虚拟环境中人的操作判断及反应特性的实验研究

目的 研究被试者头戴头盔显示器、着数据手套在虚拟环境中进行操作时的判断及反应特性,探索利用虚拟现实系统获取工效学实验数据的真实性,以增强虚拟环境应用的可信度,为虚拟现实技术在栽人航天中深层次的应用(如人机界面设计方案模型的工效评价、虚拟训练)提供数据支撑。方法 利用自行开发与集成的虚拟现实实验系统,选定被试者并完成虚拟环境中人的操作判断及反应特性的实验设计。首先进行预实验,确定判断目标的差别等级和虚拟台体的高度,然后开始单因素的完全随机正式实验,同时设计主观问卷表对被试者进行虚拟效果的真实感调查。结果 被试者戴头盔显示器、利用数据手套将虚拟乘员舱内抽屉中的小球放置在一台体上的作业时间服从均值36．72s、方差13．798s正态分布。调查显示70．2％的被试者认为头盔显示器的立体效果明显,可以产生一种沉浸感,作业感受与真实世界一样。结论 建立虚拟环境进行人机界面的工效评价或操作虚拟训练时,首先应使系统硬件能够模拟真实任务背景,关键是头盔显示器和数据手套的交互性满足需要。这样,人在其中的判断及反应操作与真实世界就可以类比,从而可保证评价或训练效果的有效性。     

用于人-计算机界面设计的眼动时空特性研究

目的研究人 -计算机界面设计中的眼动时空特性 ,为优化基于视线追踪技术的人 -计算机界面设计提供工效学参数。方法 1 2名被试者在对象大小、对象间距和驻留时间的不同处理水平下 ,通过眼动完成目标选择任务 ,由计算机自动记录作业时间以及选择错误和超时数目。结果交互对象大小和驻留时间显著地影响了作业时间 ;对象间距和驻留时间对选择错误存在显著影响。结论驻留时间、对象大小和对象间距均为优化基于视线追踪的人 -计算机界面设计的主要参数。对一般的交互系统 ,作者推荐驻留时间取为 5 0 0ms,对象尺寸不小于 1 .5° ,对象间距不小于 1 .0°。     

不同体位着陆冲击时人体的动态响应

目的探讨不同体位着陆冲击时人体动态响应的变化。方法 5名健康男青年 ,承受峰值 1 0G ,作用时间为 50ms的半正弦脉冲的着陆冲击 ,冲击方向与人体纵轴的夹角 (体位角 )从 30°～ 70°间隔 1 0°增加 ,分别在人体头、肩、胸、髂部安装二维加速度计记录人体的动态响应。结果在本实验条件下 ,人体头Z向 (头盆向 )响应在 50°角时达最小 ,其值为 1 0 .36± 2 .44G ;在 70°角时响应达最大 ,其值为 1 8.0 7± 3.2 9G。胸Z向响应在 70°时达最小 ,其值为 1 0 .39± 3.97G ;在 60°时达最大 ,其值为 1 5.42± 3.61G。头X向 (胸背向 )响应在 30°时达最小 ,其值为 7.58± 1 .1 8G ;在 70°时响应达最大 ,其值为 1 8.89± 1 .85G。胸X向响应在 30°达最小 ,其值为 7.2 1± 1 .99G ;在 70°角时响应达最大 ,其值为 1 7.67± 2 .1 6G。结论在本实验条件下 ,人体对抗着陆冲击的最佳体位角为 50°。     

膝关节 Q 角变化规律的实验研究

本研究利用精密三维位移测读仪，研究分析了Ｑ角的变化趋势，以及对髌股关节运动的影响。研究结果表明，Ｑ角是一空间夹角，随屈膝角的增大而增大。力线在平面上的投影所呈的平面夹角Ｑｐ也就是通常所指的Ｑ角，在屈膝１５°左右达最大，而在９０°左右达最小。整个屈膝过程中，ＱＰ在５°－１５°之间变化，变化幅度达１０°左右。     

