basilar artery plaques and is independently associated with symptomatic stroke status. Intraplaque hemorrhage may identify high-risk plaque and provide new insight into the management of patient with stroke without significant stenosis.

Carotid Artery Wall Imaging: Perspective and Guidelines from the ASNR Vessel Wall Imaging Study Group and Expert Consensus Recommendations of the American Society of Neuroradiology.

Identification of carotid artery atherosclerosis is conventionally based on measurements of luminal stenosis and surface irregularities using in vivo imaging techniques including sonography, CT and MR angiography, and digital subtraction angiography. However, histopathologic studies demonstrate considerable differences between plaques with identical degrees of stenosis and indicate that certain plaque features are associated with increased risk for ischemic events. The ability to look beyond the lumen using highly developed vessel wall imaging methods to identify plaque vulnerable to disruption has prompted an active debate as to whether a paradigm shift is needed to move away from relying on measurements of luminal stenosis for gauging the risk of ischemic injury. Further evaluation in randomized clinical trials will help to better define the exact role of plaque imaging in clinical decision-making. However, current carotid vessel wall imaging techniques can be informative. The goal of this article is to present the perspective of the ASNR Vessel Wall Imaging Study Group as it relates to the current status of arterial wall imaging in carotid artery disease.

Assessment of vasculature of meningiomas and the effects of embolization with intra-arterial MR perfusion imaging: a feasibility study.

BACKGROUND AND PURPOSE: Embolization of meningiomas has emerged as a preoperative adjuvant therapy that has proved effective in mitigating blood loss during surgical resection. Arterial supply to these tumors is typically identified by diffuse areas of parenchymal staining after selective x-ray angiograms. We investigate the benefits that selective injection of MR contrast may have in identifying vascular territories and determining the effects of embolization therapy. MATERIALS AND METHODS: Selective intra-arterial (IA) injection of dilute MR contrast media was used to assess the vascular distribution territories of meningeal tumors before and after embolization therapy. Regions of the tumor that experienced loss of signal intensity after localized contrast injections into the external and common carotid as well as vertebral arteries were used to quantify the specific vessel's volume of distribution. Assessments were made before and after embolization to reveal changes in the vascular supply of the tumor. MR findings were compared with radiographic evaluation of tumor vascular supply on the basis of conventional x-ray angiography. RESULTS: MR proved to be an excellent means to assess tissue fed by selected arteries and clearly demonstrated the treated and untreated portions of the neoplasm after therapy. In some instances, MR revealed postembolization residual enhancement of the tumor that was difficult to appreciate on x-ray angiograms. Very low contrast dose was necessary, which made repeated assessment during therapy practical. CONCLUSION: MR perfusion imaging with selective IA injection of dilute contrast can reveal the distribution territory of vessels. Changes in tumor vasculature could be detected after embolization, which reveal the volumetric fraction of the tumor affected by the therapy.

Identification and Quantitative Assessment of Different Components of Intracranial Atherosclerotic Plaque by Ex Vivo 3T High-Resolution Multicontrast MRI.

BACKGROUND AND PURPOSE: High-resolution 3T MR imaging can visualize intracranial atherosclerotic plaque. However, histologic validation is still lacking. This study aimed to evaluate the ability of 3T MR imaging to identify and quantitatively assess intracranial atherosclerotic plaque components ex vivo with histologic validation. MATERIALS AND METHODS: Fifty-three intracranial arterial specimens with atherosclerotic plaques from 20 cadavers were imaged by 3T MR imaging with T1, T2, and proton-density-weighted FSE and STIR sequences. The signal characteristics and areas of fibrous cap, lipid core, calcification, fibrous tissue, and healthy vessel wall were recorded on MR images and compared with histology. Fibrous cap thickness and maximum wall thickness were also quantified. The percentage of areas of the main plaque components, the ratio of fibrous cap thickness to maximum wall thickness, and plaque burden were calculated and compared. RESULTS: The signal intensity of the lipid core was significantly lower than that of the fibrous cap on T2-weighted, proton-density, and STIR sequences (P < .01) and was comparable on T1-weighted sequences (P = 1.00). Optimal contrast between the lipid core and fibrous cap was found on T2-weighted images. Plaque component mean percentages were comparable between MR imaging and histology: fibrous component (81.86% ± 10.59% versus 81.87% ± 11.59%, P = .999), lipid core (19.51% ± 10.76% versus 19.86% ± 11.56%, P = .863), and fibrous cap (31.10% ± 11.28% versus 30.83% ± 8.51%, P = .463). However, MR imaging overestimated mean calcification (9.68% ± 5.21% versus 8.83% ± 5.67%, P = .030) and plaque burden (65.18% ± 9.01% versus 52.71% ± 14.58%, P < .001). CONCLUSIONS: Ex vivo 3T MR imaging can accurately identify and quantitatively assess intracranial atherosclerotic plaque components, providing a direct reference for in vivo intracranial plaque imaging.

