Three dimensional (3D) printing is considered as an advanced manufacturing technology because of its additive nature. Electron beam melting (EBM) is a widely used 3D printing processes for the manufacturing of metal components. However, the products printed via this process generally contain micro porosities which affect mechanical properties, especially the fatigue property. In this paper, two types of EBM printed samples of the Ti-6Al-4V alloy, one with a round cross section and the other with a triangle cross section, were employed to investigate the existence of porosities using computed tomography (CT). Statistical analyses were conducted on the number, volume, shape, and distribution of pores. The results show that small pores (less than 0.000 2 mm3) account for 80% of all pores in each type of samples. Additionally, to some extent, the shape of sample has influence on the number of micro porosities in EBM made Ti-6Al-4V. The sphericity of the pores is relatively low and is inversely proportional to pore volume. It is found that re-melting on the free surface effectively reduce pore density near the surface. This study may help produce a medical implant with better fatigue resistance.
The effect of relaxation time in hyperbolic heat transfer model on the temperature field of microwave ablation of atrial fibrillation was investigated. And the results were compared with those calculated by Pennes model. A three-dimensional model of microwave ablation of atrial fibrillation was constructed. The relaxation time (τ) was 0, 1, 5, 8, 10, 15 and 20 s, respectively. And the temperature field of myocardial tissue was obtained. The results showed that the highest temperature of the hyperbolic model was 21.8 ℃ lower than that of the Pennes model at the beginning of ablation. With the increase of ablation time, the highest temperature tended to be the same. The lesion dimensions appeared at 3, 4, 6, 7, 8, 9, and 10 s, respectively after ablation. Therefore, the influence of hyperbolic model on temperature will decrease with the increase of the ablation time. At the beginning of ablation, the relaxation time will hinder the speed of myocardial thermal diffusion. The larger the relaxation time is, the slower the speed of thermal diffusion is. This study provides a reference for the application of hyperbolic model in microwave ablation of atrial fibrillation.
Objective To investigate the load distribution on the more painful and less painful limbs in patients with mild-to-moderate and severe bilateral knee osteoarthritis (KOA) and explore the compensatory mechanisms in both limbs among bilateral KOA patients with different severity levels. Methods A total of 113 participants were enrolled between July 2022 and September 2023. This cohort comprised 43 patients with mild-to-moderate bilateral KOA (Kellgren-Lawrence grade 2-3), 43 patients with severe bilateral KOA (Kellgren-Lawrence grade 4), and 27 healthy volunteers (healthy control group). The visual analogue scale (VAS) score for pain, the Hospital for Special Surgery (HSS) score, passive knee range of motion (ROM), and hip-knee-ankle angle (HKA) were used to assess walking pain intensity, joint function, and lower limb alignment in KOA patients, respectively. Motion trajectories of reflective markers and ground reaction force data during walking were captured using a gait analysis system. Musculoskeletal modeling was then employed to calculate biomechanical parameters, including the peak knee adduction moment (KAM), KAM impulse, peak joint contact force (JCF), and peak medial/lateral contact forces (MCF/LCF). Statistical analyses were performed to compare differences in clinical and gait parameters between bilateral limbs. Additionally, one-dimensional statistical parametric mapping was utilized to analyze temporal gait data. Results Mild-to-moderate KOA patients showed the significantly higher HSS score (67.7±7.9) than severe KOA patients (51.9±8.9; t=8.747, P<0.001). The more painful limb in all KOA patients exhibited significantly greater HKA and higher VAS scores compared to the less painful limb (P<0.05). While bilateral knee ROM did not differ significantly in mild-to-moderate KOA patients (P>0.05), the severe KOA patients had significantly reduced ROM in the more painful limb versus the less painful limb (P<0.05). Healthy controls showed no significant bilateral difference in any biomechanical parameters (P>0.05). All KOA patients demonstrated longer stance time on the less painful limb (P<0.05). Critically, severe KOA patients exhibited significantly higher peak KAM, KAM impulse, and peak MCF in the more painful limb (P<0.05), while mild-to-moderate KOA patients showed the opposite pattern with lower peak KAM and KAM impulse in the more painful limb (P<0.05) and a similar trend for peak MCF. Conclusion Patients with mild-to-moderate KOA effectively reduce load on the more painful limb through compensatory mechanisms in the less painful limb. Conversely, severe bilateral varus deformities in advanced KOA patients nullify compensatory capacity in the less painful limb, paradoxically increasing load on the more painful limb. This dichotomy necessitates personalized management strategies tailored to disease severity.
