一种提高图像对比度和视觉质量的新型区域背光算法

为尽可能高地提高液晶显示器（LCD）的动态范围以实现高动态范围显示，提出了一种基于动态阈值背光亮度提取和液晶像素补偿两步法的区域背光算法，以提高液晶显示器背光模组和液晶面板的动态范围，从而使调光后图像的对比度和视觉质量都得到增强.仿真结果表明，用该算法区域调光后图像的对比度平均提高了113.60%.此外，用自主研发的直下式白光LED分区背光液晶显示样机通过显示具体图像对所提出算法进行性能测试，显示结果表明区域调光后图像的层次和色彩得到了增强且提高了对比度，证明了所提出算法能有效提高液晶显示器的对比度并改善显示画质.      

A client/server system for Internet access to biomedical text/image databanks

Internet access to mixed text/image databanks is finding application in the medical world. An example is a database of medical X-rays and associated data consisting of demographic, socioeconomic, physician's exam, medical laboratory and other information collected as part of a nationwide health survey conducted by the government. Another example is a collection of digitized cryosection images, CT and MR taken of cadavers as part of the National Library of Medicine's Visible Human Project. In both cases, the challenge is to provide access to both the image and the associated text for a wide end user community to create atlases, conduct epidemiological studies, to develop image-specific algorithms for compression, enhancement and other types of image processing, among many other applications. The databanks mentioned above are being created in prototype form. This paper describes the prototype system developed for the archiving of the data and the client software to enable a broad range of end users to access the archive, retrieve text and image data, display the data and manipulate the images. System design considerations include; data organization in a relational database management system with object-oriented extensions; a hierarchical organization of the image data by different resolution levels for different user classes; client design based on common hardware and software platforms incorporating SQL search capability, X Window, Motif and TAE (a development environment supporting rapid prototyping and management of graphic-oriented user interfaces); potential to include ultra high resolution display monitors as a user option; intuitive user interface paradigm for building complex queries; and contrast enhancement, magnification and mensuration tools for better viewing by the user.     

Neuroradiology workstation reading in an inter-hospital environment: a nineteen month study

Two workstations (WS) each with two, 2500 line display monitors were installed in the in-patient and the out-patient neuroradiology reading areas for inter-hospital workstation readings. These WSs are part of the display component of a hospital-integrated picture archiving and communication system (PACS). Direct digital neuro images from 10 CT and MR scanners located at various buildings from two medical centers are first transmitted to the PACS database and then distributed to these two WSs automatically. This paper attempts to answer two questions. First, do the WSs facilitate neuroradiology operation? Second, does it cost less for preparing WS reading than that for the traditional film reading? Two parameters, the "time required before images become available for reading after the examination" and a "workstation utilization index" were derived as a means for answering these two questions. Nineteen months of clinical data were collected and analyzed. The results demonstrate that the workstation utilization index goes up from 40% in September 1994 when the WS was first introduced to over 80% in March 1996. This upward trend substantiates the hypothesis that these WSs do facilitate the neuroradiology operation. The derived results also exhibit that it costs much less to prepare images for WS reading than for film reading. Other indirect results derived from this study including the WS utilization hours, WS functions used, and the time duration of each WS session are also presented.     

Caspases: intracellular signaling by proteolysis

The standard working assumption of careful CRT imaging is that each pixel is imaged independently, through a point nonlinearity (the monitor's gamma function, relating screen luminance to input voltage), and then blurred by the point-spread function of the beam spot on the phosphor. Unfortunately most monitors have inadequate video bandwidth, DC restoration, and high-voltage regulation to live up to this ideal model. Two tests are recommended for assessing a CRT's deviation from the pixel-independence model.     

On the dynamic range of different X-ray photon detectors in intra-oral radiography. A comparison of image quality in film, charge-coupled device and storage phosphor systems

OBJECTIVE: To compare film for intra-oral radiography with two charge-coupled device (CCD) and one storage phosphor system for digital imaging in respect of subjective image quality, detectability of small mass differences and appearance of burn-out effects and blooming phenomena at various exposure times. METHODS: Dried mandibles with teeth from different areas were radiographed at exposures covering a relative range from 1 to 100. Image quality was subjectively evaluated after image processing, when applicable, using a visual grading scale from 0 to 10. The number of visible holes in an aluminium block was used to measure the detectability of small mass differences. Burn-out effects and blooming were evaluated by measuring widths of roots and of aluminium and plastic cylinders. RESULTS: Radiographs with the storage phosphor system achieved image quality scores similar to those of film but over a larger exposure range, while CCD images were rated lower and over a smaller range. All holes in the aluminium block were only detected with the storage phosphor system. While the widths of roots were strongly affected by sensor saturation in CCD images and by burn-out in film images, smaller effects were seen with the storage phosphor system. Similar results were obtained with aluminium and plastic cylinders. CONCLUSIONS: Higher image quality was achieved over a much wider exposure range with the storage phosphor system than with either film or the CCD systems.     

