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OBJECTIVES: To quantify the radiation dose received during thoracic spine computed tomography (CT) versus plain radiographs as well as the theoretical risk of breast cancer induction in a pediatric trauma population. METHODS: A retrospective evaluation of 179 female pediatric trauma patients who received CT or plain radiographs for clearance of the thoracic spine was performed. Subjects were secondarily grouped as children (0– RESULTS: The average radiation dose to the breast from a thoracic spine CT was 41.1 (SD 11.4) mSv and 1.8 (SD 0.9) mSv for plain radiographs. The EAR for plain radiographs was 2.7 (95% confidence interval [CI] 2.48–2.85) excess cases of breast cancer per 10 000 studies for female children and 1.4 (95% CI 1.14–1.55) for female adolescents. The breast cancer EAR for thoracic spine CT was significantly higher –79.6 (95% CI 58.6–100.5) and 45.8 (95% CI 42.0–49.6) excess cases per 10 000 scans for female children and adolescents, respectively. There was a substantially higher risk of breast cancer induction for children receiving thoracic spine CT compared with adolescents. CONCLUSIONS: CT clearance of the thoracic spine in the pediatric trauma patient results in a high dose of radiation and an age-dependent increase in theoretical breast cancer induction.

The trend of increasing cervical spine multidirectional computed tomography (MDCT) imaging of pediatric trauma patients is characteristic of the overall dramatic increase in computed tomography utilization in the United States. The purpose of this study is to compare the amount of radiation a pediatric trauma patient absorbs to the thyroid from plain radiographs and MDCT of the cervical spine and to express risk by calculation of theoretical thyroid cancer induction.A retrospective evaluation of pediatric trauma patients admitted from October 1, 2004, to October 31, 2009, was performed at an academic, Level I trauma center. Inclusion criteria were Level I/II trauma patients, cervical spine imaging performed at our institution, and age18 years. Absorbed thyroid radiation was calculated for patients receiving plain radiographs or MDCT. Thyroid cancer risk was calculated using the 2006 Biological Effects on Ionizing Radiation VII report.Six hundred seventeen patients met inclusion criteria: 224 received cervical spine radiographs and 393 received cervical spine MDCT. The mean thyroid radiation absorbed from radiographs was 0.90 mGy for males and 0.96 mGy for females compared with 63.6 mGy (males) and 64.2 mGy (females) receiving MDCT (p0.001). The median excess relative risk of thyroid cancer induction from one cervical spine MDCT in males was 13.0% and females was 25.0%, compared with 0.24% (males) and 0.51% (females) for radiographs (p0.001).The significant difference in radiation that MDCT delivers to the pediatric trauma patient when compared with plain radiographs should temper routine use of computed tomography in pediatric cervical spine clearance algorithms.

X-ray mammography is currently the primary tool used for breast cancer detection. However, studies have shown that 5%-15% of breast cancers are not visualized mammographically. The long term goal of this project is to improve the x-ray mammographic imaging system using capillary optics. A post-patient capillary optic lens has the potential to increase spatial resolution and eliminate the detection of scattered x rays, thereby improving image contrast and the signal-to-noise ratio (SNR). Several individual and two prototype multitapered optics were studied to determine the feasibility of a full-field multitapered optic. Scatter fraction, contrast, transmission, uniformity, and the modulation transfer function (MTF) were measured for a Mo target tube/computed radiography (CR) imaging system when this prototype was applied. The results were compared with standard grid and airgap techniques. The multitapered optic lens removed 85% of the scattered photons as compared to 66% and 39% for the air gap and grid methods, respectively. This resulted in an improvement of contrast by approximately 80% for the optics, 51% for the air gap, and 30% for grid methods. The single optic lens improved the limiting resolution (5% MTF level) of the CR detector by 78% due to magnification with very little focal spot blurring, while the multitapered prototype improved resolution significantly, but not as much as the single optic. These measurements have shown that it is feasible to create a multitapered optic lens that significantly improves system MTF and virtually eliminates scatter. With continued improvements in fabrication techniques, a full-field multitapered lens will be feasible.

Polycapillary x-ray optics provide an innovative new way to control x-ray beams. Placing these optics after the object to be imaged provides very efficient rejection of Compton scatter, while allowing image magnification without loss of resolution, image demagnification, or image shaping to match with digital detectors. Measured scatter rejection optics had primary transmissions greater than 50% and scatter transmission of less than 1%. For a 5-cm thick Lucite phantom, this resulted in a contrast enhancement of nearly a factor of two at 20 keV and three at 40 keV. The magnification from the tapered capillary optics improved the MTF at all frequencies out to 1.8 times the original system resolution. Increases below the system resolution are most important because clinically relevant structures generally occupy lower spatial frequencies. Alternatively, placing a collimating optic and diffracting crystal before the patient provides sufficient monochromatic beam intensity for medical imaging. Contrast, resolution, and intensity measurements were performed with both high and low angular acceptance crystals. At 8 keV, contrast enhancement was a factor of 5 relative to the polychromatic case, in good agreement with theoretical values. At 17.5 keV, monochromatic subject contrast was more than a factor of 2 times greater than the conventional polychromatic contrast. An additional factor of two increase in contrast, for a total factor of four, is expected from the removal of scatter in a large beam clinical system. The measured angular resolution after the crystal was 0.4 mrad for a silicon crystal.

