PubMed Health⌕ Search

Biomedical subjects

H G Chotas

Publications and source records attributed to H G Chotas.

At least 19 recordsLinked to original sources
PubMed2001

Imaging characteristics of an amorphous silicon flat-panel detector for digital chest radiography.

PURPOSE: To evaluate the imaging characteristics of an amorphous silicon flat-panel detector (FPD) for digital chest radiography. MATERIALS AND METHODS: The 41 x 41-cm digital FPD is constructed on a single monolithic glass substrate with a structured cesium iodide scintillator layer and an amorphous silicon thin-film transistor array for image readout. Basic imaging characteristics of the FPD and associated image processing system were assessed on acquired images, including linearity, repeatability, uniformity of response, modulation transfer function (MTF), noise power spectrum, detective quantum efficiency (DQE), contrast sensitivity, and scatter content. Results with the FPD system were compared to those with a storage phosphor computed radiography (CR) system. RESULTS: Images obtained with the FPD demonstrated excellent uniformity, repeatability, and linearity, as well as MTF and DQE that were superior to those with the storage phosphor CR system. The contrast and scatter content of images acquired with the FPD were equivalent to those acquired with the storage phosphor system. CONCLUSION: The FPD provides radiographic images with excellent inherent physical image quality.

Evaluation Studies as Topic↗
PubMed2001

Digital chest radiography with a solid-state flat-panel x-ray detector: contrast-detail evaluation with processed images printed on film hard copy.

PURPOSE: To evaluate and compare human observer performance in a contrast-detail test by using postprocessed hard-copy images from a digital chest radiography system and conventional screen-film radiographs. MATERIALS AND METHODS: The digital radiography system is based on a large-area flat-panel x-ray detector with a structured cesium iodide scintillator layer and an amorphous silicon thin-film transistor array for image readout. Images of a contrast-detail phantom were acquired at two exposure levels by using two standard thoracic screen-film systems and the digital system at matched dose. By using images of the phantom processed with standard chest image postprocessing techniques, a four-alternative forced-choice observer perception study was performed, and the number of detectable test signals (disk-shaped objects 0.3-4.0 mm in diameter) was determined for each image type. RESULTS: On average, observers detected more test signals on digital images than on screen-film radiographs at all diameters up to 2.0 mm and an equivalent number at larger diameters. Test signals with lower inherent subject contrast were detected more readily on digital images than on screen-film images, even when x-ray exposure levels for the digital system were reduced by 20%. CONCLUSION: Observer performance in a contrast-detail detection task can be improved by using images acquired with the flat-panel digital chest radiography system as compared with those acquired with state-of-the-art screen-film combinations.

Humans↗
PubMed1997

Quality control phantom for digital chest radiography.

PURPOSE: To develop and test a chest phantom for routine quality control testing of digital radiography systems. MATERIALS AND METHODS: The phantom was constructed from sheets of copper, aluminum, and acrylic, which were cut and arranged to yield a radiographic projection resembling that of a human thorax. Regional test objects allowed quantitative assessment of optical density, contrast detail, and spatial resolution. Validation tests were performed to assess image stability in a stable imaging environment and sensitivity to changes in image quality when they occur. RESULTS: The phantom yielded consistent pseudoclinical images when used in a routine quality control program and facilitated detection of simulated problems that were induced in imaging system performance. CONCLUSION: The chest phantom enables quantitative, full-system testing of digital radiography system as they are used clinically for chest radiography.

Humans↗
PubMed1997

Memory artifact related to selenium-based digital radiography systems.

Digital images acquired on radiography systems with amorphous selenium detectors are susceptible to "memory artifacts" from prior x-ray exposures. In routine clinical use and in a laboratory experiment, artifacts appeared in chest radiographs until the selenium recovered from initial exposure. Memory artifacts were eliminated when 3 minutes or more elapsed between acquisition of a lateral chest radiograph and acquisition of the next radiograph.