The effect of leg flexion angle on the mechanomyographic responses to isometric muscle actions

INTRODUCTION: An ROC analysis was carried out in order to determine the reliability of digital luminescence radiography review at a PC and this was compared with a radiological work station and with X-ray film on a viewing box. MATERIAL AND METHOD: 54 chest images obtained by digital luminescence radiography were selected, 31 of these contained small pulmonary nodules. In order to evaluate critical detail, five images of a phantom showing round foci were used. Five radiologists examined these, using a Siemens Magic View work station, a PC with proprietary software (ViewMed) and X-ray films on a viewing box. Image processing of the work station used the standard clinical application. ViewMed performs linear scaling of grey levels to 8 Bit. The results were examined statistically by means of a t-test. RESULTS: As far as the chest images were concerned there was no significant difference in the diagnostic value of these methods. There was, however, a highly significant loss of diagnostic information with respect to the round focus phantom when using the PC compared with the other methods. CONCLUSION: In the configuration in which it was used, the PC should not be relied on as a primary means of examination since critical details cannot always be seen. In routine use these play a subordinate role and there was no significant diagnostic loss where the chest images were concerned. We expect that by improvements in the frequency and contrast processing the PC accuracy will be considerably increased.     

Brain death and organ donation

Large-scale picture archiving and communication systems (PACS) have not been widely implemented in this or other countries. In almost all radiology departments film remains the medium for diagnostic interpretation and image archive. Chest imaging is the dominant screening examination performed within most imaging departments and as such, is an extremely high-volume, low-margin examination. Digital technologies are being applied to chest imaging to overcome limitations of screen-film receptors (limited latitude) and current film management systems (single-image copy). Efficient management of images and information is essential to the success of a chest imaging program. In this article we report on a digital imaging and communications in medicine (DICOM)-based centralized printing network for chest imaging. The system components and their operational characteristics are described. Our experience integrating DICOM-compliant equipment supplied by several vendors is described. We conclude that the print model supported by DICOM is adequate for cross-sectional (eg, computed tomography and magnetic resonance) imaging but is too simplistic to be generally applied to projection radiography.     

N2-amination of guanine to 2-hydrazinohypoxanthine, a novel in vivo nucleic acid modification produced by the hepatocarcinogen 2-nitropropane

OBJECTIVE: Over the last twenty years, imaging modalities featuring new image production methods (ultrasound, nuclear magnetic resonance, etc.) have appeared on the market. Nevertheless, conventional radiology still accounts for 70% of the image examinations carried out in most western countries, including France. The conventional radiological image is in the process of evolving from analog to digital form. Digitalization of radiology means that image acquisition, archiving and distribution functions that were previously carried out by hand can now be automated using a Picture Archiving and Communication System. Decision-makers are having to decide whether or not to promote the development of PACS which, while they considerably modernize the way in which images are managed, also require heavy capital outlays. METHOD: A critical appraisal of the literature allowed us to evaluate the relative cost and the efficiency of these image networks in comparison with film-based archiving and communication systems. RESULTS: It is clear from the economic evaluation that a PACS strategy involves greater costs than a film system. While PACS systems do generate savings on film and on storage space and obviate the need for certain staff, these savings do not offset the extra equipment and maintenance costs. This situation is likely to persist for some years yet, even when future price reductions are taken into account. The objective of this new radiological information management method is to improve organizational efficiency and hospital productivity. However, the economic evaluations that have been published to date are cost studies which do not take the efficiency criterion into account. A number of potential organizational benefits such as the fact that medical decisions can be made more quickly or that the average length of hospital stays can be reduced, are often claimed for PACS. However, for methodological reasons, these results cannot be generalised to cover all PACS. It is difficult to compare PACS and film systems because the PACS technology is continuously evolving and because each PACS is specific to a site. CONCLUSION: After having weighted these different points, the ANAES has made the following recommendations concerning the development of PACS. A strategic analysis should be carried out before any decision is made to install a PACS. Moreover, hospitals will have to define the precise functions of their PACS in relation to the objectives of their medical project and each network must be configurated coherently.     