ObjectiveStudy how to quantify the bias of each study and how to estimate them. MethodIn the random-effect model, it is commonly assumed that the effect size of each study in meta-analysis follows a skew normal distribution which has different shape parameter. Through introducing a shape parameter to quantify the bias and making use of Markov estimation as well as maximum likelihood estimation to estimate the overall effect size, bias of each study, heterogeneity variance. ResultIn simulation study, the result was closer to the real value when the effect size followed a skew normal distribution with different shape parameter and the impact of heterogeneity of random effects meta-analysis model based on the skew normal distribution with different shape parameter was smaller than it in a random effects metaanalysis model. Moreover, in this specific example, the length of the 95%CI of the overall effect size was shorter compared with the model based on the normal distribution. ConclusionIncorporate the bias of each study into the random effects meta-analysis model and by quantifying the bias of each study we can eliminate the influence of heterogeneity caused by bias on the pooled estimate, which further make the pooled estimate closer to its true value.
In order to check the neck response and injury during motor vehicle accidents, we developed a detailed finite element model for human cervical spine C4-C6. This model consisted of cortical bone, cancellous bone, annulus, nucleus, ligaments and articular facet, and it also set up contact in the contacting parts for simulating the movement perfectly under frontal impact. This model could be used for stress and strain distribution after the frontal impact load was applied on this model. During the process of frontal impact, the most displacement simulated data were in the interval range of experimental data. The experimental results showed that this model for the human cervical spine C4-C6 simulated the movement under the frontal impact with fidelity, and reflected the impact dynamics response on the whole.
Missing data represent a general problem in many scientific fields, especially in medical survival analysis. Dealing with censored data, interpolation method is one of important methods. However, most of the interpolation methods replace the censored data with the exact data, which will distort the real distribution of the censored data and reduce the probability of the real data falling into the interpolation data. In order to solve this problem, we in this paper propose a nonparametric method of estimating the survival function of right-censored and interval-censored data and compare its performance to SC (self-consistent) algorithm. Comparing to the average interpolation and the nearest neighbor interpolation method, the proposed method in this paper replaces the right-censored data with the interval-censored data, and greatly improves the probability of the real data falling into imputation interval. Then it bases on the empirical distribution theory to estimate the survival function of right-censored and interval-censored data. The results of numerical examples and a real breast cancer data set demonstrated that the proposed method had higher accuracy and better robustness for the different proportion of the censored data. This paper provides a good method to compare the clinical treatments performance with estimation of the survival data of the patients. This provides some help to the medical survival data analysis.
Functional imaging method of biological electrical characteristics based on magneto-acoustic effect gives valuable information of tissue in early tumor diagnosis, therein time and frequency characteristics analysis of magneto-acoustic signal is important in image reconstruction. This paper proposes wave summing method based on Green function solution for acoustic source of magneto-acoustic effect. Simulations and analysis under quasi 1D transmission condition are carried out to time and frequency characteristics of magneto-acoustic signal of models with different thickness. Simulation results of magneto-acoustic signal were verified through experiments. Results of the simulation with different thickness showed that time-frequency characteristics of magneto-acoustic signal reflected thickness of sample. Thin sample, which is less than one wavelength of pulse, and thick sample, which is larger than one wavelength, showed different summed waveform and frequency characteristics, due to difference of summing thickness. Experimental results verified theoretical analysis and simulation results. This research has laid a foundation for acoustic source and conductivity reconstruction to the medium with different thickness in magneto-acoustic imaging.
