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Coral Reef Bleaching under Climate Change: Prediction Modeling and Machine Learning
(2022-05-01)
Boonnam, Nathaphon
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Udomchaipitak, Tanatpong
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Puttinaovarat, Supattra
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Chaichana, Thanapong
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Boonjing, Veera
The coral reefs are important ecosystems to protect underwater life and coastal areas. It is also a natural attraction that attracts many tourists to eco-tourism under the sea. However, the impact of climate change has led to coral reef bleaching and elevated mortality rates. Thus, this paper modeled and predicted coral reef bleaching under climate change by using machine learning techniques to provide the data to support coral reefs protection. Supervised machine learning was used to predict the level of coral damage based on previous information, while unsupervised machine learning was applied to model the coral reef bleaching area and discovery knowledge of the relationship among bleaching factors. In supervised machine learning, three widely used algorithms were included: Naïve Bayes, support vector machine (SVM), and decision tree. The accuracy of classifying coral reef bleaching under climate change was compared between these three models. Unsupervised machine learning based on a clustering technique was used to group similar characteristics of coral reef bleaching. Then, the correlation between bleaching conditions and characteristics was examined. We used a 5-year dataset obtained from the Department of Marine and Coastal Resources, Thailand, during 2013–2018. The results showed that SVM was the most effective classification model with 88.85% accuracy, followed by decision tree and Naïve Bayes that achieved 80.25% and 71.34% accuracy, respectively. In unsupervised machine learning, coral reef characteristics were clustered into six groups, and we found that seawater pH and sea surface temperature correlated with coral reef bleaching.
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Flow simulation in coronary artery models: An investigation of the effect of variable angulations at the left coronary artery
(2010-12-01)
Chaichana, Thanapong
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Sun, Zhonghua
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Tungjitkusolmun, Supan
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Sangworasil, Manas
This study was designed to investigate the hemodynamics in the left coronary artery with the aim of identifying the relationship between angulations of left coronary bifurcation and development of atherosclerosis. Six 3D left coronary models were simulated for computational fluid dynamic analysis. The left coronary model was composed of left main stem, left anterior descending and left circumflex branches. The angulations at the left bifurcation were simulated with angles ranging from 90°, 75°, 60°, 45°, 30° to 15°. The computational fluid dynamic was used for analysis of flow velocity, wall pressure and wall shear stress. Our results showed that apparent low shear stress and high wall pressure was noticed at the left coronary bifurcation regions with wide angled models. Flow pattern was also changed with angled becoming wide in the simulated models. Our analysis shows direction relationship between coronary angulation and development of atherosclerosis. Future studies are required to perform computational fluid dynamic analysis in coronary models from patients' data with different degree of coronary stenosis. © 2010 IEEE.
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Fenestrated stent graft repair of abdominal aortic aneurysm: Hemodynamic analysis of the effect of fenestrated stents on the renal arteries
(2010-01-01)
Sun, Zhonghua
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Chaichana, Thanapong
Objective: We wanted to investigate the hemodynamic effect of fenestrated stents on the renal arteries with using a fluid structure interaction method. Materials and Methods: Two representative patients who each had abdominal aortic aneurysm that was treated with fenestrated stent grafts were selected for the study. 3D realistic aorta models for the main artery branches and aneurysm were generated based on the multislice CT scans from two patients with different aortic geometries. The simulated fenestrated stents were designed and modelled based on the 3D intraluminal appearance, and these were placed inside the renal artery with an intra-aortic protrusion of 5.0-7.0 mm to reflect the actual patients' treatment. The stent wire thickness was simulated with a diameter of 0.4 mm and hemodynamic analysis was performed at different cardiac cycles. Results: Our results showed that the effect of the fenestrated stent wires on the renal blood flow was minimal because the flow velocity was not significantly affected when compared to that calculated at pre-stent graft implantation, and this was despite the presence of recirculation patterns at the proximal part of the renal arteries. The wall pressure was found to be significantly decreased after fenestration, yet no significant change of the wall shear stress was noticed at post-fenestration, although the wall shear stress was shown to decrease slightly at the proximal aneurysm necks. Conclusion: Our analysis demonstrates that the hemodynamic effect of fenestrated renal stents on the renal arteries is insignificant. Further studies are needed to investigate the effect of different lengths of stent protrusion with variable stent thicknesses on the renal blood flow, and this is valuable for understanding the long-term outcomes of fenestrated repair.