The slit camera was analyzed in order to establish its utility and limitations as an MTF measurement tool for characterizing radiographic imaging systems. Commercial slit cameras are attractive for MTF measurements because the beveled edges significantly reduce their alignment sensitivity as compared to the conventional parallel jaw slit. Radiation passing through the beveled edges increases the effective width of the slit camera so that a correction based on the nominal slit width would leave residual error in the MTF measurement. Experimental and Monte Carlo simulated MTF measurements were made on a slit camera (10 microm nominal slit width) in order to estimate its sensitivity in alignment, quantify the error in MTF due to transmission through the beveled jaws, and provide a correction factor. The alignment tolerances of the slit camera were found to be about 12 times larger than for the parallel jaw slit at small HVLs (approximately 1.3 mm Al) of the incident beam and 9 times larger at higher HVLs (approximately 7 mm Al). The magnitude of the residual error in MTF was dependent on the quality of the incident spectrum. For incident spectra with high kVp and HVL (or = 120 kVp,or =5 mm Al HVL), transmission through the beveled edges produced errors in MTF up to 15% at 5 cycles/mm and 30% at 10 cycles/mm. By assuming a rectangular slit profile with an effective width based on the kVp, HVL, and filtration material of the incident beam, an MTF correction factor was determined. Application of this correction factor reduced the errors to less than 4% up to 10 cycles/mm. At low beam energies and spatial frequencies, the correction is less critical. Ease of alignment and greater availability make a commercial slit camera useful for MTF measurements. Accurate MTF measurements can be made if appropriate correction factors are applied.

The performance characteristics of a photostimulable phosphor based computed radiographic (CR) system were studied. The modulation transfer function (MTF), noise power spectra (NPS), and detective quantum efficiency (DQE) of the Kodak Digital Science computed radiography (CR) system (Eastman Kodak Co.-model 400) were measured and compared to previously published results of a Fuji based CR system (Philips Medical Systems-PCR model 7000). To maximize comparability, the same measurement techniques and analysis methods were used. The DQE at four exposure levels (30, 3, 0.3, 0.03 mR) and two plate types (standard and high resolution) were calculated from the NPS and MTF measurements. The NPS was determined from two-dimensional Fourier analysis of uniformly exposed plates. The presampling MTF was determined from the Fourier transform (FT) of the system's finely sampled line spread function (LSF) as produced by a narrow slit. A comparison of the slit type ("beveled edge" versus "straight edge") and its effect on the resulting MTF measurements was also performed. The results show that both systems are comparable in resolution performance. The noise power studies indicated a higher level of noise for the Kodak images (approximately 20% at the low exposure levels and 40%-70% at higher exposure levels). Within the clinically relevant exposure range (0.3-3 mR), the resulting DQE for the Kodak plates ranged between 20%-50% lower than for the corresponding Fuji plates. Measurements of the presampling MTF with the two slit types have shown that a correction factor can be applied to compensate for transmission through the relief edges.

Computed radiography (CR) has shown promise in digital mammographic screening due to its good low spatial frequency MTF and its relatively wide exposure latitude. The CR image format has not gained acceptance clinically because of reduced high spatial frequency resolution as compared to film-screen images. X-ray capillary optics, aligned between the breast and CR phosphor imaging plate, will capture primary x-ray photons almost exclusively. Due to the very small angle of acceptance, scattered photons angled more than about 1.6 x 10(-3) radians from primary trajectory will not be accepted at the capillary optic entrance. The virtual elimination of detected scatter means almost 100% of the possible primary contrast should be visible in the image. In addition, the image can be magnified without focal spot blurring. Effective resolution of CR images can be increased by a factor equal to that magnification. Clinical implementation of future capillary optics are expected to be either in the form of a large, stationary, post-patient optic that accepts primary from the entire breast or a fan-shaped optic that is scanned across the breast. Measurements of a test capillary optic showed a reduction of scatter fraction to 0.018. Images of a lucite contrast detail phantom revealed a corresponding increase in image contrast when compared to anti-scatter grid and no grid methods. Spectral transmission measurements using a high-purity germanium detector showed good primary transmission (45%-50%) in the mammographic energy range. The MTF measurements of both stationary and scanned capillary optics showed improvement at the 5% MTF level to 8.4 mm-1 for scanned optics and 9.2 mm-1 for stationary optics representing a 68% and 84% respective increase over the CR MTF without magnification or capillary optics.

The implementation of presentation of grouped procedures (PGP) integration profile, as described in the Integrating the Healthcare Enterprise (IHE) Technical Framework, on computed tomography (CT) and magnetic resonance (MR) scanners as well as the picture archiving communication system (PACS) addresses the problem faced by many institutions in which there are multiple-requested procedures performed in one acquisition. It is a solution that, just like the initial implementation of PACS, requires substantial modification to workflow. Implementation of PGP not only speeds access to relevant images for the requested procedure, it reduces network traffic and is less demanding on workstation hardware because of the smaller data sets transmitted. These workflow issues show that PGP implementation is not complete when the vendors install the necessary hardware and software modifications. This report discusses the workflow modifications and the barriers to implementing the PGP solution.

