Background and Purpose-Retrospective analysis of clinical data has demonstrated major variations in carotid bifurcation geometry, in support of the notion that an individual's vascular anatomy or local hemodynamics may influence the development of atherosclerosis. On the other hand, anecdotal evidence suggests that vessel geometry is more homogenous in youth, which would tend to undermine this geometric risk hypothesis. The purpose of our study was to test whether the latter is indeed the case. Methods-Cross-sectional images of the carotid bifurcations of 25 young adults (24Ϯ4 years) and a control group of 25 older subjects (63Ϯ10 years) were acquired via MRI. Robust and objective techniques were developed to automatically characterize the 3D geometry of the bifurcation and the relative dimensions of the internal, external, and common carotid arteries (ICA, ECA, and CCA, respectively).

A thorough understanding of the relationship between local hemodynamics and plaque progression has been hindered by an inability to prospectively monitor these factors in vivo in humans. In this study a novel approach for noninvasively reconstructing artery wall thickness and local hemodynamics at the human carotid bifurcation is presented. Three-dimensional (3D) models of the lumen and wall boundaries, from which wall thickness can be measured, were reconstructed from blackblood magnetic resonance imaging (MRI). Along with time-varying inlet/outlet flow rates measured via phase contrast (PC) MRI, the lumen boundary was used as input for computational fluid dynamic (CFD) simulation of the subject-specific flow patterns and wall shear stresses (WSSs). Results from a 59-yearold subject with early, asymptomatic carotid artery disease show good agreement between simulated and measured velocities, and demonstrate a correspondence between wall thickening and low and oscillating shear at the carotid bulb. High shear at the distal internal carotid artery (ICA) was also colocalized with higher WSS; however, a quantitative general relationship between WSS and wall thickness was not found. Similar results were obtained from a 23-year-old normal subject. Wall shear stress (WSS) is widely believed to play a key role in the development and progression of atherosclerotic plaques. Studies comparing human post-mortem distributions of plaque to in vitro fluid dynamic models have perhaps provided the most direct observational evidence for the relationship between WSS and the focal development of atherosclerotic lesions (1-4). The mechanisms by which shear stresses alter endothelial function at the cellular, molecular, and genetic level are also now being elucidated (5). Despite these advances, however, many questions still remain regarding the role of fluid dynamics in the development and progression of atherosclerosis. One reason for this has been the difficulty of identifying and monitoring the relationships between local fluid dynamic factors and plaque development on a subject-specific basis.In principle, both MR and ultrasound imaging can be used to measure wall thickness (a marker for atherosclerotic burden) and blood velocities (from which WSSs are derived) directly. However, difficulties associated with the quantification of blood velocities in regions of complex flow have in the past limited the application of such an "imaging-only" approach to relatively straight sections of the abdominal aorta (6), femoral artery (7), and common carotid artery (8 -10). While these studies were able to confirm an inverse relationship between mean or peak shear and intimal or intima-media thickness, it is not yet possible to use imaging techniques alone to map WSS in the regions of complex flow where plaques are known to localize, such as at the carotid bifurcation. Recent work by Stokholm et al. (11) suggests that WSS from individual slices at the carotid bifurcation itself can be quantified in vivo by sophisticated postprocessing of ph...

ObjectiveThe aim of this study was to investigate the feasibility of using augmented reality (AR) glasses in central line simulation by novice operators and compare its efficacy to standard central line simulation/teaching.DesignThis was a prospective randomized controlled study enrolling 32 novice operators. Subjects were randomized on a 1:1 basis to either simulation using the augmented virtual reality glasses or simulation using conventional instruction.SettingThe study was conducted in tertiary-care urban teaching hospital.SubjectsA total of 32 adult novice central line operators with no visual or auditory impairments were enrolled. Medical doctors, respiratory therapists, and sleep technicians were recruited from the medical field.Measurements and main resultsThe mean time for AR placement in the AR group was 71±43 s, and the time to internal jugular (IJ) cannulation was 316±112 s. There was no significant difference in median (minimum, maximum) time (seconds) to IJ cannulation for those who were in the AR group and those who were not (339 [130, 550] vs 287 [35, 475], p=0.09), respectively. There was also no significant difference between the two groups in median total procedure time (524 [329, 792] vs 469 [198, 781], p=0.29), respectively. There was a significant difference in the adherence level between the two groups favoring the AR group (p=0.003).ConclusionAR simulation of central venous catheters in manikins is feasible and efficacious in novice operators as an educational tool. Future studies are recommended in this area as it is a promising area of medical education.

