Stationary Grid Research Articles

A simple and accurate method of x-ray pelvimetry.

If one agrees that x-ray pelvimetry is ever of value, one must demand that the method used fulfill the basic criteria of safety, accuracy, ease of taking films, and ease of reading them. Because other methods fail in some or several of these requirements, a new procedure has been devised. It is based on the principle that, if the distance from the object to the film is known, the distortion of measurement due to the divergence of the rays may be overcome by reference to a known correction factor for that distance, provided the tube-film distance remains constant. This method embodies the advantages of simplicity for the radiographer, a built-in method of checking any error on the part of the technician, a minimum of movement for the patient (which is a particular advantage when she is in labor), ease of film reading and of measuring, and maximum accuracy. A special seat has been constructed (Fig. 1) to be placed on the x-ray table. Under the seat is a chamber for a film cassette; at one side another (vertical) chamber accommodates a second cassette. An adjustable back rest permits correct positioning of the patient for a true inlet film. On the top of the seat, running in an anteroposterior direction, is a metal measuring rod, 1 cm. in diameter, with circular grooves around it at 1-cm. intervals. This is 21 cm. from the vertical film cassette. The patient is seated in such a manner that the front end of the measuring rod is visible in the midline, directly beneath the symphysis pubis, and the other end may be seen between the cleft of the buttocks, directly in the center of the sacrum, at the back. Two films are taken, one lateral and one supera-inferior, each with a focal-film distance of 40 inches. Before the patient is seated, a sheet of lead is placed over the left half of the seat; this cuts down secondary radiation while the lateral view is being obtained, and can then be removed. A second lead sheet, on the bottom of the horizontal slot under the seat, remains always in place; the film cassette for the vertical view fits above this lead sheet. A stationary grid is used for each film. With a fixed (40 inches) focal-film distance, a grid is made as in Figure 2, which shows the equivalent of a centimeter scale at points from 1 to 24 cm. above the seat top. A transparency is made of this grid on x-ray film. On this two other distorted scales are marked. Both of our views are taken with a focal-film distance of 40 inches. Since the measuring rod on the seat top is at a fixed distance from each film, the distortion of the centimeter grooves on the rod is the same for all inlet films and for all lateral films. These two scales are included on the transparency. Both films should be on the viewing box at the same time (Figs. 3 and 4).

The Johns Hopkins fluoroscopic screen intensifier.

In recent years, considerable attention has been focused upon our need for brighter fluoroscopic screens. It has been pointed out that the clarity of fluoroscopic vision should be improved many times, that the need for dark adaptation before fluoroscopy should be eliminated, and that the radiation dosage delivered to the patient and radiologist during fluoroscopy should be reduced if brighter screens were available to us. A few years ago work was begun in at least three laboratories in this country to develop devices by which fluoroscopic screens may be brightened or intensified. Coltman (1) at the Westinghouse laboratories in East Pittsburgh undertook investigations which have recently culminated in the development of an electronic image tube capable of intensifying the fluoroscopic screen approximately one hundred and fifty times. A short time later, Moon (2), at the University of Chicago, began work directed toward the development of a screen intensifier based on the “flying spot” system used in television. Although practical results have not yet been achieved, Moon (3) anticipates large gains in screen brightness with this system. Early in 1948, studies in screen intensification were undertaken at the Johns Hopkins Hospital. Our first research was concerned with investigation of the fundamental physical and physiological factors influencing fluoroscopic vision (4). Work was then begun on the development of a screen intensifier which, we hoped, would yield gains in screen brightness of 1,000 times or more. This instrument has just been completed and placed under test in our laboratory. It has not been described heretofore. Constructional Details The complete intensifier, arranged for clinical study, is illustrated in Figure 1. It compris es three principal units: (a) a conventional fluoroscopic x-ray generator operating at kilovoltages ranging from 70 to 100 kv.p. and at a tube current of 5 ma.; (b) an x-ray image detector; (c) a fluoroscopic viewing unit. The principles upon which these three units operate together may be visualized in Figure 2. The x-rays produced by the fluoroscopic generator, A, pass through the anatomical structure under examination, B, and enter the x-ray image detector unit. Within this unit, the radiation first passes through a stationary wafer grid, C, and then impinges upon a fluorescent screen of a conventional zinc sulfide type, D. The images appearing on the fluorescent screen are then focused on the sensitive surface of an image orthicon, G, by a folded Schmidt optical system consisting of three plane mirrors, M, a corrector plate, P, and a spherical mirror, F. The image orthicon, an electronic tube used in many television cameras, converts the fluorescent images into an electric current which is amplified many times, first by a preamplifier, H, and after that by a final amplifier, J.

Fluoroscopic preselection of the tomographic plane in chest lesions, with a note on the use of a double grid.

1. Fluoroscopy is suggested as a method to enable the preselection of tomographic planes of section in pulmonary lesions. 2. The principle of the method as applied to the oblique tomographic views for a given lesion at any angle of rotation of the patient is discussed, and its usefulness demonstrated. 3. The “double grid technique” is advocated in tomography. The effect of the stationary grid is briefly discussed and its efficacy illustrated by radiographs.