Three-dimensional display of cardiac structures using reconstructed magnetic resonance imaging

It is sometimes difficult to understand the three-dimensional (3D) relationship of cardiac and mediastinal structures despite advances in magnetic resonance (MR) imaging techniques. We present a low-cost system for 3D reconstruction of the major mediastinal structures by processing the MR imaging data on a NeXT workstation. MR images of multisection, multiphase, spin-echo techniques stored in a picture archiving and communication system (PACS) data base were used for the reconstruction. The computer program obtained the contours of the multiple components of the mediastinal structures by the combination of automatic and manual procedure. The bundled software of a 3D kit was used for surface rendering of hidden surface removal, shading of the visible parts of the surfaces, perspective transformation, and motion parallax by rotation of the surfaces. 3D reconstruction was performed in 15 patients with cardiac diseases, and the 3D-reconstructed images were compared with the plain chest x rays of the patients. The 3D presentation clearly showed the complex anatomy of cardiovascular diseases and helped elucidate the misconceptions in the interpretation of the plain chest x rays. Our 3D images are used for education and should be viewed by medical students and beginners in radiology at an individual pace with plain chest radiographs, MR images, and legends. Although applied to the heart and the great vessels in this report, this system is also applicable to other structures.     

Digital imaging of black and white photomicrographs: impact of file size

The publication of black and white photomicrographs has a long tradition in pathology. High-resolution film and quality objectives have been the backbone of generating quality photomicrographs suitable for publication. However, the digital imaging revolution has changed the way we view and capture images. As the quality of image capture devices increases and as their price decreases, more and more investigators are using digital imaging, and the use of color digital imaging for teleconferencing, telediagnosis, and reproduction is now well established. The purpose of this study was to determine the file sizes needed to obtain publication-quality black and white images using digital imaging technology. In this study, four experts in renal pathology reviewed 70 black and white images of various file sizes obtained from specimens representing a variety of renal histopathology. Without knowledge of the file size, the four renal pathologists graded the degree of pixelation, and the overall diagnostic and publication quality of the images. In all cases, digital imaging was capable of obtaining publication quality images equal to those achieved using film. The file size needed to achieve publication quality black and white images depended on magnification, with lower magnification images requiring larger file sizes.     

Advanced multiple beam equalization radiography (AMBER) combined with computed radiography. Preliminary evaluation

The combined use of AMBER (Advanced Multiple Beam Equalization Radiography) and a digital storage phosphor (SP) radiography system was evaluated for chest radiography in a pilot study with 4 patients. Four image modes with different dose levels were compared: the SP in combination with an AMBER equalized exposure (SP/AMBER) and 3 nonequalized exposures with dose levels corresponding to the respective calculated AMBER lung dose (SP/lung field dose), the calculated AMBER mediastinal dose (SP/mediastinal dose) and the calculated AMBER average dose (SP/average dose). All image modes were matched for Hurter and Driffield characteristics and subjectively rated according to visibility of details. The improved signal-to-noise (S/N) ratio of SP/AMBER resulted in a better visualization of structures in the mediastinum and the basal lung where SP/lung field dose scored lowest. For the central lung no quality differences were seen between techniques. The compressed dynamic range of the SP/AMBER images was more easily displayed on the hard-copy film. The combination of AMBER with SP radiography promises to overcome the dynamic range limitations of digital displays while, at moderate doses, giving better S/N and image quality than standard SP technique.     

Focal pachypolymicrogyria in three siblings

Low-power bright field photomicrographs often suffer from insufficient sharpness, uneven illumination, and colour hues. Using a film scanner, commercially available and designed for digitizing 35-mm transparencies, we directly scanned microscopic slides that carried dye-labelled and stained sections. The digital images covered a field of up to 24 x 36 mm and revealed excellent sharpness, absolutely even illumination and superior colour reproduction as compared to conventional photomicrographs taken with binoculars, macro lenses, or microscopes. As the method requires neither specialized instrumentation nor expert knowledge of photomicrographic techniques, it reduces costs and saves time. The high-quality digital survey micrographs can easily be used for image processing, image analysis and morphometry. Thus, this new method is valuable not only for pathology, embryology, histochemistry, and the neurosciences, but also for the exchange of low-power micrographs via the internet and for computer media that are increasingly used in medical education.     