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3D virtual intravascular endoscopy visualization of coronary artery plaques: Virtual intravascular endoscopy of coronary plaques
(2009-12-31)
Sun, Zhonghua
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Chaichana, Thanapong
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Dimpudus, Franky Jacobus
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Adipranoto, Jeffrey Daniel
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Nugroho, Johanes
The purpose of the study is to investigate the potential diagnostic value of 3D virtual intravascular endoscopy in the visualization of coronary artery plaques in patients with suspected coronary artery disease. Ten patients suspected of coronary artery disease undergoing 64-slice computed tomography scans were included in the study. Four main coronary artery branches including right coronary artery, left main stem, left anterior descending and left circumflex were assessed using virtual intravascular endoscopy with emphasis on the intraluminal appearance of coronary plaques (calcified and noncalcified plaques). Position of the plaques and degree of vessel stenosis was compared with 2D axial images in each patient. Coronary artery disease with >50% stenosis was found in 6 patients involving 7 left anterior descending and 3 right coronary artery branches. Left anterior descending branch was commonly affected with extensive calcification, while more than half of the right coronary arteries were involved with noncalcified plaques. Our results showed that virtual intravascular endoscopy provides unique information of the coronary plaques by demonstrating the intraluminal configuration of coronary plaques, position of the plaques in relation to the artery branches. Both calcified and noncalcified plaques can be identified on virtual endoscopy images. Further studies are needed to clarify the role of virtual intravascular endoscopy in the quantification of plaque volume, stratification of patients suffering from coronary artery disease and patients management. ©2009 IEEE.
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Hemodynamic effect of calcifed plaque on blood flow in carotid artery disease: A preliminary study - Hemodynamic effect of calcified plaque
(2009-12-31)
Sun, Zhonghua
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Mwipatayi, Bibombe
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Chaichana, Thanapong
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Ng, Curtise
The purpose of the study is to investigate the hemodynamic effect of calcified carotid plaque on blood flow in patients diagnosed with carotid artery disease. Two carotid artery models were generated based on a sample patient data, with normal and calcified carotid artery appearances. Circular calcified carotid plaque was found at the carotid bifurcation based on 3D computed tomography images. A computational fluid dynamics was performed to analyze the changes of blood flow in different situations. Our results showed that apparent turbulence was found in the diastolic phase at the carotid bifurcation in normal carotid artery geometry. In the presence of the calcified plaque, the flow velocity was increased to some extent, indicating the effect of plaque on hemodynamic changes. Wall shear stress was noticed to decrease at the aortic branches, and this indicates the potential risk of developing stenosis at this area. Our preliminary study demonstrates fluid structure interaction between calcified plaque and artery in terms of flow changes and wall shear stress. ©2009 IEEE.
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Investigation of hemodynamic changes in abdominal aortic aneurysms treated with fenestrated endovascular grafts
(2009-12-01)
Sun, Zhonghua
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Chaichana, Thanapong
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Allen, Yvonne B.
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Sangworasil, Manas
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Tungjitkusolmun, Supan
Fenestrated stent grafts are becoming widely used in clinical practice to treat patients with complicated aortic aneurysms, with short to mid-term satisfactory outcomes being achieved. However, long-term results are yet to be determined. One of the main concerns about the safety of fenestrated repair is the patency of fenestrated renal arteries and subsequent renal function. The purpose of this study is to investigate the hemodynamic changes in patients treated with fenestrated stent grafts using a two-way fluid-structure interaction. 4 patients undergoing fenestrated stent graft repair were selected for inclusion in our analysis. All of the fenestrated renal arteries remained patent after implantation of stent grafts with one patient developing post-procedural complication, endoleak. Our results showed that with insertion of fenestrated stents into the renal arteries with variable lengths, no significant changes of blood flow velocity were noticed based on the flow analysis. Our preliminary study indicates the safety of fenestrated stent grafts, however, further studies are required to verify the long-term outcome of this procedure.
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Computational fluid analysis of blood flow characteristics in abdominal aortic aneurysms treated with suprarenal endovascular grafts
(2009-12-01)
Sun, Zhonghua
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Chaichana, Thanapong
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Sangworasil, Manas
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Tungjitkusolmun, Supan
The purpose of this study is to investigate the hemodynamic effects of suprarenal stent grafts on the renal arteries in the treatment of patients with abdominal aortic aneurysm. Suprarenal stent grafts have been increasingly used for treatment of aortic aneurysms with suboptimal aneurysm necks. However, the long-term safety of this procedure is yet to be determined. 2 sample patients undergoing suprarenal stent grafting were included in the study. Four variable configurations of stent wires crossing the renal artery ostium were simulated in aorta models based on CT generated data, at different cardiac cycles. The stent wires thickness was set 0.5 mm which is similar to the actual diameter of a stent wire. Computational fluid dynamic analysis showed slightly decrease of flow velocity to the renal arteries with multiple wires crossing, and no changes of flow velocity to the renal arteries with single wire crossing. Our preliminary results demonstrated the safety of suprarenal stent grafting. Further studies are required to investigate the effect of different wire thickness on subsequent hemodynamic changes to the renal arteries.
