A method for measuring the presampled MTF of digital radiographic systems using an edge test device

The modulation transfer function (MTF) of radiographic systems is frequently evaluated by measuring the system's line spread function (LSF) using narrow slits. The slit method requires precise fabrication and alignment of a slit and high radiation exposure. An alternative method for determining the MTF uses a sharp, attenuating edge device. We have constructed an edge device from a 250-microm-thick lead foil laminated between two thin slabs of acrylic. The device is placed near the detector and aligned with the aid of a laser beam and a holder such that a polished edge is parallel to the x-ray beam. A digital image of the edge is processed to obtain the presampled MTF. The image processing includes automated determination of the edge angle, reprojection, sub-binning, smoothing of the edge spread function (ESF), and spectral estimation. This edge method has been compared to the slit method using measurements on standard and high-resolution imaging plates of a digital storage phosphor (DSP) radiography system. The experimental results for both methods agree with a mean MTF difference of 0.008. The edge method provides a convenient measurement of the presampled MTF for digital radiographic systems with good response at low frequencies.     

Advances and dilemmas in factor XI

Factor XI is a key component of the intrinsic pathway of blood coagulation in vitro. The poor correlation between the clinical bleeding diathesis in factor XI deficiency and abnormalities in clotting assays that measure intrinsic coagulation brings into question the role of this serine protease in in vivo hemostasis. The characterizations of the point mutations responsible for the majority of cases of severe factor XI deficiency in Ashkenazi Jews and subsequent epidemiologic studies have provided insight into the perplexing hemostatic abnormalities in this disorder. It appears that excessive bleeding in factor XI deficiency depends on the severity of the deficiency in certain situations and on the location of the hemostatic challenge in others. Additional coexisting abnormalities of hemostasis, such as von Willebrand's disease, may also be responsible for variation in clinical presentation, particularly in those individuals with mild factor XI deficiency. The absence of abnormal bleeding in congenital deficiency of factor XII, the protease that activates factor XI in the intrinsic cascade, has stimulated a search for other mechanisms for factor XI activation. Recent studies have pointed to the serine protease thrombin and autoactivation by activated factor XI as possible alternatives to factor XII as activators of factor XI. These findings suggest that factor XI, rather than operating in a pathway for the initiation of hemostasis, may function in the consolidation of clot formation after the initiation of the hemostatic process by other mechanisms.     

Technology transfer in digital mammography. Report of the Joint National Cancer Institute-National Aeronautics and Space Administration workshop of May 19-20, 1993

Digital mammography is one of the most promising novel technologies for further improvement of early detection of breast cancer, offering important potential advantages: 1) improved image quality; 2) digital image processing for improved lesion contrast; 3) computer-aided diagnosis for enhanced radiologic interpretation; and 4) teleradiology for facilitated radiologic consultation. The Diagnostic Imaging Research Branch of the National Cancer Institute (NCI) recently funded an international, multidisciplinary, multi-institutional Digital Mammography Development Group for collaborations between NCI, the academic community, and industry to facilitate the integrated development and implementation of digital mammographic systems. Currently, however, digital mammography faces a number of fundamental technological roadblocks: 1) cost-effective digital detectors and displays for imaging systems; 2) the need for novel algorithms for image processing and computer-aided diagnosis; and 3) high performance, low cost digital networks to provide an "information superhighway" for teleradiology. To solve some of these technological problems, the Diagnostic Imaging Research Branch of NCI joined efforts with the Technology Transfer Division of the National Aeronautics and Space Administration to pursue a federal technology transfer program in digital mammography. The authors discuss the findings and recommendations of the workshop entitled "Technology Transfer in Digital Mammography," which was organized and held jointly by the NCI and the National Aeronautics and Space Administration in May, 1993. Numerous innovative technologies of varying degree of promise for digital mammography were presented at the conference. In this article, specific technologies presented at the workshop by the federal and federally-supported laboratories are described, and critiques of these technologies by the leaders of the medical imaging community are presented.     

