应用一维、二维、三维探测器阵列进行螺旋断层调强放疗计划剂量验证

目的：比较Tomotherapy标配Cheese模体联合EBT3免冲洗胶片（一维探测器阵列）、Octavius八角模体配合PTW Seven29二维探测器阵列（二维探测器阵列）、Delta4三维探测器阵列用于螺旋断层放疗系统（Tomo Therapy,TOMO）的调强计划实施剂量验证的差异。方法：分别采用一维、二维、三维探测器对10例患者TOMO的调强计划实施验证。通过TOMO系统MVCT成像和配准消除床面沉降的影响,确保实现体模和探测器阵列的精确摆位。实施治疗质量保证（Delivery Quality Assurance,DQA）计划照射后将测量获得的平面剂量分布与TOMO计划系统模体计划计算获得的平面剂量分布进行比较。采用Gamma分析方法,选择多个不同的剂量标准分析评估验证情况。结果：采用3%/2mm、3%/3 mm、3%/4 mm、3%/5 mm四种不同剂量偏差/吻合距离剂量标准,γ≤1的平均通过率均超过95.2%,测量所得剂量分布与计算结果在相应平面的几何分布均呈现出良好的一致性。结论：胶片空间分辨率高于二维、三维探测器阵列,是调强计划验证的＂金标准＂。而二维和三维探测器阵列凭借其操作简便、数据处理快捷的特点可作为一维验证方法的有效补充。     

Mapcheck的剂量学质量保证

目的:评价我中心新购美国Sun Nuclear公司生产二维半导体阵列Mapcheck的剂量学特点。方法:使用美国瓦里安公司23EX直线加速器高能光子束照射Mapcheck研究其重复性,线性以及验证其本身阵列校准方法的准确性;同时在研究其重复性,脉冲率依赖性及输出因子时使用德国PTW30013电离室测量数据并比较。结果:实施Mapcheck专用阵列校准方法后在0o和180o测量结果差异介于-0.5%至0.7%之间。矩阵重复性最大标准差是±0.16%,中心轴半导体探头(C点)12次测量标准差为0.065%。中心探头随剂量率变化最大范围是0.78%。同指形电离室结果比较,小于4cm×4cm射野时,Mapcheck低估了输出因子最大达1.1%,大于15cm×15cm射野时,Mapcheck开始高估输出因子最大达0.9%。结论:Mapcheck的各项剂量学检测结果符合出厂指标,适合应用于临床作常规射野剂量学质量保证及调强剂量学验证。     

基于Shepp-Logan模型的并行MRI数值模拟平台

我们以Shepp-Logan模型为基础,对并行MRI成像进行了仿真,采用Matlab的图形用户界面创建了并行MRI数值模拟平台.该平台可以建立不同分辨率的数值模型,设置阵列线圈的尺寸和摆放位置,计算线圈的灵敏度,模拟k-空间数据的采集,得到多通道的原始数据,并进行图像重建.为国内研究各种MRI重建算法提供了数值模拟的参...     

恶性肿瘤调强适形放射治疗质量保证的研究

目的：探讨调强适形放射治疗的质量保证方法。方法：用CMS放射治疗计划系统设计调强适形放射治疗计划。采用CT模拟的方法验证射野等中心位置，比较各照射野实际胶片调强图与治疗计划系统得到的相应照射野的测强图的一致性，采用多通道剂量仪验证多点绝对剂量。结果：射野等中心位置误差在3mm以内。各射束垂直方向测得的调强图与计划系统计算的调强图一致。等中心点实测剂量与计划剂量的误差在3％以内，其余偏离点的实测剂量与计划剂最误差在5％以内。近期疗效为完全缓解（CR）58．8％（10／17），部分缓解（PR）17．6％（3／17），无变化（NR）23．5％（4／17），总有效率（CR＋PR）为76．5％（13／17），所有17例患者均能耐受放射治疗，按计划完成调强透形放射治疗。结论：上述质量保证措施切实可行。调强适形放射治疗对恶性肿瘤有较好的近期疗效。     

Artifacts Found During Quality Assurance Testing of Computed Radiography and Digital Radiography Detectors

A series of artifact images, obtained over 5 years of performance testing, of both computed radiography (CR) and integrated digital radiographic X-ray imaging detectors are presented. The images presented are all either flat field or test object images and show artifacts previously either undescribed in the existing literature or meriting further comment. The artifacts described are caused by incorrect flat field corrections, a failing amplifier, damaged detector lines affecting their neighbors, lost information between neighboring detector tiles, image retention, delamination of a detector, poor setup of mechanical movements in CR, suckers damaging a CR plate, inappropriate use of grid suppression software, inappropriate use of a low pass spatial frequency filter, and unsharp masking filters. The causes and significance of the artifacts are explained and categorized as software or hardware related. Actions taken to correct the artifacts are described and explained. This work will help physicists, radiographers, and radiologists identify various image quality problems and shows that quality assurance is useful in identifying artifacts.     

