Flat panel digital radiography compared with storage phosphor computed radiography: assessment of dose versus image quality in phantom studies

RATIONALE AND OBJECTIVE: To assess and quantify the dose reduction by use of a CsI-flat panel digital radiography (DR)-system compared with digital computed radiography (CR). MATERIALS AND METHODS: A TCDD-test using the CDRAD-phantom was performed at mAs-values of 5, 4, 2.5, 2, 1, and 0.5 mAs for both digital systems. Entrance surface doses were recorded for all images. Images were presented to four independent observers. For quantitative comparison the image quality figure (IQF) was calculated. Statistical analysis was performed using the Pearson correlation and the Wilcoxon test. A ROC analysis was performed using the TRG-phantom. Settings of 4, 2.5, 2 mAs for both systems were used. In addition, 1 and 0.5 mAs were used for the DR system only. Statistical significance was evaluated using Student test. RESULTS: The DR system provided equivalent results compared with CR with respect to high frequency information and superior results with respect to low contrast details. Compared with computed radiography, the flat panel detector demonstrated significantly lower IQFs, ensuring a better image quality with respect to contrast and detail detectability. IQFs for DR and CR were equal at a surface dose reduction of 87% for DR. ROC analysis revealed significantly higher values under the curve for DR up to a surface dose reduction of 70%. CONCLUSIONS: Image quality of DR proved to be far superior to CR in particular for low contrast details. The image quality of CR is similar to that of DR only at high dose levels.     

数字X线摄影系统中低剂量应用的探讨

目的 通过数字X线摄影系统（DR）在胸部摄影检查中的应用评价DR的低剂量的优越性。方法 利用CDRAD 2.0低对比细节体模评价计算机X线摄影（CR）和DR的影像质量和表面空气吸收剂量（ESD）关系,分别利用两个系统（DR使用ESD约为CR的1/3）得到成人胸部30幅影像。由6位影像科医生来评价以上两者的影像系统对于肩胛骨内侧边缘等胸部结构的清晰程度。结果 CR影像和减少ESD的DR影像在影像诊断质量上差异没有统计学意义（P＞0.05）。结论 DR的较好的分辨率和低噪声特性,以及高DQE有助于减少患者接受的辐射剂量,而不影响诊断质量。     

床旁DR与CR胸部摄影质量的对比研究

目的通过床旁数字化X线摄影(digitalradiography,DR)系统与计算机X线摄影(computedradiography,CR)系统胸部摄影图像质量的对比分析,探讨床旁DR摄影的优势。方法随机抽取2010年拍摄的DR床旁X线胸片1000份和既往CR床旁X线胸片1000份进行对比分析。结果床旁DR摄影的应用提供了更加优良的图像质量,明显减少了放射技师的工作量,同时还降低了患者接受的辐射剂量。结论床旁DR胸部摄影比CR胸部摄影有着明显的优势,对手术患者和危重患者的诊治起到了积极作用。     