Hybrid membrane IgM with the transmembrane region of I-A alpha facilitates enhanced presentation of distinct epitopes to T cells

The role of B cell Ag receptors (membrane Ig or mIg) in the efficient Ag presentation to T cells, including the requirement of mIgM-associated Ig alpha/Igbeta, remains unclear. We report here that mIgM, substituted with greater than two-thirds of the NH2-terminal A alpha transmembrane (TM) regions of the MHC class II molecule, are capable of mediating the efficient presentation of specific Ag to some (Group 1) but not all (Group 2) T cell hybridomas. In contrast, the generation of epitopes recognized by the Group 2 hybridomas can be mediated only by the wild-type mIgM. Tyrosine phosphorylation appears to be necessary for the enhanced Ag presentation to Group 2 hybridomas, while it does not for Group 1 hybridomas. In addition, differential sensitivity of Ag processing to leupeptin, different duration required for epitope generation/presentation, as well as the involvement of distinct epitopes for stimulation of these groups of T cell hybridomas were observed. These results suggest that transport of the mIgM/Ag complexes to an endocytic compartment(s) for generation of certain T cell epitopes may be mediated by the N-terminal TM sequence of mIgM, independent of Ig alpha/Igbeta association. This function can be replaced by two-thirds of the NH2-terminal TM region of A alpha chain of class II molecules.     

Current status of digital mammography

Some inherent limitations to further technical improvement in film-screen mammography exist. Many of these limitations can be overcome effectively with digital mammography, in which image acquisition, display, and storage are performed independently, thus allowing the optimization of each. Presented is a brief background of digital and analog imaging with emphasis on the features and drawbacks of digital mammography systems. Image storage, processing, and display, computer-aided detection and diagnosis, as well as telemammography are also discussed.     

Proposed criteria for diagnosis of celiac disease in children]

At a seminar arranged in September 1997 by the Swedish Paediatric Working Group for Coeliac Disease, a diagnostic protocol proposed by the working group was approved by a majority of the paediatricians present, representing almost all paediatric units in Sweden. Briefly, a small bowel biopsy is called for in all children, both at presentation and as a control during gluten-free dieting. Subsequent gluten challenge and biopsy are mandatory only in cases of atypical presentation or if the diagnosis is questioned at some future date. Serum antigliadin and anti-endomysial antibody tests are complementary tools. Agreement was also reached regarding the institution of a national coeliac disease registry.     

TAP (transporter associated with antigen processing)-independent presentation of endogenously synthesized peptides is enhanced by endoplasmic reticulum insertion sequences located at the amino- but not carboxyl-terminus of the peptide

Under most circumstances, cell surface MHC class I molecules display peptides derived from a cytosolic pool of proteins. The efficient presentation of such peptides requires the functioning of two MHC gene products [TAP1 and TAP2 (transporter-associated with Ag processing 1 and 2)] that form a complex that facilitates transmembrane movement of peptides from the cytosol to the endoplasmic reticulum, the site of peptide association with class I molecules. It has been previously shown that peptides can be presented in a TAP-independent manner in association with HLA A2.1 or H-2 Kd if they are expressed COOH-terminal to an endoplasmic reticulum insertion/signal sequence derived from the adenovirus E3/19K glycoprotein (Anderson et al., 1991. J. Exp. Med. 174: 489; Eisenlohr et al., 1992. Cell 71: 963). We show that: 1) the E3/19K signal sequence greatly enhances the presentation of each of four additional peptides tested in association with H-2 Kb or Kk, 2) the E3/19K signal sequence can be substituted by a signal sequence derived from beta-IFN, and 3) the E3/19K signal sequence does not function when located at the COOH terminus of antigenic peptides. These findings indicate that first, many peptides require TAP for efficient presentation to T cells, second, expression of peptides COOH-terminal to signal sequences is a generally applicable method of bypassing the TAP-dependence of peptide presentation and third, the leader sequence does not act to bypass TAP simply by increasing the hydrophobic nature of peptides.     

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.     

