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Reflections |
1 From the Department of Radiology, SUNY Health Science Center at Syracuse, 750 E Adams St, Syracuse, NY 13210. Received August 10, 1999; revision requested September 1; revision received October 20; accepted October 20. Address reprint requests to the author.
Abstract
The radiology of 50 years ago was a primitive science compared with the radiology of today. Hospital departments were small and radiologists few in number. Night call was uncommon. Examinations consisted primarily of radiographs of the chest, bones, and gastrointestinal tract, although some early neuroradiologic studies were performed. Chest fluoroscopy was common. Film processing was done manually, often with poor results. Radiographic examinations of the chest were likewise unsophisticated by today's standards. Chest radiographs were made with low-kilovoltage, calcium tungstate phosphors and relatively large focal spots. There were no image intensifiers, nuclear medicine studies, ultrasonography, computed tomography, or magnetic resonance studies. How far we have come!
Index terms: Radiology and radiologists, history • Reflections
As a part of an ongoing series of articles in Radiology commemorating the year 2000, the Editor has asked me to compare and contrast thoracic imaging as it was at the beginning of my career with the way it is practiced today. This has proved to be an interesting exercise.
I first became involved with medicine as a career in the 1940s. I began medical school in 1947; several important breakthroughs in radiology and chest radiology occurred in the early years of my medical training.
CONVENTIONAL RADIOGRAPHY
Although portable units for chest radiography were available from several companies in the 1930s, the Picker Corporation was the sole supplier of the army field x-ray unit, which was widely used in the front lines as well as in mobile hospitals in the Second World War (Fig 1). James Picker, then president of the company, donated all profits from sale of the unit to the U.S. Treasury (1). Although these units were widely used for the diagnosis of trauma, especially fractures, they became the backbone of the diagnosis of chest disease (1).
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Morgan's phototimer was initially designed for use with photofluorographic units. Early in the history of chest radiography, camera photography of the fluorescent screen was developed as an alternative to radiography for documenting fluoroscopy of the chest. These efforts led to photofluorography as a means of screening for chest disease, notably tuberculosis. With this method (3), de Abreu instigated large surveys. Often, 80–1,000 individuals were examined per day. Photofluorography was widely used for chest screening examinations in the 1930s and 1940s. This continued into the 1950s, and as a staff radiologist in the U.S. Air Force in the mid-1950s, I routinely read approximately 100 such images per day from U.S. Air Force personnel. Eventually, the higher radiation dose required for photofluorography caused it to be abandoned as more modern technology was developed.
Another important advance in radiographic technique occurred in the 1940s. This was the development of the automatic film processor introduced by the PAKO Corporation of Minneapolis, Minnesota, in 1942 (1). About 40 minutes was required to process a single image, but 120 images could be processed in an hour. Images were hung on special hangers and then transported through the system. The automatic film processor was a great boon to the standardization of radiography. Prior to the advent of the automatic film processor, films were moved manually through the developing, fixing, washing, and drying cycles. Clothing was often destroyed by chemical stains. Radiographs were often of substandard quality. In fact, it was a frequent practice in radiography to overexpose the film when exposure factors were in doubt, the rationale being that one could always compensate by underdevelopment in the darkroom. Overexposed and underdeveloped films were commonplace. Sharp film corners were cut off manually using a "corner cutter."
A further advance in film processing occurred with the introduction in 1956 of the X-O-MAT unit, which used a nylon roller system instead of hangers (1). About 600 images could be processed per hour and single images in 7–10 minutes. Modern processors, of course, produce a finished film in 90 seconds. X-O-MAT units were bulky, being about 10 ft (3 m) in length and weighing about three-fourths of a ton (about 675 kg) (4).
In subsequent years, many technologic advances improved the quality of radiographs, including, of course, chest radiographs. Shorter exposures became possible, in part because of the development of more powerful generators. These generators permitted images to be obtained at 120–140 kVp, increasing film latitude. In 1968, rare-earth phosphors were adapted for use in screens for general radiography. The rare-earth phosphors replaced calcium tungstate phosphors, which had been in continuous use from before the turn of the century until the 1970s (1). Rare-earth phosphors are twice-as-efficient absorbers of diagnostic x rays as are calcium tungstate screens and emit much more light per x-ray photon absorbed (1). This benefit was, of course, important to chest radiography, with improvement in film speed and reduction in the patient dose.
Another advance during this period was the development of better stationary fine-line grids with more than 100 lines per inch. These grids improved the quality of bedside radiographs, particularly in heavy patients. Tubes with small focal spots (0.1–0.3 mm) were developed in the 1970s, and automatic collimation was mandated (5).