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Investigation of the hemodynamic effect of stent wires on renal arteries in patients with abdominal aortic aneurysms treated with suprarenal stent-grafts
(2009-07-01)
Sun, Zhonghua
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Chaichana, Thanapong
The purpose of the study was to investigate the hemodynamic effect of stent struts (wires) on renal arteries in patients with abdominal aortic aneurysms (AAAs) treated with suprarenal stent-grafts. Two sample patients with AAA undergoing multislice CT angiography pre- and postsuprarenal fixation of stent-grafts were selected for inclusion in the study. Eight juxtarenal models focusing on the renal arteries were generated from the multislice CT datasets. Four types of configurations of stent wires crossing the renal artery ostium were simulated in the segmented aorta models: a single wire crossing centrally, a single wire crossing peripherally, a V-shaped wire crossing centrally, and multiple wires crossing peripherally. The blood flow pattern, flow velocity, wall pressure, and wall shear stress at the renal arteries pre- and post-stent-grafting were analyzed and compared using a two-way fluid structure interaction analysis. The stent wire thickness was simulated with a diameter of 0.4, 1.0, and 2.0 mm, and hemodynamic analysis was performed at different cardiac cycles. The interference of stent wires with renal blood flow was mainly determined by the thickness of stent wires and the type of configuration of stent wires crossing the renal ostium. The flow velocity was reduced by 20-30% in most of the situations when the stent wire thickness increased to 1.0 and 2.0 mm. Of the four types of configuration, the single wire crossing centrally resulted in the highest reduction of flow velocity, ranging from 21% to 28.9% among three different wire thicknesses. Wall shear stress was also dependent on the wire thickness, which decreased significantly when the wire thickness reached 1.0 and 2.0 mm. In conclusion, our preliminary study showed that the hemodynamic effect of suprarenal stent wires in patients with AAA treated with suprarenal stent-grafts was determined by the thickness of suprarenal stent wires. Research findings in our study are useful for follow-up of patients treated with suprarenal stent-grafts to ensure long-term safety of the suprarenal fixation. © 2009 Springer Science+Business Media, LLC.
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Effect of fenestrated stents on the renal arteries: Investigation of hemodynamic changes in abdominal aortic aneurysms treated with fenestrated endovascular grafts
(2008-12-01)
Sun, Zhonghua
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Chaichana, Thanapong
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Tangjitkusolmun, Supan
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Sangwatthana, Surasak
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Allen, Yvonne B.
This article uses a novel method of combining 3D image visualization and computational fluid dynamics to investigate the potential effect of fenestrated stents on the renal arteries in terms of blood flow pattern, flow rate at different cardiac cycles, based on patients with abdominal aortic aneurysm treated with fenestrated stent grafts. 3D imaging appearance of the fenestrated stents inserted into the renal arteries is used to guide the simulation of the stent protrusion into the abdominal aorta model for analysis of hemodynamic changes. A circular stent protrusion with a length of between 5-7 mm inside the abdominal aorta is simulated in two aorta models, and computational fluid dynamics is performed to detect the change of flow pattern and flow rate at the renal arteries. Our results demonstrate change of the renal flow rate is minimal following implantation of fenestrated stents, indicating the safety of fenestrated stent graft repair of patients with aortic aneurysms. © 2008 IEEE.
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Edge detection of the optic disc in retinal images based on identification of a round shape
(2008-12-01)
Chaichana, Thanapong
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Yoowattana, Sarat
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Sun, Zhonghua
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Tangjitkusolmun, Supan
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Sookpotharom, Supot
This paper presents a novel method for identification of the position of the optic disc in retinal images. The method is based on the preliminary detection of the main edge detection of retinal image. The segmentation optic disc is estimated as a circular area. We searched for areas of optic disc using Hough transform which detected several straight lines and approximated them as a circular line. The position of optic disc was identified as the center of the circle. An evaluation of the proposed procedure was performed using a set of 40 images from the DRIVE database, containing images from both healthy (33) and diseased (7) subjects. The optic disc position was correctly identified in 39 out of 40 images and the efficiency was 97.5 percent. The results illustrate that the proposed method can be used for pathological analysis of retinal images. © 2008 IEEE.

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