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Biomedical subjects

C E Ravin

Publications and source records attributed to C E Ravin.

At least 19 recordsLinked to original sources
PubMed1992

Digital chest radiography with storage phosphor systems: potential masking of bilateral pleural effusions.

A photostimulable storage phosphor (PSP) computed radiography imaging system was analyzed for its potential to mask pleural effusion during normal image processing. This phenomenon has been observed in several clinical cases in our hospital. To better understand the relationship between pleural effusion and the PSP radiograph appearance, portable radiographs of an athropomorphic chest phantom were acquired with the PSP system in conditions simulating various quantities and distributions of pleural fluid. It was observed that the optical density of the film in one hemithorax was significantly influenced by whether or not fluid was present in the opposite hemithorax. This optical density dependence was determined to be a system-induced effect that results from the image processing (histogram analysis) technique used by the PSP system during image plate readout. It is important to recognize that the PSP system's normal optical density (sensitivity) adjustment can obscure the presence of bilateral pleural fluid accumulation, particularly if the opposite hemithorax contains fluid in an equal or greater amount.

Humans↗
PubMed1992

Posterior beam-stop method for scatter fraction measurement in digital radiography.

The authors presented a new posterior beam-stop (PBS) technique for measuring the ratio of scattered to total-detected photon flux (scatter fraction) in a radiographic examination while preserving the diagnostic quality of the image. The scatter measurement was made using a standard imaging geometry with both beam stops and an additional x-ray detector placed behind the standard imaging detector. This PBS geometry differs from the standard beam-stop (SBS) technique for scatter measurement. With SBS, a beam-stop shadow appears on the image. To evaluate the PBS technique, scatter fraction measurements were performed on an anatomic phantom using both the PBS and SBS techniques. When compared with the standard technique, PBS provided accurate estimation of scatter fractions. Since the measurement can be performed without degrading a standard clinical radiographic examination, the PBS technique allows simultaneous acquisition of scatter measurements from human patients in combination with a standard radiographic examination.

Filtration↗
PubMed1992

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

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

Humans↗
PubMed1992

Threshold perception performance with computed and screen-film radiography: implications for chest radiography.

Images of a phantom obtained with computed radiography and standard screen-film imaging were compared to evaluate observer threshold perception performance with a modified contrast-detail technique. Optimum exposure necessary for performance with the imaging plate technique to match that with screen-film techniques was determined, as was comparative performance with variation in kilovoltages, plate type, spatial enhancement, and hard-copy interpolation method. It was found that computed radiography necessitates about 75%-100% more exposure than screen-film radiography to optimally match performance with Ortho-C film with Lanex regular or medium screens (Eastman Kodak, Rochester, NY) for detection of objects 0.05-2.0 cm in diameter. However, only minimal loss of detection performance (approximately 10% overall) was experienced if standard screen-film exposures were used with computed radiography. Little change in observer performance was found with variation in plate type, spatial enhancement, or method of hard-copy interpolation. However, perception performance with computed radiographic images was better at lower kilovoltages.

Humans↗
PubMed1992

Measurement of scatter fractions in clinical bedside radiography.

The authors present measurements of scatter fraction (SF), the ratio of scattered to total imaged photons, from clinical bedside radiographs of 102 patients. These measurements were obtained by using a new posterior beam-stop technique that does not alter the diagnostic image but that simultaneously provides SF measurements at 224 locations in the image. The SF values in the lung were found to be consistent with previous measurements, while the SF values in the mediastinal and retrocardiac areas were larger than previously reported. SFs in diseased lung were significantly larger than SFs in normal lung. The range of SF values was large for all anatomic locations. For applications in which accurate scatter estimation is required, this wide range of values suggests that SFs should be measured in each individual image.

Female↗
PubMed1991

Single-exposure conventional and computed radiography image acquisition.

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

Humans↗
PubMed1991

Small object contrast in AMBER and conventional chest radiography.

The ability of a commercially available scanning equalization system for chest radiography to render small object contrast in the lung-, mediastinum-, and subdiaphragm-equivalent regions of an acrylic chest phantom was quantitatively evaluated. Images from nine chest phantoms that represented a wide range of patient sizes and dynamic ranges of x-ray transmittance were analyzed. Subject contrast was measured with a photostimulable phosphor detector, and images were acquired in both equalized and nonequalized (conventional) imaging modes. Available subject contrast in the lung-equivalent region was 8%-15% lower in the equalized images compared with the nonequalized images in all phantoms (patient types); contrast in the mediastinum-, retro-cardiac-, and subdiaphragm-equivalent regions was 11%-63% higher in the equalized images, with the degree of improvement increasing as patient size and dynamic range increased. Images of each phantom were also acquired with the screen-film systems currently in use at the authors' institution, permitting an assessment of the relative performance (in terms of radiographic contrast) of these imagers with and without use of equalization.

Diaphragm↗
PubMed1991

Imaging of the intensive care unit patient.

Despite advances in "high tech," it is anticipated that plain chest film radiography will continue to play a significant role in the management of patients in the ICU. Digital radiography will most likely displace conventional approaches. As demonstrated throughout this article, CT has played an increasingly important role in the evaluation of the critically ill patient. The results are especially impressive, because most were obtained on earlier-generation CT machines, which are now totally outdated. Newer scanners have many technical improvements, including rapid scanning, which permits breathholding, and thin-section scanning, which has been discussed in great detail throughout this volume. Whether MR imaging will play an important role in ICU care remains to be determined.