金属植入物在体模状况下的MRI研究

目的：探讨有金属（纯钛或钛合金）植入物的病人旋行磁共振检查的可行性，寻求伪影最小的最佳成像序列，使得该部分病人能够进行常规的磁共振检查，用以诊断病情、评价手术效果。结论：凡是植入物属于抗磁性金属（如：纯钛、钛合金）的病人，能施行常规的磁共振检查。正确的成像参数、成像序列、成像方法的选择，可以得到好的、能够清楚诊断的MR图像。     

A Clinical Evaluation of the Image Quality Computer Program, CoCIQ

To provide an objective way of measuring image quality, a computer program was designed that automatically analyzes the test images of a contrast-detail (CD) phantom. The program gives a quantified measurement of image quality by calculating an Image Quality Figure (IQF). The aim of this work was to evaluate the program and adjust it to clinical situations in order to find the detectable level where the program gives a reliable figure of the contrast resolution. The program was applied on a large variety of images with lumbar spine and urographic parameters, from very low to very high image qualities. It was shown that the computer program produces IQFs with small variations and there were a strong linear statistical relation between the computerized evaluation and the evaluation performed by human observers (R² = 0.98). This method offers a fast and easy way of conducting image quality evaluations.     

放疗靶区呼吸运动对CT模拟定位图像重建的几何体积精度的体模实验研究

目的:研究放射治疗病人的不同呼吸运动状态对CT模拟定位扫描的图像重建精度的影响以及对放射治疗计划设计和评估的影响。方法:使用动态体模模拟放疗患者肺部靶区的呼吸运动,测试和计算不同运动周期和幅度下用于治疗计划设计的CT扫描的图像重建几何体积的变化。体模运动单元包含1cm和2cm的两个统一密度的球体和边长3cm的正方体,分别设定在沿CT定位床轴向以±1cm和±2cm的幅度作运动周期为3s,4s,5s,6s和10s的匀速振动。CT扫描条件为螺距1.5,层厚5mm,扫描速度1Slice/s。在CT模拟定位工作站上对扫描的原始数据进行三维图像重建,以自动阈值勾画方式计算模拟靶区体积大小,并与体模的实际几何体积比较确定误差。结果:(1)在体模运动方向有明显的几何体积误差,且可能形成明显的成像间隙。(2)重建的模拟运动靶区体积变化与其物理体积大小和运动状态相关。在选定的CT扫描参数和靶区体积的运动状态下,CT扫描图像重建的体积误差最大达66.7%,在振幅为2cm时相隔2cm的模体图像甚至可能发生部分重迭。(3)靶区图像的几何中心可能发生偏差,从而造成治疗计划设计的射野中心偏差。结论:在呼吸运动幅度和周期分别大于2cm和4s时有必要对定位患者采取呼吸限制方式进行CT模拟定位扫描或根据实际测量结果评估靶区体积误差可能带来的计划误差。     

医学影像质量控制及保证检测设备综述

本文对研发医学影像质量控制及保证检测设备的必要性、国内外检测设备的现状、以及我们将来要开展的工作进行了综合评述.首先阐述了开展医学影像质量控制及保证工作的必要性,以及目前国内外医学影像质量控制和质量保证工作的开展情况.结合目前医学影像质量控制及保证检测设备的现状,预测其未来的发展情况.提出我国国产检测设备研制和开发任务重点与发展模式.     

Varian On-Board Imager(OBI)常规测量方法及质量保证

目的:通过建立一套OBI系统的常规测量方法,探讨放射治疗中利用OBI系统进行摆位验证的质量保证(QA)内容.方法:利用质量保证工具和体模对VarianIX加速器的OBI系统进行每日、每周、每月、每年的常规测量,完成质量保证项目检测.结果:OBI系统的操作安全性,几何准确性和图像质量均在允许范围内.OBI系统的等中心准确...     

