Geometric Variability of the Abdominal Aorta and Its Major Peripheral Branches

Evaluation of the celiac trunk and its branching pattern by magnetic resonance angiography

OBJECTIVE

The study aimed to examine the celiac trunk (CT) in detail by magnetic resonance angiography, to determine the locations, positions and variations of the CT, to provide detailed information for surgeons and interventional radiologists, and to reduce the time spent in the catheter angiography.

MATERIAL AND METHODS

MR angiography images of 185 patients with abdominal imaging in PACS (Picture Archiving Communication Systems) were retrospectively analyzed. The level of origin of CT, according to the vertebral column, angle of origin, distance between CT and branches of the abdominal aorta (AA), and the branching pattern of CT were evaluated. Parameters were evaluated according to gender and age.

RESULTS

The most common origin site for CT, according to the vertebral column, was found to be at T12-L1 in both genders. There was a low, positive correlation between age and CT-Sagittal angle (SA) in the whole study group (p<0.05). The most common CT branching pattern was the hepatogastrosplenic trunk in both genders, according to Adachi and Uflkacker's classification. The distance between CT and the inferior mesenteric artery (IMA) and CT and the aortic bifurcation (AB) of males was greater than in females, and the differences were statistically significant (p<0.05).

CONCLUSION

Knowledge of the locations, positions, and variations of CT is essential in the diagnosis, differential diagnosis and decision-making mechanisms regarding the type of intervention to be performed for this vessel and related structures. In addition, the fact that data on these vessels can be obtained by MR angiography due to the improved image quality will prevent patients and physicians from the problems caused by the ionizing radiation of computed tomography. The data presented will constitute a basis for detailed and individualized interpretation and evaluation of each patient, as they provide important details about the configuration of the CT concerning gender and age using MRA.

Geometrical Changes of the Aorta as Predictors for Thromboembolic Events After EVAR With the Anaconda Stent-Graft

PURPOSE

Thromboembolic events (TE), including limb graft occlusion (LGO) and distal limb embolization (DLE), are common complications after endovascular aneurysm repair (EVAR). The aim of this study was to find predictors for TE in patients treated with the Anaconda stent-graft for infrarenal aneurysms.

MATERIALS AND METHODS

Geometrical and anatomical variables were retrospectively analyzed in a consecutive Anaconda cohort. Pre- and postoperative CT scans were used to derive geometrical parameters length, curvature, torsion, and tortuosity index (TI) from the center lumen lines (CLLs). Limb characteristics, pre-to-post EVAR and mid-term-follow-up changes in the parameters were evaluated for their predictive value for TE.

RESULTS

Eighty-four patients (mean age 74±8.3 years, 74 men) were enrolled. The risk of TE was lowered with pre-to-post implant decreasing TI (steps of 0.05: OR: 1.30, 95% CI: 1.01-1.66, p=0.04), pre-to-post implant decreasing mean curvature (OR: 1.08, 95% CI: 1.01-1.16, p=0.03), and a larger degree of circumferential common iliac artery (CIA) calcification (OR: 0.98, 95% CI: 0.97-1.00, p=0.03). The only LGO predictor was the caudal relocation of maximal curvature after EVAR (OR: 1.01, 95% CI: 1.00-1.01, p=0.04). Preventors of DLE were CIA diameter (OR: 0.87, 95% CI: 0.76-0.99, p=0.04), circumferential CIA calcification (OR: 0.97, 95% CI: 0.95-1.00, p=0.03), mean and maximal curvature of the preoperative aortoiliac trajectory (OR: 0.86, 95% CI: 0.79-0.94, p<0.01 and OR: 0.97, 95% CI: 0.95-1.00, p=0.03, respectively) and pre-to-postoperative decrease in mean curvature (OR: 1.11, 95% CI: 1.02-1.21, p=0.02). Midterm TE predictors were length (OR: 0.95, 95% CI: 0.89-1.01, p=0.08) and torsion maximum location (OR: 1.01, 95% CI: 0.99-1.01, p=0.10).

CONCLUSION

The present study confirms that treatment of infrarenal AAA with an Anaconda stent-graft is related to a relatively high TE rate which decreases with a pre-to-postoperative reduction in curvature and TI, and a larger degree of circumferential CIA calcification. In other words, more aortoiliac straightening and more circumferential CIA calcification may prevent TE development after EVAR with this stent-graft.