乳腺数字化X线射影术、计算机X线射影术和屏-胶片系统影像质量和放射剂量的比较

目的 比较增感屏-胶片乳腺X线摄影、数字乳腺摄影(DR)和计算机乳腺摄影(CR)3种系统的模体影像质量、辐射剂量和临床对疾病诊断的准确率.方法 选择3台临床使用中的屏-胶片、DR和CR乳腺摄影设备,进行性能测试,确保质量符合规定,具有可比性.以屏-胶片系统的辐射剂量为标准,使用DR和CR分别对Manuno-152模体和美国放射学院(ACR)模体摄影.再使用DR和CR的最优模式对模体摄影并记录辐射剂量.所获图像照片按模拟病变结构编号,由8名专业乳腺放射学医师在相同条件下分别进行ACR评分.3种方法的评分结果采用随机区组设计的方差分析进行统计学处理.连续收集一段时期内采用3种检查方法检查,并且有病理诊断结果的患者的影像资料,应用Kappa检验方法进行2种诊断结果一致性检验,并以病理结果为金标准,比较3种影像检查结果诊断的准确率.结果 对于Mammo-152模体,无论DR、CR的辐射剂量是否超过屏一胶片乳腺X线摄影的2.25 mGy乳腺平均剂量,屏-胶片摄影的空间分辨率都最高(7.0～8.0 Lp/mm),DR次之(4.7～5.2 Lp/mm),CR最差(2.5 Lp/mm).增加辐射剂量(27.0%～30.0%),DR的空间分辨率略有改善(上升11.0%),而CR几乎没有改变(上升1.5%).对ACR模体摄影时,DR的辐射剂量没有超过屏-胶片乳腺X线摄影的2.22 mGy乳腺平均剂量,且模拟结构显示度最好.屏-胶片乳腺x线摄影的团块显示优于CR,但CR的纤维和点阵显像优于屏-胶片乳腺X线摄影.CR检查时辐射剂量提高25.0%,纤维和点阵显像接近DR,团块显像接近屏-胶片乳腺x线摄影.3台设备的X线诊断和病理诊断结果的一致性极好(屏-胶片系统的一致率50/56,DR系统83/90,CR系统61/69,P值均<0.01且Kappa值均>0.75),在疾病诊断准确率上差异没有统计学意义[屏-胶片系统的准确率为89.3%(50/56),DR系统为92.2%(83/90),CR系统为88.4%(61/69),PearsonX2值为0.722,P=0.697].结论 屏-胶片乳腺X线摄影分辨率最高,DR的模拟病变显像最好且辐射剂量最低.当CR的辐射剂量与屏-胶片乳腺X线摄影相当时,两者对模拟病变的显像各有优劣;当增加CR的摄影剂量时,其模拟结构显像质量高于屏-胶片乳腺X线摄影,低于DR.在临床对疾病的诊断准确率方面,三者无明显差别.     

Direct detector radiography versus dual reading computed radiography: feasibility of dose reduction in chest radiography

The image quality of dual-reading computed radiography and dose-reduced direct radiography of the chest was compared in a clinical setting. The study group consisted of 50 patients that underwent three posteroanterior chest radiographs within minutes, one image obtained with a dual read-out computed radiography system (CR; Fuji 5501) at regular dose and two images with a flat panel direct detector unit (DR; Diagnost, Philips). The DR images were obtained with the same and with 50% of the dose used for the CR images. Images were evaluated in a blinded side-by-side comparison. Eight radiologists ranked the visually perceivable difference in image quality using a three-point scale. Then, three radiologists scored the visibility of anatomic landmarks in low and high attenuation areas and image noise. Statistical analysis was based on Friedman tests and Wilcoxon rank sum tests at a significance level of P<0.05. DR was judged superior to CR for the delineation of structures in high attenuation areas of the mediastinum even when obtained with 50% less dose (P<0.001). The visibility of most pulmonary structures was judged equivalent with both techniques, regardless of acquisition dose and speed level. Scores for image noise were lower for DR compared with CR, with the exception of DR obtained at a reduced dose. Thus, in this clinical preference study, DR was equivalent or even superior to the most modern dual read-out CR, even when obtained with 50% dose. A further dose reduction does not appear to be feasible for DR without significant loss of image quality.     

