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.     

Digital chest radiology.

With an increasing number of storage phosphor computed radiography units being installed worldwide, the evaluation of digital chest radiology is no longer being confined to experimental determinations of adequate imaging variables. There has been a substantial increase in the number of clinically based studies that have compared computed radiography with conventional film radiography. The applications of computed radiography are widening and further developments in dual-energy imaging and scanning equalization radiography have become possible through the use of phosphor storage computed radiography. Computer-assisted diagnosis applied to chest radiography may shortly be revolutionized by artificial intelligence, which is capable of assimilating both radiographic and clinical data.     

Receiver-operating-characteristic study of chest radiographs in children: digital hard-copy film vs 2K x 2K soft-copy images.

Two methods are commonly used to visualize digital radiologic imaging data: (1) hard-copy viewing, in which the digital data are used to modulate the intensity of a laser beam that exposes an analog film and (2) soft-copy viewing, in which the digital data are converted to an analog video signal and presented on a CRT monitor. The film method allows new digital imaging systems to be easily integrated into conventional radiologic management and viewing methods. The second method, soft-copy viewing, allows digital imaging data to be managed and viewed electronically in a picture archiving and communication system (PACS). These PACS systems are hypothesized to have improved operational efficiency and enhanced image-analysis capabilities. The quality of soft-copy images is still not widely accepted. This article reports on the results of a large-scale receiver-operating-characteristic study comparing observers' performance in detecting various pediatric chest abnormalities on soft-copy 2048 x 2048K byte displays with their performance with digital laser-printed film from computed radiography. The disease categories studied were pneumothorax, linear atelectasis, air bronchogram, and interstitial disease. The selected data set included 239 images; 77 contained no proved abnormality and 162 contained one or more of the abnormalities mentioned. Seven pediatric radiologists participated in the study, two as judges and five as observers. Our results show no significant difference between viewing images on digital hard copy and soft copy for the detection of pneumothoraces and air bronchograms. A slight performance edge for soft copy was seen for interstitial disease and linear atelectasis. This result indicates that computed chest radiographs in children viewed in a soft-copy PACS environment should result in diagnoses similar to or slightly more accurate than those obtained in a laser-printed film-based environment.     

通过工作列表实现数字化网络各系统之间患者信息的一致性

目的 实现图像存储与传输系统(picture archiving and communication system，PACS)、放射学信息系统(radiology information systems，RIS)、影像设备之间患者检查信息的一致性。方法 我院引进GE Signa 1．5T磁共振、数字乳腺，Agfa数字X线摄影、计算机X线摄影及GE CT等数字化医学设备。GE PACS是英文系统，所以前期医院在未解决信息一致性时只通过PACS对检查影像进行保存，通过PACS系统中简单的信息管理工作，并没有真正意义上的worklist。2个月后，我院采用国际上先进的解决方法即通过医学数字成像及通讯(digital imaging and communication in medicine，DICOM)标准的工作列表(worklist)的方法实现信息的一致性。在RIS系统中将患者中文信息转换为英文信息，保存并为worklist提供患者的英文信息。结果 我院在集成PACS和RIS的2年多时间以来，通过worklist来保证RIS与影像设备患者检查信息的一致性，取得了非常好的效果。在所有诊断工作站上，诊断医生通过中文RIS系统，对病人的信息进行编辑、修改、产生。结论 通过worklist实现PACS、RIS、影像设备之间患者检查信息的一致性是可行的。     

Single-exposure dual-energy computed radiography: improved detection and processing

Recent reports have emphasized the potential for dual-energy computed radiographic applications. An improved method for single-exposure material-selective imaging with a photostimulable phosphor computed radiography system was investigated. The essential elements of the technique are (a) prefiltration with gadolinium, which divides the incident broad-beam x-ray spectrum into low-energy and high-energy peaks; (b) a cassette consisting of four photostimulable phosphor plates that record images of increasing mean energies, with a computed energy separation of 23 keV from the front to the rear plate; (c) spatially dependent scatter and beam-hardening corrections; and (d) a noise-reduction algorithm based on noise correlations between bone-selective and soft-tissue-selective dual-energy images. These elements result in improved material cancellation and signal-to-noise ratio throughout the image.     

Review of optical storage technology for archiving digital medical images

Digital optical recording (DOR) is a data-acquisition and storage technology important to the development of picture archiving and communication systems (PACS). DOR offers attractive advantages in high-density, low-cost archival storage of images and other information. At present, film is used as the storage medium for archiving images generated by both conventional equipment and digital technologies such as computed tomography, digital subtraction angiography, magnetic resonance imaging, and nuclear medicine. The basic methods of DOR data storage are discussed together with requirements essential for making DOR an acceptable alternative to film archiving. The impact of DOR technology on the operation of an imaging department is projected.     