Effect of aortic bifurcation geometry on pressure and peak wall stress in abdominal aorta: Fluid-structure interaction study

BACKGROUND AND OBJECTIVE

Geometry of aorto-iliac bifurcation may affect pressure and wall stress in aorta and thus potentially serve as a predictor of abdominal aortic aneurysm (AAA), similarly to hypertension.

METHODS

Effect of aorto-iliac bifurcation geometry was investigated via parametric analysis based on two-way weakly coupled fluid-structure interaction simulations. The arterial wall was modelled as isotropic hyperelastic monolayer, and non-Newtonian behaviour was introduced for the fluid. Realistic boundary conditions of the pulsatile blood flow were used on the basis of experiments in literature and their time shift was tailored to the pulse wave velocity in the model to obtain physiological wave shapes. Eighteen idealized and one patient-specific geometries of human aortic tree with common iliac and renal arteries were considered with different angles between abdominal aorta (AA) and both iliac arteries and different area ratios (AR) of iliac and aortic luminal cross sections.

RESULTS

Peak wall stress (PWS) and systolic blood pressure (SBP) were insensitive to the aorto-iliac angles but sensitive to the AR: when AR decreased by 50%, the PWS and SBP increased by up to 18.4% and 18.8%, respectively.

CONCLUSIONS

Lower AR (as a result of the iliac stenosis or aging), rather than the aorto-iliac angles increases the BP in the AA and may be thus a risk factor for the AAA development.

Optimal Renal Artery-Aorta Angulation Revealed by Flow Simulation

INTRODUCTION

In the circulatory system, the vessel branching angle may have hemodynamic consequences. We hypothesized that there is a hemodynamically optimal range for the renal artery's branching angle.

METHODS

Data on the posttransplant kinetics of estimated glomerular filtration rate (eGFR) were analyzed according to the donor and implant sides (right-to-right and left-to-right position; n = 46). The renal artery branching angle from the aorta of a randomly selected population was measured using an X-ray angiogram (n = 44). Computational fluid dynamics simulation was used to elucidate the hemodynamic effects of angulation.

RESULTS AND DISCUSSION

Renal transplant patients receiving a right donor kidney to the right side showed faster adaptation and higher eGFR values than those receiving a left donor kidney to the right side (eGFR: 65 ± 7 vs. 56 ± 6 mL/min/1.73 m2; p < 0.01). The average branching angle on the left side was 78° and that on the right side was 66°. Simulation results showed that the pressure, volume flow, and velocity were relatively constant between 58° and 88°, indicating that this range is optimal for the kidneys. The turbulent kinetic energy does not change significantly between 58° and 78°.

CONCLUSION

The results suggest that there is an optimal range for the renal artery's branching angle from the aorta where hemodynamic vulnerability caused by the degree of angulation is the lowest, which should be considered during kidney transplantations.

Evaluation of electrocardiogram-gated computed tomography angiography to quantify changes in geometry and dynamic behavior of the iliac artery after placement of the Gore Excluder Iliac Branch Endoprosthesis

BACKGROUND

The GORE^® EXCLUDER^® Iliac Branch Endoprosthesis (IBE) is designed to treat iliac aneurysms with preservation of blood flow through the internal iliac artery (IIA). Little is known about the influence of IBE placement on the IIA geometry. This study aimed to provide detailed insights in the dynamic behavior and geometry of the common iliac artery (CIA) and IIA trajectory and how these are influenced after treatment with an IBE.

METHODS

Pre- and postoperative electrocardiogram-gated computed tomography angiography (ECG-gated CTA) scans were acquired in a prospective study design and analyzed with in-house written algorithms designed for aorto-iliac and endoprosthesis deformation evaluation. Cardiac pulsatility-induced motion patterns and pathlengths were computed by tracking predefined locations on the aorto-iliac tract. Centerlines through the CIA-IIA trajectory were used to investigate the static and dynamic geometry, including curvature, torsion, length and Tortuosity Index (TI).

RESULTS

Fourteen CIA-IIA trajectories were analyzed before and after IBE placement. Cardiac pulsatility-induced motion and pathlengths increased after IBE placement, especially at mid IIA and the first IIA bifurcation (P≤0.04). After IBE placement, static and dynamic curvature, length and TI decreased significantly (P<0.05). Furthermore, the average dynamic torsion increased significantly (P=0.030). The remaining geometrical outcomes were not statistically significant.

CONCLUSIONS

The placement of an IBE device stiffens and straightens the CIA-IIA trajectory. Its relation with clinical outcome is yet to be investigated, which can be done thoroughly with the ECG-gated CTA algorithms used in this study.

