Abstract Background and aims Recent development of high resolution MRI techniques have enabled imaging of intracranial atherosclerotic plaque in vivo . However, identifying plaque composition remains ...challenging given the small size and the lack of histological validation. This study aims to quantify the relaxation times of intracranial plaque components ex vivo at 3 T and to determine whether multi-contrast MRI could classify intracranial plaque according to the American Heart Association classification with histological validation. Methods A total of 53 intracranial arteries with atherosclerotic plaques from 20 cadavers (11 male, age 73.8 ± 10.9) were excised. Quantitative T1 /T2 /T2 * mapping sequences and multi-contrast fast-spin echo sequences (T1 , T2 , proton-density weighted and short time inversion recovery) were acquired. Plaque components including: fibrous cap, lipid core, fibrous tissue, calcification, and healthy wall were segmented on histology, and their relaxation times were derived from quantitative images. Two radiologists independently classified plaque type blinded to the histology results. Results Relaxation times of plaque components are distinct and different. T2 and T2 * values of lipid core are lower than fibrous cap (p = 0.026 & p < 0.0001), but are comparable with fibrous tissue and healthy wall (p = 0.76 & p = 0.42). MRI reliably classified plaque type compared with histology (κ = 0.69) with an overall accuracy of 80.7%. The sensitivity and specificity using MRI to identify fibro-lipid atheroma (type IV-V) was 94.8% and 77.1%, respectively. Inter-observer agreement was excellent (κ = 0.77). Conclusion Intracranial plaque components have distinct and different relaxation times at 3 T. High-resolution MRI is able to characterize intracranial plaque composition and classify plaque types ex vivo at 3 T.
Flow-induced blood damage plays an important role in determining the hemodynamic impact of abnormal blood flow, but quantifying of these effects, which are dominated by shear stresses in highly ...fluctuating turbulent flow, has not been feasible. This study evaluated the novel application of turbulence tensor measurements using simulated 4D Flow MRI data with six-directional velocity encoding for assessing hemodynamic stresses and corresponding blood damage index (BDI) in stenotic turbulent blood flow. The results showed that 4D Flow MRI underestimates the maximum principal shear stress of laminar viscous stress (PLVS), and overestimates the maximum principal shear stress of Reynolds stress (PRSS) with increasing voxel size. PLVS and PRSS were also overestimated by about 1.2 and 4.6 times at medium signal to noise ratio (SNR) = 20. In contrast, the square sum of the turbulent viscous shear stress (TVSS), which is used for blood damage index (BDI) estimation, was not severely affected by SNR and voxel size. The square sum of TVSS and the BDI at SNR >20 were underestimated by less than 1% and 10%, respectively. In conclusion, this study demonstrated the feasibility of 4D Flow MRI based quantification of TVSS and BDI which are closely linked to blood damage.
To investigate joint contributions of cognitive and physiologic reserve to neurocognitive SuperAging in older persons with HIV (PWH).
Participants included 396 older PWH (age range: 50-69 years) who ...completed cross-sectional neuropsychological and neuromedical evaluations. Using published criteria, participants exhibiting global neurocognition within normative expectations of healthy 25-year-olds were classified as SuperAgers (SA; n = 57). Cognitively normal (CN; n = 172) and impaired (n = 167) participants were classified with chronological age-based norms. Cognitive reserve was operationalized with an estimate of premorbid verbal intelligence, and physiologic reserve was operationalized with a cumulative index of 39 general and HIV-specific health variables. Analysis of variance with confirmatory multinomial logistic regression examined linear and quadratic effects of cognitive and physiologic reserve on SA status, adjusting for chronological age, depression, and race/ethnicity.
Univariably, SA exhibited significantly higher cognitive and physiologic reserve compared with CN and cognitively impaired ( d s ≥ 0.38, p s < 0.05). Both reserve factors independently predicted SA status in multinomial logistic regression; higher physiologic reserve predicted linear increases in odds of SA, and higher cognitive reserve predicted a quadratic "J-shaped" change in odds of SA compared with CN (ie, odds of SA > CN only above 35th percentile of cognitive reserve).
Each reserve factor uniquely related to SA status, which supports the construct validity of our SA criteria and suggests cognitive and physiologic reserve reflect nonoverlapping pathways of neuroprotection in HIV. Incorporation of proxy markers of reserve in clinical practice may improve characterization of age-related cognitive risk and resilience among older PWH, even among PWH without overt neurocognitive impairment.
