¤ ¤Purpose: To determine the effect of curvature on the magnitude and direction of displacement forces acting on aortic endografts in 3-dimensional (3D) computational models.Method: A 3D computer model was constructed based on magnetic resonance angiography data from a patient with an infrarenal aortic aneurysm. Computational fluid dynamics tools were used to simulate realistic flow and pressure conditions of the patient. An aortic endograft was deployed in the model, and the displacement forces acting on the endograft were calculated and expressed in Newtons (N). Additional models were created to determine the effects of reducing endograft curvature, neck angulation, and iliac angulation on displacement forces. Results: The aortic endograft had a curved configuration as a result of the patient's anatomy, with curvature in the anterolateral direction. Total displacement force acting on the endograft was 5.0 N, with 28% of the force in a downward (caudal) direction and 72% of the force in a sideways (anterolateral) direction. Elimination of endograft curvature (planar graft configuration) reduced total displacement force to 0.8 N, with the largest component of force (70%) acting in the sideways direction. Straightening the aortic neck in the curved endograft configuration reduced the total force acting on the endograft to 4.2 N, with a reduction of the sideways component to 55% of the total force. Straightening the iliac limbs of the endograft reduced the total force acting on the endograft to 2.1 N but increased the sideways component to 91% of the total force. Conclusion: The largest component of the force acting on the aortic endograft is in the sideways direction, with respect to the blood flow, rather than in the downward (caudal) direction as is commonly assumed. Increased curvature of the aortic endograft increases the magnitude of the sideways displacement force. The degree of angulation of the proximal and distal ends of the endograft influence the magnitude and direction of displacement force. These factors may have a significant influence on the propensity of endografts to migrate in vivo.

The orientation of the DF varies depending on curvature and location of the endograft, but in all instances, it is in the cranial rather than caudal direction on axial imaging. This is counter to the intuitive notion that displacement forces act in the downward direction of blood flow. Therefore, we postulate that migration of thoracic endografts may be different from abdominal endografts since it may involve upward rather than downward movement of the graft. Computational methods can enhance the understanding of the magnitude and orientation of the loads experienced in vivo by thoracic aortic endografts and therefore improve their design and performance.

Objective Endograft migration is usually described as a downward displacement of the endograft with respect to the renal arteries. However, change in endograft position is actually a complex process in three dimensional space. Currently, there are no established techniques to define such positional changes over time. The purpose of this study is to determine whether the direction of aortic endograft movement as observed in follow-up CT scans is related to the directional displacement force acting on the endograft. Methods We quantitated the 3D positional change over time of 5 abdominal endografts by determining the endograft centroid at baseline (post-operative scan) and on follow-up CT scans. The time interval between CT scans for the 5 patients ranged from 8 months to 8 years. We then used 3D image segmentation and computational fluid dynamics (CFD) techniques to quantitate the pulsatile displacement force (in Newtons [N]) acting on the endografts in the post-operative configurations. Finally, we calculated a correlation metric between the direction of the displacement force vector and the endograft movement by computing the cosine of the angle of these two vectors. Results The average 3D movement of the endograft centroid was 18 mm (range 9 mm to 29 mm) with greater movement in patients with longer follow-up times. In all cases, the movement of the endograft had significant components in all 3 spatial directions: Two of the endografts had the largest component of movement in the transverse direction, whereas 3 endografts had the largest component of movement in the axial direction. The magnitude and orientation of the endograft displacement force varied depending on aortic angulation and hemodynamic conditions. The average magnitude of displacement force for all endografts was 5.8 N (range 3.7 N to 9.5 N). The orientation of displacement force was in general perpendicular to the greatest curvature of the endograft. The average correlation metric, defined as the cosine of the angle between the displacement force and the endograft centroid movement, was 0.38 (range 0.08 to 0.66). Conclusions Computational methods applied to patient-specific post-operative image data can be used to quantitate three-dimensional displacement force and movement of endografts over time. It appears that endograft movement is related to the magnitude and direction of the displacement force acting on aortic endografts. These methods can be used to increase our understanding of clinical endograft migration.

