Digital imaging and picture archiving and communication systems

Great progress has been made in digital imaging of the chest. Most studies are dealing with computed radiography. Chest radiography in the intensive care unit may, in most cases, be performed using computed radiography. However, subtle pulmonary interstitial disease can be demonstrated less confidently using computed radiography. Significantly better detection of calcified lung nodules can be obtained by using simplified single-exposure dual-energy technique that uses storage phosphor. The wide latitude of computed radiography permits images of high quality in areas other than chest radiography. Encouraging results are presented especially in the diagnostic evaluation of scoliosis and other musculoskeletal abnormalities. An important technical innovation in digital radiography is an improved method for single-exposure dual-energy digital imaging using prefiltration with gadolinium, a cassette consisting of four photostimulable phosphor plates, spatially dependent scatter and beam hardening corrections, and noise reduction algorithm. Other groups tested algorithms for enhancement of digital images that allowed significant data compression. The implementation of picture archiving and communication systems (PACS) is inevitable; the question concerning PACS implementation is not why, but when. A comparison of the cost-effectiveness of PACS with conventional film archiving and communication systems shows that PACS should provide indirect savings when regarding the hidden costs of conventional systems. Much more experience will be needed before there is general agreement on the best design for the radiologist's workstation. Teleradiology should contribute to radiologic consultation for remote locations, because it improves the efficacy of management of patients in such locations.     

Digital radiology. Clinical experience

The authors report the experience achieved at the Stanford University (USA) with a digital radiography system which allows the digitization of the film and of the images collected with photostimulable phosphors. The phosphor is essentially an intensifying screen where a latent image is stored after exposure to X-rays and is extracted by a laser scanning. The images collected with the digitized film and with the phosphor (chest, breast, bone) have been analyzed. The digitized film offers potential diagnostic advantages over the conventional film, because of the contrast manipulation and many other processing options. The possibility to recover the information of overexposed films appears very attractive. The photostimulable phosphors allow to get good quality images, with a consistent reduction of dose and costs. These plates offer the possibility, in the next future, to replace the conventional screen-film systems.     

Photostimulable phosphor digital radiography of the extremities: diagnostic accuracy compared with conventional radiography

A direct comparison was made between digital and conventional radiographs to assess the relative accuracy of a photostimulable phosphor digital imaging system in detecting and localizing minor trauma in the extremities. Matched sets of images were obtained on 103 patients who came to the emergency department for radiographs of the hand, wrist, foot, or ankle. One set was obtained with a conventional screen/film system. The other set was obtained with photostimulable phosphor digital cassettes. The two sets of images of each patient were independently interpreted by three radiologists in a blinded fashion. The findings of each of these three readers were compared with the consensus opinion of two different radiologists. Receiver-operating-characteristic (ROC) curves were plotted for each of the three readers, areas under the curves were calculated, and true-positive fractions were determined at false-positive fractions of 0.1. Although no significant differences in the areas under the ROC curves for the two imaging systems were detected, conventional radiography showed a slight advantage. However, when true-positive fractions for fracture detection were compared at false-positive fractions of 0.1 a statistically significant difference was shown, with conventional screen/film radiography being more sensitive. This study raises questions about the use of currently available photostimulable phosphor systems for imaging trauma of the extremities and suggests that those systems should not be used exclusively.     

Digital imaging with a photostimulable phosphor in the chest of newborns

To evaluate use of a digital photostimulable phosphor imaging system in the neonatal nursery, 150 newborns were divided into three groups of 50. In the first two groups, screen-film and computed radiographs of the chest were obtained at the same radiation exposure; in the third group, computed radiographs were obtained with a 50% dose reduction (half-exposure computed radiographs). All images were blindly evaluated by three readers who scored the quality of visualization of the mediastinum, lung, bone, soft tissues, and endotracheal and nasogastric tubes, and also image density. No statistical differences in visualization of tubes existed among the three groups. Visualization of the mediastinum, lung, bones, and soft tissues was statistically significantly better on computed radiographs than on half-exposure computed radiographs; visualization of the lungs, bones, and soft tissues was statistically significantly better on screen-film radiographs than half-exposure computed radiographs. Image density was statistically better on computed and half-exposure computed radiographs than on screen-film radiographs.     

A financial analysis of digital image acquisition for portable and table-top radiography.

The use of photostimulable phosphors as a method for obtaining digital radiographic images during traditional portable and table-top radiography has become a subject of increased interest and controversy in recent years. Proponents of this technology argue that a Picture Archival and Communications System--or PACS--is now within the grasp of most medical communities. However, there still exists concerns relating to the financial and economic effectiveness of this technological development. Does direct digital image acquisition during portable and table-top radiography present a financial benefit to the average health care facility? An in-depth financial analysis of the costs incurred by computed radiographic imaging provides sufficient information to state that financial benefits are a function of exposure-related repeat procedure volumes which can be reduced or eliminated through the use of this new technology. Repeat procedure volumes must be reduced by at least 6,000 procedures if the health care facility intends to avoid a financial loss from the use of photostimulable phosphor technology during portable and table-top radiography.     

