Huston, John

Carotid artery stenosis is a well-established risk factor of ischemic stroke, contributing to up to 10%-20% of strokes or transient ischemic attacks. Many clinical trials over the last 20 years have used measurements of carotid artery stenosis as a means to risk stratify patients. However, with improvements in vascular imaging techniques such as CT angiography and MR angiography, ultrasonography, and PET/CT, it is now possible to risk stratify patients, not just on the degree of carotid artery stenosis but also on how vulnerable the plaque is to rupture, resulting in ischemic stroke. These imaging techniques are ushering in an emerging paradigm shift that allows for risk stratifications based on the presence of imaging features such as intraplaque hemorrhage (IPH), plaque ulceration, plaque neovascularity, fibrous cap thickness, and presence of a lipid-rich necrotic core (LRNC). It is important for the neurosurgeon to be aware of these new imaging techniques that allow for improved patient risk stratification and outcomes. For example, a patient with a low-grade stenosis but an ulcerated plaque may benefit more from a revascularization procedure than a patient with a stable 70% asymptomatic stenosis with a thick fibrous cap. This review summarizes the current state-of-the-art advances in carotid plaque imaging. Currently, MRI is the gold standard in carotid plaque imaging, with its high resolution and high sensitivity for identifying IPH, ulceration, LRNC, and inflammation. However, MRI is limited due to time constraints. CT also allows for high-resolution imaging and can accurately detect ulceration and calcification, but cannot reliably differentiate LRNC from IPH. PET/CT is an effective technique to identify active inflammation within the plaque, but it does not allow for assessment of anatomy, ulceration, IPH, or LRNC. Ultrasonography, with the aid of contrast enhancement, is a cost-effective technique to assess plaque morphology and characteristics, but it is limited in sensitivity and specificity for detecting LRNC, plaque hemorrhage, and ulceration compared with MRI. Also summarized is how these advanced imaging techniques are being used in clinical practice to risk stratify patients with low- and high-grade carotid artery stenosis. For example, identification of IPH on MRI in patients with low-grade carotid artery stenosis is a risk factor for failure of medical therapy, and studies have shown that such patients may fair better with carotid endarterectomy (CEA). MR plaque imaging has also been found to be useful in identifying revascularization candidates who would be better candidates for CEA than carotid artery stenting (CAS), as high intraplaque signal on time of flight imaging is associated with vulnerable plaque and increased rates of adverse events in patients undergoing CAS but not CEA.

PurposeTo describe how integrated gradient nonlinearity (GNL) correction can be used within noniterative partial Fourier (homodyne) and parallel (SENSE and GRAPPA) MR image reconstruction strategies, and demonstrate that performing GNL correction during, rather than after, these routines mitigates the image blurring and resolution loss caused by postreconstruction image domain based GNL correction.MethodsStarting from partial Fourier and parallel magnetic resonance imaging signal models that explicitly account for GNL, noniterative image reconstruction strategies for each accelerated acquisition technique are derived under the same core mathematical assumptions as their standard counterparts. A series of phantom and in vivo experiments on retrospectively undersampled data were performed to investigate the spatial resolution benefit of integrated GNL correction over conventional postreconstruction correction.ResultsPhantom and in vivo results demonstrate that the integrated GNL correction reduces the image blurring introduced by the conventional GNL correction, while still correcting GNL‐induced coarse‐scale geometrical distortion. Images generated from undersampled data using the proposed integrated GNL strategies offer superior depiction of fine image detail, for example, phantom resolution inserts and anatomical tissue boundaries.ConclusionNoniterative partial Fourier and parallel imaging reconstruction methods with integrated GNL correction reduce the resolution loss that occurs during conventional postreconstruction GNL correction while preserving the computational efficiency of standard reconstruction techniques. Magn Reson Med 75:2534–2544, 2016. © 2015 Wiley Periodicals, Inc.