Analysis of pulmonary manifestations in patients with rheumatoid arthritis

We studied chest X rays of 911 patients with rheumatoid arthritis (RA). The findings showed interstitial shadow in 28 patients (3.1%), pleuritis in 13 patients (1.4%) and nodular shadow in 3 patients (0.3%). RA patients with interstitial pneumonia were commonly male and older. And they had significantly high levels of rheumatoid factor (RF), RAPA and IgG-RF in serum, but they were not associated with high score of Lansbary index. All patients with more than 1500 IU/ml in RF value had a complication of interstitial pneumonia. These results suggest the importance of chest X-ray in the management of RA patients with high titer in RF.     

Red-green chromatic discrimination with variegated and homogeneous stimuli

Chromatic discrimination thresholds were measured under conditions which yielded fine and degraded discrimination steps. Discrimination was assessed by identification of the location of one of four homogeneous equiluminant stimuli arranged in a square or with pseudoisochromatic (PIC) figures using the stimulus design of Regan, Reffin and Mollon (Vis Res 1994; 34: 1279-1299). Stimuli were presented on CRT monitors and specified in units of cone trolands. They were viewed within a surround metameric to the equal energy spectrum. L troland threshold versus retinal illuminance (TVR) functions were measured by four-alternative spatial forced-choice staircase procedures for (1) a four 1 x 1 degree equiluminant stimuli arranged in a square and (2) 'C' shaped pseudoisochromatic figures in which the observer had to identify the gap location. The 'C' was constructed of spatially discrete patches of varying size and luminance to ensure that the observer's responses depended on chromatic signals. The TVR functions appeared V-shaped and were similar for the two paradigms. The minimum occurred near the L excitation of equal-energy white. The PIC stimuli yielded poorer discrimination with the TVR function being displaced by approximately 0.5 log unit. Discrimination for stimuli degraded by luminance and spatial noise presented within an achromatic appearing surround is sharpest near the chromaticity metameric to the equal energy spectrum.     

Tissue harmonic imaging: why does it work?

The recent utilization of harmonic frequencies in the imaging of both tissue and contrast agents has dramatically improved echocardiographic image quality. In contrast harmonics, the harmonic frequency energy is generated on reflection from the microbubble contrast agent. In tissue harmonics, the harmonic frequency energy is generated gradually as the ultrasonic wave propagates through the tissue. Critical to the utility of tissue-generated harmonic frequencies is their origin beyond the chest wall and their nonlinear relation to the fundamental frequency energy strength. These two characteristics of tissue-generated harmonics ensure that the echoes most likely to produce artifact are least likely to produce harmonic waves. Armed with an understanding of how these images are produced and with data emerging as to their clinical utility, we anticipate that harmonic imaging will become the standard for assessing regional and global left ventricular function in technically difficult studies.     

Perceptual learning of the detection of features in X-ray images: A functional role for improvements in adults' visual sensitivity?

Recent perceptual learning research has found long-term increases in the sensitivity of adults' perceptual systems. The authors examined whether such changes could partly explain improvement on tasks such as perception of medical X-ray images. Experiment 1 found experts' sensitivity to low-contrast dots in X-rays was better than novices'. Experiment 2 found a direction of luminance contrast-specific improvement in novices' detection of low-contrast dots in X-rays as a result of practice. Experiment 3 found a partly specific improvement in novices' detection of low-contrast features in real medical X-rays as a result of practice. Results suggest that experience enhances sensitivity to the critical dimensions of visual analysis for detecting abnormalities in X-ray images. Importantly, they demonstrate a real-world adaptive functional role for the long-term flexibility of sensory systems in adulthood. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Psychophysical foundations of a model of amplified night vision in target detection tasks

In this article we examine some of the basic psychophysics relevant to amplified night vision devices. These devices produce images that are substantially different from ordinary visual scenes. Distortions in contrast and luminance and the introduction of visual interference and geometrical artifacts contribute to unusual viewing conditions. We carried out experiments to determine the effect of these parameters of the image on a highly controlled visual target detection task simulated on a computer graphics system that closely models a night vision device. Our results indicate that display luminance and geometrical artifacts degrade detection performance only slightly, whereas contrast and visual interference have a substantial degrading effect.     