BackgroundThe determination of left ventricular ejection fraction using cardiovascular magnetic resonance (CMR) requires a steady cardiac rhythm for electrocardiogram (ECG) gating and multiple breathholds to minimize respiratory motion artifacts, which often leads to scan times of several minutes. The need for gating and breathholding can be eliminated by employing real-time CMR methods such as through-time radial GRAPPA. The aim of this study is to compare left ventricular cardiac functional parameters obtained using current gold-standard breathhold ECG-gated functional scans with non-gated free-breathing real-time imaging using radial GRAPPA, and to determine whether scan time or the occurrence of artifacts are reduced when using this real-time approach.Methods63 patients were scanned on a 1.5T CMR scanner using both the standard cardiac functional examination with gating and breathholding and the real-time method. Total scan durations were noted. Through-time radial GRAPPA was employed to reconstruct images from the highly accelerated real-time data. The blood volume in the left ventricle was assessed to determine the end systolic volume (ESV), end diastolic volume (EDV), and ejection fraction (EF) for both methods, and images were rated for the presence of artifacts and quality of specific image features by two cardiac readers. Linear regression analysis, Bland-Altman plots and two-sided t-tests were performed to compare the quantitative parameters. A two-sample t-test was performed to compare the scan durations, and a two-sample test of proportion was used to analyze the presence of artifacts. For the reviewers´ ratings the Wilcoxon test for the equality of the scores’ distributions was employed.ResultsThe differences in EF, EDV, and ESV between the gold-standard and real-time methods were not statistically significant (p-values of 0.77, 0.82, and 0.97, respectively). Additionally, the scan time was significantly shorter for the real-time data collection (p<0.001) and fewer artifacts were reported in the real-time images (p<0.01). In the qualitative image analysis, reviewers marginally preferred the standard images although some features including cardiac motion were equivalently rated.ConclusionReal-time functional CMR with through-time radial GRAPPA performed without ECG-gating under free-breathing can be considered as an alternative to gold-standard breathhold cine imaging for the evaluation of ejection fraction in patients.

Plaque progression is a multi-faceted process characterized by the incidence, extent, stenosis, burden, morphology, and vulnerability of plaque, which may ultimately result in myocardial infarction or death. For years, intravenous ultrasound (IVUS) has been the primary modality to study progression. However, it is invasive and impractical for screening or monitoring. While coronary artery calcium scoring (CAC) has been widely studied as a non-invasive method to measure plaque progression, it is limited to visualization of stenosis and non-calcified plaque. Coronary computed tomographic angiography (CCTA) allows for visualization of the severity of stenosis, plaque burden, plaque morphology, and ability to differentiate between plaque types. Furthermore, certain CCTA plaque features are useful in identifying vulnerable plaque including low attenuation plaque, positive remodeling, spotty calcification, and napkin-ring sign. This review covers multiple aspects of plaque progression--its pathophysiology, clinical implications, and use of novel noninvasive technology for the assessment of plaque progression over time.

Objectives: Purpose: to compare the safety of percutaneous access (PA) to open repair (OR) of the femoral artery during endovascular aortic repair (EVAR and TEVAR).Methods: Methods: A prospective nonrandomized study was performed between January 2006 and November 2009. Parameters of patients who underwent endovascular aortic repairs with either open femoral repair or percutaneous closure system (Preclose-proglide or Prostar technique) were collected in a dedicated database. Each patient underwent CT angiography preoperatively and postoperatively at 1 and 12 months. Patient' variables (Age, gender, subcutaneous tissue depth, femoral artery diameter, type of calcifications, type of closure device, and size of sheath) were compared by using Chi-square, Fisher exact test, and paired and independent samples t tests when appropriate.Results: Results: Among 405 patients who underwent endovascular aortic repair, we performed 185 OR (EVAR-160, TEVAR-25) and 220 PA (EVAR-206, TEVAR-14). Immediate conversion from PA to OR was necessary in 34 patients (15.6%), and was significantly more frequent in patients with a femoral artery diameter Ͻ10mm (76.5% vs 4.6%; p ϭ 0.006). No significant difference was observed between the 2 groups regarding the length of in-hospital stay, the rate of postoperative infections and of late complications (7.4% in the PA group vs 4.3% in the OR group). The type of closure device, the size of the sheath did not significantly influence the outcome. However, late complications in PA group only occurred on the side of the larger sheath.Conclusions: Conclusions: In our study, PA carries a higher risk of complications than OR. PA is a safe technique in patients with a femoral artery diameter Ͼ 10 mm (4.6% immediate conversion) but it did not decrease the length of stay nor the postoperative complication rate.

The carotid arteries, located in both sides of the neck, are critical to supplying oxygenated blood to the brain. Over time, atherosclerotic plaque may accumulate in these vessels, causing them to narrow, which results in a reduced cerebral blood supply. This condition is known as carotid artery stenosis. In addition, small pieces of this plaque may become dislodged and travel to the brain, resulting in a stroke. Seven hundred thousand Americans suffer a stroke in the United States each year, and 150,000 cases are fatal, making it the third leading cause of death in the United States.

Background Real-time cardiac imaging with through-time radial GRAPPA has been shown to yield high quality functional images [Seiberlich, et al. MRM2011 Feb;65(2):492-505]. The goal of this work is to evaluate through-time radial GRAPPA in terms of overall scan time, quantitative measures of ESV, EDV, and EF, and image quality in a patient population.