电镀锡机组软熔系统自动控制

阐述了电镀锡机组软熔系统的工作原理以及对软熔系统的自动控制。运用大功率晶闸管功率单元、全数字控制系统、PLC等控制技术,对武钢冷轧厂镀锡线软熔系统进行了成功改造,实现了对镀锡软熔电流、软熔温度、带钢运行速度等的综合控制和调节,在控制技术上达到国内外先进水平。实践证明,该软熔系统运行稳定,性能可靠,控制精度高,完全满足了生产工艺的要求,提高了镀锡带钢的产品质量和产量。     

Large Scale Particle Image Velocimetry for Low Velocity and Shallow Water Flows

Large scale particle image velocimetry (LSPIV) is an extension of quantitative imaging techniques for measurements of water surface velocities using inexpensive standard video equipment. The present Technical Note describes capabilities and limitations of LSPIV for low velocity shallow flows. Measurements in low velocity shallow flume flows were performed to investigate the LSPIV sensitivity to seeding density and time interval between successive images. The results show that the accuracy of the LSPIV technique does not deteriorate as the flow velocity is reduced to as low as 0.015 m/s provided an adequate seeding and suitable time difference between images are selected. The results suggest that LSPIV is well-suited for flow fields with small velocities that are often below the limit of detection of most conventional devices.     

Computer-based assessment of visual acuity--technical realization

Testing of visual acuity for distant vision can be computerized by using monitor screens to present optotypes. Because of the limited spatial resolution of conventional monitors, measurement of visual acuity for near vision is not possible. This paper describes a new computer-aided method for the measurement of both near and distant visual acuity. Our approach to the assessment of visual acuity for near vision is based on a recently developed liquid crystal display (a screen, LCD) measuring 10.5 mm x 15 mm. The LCD permits the presentation of optotypes for the measurement of visual acuity between 0.063 and 1.25 at a viewing distance of 40 cm (near/distant). The presentation of optotypes for the assessment of the acuity of distant vision uses a standard 17" monitor that permits visual acuity figures of between 0.032 and 1.6 to be assessed.     

Spatial resolution of body surface potential maps and magnetic field maps: a simulation study applied to the identification of ventricular pre-excitation sites

Telemedicine is defined as the "delivery of health care and sharing of medical knowledge over a distance using telecommunication systems." The concept of telemedicine is not new. Beyond the use of the telephone, there were numerous attempts to develop telemedicine programs in the 1960s mostly based on interactive television. The early experience was conceptionally encouraging but suffered inadequate technology. With a few notable exceptions such as the telemetry of medical data in the space program, there was very little advancement of telemedicine in the 1970s and 1980s. Interest in telemedicine has exploded in the 1990s with the development of medical devices suited to capturing images and other data in digital electronic form and the development and installation of high speed, high bandwidth telecommunication systems around the world. Clinical applications of telemedicine are now found in virtually every specialty. Teleradiology is the most common application followed by cardiology, dermatology, psychiatry, emergency medicine, home health care, pathology, and oncology. The technological basis and the practical issues are highly variable from one clinical application to another. Teleradiology, including telenuclear medicine, is one of the more well-defined telemedicine services. Techniques have been developed for the acquisition and digitization of images, image compression, image transmission, and image interpretation. The American College of Radiology has promulgated standards for teleradiology, including the requirement for the use of high resolution 2000 x 2000 pixel workstations for the interpretation of plain films. Other elements of the standard address image annotation, patient confidentiality, workstation functionality, cathode ray tube brightness, and image compression. Teleradiology systems are now widely deployed in clinical practice. Applications include providing service from larger to smaller institutions, coverage of outpatient clinics, imaging centers, and nursing homes. Teleradiology is also being used in international applications. Unresolved issues in telemedicine include licensure, the development of standards, reimbursement for services, patient confidentiality, and telecommunications infrastructure and cost. A number of states and medical boards have instituted policies and regulations to prevent physicians who are not licensed in the respective state to provide telemedicine services. This is a major impediment to the delivery of telemedicine between states. Telemedicine, including teleradiology, is here to stay and is changing the practice of medicine dramatically. National and international communications networks are being created that enable the sharing of information and knowledge at a distance. Technological barriers are being overcome leaving organizational, legal, financial, and special interest issues as the major impediments to the further development of telemedicine and realization of its benefits.     