岩矢角的CT测定在岩锥X线摄影中的应用

目的评价CT测定头颅指数与岩矢角的动态关系在颞骨岩部X线摄影中的应用价值。方法选择无畸形的正常头颅1000例,在其CT平扫所得骨窗像中应用CT的功能测量岩锥角及头颅的最大前后径与横径,计算出修正的头颅指数,寻求二者之间的动态关系。结果成年男性头颅最大前后径在166mm～195mm之间,最大横径在140mm～163mm之间。头颅指数在76%～93%之间。岩矢角最大范围为51°～66°,其中短头型者平均在58～61之间,中头型者平均在54°～56°之间。成年女性头颅最大前后径在164mm～187mm之间,最大横径在130mm～153mm之间。头颅指数在75%～86%,岩矢角最大范围为51°～66°,其中短头型者平均在55°～57°之间,中头型者平均在53°～54°之间。结论通过CT测量可以方便、精确地计算岩矢角的大小,对于头颅复杂部位的特殊摄影,提高耳部及岩骨等病变的影像诊断具有较高的价值。     

手工计算非对称动态楔形野处方剂量的校正

目的 研究非对称射野情况下使用动态楔形板时手工计算处方剂量的校正。方法 利用VarianEclipse治疗计划系统和23EX加速器的数据计算射野分别为6cm×6cm、8cm×8cm、10cm×10cm、12cm×12cm、14cm×14cm、16cm×16cm、18cm×18cm、20cm×20cm的处方剂量。计算时保持射野不变,非楔方向为对称,改变楔形方向的准直器大小,使射野的几何中心与等中心的距离以1cm为步长递增。动态楔形板度数取10°、15°、20°、25°、30°、45°和60°,能量取6和10MV。根据计算结果模拟出射野几何中心与等中心的距离与校正因子之间的关系曲线图。选择有代表性的角度和射野,利用该校正因子对手工计算所得到的结果进行校正,并进行实际测量,验证结果是否在误差允许范围内。结果 射野大小对校正因子的影响很小,所以取不同射野时的平均值作为实际计算时使用的校正因子。不做校正时,能量为6MVX线的情况下,30°楔形板最大误差可达18%,45°楔形板最大误差可达30%,与实际所需要的处方剂量相差很多,校正以后测量结果的误差范围分别为-1.8%～0.09%和-1.8%～-0.25%,该误差大小可以接受。结论 在非对称动态楔形野的情况下,手工计算时采用对称野的楔形因子得到的处方剂量与实际治疗时应该使用的处方剂量有很大差别,采用校正因子校正后,误差缩小到临床能够接受的范围。     

离心机旋转时的定向知觉和运动知觉

前言 在离心机旋转时,当面切向朝前直坐时,受试者感到横滚倾侧。这种感知到的倾侧取决于重力惯性力矢量的综合角。研究揭示受试者面朝前比朝后前庭性眼球震颤持续时间要长。我们比较了面朝前和朝后时感知地平线判断以及在这些朝向时自动感知的持续时间。方法 受试者(n=29)在黑暗中旋转,离心机半径为20英尺,产生重力惯性力矢量为45°或60°倾     

中国人胫骨平台与半月板后倾角MRI测量

目的:测量、比较分析中国人胫骨后倾角与半月板后倾角,为人工全膝关节置换术中胫骨侧截骨提供参考。方法:对60例健康志愿者行膝关节核磁共振成像(MRI)检查,在MRI工作平台上进行操作,取冠状位内侧胫骨平台中间为测量平面,在该平面的矢状位对半月板及胫骨后倾角进行测量。结果:胫骨平台后倾角平均为9.87°±1.56°,半月板后倾角平均为0.96°±0.09°,半月板后倾角与胫骨平台后倾角有显著性差异(P<0.05)。本实验结果表明,中国人半月板的后倾角几乎为0°,并不随胫骨平台骨性结构的后倾而变化。膝关节胫、股骨关节面的最高接触面是股骨髁与半月板的接触。人工膝关节置换时进行胫骨侧切骨时可水平切骨,胫骨假体的安装亦可水平安装。     

参照系整合条件下的空间方位判断

目的考察空间方位判断（物体方位判断和前行方向判断）如何受目标物体位置和观察者前行方向的影响。方法采用4个组内设计的实验，分别以视图和记忆基础上的物体方位判断和前行方向判断作为实验任务；因变量以判断时间为主；被试者为80名大学生。结果1）0&#176;（前）和180&#176;位置（后）优势效应、朝北优势效应（除实验3以外）和正方向R90&#176;位置（左／右）优势效应明显：2）实验1和实验2、实验3和实验4在判断时间上没有显著差异；实验3和实验4中定位所用时间没有明显差异，但都长于判断时间。结论这两种判断受前行方向和目标位置的影响模式总体上是一致的，一定程度上不会因为信息载体和获取方式上的不同而改变。     

