This invention relates generally to diagnostic x-ray apparatus and particularly to an x-ray table system that is adapted for performing conventional radiography and tomography.
For conventional radiography, the patient is positioned on an x-ray transmissive table top. An x-ray tube is stationarily located above the patient and an x-ray image receptor, such as a film in a bucky tray, is stationarily located below the patient in the table housing. The focal spot of the x-ray tube is usually located over the center of the film and the central ray of the x-ray beam is usually perpendicular to the film plane. The differentially attenuated x-ray image that results from the x-ray beam penetrating the patient is projected onto the film in a cassette within the bucky tray so the image is recorded on the film. In projection radiography various organs including tissue and bone that are actually at different levels in the body are superimposed on the projected image on the radiographic film and give the appearance of lying in a single plane or level within the body. Sometimes this makes interpretation of the radiograph difficult.
As is known, projection tomography permits recording on film and visualization of a relatively thin single plane or level in the body by blurring or making uniformly gray all layers in the anatomy above and below the plane of interest. For performing tomography, the patient is positioned on the x-ray table top and the x-ray source is energized and translated in one direction along a horizontal line at a fixed distance from the plane of interest in the patient while the bucky tray containing the film cassette is translated in the opposite direction at a fixed distance from the plane of interest. As the x-ray tube is translated it is also rotated so that the central ray remains directed through the same point, usually the center, of the radiographic film. Coordinate opposite movement of the x-ray tube and bucky is usually achieved by connecting the bucky and x-ray tube together with a telescoping fulcrum arm. This arm is parallel to the central ray of the x-ray beam. A bracket or carriage is typically fixed at a side of the x-ray table top and extends above the top. The bracket has an element that can be raised or lowered relative to the plane of the table top. The fulcrum arm pivots on this element. The pivot axis is coincident with the plane of interest in the patient. Because the pivot axis is on the plane of interest, there is no relative movement between this plane and the x-ray beam, whereas, there is relative movement of the planes above and below the plane of interest so said planes are blurred in the projected image and a relatively sharp image of the plane of interest remains.
The traditional bracket that extends above the x-ray table top and provides the adjustable pivot element constitutes an interference with some x-ray procedures that are intended to be performed with x-ray apparatus of the type hereunder consideration. For example, the x-ray tube is usually mounted on a vertically extending column that is driven translationally in order to translate the x-ray tube and bucky as is required for tomography and as is required for ordinary radiography where the x-ray tube focal spot and central ray must be kept in alignment and perpendicular to the film plane. For some procedures, however, it is necessary to rotate the x-ray tube for projecting its beam, particularly its central ray, parallel to the table top instead of perpendicularly or at a limited angle away from perpendicular as is required for radiography. For example, for some procedures the patient is not located on the x-ray table top but is standing at some distance from the table in juxtaposition to a wall-mounted film cassette that can be raised and lowered to align with the anatomy of interest in the patient. At the same time, the x-ray tube must be rotated to cause its central ray to be projected horizontally and must be raised or lowered to align with the anatomy of interest so the projected image will fall on the film cassette. Very often, the tomographic arm bracket or pivot element support interferes with the beam path, especially when it is desired to radiograph the lower part of a patient who is standing in juxtaposition to a wall-mounted film cassette. Interferences can also occur when an attempt is made to project the x-ray beam laterally of the table top through a patient lying thereon for imaging on a film that is held in a vertical plane.
U.S. Pat. Nos. 3,838,286 and 4,335,312 illustrate tomographic apparatus wherein the tomographic fulcrum arm adjustable level pivot element is located in a structure that extends above the x-ray table top. U.S. Pat. No. 4,315,156 illustrates an x-ray table adapted for tomography wherein having the fulcrum arm pivot located above the table top is avoided by using a complicated mechanism wherein elements corresponding to the tomographic fulcrum arm and its pivot are located below the table and the action that they produce is transmitted through a shaft which angulates the x-ray tube during tomography and is concealed within the column that supports the x-ray tube for angulation and translation.