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Biomedical subjects

C E Ravin

Publications and source records attributed to C E Ravin.

At least 37 records · Page 2Linked to original sources
PubMed1994

Bayesian restoration of chest radiographs. Scatter compensation with improved signal-to-noise ratio.

OBJECTIVES: The authors introduce a Bayesian algorithm for digital chest radiography that increases the signal-to-noise ratio, and thus detectability, for low-contrast objects. METHOD: The improved images are formed as a maximum a posteriori probability estimation of a scatter-reduced (contrast-enhanced) image with decreased noise. Noise is constrained by including prior knowledge of image smoothness. Variations between neighboring pixels are penalized for small variations (to suppress Poisson noise), but not for larger variations (to avoid affecting anatomical structure). The technique was optimized to reduce residual scatter in digital radiographs of an anatomical chest phantom. RESULTS: The contrast in the lung was improved by a factor of two, whereas signal-to-noise ratio was improved by a factor of 1.8. Image resolution was unaffected for objects with a contrast greater than 2%. CONCLUSION: This statistical estimation technique shows promise for improving object detectability in radiographs by simultaneously increasing contrast, while constraining noise.

Algorithms↗
PubMed1994

Scatter compensation in digital chest radiography using the posterior beam stop technique.

A new scatter compensation technique for computed radiography based on posterior beam stop (PBS) sampled scatter measurements and the bicubic spline interpolation technique was proposed. Using only a single exposure, both the clinical image and an array of scatter measurements, which were interpolated into a smooth scatter-only image, were simultaneously acquired. The scatter was subtracted from the clinical image to generate the primary-only image. To gauge the accuracy of scatter estimation, both quantitative and interpolation errors were evaluated. The PBS measurements were compared against the standard beam stop method at 16 locations in an anatomical phantom, resulting in quantitative errors of 2.7% relative to the scatter or 6.8% relative to the primary. Also measured were the interpolation error over 64 interpolation sample locations and 64 midpoint sample locations in the anatomical phantom. The combined interpolation error was 1.9% relative to the scatter or 8.0% relative to the primary. At the interpolation sample locations, the errors were identical between the phantom radiograph and digital portable chest radiographs from five patients. By summing the quantitative and interpolation errors in quadrature, the overall error of the PBS SISTER (scatter interpolation-subtraction technique for radiography) method was 3.3% relative to the scatter or 10% relative to the primary, which was adequate for dual-energy imaging purposes (less than 10% error relative to the scatter or 20% relative to the primary). The change of image contrast, noise, and signal-to-noise ratio (SNR) at six locations in the anatomical phantom were quantitatively analyzed. Contrast and noise were equally enhanced in all anatomical regions, resulting in approximately the same SNR before and after compensation.(ABSTRACT TRUNCATED AT 250 WORDS)

Algorithms↗
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

Physician experience with viewing digital radiographs in an intensive care unit environment.

After several years of continuous operation, the utility of digital viewing stations as assessed by bedside clinicians has been investigated through the distribution of questionnaires to past and present users. The results of the questionnaire have indicated that the bedside physicians prefer using the workstations over handling film. For evaluation of line placements, chest tubes, and pleural effusions, the physicians prefer softcopy display over hardcopy. However, for analysis of air space disease and diagnosis of pneumothorax, images displayed on the workstation were not believed to be as useful as standard hardcopy.

Attitude of Health Personnel↗
PubMed1993

Time comparison of intensive care units with and without digital viewing systems.

As hospital radiology departments and intensive care units (ICUs) make plans to use or expand the usage of digital data outside of the radiology department, the need to assess the requirements of the potential recipients in the ICUs has become more important. The present operations in an ICU that uses digital viewing instead of film has been compared with a unit that does not. The difference in time between x-ray exposure and final image viewing was determined in both settings and compared. In this preliminary study, significant differences were found between the two units. The odds of having examination results actually accessed by the ordering physician in an hour or less were 9.5 times greater for the unit with digital viewing capability than for the one without it.

Coronary Care Units↗
PubMed1993

Scatter compensation for digital chest radiography using maximum likelihood expectation maximization.

RATIONALE AND OBJECTIVES: An iterative maximum likelihood expectation maximization algorithm (MLEM) has been developed for scatter compensation in chest radiography. METHODS: The MLEM technique produces a scatter-reduced image which maximizes the probability of observing the measured image. We examined the scatter content and the low-contrast signal-to-noise ratio (SNR) in digital radiographs of anatomical phantoms before and after compensation. RESULTS: MLEM converged to an accurate (6.4% RMS residual scatter error) estimate within 12 iterations. Both contrast and noise were increased in the processed images as iteration progressed. In the lung, contrast was increased 108% and SNR was improved by 10%. In the retrocardiac region, contrast was increased 180% while SNR decreased by 6%. CONCLUSIONS: This is the first report of a post-acquisition scatter compensation technique which can increase SNR. These results suggest that statistical estimation techniques can enhance image quality and quantitative accuracy for digital chest radiography.