股四头肌腱与髌韧带张力关系的生物力学研究

本实验使用扣带式传感器对7例尸体膝关节在生理Q角、Q角增大10°、Q角减小10°和胫骨结节抬高术四种状态下,从90°到0°的伸膝过程中7个屈膝角度时的髌韧带张力和股四头肌腱张力进行测试。不同于传统的观点,我们的实验结果表明:髌骨不是只改变股四头肌腱和髌韧带张力方向的简化滑轮结构。Fp/Fq随膝关节屈曲角度的变化而明显改变,这种比率关系是由髌股关节接触区部位的移行决定的。髌骨不仅按照一定的比率传递股四头肌力,而且还起着增大髌韧带张力伸膝力臂的作用。本文还就Q角改变和胫骨结节抬高术对伸膝装置力学机制的影响进行了探讨。     

Computerunterstützte Mund-, Kiefer- und Gesichtschirurgie

BACKGROUND: Methods from the area of virtual reality are used in oral and maxillofacial surgery for the planning and three-dimensional individual simulation of surgeries. SIMULATION: In order to simulate complex surgeries with the aid of a computer, the diagnostic image data and especially various imaging modalities (CT, MRT, US) must be arranged in relation to each other, thus enabling rapid switching between the various modalities as well as the viewing of mixed images. Segmenting techniques for the reconstruction of three-dimensional representations of soft-tissue and osseous areas are required. We must develop ergonomic and intuitively useable interaction methods for the surgeon, thus allowing for precise and fast entry of the planned surgical intervention in the planning and simulation phase. SURGERY: During the surgical phase, instrument navigation tools offer the surgeon interactive support through operation guidance and control of potential dangers. This feature is already available today. Future intraoperative assistance will take the form of such passive tools for the support of intraoperative orientation as well as so-called tracking systems (semi-active systems) which accompany and support the surgeons' work. The final form are robots which execute specific steps completely autonomously. DISCUSSION: The techniques of virtual reality keep gaining in importance for medical applications. Many applications are still being developed or are still in the form of a prototype. However, it is already clear that developments in this area will have a considerable effect on the surgeon's routine work.     

Optimal clinical implementation of the Siemens virtual wedge.

Installation of a modern high-energy Siemens Primus linear accelerator at the Northern Centre for Cancer Treatment (NCCT) provided the opportunity to investigate the optimal clinical implementation of the Siemens virtual wedge filter. Previously published work has concentrated on the production of virtual wedge angles at 15 degrees, 30 degrees, 45 degrees, and 60 degrees as replacements for the Siemens hard wedges of the same nominal angles. However, treatment plan optimization of the dose distribution can be achieved with the Primus, as its control software permits the selection of any virtual wedge angle from 15 degrees to 60 degrees in increments of 1 degrees. The same result can also be produced from a combination of open and 60 degrees wedged fields. Helax-TMS models both of these modes of virtual wedge delivery by the wedge angle and the wedge fraction methods respectively. This paper describes results of timing studies in the planning of optimized patient dose distributions by both methods and in the subsequent treatment delivery procedures. Employment of the wedge fraction method results in the delivery of small numbers of monitor units to the beam's central axis; therefore, wedge profile stability and delivered dose with low numbers of monitor units were also investigated. The wedge fraction was proven to be the most efficient method when the time taken for both planning and treatment delivery were taken into consideration, and is now used exclusively for virtual wedge treatment delivery in Newcastle. It has also been shown that there are no unfavorable dosimetric consequences from its practical implementation.     

Are avatars treated like human obstacles during aperture crossing in virtual environments?

Research ObjectiveThe current study set out to determine whether individuals walking in a virtual reality environment pass through apertures made of two avatars differently than apertures created by two pole obstacles, as previously observed between pole and human obstacles in real-world environments.MethodsEleven healthy young adults wore a head-mounted virtual reality display, walked along a 10 m path and passed through a virtual aperture located 5 m from the starting location. Participants were instructed to avoid colliding with the obstacles when passing through the aperture. The experiment was conducted in a block design, where the aperture was either created by two pole obstacles or by two avatars. In both conditions, the width of the aperture ranged between 1.0–1.8x each participant’s shoulder width.ResultsRegardless of whether the aperture was created by the virtual poles or the avatars, participants rotated their shoulders for all aperture sizes and results found no significant differences in shoulder rotation angle, onset of rotation, walking speed or velocity at time of crossing between the two types of obstacles. Therefore, it appears that the differences in avoidance behaviours observed in real-world settings between people and pole obstacles is not translated to a virtual reality environment.SignificanceIt is possible that during experiments in which the avatars do not move, they do not possess human-like qualities suggested to be responsible for the increased caution used when walking through real human obstacles and instead, are treated as any ordinary obstacle.     