Measurement of extrafocal radiation by computed radiography.

Measurement of radiation differences from image data is made possible by computed radiography (CR) based on storage phosphor imaging plates. The photostimulable luminescence (PSL) response is linear in a range greater than four orders of magnitude. Pinhole radiographs of focal and extrafocal radiation obtained by CR were quantitatively analysed using the technique originally introduced in recent scatter studies. No films or hard copies were used in the analysis. The material consisted of 54 images for measurement of the focal peak intensity, and a corresponding set of 54 images obtained at a 250 times greater operating sensitivity for the imaging of the extrafocal emission. The extrafocal-to-focal emission ratio was in the range of 0.001-0.006 depending on the off-focus distance. Because of the relatively large area of origin, exposure resulting from extrafocal radiation is estimated to reach up to 20% of the total radiation dosage. The results are in agreement with previous reports using other techniques and show that CR can also be used in a quantitative manner in this kind of comparative measurement.     

Clinical experiences with computed radiography

Computed radiography (CR) based on photostimulable phosphor is currently the only feasible way for a radiological department to digitize the bulk of radiological data: the lung and skeletal examinations. Regarding the quality of images for diagnostic purposes, CR imaging is never inferior to a screen/film system (SF) and for several clinical entities CR is superior. Of the many processing possibilities of the image plate (IP) image, the unsharp masking or edge enhancement should be used at a minimum. Dose reduction with CR ranges from 15% to 95%; at our institution it is 37%. Softcopy reading of CR images is advantageous due to the many postprocessing and improved display facilities. Currently there is little use for a 4000 × 4000 (4 K) pixel imaging and display. All images (including mammograghy) can be read in 2 K without any loss of clinically important information. To include CR in a picture archive and communication system (PACS) is demanding because of the load of data that each CR image represents. Networks for image distribution are essential if digital imaging is to have any impact on patient treatment and hospital organization.     

Binary screen detector system for single-pulse dual-energy radiography.

Dual-energy radiographic acquisition performed with a single pulse of x rays has been limited to use of stacked detectors such as photo-stimulable phosphor plates. In this study, a binary screen system is introduced that enables single-pulse dual-energy acquisition with nonstacked detectors such as charge-coupled devices (CCDs). Two x-ray phosphors with different K edges, designed to emit light of different wavelengths, were bound together in a single screen. Two CCD cameras, each sensitive to the respective wavelengths emitted by each phosphor, are proposed to be coupled to the binary screen. Optical isolation and detection of the optical emissions from the screen would enable simultaneous acquisition of both low- and high-energy images, which can then be used in dual-energy subtraction. Computer simulation results and experimentally acquired images suggest that the binary screen approach may be a viable alternative to stacked detector technology for dual-energy radiographic imaging.     

Diagnostic potential of double contrast arthrography of the knee with the digital technique

Experience with digital radiography applied to double contrast arthrography of the knee performed with a photostimulable phosphor plate is reported. The image processing technique used to improve the digital image is described, and some theoretical considerations are discussed. A preliminary comparison is also made between arthrographic images obtained with conventional screen-film systems and the digital system, especially in respect of the image quality and visualization of the soft tissue structures least well demonstrated with conventional arthrography.     

The effect of X-ray tube potential on the image quality of PA chest radiographs when using digital image acquisition devices

The rapid development in digital acquisition technology in radiography has not been accompanied by information regarding optimum radiographic technique for use with newly developed systems. Three of the most common technologies for digital radiographic examinations of the chest are flat panel amorphous Silicon Caesium Iodide systems (FPD), amorphous Selenium drums (DSD) and photostimulable storage phosphor computed radiography (CR). Published data on the effect of X-ray beam energy on image quality and patient dose when using these digital image acquisition devices are reviewed. It is important that radiographers are aware of optimum kVp selection for these systems, particularly for the commonly performed chest examination.     

Digital detectors for mammography: the technical challenges

This paper reviews the different techniques available and competing for full-field digital mammography. The detectors are described in their principles: photostimulable storage phosphor plates inserted as a cassette in a conventional mammography unit, dedicated active matrix detectors (i.e., flat-panel, thin-film transistor-based detectors) and scanning systems, using indirect and direct X-ray conversion. The main parameters that characterize the performances of the current systems and influence the quality of digital images are briefly explained: spatial resolution, detective quantum efficiency and modulation transfer function. Overall performances are often the result of compromises in the choice of technology.     