Donor work-up and transport of bone marrow--recommendations and requirements for a standardized practice throughout the world from the Donor Registries and Quality Assurance Working Groups of the World Marrow Donor Association (WMDA)

In October 1995 the World Marrow Donor Association (WMDA) was restructured in order to facilitate its primary function of establishing guidelines in relation to international bone marrow and blood stem cell transplants -- transplants in which the donor is in one country and the patient is in another country. Five new working groups were established -- Donor Registries, Ethics, Quality Assurance, Finances, and Stem Cells. This paper, prepared by members of the Donor Registries Working Group, in consultation with the Quality Assurance Working Group, provides recommendations for the 'donor work-up'. This term covers events that start when the definitive donor has been identified, includes the harvesting (collection) and transportation of the stem cell product and ends when the product reaches the transplant centre. The paper includes examples of the documentation intended to ensure compliance with the recommendations at all key points in the sequence.     

Clinical polymorphic presentation and natural history of active myocarditis: experience in 60 cases

Eight-hundred thirty patients (pts) with suspected myocardial disease of undefined etiology were observed from 1978 to 1996. In 350 pts, the clinical diagnosis was of dilated cardiomyopathy (DCM) or myocarditis. An endomyocardial biopsy was performed on all patients and in 54 of them (15%), an active myocarditis was identified. In six cases, myocarditis was detected at autopsy. There were 37 male patients and 23 females, with an average age of 35.5 +/- 15 years (range 1.67). Mean time interval between clinical onset and diagnosis was 4 +/- 10 months. Clinical presentation was characterized in 4 cases by fulminant myocarditis (Group I), in 8 cases by chest pain (Group II), in 14 cases by arrhythmia (Group III: hypokinetic in 9 pts and hyperkinetic in 5) and, in the last 34 pts, by congestive heart failure (CHF) (Group IV). Improvement was defined at 9 +/- 3 months according to a clinical score based on left ventricular shortening fraction (increase > or = 5 units), New York Heart Association Class improvement by (at least one Class) and left ventricular end-diastolic diameter (decrease > or = 10%). The main clinical and instrumental parameters characterizing the groups were: a more severe dilatation and left ventricular dysfunction in the pts belonging to Group I or IV with respect to those in Group II and III; a significantly worse prognosis in terms of evolution in DCM or death/cardiac transplantation (CT) in the pts from the Group II and III. After a follow-up period of 48 +/- 46 months, the mortality in the four groups was: 100% (4/4), 0% (0/8), 21% (3/14), 38% (13/34). Fifty percent of deaths were concentrated in the first 2 years of follow-up. Left ventricular end-diastolic diameter (OR 1.09, p < 0.05), age (OR 0.95), presence of left ventricular bundle branch block (OR 2.32), right ventricular function (OR 2.43) at clinical onset and the status of improvement at 9 +/- 3 months of follow-up (OR 0.24, p < 0.05) are predictors of evolution in DCM or death/CT for the pts with onset from CHF (Group IV). Immunosuppressive treatment has been utilized for the 76% of the pts. No conclusion can be drawn on the efficacy of this therapy, but no adverse events significantly related to therapy have been observed in a 9 +/- 3 months follow-up period. In conclusion, myocarditis can show a clinical presentation polymorphism, which influences the prognosis and natural history of the disease. Evolution in DCM and adverse events (death/CT) are more common in Groups I and IV. Some simple parameters evaluated at clinical presentation and the proposed classification as "improved" or "not improved" after a short-term follow-up (9 +/- 3 months) show good predictive accuracy. The present study does not allow us to draw any conclusion about the efficacy of immunosuppressive treatment. A randomized, controlled, large-scale trial, with adequate follow-up and advanced histological diagnosis techniques will help define the role of immunosuppressive therapy and patient eligibility criteria for this treatment.     