Improving Blood Vessel Tortuosity Measurements via Highly Sampled Numerical Integration of the Frenet-Serret Equations

Measures of vascular tortuosity-how curved and twisted a vessel is-are associated with a variety of vascular diseases. Consequently, measurements of vessel tortuosity that are accurate and comparable across modality, resolution, and size are greatly needed. Yet in practice, precise and consistent measurements are problematic-mismeasurements, inability to calculate, or contradictory and inconsistent measurements occur within and across studies. Here, we present a new method of measuring vessel tortuosity that ensures improved accuracy. Our method relies on numerical integration of the Frenet-Serret equations. By reconstructing the three-dimensional vessel coordinates from tortuosity measurements, we explain how to identify and use a minimally-sufficient sampling rate based on vessel radius while avoiding errors associated with oversampling and overfitting. Our work identifies a key failing in current practices of filtering asymptotic measurements and highlights inconsistencies and redundancies between existing tortuosity metrics. We demonstrate our method by applying it to manually constructed vessel phantoms with known measures of tortuousity, and 9,000 vessels from medical image data spanning human cerebral, coronary, and pulmonary vascular trees, and the carotid, abdominal, renal, and iliac arteries.

A penalized spline fitting method to optimize geometric parameters of arterial centerlines extracted from medical images

In order to grasp the spatial and temporal evolution of vascular geometry, three-dimensional (3D) arterial bending structure and geometrical changes of arteries and stent grafts (SG) must be quantified using geometrical parameters such as curvature and torsion along the vasculature centerlines extracted from medical images. Here, we develop a robust method for constructing smooth centerlines based on a spline fitting method (SFM) such that the optimized geometric parameters of curvature and torsion can be obtained independently of digitization noise in the images. Conventional SFM consists of the 3rd degree spline basis function and 2nd derivative penalty term. In contrast, the present SFM uses the 5th degree spline basis function and 3rd and 4th derivative penalty terms, the coefficients of which are derived by the Akaike information criterion. The results show that the developed SFM can reduce the errors of curvature and torsion compared to conventional SFM. We then apply the present SFM to the centerline of the SG in an abdominal aortic aneurysm (AAA), and those of bilateral internal carotid arteries (ICA) in 6 cases: 3 cases with aneurysms and 3 cases without any aneurysm. The SG centerlines were obtained from temporal medical images at three scan times. The strong peak of the curvature could be clearly observed in the distal area of the SG, the inversion of the torsion at 0 months in the middle area of SG disappeared over time, and the torsions around the SG bifurcation at the three time periods were inverted. The curvature-torsion graphs along the ICA centerlines superimposing five aneurysmal positions were useful for investigating the relationship between arterial bending structure and aneurysmal positions. Both ICAs had curvature peak values higher than 0.4 within the ICA syphons. The ICA torsion graphs indicated that left and right ICA tended to be a right- and left-handed helix, respectively. In the left ICA syphon, the biggest aneurysm could be observed downstream of the salient torsion inversion. All aneurysms for 3 cases were positioned at the downstream of the inverted torsion.

Analysis of Iliac Artery Geometric Properties in Fenestrated Aortic Stent Graft Rotation

Introduction:

A complication of fenestrated endovascular aneurysm repair is the potential for stent graft rotation during deployment causing fenestration misalignment and branch artery occlusion. The objective of this study is to demonstrate that this rotation is caused by a buildup of rotational energy as the device is delivered through the iliac arteries and to quantify iliac artery geometric properties associated with device rotation.

Methods:

A retrospective clinical study was undertaken in which iliac artery geometric properties were assessed from preoperative imaging for 42 cases divided into 2 groups: 27 in the nonrotation group and 15 in the rotation group. Preoperative computed tomography scans were segmented, and the iliac artery centerlines were determined. Iliac artery tortuosity, curvature, torsion, and diameter were calculated from the centerline and the segmented vessel geometry.

Results:

The total iliac artery net torsion was found to be higher in the rotation group compared to the nonrotation group (23.5 ± 14.7 vs 14.6 ± 12.8 mm−1; P = .05). No statistically significant differences were found for the mean values of tortuosity, curvature, torsion, or diameter between the 2 groups.

Conclusion:

Stent graft rotation occurred in 36% of the cases considered in this study. Cases with high iliac artery total net torsion were found to be more likely to have stent graft rotation upon deployment. This retrospective study provides a framework for prospectively studying the influence of iliac artery geometric properties on fenestrated stent graft rotation.