In the 1980s, a major change occurred in radiography with the development and refinement of digital radiography. In all digital systems, the x-ray beam exiting the patient is captured by a detector system. In 1983, Sonada and colleagues introduced a scanning-laser stimulated luminescence technique that used photostimulable phosphors (1). During exposure, the phosphor captures electrons; the energy is released as light when scanned by a high-intensity laser. Balanced exposure results, and therefore this technique has been rather widely used for bedside chest radiography, where repeat examinations have essentially been eliminated. In 1983, Plewes and Vogelstein (6,7) discussed computer equalization and introduced scanning equalization radiography. A variant of this system is available and is sold as the advanced multiple-beam equalization radiography (AMBER) system (8,9). Both of these digital systems have shown considerable diagnostic advantage over older conventional radiography.
CHEST FLUOROSCOPY
Another innovation of the 1940s was the development of the image intensifier by J. W. Coltman of Westinghouse in 1948 (1). A commercial unit was first marketed by Westinghouse in 1953 (1). With this unit, a brightness gain of 1,000 became available for fluoroscopy (1). Cone vision, rather than rod vision, was now possible (1). Prior to this innovation, dark adaptation with red goggles for 15–20 minutes was required before fluoroscopy could begin. Since little else could be done during this time, it was commonly used for drinking coffee and swapping jokes. With the advent of the image intensifier, fluoroscopy of all areas of the body, including the thorax, took a giant step forward, and television display of the image became possible. Meaningful recording of images in motion became a reality; cineradiography was introduced in 1954 (5).
Chest fluoroscopy was a popular procedure a generation ago, and most hospitals scheduled several such examinations per day. One common indication was to determine cardiac chamber size because, of course, echocardiography was unavailable. Patients were examined fluoroscopically in various projections, and multiple spot radiographs were obtained with barium in the esophagus. It was usually easy to determine if the left atrium was enlarged; it was usually difficult to determine the size of the right atrium. Examinations to evaluate pericardial effusion also were frequent. Overall diminution in cardiac pulsation and greater pulsation of the posterior cardiac wall in the lateral projection were thought to be signs of effusion. Other indications for fluoroscopy included the investigation of foreign bodies determined by air trapping and appropriate mediastinal shift and the evaluation of diaphragmatic paralysis. Some radiologists use these as indications for fluoroscopy today.
ROENTGEN KYMOGRAPHY
Roentgen kymography was developed by Goldenthal et al (10) in the 1950s as a technique for assessing diaphragmatic movement. The kymographic grid consisted of a series of lead strips 30 mm wide and 1 mm apart. The grid was stationary at the level of the diaphragm, with the lead strips parallel to the body. A prolonged x-ray exposure was performed while the x-ray film moved at right angles at a fixed speed controlled by a motor-driven timer. As the patient performed a single forced expiration, the excursions of 1-mm segments of each hemidiaphragm were recorded (11). Roentgen kymography was also used extensively as an objective record of cardiac pulsations (Fig 2) in a variety of diseases, including pericardial effusion and after myocardial infarction (12).
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Another popular radiographic technique of a generation ago was bronchography. Although the technique had some usefulness for studies of congenital anomalies of the lung, bronchography was most frequently used to diagnose bronchiectasis and to plot the involved segments for surgery (Fig 3). Bronchiectasis was a common disease in those days, and most fluoroscopy schedules in busy hospitals contained two or three such studies each day.
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With the development of computed tomography (CT), bronchography underwent a rapid demise. Certainly, this is just as well, because it was a miserable examination for the patient to undergo and not much fun for the radiologist either.
CONVENTIONAL (ANALOG) TOMOGRAPHY
Another popular technique in early chest radiology was conventional or analog tomography, which was introduced by Ziedses des Plantes in 1931 (1). The basic principle of tomography was to produce selective visualization of a predetermined layer of tissue to the exclusion of structures lying superficial or deep to it. The technique involved reciprocal movement of the x-ray tube and film so that the image of only a thin section was recorded on the radiograph (15,16) (Fig 4). The level of the tomographic "cut" was controlled by the ratio of the tube-object distance to the object-film distance; the level was altered by varying the ratio. The thickness of the section was determined by the length of the tube-film travel—the shorter the excursion, the thicker the layer recorded. Very thin layers could be recorded, as well as thicker sections of tissue referred to as zonograms. For some time, rectilinear tomography, with the tube and film moving in opposite linear directions, was most common. The images from these studies were popularly referred to as planigrams. However, a major limiting factor with planigraphy was its failure to obscure or "blur" shadows of linear structures that lay in the same direction as the tube-film excursion.
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An interesting approach that represented a forerunner of transverse imaging was transverse tomography. With this technique, the body was "cut" in cross section, rather than longitudinally (15). The technique involved reciprocal movement of the patient and the film, with the x-ray tube remaining stationary (Fig 5). Images made with this technique showed marked geographic distortion, and resultant radiographs were difficult to interpret. For these reasons, transverse tomography was never widely used.
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THE PRACTICE OF THORACIC IMAGING
It is interesting to reflect on the differences in the way radiology was practiced a generation or more ago and the way it is practiced today. Solo practitioners were common then, and hospital radiology staffs usually numbered two, three, or four individuals. The day always began with the fluoroscopy schedule, which generally was considerably larger than the schedules of today. Fluoroscopy continued until noon—and sometimes later. Special examinations such as bronchography and myelography were commonly performed in the afternoon.
