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1、Quality Control for Computed Tomography (CT), CT, 的质量控制Melissa C. Martin, M.S., DABR Certified Medical Physicist Fellow- ACR, ACMP, AAPMNIM - China Meeting June 13, 2005Qualifications and Professional Activities 专业资质和业务活动American College of Radiology 美国放射学会 - Commission on Medical Physics 医学物理学委员会 -
2、 Chair of Government Relations Committee 政府关系委员会主席 - Mammography Accreditation Committee 乳腺X线照相术认证委员会 - Image Quality Committee for Digital Imaging 数字影像质量委员会 American Association of Physicists in Medicine (AAPM) 美国医学物理学家 协会 - Liaison (Advisor) to the Conference of Radiation Control Program Directors
3、 辐射控制计划理事会大会顾问CT Dose and Image Quality CT辐射剂量和影像质量Quality Control and Quality Assurance Procedures and Issues 质量控制和质量保证步骤CT and MRI imaging modalities were CT and MRI imaging modalities were named as the most important medical named as the most important medical advances in the last half of the 20a
4、dvances in the last half of the 20ththcenturycentury CTCT和和MRIMRI被认为是人类二十世纪下半叶最重被认为是人类二十世纪下半叶最重 要的进展要的进展Developments in CT TechnologyCT技术的发展Early CT detectors and scanner早期的CT检测和扫 描装置Modern Multi-Slice CT Scanner现代多层CT扫描仪Early CT Image (Siemens)早期的CT影像Multi-Slice CT Images (2004) 多层CT影像Quality Assur
5、ance 质量保证There are a variety of artifacts than can occur because of poor adjustment of the scanner由于扫描仪调节不到位，产生很多干扰伪影 Loss of resolution 分辨率下降 Accuracy of CT numbersCT值的精度 Table Location扫描床的定位 CT is a high dose procedureCT诊断是一个高剂量辐射的过程- It is important to know the dose for various studies and to sel
6、ect appropriate dose for optimal clinical performance重要的是了解各种研究所需的剂量，从而选择适当的量以获得最优的临床表现Clinical Technique 临床技术 Once the basic dose performance of the scanner is determined, the physicist should work with physician colleagues to optimize image-quality and dose一旦确定了扫描仪的工作剂量，物理学家就要与临床医师合 作优化影像质量 Each s
7、ite should have techniques tailored to the local needs每一个地区应当使用满足当地需要的技术 Manufacturer supplied techniques may not be optimum制造商提供的技术并不一定是最适宜的Clinical Technique 临床技术 Technique should be adjusted so that small patients have reduced dose and large patients have increased dose应作适当的调整，根据病人的实际情况增减剂量 The r
8、econstruction filter should be selected to trade noise vs resolution应对重建滤波器进行选择以提高分辨率、减少噪声 kV, pitch and slice thickness should be selected to optimize dose-image quality应对kV值、螺距和层厚进行选择以优化剂量-影像关系Image Uniformity 影像均一性 CT uses many detectorsCT使用很多检测器 The detectors may not be completely uniform检测器并不一定
9、完全一致 They may drift它们可能漂移 Quality control is necessary to insure uniformity对于均一性而言，质控是必需的Hounsfield Number Hounsfield值Average attenuation value for Voxel像素的平均衰 减值Tissue Density X-ray Energy 组织密度 X线能量utissue -uwuwCT number = 1000Uniformity Checked 均一性检测 Scanning Air 扫描空气 “Air Cals” 空气校准 Scanning Wate
10、r 扫描水 Accuracy of Hounsfield Numbers Hounsfield值精 度 Uniformity 均一性 Noise 噪声 Absence of Artifacts 干扰伪影的消失Phantoms 模体 Scanning Water Requires 需要扫描水 Water filled phantom 充满水的模体 Carefully made “solid water” 特制的“固体水” Solid water has the same density and atomic number as water 固体水具有与水相同的密度和原 子数Phantoms 模体
11、 Phantoms supplied by scanner manufacturer模体由扫描仪制造商提供 Often designed to work with scanner specific software通常是被设计用来与扫描仪软件配套的 Software may check and adjust the scanner软件可以用来检查和调整扫描仪 Some manufacturers use tighter specifications than others一些制造商使用比较苛刻的技术指标Standards 标准 Hounsfield values Hounsfield值 Dep
12、end on scanner 取决于扫描仪 Should be no more than +/-7 应在+/-7 之内 Uniformity depends on scanner 均一性取决于扫描仪 Noise depends on technique used for scan 噪声取决于 所使用的扫描技术 Data should be charted so trends can be seen 应将有 关数据作图以观察趋势变化CT Number Accuracy CT值精度 Check accuracy and constancy of known materials检查已知物质的精度和稳
13、定性CT Numbers CT值 Air 空气-1000-970 Polyethylene 聚乙烯-107-87 Water 水-7-7 Acrylic 丙烯酸110130You need to verify which material is in the phantom. If in doubt, check with the manufacturer. 需确认模体中是何种物质，如有疑问，与制造商沟通。Resolution 分辨率 Resolution Test Object受试目标分辨率Commercial Phantoms 商业模体 Variety of phantoms availa
14、ble 可选的模体很多 Accreditation program in the U.S. requires use of phantom designed by American College of Radiology (ACR) which measures more than QC Phantoms from manufacturers在美国，认证过程中需使用放射协会设计的模体，而不仅仅 是制造商提供的质控模体 - Costly 昂贵 - Doesnt work with manufacturers software 不能与制造商提供的 软件一起使用 - Requires annual
15、 physicist evaluation 每年需要评估Monitor Display & Film Printing 监视器显示和底片打印 Monitor should be adjusted to have a proper gray scale监视器应进行调节，以便获得适当的灰度 Printed films should match monitor display底片的打印应与监视器显示状态相匹配 Printers and monitors must function in DICOM format打印机和监视器应在DICOM格式状态下工作 SMPTE Test Pattern used
16、 for image quality evaluation of both monitors and printers对于打印机和监视器，应用SMPTE图形进行影像质量的监 测SMPTE Test PatternAccuracy of Table Location 扫描床的定位精度 Accuracy of Positioning Lights and Table Motion should be within + 2 mm定位光与扫描床位移之间的精度应在+ 2 mm之内 Return of table to the same location is especially important for interventional studies扫描床的归位对于干涉分析特别重要Protocol