两种数字化X射线摄影技术影像质量与成像剂量的比较

目的对比研究非晶硒平板探测器直接数字化X射线摄影(DR)及计算机x射线摄影(CR)两种数字化X射线摄影技术影像质量与吸收剂量的关系。方法应用DR和CR系统分别对对比度．细节体模(CDRAD2．0)进行不同吸收剂量的曝光成像。记录每次曝光的体模表面吸收剂量，并将所获取的影像在图像诊断工作站显示器上由4位观片者进行观察，计算影像质量表征因子(IQF)。应用ANOVA检验法统计、比较两种数字化摄影技术的图像质量与吸收剂量的差别。结果与CR相比，DR具有更低的IQF值，对人体组织对比度和结构细节有更好的信息检出特性。两种成像技术产生相同IQF值时，DR系统在体模表面产生的表面剂量比CR系统降低了77％。结论DR技术对于低对比度组织细节的检测好于CR技术。在获得相同影像信息的前提下，与CR相比应用DR大大降低了被检者吸收剂量。     

Radiation dose in digital chest radiography: comparison among three technologies

PURPOSE: To compare the Entrance Surface Dose (ESD) for a normal patient, measured on three types of dedicated digital equipment for chest radiography: an amorphous selenium system, a CR (Computed Radiography) system, and a system for direct radiography (DR) based on an amorphous silicon active matrix (a-Si) connected to a CsI(T1) detector. MATERIALS AND METHODS: The ESD values were measured with different dosimeters placed in the air parallel to the detector plane, and at a distance equal to the thickness of a normal-build patient. The measurements were taken with the radiological parameters (Posterior-Anterior projection (PA) and Lateral projection (L)) used in diagnostic practice to obtain high-quality diagnostic radiographic images. The measurements taken with the DR equipment were repeated after the manufacturer added a 0.2 mm-thick Cu filter. The ESD values obtained by this series of measurements were reported as mean and standard deviation values (M+/-SD). RESULTS: With the PA projection, the doses measured for the different devices were the following: amorphous selenium system 0.12+/-0.06 mGy, CR system 0.3+/-0.05 mGy, DR system 0.05+/-0.02 mGy. With the L projection: amorphous selenium system 0.40+/-0.13 mGy, CR system 0.9+/-0.17 mGy, and DR system 0.21+/-0.15 mGy. CONCLUSIONS: The use of digital systems allows a significant reduction of the patient dose. In particularly the Direct Radiography system, based on a CsI/a-Si detector, administers the lowest patient dose.     

Investigation of optimum energies for chest imaging using film-screen and computed radiography

The purpose of the study was to compare the image quality of film-screen (FS) and computed radiography (CR) for adult chest examinations across a range of beam energies. A series of images of the CDRAD threshold contrast detail detection phantom were acquired for a range of tube potential and exposure levels with both CR and FS. The phantom was placed within 9 cm of Perspex to provide attenuation and realistic levels of scatter in the image. Hardcopy images of the phantom were scored from a masked light-box by two scorers. Threshold contrast indices were used to calculate a visibility index (VI). The relationships between dose and image quality for CR and for FS are fundamentally different. The improvements in VIs obtained using CR at 75 kVp and 90 kVp were found to be statistically significant compared with 125 kVp at matched effective dose levels. The relative performance of FS and CR varies as a function of energy owing to the different k-edges of each system. When changing from FS to CR, the use of lower tube potentials may allow image quality to be maintained whilst reducing effective dose. A tube voltage of 90 kVp is indicated by this work, but may require clinical verification.     

数字X线成像系统图像质量影响因素的实验研究

目的 比较非晶体硒平板探测器DR系统和CR系统的图像噪声、空间分辨率和入射体表剂量（ESD），研究数字X线图像质量影响因素的相关性。方法 采用相同管电压（125kVp）和不同mAs对仿真胸部体模用分辨率测试卡进行DR和CR曝光成像，测量ESD、空间分辨率，计算均方根（RMS）值，分析mA8、ESD、RMS及空间分辨率之间的变化关系。结果 两种系统的RMS随mAs的增加而降低，ESD随mAs的增加而增加。两种系统成像相同ESD时，DR的RMS略高于CR。ESD增加至一定量时，空间分辨率达到极限值（CR为3．1lp／mm，DR为3．4lp／mm）。结论 数字系统放射线剂量的改变会导致噪声、分辨率变化。适度的噪声水平对空间分辨率影响不明显。     