The effect of adapting luminance on the latency of visual search

Computational models of attentional processing typically view the "attentional spotlight" as a winner-take-all network whose focus can be shifted serially about a display if required. As a result, lateral inhibition is assumed in these models to be an important mechanism involved in visual search. On the basis of this assumption, we predicted that changes in adapting luminance would produce specific changes in search latency functions in virtue of affecting visual inhibition. The results of our first two experiments confirmed these predictions: when search was difficult, and produced reaction time results characteristic of serial processing, there was a main effect of adapting luminance and a significant interaction between adapting luminance and the number of display elements. These effects were both reflected in increases in the slopes and the intercepts of average search latency functions when adapting luminance was decreased. When search was easy, and produced pop out effects characteristic of parallel processing, there were no significant effects of adapting luminance on search latency. The third experiment used adapting luminance to further explore the possibility that arrow junctions are detected preattentively. The results suggested that a visual search for such elements involves a substantial serial component, which weighs against the claim that they are detected by low-level vision.     

Clinical evaluation of single-exposure dual-energy subtraction chest radiography: with FCR 9501 ES]

Using the one-shot energy subtraction method, we took chest radiography of 1,031 outpatients of Kanazawa University Hospital. Chest radiographs were taken with the FCR 9501 ES system, with patients upright. We studied the clinical efficacy of this diagnostic method. The method and usage procedures involved have been sufficiently technologically refined to permit handling of an adequate number of patients in a reasonable time at a permissible exposure dose. However, the system can be further improved technologically in order to obtain fully consistent high-quality images, regardless of the patient's physique. For well-rounded image reading, three kinds of images must be generated simultaneously: an original image; soft tissue (bone subtracted image) and bone (soft tissue subtracted image) Some soft tissue image were helpful for detecting non-calcified parenchymal nodules that overlapped the rib shadow, and some bone image served to precisely diagnose the existence of abnormal ribs, calcified lymph nodes, and calcified nodules. Furthermore, the bone images were helpful for revealing that the fine infiltrative shadows in the lung fields in original images were actually pleural calcifications and that the poorly defined nodular opacities were, in reality, abnormal rib calcifications. In light of the above, we wish to stress the importance of clinical efficacy of not only soft tissue images but bone images derived using the energy subtraction method. The clinical usefulness of this method was confirmed in 66 of 1,031 patients (6.4%) who had initially been scheduled for routine chest radiography. This result indicates how frequently the method encounters applicable cases when applied non-selectively to general patients who require radiographic chest examination. The advantages of this method will become much more evident with an examination protocol that minimizes unnecessary special examinations or optimizes the balance between screening and special examinations.     

A cryptologic based trust center for medical images

OBJECTIVE: To investigate practical solutions that can integrate cryptographic techniques and picture archiving and communication systems (PACS) to improve the security of medical images. DESIGN: The PACS at the University of California San Francisco Medical Center consolidate images and associated data from various scanners into a centralized data archive and transmit them to remote display stations for review and consultation purposes. The purpose of this study is to investigate the model of a digital trust center that integrates cryptographic algorithms and protocols seamlessly into such a digital radiology environment to improve the security of medical images. MEASUREMENTS: The timing performance of encryption, decryption, and transmission of the cryptographic protocols over 81 volumetric PACS datasets has been measured. Lossless data compression is also applied before the encryption. The transmission performance is measured against three types of networks of different bandwidths: narrow-band Integrated Services Digital Network, Ethernet, and OC-3c Asynchronous Transfer Mode. RESULTS: The proposed digital trust center provides a cryptosystem solution to protect the confidentiality and to determine the authenticity of digital images in hospitals. The results of this study indicate that diagnostic images such as x-rays and magnetic resonance images could be routinely encrypted in PACS. However, applying encryption in teleradiology and PACS is a tradeoff between communications performance and security measures. CONCLUSION: Many people are uncertain about how to integrate cryptographic algorithms coherently into existing operations of the clinical enterprise. This paper describes a centralized cryptosystem architecture to ensure image data authenticity in a digital radiology department. The system performance has been evaluated in a hospital-integrated PACS environment.