Computational analysis of cutting parameters based on gradient Voronoi model of cancellous bone.

Bone cutting is a complicated surgical operation. It is very important to establish a kind of gradient porous bone model in vitro which is close to human bone for the research of bone cutting. Due to the existing bone cutting researches are based on solid bone model, which is quite different from human bone tissue structure. Therefore, Voronoi method was used to establish a gradient porous bone model similar to real bone tissue to simulate the process of bone drilling in this paper. High temperature and large cutting force during bone drilling can cause serious damage to bone tissue. Urgent research on bone drilling parameters is necessary to reduce cutting temperature and cutting force. The finite element analysis (FEA) of Voronoi bone models with different gradients is carried out, and a Voronoi model which is similar to real bone tissue is obtained and verified by combining the cutting experiment of pig bone. Then orthogonal experiments are designed to optimize the cutting parameters of Voronoi bone model. The range method is used to analyze the influence weights of cutting speed, feed speed and tip angle on cutting temperature and cutting force, and the least square method was used to predict the cutting temperature and cutting force, respectively. The gradient porous bone model constructed by Voronoi method was studied in detail in this paper. This study can provide theoretical guidance for clinical bone drilling surgery, and the prediction model of bone drilling has practical significance.

The Mechanism of Fracture and Damage Evolution of Granite in Thermal Environment.

In the study of rock mechanics, the variation of rock mechanical characteristics in high-temperature environments is always a major issue. The discrete element method and Voronoi modeling method were used to study the mechanical characteristics and crack evolution of granite specimens subjected to the high temperature and uniaxial compression test in order to study the internal crack evolution process of granite under the influence of high temperatures. Meanwhile, dependable findings were acquired when compared to experimental outcomes. A modified failure criterion was devised, and a Fish function was built to examine the evolution behavior of tensile and shear cracks during uniaxial compression, in order to better understand the evolution process of micro-cracks in granite specimens. Shear contacts occurred first, and the number of shear cracks reached its maximum value earliest, according to the findings. The number of tensile contacts then rapidly grew, whereas the number of shear cracks steadily declined. Furthermore, it was found that when temperature rises, the number of early tensile cracks grows. This study develops a fracture prediction system for rock engineering in high-temperature conditions.

Longer diabetes duration reduces myocardial blood flow in remote myocardium assessed by dynamic myocardial CT perfusion.

AIMS: To investigate the relationship of type 2 diabetes duration and myocardial blood flow (MBF) assessed by myocardial CT perfusion. MATERIALS AND METHODS: We prospectively included 140 patients with type 2 diabetes who underwent dynamic myocardial CT perfusion exam. MBF of the remote myocardium was calculated using the deconvolution technique and the Voronoi method. The relationships of MBF and diabetic duration, diabetic complications, conventional risk factors, coronary calcium, and coronary stenosis were assessed by logistic regression analysis. RESULTS: A weak but significantly negative relationship was present between diabetes duration and MBF (R2 = 0.05, p < 0.01). The average MBF of patients with a duration of >8 years was 13% lower than that of the remaining patients (1.11 ±â€¯0.35 vs 1.28 ±â€¯0.27 ml min-1 g-1, p < 0.01). Duration of one year was associated with a 6% increased risk for low MBF (<1.18 ml min-1 g-1) (odds ratio 1.06, 95% confidence interval 1.01-1.12, p < 0.05). Calcium score was also a significant factor for low MBF (odds ratio 1.08 (per 100 Agatston units), 95% confidence interval 1.01-1.17, p < 0.05). CONCLUSION: Longer diabetes duration is associated with lower MBF independent of conventional cardiac risk factors or the presence of coronary stenosis.

Cardiac computed tomography-derived myocardial mass at risk using the Voronoi-based segmentation algorithm: A histological validation study.

BACKGROUND: Myocardial mass at risk (MMAR) is an important predictor of adverse cardiac events in patients with ischemic heart disease. This study aims to validate the accuracy of MMAR calculated from cardiac computed tomography (CCT) data using the Voronoi-based segmentation algorithm in comparison with actual MMAR measured on ex-vivo swine hearts prepared by injecting a dye into the coronary arteries. METHODS: Fifteen extracted swine hearts had India ink injected into one of the major coronary arteries. Subsequently, all coronary arteries manually injected with methylcellulose-based iohexiol-370 were imaged by 16-row CT. The ventricles were cross-sectioned perpendicularly to the long axis of the left ventricle (LV). The stained area and the total LV area of individual slices were measured, and actual MMAR was calculated as the ratio of the LV volume with the disc-summation method. CT-based MMAR of each coronary artery was calculated automatically with the Voronoi-based segmentation algorithm. The results were compared using Pearson's correlation coefficient. RESULTS: The median value of CT-based MMAR was 50.8% for the left anterior descending artery (LAD), 36.6% for the left circumflex artery (LCX), and 23.0% for the right coronary artery (RCA). Actual MMAR was 49.8% for LAD, 32.2% for LCX, and 25.9% for RCA. CT-based MMAR was significantly related to actual MMAR (r = 0.92, p = 0.02 for LAD; r = 0.96, p = 0.009 for LCX; r = 0.96, p = 0.009 for RCA). CONCLUSION: CT-based MMAR obtained by Voronoi-based segmentation algorithm reliably estimates actual MMAR measured on ex-vivo swine hearts.

Reproducibility and clinical potential of myocardial mass at risk calculated by a novel software utilizing cardiac computed tomography information.

To select the best revascularization strategy a correct understanding of the ischemic territory and the coronary anatomy is crucial. Stress myocardial perfusion single photon emission computed tomography (SPECT) is the gold standard to assess ischemia, however, SPECT has important limitations such as lack of coronary anatomical information or false negative results due to balanced ischemia in multi-vessel disease. Angiographic scores are based on anatomical characteristics of coronary arteries but they lack information on the extent of jeopardized myocardium. Cardiac computed tomography (CCT) has the ability to evaluate the coronary anatomy and myocardium in one sequence, which is theoretically the ideal method to assess the myocardial mass at risk (MMAR) for any target lesion located at any point in the coronary tree. In this study we analyzed MMAR of the three main coronary arteries and three major side branches; diagonal (Dx), obtuse marginal (OM), and posterior descending artery (PDA) in 42 patients with normal coronary arteries using an algorithm based on the Voronoi method. The distribution of MMAR among the three main coronary arteries was 44.3 ± 5.6 % for the left anterior descending artery, 28.2 ± 7.3 % for the left circumflex artery, and 26.8 ± 8.6 % for the right coronary artery. MMAR of the three major side branches was 11.3 ± 3.9 % for the Dx, 12.6 ± 5.2 % for the OM and 10.2 ± 3.4 % for the PDA. Intra- and inter-observer analysis showed excellent correlation (r = 0.97; p < 0.0001 and r = 0.95; p < 0.0001, respectively). In conclusion, CCT-based MMAR assessment is reliable and may offer important information for selection of the optimal revascularization procedure.