Algorithms↗
PubMed1993

Observer evaluation of scatter subtraction for digital portable chest radiographs.

RATIONALE AND OBJECTIVES: The authors compared standard digital portable chest radiographs (DPCXR) to scatter-subtracted DPCXR: METHODS: Thirty DPCXR were obtained using a photostimulable phosphor digital imaging system and a posterior beam stop (PBS) technique that allowed measurement of the scatter component of the DPCXR: The scatter component was subtracted from the clinical image to form a scatter-subtracted image. Six observers recorded preference for the standard image or scatter-subtracted image for identifying five radiographic landmarks and for image quality. RESULTS: A statistically significant preference was demonstrated for the scatter-subtracted images and for viewing the tracheo-bronchial tree, right paratracheal stripe, vertebral column, and support apparatus position. For unprocessed images, there was a statistically significant preference for viewing the pulmonary vasculature. No statistically significant preference was demonstrated for overall image quality. CONCLUSIONS: These results suggest that PBS scatter subtraction holds promise for improving visualization of structures in high-scatter regions of chest radiographs.

Evaluation Studies as Topic↗
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

Variable compensation chest radiography performed with a computed radiography system: design considerations and initial clinical experience.

The authors describe a variable compensation (VC) technique in which an x-ray equalizer and a computed radiography system are used. The VC technique allows retrospective alteration of equalized chest appearance with maintenance of improved signal-to-noise ratio in dense regions. Two imaging plates are used: one upstream of the patient to record the incident beam profile and one down-stream to record the equalized image. Subtraction of a weighted version of the upstream image from the down-stream image permits alteration of the appearance of the VC image, from the extremes of stimulated-unequalized to highly equalized. VC image appearance was optimized with a real-time workstation. The quality of VC images obtained in 33 patients was evaluated by three chest radiologists. Mediastinal appearance was better on VC equalized images than on conventional screen-film images. The stimulation of the appearance of a conventional radiograph with VC proved useful in interpretation of lung appearances on equalized radiographs.

Aged↗
PubMed1993

Measurement of scatter fractions in erect posteroanterior and lateral chest radiography.

Scatter fractions (SFs) measured in patients undergoing erect posteroanterior (PA) and lateral chest radiography with a 12:1 antiscatter grid are reported. Modifications to the posterior beam-stop (PBS) technique allowed measurement of scatter in these patients, without altering the diagnostic image and without additional radiation exposure. The SF measurements are reported by anatomic location on 42 clinical chest images. Average SF values ranged from 0.27 to 0.90 on lateral radiographs and from 0.27 to 0.68 on PA radiographs. Scatter measurements with the 12:1 grid were found to be greater than estimates from previous PA chest phantom experiments. To the authors' knowledge, they were the first to measure radiation scatter with the PBS technique in patients undergoing PA and lateral chest radiography with the antiscatter grid.

Adult↗
PubMed1993

Chest radiographic findings in patients with acute pulmonary embolism: observations from the PIOPED Study.

PURPOSE: To determine the sensitivity, specificity, and positive and negative predictive values of chest radiographic findings in patients suspected of having acute pulmonary embolism (PE). MATERIALS AND METHODS: Chest radiographs of 1,063 patients with suspected PE were reviewed. PE was confirmed angiographically in 383 patients and excluded in 680 patients. RESULTS: The chest radiograph was interpreted as normal in only 12% of patients with PE. The most common chest radiographic finding in patients with PE was atelectasis and/or parenchymal areas of increased opacity; however, the prevalence was not significantly different from that in patients without PE. Oligemia (the Westermark sign), prominent central pulmonary artery (the Fleischner sign), pleural-based area of increased opacity (the Hampton hump), vascular redistribution, pleural effusion, elevated diaphragm, and enlarged hilum were also poor predictors of PE. CONCLUSION: Although chest radiographs are essential in the investigation of suspected PE, their main value is to exclude diagnoses that clinically mimic PE and to aid in the interpretation of the ventilation-perfusion scan.

Acute Disease↗
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↗
PubMed1993

Cardiopulmonary complications of pregnancy: radiographic findings.

Physiologic changes during pregnancy affect nearly every organ system. In the thorax, the diaphragm elevates as much as 4 cm because of displacement of the abdominal organs by the gravid uterus, resulting in lower lung volumes. Maternal blood volume and cardiac output increase approximately 45% by mid-pregnancy. Cardiac output can increase as much as 80% during vaginal delivery and up to 50% with cesarean section. These changes result in pulmonary vascular engorgement, progressive left ventricular dilatation, and mild hypertrophy (Fig. 1). Pregnant patients are also prone to a number of pulmonary insults, including infection, aspiration, and neoplastic disease. These abnormalities have several radiographic patterns: cardiogenic and noncardiogenic pulmonary edema, focal pulmonary abnormalities, and extraalveolar air. Radiologists must recognize not only the normal chest radiographic appearance in these patients but also the thoracic complications associated with pregnancy.

Adult↗
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↗