Hemodynamic Simulation of Pancreaticoduodenal Artery Aneurysm Formation Using an Electronic Circuit Model and a Case Series Analysis.

Objective: To assess mechanisms underlying aneurysm formation using a simple electronic circuit model. Materials and Methods: We created a simple circuit model connecting the celiac artery (CA) to the superior mesenteric artery via the pancreaticoduodenal arcade. We retrospectively reviewed 12 patients with true pancreaticoduodenal artery aneurysms (PDAAs) who received open or endovascular treatment between 2004 and 2017. We set the resistance of each artery and organ voltage and calculated flow volume and rate in response to degrees of simulated CA stenosis from 0% to 99.9%. Results: Flow volume rates of the anterior pancreaticoduodenal artery and posterior pancreaticoduodenal artery decreased to zero when CA stenosis increased from 0% to 50% and then increased drastically, at which point flow direction reverted and the flow was up to three times the initial rate. The gastroduodenal artery (GDA) also showed reversed flow with severe CA stenosis. In 12 patients with PDAA, eight presented with a CA lesion, and the other patients presented with comorbidities causing the arteries to be pathologically fragile, such as Marfan syndrome, Behçet's disease, and segmental arterial mediolysis. All four GDA aneurysms were not accompanied by CA lesions. Conclusion: The mechanism underlying CA-lesion-associated PDAA formation may be partially explained using our model.

Geometric analysis of ruptured and nonruptured abdominal aortic aneurysms.

OBJECTIVE: The objective of this study was to use parameters to determine the geometric differences between ruptured abdominal aortic aneurysms (AAAs) and nonruptured AAAs. METHODS: Computed tomography data of 38 ruptured AAAs and 215 electively repaired (nonruptured) AAAs were collected from multiple institutes. We compared the ruptured AAA group and nonruptured AAA group with 1:1 matching by using the Mahalanobis distance, which was calculated using the patient's age, sex, and AAA diameter. We selected the longitudinal AAA image in multiplanar reconstruction view, placed a hypothetical ellipse on the aneurysm's protruded curve, and placed a circle on the portion connecting the aneurysm and the aorta. We then measured the aspect ratio (the vertical diameter divided by the horizontal diameter) and fillet radius (the radius of arc). RESULTS: The aspect ratio was significantly lower in the ruptured group than in the nonruptured group (2.02 ± 0.53 vs 2.60 ± 1.02; P = .002), as was the fillet radius (0.28 ± 0.18 vs 0.81 ± 0.44; P < .001). Receiver operating characteristic analysis revealed that the area under the curve of the aspect ratio was 0.688, and the optimal cutoff point was 2.23, with sensitivity and specificity of 0.55 and 0.76, respectively. The area under the curve of the fillet radius was 0.933, and the optimal cutoff was 0.347, with sensitivity and specificity of 0.97 and 0.87, respectively. CONCLUSIONS: The geometric analysis performed in this study revealed that ruptured AAAs had a smaller fillet radius and smaller aspect ratio than nonruptured AAAs did.

Morphological analysis using geometric parameters for splenic aneurysms.

Background Considering the unique characteristics of splenic artery aneurysms, we hypothesized that hemodynamic forces could play an important role in splenic artery aneurysm formation and that splenic artery geometry should be correlated with aneurysm development. Methods Tortuosity of the splenic artery was evaluated three-dimensionally by calculating the curvature using software and the original modeling system. We selected 54 splenic artery aneurysm patients who had undergone thin-slice computed tomography imaging with contrast. We compared the splenic artery aneurysm group to non-vascular patients via propensity-score matching (35 patients in each group). The splenic artery length index, average curvature, and maximum curvature were analyzed. Results Splenic artery aneurysm patients tended to have a longer splenic artery and the curvature was more severe compared to the non-vascular control patients. The average curvature of splenic artery aneurysm patients was associated with the dilatation rate in female patients. Conclusion Females with a tortuous splenic artery may have an increased risk of aneurysm formation.

Morphological Changes and Device Migration After Stent Graft Insertion　- Clinical Application of an Image-Based Modeling System and Analysis With Geometric Parameters.