An experimental assessment of catheter trackability forces with tortuosity parameters along patient-specific coronary phantoms

Coronary artery disease is one of the leading causes of cardiovascular deaths worldwide. Approximately 70% of patients requiring coronary revascularisation receive endovascular stents. The endovascular procedure is the preferred option due to its minimally invasive nature when compared to open heart surgery. Stent delivery is paramount for the success of the endovascular procedure. Catheter delivery forces within tortuous blood vessels can produce vasoconstriction and injury, resulting in reactive intimal proliferation or distal embolisation associated with end-organ ischaemia and infarction. Trackability is evaluated by most medical device companies for further development of their delivery systems. Relevant device design attributes must be tested in settings which simulate aspects of the intended use conditions, such as vessel geometry and compliance. Various tortuosity parameters are used to facilitate endovascular intervention planning. This study assessed the significance and correlation between the trackability forces for a coronary stent system with various geometrical parameters based on patient-specific geometries. A motorised delivery system delivered a commercially available coronary stent system and monitored the trackability forces along three phantom patient-specific thin-walled, compliant coronary vessels supported by a cardiac phantom model. The maximum trackability forces, curvature and torsion values ranged from 0.31 to 0.87 N, 0.06 to 0.22 mm(-1) and -11.1 to 5.8 mm(-1), respectively. The trackability forces were significantly different between all vessels (p < 0.002), while the tortuosity parameters were not significantly different (p > 0.05). A new tortuosity parameter-coined tracking curvature which considers the lumen radius as well as the curvature along the centreline was statistically different (p < 0.002) for all vessels and correlated with the trackability forces. There was a strong correlation between the cumulative trackability force and the cumulative tracking curvature. Tracking curvature could be used as a predictive clinical tool to aid stent delivery to the vicinity of the lesion.

The Effects That Cardiac Motion has on Coronary Hemodynamics and Catheter Trackability Forces for the Treatment of Coronary Artery Disease: An In Vitro Assessment

The coronary arterial tree experiences large displacements due to the contraction and expansion of the cardiac muscle and may influence coronary haemodynamics and stent placement. The accurate measurement of catheter trackability forces within physiological relevant test systems is required for optimum catheter design. The effects of cardiac motion on coronary flowrates, pressure drops, and stent delivery has not been previously experimentally assessed. A cardiac simulator was designed and manufactured which replicates physiological coronary flowrates and cardiac motion within a patient-specific geometry. A motorized delivery system delivered a commercially available coronary stent system and monitored the trackability forces along three phantom patient-specific thin walled compliant coronary vessels supported by a dynamic cardiac phantom model. Pressure drop variation is more sensitive to cardiac motion than outlet flowrates. Maximum pressure drops varied from 7 to 49 mmHg for a stenosis % area reduction of 56 to 90%. There was a strong positive linear correlation of cumulative trackability force with the cumulative curvature. The maximum trackability forces and curvature ranged from 0.24 to 0.87 N and 0.06 to 0.22 mm(-1) respectively for all three vessels. There were maximum and average percentage differences in trackability forces of (23-49%) and (1.9-5.2%) respectively when comparing a static pressure case with the inclusion of pulsatile flow and cardiac motion. Cardiac motion with pulsatile flow significantly altered (p value <0.001) the trackability forces along the delivery pathways with high local percentage variations and pressure drop measurements.

Validation of an arterial tortuosity measure with application to hypertension collection of clinical hypertensive patients

Background

Hypertension may increase tortuosity or twistedness of arteries. We applied a centerline extraction algorithm and tortuosity metric to magnetic resonance angiography (MRA) brain images to quantitatively measure the tortuosity of arterial vessel centerlines. The most commonly used arterial tortuosity measure is the distance factor metric (DFM). This study tested a DFM based measurement’s ability to detect increases in arterial tortuosity of hypertensives using existing images. Existing images presented challenges such as different resolutions which may affect the tortuosity measurement, different depths of the area imaged, and different artifacts of imaging that require filtering.

Methods

The stability and accuracy of alternative centerline algorithms was validated in numerically generated models and test brain MRA data. Existing images were gathered from previous studies and clinical medical systems by manually reading electronic medical records to identify hypertensives and negatives. Images of different resolutions were interpolated to similar resolutions. Arterial tortuosity in MRA images was measured from a DFM curve and tested on numerically generated models as well as MRA images from two hypertensive and three negative control populations. Comparisons were made between different resolutions, different filters, hypertensives versus negatives, and different negative controls.

