Manuel Viamonte Jr. Errors in Chest Radiography With 102 Figures in 296 Separate Illustrations Springer-Verlag Berlin Heidelberg New York London Paris Tokyo Hong Kong Barcelona Prof. Manuel Viamonte Jr., M.D., M.Sc. Chairman and Director Department of Radiology Mount Sinai Medical Center University of Miami School of Medicine 4300 Aiton Road Miami Beach, FL 33140 USA ISBN 978-3-540-52906-4 ISBN 978-3-642-86643-2 (eBook) DOl 10.1007/978-3-642-86643-2 Library of Congress Cataloging-in-Publication Data. Viamonte, Manuel, 1931-. Errors in chest radiography / Manuel Viamonte Jr., p. cm. ISBN 978-3-540-52906-4 1. Chest-Radiography. 2. Diagnostic errors. I. Title. [DNLM: 1. Diagnostic Errors-atla ses. 2. Thoracic Radiography-atlases. WF 17 V613e] RC941.V46 1991 617.5'407572- dc20 DNLMlDLC for Library of Congress 90-10322 CIP This work is subject to copyright. 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In every individual case the respective user must check its accuracy by consulting other pharmaceutical literature. Reproduction of the figures: Gustav Dreher GmbH, W-7000 Stuttgart, FRG 21/3130-543210 - Printed on acid-free paper Contents Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . I Technical Aspects. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 Film-Screen Combination. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 Techniques for Scatter Reduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 Digital Radiography. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 Automated Chest Unit. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 Summary.................. ...................... ........... 6 Errors in Chest Radiology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 Errors in Technique. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 Errors in Interpretation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 Difficult Areas of Interpretation ...... ~ . . . . . . . . . . . . . . . . . . . . . . . . 8 Pitfalls of Improper Technique and of Interpretation. .. .. ... .. .. 10 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 Atlas.......................................................... 15 Air-Soft Tissue Interfaces with the Mediastinum.. .. .. . . ... .. . .. 17 Importance of Using the High kVp Technique. . . . . . . . . . . . . . . . . . 18 Importance of Proper Centering. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 22 Underexposure.............................................. 24 Overexposure .............................................. " 25 Effect of Poor Inspiratory Effort . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27 Importance of Including a Lateral View. . . . . . . . . . . . . . . . . . . . . . .. 29 Importance of Including an Oblique View. . . . . . . . . . . . . . . . . . . . . . 33 Failure to Interpret Results Correctly . . . . . . . . . . . . . . . . . . . . . . . . . . 35 Difficult Areas to Assess . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44 Hyperlucency Which is Often Misinterpreted. . . . . . . . . . . . . . . . . .. 45 Importance of Correct Examination of the Upper Airways. . . . . .. 72 Importance of Correct Examination of the Bones ............. " 78 Importance of Correct Examination of the Soft TIssues. . . . . . . . .. 87 Importance of Correct Examination of the Abdomen. . . . . . . . . . . . 90 Importance of Adequate Knowledge of Patient's Clinical History 96 Importance of Careful Examination of the Hila. . . . . . . . . . . . . . . .. 106 VI Learn About Your Patient .................................... 109 Don't Procrastinate .......................................... 110 Value of the Esophagogram ................................... 111 Value of Linear Thmogmphy .................................. 117 Value of Computed Tomogmphy .............................. 122 Value of Ultrasonography ..................................... 127 Value of Arteriogmm ......................................... 128 Value of AMBER Study ...................................... 130 Acknowledgements. I am most grateful for the comments and constructive crit icism made by Jack Cullinan of the Eastman Kodak Company and his wife, Angeline Cullinan, author of Producing quality radiographs. My thanks are also due to Peter Balanag, Head of our School of Radiologic Technology, for his valuable comments. To my executive secretary, Peggy Litka, to my editorialist, Jan Holle, and to Lucy Kelley, program coordinator, my deepest appreciation. Introduction Chest radiography is the most commonly perfonned diagnostic radiological exam ination in the United States. More than 80 million chest radiographs are perfonned annually in the United States and this type of radiograph accounts for 30%-50% of the total volume of diagnostic studies. Standard chest radiographic examinations are difficult to optimize, primarily because of the seven- to tenfold greater attenuation of the mediastinum and heart than of the lungs. In order to obtain the best results, we must be able to see with distinct clarity the vascular markings of the lungs, particularly when these are superimposed on the rib cage, the bony structures, and the air-soft tissue interfaces of the mediastinum. The large variation in attenuation caused by the mediastinal structures cannot be recorded routinely on a radiograph with maximum image contrast. The lungs are shaped like a truncated cone. The apices are volumetrically smaller than the bases and are crisscrossed by bony structures (the upper ribs, clavicle, and sometimes the scapula and manubrium of sternum). Often in women, the density of the breasts overlaps the lung bases, and X-rays must therefore traverse more