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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
PubMed1998

Characteristics of regions suspicious for pulmonary nodules at chest radiography.

RATIONALE AND OBJECTIVES: This study was performed to determine physical characteristics of areas on chest radiographs that are suspicious but not definitive for the presence of a pulmonary nodule and the characteristics of areas that contain an obvious nodule. MATERIALS AND METHODS: Two groups of patients were identified: those who had an area at plain radiography that was suspicious for a pulmonary nodule and underwent fluoroscopy for further evaluation (138 patients, 142 areas) and those who had an obvious nodule at plain radiography who underwent computed tomography for further evaluation (72 patients, 97 areas). The measured characteristics of the region of interest included size, circularity, compactness, contrast, and location. RESULTS: A comparison of the data show that while there was some difference between these groups of patients with regard to location of the nodules, there were essentially no differences with regard to size, circularity, compactness, and contrast of the regions of interest. CONCLUSION: Size, circularity, compactness, contrast, and location are not sufficient to distinguish pulmonary nodules from other suspicious regions on the chest radiograph.

Fluoroscopy↗
PubMed1998

The Fleischner Society. Future directions in pulmonary imaging.

The next 5-10 years promise a continuation of the enormous excitement we have experienced over the past 10-20 years in pulmonary imaging. In each case, advancements in technology have been or will be applied to the analysis of disease processes in ways previously unimagined. At this point, the major pathways to the future seem to lie in more complete implementation of digital imaging of the thorax, which will be accomplished through the perfection of digital detector systems and which will allow more spectacular display and more accurate analysis of underlying morphometry. Potentially even more exciting is the opportunity to evaluate metabolic function and to establish tissue specificity through tissue-specific radionuclides and/or the application of MR spectroscopy to tissue and organ analysis.

Diagnostic Imaging↗
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↗
PubMed1996

Human lung air spaces: potential for MR imaging with hyperpolarized He-3.

Two healthy volunteers who had inhaled approximately 0.75 L of laser-polarized helium-3 gas underwent magnetic resonance imaging at 1.5 T with fast gradient-echo pulse sequences and small flip angles ( < 10 degrees). Thick-section (20 mm) coronal images, time-course data (30 images collected every 1.8 seconds), and thin-section (6 mm) images were acquired. Subjects were able to breathe the gas (12% polarization) without difficulty. Thick-section images were of good quality and had a signal-to-noise ratio (S/N) of 32:1 near the surface coil and 16:1 farther away. The time images showed regional differences, which indicated potential value for quantitation. High-resolution images showed greater detail and a S/N of approximately 6:1.

Adult↗
PubMed1995

Initial experience with asynchronous transfer mode for use in a medical imaging network.

Picture archiving and communication Systems (PACS) for medical imaging have always suffered from band-width limitations, throughput, and proprietary protocols. Commercially available local area networks have been hard pressed to meet the requirements of image transfer in a time consistent with patient-care needs. Recent technologic advances provide potential solutions to these constraints. Asynchronous transfer mode (ATM) provides the aggregate bandwidth and throughput that may be sufficient to satisfy the medical imaging community. Networks using prototype ATM technology have been available and commercial hardware is now becoming available. This report presents initial performance results of an ATM network and its suitability for use in a digital imaging network. Throughput of 10 Mbytes/sec was attained with Transmission Control Protocol/Internet Protocol using commercially available hardware.

Computer Communication Networks↗
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

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↗