Recent studies have demonstrated the ability of magnetic resonance imaging (MRI) to provide anatomically realistic boundary conditions for computational fluid dynamics (CFD) simulations of arterial hemodynamics. To date, however, little is known about the overall reproducibility of such image-based CFD techniques. Towards this end we used serial black blood and cine phase contrast MRI to reconstruct CFD models of the carotid bifurcations of three subjects with early atherosclerosis, each imaged three times at weekly intervals. The lumen geometry was found to be precise on average to within 0.15 mm or 5%, while measured flow and heart rates varied by less than 10%. Spatial patterns of a variety of wall shear stress (WSS) indices were largely preserved among the three repeat models. Time-averaged WSS was reproduced best, on average to within 5 dyn/cm2 or 37%, followed by WSS spatial gradients, angle gradients, and oscillatory shear index. The intrasubject flow rate variations were found to contribute little to the overall WSS variability. Instead, reproducibility was determined largely by the precision of the lumen boundary extraction from the individual MR images, itself shown to be a function of the image quality and proximity to the geometrically complex bifurcation region.

Black blood magnetic resonance imaging (MRI) has become a popular technique for imaging the artery wall in vivo. Its noninvasiveness and high resolution make it ideal for studying the progression of early atherosclerosis in normal volunteers or asymptomatic patients with mild disease. However, the operator variability inherent in the manual measurement of vessel wall area from MR images hinders the reliable detection of relatively small changes in the artery wall over time. In this paper we present a semi-automatic method for segmenting the inner and outer boundary of the artery wall, and evaluate its operator variability using analysis of variance (ANOVA). In our approach, a discrete dynamic contour is approximately initialized by an operator, deformed to the inner boundary, dilated, and then deformed to the outer boundary. A group of four operators performed repeated measurements on 12 images from normal human subjects using both our semiautomatic technique and a manual approach. Results from the ANOVA indicate that the inter-operator standard error of measurement (SEM) of total wall area decreased from 3.254 mm2 (manual) to 1.293 mm2 (semi-automatic), and the intra-operator SEM decreased from 3.005 mm2 to 0.958 mm2. Operator reliability coefficients increased from less than 69% to more than 91% (inter-operator) and 95% (intra-operator). The minimum detectable change in wall area improved from more than 8.32 mm2 (intra-operator, manual) to less than 3.59 mm2 (inter-operator, semi-automatic), suggesting that it is better to have multiple operators measure wall area with our semi-automatic technique than to have a single operator make repeated measurements manually. Similar improvements in wall thickness and lumen radius measurements were also recorded. Since the semi-automatic technique has effectively ruled out the effect of the operator on these measurements, it may be possible to use such techniques to expand prospective studies of atherogenesis to multiple centers so as to increase access to real patient data without sacrificing reliability.

Background: The risk of failing or delaying endotracheal intubation in critically ill patients has commonly been associated with inadequate procedure preparation. Clinicians and trainees in simulation courses for tracheal intubation are encouraged to recall the steps of how to intubate in order to mitigate the risk of a failed intubation. The purpose of this study was to assess the effectiveness of using optical head mounted display augmented reality (AR) glasses as an assistance tool to perform intubation simulation procedure. Methods: A total of 32 subjects with a mean age of 30±7.8, AR (n 1 =15) vs non-augmented reality(non-AR) (n 2 =17). The majority were males (n=22, 68.7%). Subjects were randomly assigned into two groups: the AR group and the non-AR group. Both groups reviewed a video on how to intubate following the New England Journal of Medicine (NEJM) intubation guidelines. The AR group had to intubate using the AR glasses head mount display compared to the non-AR where they performed regular intubation. Results: The AR group took longer median (min, max) time (seconds) to ventilate than the non-AR group (280 (130,740) vs 205 (100,390); η 2 =1.0, p =0.005, respectively). Similarly, there was a higher percent adherence of NEJM intubation checklist (100% in the AR group vs 82.4% in the non-AR group; η 2 =1.8, p <0.001). Conclusion: The AR glasses showed promise in assisting different health care professionals on endotracheal intubation simulation. Participants in the AR group took a longer time to ventilate but scored 100% in the developed checklist that followed the NEJM protocol. This finding shows that the AR technology can be used in a simulation setting and requires further study before clinical use.