tissue. Despite the cephalocaudal increase in tissue volume, it is possible in most in stances to obtain a balanced density and contrast from the apices to the bases using the high kilovoltage peak (kVp) technique. Optimal image quality demands appro priate resolution and contrast that will pennit the detection of pulmonary opacities and lucencies and of mediastinal and chest wall abnonnalities. Resolution is a measure of the sharpness of small anatomical structures and is characterized by the modulation transfer function (MTF), which is defined as line pairs per millimeter (lp/mm). Contrast measures the difference in the attenuation of the X-ray beam which occurs between the bony structures and the soft tissues. It is influenced by object contrast (kVp and tissue attenuation coefficients) and scattered radiation. Technical Aspects The proper technique for chest radiography requires that the high kVp technique be used and maximal contrast, spatial, and temporal resolutions be obtained. A high-powered generator - ideally three-phase -, which allows the use of high kVp (120-140 kVp), should be used. If a single-phase generator is used, the same penetrations are obtained with 147 kVp, as with 120 kVp, when using a three phase generator. In addition to high kVp, ultrashort exposure allows detection of cardiac calcification as well as assessment of the pericardium. Ultrashort exposure is more advantageous for evaluating the heart than for studying the lungs. The radiation dose absorbed by the patient is lower with the high kVp technique than with the lower kilovoltage range (80-90 kVp). Although high kVp reduces contrast, presenting a grayer image, the total information content from the lungs and the mediastinum is greatly improved. This means better detection of parenchymal densities overlying bone in the lungs, and good delineation of trachea and proximal bronchi and of the mediastinal air-soft tissue interfaces. Film-Screen Combination Screen. Absorption ability is the capacity of the screen to capture incident X-ray photons, and conversion efficiency is the ability of the screen to convert the captured photons into light. When we looked for the best screen, the rare-earth phosphor screens appeared to be superior to conventional calcium tungstate screens. High speed calcium tungstate screens capture about 40% of the incident X-ray photons, but the rare-earth screens capture in the range of 60% of the incident X-ray photons. They also are more efficient in converting captured photons into light (5% vs. 18%, approximately). Because rare-earth intensifying screens admit the majority of their light in the green portion of the light spectrum, a special green-sensitive or orthochromatic film must be used in conjunction with these screens. Film. Extended-latitude film should be employed. This allows proper exposure of the lungs and proper contrast of the mediastinal structures. With extended-latitude film, increasing exposure of the mediastinum still permits lung density to fall into an adequate and acceptable range. 4 Techniques for Scatter Reduction Grids. Scatter radiation is increased in the 100-140 kVp range. A 10:1 or 12:1 grid appears to be the most appropriate for this kVp range (a 12:1 grid at 140 kVp provides similar results to a 10:1 grid at 120 kVp). The airgap technique, where the patient is at a distance from the film, usually 10 feet ("" 3 m), and no grids are employed, is recommended by some authors. Fixed vs. Moveable Grids. Some fine-line grids can be used as stationary ones. They will not produce grid lines that are objectionable. Many automatic changers use reciprocating grids. The use of a grid or a Bucky diaphragm improves contrast. Filtration oJX-Ray Beams. It is generally impossible to modify compensating filters for individual patients. Some manufacturers propose individual filters be used in given situations. Many people dismiss the use of these filters and believe that the high kVp technique and extended-iatitude film suffice. Digital Radiography Advantages over conventional film-screen systems can be achieved by using digital radiography. Among the advantages are the wider dynamic ranges allowing for unique contrast resolutions. It is also possible to have digital data immediately available for image transmission as well as multi-user display, manipulation, and archiving of images. On a theoretical basis, the radiation dose to which the patient is exposed can be potentially reduced by performing fewer repeat examinations. Therefore, for digital systems to be acceptable, they should first match the resolution provided by film-screen combinations. It has been stated that objects I mm in diameter require a spatial resolution of at least 2.5 lp/mm, a pixel size of 0.2 mm or smaller, and a contrast of 8-12 bits. Commercially available digital radiography systems do not yet match the overall resolution of the film-screen combination. A second objection has been the high cost of digital technology. Despite the high cost of digital radiography systems, the quality of digitized images has improved to such a degree that we can predict that in time they may replace conventional film-screen combinations. Automated Chest Unit New Advances. Automated chest units provide for phototimed exposure and pro duce consistent results. Most recently the advanced multiple-beam, equalization radiography (AMBER) system, in combination with the scanning equalization ra diography (SER) technique, appears to be the best automated system for chest radiography. The SER system was developed by Plewes and colleagues at the Uni- 5 versity of Rochester. The AMBER system was developed by Odelft