Digital radiography: image quality and radiation dose

Digital radiography devices, rapidly replacing analog screen-film detectors, are now common in diagnostic radiological imaging, where implementation has been accelerated by the commodity status of electronic imaging and display systems. The shift from narrow latitude, fixed-speed screen-film detectors to wide latitude, variable-speed digital detectors has created a flexible imaging system that can easily result in overexposures to the patient without the knowledge of the operator, thus potentially increasing the radiation burden of the patient population from radiographic examinations. In addition, image processing can be inappropriately applied causing inconsistent or artifactual appearance of anatomy, which can lead to misdiagnosis. On the other hand, many advantages can be obtained from the variable-speed digital detector, such as an ability to lower dose in many examinations, image post-processing for disease-specific conditions, display flexibility to change the appearance of the image and aid the physician in making a differential diagnosis, and easy access to digital images. An understanding of digital radiography is necessary to minimize the possibility of overexposures and inconsistent results, and to achieve the principle of as low as reasonably achievable (ALARA) for the safe and effective care of all patients. Thus many issues must be considered for optimal implementation of digital radiography, as reviewed in this article.     

迈瑞DigiEye760数字X射线摄影系统成像质量与辐射剂量优化初探

目的：探讨迈瑞DigiEye760医用数字X射线摄影系统所采用的3种不同图像后处理方法对图像质量与辐射剂量优化的影响。方法：采用对比度阈值测试模块TO20和数字胸部X射线摄影QC体模Model 07-646,测试不同曝光条件及不同图像后处理模式下图像的阈值对比度细节探测力。结果：原始图像受曝光条件的影响较为明显,经过图像后处理和细节增强后,曝光条件对图像质量的影响减轻甚至消失。对于图像对比度细节探测力指数来说,Esa要好于原始图像,增强模式要好于Esa模式;随着曝光管电流的增大,强增强模式提高图像质量的效果逐渐减弱,当曝光管电流提高至200 mA时,强增强模式与弱增强模式具有相同的阈值对比度细节探测力。结论：图像后处理模式可以在较低曝光剂量条件下取得较好的图像阈值对比度细节探测力。只有选取适合的曝光条件,才能做到成像质量与辐射剂量的最大程度优化。     

数字化X线摄影图像后处理参数调整在建立尘肺病诊断参考片中的作用

目的 探讨图像后处理参数在数字化X线摄影(digital radiography,DR)胸片用于尘肺病诊断中的作用.方法 随机选择83例某煤矿接尘工人,同时拍摄高仟伏X线胸片和DR胸片.在Philips Essenta DR机上对密度和对比度等图像后处理参数进行设置,研究合适的图像后处理参数.比较高仟伏X线胸片和DR胸片的质量.结果 通过调节图像后处理参数,DR胸片在上中肺野最高密度、膈下和直接曝光区的光密度分别为1.58±0.10、0.23±0.02和2.80±0.21,胸片质量符合尘肺病诊断标准的要求.83例DR胸片的优良片率(79例,95.18％)明显高于高仟伏X线胸片(67例,80.72％),差异有统计学意义(P＜0.01).结论 合适的图像后处理参数可以使DR胸片达到尘肺病诊断的胸片质量要求.     

数字成像对尘肺病诊断的研究

目的 探讨直接数字化X射线摄影(DR)对尘肺病诊断的应用价值及优势.方法 对75例初诊高度怀疑或已经确诊为尘肺病的复查患者,同时给予高千伏胸片和DR胸片检查,分析2种照片方法在诊断中的差异.结果 DR胸片组:优片73例,优片率达97%,诊断尘肺病57例,检出率76%;高千伏胸片组:优片27例,优片率36%,诊断尘肺病45例,检出率60%.两种方法的优片率以及对尘肺病的检出率在统计学上差异具有显著性(P＜0.05).结论 数字X射线成像技术的应用能为尘肺病的诊断提供更有价值的信息,能在尘肺病原诊断的基础上发现新的影像线索,作出更加客观的诊断.     

Mammography in New Zealand: radiation dose and image quality.

The mean glandular doses to the breast, image quality and machine performance have been determined for all mammographic x-ray facilities in New Zealand, during 1988-89. For 30 mm and 45 mm phantoms the mean doses per film were 1.03 +/- 0.56 mGy and 1.97 +/- 1.06 mGy. These doses are within international guide-lines. Image quality (detection of simulated microcalcifications, and contrast-detail performance) was found to depend on focal spot size/FFD combination, breast thickness, and film processing. The best machines could resolve 0.2 mm aluminium oxide specks with the contact technique. The use of a grid improved image quality as did magnification. Extended cycle film processing reduced doses, but the claimed improvement in image quality was not apparent from our data. The machine calibration parameters kVp, HVL and timer accuracy were in general within accepted tolerances. Automatic exposure controls in some cases gave poor control of film density with changing breast thickness.     