Aluminum↗
PubMed1995

Technical evaluation of a digital chest radiography system that uses a selenium detector.

PURPOSE: To evaluate a digital chest radiography system that uses a selenium detector. MATERIALS AND METHODS: The relative amounts of scattered radiation in the images (scatter fractions), the effect of x-ray exposure levels on image appearance, the potential "throughput" in a clinical environment, and the effects of image processing options were evaluated. RESULTS: Scatter fractions in digital images acquired with an antiscatter grid were lower in the lung region and higher in the retrocardiac and central mediastinal regions than in conventional images. Digital images acquired without an antiscatter grid had higher scatter fractions in all areas. Increases in exposure intensity reduced the appearance of noise. A new image could be acquired every 37 seconds, and a "preview image" appeared on the monitor after approximately 23 seconds. Laser-printed images were available after at least 5 minutes; the time required increased when many images were acquired in a short time. CONCLUSION: The selenium-based chest radiography system allows for rapid chest examination and excellent image quality when used with an antiscatter grid.

Evaluation Studies as Topic↗
PubMed1995

Selenium-based digital radiography of the chest: radiologists' preference compared with film-screen radiographs.

OBJECTIVE: A new digital thoracic radiography system (Thoravision; Philips Medical Systems, Hamburg, Germany), which uses selenium as a detector material, was evaluated for observer preference. The system has been shown to have higher detection efficiency than conventional film-screen systems and thus could provide an image with reduced noise. The hypothesis tested in this study was that the selenium-based digital system would provide an image appearance for conventional thoracic imaging that would be equal or superior to that provided by a conventional film-screen system. MATERIALS AND METHODS: Fifty-three patient volunteers were imaged at 120 kV with both the selenium-based system and a thoracic film-screen combination system (InSight HC; Kodak, Rochester, NY). Posteroanterior and lateral images were acquired with both systems, for a total of 212 images. Both imaging systems included a stationary 12:1 antiscatter grid. Exposures were the same for both imaging systems, and the digital images were printed to film. Images for the same patient were compared by six observers--three specialized chest radiologists and three general radiologists. Images included both normal chest radiographs and radiographs with abnormal findings. Each pair of images was ranked on a scale from 1 to 5 for preference of technique, with a score of 3 indicating no preference. Eleven anatomic features were evaluated in the posteroanterior views, and six features were evaluated in the lateral views. Statistical significance of preference was evaluated with Student's t test. RESULTS: The chest radiologists had a statistically significant preference for the selenium-based system for all 17 features (p < .001). The general radiologists had a statistically significant preference for the selenium-based system for visualization of 10 of the 17 features (p < .05). Neither group had a statistically significant preference for the conventional images in any category. CONCLUSION: The selenium-based system provided an image appearance that was significantly preferred by all radiologists, more strongly by those specializing in chest radiography. This study demonstrates that a digital thoracic imaging system can routinely produce images that are perceived as equal or superior to conventional images.

Artifacts↗
PubMed1994

Scatter-reduction characteristics of an infinity-focused gridded radiographic cassette.

RATIONALE AND OBJECTIVES: The scatter-reduction properties of a new infinity-focused grid incorporated into a radiographic imaging cassette were analyzed. METHODS: A polystyrene chest phantom was imaged using the cassette and bedside radiographic procedure. Scatter fractions were measured using a beam-stop technique at several anatomically equivalent locations. The performance of this cassette also was evaluated as a function of the orientation angle. RESULTS: The gridded cassette provided a decrease in scatter fraction from 61% to 49% in the lung and from 87% to 76% in the mediastinum. To obtain equivalent film density when the grid was used, the exposure was increased by a factor of 3.0. While there was a decrease in scatter clean-up as the film cassette was tilted from the perpendicular, the grid performed well out to an angle of 10 degrees. CONCLUSION: The gridded cassette for portable radiography provides scatter reduction with little sensitivity to alignment. The availability of this device could improve scatter rejection, and therefore, contrast in portable radiographic imaging.