OBJECTIVE—Macrophages play a critical role in cerebral aneurysm formation and rupture. The purpose of this study is to demonstrate the feasibility and optimal parameters of imaging macrophages within ...human cerebral aneurysm wall using ferumoxytol-enhanced MRI.
METHODS AND RESULTS—Nineteen unruptured aneurysms in 11 patients were imaged using T2*-GE–MRI sequence. Two protocols were used. Protocol A was an infusion of 2.5 mg/kg of ferumoxytol and imaging at day 0 and 1. Protocol B was an infusion of 5 mg/kg of ferumoxytol and imaging at day 0 and 3. All images were reviewed independently by 2 neuroradiologists to assess for ferumoxytol-associated loss of MRI signal intensity within aneurysm wall. Aneurysm tissue was harvested for histological analysis. Fifty percent (5/10) of aneurysms in protocol A showed ferumoxytol-associated signal changes in aneurysm walls compared to 78% (7/9) of aneurysms in protocol B. Aneurysm tissue harvested from patients infused with ferumoxytol stained positive for both CD68+, demonstrating macrophage infiltration, and Prussian blue, demonstrating uptake of iron particles. Tissue harvested from controls stained positive for CD68 but not Prussian blue.
CONCLUSION—Imaging with T2*-GE–MRI at 72 hours postinfusion of 5 mg/kg of ferumoxytol establishes a valid and useful approximation of optimal dose and timing parameters for macrophages imaging within aneurysm wall. Further studies are needed to correlate these imaging findings with risk of intracranial aneurysm rupture.
This study proposes and evaluates a novel method for generating efficient undersampling patterns for 3D Cartesian acquisition with compressed sensing (CS) and parallel imaging (PI).
Image quality ...achieved with schemes that accelerate data acquisition, including CS and PI, are sensitive to the design of the specific undersampling scheme used. Ideally random sampling is required to recover MR images from undersampled data with CS. In practice, pseudo-random sampling schemes are usually applied. Radial or spiral sampling either for Cartesian or non-Cartesian acquisitions has been using because of its favorable features such as interleaving flexibility. In this study, we propose to undersample data on the ky-kz plane of the 3D Cartesian acquisition by circularly selecting sampling points in a way that maintains the features of both random and radial or spiral sampling.
The proposed sampling scheme is shown to outperform conventional random and radial or spiral samplings for 3D Cartesian acquisition and is found to be comparable to advanced variable-density Poisson-Disk sampling (vPDS) while retaining interleaving flexibility for dynamic imaging, based on the results with retrospective undersampling. Our preliminary results with the prospective implementation of the proposed undersampling strategy demonstrated its favorable features.
The proposed undersampling patterns for 3D Cartesian acquisition possess the desirable properties of randomization and radial or spiral trajectories. It provides easy implementation, flexible sampling, and high accuracy of image reconstruction with CS and PI.
Ferumoxytol is increasingly reported as an alternative to gadolinium-based contrast agents for MR angiography (MRA), particularly for patients with renal failure. This article summarizes more than 3 ...years of clinical experience with ferumoxytol-enhanced MRA for a range of indications and anatomic regions.
Ferumoxytol-enhanced MRA has many advantages including that it is safe for patients with renal failure and provides a lengthy plateau of vascular signal as a blood pool agent that allows longer navigated MRA sequences.
Objectives
To determine if three-dimensional (3D) radiomic features of contrast-enhanced CT (CECT) images improve prediction of rapid abdominal aortic aneurysm (AAA) growth.
Methods
This longitudinal ...cohort study retrospectively analyzed 195 consecutive patients (mean age, 72.4 years ± 9.1) with a baseline CECT and a subsequent CT or MR at least 6 months later. 3D radiomic features were measured for 3 regions of the AAA, viz
.
the vessel lumen only; the intraluminal thrombus (ILT) and aortic wall only; and the entire AAA sac (lumen, ILT, and wall). Multiple machine learning (ML) models to predict rapid growth, defined as the upper tercile of observed growth (> 0.25 cm/year), were developed using data from 60% of the patients. Diagnostic accuracy was evaluated using the area under the receiver operating characteristic curve (AUC) in the remaining 40% of patients.
Results
The median AAA maximum diameter was 3.9 cm (interquartile range IQR, 3.3–4.4 cm) at baseline and 4.4 cm (IQR, 3.7–5.4 cm) at the mean follow-up time of 3.2 ± 2.4 years (range, 0.5–9 years). A logistic regression model using 7 radiomic features of the ILT and wall had the highest AUC (0.83; 95% confidence interval CI, 0.73–0.88) in the development cohort. In the independent test cohort, this model had a statistically significantly higher AUC than a model including maximum diameter, AAA volume, and relevant clinical factors (AUC = 0.78, 95% CI, 0.67–0.87 vs AUC = 0.69, 95% CI, 0.57–0.79;
p
= 0.04).