At the Department of Medical Physics at the University of Wisconsin-Madison, research on dual energy chest imaging including the algorithm and patient studies is done using a Pixar image processor computer. In the project described here, a study was made of which low-cost system is able to replace the Pixar and provide high-speed dual energy image processing. The dual energy algorithm was analyzed and the user and system requirements were obtained. A single workstation (e.g. Sun Sparc Station 2) does not provide enough processing power. Therefore accelerator boards for the workstation were reviewed. A prototype system was developed, using an i860-based accelerator board, i.e. the CSPI SuperCard-1, in a Sun 3/150 host computer. Bare computer time for the dual energy algorithm was reduced from 25 min using the Pixar image computer to less than three minutes using the SuperCard-1 processor board. >

The application of dual energy (DE) subtraction techniques to quantitative coronary arteriography (QCA) has the advantage of removing the tissue signal surrounding the vessel profile. We have compared the performance of two geometric QCA algorithms on DE-subtracted and -unsubtracted images to determine, for each, if DE subtraction is advantageous. The two algorithms under study were an edge detection algorithm and a Fourier analysis-based algorithm. For each algorithm, linear regression analysis was performed of measured cross-sectional area (CSA) versus actual CSA of coronary vessel phantoms. The edge detection algorithm was found to have improved precision (P less than .05) when applied to the DE-subtracted images. The Fourier analysis algorithm, however, was not effected by the DE subtraction. Among the unsubtracted image results, the Fourier measurements were more accurate (P less than .05) than the edge detection measurements. We conclude that the benefits to edge detection QCA of DE tissue subtraction outweigh the disadvantages of increased image noise and possible misregistration artifacts. However, the Fourier algorithm is relatively insensitive to tissue signal variations.

K-edge energy subtraction radiography is a method for detecting the presence of iodinated contrast material by subtracting two digital radiographs produced by X-ray beams with energies above and below the iodine K edge. We performed a feasibility study on the application of K-edge energy digital subtraction arthrography (KEDSA) to painful hip prostheses. During arthrography, loosening of the prosthesis is implied if contrast material is seen dissecting around the prosthesis, an often difficult detection task because of adjacent prosthesis metal or cement. In conventional arthrography a preliminary mask image is thus used from which films obtained after injection of iodinated contrast material are subtracted. Movement by the patient during this process may preclude subsequent subtraction. With KEDSA, since multiple image pairs may be obtained after the injection of contrast material, the problem of patient motion is virtually eliminated. A conventional X-ray tube operating between 55 and 65 kVp was alternately filtered by iodine and cerium filters to produce the KEDSA images. The apparatus was capable of producing a subtracted image within 3 sec. The technique was applied to phantoms and to six patients immediately after hip arthrography that had been positive for prosthesis loosening. Although of lower spatial resolution, the KEDSA images were, in all cases, positive for loosening in a pattern consistent with the conventional arthrographic images. KEDSA was shown to be successful in detecting extraarticular contrast material. During a single study, subtraction in various imaging planes as well as postexercise subtraction imaging can be accomplished-techniques not heretofore possible in routine subtraction arthrography.

Modulation transfer function (MTF), noise power spectrum (NPS), and detective quantum efficiency (DQE) are widely accepted measures of digital radiographic system performance. However the implementation of these measurement methodologies has been limited to a handful of researchers using an assortment of techniques. A prototype edge tool and easy-to-use software program, which can generate MTF, NPS, and DQE results quickly and easily in the field, have been developed. The edge tool consists of 1mm or 250 μ thick tungsten with two polished edges. Edge and NPS data were obtained and analyzed by 3 investigators using three analysis methods: Method A, the software under development for this report; Method B, code available on the web site of one of the investigators [Saunders and Samei, Med. Phys. 33, 308-319 (2006)]; and Method C, code developed by two other of the investigators [Samei and Flynn, Med Phy. 30, 608-622, (2003)]. In all cases the differences between the results using Method B and Method A were less than 1%. The differences between Method A and Method C were larger, up to 5.26%. NPS were calculated using Method A and B. The results were very close, with average errors less than 2.5% for exposures of 27.3, 9.3, and 2.7 μGy. Analysis of data for a 10 cm misalignment shows no significant error for either the 250 μ or 1mm edge. The method developed gives results that correlate closely with results obtained from established methods. The software is easy-to-use and flexible in its application. The Edge Tool developed has the necessary precision to accurately determine the MTF values of the system. Further validation of NPS and DQE is ongoing.

The visual displays of contemporary military flight simulators lack adequate definition to represent scenes in basic fast-jet fighter tasks. For example, air-to-air and air-to-ground targets are not projected with sufficient contrast and resolution for a pilot to perceive aspect, aspect rate and object detail at real world slant ranges. Simulator display geometries require the development of ultra-high resolution projectors with greater than 20 megapixel resolution at 60 Hz frame rate. A new micromirror device has been developed to address this requirement; it is able to modulate light intensity in an analog fashion with switching times shorter than 5 μs. When combined with a scanner, a microlaser and Schlieren optics, a linear array of these flexible micromirrors can display images composed of thousands of lines at a frame rate of 60 Hz. The approach selected for light modulation and the micromirror fabrication process flow are reviewed. Static and dynamic performances of these electrostatic MOEMS are described. Preliminary results following the integration of the described modulator into a projector prototype are reported. Developments toward a fully addressable 2000 × 1 flexible micromirror array are presented. The specifications and design of the CMOS circuit required to control this micromirror array are described. Packaging issues related to these large arrays are discussed.

A frequently cited reason for not using commercial off-the-shelf (COTS) hardware in picture archiving and communications systems (PACS) is lack of capacity, reliability, and scalability. This report describes the evaluation the scalability of COTS hardware in a clinical PACS by migrating from an active server-passive backup server environment to an active-active cluster server arrangement.