Association of factor XI and high molecular weight kininogen in human plasma

Factor XI and high molecular weight kininogen were found associated in normal human plasma at mol wt 380,000 as assessed by gel filtration on Sephadex G-200. The molecular weight of Factor XI in high molecular weight kininogen-deficient plasma was 175,000, the same value obtained for purified Factor XI. When high molecular weight kininogen-deficient plasma was reconstituted with purified high molecular weight kininogen, all of the Factor XI was then found at mol wt 380,000. Complex formation was also demonstrable upon incubation of Factor XI and highly purified high molecular weight kininogen. This complex was distinct from the prekallikrein-high molecular weight kininogen complex; thus high molecular weight kininogen forms bimolecular complexes with either Factor XI or prekallikrein but does not form a trimolecular complex that includes both Factor XI and prekallikrein. Neither Hageman factor nor plasminogen were found associated with high molecular weight kininogen; binding to high molecular weight kininogen appeared to be a specific property of the Hageman factor substrates.     

Consequences of the 1979 Three Mile Island accident continued: further comment

The development of multimedia image review stations offers the cardiologist the ability to review multiple image sets in a single setting rather than moving from one review station to another. To accomplish this goal there are three essential barriers: 1) memory requirements for digital images; 2) standardization of data format; and 3) practical user interfaces. Image compression algorithms can be used to overcome the digital barrier; however, these must be used cautiously so as to not adversely affect image quality. The lack of standardization is being addressed by the implementation of the Digital Communication in Medicine (DICOM) standard, and practical user interfaces are being developed every day with the widespread implementation of World Wide Web technology. These solutions will allow the clinician to review all of a patient's image data in one location, such as in the office, on the nursing unit, or at home.     

Thrombin activates factor XI on activated platelets in the absence of factor XII

Thrombin can activate factor XI in the presence of dextran sulfate or sulfatides. However, a physiological cofactor for thrombin activation of factor XI has not been identified. We examined this question in a cell-based, tissue factor-initiated model system. In the absence of factor XII, factor XI enhanced thrombin generation in this model. The effect on thrombin generation was reproduced by 2 to 5 pmol/L factor XIa. A specific inhibitor of factor XIIa did not diminish the effect of factor XI. Thus, factor XI can be activated in a model system that does not contain factor XIIa or nonphysiological cofactors. Preincubation of factor XI with activated platelets and thrombin or factor Xa enhanced subsequent thrombin generation in the model system. Preincubation of factor XI with thrombin or factor Xa, but without platelets, did not enhance thrombin generation, suggesting that these proteases might activate factor XI on platelet surfaces. Thrombin and factor Xa were then directly tested for their ability to activate factor XI. In the presence of dextran sulfate, thrombin or factor Xa activated factor XI. Thrombin, but not factor Xa, also cleaved detectable amounts of factor XI in the presence of activated platelets. Thus, thrombin activates enough factor XI to enhance subsequent thrombin generation in a model system. Platelet surfaces might provide the site for thrombin activation of functionally significant amounts of factor XI in vivo.     

Endoscopic imaging of vocal cord vibrations. Digital high speed recording with various systems]

Vocal fold vibration patterns during phonation are presented with different digital imaging systems. With newly developed technical equipment color images up to 1000 digital images/s were obtained without light intensifying enhancement techniques via rigid and flexible endoscopy. With this color high-speed system, morphologic structures, such as small blood vessels, were visualized in high-resolution quality as a result of additional color information. In another system, zooming of endoscopic pictures via pixel interpolation algorithms provided full-monitor presentation of vocal fold vibratory patterns. This system allows PC-based synchronization with microphone and electroglottographic signals in a frame-by-frame technique. Although only processing gray scale images, analyses of dynamic changes in modes of vibration were facilitated by the higher frame rate recording of up to 2000 frames/s and, in addition, they display corresponding analog signals. Both methods provide clinically important information. Furthermore, we demonstrated irregular vocal fold vibration patterns in a healthy adult volunteer. In this experiment, the irregular vibratory modes were induced by voluntarily applying asymmetric vocal fold tension. The asymmetric vocal fold vibration pattern resulted in (functionally induced) roughness of the voice as predicted by computer models of asymmetric vocal fold vibration. Digital high-speed cinematography proved to be a highly promising technique in the analysis of dysphonia and provided physiological examples that could be compared with models of coupled nonlinear oscillators.