Company of the Netherlands. With these two systems the end result is uniform film exposure and improved image quality (contrast and resolution). These systems control the local exposure delivered to the film and use a slit technique to provide a fan-shaped X-ray beam which scans the patient vertically. The system consists of an X-ray source, filtrated by 1 mm Al and 0.5 mm Cu, and collimated through a front slit into a thick horizontal fan beam (14" x 1.6"). This radiation fan passes through a 20-channel harmonica-like aperture, where the height of each of the channels can be modulated from fully open (2 cm at the patient) to virtually closed (0.2 cm at the patient). The height of these apertures is continuously controlled by a feedback microprocessor. The patient's chest is scanned, from bottom to top in 0.8 s through a radiolucent set of 20 horizontally positioned detectors, which provide the micro processor with the information needed to control the aperture heights, given the film speed and characteristic curve it has been designed to simulate. This horizon tal linear array of detectors is itself protected by top and bottom lead-collimating panels, forming a rear slit The film-screen combination, either in a cassette or fixed chamber, is exposed in a focal plane slit-shutter mode similar to some single lens reflex camera designs. The Beam Modulator. Each beam segment has a modulator poSitioned in front of the X-ray tube and a detector between the Bucky diaphragm and the film cassette. The modulator uses absorbers on the tips of piezoelectric actuators as attenuation elements. Voltage to the actuators causes the attenuation element to bend, thereby partially or completely absorbing local radiation. Actuator voltage is controlled via a feedback loop from a corresponding detector, each of which is composed of eight xenon detector strips. The beam segments from the harmonica-like beam modulator move across the chest field at constant speed with straight, aligned front edges. The rear edge of each of the 20 channels closes in to reduce the area of irradiatioQ at each moment of the exposure independently in each vertical track. This acts as a real-time exposure control mechanism, activated by the feedback signals from the detectors and processed by the microcomputer software, which simulates the sensitometric response of the film. Dosage Criteria. The AMBER system initially aims for the exposure level needed to produce a chest image in which the mediastinum is ideally represented. In a conventional situation this would lead to blackened images of the lung field. To avoid this, the modulator locally modifies the beam segment size to make the average image density of the lung field areas similar to that of the mediastinum, enabling the diagnostician to see microstructures equally well in all regions. This approach suggests that only the dosage required for the mediastinum and diaphragm areas is slightly higher than when a conventional radiographic approach is used. In addition, however, most scatter radiation effects are eliminated due to the slit-scan design. This means that some film blackening attributed to scatter radiation has to be compensated for by modest increases in primary radiation. This overall dosage increase ranges between 5% for thin patients and 40% for heavy patients, according 6 to Vlasbloem and Schultze Kool (1988) of the University Hospital of Leiden, The Netherlands. It is important to note that these calculations were done using a 400- speed film-screen system for both conventional and AMBER exposures. Using this system, chest images are achieved with much more readily detectable fine structures in all areas. The lung images obtained with the AMBER system are the best achievable today, and the images of the mediastinum and retrocardiac space are significantly improved and match the lung image quality. Posterior and inferior portions of the lung, especially behind the diaphragm, can be visualized even in the PA view, a fact which will possibly affect the decision to order routine lateral views. Many chest examinations are today done on medium-speed rare-earth systems (speed 250). AMBER exposure protocols are set up for high-speed rare earth systems (speed> 400). The potential to move to these higher-speed systems exists due to the strong signal content of the AMBER image-in-space. Regarding new types of X-ray detectors, storage phosphor imaging is one of the most promising new techniques. It was first developed by the Fuji Corporation (computer radiography) and is now offered by Philips Medical Systems, Konica, Eastman Kodak, General Electric, and others. The storage phosphor system is expensive and connnecting this digital imaging method to a picture archiving and communication system (PACS) will cost even more. Storage phosphor and equalization radiography appear to be the most promising and most developed methods. Summary The requirements for optimal technique in chest radiography are: 1. Optimal technical aspects (see Table 1) 2. Optimal inspiration 3. Proper centering of the patient 4. Two views (occasionally supplemented by oblique or special views) Table 1. Optimal technical aspects and conditions for chest radiography Generator Three-phase, 1000 rnA, 100 kW, 150 kVp X-ray tube 0.6 mm (10° target angle), 1.3 mm (12° angle), 10000 rpm Filtration 2.5 mm Al (0.5 mm inherent; 2 mm Al added) of X-ray beam Grid 103 lines, (minimum); 10:1 or 12:1 Intensifying screens High speed, rare earth Film Medium speed Processing Temperature Adjusted to radiographic technique and film-screen combinaton Replinisher rate Technique Distance, 72"; 140 kVp; automatic exposure control