Black blood MRI has become a popular technique for measuring arterial wall area as an indicator of plaque size. Computerassisted techniques for segmenting vessel boundaries have been developed to increase measurement precision. In this study, the carotid arteries of four normal subjects were imaged at seven different fields of view (FOVs), keeping all other imaging parameters fixed, to determine whether spatial resolution could be increased at the expense of image quality without sacrificing precision. Wall areas were measured via computerassisted segmentation of the vessel boundaries performed repeatedly by two operators. Analysis of variance (ANOVA) demonstrated that the variability of wall area measurements was below 1.5 mm 2 for in-plane spatial resolutions between 0.22 mm and 0.37 mm. An inverse relationship between operator variability and the signal difference-to-noise ratio (SDNR) demonstrated that semi-automatic segmentation of the wall boundaries was robust for SDNR >3, defining a criterion above which subjective image quality can be degraded without an appreciable loss of information content. Our study also suggested that spatial resolutions higher than 0.3 mm may be required to quantify normal wall areas to within 10% accuracy, but that the reduced SNR associated with the higher resolution may be tolerated by semi-automated wall segmentation without an appreciable loss of precision. Magn Reson Med 46:299 -304, 2001.

Purpose: To provide anthropometric data applicable to the design of protocols for high-resolution magnetic resonance imaging (MRI) of the carotid bifurcation, particularly those aimed at elucidating the role of local factors in carotid atherogenesis. Materials and Methods:Axial black-blood MR images of the carotid bifurcation were acquired from 25 young, healthy volunteers and 25 older, asymptomatic patients, from which were measured a variety of quantities related to the orientation and placement of the bifurcation within the neck.Results: Descriptive statistics were obtained for the following quantities: separation of the bifurcation apices within (57.8 Ϯ 6.7 mm) and between (4.9 Ϯ 4.1 mm) axial slices; orientation of the bifurcation within the axial plane (31.7 Ϯ 26.9°), and of the common carotid artery (CCA) relative to the sagittal (7.5 Ϯ 7.1°) and coronal (7.9 Ϯ 7.8°) planes; depth of the bifurcation from the skin surface (29.5 Ϯ 7.2 mm); and neck width (125.9 Ϯ 14.4 mm). Conclusion:In most cases, both carotid arteries may be captured, without aliasing, within a 12-cm field-of-view axial image; however, the two apices will rarely be captured within the same axial slice. The CCA is significantly oblique to the body axis, but at angles sufficiently acute to permit the use of axial slices. Finally, a significant linear relationship between neck width and carotid depth may be used to inform radio frequency (RF) coil selection prior to scanning a subject, and hence facilitate optimal imaging in light of the wide anatomic variations observed. MAGNETIC RESONANCE IMAGING (MRI) has emerged as an important modality for high-resolution imaging of the carotid bifurcation (1). Its ability to interrogate the vessel wall and uncover the morphologic features of atheroma provides insight into early plaque formation and stroke risk not achievable by conventional angiography. Carotid wall thickness measurements not only predict cerebrovascular events, but provide a window into the cardiovascular system as a whole. Furthermore, MRI can identify early atherosclerosis before it begins to narrow the lumen, and can provide a longitudinal assessment of the effect of therapy not detectable by angiography. However, unlike conventional angiographic techniques, the reliability of high-resolution carotid MRI is constrained by carotid artery anthropometry, since the signal from the vessel depends on the relative size and position of the surface coils, and the accuracy of vessel wall measurements requires minimizing obliquity of slices positioned through the target. This is particularly important for population-based studies, which rely on standard protocols that must acquire anatomic measurements for a wide variety of carotid artery geometries and orientations. Longitudinal studies demand even more consideration to ensure that anatomic landmarks are clearly visualized and reliably included within the image so that follow-up measurements can be precisely located and repeated.With these considerations, the design of MRI protocols for imag...