Conclusion
A radiomics-based method focused on the ILT and wall improved prediction of rapid AAA growth from CECT imaging.
Key Points
• Radiomic analysis of 195 abdominal CECT revealed that an ML-based model that included textural features of intraluminal thrombus (if present) and aortic wall improved prediction of rapid AAA progression compared to maximum diameter.
• Predictive accuracy was higher when radiomic features were obtained from the thrombus and wall as opposed to the entire AAA sac (including lumen), or the lumen alone.
• Logistic regression of selected radiomic features yielded similar accuracy to predict rapid AAA progression as random forests or support vector machines.
Abstract
BACKGROUND
Many significant microsurgical series of patients with giant aneurysms predate changes in practice during the endovascular era.
OBJECTIVE
A contemporary surgical experience is ...presented to examine changes in management relative to earlier reports, to establish the role of open microsurgery in the management strategy, and to quantify results for comparison with evolving endovascular therapies.
METHODS
During a 13-year period, 140 patients with 141 giant aneurysms were treated surgically. One hundred aneurysms (71%) were located in the anterior circulation, and 41 aneurysms were located in the posterior circulation.
RESULTS
One hundred eight aneurysms (77%) were completely occluded, 14 aneurysms (10%) had minimal residual aneurysm, and 16 aneurysms (11%) were incompletely occluded with reversed or diminished flow. Three patients with calcified aneurysms were coiled after unsuccessful clipping attempts. Eighteen patients died in the perioperative period (surgical mortality, 13%). Bypass-related complications resulted from bypass occlusion (7 patients), aneurysm hemorrhage due to incomplete aneurysm occlusion (4 patients), or aneurysm thrombosis with perforator or branch artery occlusion (4 patients). Thirteen patients were worse at late follow-up (permanent neurological morbidity, 9%; mean length of follow-up, 23 ± 1.9 months). Overall, good outcomes (Glasgow Outcome Score 5 or 4) were observed in 114 patients (81%), and 109 patients (78%) were improved or unchanged after therapy.
CONCLUSION
A heavy reliance on bypass techniques plus indirect giant aneurysm occlusion distinguishes this contemporary surgical experience from earlier ones, and obviates the need for hypothermic circulatory arrest. Experienced neurosurgeons can achieve excellent results with surgery as the “first-line” management approach and endovascular techniques as adjuncts to surgery.
Background
Few studies directed at assessing the visualization of the walls of unruptured aneurysms have used higher‐resolution 3D MRI vessel wall imaging. Prospective longitudinal studies are also ...needed to screen vessel wall changes in unruptured aneurysms.
Purpose
To compare the aneurysm wall visualization on pre‐ and post‐3D isotropic T1‐weighted Sampling Perfection with Application‐optimized Contrasts by using different flip angle Evolutions (SPACE) images and to explore whether there is a change in wall enhancement at follow up.
Study Type
Prospective.
Population
Twenty‐nine patients with a total of 35 unruptured intracranial aneurysms.
Sequence
3D T1‐weighted pre‐ and postcontrast SPACE (0.5 mm isotropic) at 3.0T.
Assessment
The aneurysm wall visibility (0–5 scale) between pre‐ and postcontrast images as well as the wall enhancement (0–5 scale) between follow‐up and baseline studies (6–30 months, average 12.7 months) were compared. Differences in wall visibility and enhancement were also investigated as a function of aneurysm diameter and location.
Statistical Test
The Wilcoxon signed rank paired test was used to compare the wall visibility score between pre‐ and postcontrast SPACE images, as well as wall enhancement between follow‐up and baseline. The Mann–Whitney and Kruskal–Wallis tests were used to investigate the enhancement difference between different diameters and locations.
Results
Postcontrast images had significantly higher wall visibility (P = 0.01). A wall enhancement score ≥2 was found in 71% of the aneurysms. Changes in levels of wall enhancement were found in 17% of the aneurysms at follow‐up studies, but those changes were small. Wall visibility and enhancement scores of large aneurysms were significantly higher than small ones (P < 0.001).
Data Conclusion
3D T1‐weighted higher resolution SPACE can be used to assess changes in enhancement at follow‐up studies. Contrast SPACE image provides better aneurysm wall visibility and improves visualization of the aneurysm wall.
Level of Evidence: 2
Technical Efficacy: Stage 3
J. Magn. Reson. Imaging 2019;50:193–200.
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