Objective To investigate the effect of the change of tube voltage on radiation dose and image quality in head-neck and chest scanning under automatic tube current modulation ( ATCM ) . Methods CT scanning was performed on the head-neck and chest phantom with ATCM and automatic tube voltage(CARE kV). The tube voltage was manually selected at 70, 80, 100, 120 and 140 kV separately, and a routine CT scanning of the head-neck and chest with ATCM was performed. The scout was scanned for 3 times and a spiral scanning was performed once at each of tube voltage. The regions of interest( ROIs) were selected in the slices of orbital center and C5 upper edge level for the head-neck phantom, in the slices of apical and tracheal bifurcation level for the chest phantom. The contrast to noise ratios ( CNRs) were measured and recorded. The organ dose of eye lens and mammary are measured with thermoluminescent dosimeters ( TLDs ) for every scanning ( the average of 3 measurements ) . The cumulative dose value of the scout and spiral scanning was calculated. The volume CT dose index ( CTDIvol ) of each scan was recorded, and the cumulative value of CTDIvol was calculated. Finally, the optimized tube voltage was obtained by calculating the FOM ( figure of merit) . Results With ATCM and CARE kV, 120 kV and 108 mAs were chose automatically by system for head-neck phantom, 80 kV and 167 mAs for chest phantom. With ATCM, the radiation dose of eye lens and CTDIvol were minimal with manually selected 70 kV ( 0.779 and 4.070 mGy respectively ) , and maximaum with manually selected 140 kV (2.571 and 25.670 mGy). The radiation dose of the mammary gland and CTDIvol were minimal with manually selected 70 kV ( 0.698 and 0.900 mGy ) , and maximal with manually selected 140 kV (3.452 and 7.400 mGy). The CNR values of orbital center and C5 upper edge level were 51.30-118.36 and 80.78 - 173.12 respectively. The CNR values of the apical and tracheal bifurcation level were 50.15-129.58 and 49.63-115.40, respectively. The optimal FOM was appeared at orbital center slice with 80 kV, at C5 upper edge level slice with 120 kV and at both the apical and tracheal bifurcation level with 70 kV. Optimum tube voltage for head-neck phantom: manual 100 kV at orbital level, CARE kV mode(120 kV) at neck level. Optimal tube voltage for chest phantom: manual 100 kV. Conclusions The selection of tube voltage is responsible for the radiation dose and image quality of CT scanning. For conventional CT scan, manual 100 kV is suitable for orbital scanning, automatic 120 kV is suitable for neck scanning, manual 100 kV is suitable for chest scanning.

Objective To investigate the influences of iterative algorithm(using iDose algorithm) on image quality and radiation dose in temporal bone MSCT.Methods A proper cadaveric head based on the noise level in routine clinical MSCT examination protocol with filtered back-projection(FBP) algorithm was selected as the research object.The cadaveric head was scanned with different effective tube current,and the images were reconstructed with FBP and iDose algorithms,respectively.The subjective and objective evaluations were performed for all the images,and the optimal parameter combination was found.The values of CT volume dose index and dose length product(DLP) at various scan parameters and reconstruction algorithms were analyzed,and effective doses of subject were calculated as well.Results The noise level of iDose algorithm was lower than that of FBP under the same effective tube current,and it decreased with the increasing of iDose levels.The noise level decreased with the increasing of the effective tube current under different effective tube current.The combination of 100 mAs/silce and iDose 5 algorithm could met the requirements of clinical diagnosis,and the noise level of resultant images was lower than that obtained with the combination of 200 mAs/silce and FBP algorithm.The diagnostic acceptability of coronary images was slightly higher than that of axial images.Conclusion The iDose algorithm can not only meet the requirements of the temporal bone CT image quality,but also reduce the radiation dose of the patients.

CR系统已经在临床上广泛应用,不同品牌和型号所产生伪影的原因和表现也各具特点.笔者就临床应用中容易引起误诊的CR伪影,分析其影像表现和产生原因,从影像诊断准确性方面探讨其意义.

目的 探讨数字X线摄影中混叠效应的产生原因及其对影像质量的影响.方法 使用Kodak CR900系统分别对矩形波测试卡和固定滤线栅成像.测试卡铅条在平行于激光扫描方向和呈45.角的放置方式下分别成像,观察两种影像对分辨率测试卡的显示情况.使滤线栅铅条的方向在平行和垂直于激光扫描方向时分别成像,在显示器上使用不同的放大率对滤线栅影像进行观察,并比较两种影像外观的差异.结果 测试卡影像上,3.93线对/mm以上频率的铅条影无法相互分辨,因此尼奎斯特频率为3.93 LP/mm.但在测试卡45°放置的影像中,频率为4.86 LP/mm的铅条仍能相互分辨.滤线栅铅条平行于成像板的激光扫描方向时,最终影像中显示出明显的条纹影.在显示器上使用不同的放大率观察时,栅条形成的条纹影宽度和方向都发生明显变化.铅条与激光扫描方向垂直时影像中的条纹影显著减弱.结论 CR应用中混叠效应会对数字影像产生不利影响,应根据设备的极限分辨率选择适当的固定滤线栅,栅频率应大于尼奎斯特频率.在摄影中,滤线栅的铅条方向应与成像板的激光扫描方向相垂直.在显示器上观察固定滤线栅摄影影像时,建议使用原始图像的整数倍的放大率.

目的建立以焦点胶片距离的改变，取得Ｘ线阶段曝光的屏片体系感光测定方法。方法利用常规Ｘ线机在焦点胶片距离４０～３２０ｃｍ的范围内，取７个距离曝光点，对ＯｋａｍｏｔｏＤＭＳ（蓝屏）／ＦｕｊｉｎｅｗＲＸ（感蓝片）及ＦｕｊｉＨＲＲｅｇｕｌａｒ（绿屏）／ＦｕｊｉＨＲＮ（感绿片）两种屏片体系样本做感光测定，绘制特性曲线、斜率密度曲线，求取特性值。同时与感光仪和铝梯定量测定法（Ｂｏｏｔｓｔｒａｐ法）作比较。结果（１）测试用Ｘ线机的平均管电压值、高压纹波率、输出剂量、曝光时间等四项指标的变动系数均小于０．０２，重复性良好。（２）Ｘ线强度与距离平方在测试距离内呈线性关系，倾斜值为－２．０４，证明本实验中的“距离反平方定律”成立。（３）实验证明，距离法的曝光条件确定在６０～８０ｋＶｐ，ｍＡｓ以在距离８０．３ｃｍ［相对曝光量对数（ＬｏｇＲＥ）＝１．２］时得到２．０＋本底灰雾的密度值为调节指标，总滤过３．０ｍｍＡｌ＋０．５ｍｍＣｕ（三相工频机）或３．５ｍｍＡｌ（中频机）。结论距离法与感光仪法、时间阶段曝光法、铝梯定量法相比，重复性较好，曝光机制符合Ｘ线摄影实际，便于统一。

目的评价不同屏片组合下Ｘ线照片影像的颗粒性，以期掌握照片颗粒性的客观评价方法，并获得影响影像颗粒度的相关因素。方法利用显微密度计对测试样本进行扫描，通过均方根（ｒｏｏｔｍｅａｎｓｑｕａｒｅ，ＲＭＳ）值的计算，对不同屏片组合的Ｘ线影像进行颗粒度的物理评价。结果通过测试和数据整理，得出颗粒度与管电压、密度、对比度及清晰度的关系。结论Ｘ线照片影像颗粒度随着管电压、清晰度和对比度的升高而升高，随密度的升高而降低