The purpose of this study is to develop a full-field digital mammography system utilizing capillary optics. Specific aims are to identify optic properties that affect image quality and to optimize those properties in the design of a multi-element capillary array. It has been shown that polycapillary optics significantly improve mammographic image quality through increased resolution and reduced x-ray scatter. For practical clinical application much larger multi-element optics will be required. This study quantified the contributing factors to the multi-element optic MTF and investigated methods to determine optimal parameters for a practical design. Individual and a prototype multi-element array of linearly tapered optics with a common focal point were investigated. A conventional (MO/MO) mammography tube and computed radiography system were used. The system and optic MTF were measured using the angled slit method with a slit camera (10 micron slit). MTF measurements were performed with both stationary and scanned optics. Contributions to MTF included: distortion within individual optics, misalignment between optics, capillary channel size, and vibration. Measurement techniques used to identify and quantify the contributions to optic MTF included a phantom chosen specifically for polycapillary optics. This phantom provided a method for assessing the coherence among capillaries within an optic as well as the relative alignment of the optics within the array. In addition, modifications to the scanning procedure allowed for the isolation and quantification of several contributors to the system MTF. Specifically, measurements were made using a stationary optic, a scanning optic, and an optic placed at multiple locations within the imaged field of view. These techniques yielded the optic MTF, the degradation of MTF due to loss of coherence within the optic, and the degradation of MTF due to vibration of the scanning mechanism. Distortion within individual optics was, typically, quite small. However, MTF degradation resulting from twist was significant in some optics. MTF degradation due to misalignment was relatively large in the prototype triad. Modeling found that misalignment up to 50 microns reduced MTF by less than 10 percent up to 3 cycles/mm. Channel diameters of 52 microns and 85 microns reduced MTF by 9 percent to 20 percent at 5 cycles/mm and provided an optimal tradeoff between transmission and MTF. Vibration was identified as a significant degradation to MTF but can easily reduced with simple modifications. In spite of some reduced optic MTF values, system MTF has always been significantly improved - in some cases almost by the magnification ratio. These results allow for accurate modeling of optic performance and optimization of design parameters. This study demonstrates that a multi-element array can be produced with nearly optimal properties. A large area array suitable for clinical trial is feasible and is the next step in this program.© (2002) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Head and helmet mounted displays (HMDs) can benefit greatly from new wide field-of-view, compact visor optics to project very high resolution (e.g., 5k X 4k) imagery. Physical Optics Corporation (POC) is developing novel, compact, lightweight wide field-of-view optics based on three-color multiplexed aberration-compensated holographic optical elements (MAC-HOEs). Taking advantage of the flexibility of holography, the HMD optics can be made compact using waveguide projection through the curved visor substrate, so that the see-through visor can have a wide field-of-view without large, bulky optical components. Using narrowband red-green-blue hologram multiplexing, MAC-HOEs can significantly reduce the chromatic and geometrical aberration introduced by conventional HOEs and refractive optics. In the initial phase of development, POC demonstrated the feasibility of the HMD optics through computer design and analysis, and by fabricating and demonstrating a MAC-HOE component.© (2001) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

The benefits and pitfalls of implementing a Java-based system to distribute results and images to referring physicians are addressed. The basic requirements for and barriers to implementing this system in a non-picture archiving and communication system (PACS) environment will also be discussed. The majority of radiology information systems (RIS) and hospital information systems (HIS) currently only distribute the text data for radiology examinations. This is generally adequate for low-acuity exams in a relatively healthy patient; however, many clinicians prefer to review images so they can correlate the reported findings with the image data, as well as review the exam themselves. A web-based solution eliminates the need for specialized review software and/or hardware at each review site. In addition, there is no need for support personnel to travel to each site to set up and upgrade software.

This report addresses the issue of the suitability of available rear-projection screens for displaying high line-rate laser projector images. Although there were some differences among the screens tested, there was no indication that the screen was the limiting factor in the spatial resolution of the display system.

The Mobile Modular Display for Advanced Research and Training (M2DART) was designed and fabricated at the Air Force Research Laboratory (AFRL) Warfighter Training Research Facility. The M2DART is part of a long term development goal of AFRL to produce a display and imaging system combination with significantly improved visual acuity in a full field-of- view/field-of-regard environment. The M2DART is an eight- channel, state-of-the-art, real image, rear-projection visual display system. It is a full color, high resolution, wraparound display designed for use with single-seat cockpit simulators. Depending on the number of available image generator channels, the system allows for a wide instantaneous field-of-view, when used in conjunction with a magnetic head tracker and video router combination to provide a full field- of-regard. The display is designed to accommodate a variety of visual image generators and cockpit simulators. The system uses commercial off-the-shelf (COTS) BARCO CRT projectors to display the out-the-window (OTW) visual imagery to the pilot. The M2DART concept demonstrates that a rear-projected, real image approach is a viable means of providing full color imagery to flight simulators with improved brightness and resolution characteristics. The final design of the M2DART represents a balance between such considerations as training requirements, the number of available image generator channels, system resolution, field of view, brightness, image stability and maintainability. This paper will provide a system description, which includes design trade-off considerations, hardware configuration, screen geometry, field of view, and performance specifications.

This report describes the Mobile Modular Display for Advanced Research and Training (M2DART) that was designed and fabricated at the Air Force Research Laboratory's Warfighter Training Research Division in Mesa, Arizona. The M2DART is an eight-channel, state-of-the-art, real-image, rear-projection, visual display system. It is a full-color, high-resolution, wraparound display system designed for use with single-seat cockpit simulators. This report provides a system description, which includes hardware configuration, screen geometry, field of view, spatial resolution, luminance, and contrast values.

Laser Power Corporation has developed a new type of projection display, based upon microlaser technology and a novel scan architecture, which provides the foundation for bright, extremely high resolution images. A review of projection technologies is presented along with the limitations of each and the difficulties they experience in trying to generate high resolution imagery. The design of the microlaser based projector is discussed along with the advantage of this technology. High power red, green, and blue microlasers have been designed and developed specifically for use in projection displays. These sources, in combination with high resolution, high contrast modulator, produce a 24 bit color gamut, capable of supporting the full range of real world colors. The new scan architecture, which reduces the modulation rate and scan speeds required, is described. This scan architecture, along with the inherent brightness of the laser provides the fundamentals necessary to produce a 5120 by 4096 resolution display. The brightness and color uniformity of the display is excellent, allowing for tiling of the displays with far fewer artifacts than those in a traditionally tiled display. Applications for the display include simulators, command and control centers, and electronic cinema.