Diagnostic yield of conventional and digital cephalometric images: a human cadaver study

OBJECTIVES: To compare the clinical efficacy of digital and conventional cephalometric imaging. METHODS: Conventional and photostimulable phosphor cephalometric radiographs were obtained from three human cadavers at nine different exposure settings. Subjective image quality was assessed by six observers who evaluated six cephalometric landmarks. Organ doses were measured with TLDs and effective doses calculated. RESULTS: Compared with conventional cephalometric images, digital images had a consistently better subjective image quality for all exposure settings which was significant (P<0.05) for all but two. Organ doses were comparable. Higher kV and lower mAs settings yielded the lowest effective dose, which was highly dependent on the position of the thyroid gland in the beam. CONCLUSION: Relatively small variations in exposure settings do not influence subjective diagnostic image quality of digital cephalometric radiographs. Higher kV and lower mAs settings have the lowest effective dose and should therefore be preferred.     

Energy dependence of photostimulable phosphor

In this study, phantoms were used to illustrate the dependence of photostimulable phosphor's characteristic response on beam quality. These phantoms, consisting of sheets of acrylic and aluminum, represented an extremity, an abdomen, a skull and a chest. Images were taken with 50 to 65 kVp, 60 to 110 kVp, 65 to 80 kVp and 70 to 120 kVp, respectively. In general, the amount of resulting luminescence of the photostimulable phosphor per unit of air kerma (exposure) increased with kVp.     

Computed radiography: photostimulable phosphor image plate technology

Computed radiography is emerging as a digital imaging modality for use in conventional radiography. It is based on photostimulable phosphor image plate technology. The image plate (IP) is housed in a cassette similar to a standard radiographic cassette. The IP phosphor retains a latent image of the energy pattern to which it was exposed. This latent image is "read" as it is released from the phosphor by laser light exposure. The image is laser printed on 10 in x 14 in film.     

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.     

A preliminary investigation of the imaging performance of photostimulable phosphor computed radiography using a new design of mammographic quality control test object.

Leeds Test Object TOR[MAM] has been designed to supplement the current FAXIL mammography test object TOR[MAX]. It contains a range of details that have a more natural radiographic appearance and has been designed as a test that more closely approximates the image quality achieved in clinical mammography. Physical aspects of the design and implementation of TOR[MAM] are presented. The TOR[MAM] has been used in a preliminary physical evaluation of the comparative image qualities produced by conventional (screen-film) and photostimulable phosphor computed mammography and the results are discussed. TOR[MAX] results are also presented. The influence of digital image processing (enhancement) on the image quality of computed mammograms is also considered. The results presented indicate the sensitivity of TOR[MAM].     

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.     

Digital radiography with photostimulable storage phosphors. Control of detector latitude in chest imaging.

RATIONALE AND OBJECTIVES. A widely used digital radiography system based on a photostimulable storage phosphor (PSP) detector was analyzed with regard to radiographic contrast changes that result from the adjustment of detector latitude (x-ray sensitivity range) in the normal processing of chest images. METHODS. Images of an acrylic step wedge were acquired using the digital system in a mode that permitted direct control of effective detector latitude. The images were post-processed in conditions duplicating those used for portable chest examinations, and contrast was measured. RESULTS. Increases in effective detector latitude provided only marginal radiographic contrast gains in the subdiaphragm-equivalent areas of the laser-printed digital film image, while causing large reductions in radiographic contrast in the lung-equivalent region. CONCLUSION. Detector latitude is an important variable that should be monitored or controlled in investigations that compare reader performance using conventional and digital systems.     

下肢双能CTA去骨去钙化功能临床应用价值的研究

目的研究双能CT下肢动脉成像去骨去钙化功能的临床应用价值。资料与方法 43例患者进行双能CT下肢动脉检查,得到双能去骨后的图像(包括去除钙化斑块后的图像)及传统自动去骨后的图像,残留骨手动去除,记录各自去骨时间及对各节段血管的侵蚀度。判定斑块去除前后对血管狭窄度测量的影响。结果残留骨仅在未去除钙化斑块图像上观察到,双能去骨时间(1.86±0.28)min低于传统自动去骨时间(2.00±0.24)min(P<0.01,t=-4.382);共对822节段血管进行分析,血管侵蚀率前者低于后者,且最常发生于小腿部血管(χ2=13.13,P<0.01)。结论双能CTA明显优于传统多层螺旋CTA,双能自动去骨软件提高了工作效率,有助于小腿部血管的显示,自动去斑块功能可提高诊断准确性。     

Dose reduction in general radiography for adult patients by use of a dual-side-reading photostimulable phosphor plate in a computed radiography system

Our purpose in this study was to evaluate the potential of dose reduction in general radiography for adult patients by use of a dual-side-reading (DSR) photostimulable phosphor plate in a computed radiography system. The image quality and low-contrast detectability in terms of the contrast-detail diagram of the DSR system with use of the X-ray beam quality of the RQA 5 defined by the International Electrotechnical Commission 61267 were compared with those of a conventional single-side-reading (SSR) system. The radiographic noise of the DSR system was lower compared to that of the SSR system under the same exposure conditions. Although there were no statistical differences in low-contrast detectabilities between the SSR system and the DSR system under the same exposure levels, the DSR system showed superior detectability compared to the SSR system. We conclude that the DSR system for general radiography has the potential to reduce the patient dose.