Intracranial Vessel Wall MRI: Principles and Expert Consensus Recommendations of the American Society of Neuroradiology.

Intracranial vessel wall MR imaging is an adjunct to conventional angiographic imaging with CTA, MRA, or DSA. The technique has multiple potential uses in the context of ischemic stroke and intracranial hemorrhage. There remain gaps in our understanding of intracranial vessel wall MR imaging findings and research is ongoing, but the technique is already used on a clinical basis at many centers. This article, on behalf of the Vessel Wall Imaging Study Group of the American Society of Neuroradiology, provides expert consensus recommendations for current clinical practice.

Computational modeling of flow-altering surgeries in basilar aneurysms.

In cases where surgeons consider different interventional options for flow alterations in the setting of pathological basilar artery hemodynamics, a virtual model demonstrating the flow fields resulting from each of these options can assist in making clinical decisions. In this study, image-based computational fluid dynamics (CFD) models were used to simulate the flow in four basilar artery aneurysms in order to evaluate postoperative hemodynamics that would result from flow-altering interventions. Patient-specific geometries were constructed using MR angiography and velocimetry data. CFD simulations carried out for the preoperative flow conditions were compared to in vivo phase-contrast MRI measurements (4D Flow MRI) acquired prior to the interventions. The models were then modified according to the procedures considered for each patient. Numerical simulations of the flow and virtual contrast transport were carried out in each case in order to assess postoperative flow fields and estimate the likelihood of intra-aneurysmal thrombus deposition following the procedures. Postoperative imaging data, when available, were used to validate computational predictions. In two cases, where the aneurysms involved vital pontine perforator arteries branching from the basilar artery, idealized geometries of these vessels were incorporated into the CFD models. The effect of interventions on the flow through the perforators was evaluated by simulating the transport of contrast in these vessels. The computational results were in close agreement with the MR imaging data. In some cases, CFD simulations could help determine which of the surgical options was likely to reduce the flow into the aneurysm while preserving the flow through the basilar trunk. The study demonstrated that image-based computational modeling can provide guidance to clinicians by indicating possible outcome complications and indicating expected success potential for ameliorating pathological aneurysmal flow, prior to a procedure.

Structure of plaque at carotid bifurcation: high-resolution MRI with histological correlation.

BACKGROUND AND PURPOSE: The composition of carotid atherosclerosis was visualized by using 3D MRI at high resolution with 200-micrometer (3) voxels. Magnetic resonance signal characteristics were correlated with plaque components, including collagenous cap, necrotic core, and calcification, to define resolution and other requirements for future clinical carotid MRI. METHODS: Twenty-one en bloc carotid endarterectomy specimens were imaged ex vivo by 3D gradient-echo MRI by using a 1.5-T clinical scanner with repetition time, echo time, and flip angle of 40 ms, 18 ms, and 20 degrees, respectively. Plaques were placed in Gd-saline and imaged in a solenoid radiofrequency coil. For quantitative tissue-specific signal analysis, techniques were developed to match tissue sections analyzed by MRI and histology. RESULTS: Three-dimensional imaging resolved complex morphological features not visualized by density- or T(2)-weighted 2D spin-echo imaging. The collagenous cap, necrotic core, and areas of focal calcification showed differing signal characteristics: mean contrast-to-noise ratio for cap versus underlying core was 20. The signal distributions for media and necrotic core overlapped but were resolvable in most specimens. The signal from thrombus was variable. CONCLUSIONS: En bloc specimens provide a useful model for studying plaque MRI. By use of isotropic submillimeter resolution, the collagenous cap and underlying necrotic core typically can be distinguished, and calcification can be identified. Thrombus displays a wide variation in signal intensity. The techniques presented could facilitate future clinicohistological correlation studies for atherosclerotic plaque MRI.

Determinants of image appearance in contrast-enhanced magnetic resonance angiography. A review.

The use of contrast agents in magnetic resonance (MR) studies of vascular pathology has permitted the exploration of regions that were heretofore poorly evaluated with conventional magnetic resonance angiography (MRA). An important feature of contrast-enhanced MRA (CE-MRA) is the very short acquisition times that are possible. The determination of the parameters to be used in a CE-MRA study rests on an understanding of the dynamics of the passage of the injected contrast agent and the response of the magnetization to the parameters of the MR imaging sequence. An overview of this interaction is presented.