In larger offices or hospital departments, image reading continued throughout the day. Multiviewers were not available until the 1960s, and images were read on banks of four or eight view boxes. Images were commonly mixed and, with the exception of fluoroscopic images, were usually not "batched" by type of examination. Each radiologist was a true generalist and read images of all types, although in some departments, one individual might be recognized for his or her expertise in a given area. Residents, and the rare fellow, were allowed to perform procedures and read images on their own after their mentors were assured of their competence. Reports were dictated into a standard dictating machine, although rarely reports were dictated directly to a secretary.
The typical work-up of a patient who was suspected of having or known to have bronchogenic carcinoma included posteroanterior and lateral chest radiographs (usually obtained in the 70- or 80-kV range), sometimes supplemented by an oblique a lordotic view. Conventional tomography in frontal and lateral projections would usually follow (Fig 6). Oblique tomograms were often made to "lay out" the central bronchi in profile (Fig 7). We were only moderately successful in evaluating hilar and mediastinal disease with conventional tomography.
Today, of course, CT has become the backbone of the work-up of bronchogenic carcinoma. CT can be used to clearly depict the morphologic structure of the lesion and is useful in assessing direct mediastinal extension and, to a lesser extent, direct chest wall invasion. CT is our best modality for assessing enlargement of lymph nodes, particularly in the mediastinum, but also in the axilla. With contrast agent enhancement, vascular invasion can be evaluated. Bronchial invasion or displacement is usually shown well. Special algorithms allow for three-dimensional rendering of bronchial anatomic and pathologic findings (18). In most radiology departments and offices, the thoracic CT study covers the upper portion of the abdomen, where it can show liver and adrenal metastases.
The technologic advances in CT since 1975 have been truly remarkable. Early machines were slow, respiratory motion was a problem, and resolution was poor. Nevertheless, most of us believed that the images were a fantastic advance—and of course they were. For the first time, we could produce images in the transverse plane that were readable. The high-speed scanners of today produce very thin sections with exquisite detail in one or two breath holds. Examination throughput has been markedly increased.
Thin-section CT of the thorax is capable of showing smaller metastases in the lung but, in the opinion of this observer, has not added greatly to our evaluation of pulmonary neoplastic disease. Thin-section CT can, however, be used to make specific diagnoses in some diseases (eg, Langerhans cell histiocytosis and lymphangioleiomyomatosis). It is helpful in detecting minimal disease, in assessing the progress of disease and response to therapy, and in aiding in the selection of sites for lung biopsy. CT may prove useful in the selection of patients for lung reduction surgery for emphysema (19).
Another clinical problem that was common years ago and is equally frequent today is that of the solitary pulmonary nodule. In the days before CT, the conventional radiographs demonstrating the lesion might be supplemented by a low-kilovolt radiograph of the lesion to determine whether calcification could be demonstrated within the lesion. Subsequently, conventional tomography was usually performed to determine the morphologic structure of the lesion in greater detail and to assess possible calcification. Diffuse calcification, arcuate calcification, "popcorn" calcification, and central calcification were considered signs strongly suggestive of a benign lesion. Eccentric calcification was considered a nondiagnostic finding. A search was always made for old images. If the lesion had been present on earlier studies and was unchanged for a period of 2 years or more, a benign cause was assured.
Today, the finding of a solitary nodule would also initiate a search for old images, and CT would be undertaken. The general aims of the examination would be to evaluate the morphologic structure of the lesion, to assess for calcification, and to determine if other nodules were present.
Some years ago, it was common to assess the attenuation of the solitary pulmonary nodule by determining its mean CT number in Hounsfield units. Although this method produced statistically good results, it has waned in popularity, at least at our institution. More recently, an approach to evaluating the lesion has used a change in Hounsfield units after contrast material enhancement. Swenson et al (20) found that a median enhancement of 40 HU occurred in malignant nodules. Using 20 HU as a threshold for distinguishing malignant from benign lesions, these authors reported a sensitivity of 100%, a specificity of 76.9%, and an accuracy of 92.6%. Despite radiologic efforts to prove that a nodule is malignant, many are surgically removed even if the findings from needle biopsy have proved negative for malignant tissue.
Thus far, the role of magnetic resonance (MR) imaging in the evaluation of the thorax has been confined largely to the heart and major vessels. MR imaging has proved to be of considerable value in assessing the extent of superior sulcus tumors. In this regard, MR imaging seems to be superior to CT in most cases. In occasional cases, MR imaging is useful in the tissue characterization of mediastinal lesions. Undoubtedly, MR imaging will assume a larger role in thoracic imaging as technology evolves.
It is truly amazing to see how far we have come in the sophistication of our thoracic imaging evaluations in the past 50 years. I have no doubt that innovation and knowledge will continue to be added far into the future.
References
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