Publications by authors named "Hiroichi Yokoyama"

3 Publications

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Investigations into the Potential of Using Open Source CFD to Analyze the Differences in Hemodynamic Parameters for Aortic Dissections (Healthy versus Stanford Type A and B).

Ann Vasc Surg 2021 Oct 12. Epub 2021 Oct 12.

Department of Cardiac Surgery, Asahikawa Medical University, Asahikawa, Japan.

Background: The objective of this study was to develop a method to evaluate the effects of an aortic dissection on hemodynamic parameters by conducting a comparison with that of a healthy (nondissected) aorta. Open-source software will be implemented, no proprietary software/application will be used to ensure accessorily and repeatability, in all the data analysis and processing. Computed tomography (CT) images of aortic dissection are used for the model geometry segmentation. Boundary conditions from literature are implemented to computational fluid dynamics (CFD) to analyze the hemodynamic parameters.

Methods: A numerical simulation model was created by obtaining accurate 3-dimensional geometries of aortae from CT images. In this study, CT images of 8 cases of aortic dissection (Stanford type-A and type-B) and 3 cases of healthy aortae are used for the actual aorta model geometry segmentation. These models were exported into an open-source CFD software, OpenFOAM, where a simplified pulsating flow was simulated by controlling the flow pressure. Ten cycles of the pulsatile flow (0.50 sec/cycle) conditions, totaling 5 sec, were calculated.

Results: The pressure distribution, wall shear stress (WSS) and flow velocity streamlines within the aorta and the false lumen were calculated and visualized. It was found that the flow velocity and WSS had a high correlation in high WSS areas of the intermittent layer between the true and false lumen. Most of the Stanford type-A dissections in the study showed high WSS, over 38 Pa, at the systole phase. This indicates that the arterial walls in type-A dissections are more likely to be damaged with pulsatile flow.

Conclusions: Using CFD to estimate localized high WSS areas may help in deciding to treat a type-A or B dissection with a stent graft to prevent a potential rupture.
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http://dx.doi.org/10.1016/j.avsg.2021.08.007DOI Listing
October 2021

Can 64-row computed tomography replace angiography after coronary bypass?

Asian Cardiovasc Thorac Ann 2008 Dec;16(6):444-9

Department of Cardiovascular Surgery, Cardiovascular Center, Hokkaido Ohno Hospital, Sapporo, Hokkaido 063-0034, Japan.

Multi-detector (64-row) computed tomography has become an alternative to coronary angiography to diagnose graft occlusion and stenosis after coronary artery bypass. We compared the power of evaluation of multi-detector computed tomography with that of conventional coronary angiography in 60 patients who underwent coronary artery bypass with 135 grafts and 210 graft anastomoses. The diagnostic power of multi-detector computed tomography for graft occlusion was: 100% (2/2) sensitivity, 98.5% (131/133) specificity, 50% (2/4) positive predictive value, and 100% (133/133) negative predictive value; there were no significant differences in rates of occlusion among the different types of graft. The diagnostic power of multi-detector computed tomography for stenosis of the graft anastomosis was: 100% (2/2) sensitivity, 95.1% (194/204) specificity, 16.6% (2/12) positive predictive value, and 100% (194/194) negative predictive value, with no significant differences among grafts. Multi-detector computed tomography permits evaluation of bypass grafts and is much less invasive for the patients.
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http://dx.doi.org/10.1177/021849230801600603DOI Listing
December 2008

Three-dimensional reconstruction of computed tomographic images of anomalous origin of the left main coronary artery from the pulmonary trunk in an adult.

Am J Cardiol 2003 Oct;92(7):898-9

Department of Cardiology, Nakadori General Hospital, Akita, Akita, Japan.

We present a 49-year-old female case of anomalous origin of the left main coronary artery from the pulmonary trunk. Multidetector computed tomography was performed, and 3-dimensional reconstruction of computed tomographic images found that the left main coronary artery originated from left sinus of the pulmonary trunk and the right coronary artery from the right coronary cusp of the aorta. We speculate that this patient's long life may be due to the dominant right coronary artery and rich collateral from the right coronary artery to the left coronary artery.
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http://dx.doi.org/10.1016/s0002-9149(03)00913-5DOI Listing
October 2003
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