Digital radiography of the chest: state of the art

Digital image acquisition possesses a number of advantages over conventional systems in radiographic examination of the chest, the most important of which is its greater dynamic range. In addition, one digital images are acquired, they can be processed by computer in ways that cannot be rivalled by conventional analog techniques. Finally, digital images can be stored, retrieved and transmitted to local or remote sites. Here the status of the different digital systems employed in chest radiology and commonly used image processing techniques are reviewed. Also discussed are the current clinical applications of integrating digital chest radiography with a picture archiving and communication system (PACS) along with the difficulties typically encountered. Studies with a variety of digital techniques have been carried out on several fronts. Computer radiography based on photostimulabe phosphor (CR) has replaced screen-film imaging in certain applications (i.e. bedside imaging). However, CR has limitations, namely its poor X-ray utilisation efficiency at high X-ray tube voltages and sensitivity to scatter; therefore, it is not ideal for all applications. Recently, a dedicated digital chest unit with excellent X-ray utilisation efficiency at high X-ray tube potentials has been introduced. On the basis during the past decade, recommendations are made regarding the most desirable equipment specifications for dedicated and bedside digital chest radiography.     

Computed radiography and direct radiography: influence of acquisition dose on the detection of simulated lung lesions

PURPOSE: We sought to evaluate the performance of dual-readout and single-readout computed radiography compared with direct radiography for detecting subtle lung abnormalities with a standard and a low-dose technique. MATERIALS AND METHODS: Posteroanterior radiographs of an anthropomorphic chest phantom were obtained with a single-readout storage phosphor radiography system (CRS, pixel size 200 microm), a dual-readout storage phosphor radiography system (CRD, pixel size 100 microm), and a direct detector (DR, pixel size 143 microm) at dose levels of 400 and 800 speed. Ten templates were superimposed to project 4 types of lesions over low- and high-attenuation areas, simulating nodules, micronodules, lines, and patchy opacities. Six radiologists evaluated 60 hard-copy images for the presence or absence of lesions. Statistical significance of differences was evaluated using receiver operating characteristic analysis and analysis of variance. RESULTS: For both low- and high-attenuation areas, CRD (Az = 0.85 and 0.66) was superior to CRS (Az = 0.75 and 0.58) for overall performance and all lesion subtypes (P < 0.05). DR (Az = 0.87 and 0.67) performed slightly better than CRD, being significant only for the detection of micronodules. Acquisition dose significantly affected only the detection of lines and micronodules, whereas the detection of nodules and patchy opacities was not significantly different with reduced exposure, regardless of the system used. CONCLUSION: The dual-readout CR system significantly outperformed the single-readout CR and almost equaled the performance of DR. Dose reduction was more critical for small-sized lesions (micronodules, lines) than for nodular or patchy opacifications and affected mainly the lesions in high attenuation areas.     

两种平板探测器X线摄影系统的成像剂量与成像质量的比较研究

目的 定量分析、比较非晶硅平板探测器X射线摄影系统与非晶硒平板探测器X射线摄影系统在不同成像剂量条件下成像质量的差别。方法 以非晶硅平板探测器系统和非晶硒平板探测器系统分别摄取对比度-细节体模CDRAD2.0在相近曝光剂量条件下的X射线影像,由4位独立观察者分别阅读影像,并计算所对应的曝光剂量下图像质量因子（image quality figure,IQF）,应用ANOVA分析两成像系统对比度及细节检测能力。使用X射线摄影统计学体模（TRG）测量两系统在不同曝光剂量条件下操作者特性曲线（receive operating characteristics,ROC）,应用Wilcoxon检验分析、比较两种成像技术的影像信息检测能力的差别。结果 在低曝光剂量条件下,两系统CDRAD体模影像IQF值及ROC曲线AZ值差别有显著意义,在对比度、组织细节检测能力上非晶硅平板探测器系统优于非晶硒平板探测器系统。在高曝光剂量条件下,两系统差异无统计学意义。结论 在低曝光剂量条件下,成像质量非晶硅平板探测器系统优于非晶硒系统。在获得相同的影像质量的前提下,使用前者进行X射线摄影可以降低被检者受照剂量。     

