Takafumi Akai

The University of Tokyo, Tōkyō, Japan

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Publications (6)15.24 Total impact

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    ABSTRACT: 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. 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.
    Circulation Journal 03/2015; DOI:10.1253/circj.CJ-15-0037 · 3.69 Impact Factor
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    ABSTRACT: 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. 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. 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. © 2015 The Authors. Published on behalf of the American Heart Association, Inc., by Wiley Blackwell.
    Journal of the American Heart Association 01/2015; 4(1). DOI:10.1161/JAHA.114.001547 · 2.88 Impact Factor
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    ABSTRACT: There are various angiographic and runoff scoring systems for evaluating stenosis and arterial occlusion in patients with peripheral artery disease (PAD). The report from the BASIL trial revealed that the Bollinger scoring system, originally designed to classify intra-arterial digital subtraction angiography (IADSA), was sensitive to differences in PAD. The purpose of the present study was to evaluate the application of the Bollinger scoring system to a 64-low multidetector computed tomography (MDCT) in PAD patients.
    International angiology: a journal of the International Union of Angiology 10/2014; 33(5):426-33. · 1.01 Impact Factor
  • 01/2014; 54(2):5-11. DOI:10.7133/jca.13-00044
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    ABSTRACT: Background: With respect to endovascular aneurysm repair (EVAR), the development of advanced techniques and devices, namely, Cook Zenith and Gore Excluder, has helped overcome device-related problems, including device migration. Deformities of abdominal aortic aneurysms (AAAs) can influence the long-term outcome of EVAR. The post-implantation behavior of stent grafts in AAAs with a severely angulated neck (SAN) was examined. Methods and Results: Among 190 AAA patients who underwent EVAR, 46 had SAN of more than 60 degrees. The post-implantation angle and adverse events were evaluated. Forty-one patients (89%) showed straightening of the neck angle immediately after the operation (early), with 2 types of subsequent (late) configuration changes - recoil and additional straightening. Among 34 Excluder patients, 29 showed immediate straightening, without additional straightening and 8 exhibited recoil. All 12 Zenith patients showed immediate straightening; 7 subsequently exhibited additional straightening, and none of them showed recoil. A difference (P=0.04) was noted between the 2 devices in the late angle changes. In all cases, no migration was observed at the proximal sites. Conclusions: The post-implantation configuration changes in stent placement in AAA patients with SAN were different for Excluder and Zenith. Appropriate device selection and proper planning of the procedure is necessary for EVAR.
    Circulation Journal 05/2013; 77(8). DOI:10.1253/circj.CJ-13-0204 · 3.69 Impact Factor
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    ABSTRACT: A strong degree of co-existence between coronary artery disease (CAD) and abdominal aortic aneurysm (AAA) is widely acknowledged, however, it remains to be elucidated whether the existence of CAD is associated with an accelerated expansion rate of AAA. Also, the relationship between preoperative CAD and postoperative major adverse cardiovascular events (MACE) has not been examined in Japanese patients. The aim of this study was to investigate the deleterious effects of CAD on the progression of AAA and the onset of postoperative MACE after elective AAA repair. A retrospective cohort study of 665 consecutive Japanese patients who underwent elective surgical repair for infrarenal AAA at 2 high-volume Tokyo hospitals from 2003 through 2010 was performed. Preoperative CAD was shown to be a significant determinant of postoperative MACE (HR 2.29; 95%CI, 1.12-4.66; p=0.02). In the analysis of 510 patients for whom there were at least 2 follow-up CT scans of the size of their AAA before repair, the existence of CAD was shown to be inversely associated with the accelerated expansion rate of AAA. This study on the patients undergone elective repair for infrarenal AAA identified an inverse association between the existence of CAD and progression of AAA as well as the significant impact of preoperative CAD on the occurrence of postoperative MACE after elective AAA repair.
    Atherosclerosis 03/2012; 222(1):278-83. DOI:10.1016/j.atherosclerosis.2012.02.031 · 3.97 Impact Factor