Patent Number: 047019425
Section: summary

BACKGROUND OF THE INVENTION The present invention relates to X-ray radiology and more particularly to the attenuation of X-rays by compressing filters to obtain an even X-ray field over the entire scan of the X-ray. At the present time is is known that when certain portions of the patient are to be X-rayed, those portions may be seen in more detail if they have received a suitable X-ray contrast media. For example, a barium iodine solution may be used as the radiopaque media in the alimentary tract. In an X-ray film dense bone appears white and other materials appear in various shades of gray. However, even with skillful technique, the X-ray picture may be obscured due to unequal attenuation of the X-rays by the patient's own body. Generally, the absorption of the body varies greatly so that the contrast between portions of the body cannot be reproduced within the explosure latitude of the X-ray film. Certain portions of the patient's body are thicker than others and certain portions have bones and organs which differently affect the X-ray picture. It would be desirable, in order to have an X-ray picture showing the greatest detail of the portion of the patient's body of interest, that the X-ray be evenly attenuated over the entire field (the entire scan) of the X-ray exposure. In one method of attenuation a solid aluminum three-dimensional filter(mask) is formed, see Erdhom & Jacobson, Primary X-Ray Dodging, Radiology 99:694-696, June 1971. The mask (filter) is positioned between the X-ray source and the patient, at the correct proportional distance. OBJECTIVES AND FEATURES OF THE INVENTION It is an objective of the present invention to provide, in radiology, an ink for an ink jet printer which will form an X-ray attenuation compensation mask for a relatively even distribution of the X-rays across the receiving field of an image receptor, the X-ray attenuation mask being formed by multiple passes of the ink jet printer head over an absorbent substrate. It is a further objective of the present invention to provide such an ink that may be used in a high-speed ink jet printer without clogging or settling or causing excessive corrosion or wear. It is a further objective of the present invention to provide such an ink that will, for each of its droplets, provide maximum X-ray attenuation, so that relatively fewer passes of the ink jet head over the substrate are required and the mask may be prepared in relatively less time, for example, in less than 30 seconds, to avoid inaccuracies which may occur if the patients move from their positions. It is a further objective of the present invention to provide such an ink that will be relatively inexpensive, so that an individual mask for each patient may be used in mass screening radiology programs. It is a further objective of the present invention to provide such an ink that will be retained in a substrate in a relatively thick layer and yet without spreading horizontally, to provide a mask having sharply delineated printed and unprinted areas. It is a further objective of the present invention to provide such an ink that will be deposited on the substrate with an exact selected thickness so that each of the areas (pixels) of the mask may attenuate the X-rays over a broad range of attenuation and with a reasonable number of degrees (extent) of attenuation. It is a feature of the present invention to provide a method in radiology of using an ink jet printer to prepare X-ray attenuation compensation masks. The masks are formed by depositing multi-droplets of ink on an absorbent substrate, such as thick blotting paper or a multi-cell honeycomb capillary structure. The radiology method includes the steps of determining the desired X-ray attenuation of each area (pixel) of the mask by taking an X-ray exposure and analyzing the X-ray intensity at each pixel of the image to provide intensity information. A computer is used to convert the intensity information into digital data in a digital feedback system. The digital data is used to control an ink jet printer. The printer deposits droplets on a substrate, preferably at a high rate. The number and location of the droplets is determined by the digital data. The X-ray attenuation mask comprises the substrate which is printed in selected areas (pixels) with the ink. Then the X-ray mask is positioned between the X-ray source and the receiving field (image) to attenuate the X-rays and produce an even intensity of the X-ray field. The entire procedure should be relatively fast, possibly during the suspension of the patient's respiration, i.e., holding one breath. The ink consists of a dispersant of a finely divided powdered metal in a liquid carrier. The metal is selected from the group consisting of cesium, cadmium, calcium, lithium and barium. In another embodiment the ink consists of a solute comprising a metal compound in a solution. The metal of the compound is selected from the group consisting of cesium, cadmium, calcium, lithium and barium. It is a further feature of the invention that the ink jet printer has a multi-orifice head, to reduce the number of passes of the head over the substrate. Preferably the substrate is divided into a field of at least 32.times.32 pixels and may be 64.times.64 pixels. In one embodiment the substrate is absorbent blotting paper, of at least 1/8-inch in thickness and, in another embodiment, the substrate is a multi-cell honeycomb capillary tube structure.