ObjectiveTo survey and analyze the trend of congenital heart disease (CHD) of regions distribution and medical payment model in Children's Hospital of Gansu Province over the past 11 years, and to provide evidence for diagnosis and treatment strategies for CHD children. MethodsMedical records of the CHD children hospitalized in the Children's Hospital of Gansu Province from 2001 to 2011 were completely collected. Regional distribution, year and other basic information of them were extracted. Data was then analyzed using the SPSS 16.0 software. ResultsA total of 591 CHD children were included. Most of them came from Middle-Long, accounting for 68.87%; while the number of CHD children in the region of East-Long and He-xi had a tendency of growth by year, with average growth speed of 189.42% and 27.62%, respectively. Most of them came from the region which is economic class Ⅲ, accounting for 35.64% (highest) with average growth speed (203.45%). Most of the treatment costs were self-supported before 2005, and health insurance and other social aids were consistently increasing after 2005. Most of the institutions for initial visit were town-level hospitals, accounting for 55.50%, and with average growth speed of 170.18%. ConclusionThe medical demand of CHD children in less-developed regions in Gansu province increases year by year. Government-guided healthcare system should be established and improved so as to basically guarantee the prevention and treatment of CHD in less-developed regions.
ObjectiveTo analyze the distribution, prognostic differences, and characteristics of patients with colorectal cancer (CRC) from 2007 to 2022 based on the current version of the Database from Colorectal Cancer (DACCA), so as to provide a basis for clinical decision-making. MethodsThe eligible CRC patients based on the established screening criteria from the updated DACCA were collected. The distribution and survival status of CRC patients in different residence places were analyzed. The residence places included 21 cities (prefectures) within Sichuan Province. ResultsA total of 5 416 cases that met the screening criteria from 2007 to 2022 were collected. Among these, CRC patients were predominantly concentrated in Chengdu (44.77%), Meishan (5.78%), and Nanchong (4.56%) cities. A heatmap depicting the superimposed trend of CRC patients origins revealed the distribution of patients was basically divided into eastern and western regions along the axis of “Mianyang–Chengdu–Yaan cities”. The majority of patients (5 359 cases, 98.95%) was distributed in the eastern region, while a few in the western region (57 cases, 1.05%). The patients in the eastern region were more high clustered (especially Chengdu city), while those in the western region was sporadically dispersed, and the patients in the western region increased slowly without aggregation. The 1, 3, and 5-year cumulative overall survival rates of the CRC patients in the DACCA were 96.2%, 89.7%, and 85.1%, respectively. The multivariate Cox proportional hazards regression model showed that the male, age ≥35-year old, adenocarcinoma (mucinous adenocarcinoma as a reference), poorly differentiated degree, pTNM stages Ⅲ and Ⅳ, obstruction, and perforation were the risk factors for median overall survival shortening in the CRC patients (all P<0.05). The survival curve of patients with CRC drawn by Kaplan-Meier method showed that the overall survival of CRC patients in different cities (prefectures) had no statistical differences as compared with the integral CRC patients (P>0.05), except for Neijiang city (was worse than that of the integral CRC patients, P<0.05). ConclusionsBased on data analysis for the DACCA from 2007 to 2022, the majority of CRC patients clusters in the eastern region. Chengdu city exhibits a high clustering, while the western region shows a sporadic distribution without aggregation phenomena. It is found that the cumulative overall survival of CRC patients in Neijiang city is worse than that of the integral CRC patients, while which in the other cities (prefectures) was relatively close to that of the integral CRC patients in Sichuan Province.
The temperature during the brain tumor therapy using high-intensity focused ultrasound (HIFU) should be controlled strictly. This research aimed at realizing uniform temperature distribution in the focal region by adjusting driving signals of phased array transducer. The three-dimensional simulation model imitating craniotomy HIFU brain tumor treatment was established based on an 82-element transducer and the computed tomography (CT) data of a volunteer's head was used to calculate and modulate the temperature distributions using the finite difference in time domain (FDTD) method. Two signals which focus at two preset targets with a certain distance were superimposed to emit each transducer element. Then the temperature distribution was modulated by changing the triggering time delay and amplitudes of the two signals. The results showed that when the distance between the two targets was within a certain range, a focal region with uniform temperature distribution could be created. And also the volume of focal region formed by one irradiation could be adjusted. The simulation results would provide theoretical method and reference for HIFU applying in clinical brain tumor treatment safely and effectively.