Patent Number: 053655656
Section: summary

BACKGROUND OF THE INVENTION 1. Field of the Invention The invention relates to the field of X-ray imaging equipment for producing a projection image on radiographic film or a reusable phosphor plate in combination with the moving tabletop of a computer tomography X-ray scanner. 2. Description of the Prior Art Analog radiography is a method by which projection X-ray images of the human body or other object are recorded on X-ray film or some other photosensitive surface. Analog radiology is known to provide excellent spatial resolution, but poor contrast resolution. Computerized radiography is a method by which projection X-ray images the human body or other objects are obtained by recording a latent image on a storage reusable phosphor plate which is then read under computer control by an interrogating light beam. The phosphor emits light of another wavelength which is proportional to the intensity of the X-ray. The emitted signal is digitized and displayed on a cathode ray tube monitor or laser printed on film or other media. Computerized radiography provides moderate spatial resolution and moderate contrast resolution which is improved over the contrast resolution realized by analog radiography. Computer tomography is a method by which the cross sectional images of a human body or other objects is obtained by rotating an X-ray tube and an opposing array of X-ray detectors about the human body or object. The collimated X-ray beam fans out laterally while it is narrowly collimated along its longitudinal axis. Computer tomography provides poor spatial resolution, but excellent contrast resolution. A very crude, low resolution projection image may also be obtained in a computer tomographic scanner by moving the object or human body through a collimated fanned beam and detector array. This is obtained by providing linearly moving the patient or object on a motorized tabletop on through a stationary collimated fan beam. Conventional slot analog radiography is also known. The procedure is to expose the patient with a collimated fan X-ray beam. Behind the patient is an X-ray barrier with a conforming slot defined through it. The collimated beam and its slotted barrier are moved in unison down the length of the patient as the patient stands between the two. Positioned behind the slotted X-ray barrier is a stationary film plate. The film plate is fixed relative to the patient and receives the projection X-ray image from the patient as the slotted barrier moves across it. The results are comparable to analog radiography, the only difference being that the patient is sequentially exposed to a collimated beam of X-rays as opposed to having an entire area simultaneously exposed to a shaped beam. The contrasting resolution obtainable by conventional slot radiography remains poor although the spatial resolution of the projection radiographs are good. Analog radiography and computerized radiography use traditional radiographic equipment whose fundamental technology has been substantially unchanged over the last 100 years. Computer tomography employs a radically different geometric design comprised of a gantry and motorized tabletop. In most if not all fully equipped radiology clinics and hospitals, one set of equipment is provided to produce high spatial resolution radiographs and another set of equipment to produce high contrast resolution axial radiographs. Hundreds of thousands of such units of each kind are used throughout the world. The cost of each of these units is substantial and currently both types of units are required to fully meet current standards of radiological practice. Therefore, what is needed is a single apparatus and methodology or some means by which existing radiographic equipment can be modified or used which would provide both the excellent spatial resolution of analog radiography while at the same time providing the high contrast resolution of computer tomography without the need to provide expensive duplicate sets of radiographic instrumentation. BRIEF SUMMARY OF THE INVENTION The invention is an apparatus for providing an analog radiograph of a patient. The apparatus comprises a fixed collimated X-ray source and an analog X-ray detecting assembly disposed immediately behind the patient for detecting projection X-ray images of the patient from the X-ray source. A mechanism is provided for moving the assembly in unison with the patient while the patient is being exposed to X-rays from the X-ray source. As a result, the analog radiograph is provided with high spatial resolution and contrast resolution. The collimated X-ray source is part of a computer tomography scanner. The mechanism for moving the assembly and patient in unison comprises a moveable tabletop upon which the patient is disposed and with respect to which the assembly is fixed. The moveable tabletop moves the assembly and patient past the fixed collimated X-ray source. The assembly comprises a rigid curved cassette carrier and a flexible film cassette disposed in the cassette carrier. The cassette carrier conforms the flexible film cassette to a predetermined curvature in order to minimize lateral magnification of the analog radiograph. The assembly further comprises a flexible X-ray grid. The flexible X-ray grid is disposed in the rigid cassette carrier and is conformed to the predetermined radius of curvature by the cassette carrier. The flexible X-ray grid may also be disposed in the flexible film cassette. In a retrofitted version of the invention the assembly is disposed on the mechanism for moving the patient. In an original-equipment-manufacturer (OEM) version the assembly is integrally combined in the mechanism for moving the patient. The invention can also be characterized as an improvement in a CT scanner having a moveable tabletop and a collimated X-ray source. The tabletop linearly moves the patient past the collimated X-ray source. The improvement comprises a curved analog X-ray detector for providing a record of a projection X-ray from the patient. An X-ray grid is disposed between the detector and the patient. The X-ray grid is fixed relative to the X-ray detector and patient so that the grid, detector and patient are moved in unison within the CT scanner by the moveable tabletop past the collimated X-ray source. As a result, an analog radiograph is produced with high spatial resolution and high contrast resolution. The invention is still further characterized as a method of providing a high spatial resolution and high contrast resolution analog projection radiograph comprising the steps of providing an X-ray grid and analog film X-ray detector at a relatively fixed position behind a patient. A collimated X-ray source is provided on a side of the patient opposing the X-ray grid and detector. The grid and detector simultaneously move in unison with the patient past the X-ray collimated source so that a high resolution analog radiograph is defined in the detector. The invention may be better visualized by turning to the following drawings wherein like elements are referenced by like numerals.