Humans↗
PubMed1994

Chest radiography: estimated lung volume and projected area obscured by the heart, mediastinum, and diaphragm.

PURPOSE: To estimate what fraction of the lung volume and projected lung area are obscured by the heart, mediastinum, and diaphragm on frontal chest radiographs. MATERIALS AND METHODS: Digital images from 25 computed tomographic examinations of the chest (10-mm section thickness and spacing) were analyzed, lung regions were identified in each image section, and simulated frontal radiographs were constructed from the resultant data to estimate the obscured-volume and obscured-area fractions for each patient. Means and standard deviations of the measured lung fractions were computed. RESULTS: On average, 26.4% of the lung volume (standard deviation, 5.1) and 43.0% of the lung area (standard deviation, 6.6) were obscured. CONCLUSION: These substantial lung fractions should be considered in the selection of a screen-film system for chest radiography, because the obscured portion of the lung can be poorly imaged if an inappropriate system is chosen.

Adult↗
PubMed1993

Digital chest radiography with photostimulable storage phosphors: signal-to-noise ratio as a function of kilovoltage with matched exposure risk.

A photostimulable storage phosphor (PSP) digital radiography system was evaluated regarding the signal-to-noise ratio (S/N) on chest images acquired at differing peak kilovoltage settings but with matched risk from radiation exposure. Images of two chest phantoms were acquired by using bedside (portable) imaging equipment at tube voltages ranging from 60 to 120 kV. Exposure factors were set so that the effective dose equivalent, a risk estimator weighted for various organs, was approximately equal in all exposures. The S/N in the lung-equivalent regions was found to be slightly higher (maximum, 15%) in the low-energy exposures, while the S/N values in the mediastinum- and subdiaphragm-equivalent regions were approximately equal at all kilovoltage settings. The absence of a high sensitivity of S/N to kilovoltage in risk-matched PSP images should enable institutions to select x-ray beam quality on the basis of other imaging criteria.

Electricity↗
PubMed1993

Film-based chest radiography: AMBER vs asymmetric screen-film systems.

OBJECTIVE: Contrast-to-noise ratios were measured on radiographs from two types of state-of-the-art chest imaging systems (an Advanced Multiple Beam Equalization Radiography [AMBER] system and an asymmetric screen-film system) to facilitate an objective comparison of image quality. MATERIALS AND METHODS: Radiographs of a chest phantom were obtained by using the AMBER system with a medium-latitude screen-film image recorder (Kodak T-MAT L film and Lanex regular screens) and a commercially available asymmetric, zero-crossover screen-film system optimized for chest radiography (Kodak InSight and InSight HC). Conventionally acquired radiographs (T-MAT L/Lanex regular) were also evaluated as a reference. Films were digitized, radiographic contrast and noise were measured in the lung-, mediastinum-, and subdiaphragm-equivalent regions of each image, and contrast-to-noise ratios were computed. RESULTS: Radiographic contrast and contrast-to-noise values were found to be higher on AMBER images in all chest regions when compared with radiographs obtained with the asymmetric screen-film systems (InSight contrast-to-noise ratio approximately 77% of AMBER contrast-to-noise in the lung-equivalent region, 57% in the mediastinum-equivalent region, and 43% in the subdiaphragm-equivalent region). On conventional radiographs, the contrast and contrast-to-noise values were higher than on all other image types in the lung-equivalent region and lower than on all other image types in the less well penetrated chest areas. CONCLUSION: Image quality was higher, most notably in dense phantom regions, on radiographs obtained with the AMBER system than on radiographs obtained with the new asymmetric screen-film systems. Clinical studies are needed to determine whether this level of image improvement justifies the additional expense of the exposure equalization system.

Humans↗
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

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↗
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↗
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↗