Comparison of dual-energy and conventional chest radiography for nodule detection

This paper presents the results of a nodule detection study, using a Humanoid chest phantom, which was designed to evaluate the performance of two types of dual-energy and conventional (single-energy) chest radiography. The film-screen apparatis were used as image detectors for all imaging modalities. The area under the ROC curve and the cumulative true-positive fraction both were used as performance indexes in the evaluation. Because of the small number of false-positive responses in the observer studies, the cumulative true-positive fraction was eventually regarded as a more conclusive index of accuracy than the area under the ROC curve to make a reasonable conclusion. Both dual-energy techniques, dual- and single-exposure, were found to be superior to conventional chest radiography, P less than 0.0005 and P less than 0.006 for dual- and single-exposure techniques, respectively. The difference between the two dual-energy techniques was statistically insignificant, P less than 0.47. We concluded that the dual-energy, single-exposure technique is worthy of further clinical study based on these encouraging results and because of the ease with which the technique can be implemented.     

An economic comparison between digital luminescence radiography and conventional film processing in intensive care medicine]

The costs of a conventional film-screen radiography daylight-system and storage-phosphor computed radiography (Fuji AC-1) are compared. In 1990, 3841 radiologic procedures (mostly portable chest X-rays) were performed in 3474 patients of a surgical intensive care unit. With conventional film-screen radiography 6.8% retakes were necessary for diagnostic or technical reasons. Comparing the fixed and variable costs of both systems conventional film-screen radiography was more economic under the given conditions of the test. It is concluded that computed radiography in intensive care patients has definite advantages in terms of image quality and reproducibility, however, in order to compete successfully in the economic turf CR has to be implemented in a picture archiving and communication system (PACS).     

Integrating digital systems: commitment and collaboration

One year ago, the radiology department at Ball Memorial Hospital, a 350-bed facility in Muncie, IN, was completely film-based. The need to support a new all-digital, 35-room emergency department (ED) hastened the facility's transition to a digital environment. Today, with the exception of mammography, the hospital's imaging services are now digital. To develop and implement the project, the hospital formed an internal implementation team. An independent consultant was also hired to evaluate the impact of these new technologies and to provide an estimated cost payback. After research, site visits, and vendor demonstrations, the hospital selected a single vendor for its picture archiving and communication system (PACS), digital radiography (DR), computed radiography (CR), and overall project management. The DR system was installed in the ED to provide digital image capture for a full range of trauma exams. The ED also initially began utilizing a Web-based PACS distribution originally implemented for after-hours teleradiology. The majority of the hospital's imaging studies are captured with 2 multi-cassette CR systems that serve 7 exam rooms in the radiology department. The hospital also installed remote operations panels to expedite entry of patient and exam information. Technologists readily embraced both CR and DR systems. The Web distribution system now transmits images to hospital-based computers and to 150 remote referring physicians. The PACS platform automatically e-mails key images and radiology reports to referring physicians. Authorized physicians can also request reports and images on an as-needed basis. The PACS vendor had previously performed multiple integrations with the radiology information system (RIS) vendor; the integration of PACS and RIS was extremely smooth. One of the critical components of a successful conversion is experienced, dedicated management. The hospital retained professional project management services to facilitate implementation and to ensure adequate training for all users.     

Single-exposure conventional and computed radiography image acquisition

A technique for simultaneously acquiring a conventional film-screen radiographic image and a digital computed radiography (CR) image with a single x-ray exposure is described. Measurements of image contrast, spatial resolution, and signal-to-noise ratios demonstrate that a modified film cassette in which the first intensifier screen has been replaced with a CR imaging plate permits dual-image, single-exposure imaging with only nominal degradation in film and CR image quality relative to the two standard image counterparts. This technique may be used to acquire matched image pairs for research or as a way to provide full-size conventional film images in the clinical environment, while retaining the advantages offered by computed radiography systems.     

Detection of simulated pulmonary nodules by single-exposure dual-energy computed radiography of the chest: effect of a computer-aided diagnosis system (Part 2)

OBJECTIVE: To evaluate the performance of the computer-aided diagnosis (CAD) scheme on the detection of pulmonary nodules (PNs) in single-exposure dual-energy subtraction computed radiography (CR) images of the chest, and to evaluate the effect of this CAD scheme on radiologists' detectibilaties. METHODS AND MATERIAL: We compared the detectability by the CAD scheme with the detectability by 12 observers by using conventional CR (C-CR) and bone-subtracted CR (BS-CR) images of 25 chest phantoms with a low-contrast nylon nodule. RESULTS: Both in the CAD scheme and for the observers, the detectability of BS-CR images was superior to that of C-CR images (P<0.005). The detection performance of the CAD scheme was equal to that of the observers. The nodules detected by the CAD did not necessarily coincide with those by the observers. Thus, if observers can use the results of the CAD system as a 'second opinion', their detectabilities increase. CONCLUSION: The CAD system for detection of PNs in the single-exposure dual-energy subtraction method is promising for improving radiologists' detectabilities of PNs.     