Varian多叶准直器(MLC)常规测量方法及质量保证

目的:通过建立一套多叶准直器(MLC)常规测量方法,探讨用MLC进行三维适形放射治疗(3-Dimension confor-mal radiation therapy,3D CRT)质量保证(QA)的内容.方法:物理师采用胶片法对Varian 23EX加速器,120叶MLC、Cadplan治疗计划系统进行治疗前、每日、每月、三个月的质量保证项目检测.结果:MLC形成的照射野与灯光野的重合性、叶片位移的精确度、数字化仪的精度、叶片运动的倾斜度、下垂度、照射野中心均在允许范围内,符合临床要求.结论:Varian 120叶MLC性能稳定、可靠.     

二维电离室矩阵在加速器日常质量保证中的应用与研究

目的:探讨应用二维电离室矩阵在加速器日常质量保证中的可行性。方法:使用二维电离室矩阵分别测量加速器的照射野与灯光野的重合性、等中心、照射野的对称性及平坦度、楔形板角度等。结果:加速器的照射野与灯光野的重合性、等中心、照射野的对称性及平坦度、楔形板角度等测量结果均在允许范围内,符合临床要求。结论:二维电离室矩阵可用于加速器日常质量保证的测量,是放疗设备日常质量控制的理想工具。     

模拟调强放疗照射离体细胞的质量保证

目的：在模拟调强放疗方式照射细胞的过程中，保证细胞按调强方式被照射，照射剂量准确。方法：在细胞培养瓶中装满细胞培养液，水平固定在标准水箱（30cm×30cm×30cm）电离室横梁上，在水箱中加水到电离室上方5cm，用CT机（philips brilliance bigbor CT）扫描获取图像，传到计划系统（ECLIPSE 7．0）中；再用一个空的培养瓶替换装满培养液的培养瓶，重新用CT机扫描，获取图像，传到计划系统中。采用先设野中野后合并野中野的设计方法，设计模拟调强照射计划，设定电离室处的吸收剂量400cGy。再把此水箱放到加速器（Varian 600-C／D）下，按设计的模拟调强照射计划进行照射，同时用电离室（NE 0．6cc）剂量仪（NE FARMER 2570）测量得到实际吸收剂量。结果：在细胞培养瓶中装满细胞培养液时模拟调强照射实测得到397cGy，与理论值相差-0．8％；在细胞培养瓶中不装细胞培养液时模拟调强照射实测得到395cGy，与理论值相差-1.3％。结论：用CT模拟定位，用计划系统通过设野中野的方法设计模拟调强照射计划是可行的，可以实现模拟调强照射离体细胞，理论剂量与实测剂量相差小于2％。     

Image Quality Assurance of Soft Copy Display Systems

Image quality assurance has traditionally been a high priority in medical imaging departments. Recently, it has often been neglected with the transition from hard copy (film) to soft copy (computer) display systems, which could potentially result in difficulty in reading images or even misdiagnosis. This transition therefore requires careful management such that comparable image quality is achieved at a minimum. It is particularly difficult to maintain appropriate image quality in the clinical settings outside of medical imaging departments because of the volume of display systems and the financial restraints that prohibit the widespread use of dedicated computers and high-quality monitors. In this study, a protocol to test and calibrate display systems was developed and validated by using an inexpensive calibration tool. Using this protocol, monitors were identified in a hospital in which image quality was found to be inadequate for medical image viewing. It was also found that most monitors could achieve a substantial increase in image quality after calibration. For example, the 0 and 5% luminance difference was discernable on 30% of the piloted display systems before calibration, but it was discernable on 100% post calibration. In addition, about 50% of the piloted display systems did not have the maximum luminance (white level) suitably set, and 35% of them did not have the minimum luminance (dark level) suitably set. The results indicate that medical display systems must be carefully selected and strictly monitored, maintained, and calibrated to ensure adequate image quality.     

