The application of fast screen-film systems to excretory urography.

Rare earth and barium fluorochloride screen-film combinations of different relative speeds were compared to conventional calcium tungstate systems in patients undergoing excretory urography under controlled conditions. Radiographs were ranked by subjective impressions of detail, contrast, mottle, motion unsharpness, overall quality, and acceptablility. Compared to a medium speed calcium tungstate screen/film combination (assigned a speed of 1), screen-film systems in the 2-5 speed range offered improvement in overall quality due to diminished respiratory motion unsharpness at the cost of some loss of detail and increase in mottle. Other advantages and disadvantages of fast screen-film systems are discussed.     

Dose efficiency of screen-film systems used in pediatric radiography

Twenty-one screen-film systems were examined using contrast-detail-dose methods in order to determine which were most dose-efficient for use in pediatric radiography. With a given screen, dose efficiency in the noise-limited region (contrast approximately equal to 0.05) was more or less constant (within the range of experimental error) with changes in film speed. When screens with decreased phosphor thickness were used, dose efficiency deteriorated markedly. For a given speed of up to two times Par, rare-earth phosphors offered no advantage over calcium tungstate systems with regard to low-contrast dose efficiency; however, they did increase the speed of the system. Anti-crossover film proved to be an effective means of improving high-contrast detail while maintaining low-contrast dose efficiency.     

Scatter-to-primary ratio and absorption efficiency in screen-film and computed radiography systems

Purpose: To determine whether the scatter-to-primary (s/p) ratio, measured on a screen-film or computed radiographic (CR) system, varies with chemical composition or primary attenuation properties. Materials and methods: The s/p ratios of four Gd₂O₂S screens, three CaWO₄ screens and a CR screen, were determined under uniform irradiation conditions. One simulated low scatter conditions, such as in lung imaging, and the other simulated high scatter conditions as in abdominal imaging. The absorption efficiency of each screen was measured and calculated. Results: The measured s/p ratio varied within each set of screens. The s/p ratio was related to the absorption efficiency of primary radiation for the screen-film and CR system. No difference in the s/p ratio was seen between screen-film and CR systems when normalised for the primary absorption efficiency. Conclusions: Absorption efficiency of the imaging system is a major indicator of s/p ratio, for both screen-film and CR systems.     

Absolute speeds of screen-film systems and their absorbed-energy constants

Absolute speeds (mR-1) of screen-film systems were determined accurately and precisely from ten independent measurements over a six month period at several beam qualities that included both scatter and scatter-free conditions. The absorbed x-ray energies in the screens that yielded a net film density of 1.0 were obtained by means of Monte Carlo calculations and a semianalytical method. The standard deviations of the calculated absorbed x-ray energies at different beam qualities were less than 10% for all of the screen-film systems studied. Therefore, the absorbed x-ray energy that produces a given film density for these systems can be regarded as constant at the beam qualities used. Quantum absorption and fractional energy absorption of the screens were also calculated. The predicted Wiener spectral values based on the number of photons detected were compared with the measured Wiener spectral values of the screen-film systems.     

Improvement of pulse-mode photographic images in MDS computer systems

Users of scintigraphic computer systems manufactured by Medical Data Systems (MDS) frequently experience textured distortion of oscilloscope images when scans are produced by Z-axis modulation. The source of this malfunction has been identified and a way to eliminate the problem is described. The modification is simple and inexpensive. The availability of Z-axis modulation significantly enhances the capabilities of MDS systems.     

Variation of gamma camera photographic image density with count rate

In recent years there has been a gradual shift in gamma camera image recording toward the use of transparency films. When this occurs one encounters the intermittency effect. This effect causes the image density to increase as the count rate increases. In addition, density may also increase because the light output per count from the cathode ray tube also increases as the count rate increases. If these effects are not taken into account, images obtained at low count rates may be too light and those obtained at high count rates may be too dark. This paper discusses these phenomena and presents experimental data that shows how image density varies with respect to count rate for several commonly used films.     