PACS系统的应用体会

目的：介绍我院影像医学存档与通讯系统（ＰＡＣＳ）应用的经验。材料与方法：将所有Ｂ超、ＣＴ、Ｘ线机和一台ＩＢＭ服务器、四台奔腾Ⅱ档次的工作站及惠普光盘塔连接成医学数字影像传输（ＤＩＣＯＭ）网络;ＤＩＣＯＭ服务器与各种图像浏览终端羞以太网络;通过ＨＵＢ连接成ＰＡＣＳ系统。结果：将常规放射图像的模拟信号通过数字转换器转换为数字信号后,与ＣＴ等数字成像系统的数字信号一并输入光盘塔,并进行诊断。将数字图像和诊断报告一起舆到医院各个图像浏览终端,使其可通过ＷＥＢ界面系统及咨询平台进行查询。ＰＡＣＳ投入使用２年来,效果良好。结论：ＰＡＣＳ的应用明显提高了放射科及相关科室的工作效率,方便了工作、教学、科研和会诊。     

Stimulable phosphor plates in chest radiology

LANGUAGE="EN">Summary. The stimulable phosphor plate technique has revolutionised radiology with portable equipment. The image quality permits diagnosis under difficult control conditions (ICUs). In order to achieve a signal-to-noise ratio, and therefore a contrast resolution similar to the commonly used film/screen systems, a higher radiation dose is needed. However, overall, with this technique a radiation dose reduction may be achieved as a result of the elimination of the need for retakes. The available stimulable phosphor plate systems, with adequate image processing are reliable, and at least as good as conventional film/screen systems for diagnosis in chest radiography. There are, however, other aspects that make the stimulable phosphor plate technique particularly appealing. Firstly, its reproducibility, which particularly in chest radiography allows images to be obtained with the same grey scale and darkness. Secondly, as this technique permits digital archiving and visualisation of images on screen, images can be rapidly distributed over a network making them available when and where they are needed.     

Image preprocessing for a picture archiving and communication system.

OBJECTIVES AND RATIONALE. In a picture archiving and communication system (PACS), images are acquired from multiple modalities and displayed on an electronic workstation. Each modality has different image characteristics. This variability must be addressed before the image is displayed. METHODS. The authors developed methods to automatically process magnetic resonance (MR), computed tomographic (CT), and computed radiography (CR) images before display and subjectively evaluated their effectiveness. RESULTS. Unwanted background successfully was automatically removed from 89.5% of 615 CR images. Of 803 chest, abdomen, and hand images 93% were automatically rotated to the correct orientation. CONCLUSIONS. Automated preprocessing of PACS images can be performed successfully, improving speed and convenience for the radiologist interpreting images at an electronic workstation.     

A comparison of conventional film,CR hard copy and PACS soft copy images of the chest: analyses of ROC curves and inter-observer agreement

STUDY OBJECTIVE: The aim of this study was to determine whether the accuracy of diagnosis of a spectrum of chest pathology was affected by the imaging technique used, and to compare conventional film/screen, hard copy computed (phosphor plate) radiography (CR) and soft copy CR (PACS) images. MATERIALS AND METHODS: For each of 44 patients who had a CT examination of the thorax, PA and lateral chest radiographs were produced using conventional film, hard copy CR and soft copy PACS images. Five radiologists independently scored all images for the presence of abnormalities. The data were analysed in two stages using the result of the CT scan as the reference standard diagnosis: firstly, to investigate differences in abnormality scores between image modalities and observers using ROC analysis; secondly, to investigate the agreement of the diagnoses with the reference standard by the analysis of kappa scores. RESULTS: The ROC analyses and comparison of kappa scores showed no differences between image modalities (P=0.72, P=0.87), but highly significant differences between observers (P<0.001, P=0.003). CONCLUSION: The detection of chest lesions did not vary between conventional film, CR hard copy and PACS soft copy images. For all three image types, there were statistically significant differences between observers.     