基于可变形模型的MRI脑区域分割

本文给出了一种人头部核磁共振MRI图像的脑区域分割算法，该算法基于梯度矢量流GVF的可变形模型方法，且有效地解决了该方法在轮廓的突变处存在的弱收敛问题，最后把小波的多分辨率分析来优化算法，结果证明了其有效性。     

Image Quality Assurance in the Prostate, Lung, Colorectal, and Ovarian Cancer Screening Trial Network of the National Lung Screening Trial

The National Lung Screening Trial is evaluating the effectiveness of low-dose spiral CT and conventional chest X-ray as screening tests for persons who are at high risk for developing lung cancer. This multicenter trial requires quality assurance (QA) for the image quality and technical parameters of the scans. The electronic system described here helps manage the QA process. The system includes a workstation at each screening center that de-identifies the data, a DICOM storage service at the QA Coordinating Center, and Web-based systems for presenting images and QA evaluation forms to the QA radiologists. Quality assurance data are collated and analyzed by an independent statistical organization. We describe the design and implementation of this electronic QA system, emphasizing issues relating to data security and privacy, the various obstacles encountered in the installation of a common system at different participating screening centers, and the functional success of the system deployed.*Quality Assurance Working Group: Timothy Church, Ph.D., Jill Cordes, R.N., Richard Fagerstrom, Ph.D., Glenn Fletcher, Ph.D., Mike Flynn, Ph.D., Melissa Ford, Ph.D., Melissa Fritz, M.P.H., Kavita Garg, M.D., David Gierada, M.D., Fred Larke, M.S., Guillermo Marquez, Ph.D., Alisha Moore, M.S.N., C.R.N.P., Hrudaya Nath, M.D., Pete Ohan, B.S., Tom Payne, Ph.D., and Xizeng Wu, Ph.D.     

A complex flow phantom for medical imaging: ring vortex phantom design and technical specification

Abstract

Cardiovascular fluid dynamics exhibit complex flow patterns, such as recirculation and vortices. Quantitative analysis of these complexities supports diagnosis, leading to early prediction of pathologies. Quality assurance of technologies that image such flows is challenging but essential, and to this end, a novel, cost-effective, portable, complex flow phantom is proposed and the design specifications are provided. The vortex ring is the flow of choice because it offers patterns comparable to physiological flows and is stable, predictable, reproducible and controllable. This design employs a piston/cylinder system for vortex ring generation, coupled to an imaging tank full of fluid, for vortex propagation. The phantom is motor-driven and by varying piston speed, piston displacement and orifice size, vortex rings with different characteristics can be produced. Two measurement methods, namely Laser-PIV and an optical/video technique, were used to test the phantom under a combination of configurations. Vortex rings with a range of travelling velocities (approximately 1–80?cm/s) and different output-orifice diameters (10–25?mm) were produced with reproducibility typically better than ±10%. Although ultrasound compatibility has been demonstrated, longer-term ambitions include adapting the design to support comparative studies with different modalities, such as MRA and X-ray-CTA.     

Complex flow patterns in a real-size intracranial aneurysm phantom: phase contrast MRI compared with particle image velocimetry and computational fluid dynamics

The aim of this study was to validate the flow patterns measured by high-resolution, time-resolved, three-dimensional phase contrast MRI in a real-size intracranial aneurysm phantom. Retrospectively gated three-dimensional phase contrast MRI was performed in an intracranial aneurysm phantom at a resolution of 0.2 × 0.2 × 0.3 mm(3) in a solenoid rat coil. Both steady and pulsatile flows were applied. The phase contrast MRI measurements were compared with particle image velocimetry measurements and computational fluid dynamics simulations. A quantitative comparison was performed by calculating the differences between the magnitude of the velocity vectors and angles between the velocity vectors in corresponding voxels. Qualitative analysis of the results was executed by visual inspection and comparison of the flow patterns. The root-mean-square errors of the velocity magnitude in the comparison between phase contrast MRI and computational fluid dynamics were 5% and 4% of the maximum phase contrast MRI velocity, and the medians of the angle distribution between corresponding velocity vectors were 16° and 14° for the steady and pulsatile measurements, respectively. In the phase contrast MRI and particle image velocimetry comparison, the root-mean-square errors were 12% and 10% of the maximum phase contrast MRI velocity, and the medians of the angle distribution between corresponding velocity vectors were 19° and 15° for the steady and pulsatile measurements, respectively. Good agreement was found in the qualitative comparison of flow patterns between the phase contrast MRI measurements and both particle image velocimetry measurements and computational fluid dynamics simulations. High-resolution, time-resolved, three-dimensional phase contrast MRI can accurately measure complex flow patterns in an intracranial aneurysm phantom.