Comparison of two detail screen-film systems using a rheumatoid erosion model

Two detail screen-film systems, Lanex Fine/Ortho M and Lanex Fine/Ortho G, were evaluated using a radiographic model for rheumatoid erosions. Radiographs of hand bones with cortical defects using both screen-film systems were obtained. Seven observers analyzed 48 sites on each of 22 films for the presence of these cortical defects. Using analysis of variance techniques and receiver operating characteristic curves, no significant difference was found between the two systems for the detection of these subtle cortical defects. The authors conclude that although the Lanex Fine/Ortho M system provides better definition of laboratory test objects than Lanex Fine/Ortho G, the two systems do not differ when used for detection of cortical lesions.     

旋转DSA技术在肺栓塞诊疗中应用的研究

目的研究旋转DSA技术在肺栓塞(pulmonary embolism，PE)诊疗中的应用。方法建立小型猪肺栓塞模型13头，进行常规肺动脉造影并应用旋转DSA技术，对造影结果进行分析、评价和研究。结果将每头猪的肺分为相应的15条血管，共有195条血管。以病理阳性结果为标准，评价肺动脉造影及旋转。DSA技术诊断PE的价值。肺动脉造影及旋转。DSA共有47个血管阳性(24．1％)，敏感性为98％，特异性为99％，诊断准确性98％；有2个血管数字减影肺动脉造影阳性，病理阴性，假阳性率为1％；有1个血管数字减影肺动脉造影阴性，病理阳性，假阴性率为2％。结论旋转DSA技术有助于肺栓塞诊断，尤其对疑似病变有一定临床意义。     

计算机X射线摄影系统与屏-片系统能量响应的对照研究

目的探讨计算机X射线摄影(CR)影像像素值与曝光因子(kVp和mAs)、被照体厚度的关系，传统屏-片系统照片密度与曝光因子、被照体厚度的关系，并对两种能量响应的关系进行比较，为使用CR影像像素值和成像板(IP)平均入射照射量的测量值作为自动曝光控制系统的设定参数提供依据。方法厚度为10、15、20cm的丙烯树脂板分别在50～90、70～120、90～140kVp和密度档为-2时成像，对照屏-片系统与CR系统在不同管电压、相同被照体和密度档时的自动曝光响应。以上测试都使用滤线栅，用电离室测量IP的入射照射量。结果在获得满足临床诊断要求的情况下，CR所需曝光量大约是高速屏-片系统的2倍。CR系统的管电压像素值关系曲线与管电压照射量曲线相同。10cm被照体时，50～90kVp间的照片密度差值为1．21，像素差值为270；而20cm被照体时，90～130kVp间的密度差值为0．30，像素差值为100；15cm被照体时密度和像素差值居于两者之间，分别为0．62和160。结论Kodak CR900系统的感度值与中速屏-片系统的感度比较接近。均匀野影像的曝光指示器值EI和IP照射量测量值可以用来设定自动曝光控制系统的光电计时器。屏-片系统照片密度和CR影像像素值随kVp变化的规律以及两者的差异，对自动曝光控制系统的校准起参照作用。     

Evaluation of the proper photographic density range of Lodose mammography.

An underexposed or overexposed mammogram can make it impossible for the radiologist to arrive at the proper diagnosis and may cause unnecessary radiation exposure to the patient. The range of photographic densities that can result in properly exposed, underexposed, or overexposed mammograms when the Lodose system is used has been determined. This study should be of significant value to technologists who do mammography on a routine basis and to those involved in mass screening programs.     

不同乳腺密度全野数字化乳腺X线摄影与屏-片乳腺摄影对不同组织病理学乳腺癌显示清晰度的对照研究

目的英国国家健康服务乳腺普查项目(NHSBSP)中,对普查探查到的乳腺癌病人行全野数字化乳腺X线摄影(FFDM)和屏-片乳腺摄影(SFM),比较两种方法在不同乳腺