Breast compression and radiation dose in two different mammographic oblique projections: 45 and 60 degrees.

INTRODUCTION: Standard mammography includes two views, craniocaudal and medio-lateral oblique. Depending on patient's body constitution, central beam angle in mediolateral oblique projection may vary, with 45 degrees being suitable for the majority of patients in routine daily practice. With continuous improvement in X-ray technology and radiographers' training, the risk of radiation induced cancerogenesis is considerably reduced and acceptable when compared to benefit. However, the risk still exists, being cumulative and directly related to absorbed glandular dose. There is no minimal dose of radiation which is absolutely harmless, and every effort to reduce the dose is welcome. In this retrospective study two different angles (45 vs. 60 degrees) of mediolateral oblique view were compared according to radiation dose and efficacy of breast compression. PATIENTS AND METHODS: In 52 women, additional 60 degrees oblique films were done after craniocaudal and mediolateral oblique 45 degrees-films, with the same kVp and positioning technique. Breast thickness, time-current products (mA s) and absorbed doses were compared between 45 degrees- and 60 degrees-films. Subgroups of women with large, small, prominent and pendulous breasts were analyzed separately, following the same methodology as for the whole group. RESULTS: mA s were 11.5% lower and compression 7% better with an angle of 60 degrees than with 45 degrees. In the subgroup of women with small breasts, mA s values were 13% lower and compression 9% better with 60 degrees than with 45 degrees, while in the subgroup with large breasts, mA s were 9% lower and compression 5% better. In the subgroup of patients with pendulous breasts, mA s values were 12% lower and compression 10% better with 60 degrees than with 45 degrees, while in the subgroup with prominent breasts, mA s values were 4% lower and compression 3% better. Absorbed glandular dose was estimated to be approximately 20% lower when an oblique mammogram was done with 60 degrees instead of 45 degrees. The compression with 15 kp was well tolerated by the majority of patients. DISCUSSION AND CONCLUSION: Mammograms of excellent quality should be done with as low a radiation dose as possible. Adequate breast compression is fundamental in mammography due to immobilization of the breast, shortening of the exposure times, reduction of motion and geometric blur and prevention of overpenetration by means of equalizing breast thickness. As the absorbed glandular dose cannot be accurately measured, it is convenient to estimate the dose approximately, on the basis of its linear proportionality with exposure dose. With constant technical properties of X-ray machines, exposure dose is determined only by mA s. Hence, the absorbed glandular dose in our study was influenced only by changes of mA s and breast thickness. As the absorbed dose reduction is proportional to the product of the reduction of mA s and thickness, we estimated that absorbed dose was 7-22% lower if 60 degrees is applied instead of 45 degrees. Breast compression and mA s were more favourable in women with pendulous breasts, possibly because of elongation of the glandular disc in the lateroascending direction, with its longer axis directed more perpendicularly. Fibroglandular tissue in the 60 degrees-view is thus projected onto a larger film area, with less effect of superimposition. In conclusion, because of lower mA s values and better compression, which finally result in a 25% lower absorbed dose, we recommend the oblique view be done with an angle of 60 degrees, especially for small and pendulous breasts.     

The effects of joint angle and reliability on knee proprioception

PURPOSE: The purpose of this study was to examine the reliability and effects of knee angle on the detection and subsequent response to passive knee movement. METHODS: Twenty college-aged male and 20 female volunteers were evaluated for proprioception by a newly developed perturbation test. Subjects were in a prone position on an isokinetic chair with their right lower leg attached to a freely moving resistance adapter. The knee was placed in a starting position of 15, 30, or 60 degrees of flexion. While relaxed, the knee was dropped into extension, and the subjects were instructed to "catch their leg" when movement was perceived. Five trials were completed at each angle, in a random order. An electrogoniometer was secured to the lateral portion of the knee in order to measure angular displacement after perturbation in two specific phases: detection (displacement from leg release to movement cessation) and response (displacement from movement cessation to peak knee flexion). A three-factor ANOVA (two repeated factors (knee angle and proprioception phase) and one between factor (gender)) was performed on the average and standard deviation of the five trials for significant main effects and interactions. RESULTS: The results demonstrated a significant phase by angle interaction, and no gender effect. It was shown that at a more extended knee joint position (15 degrees), significantly less knee movement occurred before perception, followed by a greater response, than in a more flexed position (30 and 60 degrees). CONCLUSION: The major findings of this study suggest that the detection of passive knee movement, and the subsequent voluntary response, may be dependent on joint angle. Considerations of the present method for proprioception assessment are warranted to enhance test-retest reliability.     

