A Grid-Front Cassette

Abstract

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.