Capillary optic arrays are bundles of hollow glass capillaries which guide x rays in a manner similar to the way fiber optics guide light. Focused postpatient capillary optic arrays have the potential to significantly improve both contrast and resolution of mammographic images compared to conventional antiscatter grids. Contrast can be improved by the nearly total scatter rejection of the optic. Effective resolution can be improved by geometric magnification without increased focal spot blurring. The best results were found for borosilicate glasses, with transmissions in excess of 60% for 22-cm-long fibers. To evaluate the scatter rejection properties, the transmission of off-axis radiation was measured. Transmission drops to < 1% at an angular displacement of 2.7 mrad. Transmission of a bulk capillary array dropped to near zero if the source was at an angle of 2.5 mrad. This implies excellent scatter rejection capabilities. To evaluate whether unchanneled photons might still reach the detector, absorption measurements were also performed on fibers and arrays. Absorption was found to be adequate for scatter rejection. All of the data agreed well with numerical simulations. Performance calculations for two potential optics geometries gave promising results.

We have reported on a single-exposure dual-energy system based on computed radiography (CR) technology. In a clinical study conducted over a two year period, the dual-energy system proved to be highly successful in improving the detection (p=0.0005) and characterization (p=0.005) of pulmonary nodules when compared to conventional screen-film radiography. The basic components of our dual-energy detector system include source filtration with gadolinium to produce a bi-modal x-ray spectrum and a cassette containing four CR imaging plates. The front and back plates record the low-energy and high-energy images, respectively, and the middle two plates serve as an intermediate filter. Since our initial report, a number of improvements have been made to make the system more practical. An automatic registration algorithm based on image features has been developed to align the front and back image plates. There have been two improvements in scatter correction: a simple correction is now made to account for scatter within the multi-plate detector; and a correction algorithm is applied to account for scatter variations between patients. An improved basis material decomposition (BMD) algorithm has been developed to facilitate automatic operation of the algorithm. Finally, two new noise suppression techniques are under investigation: one adjusts the noise filtering parameters depending on the strength of edge signals in the detected image in order to greatly reduce quantum mottle while minimizing the introduction of artifacts; a second routine uses knowledge of the region of valid low-energy and high-energy image data to suppress noise with minimal introduction of artifacts. This paper is a synthesis of recent work aimed at improving the performance of dual-energy CR conducted at three institutions: Philips Medical Systems, the University of Wisconsin, and Duke University.

We evaluated a single-exposure, phosphor-plate, dual-energy imaging device that produces, in addition to conventional chest radiographs, both tissue- and bone-selective images. Our purpose was to determine whether dual-energy radiography was more accurate than routine chest radiography for detection and characterization of pulmonary nodules.Two hundred patients undergoing chest CT were asked to volunteer to have dual-energy and conventional chest radiographs obtained immediately before or after their CT scan. Radiographs from a subset of 50 of these patients with 116 CT-detected nodules and 10 patients with normal findings on CT scans of the chest were presented to the observers for the nodule detection study. Similarly, radiographs from a subset of 29 patients with 20 calcified and 20 uncalcified nodules were presented to five observers to determine nodule calcification. Dual-energy images were produced by filtering the X-ray tube output with a gadolinium sheet while using a multiple phosphor plate receptor. A dual-energy triad of images consisting of a conventional image, a tissue-selective image, and a bone-selective image were produced. The conventional chest radiographs and dual-energy image sets were presented to observers in random order. Data from a free response receiver operating curve and a receiver operating curve were generated for nodule detection and characterization, respectively.By using the dual-energy images, all five observers improved their ability to diagnose pulmonary nodules (p = .0005) and to characterize nodules as calcified (p = .005).By eliminating rib shadows with tissue-selective images and enhancing calcified structures with bone-selective images, dual-energy chest radiography improved the ability of all observers, regardless of expertise, to detect and characterize pulmonary nodules.

Densitometric analysis of images obtained by digital subtraction angiography (DSA) allows for more reproducible and less operator-dependent quantitation of ventricular function. Conventional DSA uses temporal subtraction but is limited by misregistration artifacts. Dual-energy digital subtraction angiography (DE-DSA) is immune to such misregistration artifacts. The ability of DE-DSA to quantitate changes in regional ventricular volume resulting from ischemia was tested. Densitometric analysis of both phase-matched and ejection fraction DE-DSA images was used to quantitate regional left ventricular systolic function during four levels of ischemia ranging from mild to severe in open-chest dogs (n = 10). DE-DSA left ventriculograms were obtained by means of central venous injections of iodinated contrast medium. Ischemia was graded according to percentage of systolic wall thickening as measured by sonomicrometry. Phase-matched end-systolic images were obtained at each of four levels of ischemia by subtracting an end-systolic control image from each end-systolic ischemic image. Ejection fraction images were obtained at the control level and at each level of ischemia by subtracting an end-systolic image from an end-diastolic image of the same cardiac cycle. The resulting wall motion difference signals represent the changes in regional ventricular volumes and were quantitated by densitometry. Densitometry was able to detect the effect of all levels of ischemia on regional function, even the mildest. Densitometric analysis of both phase-matched and ejection fraction DE-DSA images provides a sensitive technique for detecting and quantitating the changes in regional left ventricular systolic volume that occur with ischemia.