We sought to obtain high resolution 3D contrast-enhanced MR angiograms of the carotid arteries, vertebral arteries and aortic arch with venous signal suppression utilizing novel timing techniques. A secondary purpose was to compare contrast-enhanced MR angiograms with 2D time-of-flight MR angiograms of the carotid arteries.

Objective To describe the treatment and outcomes of patients with primary central nervous system (CNS) vasculitis. Methods We retrospectively studied a cohort of 163 consecutive patients with primary CNS vasculitis who were seen at the Mayo Clinic over a 29‐year period. We analyzed treatments, treatment responses, and factors predictive of outcomes. Results A favorable response was observed in 85% of patients treated with prednisone alone and in 80% of patients treated with prednisone and cyclophosphamide. Relapses were observed in 27% of patients, and 25% of patients had discontinued therapy by the time of the last followup visit. Treatment with prednisone alone was associated with more frequent relapses (odds ratio [OR] 2.90), while large vessel involvement (OR 6.14) and cerebral infarcts at the time of diagnosis (OR 3.32) were associated with a poor response to treatment. Prominent gadolinium‐enhanced cerebral lesions or meninges were linked with continued treatment at the last followup encounter (OR 2.28). Higher disability scores at the last followup visit were associated with increasing age at the time of diagnosis (OR 1.44) and cerebral infarctions (OR 3.74), while lower disability scores were associated with gadolinium‐enhanced cerebral lesions or meninges (OR 0.35) and cerebral amyloid angiopathy (OR 0.24). Increased mortality was associated with increasing age at diagnosis (hazard ratio [HR] 1.39), diagnosis by angiography (HR 3.28), cerebral infarction (HR 4.44), and large vessel involvement (HR 4.98), while reduced mortality was associated with gadolinium‐enhanced cerebral lesions or meninges (HR 0.20). Conclusion The majority of patients with primary CNS vasculitis responded to treatment. Recognition of findings at diagnosis that predict the course or outcome may aid in decision‐making regarding therapy.

Objective Several definitions have been proposed to distinguish the daughter sac when treating unruptured intracranial aneurysms. The aim of this study was to evaluate interobserver variability of aneurysm morphology, including the daughter sac, using criteria from the International Study of Unruptured Intracranial Aneurysms (ISUIA) and the Unruptured Cerebral Aneurysm Study of Japan (UCAS). Materials and methods After approval by the institutional review board, we analyzed three morphological features (daughter sac, lobulation, and irregular margin) from the ISUIA and UCAS using angiographic images from 102 saccular aneurysms. Four independent readers interpreted each morphological criterion using dichotomized scales (existence or not). The κ statistic was used to measure interobserver agreement, and κ>0.6 was considered substantial agreement. Results For discrimination of the daughter sac, interobserver agreement among the four readers was substantial using the UCAS criteria (k=0.626 for two-dimensional (2D) and 0.659 for three-dimensional (3D) images) but not for the ISUIA criteria (k=0.487 for 2D and 0.473 for 3D images; significant difference). Irrespective of the images used, pairwise pooled κ values for the UCAS were >0.6, except for one case (score of 0.54 between readers A and B). Regarding the proportion of positive reads, there was a significant difference between reads for the daughter sac using the UCAS and ISUIA criteria. Conclusions For discrimination of the daughter sac, the UCAS definition showed a higher reliability than the ISUIA. However, a further prospective study is necessary to validate this definition as the treatment standard for unruptured intracranial aneurysms.