Advances in computed radiography systems and their physical imaging characteristics

Radiological imaging is progressing towards an all-digital future, across the spectrum of medical imaging techniques. Computed radiography (CR) has provided a ready pathway from screen film to digital radiography and a convenient entry point to PACS. This review briefly revisits the principles of modern CR systems and their physical imaging characteristics. Wide dynamic range and digital image enhancement are well-established benefits of CR, which lend themselves to improved image presentation and reduced rates of repeat exposures. However, in its original form CR offered limited scope for reducing the radiation dose per radiographic exposure, compared with screen film. Recent innovations in CR, including the use of dual-sided image readout and channelled storage phosphor have eased these concerns. For example, introduction of these technologies has improved detective quantum efficiency (DQE) by approximately 50 and 100%, respectively, compared with standard CR. As a result CR currently affords greater scope for reducing patient dose, and provides a more substantive challenge to the new solid-state, flat-panel, digital radiography detectors.     

碘化铯/非晶硅数字摄影系统拍摄胸片的适宜管电压:高千伏摄影是否适用于间接DR

目的探索碘化铯/非晶硅数字摄影系统(间接DR)拍摄胸片的适宜管电压。方法(1)分别对60名正常成人拍摄80、100、150 kV正位胸片,由5位放射科医师对比每人的3张图像质量,对多个解剖部位的显示情况和图像总体印象进行评分;(2)分别固定表面入射剂量和出射剂量,对人胸部体模拍摄80、100、120、150 kV正位胸片,对肺内模拟病变进行评分。结果成人胸片和肺内模拟病变的显示均随管电压增高,图像质量降低;80 kV对比度最好,但外观略接近低千伏摄影胸片。结论间接DR拍摄正位胸片的适宜管电压为80~100 kV,高千伏摄影不再适用于DR。     

Optimizing digital radiography of children

Pediatric projection imaging differs from imaging of the adult patient. Children are smaller, more radiosensitive, and less compliant than their adult counterparts. Their characteristics affect the way projection imaging is practiced and how dose is optimized.Computed radiography (CR) and digital radiography (DR) have been embraced by pediatric practitioners in order to reduce dose and improve image quality. Unfortunately, dose optimization with CR and DR has been hampered by a lack of definition of appropriate exposure levels, a lack of standardization in exposure factor feedback, and a lack of understanding of the fundamentals of CR and DR technology. The potential for over-exposure exists with both CR and DR. Both the Society for Pediatric Radiology and the American Association of Physicists in Medicine recognize the promise and shortcomings of CR and DR technology and have taken steps to join with manufacturers in improving the practice of CR and DR imaging. Although the risks inherent in pediatric projection imaging with CR and DR are low, efforts to reduce dose are worthwhile, so long as diagnostic quality is maintained. Long-standing recommendations for limiting radiation dose in pediatric projection imaging are still applicable to CR and DR.     