The implementation of this system provides a cost-effective and easy-to-use mechanism for verifying the receipt of radiology results. This provides the radiology department with assurance that their use of internet technologies is secure, effective, and reliable. Likewise, the approach outlined can be integrated into an enterprise-wide solution for the deployment of digital certificate technologies.

The lean-fat composition (%FATR) of soft tissue and the mineral mass of the skeleton were determined in vivo using dual-photon (153Gd) absorptiometry (dose under 2 mrem). A rectilinear raster scan was made over the entire body in 18 subjects (14 female, 4 male). Single-photon absorptiometry (125I) measured bone mineral content on the radius. Percentage fat (%FATD) was determined in the same subjects using body density (from underwater weighing with correction for residual lung volume). Lean body mass (LBM) was determined using both %FATR and %FATD. Percentage fat from absorptiometry and from underwater density were correlated (r = 0.87). The deviation of %FATD from %FATR was due to the amount of skeletal mineral as a percentage of the LBM (r = 0.90). Therefore, skeletal variability, even in normal subjects, where mineral ranges only from 4 to 8% of the LBM, essentially precludes use of body density as a composition indicator unless skeletal mass is measured. Anthropometry (fatfolds and weight) predicted %FATR and LBM at least as well as did underwater density. The predictive error of %FATR from fatfolds was 5% while the predictive error in predicting LBM from anthropometry was 2 to 3 kg (3%).

Under the SIMBATH programme the physical phenomena of transient material movement and relocation during severe LMFBR accidents are investigated out-of-pile. In most of the SIMBATH bundle experiments a failure of the wrapper was observed. From the safety point of view this has implications on the issue of propagation. By openings into the inter-subassembly gaps pressure relief and material release are possible. From the development of failure, based on measurements made during the simulation tests, and from post-experiment investigations three types of failure mode have been identified: • - Melt-through of the wrapper wall by a jet of hot material from a failing pin. This happened very early during the test. Sodium boiling in the annular bypass prior to failure has not been detected. • - Melt-through in the simulated fuel region by severe ablation due to local crust instability combined with intense heat input from the flowing melt. • - Melt-through in the simulated breeding regions close to blockages. This failure mode was always observed together with sodium gross boiling in the annular channel, i.e. reduced cooling of the wrapper wall. No mechanical failure was detected as a result of the stress concentration in the corners of the hexcan walls. The influence of the internal overpressure is restricted mainly to final break-through after severe ablation and drives the material motions after wrapper failure; it does not control wrapper wall failure in these experiments.

It has long been recognized that the problems of motion artifacts in conventional time subtraction digital subtraction angiography(DSA) may be overcome using energy subtraction techniques. Of the variety of energy subtraction techniques investigated, non‐k‐edge dual‐energy subtraction offers the best signal‐to‐noise ratio (SNR). However, this technique achieves only 55% of the temporal DSASNR.Noise reduction techniques that average the noisier high‐energy image produce various degrees of noise improvement while minimally affecting iodine contrast and resolution. A more significant improvement in dual‐energy DSA iodine SNR, however, results when the correlated noise that exists in material specific images is appropriately cancelled. The correlated noise reduction (CNR) algorithm presented here follows directly from the dual‐energy computed tomography work of Kalender who made explicit use of noise correlations in material specific images to reduce noise. The results are identical to those achieved using a linear version of the two‐stage filtering process described by Macovski in which the selective image is filtered to reduce high‐frequency noise and added to a weighted, high SNR, nonselective image which has been processed with a high‐frequency bandpass filter. The dual‐energy DSACNR algorithm presented here combines selective tissue and iodine images to produce a significant increase in the iodine SNR while fully preserving iodine spatial resolution. Theoretical calculations predict a factor of 2– 4 improvement in SNR compared to conventional dual‐energy images. The improvement factor achieved is dependent upon the x‐ray beam spectra and the size of blurring kernel used in the algorithm. In the limit of large blurring kernels, the noise‐reduced dual‐energy image has an iodine SNR approaching the maximum value achievable with a linear combination of the low‐ and high‐energy images, with the additional advantage that low spatial frequency tissue signals are substantially reduced. Phantom measurements confirm the predicted increase in SNR of the CNR technique while images processed both by conventional dual‐energy and CNR methods demonstrate the noise suppression of the CNR algorithm and the tissue edge artifacts which it may introduce.

A digital beam attenuator system has been developed to automatically generate patient‐specific compensating filters for chest radiography. An initial low‐dose test image is used to generate the attenuator, which is fabricated by overprinting multiple layers of a heavy‐metal material onto a nonattenuating substrate. The attenuator is subsequently inserted into the x‐ray beam for a final compensated radiograph. The effects of focal spot blurring and limited attenuator resolution result in the final compensated image containing only high‐spatial frequency information. The frequency response of the process is not strictly describable by a modulation transfer function, but an approximation of the frequencies remaining in the compensated image is obtained for low‐contrast conditions. It is found that a 4×4 blurring function on the original 64×64 test image is required for the attenuator to give appropriate compensated image appearance. A proposed attenuator printing scheme prints the attenuator in a 16×16 matrix, staggering successively printed layers to achieve the required 64×64 sampling with appropriate blurring. The resulting compensated image has good anatomical definition and contains a frequency response similar to that obtained by compensation techniques being investigated by Plewes and Sorenson.