PurposeTo describe a model‐based reconstruction strategy for routine magnetic resonance imaging that accounts for gradient nonlinearity (GNL) during rather than after transformation to the image domain, and demonstrate that this approach reduces the spatial resolution loss that occurs during strictly image‐domain GNL‐correction.MethodsAfter reviewing conventional GNL‐correction methods, we propose a generic signal model for GNL‐affected magnetic resonance imaging acquisitions, discuss how it incorporates into contemporary image reconstruction platforms, and describe efficient nonuniform fast Fourier transform‐based computational routines for these. The impact of GNL‐correction on spatial resolution by the conventional and proposed approaches is investigated on phantom data acquired at varying offsets from gradient isocenter, as well as on fully sampled and (retrospectively) undersampled in vivo acquisitions.ResultsPhantom results demonstrate that resolution loss that occurs during GNL‐correction is significantly less for the proposed strategy than for the standard approach at distances >10 cm from isocenter with a 35 cm field‐of‐view gradient coil. The in vivo results suggest that the proposed strategy better preserves fine anatomical detail than retrospective GNL‐correction while offering comparable geometric correction.ConclusionAccounting for GNL during image reconstruction allows geometric distortion to be corrected with less spatial resolution loss than is typically observed with the conventional image domain correction strategy. Magn Reson Med 74:1019–1031, 2015. © 2014 Wiley Periodicals, Inc.

Object The aim of this study was to determine age-related differences in short-term (1-year) outcomes in patients with unruptured intracranial aneurysms (UIAs). Methods Four thousand fifty-nine patients prospectively enrolled in the International Study of Unruptured Intracranial Aneurysms were categorized into 3 groups by age at enrollment: < 50, 50–65, and > 65 years old. Outcomes assessed at 1 year included aneurysm rupture rates, combined morbidity and mortality from aneurysm procedure or hemorrhage, and all-cause mortality. Periprocedural morbidity, in-hospital morbidity, and poor neurological outcome on discharge (Rankin scale score of 3 or greater) were assessed in surgically and endovascularly treated groups. Univariate and multivariate associations of each outcome with age were tested. Results The risk of aneurysmal hemorrhage did not increase significantly with age. Procedural and in-hospital morbidity and mortality increased with age in patients treated with surgery, but remained relatively constant with increasing age with endovascular treatment. Poor neurological outcome from aneurysm- or procedure-related morbidity and mortality did not differ between management groups for patients 65 years old and younger, but was significantly higher in the surgical group for patients older than 65 years: 19.0% (95% confidence interval [CI] 13.9%–24.4%), compared with 8.0% (95% CI 2.3%–13.6%) in the endovascular group and 4.2% (95% CI 2.3%–6.2%) in the observation group. All-cause mortality increased steadily with increasing age, but differed between treatment groups only in patients < 50 years of age, with the surgical group showing a survival advantage at 1 year. Conclusions Surgical treatment of UIAs appears to be safe, prevents 1-year hemorrhage, and may confer a survival benefit in patients < 50 years of age. However, surgery poses a significant risk of morbidity and death in patients > 65 years of age. Risk of endovascular treatment does not appear to increase with age. Risks and benefits of treatment in older patients should be carefully considered, and if treatment is deemed necessary for patients older than 65 years, endovascular treatment may be the best option.

In this paper, the authors review the definition of high-risk plaque as developed by experienced researchers in atherosclerosis, including pathologists, clinicians, molecular biologists, and imaging scientists. Current concepts of vulnerable plaque are based on histological studies of coronary and carotid artery plaque as well as natural history studies and include the presence of a lipid-rich necrotic core with an overlying thin fibrous cap, plaque inflammation, fissured plaque, and intraplaque hemorrhage. The extension of these histologically identified high-risk carotid plaque features to human in vivo MRI is reviewed as well. The authors also assess the ability of in vivo MRI to depict these vulnerable carotid plaque features. Next, the ability of these MRI-demonstrated high-risk carotid plaque features to predict the risk of ipsilateral carotid thromboembolic events is reviewed and compared with the risk assessment provided by simple carotid artery stenosis measurements. Lastly, future directions of high-risk carotid plaque MRI are discussed, including the potential for increased clinical availability and more automated analysis of carotid plaque MRI. The ultimate goal of high-risk plaque imaging is to design and run future multicenter trials using carotid plaque MRI to guide individual patient selection and decisions about optimal atherosclerotic treatment strategies.