BACKGROUND: Previously, we developed an image-based modeling system (V-Modeler) to investigate geometric changes in stent grafts (SGs) following their implantation for abdominal aortic aneurysms (AAAs). The aims of the present study were to improve this system for clinical use, to chronologically analyze postoperative morphological changes in SGs, and to demonstrate scenarios of SG migration.Methods and Results:Contrast-enhanced computed tomography data from 36 patients who underwent endovascular aneurysm repair (EVAR) for AAAs were used, with 72 centerline paths, in total, analyzed for bilateral SG legs. The existing V-modeler system was modified by introducing a penalty term, optimizing the number of control points using Akaike's information criterion, and changing the degree of the function from 3 to 5. Geometric parameters were then analyzed immediately, as well as >1 year after EVAR. Eight migrations were found and although overall SG curvature and curvature at the distal (leg) site did not change, curvature at the proximal (trunk) site of SGs decreased over time. Subanalysis revealed that SGs with severe curvature showed the same trend, whereas distal curvature increased in the non-severe curvature group. In addition, proximal curvature decreased more in Excluder than Zenith devices. CONCLUSIONS: The present study demonstrates SG behavior after implantation with numerical values for SG length and curvature.

Theoretical mechanism of temporary renal function improvement after abdominal aortic aneurysm surgery: Applications for clinical imaging and laboratory data.

We evaluated the effects of changes in blood flow due to abdominal aortic aneurysm (AAA) surgery by using a simple zero-dimension model and applied theoretical values to clinical data.The zero-dimension electronic circuit model and diagram of blood flow distribution were created by setting the resistance of the aorta, bilateral iliac arteries, renal arteries, and aneurysm. Resistance of the aneurysm and resistance of the aorta before surgery were compared with that of the aorta after surgery. We set the radius length of each anatomical parameter to calculate theoretical values.Renal flow increased 13.4% after surgery. Next, we analyzed contrast-enhanced computed tomography data of 59 patients who underwent AAA surgery. A total of 19 patients were treated with a Y graft and 7 patients were treated with a straight graft during open surgery. However, 33 patients were treated with a bifurcated stent graft. A significant linear relationship between the increased estimated glomerular filtration rate (eGFR) ratio and the decreased aneurysm ratio was found only for the straight graft group.Using a circuit model, renal blood flow theoretically increased after AAA surgery. Clinically, there was a correlation between volume regression and eGFR improvement only in the limited AAA group.

Development of an Image-Based Modeling System to Investigate Evolutional Geometric Changes of a Stent Graft in an Abdominal Aortic Aneurysm.

BACKGROUND: Quantification of geometric changes of the stent graft (SG) in abdominal aortic aneurysm has been required for follow up of endovascular aneurysm repair (EVAR). The aim was to develop an image-based modeling system (V-Modeler) to investigate these changes over time. METHODS AND RESULTS: V-Modeler was applied to investigate the migration of the SG. Three sets of computed tomography images were taken at 3 different times: (1) 5 days after the implantation; (2) 7 months later when the unilateral leg migrated upward; and (3) 10 months later when the limb had migrated into the common iliac aneurysm resulting in a type 1b endoleak. A spline function was used to represent the center lines of the SG to track its evolutional geometric changes in a three-dimensional manner. The characteristics of vascular geometry, as well as the SG geometry using geometric parameters such as length, curvature, torsion, angle of tangent vector (ATV), and migrated length, was evaluated. It was observed that the strong peak of the curvature in the distal area appeared, and a conversion of the torsion disappeared chronologically. CONCLUSIONS: The V-Modeler was developed, which not only can extract vascular geometry but also can identify geometric parameter, such as curvature, torsion, and ATV, to predict adverse events following EVAR.

Biomechanical analysis of an aortic aneurysm model and its clinical application to thoracic aortic aneurysms for defining "saccular" aneurysms.

BACKGROUND: We aimed to develop a simple structural model of aortic aneurysms using computer-assisted drafting (CAD) in order to create a basis of definition for saccular aortic aneurysms. METHODS AND RESULTS: We constructed a simple aortic aneurysm model with 2 components: a tube similar to an aorta and an ellipse analogous to a bulging aneurysm. Three parameters, including the vertical and horizontal diameters of the ellipse and the fillet radius, were altered in the model. Using structural analysis with the finite element method, we visualized the distribution of the maximum principal stress (MPS) in the aortic wall and identified the area(s) of prominent stress. We then selected patients with thoracic aortic aneurysms in whom the aneurysm expansion rates were followed up and applied the theoretical results to the raw imaging data. The maximum MPS drastically increased at areas where the aspect ratio (vertical/horizontal) was <1, indicating that "horizontally long" hypothetical ellipses should be defined as "saccular" aneurysms. The aneurysm expansion rate for the patients with thoracic aneurysms conforming to these parameters was significantly high. Further, "vertically long" ellipses with a small fillet might be candidates for saccular aneurysms; however, the clinical data did not support this. CONCLUSIONS: Based on the biomechanical analysis of a simple aneurysm model and the clinical data of the thoracic aortic aneurysms, we defined "horizontally long" aortic aneurysms with an aspect ratio of <1 as "saccular" aneurysms.