管电压对胸部DR影像质量的影响

目的 研究有效剂量相等条件下不同管电压对胸部DR图像质量的影响。方法 48例病人在90kV、125kV、150kV分别摄取后前位胸片，未经任何处理打印片子，五位资深放射专家采用五分法独立打分评估影像质量；采用Monte—Carlo转换因子估算有效剂量ED（mSv）。结果 绝大多数解剖结构在90千伏时得分最高（平均得分3．10），除了在心影轮廓、气管隆突和外围纹理方面以外，其余部位均有明显统计学差异。结论 有效剂量相等条件下采用较低千伏能获得更好胸部DR影像。     

Cell-oriented alternatives to dose, quality factor, and dose equivalent for low-level radiation

Randomly occurring energy deposition events produced by low levels of ionizing radiation interacting with tissue deliver variable amounts of energy to sensitive target volumes within a small fraction of the tissue cell population. A model is described in which an experimentally derived function relating event size to cell response probability operates mathematically on the microdosimetric event size distribution characterizing a given irradiation and thus determines the total fractional number of responding cells; this fraction measures the effectiveness of the given radiation. Applying this cell response or hit size effectiveness function (HSEF) to different radiations and normalizing to equal numbers of responses produced by each radiation should define its radiation quality, or relative effectiveness, on a more nearly absolute basis than do the absorbed dose and dose equivalent, both of which are confounded when applied to low-level irradiations. Similar cell response probability functions calculated from different experimental data are presented.     

A flat-panel detector digital radiography and a storage phosphor computed radiography: screening for pneumoconioses

Storage phosphor computed radiography (SR) and flat-panel detector (FPD) radiography are two types of digital X-ray utilizing different techniques. We compared these two techniques with conventional analogue chest radiograph (AR) among pneumoconiotic patients and healthy controls. Thirty individuals consisting of 20 silica-exposed ex-workers and 10 healthy controls without occupational exposure to any mineral dust were examined with chest X-ray by AR, SR and FPD. Three occupational physicians, including one NIOSH B reader, assessed the digital and conventional radiographs by the side-by-side method according to the ILO 2000 International Classification of Radiograph of Pneumoconioses (ILO/ICRP). No significant difference was shown between the subjective film qualities by AR and FPD. Inter-reader agreement of the profusion of small opacities on radiographs was high in the order of SR (kappa=0.64), FPD (kappa=0.62), and AR (kappa=0.55). The profusions of small opacity for AR and FPD by the 12-point scaled profusion of ILO/ICRP did not show a statistically significant difference, but those for AR and SR showed a significant difference. The areas under the receiver operator curves (ROC) using clinical diagnosis by a pulmonologist as the reference showed no statistically significant difference among the three radiographic techniques. FPD gives image quality as good as that of AR, and it has acceptable agreement with AR in small profusion categories, which consequently assures its application to pneumoconiosis screening. SR showed less profusion than FPD and AR, which can be fixed with image modification.     

Effect of x-ray tube potential on image quality and patient dose for lumbar spine computed radiography examinations

A study was conducted to investigate the effect of increasing x-ray tube voltage on patient dose and image quality during computed radiography (CR) examination of the lumbar spine. Images of a pelvis - lumbar spine phantom were obtained at three different tube voltages using two CR systems. The images were evaluated by image scores (IS) using the image quality criteria proposed by the Commission of the European Communities (CEC), by measuring the signal-to-noise ratio and the contrast-to-noise ratio. The entrance surface dose (ESD) to the phantom was also measured using ionisation chambers and the resulting gonad dose (G) and effective dose (E) were calculated. The CEC recommended tube voltages can be exceeded with CR systems for lumbar spine radiography. The ESD, G and E decreased by 25%-50% with both CR systems when tube voltage was increased. Although the decrease in IS was statistically significant (P < 0.05) the images obtained with the 3 tube voltages were diagnostically acceptable. The balance between image quality and patient dose can be optimised by using higher x-ray tube voltages for lumbar spine CR examinations.     