Catheterization↗
PubMed1990

Initial experience with automatic image transmission to an intensive care unit using Picture Archiving and Communications System technology.

This report describes a refinement of the interaction between a Computed Radiography (CR) system and a Picture Archiving and Communications System (PACS) that has made possible automatic distribution of images to specified locations. Those interactions between the CR and the PACS that were considered important to the acceptance of the data to be sent to the intensive care unit (ICU) are described. Display and user interface considerations important for physician acceptance of the unit are also discussed. System enhancements and future applications will be developed based on the possible implications of this technology in both Radiology and the ICUs.

Computer Communication Networks↗
PubMed1990

Magnetic resonance imaging of the thoracic cavity using a paused 3DFT acquisition technique.

A new pulse sequence designed for magnetic resonance imaging of the entire thoracic cavity is described. This sequence, called 3DPAUSE, is a rapid three-dimensional Fourier transform (3DFT) sequences with periodic pauses for breathing and additional rf pulses after each pause to restore the magnetization to steady-state before data acquisition resumes. Cardiac motion artifacts are effectively removed by signal averaging. Respiratory motion artifacts are removed by breath hold. Image artifacts caused by an inadequate number of pauses or by inappropriate placement of the pauses within a scan are shown, and ways to avoid these artifacts are discussed. 3DPAUSE provides the ability to acquire three-dimensional arrays in the thoracic cavity with minimal artifacts from respiratory and cardiac motions in a clinically reasonable time.

Animals↗
PubMed1990

Counterclockwise exit of cardiac pacemaker leads: sign of pulse-generator flip.

Clockwise exit of pacing leads from transvenous cardiac pacemakers is generally essential for proper function. The authors report a case in which counterclockwise exit of the pacing leads signified a 180 degree flip of the pulse generator. Three types of pacing system malfunction can result from pacemaker flip.

Equipment Failure↗
PubMed1990

Scatter fractions in AMBER imaging.

Images of two phantoms were obtained with use of an advanced multiple-beam equalization radiography system, and scatter fractions were estimated with use of a photostimulable phosphor imaging system. Scatter fractions in the equalized images were lower in the mediastinum-equivalent areas and higher in the lung-equivalent areas, relative to images that were conventionally acquired with use of an antiscatter grid. The differences are attributed to a reduction in incident exposure in the lungs and the presence of cross-scatter between lung and mediastinal regions.

Radiography, Thoracic↗
PubMed1989

Image optimization in a computed-radiography/photostimulable-phosphor system.

Photostimulable phosphor imaging is an exciting new technology that has several advantages over film/screen radiography, the most important of which is the linearity of the photostimulable phosphor system over a wide exposure latitude. The photostimulable phosphor image is digital, and as such, provides options of how the image is viewed by radiologists. This report discusses the various image-processing parameters available for a photostimulable phosphor system and describes a rational approach for selecting these parameters in portable chest radiography. As photostimulable phosphor imaging becomes more widely implemented, an understanding of the processing parameters will facilitate the production of images that take full advantage of the benefits of these systems.

Humans↗
PubMed1989

Scatter compensation in digital chest radiography using Fourier deconvolution.

The authors present a numerical deconvolution technique to compensate for image degrading effects caused by scattered photons in radiographic chest images. Fourier transform techniques are used to deconvolve a shift invariant model of the two dimensional point spread response functions of the scattered radiation. This approach uses a digitized radiograph acquired with a standard chest imaging protocol, so no specialized imaging equipment is required. While the shift variant shape of the scatter model is optimized for the lung field, effective compensation is provided when this model shape is applied to other chest regions. Preliminary evaluation suggests that this technique can provide improved image contrast over the entire chest region.

Computer Simulation↗
PubMed1989

Three-dimensional imaging of the thoracic cavity.

Three-dimensional (3D) surface reconstruction techniques were applied to sets of computed tomographic (CT) images of the thoracic cavity. Emphasis was placed on extracting lung images. High quality, detailed 3D images of the lung surface and internal bronchial and vascular structures were produced.

Humans↗
PubMed1989

Medical student perceptions of diagnostic radiology. Influence of a senior radiology elective.

To assess the impact of a four-week elective on medical student perceptions of diagnostic radiology, we gave questionnaires to 96 senior students on the first and last days of the rotation. Eighty-five anonymous entrance responses and 73 exit responses were obtained during a 13-month interval. Compared with other clinical specialties, the students viewed radiology as third, behind surgery and medicine, in terms of required breadth of knowledge, skill, training, and "glamour." Radiology was also perceived to have the lightest workload with the exception of psychiatry. Responses did not significantly change after completion of the elective. Perceived advantages and disadvantages of radiology were studied in detail in a subset of students. Exit responses indicated that the elective promoted favorable perceptions of radiology but did not change the relative rankings of the various specialties. It appears that at our institution basic attitudes concerning radiology are formed prior to the senior radiology elective and are affected only moderately during the elective.

Attitude of Health Personnel↗