Initial clinical results using a digital fluoroscopic implementation of the combined time-energy ("hybrid") subtraction technique are described, with emphasis on carotid and renal imaging. Where patient motion artifacts are due to soft-tissue motion alone, hybrid subtraction can remove them. Due to the need for a finite separation time between high- and low-energy pairs, however, the present implementation of the hybrid technique is not completely immune to soft-tissue motion. The intrinsic signal-to-noise ratio of hybrid imaging is less than that of conventional temporal subtraction. However, since the low-energy temporal subtraction images are included in the hybrid data set, the diagnostic quality of the examination is not compromised.

Single-photon absorptiometry has been widely accepted for biomedical research on bone (1, 4, 8). It has been apparent since the advent of single-photon absorptiometry that a dual-photon approach might be used to measure bone mineral content. The chief advantage of a dual-photon approach is the lack of the requirement for surrounding the measured bone in a constant thickness of soft-tissue. Concequently a dual-photon approach could be used on areas such as the hip or spine which are otherwise almost impossible to measure. Our initial work in this area consisted of definition of the various sources of error and their magnitude (2). Pioneering work on application of dual-photon absorptiometry to scanning of the spine was done by Reed (5) and greatly amplified by Roos and his co-workers (6, 7). We have done parallel work on spinal scanning, and have expanded to measure total body mineral as well.

The feasibility of producing patient-specific beam attenuators for chest radiography has been investigated using an anthropomorphic phantom and a human volunteer. A low-dose test exposure is digitized, processed, and used to print a small cerium filter, which is placed in the x-ray beam near the collimator. The final radiograph is recorded on film. The technique results in relatively uniform film exposure, so that structures in all regions of the chest are simultaneously displayed with optimal film contrast. The equalized exposure improves image quality in the normally underpenetrated regions and reduces the role of cross-scatter from the lungs. The image is analogous to optical or computer-processed unsharp masking techniques, but the processing is accomplished in the x-ray beam and results in an improved exposure distribution, giving advantages that cannot be achieved with image processing techniques alone.

Two series of quasi-steady state sodium boiling experiments have been carried out in an electrically heated seven-pin bundle. The power levels (130–170 and 30–40 W/cm2) and other test conditions were selected to correspond to the core and radial breeder zones of a typical LMFBR. The test procedure involved the gradual reduction of mass flow rate through the bundle in a simulation of the consequences of a slowly growing blockage in the lower part of a reactor subassembly. By this means it was possible to study the development of quasi-steady state boiling up to the onset of permanent dryout. The results obtained provide information on flow regimes in the two-phase region, vapour qualities and flow rates at which cooling of the bundle can be effectively maintained, and the ultimate incidence of dryout. A relation for the two-phase pressure drop multiplier obtained from adiabatic pressure drop measurements in this geometry is given and compared with earlier results from single-channel geometry tests.

A method was developed for measuring total body bone mineral (TBBM) and lean body mass in vivo using dual-photon absorptiometry. The entire body was scanned in a rectilinear raster (transverse speed of 1 cm/s and longitudinal steps of 2.5 cm) with a modified nuclear medicine scanner and conventional nuclear counting electronics. The source was 153Gd (1 Ci) with principal photopeaks at 44 and 100 keV. The scan time was about 70 min with an absorbed dose of under 1 mrem. The low dose allows measurements to be repeated at frequent intervals or used on children. Short-term (months) precision of TBBM was about 1.5% for isolated skeletons and about 2% on normal human subjects. Long-term (years) precision on skeletons was under 3%. The precision of percent fat was 0.9%, which would lead to an error of less than 1% in the TBBM. Geometry of measurements also had minimal (and correctable) influence on the accuracy of results. The accuracy (1 standard error of estimate) of TBBM on isolated skeletons (N = 5) was 36 g (equivalent to about 13 g of Ca) with a correlation coefficient of 0.99; this error amounts to about 1--1.5% in normal adults; 2% in older women, and 2.5% in osteoporotic females. The dual-photon absorptiometry method could be implemented in many nuclear medicine departments to follow skeletal changes during growth and aging or to follow the course of a disease or treatment.

Left ventricular ejection fractions were determined following eight intravenous injections in three dogs using area/length and digital videodensitometric techniques. Ejection fractions were measured by both techniques for all beats during left ventricular opacification. Even after noniodinated background corrections, tissue iodine accumulation produced large errors in measured iodine content late in the contrast material curve. By using a model for tissue iodine accumulation, an algorithm was developed that appears to reduce these errors. The measured ejection fraction for ten beats following the peak of the contrast material curve declined an average of 1.8% following correction, compared with 14% prior to correction. Following correction for tissue iodine accumulation, correlation between area/length and video-densitometric ejection fractions was 0.94. By correcting for tissue iodine accumulation, much more of the contrast material curve provides usable data for estimating ejection fractions.

Dual-photon absorptiometry using 153Gd (44 and 100 keV) was used to measure the bone mineral content (BMC) of the trunk and of the total body (TBBM) in 7 volunteers with no overt bone disease. These values were compared to those obtained with partial-body neutron activation of calcium (trunk Ca). The trunk Ca seemed to represent best a 60 x 30 cm area; the correlation coefficient with the corresponding BMC in that area was 0.97 (SEE congruent to 7%). Trunk Ca was also highly correlated with TBBM (r = 0.96; SEE = 8%) and with radius BMC (r = 0.92; SEE = 11%), but the correlations with the BMC of smaller subareas of the trunk were lower (r congruent to 0.9; SEE approximately 12%). The BMC of the lumbar spine was only moderately correlated with trunk Ca, radius BMC and TBBM (r approximately 0.82; SEE approximately 18%), and only slightly more associated with trunk BMC (r approximately 0.88; SEE approximately 14%). The BMC of the combined lumbar-thoracic spine showed higher correlations with trunk Ca, radius BMC and TBBM (r approximately 0.87; SEE approximately 13%), and trunk BMC (r = 0.93; SEE approximately 10%). An accurate and sensitive measure of spinal status requires a direct measurement of that area.