A survey of radiation dose and image quality in mammography: an ongoing program in Italy

A program for mammography optimization in individual x-ray units, named Dose and Quality in Mammography (DQM), is now underway in Italy. The project has three stages: measurement of the parameters that affect dose and image quality by means of devices that are practical to use (specifically designed for the purpose), analysis of data to evaluate dose and image quality and suggestion of possible improvements to each unit operator. Instruments and methods employed in our survey are described. Our results, like those of the American survey (Je78) Breast Exposure: Nationwide Trends (BENT), show widespread variations of exposure, half value layer (HVL), optical density, dose and resolution. Facilities using the same type of x-ray apparatus (Mo target-Mo filter) and film-screen combinations present very different exposure values, ranging from 1.6 X 10(-4) to 27.6 X 10(-4) C kg-1. The causes of these variations--ascribable to the individual units, radiologist preferences, processing condition, kVp indicator and timer accuracy--are being explored.     

不同定位方法对儿童胸部CT检查图像质量和辐射剂量的影响

目的:探讨不同定位方法对儿童进行胸部CT检查产生的辐射剂量及采集的图像质量的影响.方法:收集某院儿童重症医学科行胸部CT检查年龄3岁左右的患儿30例,随机分为常规定位组(采用正位定位像,常规目测腋中线定位)和辅助定位组(体厚卡尺辅助定位),每组各15例.分别采集2组患儿胸部CT容积剂量指数(CT dose index ...     

Regional survey of image quality and radiation dose in computed tomography examinations in Saudi Arabia

This study is the first regional investigation in Najran, Saudi Arabia aimed at investigating radiation dose and image quality of computed tomography (CT) examinations. The survey data was collected from five scanners in four hospitals. For all CT scanners, a correction factor was calculated to measure the weighted computed tomography dose index (CTDI $_{w}$ ) using standard dosimetry phantoms. The CTDI $_{w}$ were reported in this study and compared with other countries. It was found that most CTDI $_{w}$ values were close to the European reference levels and in line with the results of similar surveys in the other parts of world. Concerning image quality, 80 % of the scanners were found to be in compliance with the relative international guidelines for all the examined parameters     

双源CT肺动脉CT血管成像图像质量及辐射剂量研究

目的:研究双源CT对肺动脉CT血管成像图像质量及辐射剂量的影响因素。方法:选取在医院应用双源CT检查的104例疑似肺动脉栓塞(PE)患者,按照随机数表法将其分为观察组和普通单管螺旋组,每组52例。观察组采用双源CT Flash模式进行扫描,普通单管螺旋组采用双源CT常规模式进行扫描。比较两组肺动脉CT血管成像图像质量的主观评分(各级分支评分、边缘评分),并对两组的主干CT值、信号噪声比(SNR)、对比噪声比(CNR)以及辐射剂量[扫描长度、CT容积计量指数(CTDⅠ_vol)、剂量-长度乘积值(DLP)、有效剂量(ED)进行评价。结果:两组患者的图像各级分支评分、边缘评分和主干CT值、SNR及CNR比较,差异均无统计学意义,两种不同扫描模式的扫描长度比较,差异亦无统计学意义。普通单管螺旋组扫描时间为(1.98±0.58)s,长于观察组(0.98±0.25)s,差异有统计学意义(t=11.417,P<0.05)。普通单管螺旋组TDⅠ_vol、DLP及ED高于观察组,差异均有统计学意义(t=2.222,t=5.566,t=5.02;P<0...     

毫安秒对SPECT/CT检查中辐射剂量和影像质量影响的研究

目的 在保证影像质量的前提下,为降低SPECT/CT检查中CT部分受检者的辐射剂量提供参考依据。方法 使用西门子公司SymbiaT2型SPECT/CT,固定管电压130 kV,螺距2.0,分别在100 mAs、130 mAs、160 mAs、190 mAs和230 mAs的条件下测量容积CT剂量指数（CTDI_vol）,扫描Catphan 600型和Catphan 500型CT性能检测模体,分析扫描图像,得到各个条件下CT影像质量指标。结果 CTDI_vol随管电流时间积（mAs）的升高而线性升高,mAs的改变对高对比分辨力,CT值和CT值的线性指标无影响,低对比可探测能力、均匀性和噪声值指标随mAs的升高而降低。结论 SPECT/CT中的CT辐射剂量随mAs的升高而升高,影像质量随着mAs的升高而提高,由于mAs对高对比分辨力无影响,在进行特定部位的扫描时可选择适当降低mAs,实现在保证影像质量的前提下降低受检者的辐射剂量。     