The effect of viewing a virtual environment through a head-mounted display on balance

IntroductionIn the next few years, several head-mounted displays (HMD) will be publicly released making virtual reality more accessible. HMD are expected to be widely popular at home for gaming but also in clinical settings, notably for training and rehabilitation. HMD can be used in both seated and standing positions; however, presently, the impact of HMD on balance remains largely unknown. It is therefore crucial to examine the impact of viewing a virtual environment through a HMD on standing balance.ObjectivesTo compare static and dynamic balance in a virtual environment perceived through a HMD and the physical environment. The visual representation of the virtual environment was based on filmed image of the physical environment and was therefore highly similar.DesignThis is an observational study in healthy adults.ResultsNo significant difference was observed between the two environments for static balance. However, dynamic balance was more perturbed in the virtual environment when compared to that of the physical environment.ConclusionsHMD should be used with caution because of its detrimental impact on dynamic balance. Sensorimotor conflict possibly explains the impact of HMD on balance.     

Evaluation of scatter dose of dental titanium implants exposed to photon beams of different energies and irradiation angles in head and neck radiotherapy

OBJECTIVES: In this study, quantification of backscatter doses between scattering titanium dental implant and the thermoluminescent dosimeter (TLD(100)) radiation detector at axial beam irradiation-angle range of 0-90 degrees in head and neck radiotherapy is done to evaluate irradiation angle dependency of dose enhancement contributing to osteoradionecrosis. METHODS: A cylindrical titanium dental implant with diameter of 4 mm and length of 9 mm was implanted into a specially-designed human mandible phantom with a TLD100 chip placed on the buccal site and irradiated with 6 MV X, 25 MV X and Co-60 gamma sources at 19 different irradiation angles. RESULTS: Dose enhancement on a buccal site of the titanium implant depends on the incident beam angle. At angles of 65 degrees, 60 degrees and 40 degrees the maximum detected scatter doses over the titanium implant are 36%, 32% and 23% for Co-60 gamma, 6 MV X-ray and 25 MV X-ray, respectively. The dose enhancement at different beam angles was less pronounced in 25 MV X and more pronounced in Co-60 gamma irradiation. CONCLUSIONS: For the different radiation beams studied, the irradiation angle between scattering titanium dental implants and the central axis does not significantly affect the total dose that may lead to osteoradionecrosis of the mandible.     

Digital mammography: comparative performance of color LCD and monochrome CRT displays

RATIONALE AND OBJECTIVES: To evaluate the comparative performance of high-fidelity liquid crystal display (LCD) and cathode ray tube (CRT) devices for mammography applications, and to assess the impact of LCD viewing angle on detection accuracy. MATERIALS AND METHODS: Ninety 1 k x 1 k images were selected from a database of digital mammograms: 30 without any abnormality present, 30 with subtle masses, and 30 with subtle microcalcifications. The images were used with waived informed consent, Health Insurance Portability and Accountability Act compliance, and Institutional Review Board approval. With postprocessing presentation identical to those of the commercial mammography system used, 1 k x 1 k sections of images were viewed on a monochrome CRT and a color LCD in native grayscale, and with a grayscale representative of images viewed from a 30 degrees or 50 degrees off-normal viewing angle. Randomized images were independently scored by four experienced breast radiologists for the presence of lesions using a 0-100 grading scale. To compare diagnostic performance of the display modes, observer scores were analyzed using receiver operating characteristic (ROC) and analysis of variance. RESULTS: For masses and microcalcifications, the detection rate in terms of the area under the ROC curve (A(z)) showed a 2% increase and a 4% decrease from CRT to LCD, respectively. However, differences were not statistically significant (P > .05). The viewing angle data showed better microcalcification detection but lower mass detection at 30 degrees viewing orientation. The overall results varied notably from observer to observer yielding no statistically discernible trends across all observers, suggesting that within the 0-50 degrees viewing angle range and in a controlled observer experiment, the variation in the contrast response of the LCD has little or no impact on the detection of mammographic lesions. CONCLUSIONS: Although CRTs and LCDs differ in terms of angular response, resolution, noise, and color, these characteristics seem to have little influence on the detection of mammographic lesions. The results suggest comparable performance in clinical applications of the two devices.