Although intravenous (IV) digital subtraction angiography (DSA) techniques are successfully used for the diagnosis of peripheral, carotid, and aortic vascular disease, satisfactory images of the coronary arteries are much more difficult to obtain because of unique imaging problems. These include vessel and soft tissue motion, large scene dynamic range, and overlap of simultaneously opacified cardiac and noncardiac structures. Because early DSA systems were not well suited for addressing these problems, it was soon concluded that the coronary arteries could not be adequately imaged by intravenous techniques. Although it remains a difficult problem, we have recently readdressed IV DSA coronary angiography, using a system which includes several improvements relative to the early DSA systems. This chapter describes the major imaging problems associated with IV coronary DSA and presents our current approach and most recent attempts to image the coronary arteries by intravenous techniques.

Although image quality in chest radiography can be improved dramatically with compensating attenuators, it is difficult to match attenuator geometry to that of the patient and to properly position the filter in the x-ray beam. We are developing a system which will fabricate a compensating filter specific for individual patient anatomy and position the filter automatically. A low-dose image is acquired from which the attenuator is designed using a hardwired algorithm. The attenuator then is typed in multiple layers of a cerium oxide material onto a sheet of paper with a dotmatrix printer. Following positioning of the attenuator in the x-ray beam, the final compensated image is acquired with a photographic or electronic detector. Initial studies with our prototype digital beam attenuator have produced images with improved image quality. The improvement occurs because the attenuator allows the entire image to be placed in the linear portion of the film characteristic curve. In addition, decreased scatter fractions and increased signal-to-noise contribute to improved visualization of low-contrast signals behind the most attenuating regions of the patient.

In digital fluorographic techniques the video camera must accommodate a wide dynamic range due to the large variation in the subject thickness within the field of view. Typically exposure factors and the optical aperture are selected such that the maximum video signal is obtained in the most transmissive region of the subject. Consequently, it has been shown that the signal-to-noise ratio is severely reduced in the dark regions. We have developed a prototype digital beam attenuator (DBA) which will alleviate this and some related problems in digital fluorography. The prototype DBA consists of a 6x6 array of pistons which are individually controlled. A membrane containing an attenuating solu-tion of (CeC13) in water and the piston matrix are placed between the x-ray tube and the subject. Under digital control the pistons are moved into the attenuating material in order to adjust the beam intensity over each of the 36 cells. The DBA control unit which digitizes the image during patient positioning will direct the pistons under hydraulic control to produce a uniform x-ray field exiting the subject. The pistons were designed to produce very little structural background in the image. In subtraction studies any structure would be cancelled. For non-subtraction studies such as cine-cardiology we are considering higher cell densities (eg. 64x64). Due to the narrow range of transmission provided by the DBA, in such studies ultra-high contrast films could be used to produce a high resolution quasi-subtraction display. Additional benefits of the DBA are: 1) reduced dose to the bright image areas when the dark areas are properly exposed. 2) improved scatter and glare to primary ratios, leading to improved contrast in the dark areas.© (1982) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Since the early 1970's, Edholm and others have shown that compensation attenuators can provide fundamental improvements in radiographic image formation by modifying patient dose-distribution, reducing scatter fractions in dark regions of the image, and easing dynamic range requirements for film and video systems. Compensating attenuators have not yet been used widely in diagnostic radiology because of the difficulties of forming masks to compensate for the anatomical variations of individual patients. We have designed a software-based system which forms a heavy-metal attenuator from a digital image of the patient. At present, the attenuators are constructed manually from a pattern generated by the computer, but several techniques are being investigated which may permit fabrication and positioning during suspension of respiration. Phantom studies demonstrate that, in nonsubtractive applications, unsharp masking by the x-ray beam attenuator enhances local contrast, while in digitally subtracted images, attenuators eliminate dark regions where iodine signals otherwise are degraded by video and quantum noise. The technique can be used to reduce patient exposure in highly transmissive areas or, at the expense of increased tube loading, to increase exposure to highly attenuating areas in order to reduce image noise. Anticipated applications of this technique include chest radiography as well as conventional and digital subtraction angiography.

In simultation experiments the consequences of hypothetical reactor accidents are investigated. The materials involved in the tests, as well as the temperatures, require test sections of steel. To follow the materials movement and relocation X-ray cine equipment was developed. The test section is radiated from three axially positioned. X-ray sources, electro optical image amplifiers transform the material density distribution into a visible picture, which is picked up by high speed cameras with, typically, 1000 pictures per second. The resolution of the system is about 1 mm3 of steel with a small dependance on the total thickness of the test section. The technique, its main features and limitations are described and some experimental results are presented as an example. The computer aided analysis of the X-ray high speed films is also explained.© (1983) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

We have investigated the feasibility of an optical beam attenuator (OBA) for image equalization in the optical light path of a camera-based x-ray imaging system. In our OBA design, a liquid crystal device (LCD) operated in transmissive mode is used to equalize low spatial frequencies. In most camera systems, compression of image dynamic range will result in improved performance. The advantages of optical equalization include bit compression for digital applications, video-rate equalization, detective quantum efficiency (DQE) improvement at high dose rates, and high-pass frequency filtration for film-based applications. A prototype OBA system has been constructed and installed in our DSA imaging laboratory. Equalized phantom images have been obtained which demonstrate improved visualization of structures in the darker regions of the image. The effect of the OBA on system limiting spatial resolution and system noise performance has also been investigated.