CR系统的原理及影响影像质量的原因

CR系统（computed radiography)是近年在计算机数字化影像基础上发展起来的,它将普通的X线摄影转换为数字图像,使X线摄影信息直接进入图像存储与传输系统及远程医学系统,本文主要就CR系统的原理,基本组成及影响其图像质量的原因做一综述。     

Technical quality control of chest x-rays for the health surveillance of workers exposed to the risk of pneumoconiosis: proposal for a qualitative screening method

BACKGROUND: The necessity of a qualitative screening has arisen from the fact that good technical quality is of fundamental importance for evaluating initial pneumoconiosis, for reducing inter- and intra-reader variability, for effective secondary prevention and for forensic medicine purposes. OBJECTIVES: The authors report experience in use of a method to evaluate the quality of chest radiographs performed in health surveillance programs for workers at risk for development of pneumoconiosis. METHODS: 747 postero-anterior chest radiographs concerning employees of 21 ceramic factories in the Province of Viterbo were examined. A standardized pattern was created for this evaluation. The pattern considers the main factors that can influence the quality of chest radiographs and assigns points for each of them. That factors are: 1) reproduced image of the lung's vascular structure, chiefly in the peripheral portions; 2) reproduced image of heart border, aorta, diaphragm; 3) deep inspiration; 4) symmetric image of the chest; 5) position of the scapulae; 6) visualization of the costal-phrenic angles; 7) technical impairments. RESULTS: The application of the method revealed that half of the chest radiographs examined had poor image quality for a suitable reading, in conformity with the ILO 1980 guidelines. The critical points are poor visualization of the lung's vascular structure due to overexposure or underexposure, technical impairments, non-correct scapulae position. CONCLUSIONS: The authors believe that the suggested method can be a useful instrument for self-testing the quality of chest radiographs performed in radiology centers and for the National Health Service to test the quality of chest radiographs performed in health surveillance programs.     

轴位容积扫描与螺旋扫描颅脑CT图像质量与辐射剂量对比观察

目的 通过步进式轴位容积扫描与常规螺旋扫描模式为对比,探讨颅脑CT最佳扫描方式。方法 回顾性分析389例相同扫描参数及重建参数的步进式轴位容积扫描和常规螺旋扫描模式影像学资料及辐射剂量报告,对图像质量分别进行主观评价及客观评价,主观图像评价：质量优秀的图像为3级;质量好的图像为2级;质量差但足以满足诊断的图像为1级。客观图像质量评价：根据手动定位获得图像四个感兴趣的区域分析评价信噪比（SNR）,同时对剂量报告中的容积CT剂量指数（CTDI_vol）、剂量长度乘积（DLP）进行分析。结果 步进式轴位容积扫描和常规螺旋扫描图像主观评价和客观评价均无显著性差异（P>0.05）。步进式轴位容积扫描CTDI_vol略高于螺旋扫描模式,DLP明显低于螺旋扫描模式。结论 相同扫描及重建条件下,步进式轴位容积扫描辐射剂量低于常规螺旋扫描,颅脑CT推荐步进式轴位扫描模式。但日常工作中应根据特殊需要制定个体化扫描方案。     

临床应用中如何提高数字影像的图像质量

针对放射科实际应用CR系统进行数字影像的获取操作过程,分别就影像信息采集、影像信息读取、影像信息处理、影像记录和存储等四个环节进行探讨,以尽可能提高提供给临床诊断用的数字影像的图像质量。     

The concepts of critical organ and radiation dose as applied to plutonium

The concepts of critical organ or tissue and the calculation of radiation dose have been and may well continue to be central to the development of standards for most radionuclides. In the case of plutonium the occupational standard was based on a modification of the direct calculations of maximum permissible annual dose (MPAD) or dose rate but critical organs must still be chosen for different routes of entry and different compounds and for all of the derived standards. Changes in such standards by likely variations in metabolic parameters and models are shown to be significant but not large. Application of the critical organ concept to population exposure standards poses some new problems because the basic MPAD does not distinguish among organs. A simple scaling factor from occupational exposure standards thus is not satisfactory. Use of the concept of dose commitment has many advantages but it is still necessary to select a critical organ and calculate dose. By-passing some of the problems in present practices by using risk-estimates seems unlikely for plutonium at the present time because of the paucity of human effects data and the fact that the animal experiments used quite different dosage regimens from the likely exposure situations to plutonium. A brief comparison is made of radiation and chemical hazard evaluation procedures.