非晶硒平板探测器DR与CR模拟病变描述和剂量降低的对比研究

目的 比较非晶硒平板探测器DR与CR对模拟肺部病变的描述,并对剂量降低情况进行评价。方法 模拟线状、网状和结节病变结构置入仿真胸部体模内,应用DR和CR分别对不同mAs设置的体模曝光,记录体模的入射体表剂量。收集不同剂量的硬拷贝照片,由4位放射医师随机地实施模拟肺部病变显示度评价。采用秩和(Wilcoxon)检验进行统计学分析。结果 用2.0、3.2 mAs曝光时,DR与CR对模拟线状、网状病变的显示度差异有统计学意义(模拟线状病变:Z=-2.032,P=0.042;Z=-2.375, P=0.018。模拟网状病变: Z=-2.680, P=0.007;Z=-2.670, P=0.008)。用5.0、6.3 mAs曝光时,两者对模拟线状、网状病变的显示度差异无统计学意义(P＞0.05)。2.0、3.2、5.0、6.3 mAs曝光档,对于小结节(直径小于10 mm)的检测DR均优于CR(Z=-2.237, P=0.018; Z=-2.384, P=0.017; Z=-2.388, P=0.017; Z=-2.366, P=0.018)。当3种模拟肺部病变都显示清楚时,用非晶硒DR系统的入射体表剂量降低约65%。结论 对微小低对比病变的描述,非晶硒平板探测器DR优于CR且明显地降低曝光剂量。     

Small object contrast in AMBER and conventional chest radiography

The ability of a commercially available scanning equalization system for chest radiography to render small object contrast in the lung-, mediastinum-, and subdiaphragm-equivalent regions of an acrylic chest phantom was quantitatively evaluated. Images from nine chest phantoms that represented a wide range of patient sizes and dynamic ranges of x-ray transmittance were analyzed. Subject contrast was measured with a photostimulable phosphor detector, and images were acquired in both equalized and nonequalized (conventional) imaging modes. Available subject contrast in the lung-equivalent region was 8%-15% lower in the equalized images compared with the nonequalized images in all phantoms (patient types); contrast in the mediastinum-, retro-cardiac-, and subdiaphragm-equivalent regions was 11%-63% higher in the equalized images, with the degree of improvement increasing as patient size and dynamic range increased. Images of each phantom were also acquired with the screen-film systems currently in use at the authors' institution, permitting an assessment of the relative performance (in terms of radiographic contrast) of these imagers with and without use of equalization.     

DR胸部X线摄影技术在临床的应用

目的评价直接数字X线摄影系统在胸部疾病诊断与筛查中的实用意义。方法自2005年9月以来,应用西门子FX直接数字X线摄影系统对我院门诊、急诊、住院患者及来院体检者进行了胸部检查。DR影像经激光打印机打印后,以数字化形式传入我院PACS供实时共享。DR影像显示病变的能力与常规X线平片进行了比较。结果自2005年9月应用西门子FX直接数字X线摄影系统以来,基本满足了我院门诊、急诊、住院患者胸部疾病诊断和来院体检者胸部疾病筛查的实际需要。与常规X线平片比较,DR影像能更清晰、准确地显示病灶。结论DR是诊断和筛查胸部疾病的重要影像技术,尤其与PACS联合应用是医院数字化管理的重要标志。     

Digital chest radiography with a solid-state flat-panel x-ray detector: contrast-detail evaluation with processed images printed on film hard copy

PURPOSE: To evaluate and compare human observer performance in a contrast-detail test by using postprocessed hard-copy images from a digital chest radiography system and conventional screen-film radiographs. MATERIALS AND METHODS: The digital radiography system is based on a large-area flat-panel x-ray detector with a structured cesium iodide scintillator layer and an amorphous silicon thin-film transistor array for image readout. Images of a contrast-detail phantom were acquired at two exposure levels by using two standard thoracic screen-film systems and the digital system at matched dose. By using images of the phantom processed with standard chest image postprocessing techniques, a four-alternative forced-choice observer perception study was performed, and the number of detectable test signals (disk-shaped objects 0.3-4.0 mm in diameter) was determined for each image type. RESULTS: On average, observers detected more test signals on digital images than on screen-film radiographs at all diameters up to 2.0 mm and an equivalent number at larger diameters. Test signals with lower inherent subject contrast were detected more readily on digital images than on screen-film images, even when x-ray exposure levels for the digital system were reduced by 20%. CONCLUSION: Observer performance in a contrast-detail detection task can be improved by using images acquired with the flat-panel digital chest radiography system as compared with those acquired with state-of-the-art screen-film combinations.