Results

In tests using numerical models of a simple helix, the measured tortuosity increased as expected with more tightly coiled helices. Interpolation reduced resolution-dependent differences in measured tortuosity. The Korean hypertensive population had significantly higher arterial tortuosity than its corresponding negative control population across multiple arteries. In addition one negative control population of different ethnicity had significantly less arterial tortuosity than the other two.

Conclusions

Tortuosity can be compared between images of different resolutions by interpolating from lower to higher resolutions. Use of a universal negative control was not possible in this study. The method described here detected elevated arterial tortuosity in a hypertensive population compared to the negative control population and can be used to study this relation in other populations.

Unilateral anomalies of kidney development: why is left not right?

Abnormal renal development results in congenital anomalies of the kidney and urinary tract. As many studies suggest that renal malformations are more often found on the left side, a meta-analysis was performed on the distribution of five different unilateral anomalies: multicystic dysplastic kidney, renal agenesis/aplasia, renal ectopia, pelviureteral junction obstruction, and non-obstructive non-refluxing megaureter. Of these anomalies, the left side was affected in 53%, 57%, 56.9%, 63.2%, and 62.5% of patients, respectively, significantly different when compared with an anticipated 50% of left-sided anomalies. An exception to this left-side predominance was found in females with combined genital anomalies and unilateral renal agenesis that commonly present on the right side. The exact mechanisms leading to these lateralizations remain to be determined but may involve vascular development, differential gene expression, or susceptibility to environmental factors such as hypoxia. This remains largely speculative, however, illustrating our limited knowledge of embryogenesis in general and nephrogenesis in particular.

Effects of acute Rho kinase inhibition on chronic hypoxia-induced changes in proximal and distal pulmonary arterial structure and function

Hypoxic pulmonary hypertension (HPH) is initially a disease of the small pulmonary arteries. Its severity is usually quantified by pulmonary vascular resistance (PVR). Acute Rho kinase inhibition has been found to reduce PVR toward control values in animal models, suggesting that persistent pulmonary vasoconstriction is the dominant mechanism for increased PVR. However, HPH may also cause proximal arterial changes, which are relevant to right ventricular (RV) afterload. RV afterload can be quantified by pulmonary vascular impedance, which is obtained via spectral analysis of pulsatile pressure-flow relationships. To determine the effects of HPH independent of persistent pulmonary vasoconstriction in proximal and distal arteries, we quantified pulsatile pressure-flow relationships before and after acute Rho kinase inhibition and measured pulmonary arterial structure with microcomputed tomography. In control lungs, Rho kinase inhibition decreased 0 Hz impedance (Z₀), which is equivalent to PVR, from 2.1 ± 0.4 to 1.5 ± 0.2 mmHg·min·ml⁻¹ (P < 0.05) and tended to increase characteristic impedance (Z(C)) from 0.21 ± 0.01 to 0.22 ± 0.01 mmHg·min·ml⁻¹. In HPH lungs, Rho kinase inhibition decreased Z₀ (P < 0.05) without affecting Z(C). Microcomputed tomography measurements performed on lungs after acute Rho kinase inhibition demonstrated that HPH significantly decreased the unstressed diameter of the main pulmonary artery (760 ± 60 vs. 650 ± 80 μm; P < 0.05), decreased right pulmonary artery compliance, and reduced the frequency of arteries of diameter 50-100 μm (both P < 0.05). These results demonstrate that acute Rho kinase inhibition reverses many but not all HPH-induced changes in distal pulmonary arteries but does not affect HPH-induced changes in the conduit arteries that impact RV afterload.

A morphometric study concerning the branching points of the main arteries in humans: relationships and correlations

An adequate quantity of data on the branching points and important arterial segments of the main arteries in humans is missing. Moreover, a suitable data collection and thereby observed correlations might provide some important clues relating to angiogenesis issues. Thus, we chose to examine in sixty-two embalmed human cadavers of Hellenic origin: The level and angles of the branching points did not differ substantially from similar data, mentioned in the literature. Our results revealed that symmetry exists between the limbs and the aortic length and the branching positions of the abdominal aorta. The aortic length is negatively related to the length of both common iliac arteries. The lengths of the celiac and the brachiocephalic artery (correlated weakly with one another) presented fewer correlations, while the segment between the inferior mesenteric and the celiac artery was correlated with other segments from different locations mainly on the right side. This last distance, the aortic length, the distance between the celiac and inferior mesenteric arteries, the length of both common femoral arteries differed significantly according to gender, independently of body length and height. Our data support the view that the final position and length of the arteries might be due to the location of the corresponding viscera during angiogenesis, to the body length and height and to some (hypothetical) elongation angiogenetic factors.