Comparison of a digital flat-panel versus screen-film, photofluorography and storage-phosphor systems by detection of simulated lung adenocarcinoma lesions using hard copy images

The purpose of this study was to compare hard copy images from a flat-panel detector digital radiography system with conventional radiography, photofluorographic radiography and storage phosphor radiography for the detection of simulated lung adenocarcinoma lesions and also for radiation dose. To test the diagnostic performance of these four systems, the authors used 15 types of lung adenocarcinoma phantom according to Noguchi's classification and an anthropomorphic chest phantom. The visual evaluation of tumour detectability by four radiologists and two general thoracic surgeons was examined with a five-level confidence scale. Lung doses were measured with glass dosemeters for the chest radiology systems under the conditions used by each hospital and centre. Our results indicated that flat-panel detector digital radiography and storage phosphor radiography are not necessarily superior to conventional radiography and photofluorographic radiography for detecting lung adenocarcinomas when only hard copy images are used, and this suggests a need to carefully optimize chest radiography.     

A comparison of image reject rates when using film, hard copy computed radiography and soft copy images on picture archiving and communication systems (PACS) workstations

A comparison has been made of the reject rates of plain images for three separate periods when film, computed radiography (CR) and PACS systems were in operation throughout the Hammersmith Hospital, London. There was a statistically significant reduction in the overall percentage reject rate across all examinations from 9.9% to 8.1% when the hospital changed from using a conventional film based system to a CR system. There was a further reduction in the reject rate to 7.3% when the hospital moved to a hospital-wide PACS system, but this change was not statistically significant. Using estimations of the total number of images used, the percentage reject rates were 6.6% for film, 5.5% for CR and 5.5% for PACS. Thus, if the radiation dose for each image is unchanged, and the same types of images are used for the examination of each body area, a move from conventional film imaging to phosphor plate imaging provides the potential to reduce the patient population dose.     

High frequency edge enhancement in the detection of fine pulmonary lines. Parity between storage phosphor digital images and conventional chest radiography

Fine linear structures represent a severe test of the minimum spatial resolution that is needed for digital chest imaging. We studied the comparative observer performance of storage phosphor digital imaging (1760 X 2140 pixel matrix, 10 bits deep), and conventional radiography (Lanex medium screen, Ortho C film) in the detection of simulated fine pulmonary lines superimposed on the normal chest when exposure factors were identical (20mR skin entrance dose at 141 kVp). Receiver operating characteristics analysis of 2160 observations by six readers found that high frequency edge-enhanced digital images (ROC area: 0.78 +/- 0.06) performed better than unenhanced digital images (ROC area: 0.70 +/- 0.07) (P less than 0.01 for paired t-test), and that edge enhanced digital images performed on a par with conventional radiography (ROC area: 0.78 +/- 0.09). We conclude that for the detection of fine linear structures, storage phosphor digital images can perform on a par with higher resolution conventional chest radiographs when a high frequency edge-enhancement algorithm is employed.     

Development of an electronic radiologist's office in a private institute.

A computer system that improves the quality, user-friendliness, accessibility, and management of radiology data (images, reports, databases, knowledge) was implemented at a private institute. A picture archiving and communication system (PACS) was integrated with the radiology information system (RIS). Two servers and 12 personal computers form the integrated system. The first server is dedicated to management and archiving of Digital Imaging and Communications in Medicine (DICOM) images. The second server is dedicated to management of the RIS and archiving of patient data (Structured Query Language database), reports (hypertext markup language [HTML]), and images in the Joint Photographic Experts Group (JPEG) format (mini-PACS). There are three main client-server networks: a common network of imaging modalities (magnetic resonance imaging, computed tomography, ultrasonography, digital radiography) and two fast Ethernet networks (the PACS network and the RIS network). The RIS-PACS is linked remotely with other workstations and servers via Integrated Services Digital Network (ISDN). Images and reports can be distributed to referring physicians in the form of multimedia HTML and JPEG documents, which can also be used for quick and easy archiving, distribution, and reviewing within the institute. However, referring physicians have been reluctant to use electronic reports and images.     

The digital readiness of imaging facilities in Saskatchewan.

OBJECTIVE: To determine the digital readiness of Saskatchewan's imaging facilities. METHODS: A questionnaire was mailed to all 173 imaging facilities in Saskatchewan, ranging from small private clinics to tertiary care hospitals. The 129 responses were received, tabulated and summarized. RESULTS: Of the 129 facilities that responded, only 2 had picture archiving and communication systems (PACS). Both were private, urban imaging facilities. Six facilities had digital radiology information systems, 12 had digital hospital information systems and 8 had digital patient records. Only 42 sites had Internet access in their facilities. CONCLUSION: Only a small minority of Saskatchewan imaging facilities have any digital capability whatsoever. None are prepared to make the transition to a fully digital environment at this time. The infrastructure required to send or receive high-quality digital images among imaging facilities in Saskatchewan does not exist. A strategy to address the implementation of digital imaging and PACS should be developed at a provincial level.