Optimizing 4D cone-beam CT acquisition protocol for external beam radiotherapy

PURPOSE: Four-dimensional cone-beam computed tomography (4D-CBCT) imaging is sensitive to parameters such as gantry rotation speed, number of gantry rotations, X-ray pulse rate, and tube current, as well as a patient's breathing pattern. The aim of this study is to optimize the image acquisition on a patient-specific basis while minimizing the scan time and the radiation dose. METHODS AND MATERIALS: More than 60 sets of 4D-CBCT images, each with a temporal resolution of 10 phases, were acquired using multiple-gantry rotation and slow-gantry rotation techniques. The image quality was quantified with a relative root mean-square error (RE) and correlated with various acquisition settings; specifically, varying gantry rotation speed, varying both the rotation speed and the number of rotations, and varying both the rotation speed and tube current to keep the radiation exposure constant. These experiments were repeated for three different respiratory periods. RESULTS: With similar radiation dose, 4D-CBCT images acquired with low current and low rotation speed have better quality over images obtained with high current and high rotation speed. In general, a one-rotation low-speed scan is superior to a two-rotation double-speed scan, even though they provide the same number of projections. Furthermore, it is found that the image quality behaves monotonically with the relative speed as defined by the gantry rotation speed and the patient respiratory period. CONCLUSIONS: The RE curves established in this work can be used to predict the 4D-CBCT image quality before a scan. This allows the acquisition protocol to be optimized individually to balance the desired quality with the associated scanning time and patient radiation dose.     

反相高效液相色谱溶剂系统优化的正交设计法

在高效液相色谱(HPLC)中,通过改变流动相组成来调节色谱系统的选择性,以适应各种分析要求,但如何改变流动相组成以适应分析要求往往是一项费时而又复杂的工作。目前,国内外已报道了许多HPLC分析条件优化的方法,尤其是溶剂系统优化方法。本文     

医学双语教学教材优化探讨

双语教学是实现高等教育国际化的重要途径,教材是双语教学中的核心要素.为了解决教材建设滞后的问题,必须根据教学要求和实际情况对各种类型的双语教材采取优化措施,以使其能够对教学改革起到促进作用.本文对不同类型的医学双语教材进行了分析,提出了相应的优化建议.     

赤雹总黄酮提取优化工艺考察

目的：优选赤雹总黄酮的提取工艺。方法：以赤雹总黄酮的提出量为评价指标,以提取次数、提取时间、固液比为考察因素,采用正交试验法优选赤雹总黄酮的提取工艺。结果：优化的提取条件为70％乙醇回流,提取2次,每次1．5h,固液比为1：8。结论：此工艺操作简便,重复性好,稳定可行。     

An optimization model for reducing typhoid cases in developing countries without increasing public spending

This article considers the investment case for using the Vi polysaccharide vaccine in developing countries from two perspectives: reducing typhoid cases and limiting new health care spending. A case study is presented using data from South and Southeast Asia. The purpose of the paper, however, is to draw broad implications that may apply to developing countries in general. Typical consumer demand functions developed from stated preference household surveys in South and Southeast Asia are used to predict probabilities of adults and children purchasing typhoid vaccinations at different prices. These functions are incorporated in a formal mathematical model. Using data from the recent literature for South and Southeast Asia for typhoid incidence, Vi vaccine effectiveness, public cost of illness, and vaccination program cost, three mass vaccination policy alternatives are evaluated: charging adults and children different (optimal) prices, charging uniform prices, and providing free vaccines. Assuming differential pricing is politically feasible, different vaccine prices for children and adults would maximize the number of typhoid cases avoided from a mass vaccination program if the public sector faces a budget constraint on spending for the vaccination program. However, equal prices for children and adults produce very similar results, and they might be more readily accepted by the community. Alternatively, if vaccines are free, the number of cases is not significantly reduced compared to either pricing policy, but a large external financial contribution from government or donors would be required. A Monte Carlo simulation explores the effects of uncertain parameters on vaccination program outcomes.     

Loads in the spinal structures during lifting: development of a three-dimensional comprehensive biomechanical model

Summary Epidemiological studies have shown that loads imposed on the human spine during daily living play a significant role in the onset of low back pain. The loads applied to the lumbar spine are shared by a number of structures: muscles; posterior elements, including facets and ligaments; and the disc of a ligamentous motion segment. In vivo, it is not practical to determine forces in these structures using experimental techniques. Biomechanical models, based on an optimization technique or electromyographic activities of the trunk muscles, have been proposed to predict forces in the load transmitting structures. The mathematical models reported in the literature are based on information collected from a wide variety of sources, of which the subject that takes part in the experiment is only one. The present study describes techniques developed in our laboratory to collect from the subjects themselves all the data needed for the formulation of a biomechanical model. The results demonstrated that back lifting with 0 N (no load), 90 N, and 180 N in the hands created maximum external flexion moments respectively of 109.6 Nm, 137.9 Nm, and 161,7 Nm, at the L3–4 disc level. The corresponding external axial compression forces on the disc were 469.5 N, 511.8 N, and 601.5 N. The predicted disc compression varied from 3.4 to 5.0 times the body weight. In comparison to the static lifting mode, the dynamic lifting task caused an increase in the disc compression force ranging from 15.8% to 39.4% depending on the load being lifted (e.g., 3256 N for the dynamic mode vs. 2516 N for the static mode when the subject lifted 90 N). The salient features of the entire protocol developed by the authors and the need for further improvements are also presented.     

应用计算机优选和制作实验室标准工作曲线的研究

本文报道了选用11种数学模型用计算机优选和制作实验室标准工作曲线，以相关指数R值最大作为优选评估标准，同时对实验室标准工作曲线的类型和适宜的拟合方程进行了探讨．经应用表明，该方法操作简单，计算误差小，图形精致，提高了工作效率，能满足各级实验室的需要，具有广阔的推广应用前景．     

逐步logistic回归的一种算法

本文提出了逐步logistie回归的一种新的算法。这种算法是以解最优化问题的DFP-RFGS组合方法为基础建立起来的。它的主要优点是:(1)即使在变量数目多和数据量大的情况下,迭代过程能仍可靠地收敛于似然函数的极值点。(2)引入或剔除变量后,充分利用前面已有的计算结果设置迭代计算的初始值点和初始矩阵,从而简化了计算过程,使计算时间显著减小。文中介绍了实现本算法的过程,并举出计算实例。在附录中对有关的公式和结论作了证明。     

Surgical block scheduling in a system of hospitals: an application to resource and wait list management in a British Columbia health authority

Scheduling surgical specialties in a medical facility is a very complex process. The choice of schedules and resource availability impact directly on the number of patients treated by specialty, cancellations, wait times, and the overall performance of the system. In this paper we present a system-wide model developed to allow management to explore trade-offs between OR availability, bed capacity, surgeons’ booking privileges, and wait lists. We developed a mixed integer programming model to schedule surgical blocks for each specialty into ORs and applied it to the hospitals in a British Columbia Health Authority, considering OR time availability and post-surgical resource constraints. The results offer promising insights into resource optimization and wait list management, showing that without increasing post-surgical resources hospitals could handle more cases by scheduling specialties differently.