The Scientific Exhibits

There were thirty-nine scientific exhibits entered at the Thirty-third Annual Meeting of the Radiological Society of North America, held in Boston, Nov. 30–Dec. 5, 1947. On the basis of subject matter, there were seven groups: skeletal system, eight exhibits; chest, seven exhibits; gastrointestinal system, four exhibits; genitourinary system, three exhibits; therapy, eight exhibits; radioactive isotopes, three exhibits; miscellaneous, six exhibits. The space available for the exhibits made it impossible to arrange them in groups according to the above classifications. The following awards were given: First Award: Stanley A. Wilson, M.D., Salem Hospital, Salem, Mass., for his exhibit on “Granulomatosis of Lung, Probably Due to Beryllium.” Second Award: John F. Holt, M.D., and Edwin M. Wright, M.D., University Hospital, Ann Arbor, Mich., for their exhibit on “Osseous Manifestations of Neurofibromatosis.” Third Award: John D. Camp, M.D., Mayo Clinic, Rochester, Minn., for his exhibit on a “Grid Front Cassette—A Practical Application of the Stationary Grid.” Honorable Mention went to K. E. Corrigan, Ph.D., H. S. Hayden, Ph.D., E. F. Lang, M.D., and L. Reynolds, M.D., Harper Hospital, Detroit, Mich., for their exhibition “Diagnostic Tracer Studies with Radioactive Iodine.” Exhibits Pertaining to the Skeletal System Hampar Kelikian, M.D., and E. K. Lewis, M.D. (Chicago, Ill.): Arthrograms. Lipiodol-outlined arthrograms and pneumoarthrograms of the knee, ankle, elbow, and acromioclavicular joints were exhibited. The normal anatomy, capacity, contour, content, and communications of these joints as outlined by air injection were shown. Isadore Meschan, M.D. (University of Arkansas, Little Rock, Ark.): An Atlas of Pneumoarthrography of the Knee. This exhibit utilized diagrams and tracings of radiographs together with tables summarizing statistical data on pneumoarthrography of the knee. E. S. Gurdjian, M.D., J. E. Webster, M.D., and H. R. Lissner, M.S. (Wayne University College of Medicine and Grace Hospital, Detroit, Mich.): Mechanism of Production of Linear Skull Fracture— Studies with the Stresscoat. The material presented included experimental work on dogs and monkeys and human studies on cadaver and dry skulls with the stresscoat technic. This involves the application of a strain-sensitive lacquer on the external and internal surfaces of the skull. Deformation of the skull from blows causes cracks in the lacquer, showing the pattern and direction of the strains. John F. Holt, M.D., and Edwin M. Wright, M.D. (University Hospital, Ann Arbor, Mich.): Osseous Manifestations of Neurofibromatosis. This exhibit showed many skeletal abnormalities associated with neurofibromatosis (von Recklinghausen), including disorders of bone growth, bowing and pseudoarthrosis of the lower leg, intra- and extra-osseous erosive defects, periosteal thickening and profound congenital anomalies.

A Grid-Front Cassette

Since the introduction of the stationary grid for roentgenographic purposes, roentgenologists have found the device useful in circumstances in which a conventional Potter-Bucky diaphragm cannot be employed. The use of the stationary grid in many instances, however, has been complicated by a difference in the size of the grid unit and the various cassettes available. When the grid is used in the vertical position, various makeshift devices, such as sandbags, adhesive tape, clips, etc., have been necessary to hold the grid in apposition to the cassette. To overcome this difficulty and obtain a grid-cassette combination that could be placed quickly in all positions, it was felt that the grid should be an integral part of the front of the cassette. This was achieved by removing the bakelite front of a Picker cassette and replacing it with a metal Lysholm grid cut to corresponding size. The front of the metal Lysholm grid was protected by a thin bakelite or plastic sheet. Because of the thinness of the Lysholm grid, the combined thickness of the grid and protective sheet was the same as the bakelite front that had been removed. The result was a grid-front cassette which was the same size in all dimensions as a conventional cassette (Fig. 1). This combination has many advantages that are readily apparent. The detail of the resulting roentgenogram is improved, the shadows of the grid lines are narrower because of lessened distortion, and the cassette because of its standard size can be used in any cassette tunnel or stereoscopic shift device. A similar grid-front cassette has been made for use of the roentgenologists at the Mayo Clinic by replacing the bakelite front of a standard Kelley-Koett cassette with a Liebel—Flarsheim stationary grid and protecting bakelite front.1 The result was a unit similar to that first mentioned but about 1/8 inch (0.32 cm.) thicker than the standard cassette. This disadvantage can be eliminated by a slight change in the design of the cassette. Any other cassette likewise can be adapted to this purpose. Because of the difference in construction of the Lysholm and Liebel—Flarsheim grids, there is a difference in the quality of the resulting roentgenograms that in my experience favors the metal grid. My colleagues and I have used these grid-front cassettes for nearly a year and are frequently finding new applications for them, since they can be made in any standard size. They have become indispensable for bedside examination of structures that normally would require a Potter-Bucky diaphragm. Excellent bedside roentgenograms of the skull, chest, spinal column, pelvis, urinary tract, etc., are now easily obtained. In the operating room the grid-front cassette has proved most desirable in the examination of fractured hips and for cholangiograms. It is used routinely for certain projections during encephalography, ventriculography, and other special examinations.

A Tomographic Attachment suitable for most X-ray Plants

An appliance has been described, which allows tomography to be carried out with almost any existing X-ray set in both horizontal and vertical planes, with and without a mobile or stationary grid. The appliance is simple and foolproof in construction, cheap to manufacture, small in bulk and light in weight. The radiological results compare satisfactorily with those of other tomographic attachments. Its uses are, in common with tomography generally, localisation of lesions obscured by over-lying dense tissue.