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.

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.

Cystic fibrosis: combined hyperpolarized 3He-enhanced and conventional proton MR imaging in the lung--preliminary observations.

Four patients with cystic fibrosis (CF) were examined with combined hyperpolarized helium 3-enhanced and conventional proton magnetic resonance (MR) imaging. After inhalation of the polarized 3He gas, single breath-hold, gradient-echo images (resonant frequency of 3He) were obtained to depict lung ventilation. Conventional T2-weighted fast spin-echo (hydrogen) images were also obtained to depict morphologic abnormalities. 3He images were successfully and reproducibly generated that showed both morphologic abnormalities and, often more extensive, ventilation abnormalities. 3He MR imaging may provide a method for evaluating progression of pulmonary disease in patients with CF.

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.

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.

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.

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.

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.

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.

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.

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.

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.