Patent Number: 047019425
Section: description

DETAILED DESCRIPTION OF THE INVENTION The diagnostic system which uses the method of the present invention is shown in FIG. 1. It includes an X-ray tube 10 (X-ray generator) which produces X-rays enveloped in an imaginary cone 11. The X-rays are received by the image producer 12. In conventional radiology the image producer 12 is an image intensifier and a film holder in which film is positioned. The film, which is explosed by the X-rays, is developed in chemical baths to produce a negative image X-ray film. In the system of FIG. 1, the image producer 12 is an image intensifier and a transducer such as a video tube which is connected by line 13 to the digital video image processor 14 which produces a digital signal (digital data) corresponding to each area (pixel) of the video tube. The digital data is obtained by logarithmic transformation to enhance the image followed by A/D (analog/digital) conversion, i.e., digitization. A suitable real time digital video image processor (VIP) system to convert the received X-rays into digital data for each pixel of a field is described in the article, "A Digital Video Processor For Real Time X-Ray Subtraction Imaging", by Krueger, Mistretta, Lancaster, Houk, Goodsitt, Shaw and Riederer, Optical Engineering, Vol. 17, No. 6, Nov.-Dec. 1978, pgs. 652-657. It includes a standard radiographic transducer, such as a cesium iodine image intensifier, and a Plumbion TV video tube. The video output of the tube is sent to a pre-procesor including a block level clamp, a logarithmic amplifier, and a buffer. Then the signals are converted to digital data by an 8-bit analog-to-digital converter (ADC) and stored in three memories. The patient 15 is positioned between the X-ray tube 10 and the image producer 12. The cross-sectional profile of the X-ray image, with the patient 15 in position, is illustrated in FIG. 2. The opposite ends 16,17 are more intense, as the X-rays pass only through air, and the center 18 is less intense as the X-rays are unevenly attenuated (reduced) by the patient's body, for example, by scattering which reduces contrast. FIG. 3 illustrates the desirable field at the image producer 12 in which the field 19 is even across over its full extent (height and width). To obtained the even field 19, a compensation mask attenuator 20 is positioned between the X-ray tube 10 and the patient 15. The mask attenuator 20, without the patient, would produce an image as illustrated in FIG. 4. When the patient 15 is in place, and the mask 20 is also in place, the X-rays pass through both the patient 15 and the mask 20 and are attenuated by both. If the mask is correctly made, it will, along with the patient's body, attenuate the X-rays to produce an even field at the image producer 12, such an even field being shown in FIG. 3. The attenuation of the patient's body is not even; the skeleton, organs and thicker body portions will attenuate more than the thin body portions. The system of FIG. 1 computes the darkest pixel, representing the greatest attenuation of the patient's body without the mask, and produces a mask which was different attenuation values at its different areas (pixels) so that the attenuation of a pixel of the mask, plus the attenuation of the patient's body in the area corresponding to that pixel, will have a uniform value. The digital image processor 14 is connected to computer 21. The computer 21 controls the ink jet printer 22 which prints on an absorbent substrate which is in ribbon form. The ribbon, for example, one inch in width, is unreeled from source 23 and reeled up by take-up reel 24. In one type of ink jet printing a fluid ink is forced, under pressure, through one or more very small orifices in an orifice block which contains a piezoelectric crystal vibrating at high frequency (50-100,000 vibrations per second), causing the ink passing through the orifice to be broken into minute droplets equal in number to the crystal vibrations. The minute droplets pass through a charging area where individual droplets receive an electrical charge in response to a video signal. The amplitude of the charge depends on the amplitude of the video signal. The droplets then pass through an electrical field of fixed intensity, causing a varied deflection of the individual droplets (dependent on the intensity of the charge associated with the droplet). The deflected drops are allowed to infringe on the base substrate which is to receive the decorative or informative printed indicia. The ink deposited by the ink jet printer contains a metal which attenuates the X-rays. The ink may be used with an ink-on-demand type printer having a single ink jet head, which, however, operates at a slow rate, for example, 2.5 K (2500 droplets per second). Preferably, a multi-head ink jet array is used. The multi-head ink jet array is operated at a high rate for depositing droplets, the rate being in the range 50-100 K Hz (50,000-100,000 droplets per second) and, for example, is 66 K Hz. An ink jet array, available from Mead, Dayton, Ohio, has 2700 ink jets in a one-inch array. It deposits 2700.times.66,000 or 17,820,000 droplets per second in one pass of the array head. The droplets are deposited onto an absorbent substrate The substrate may absorb and retain many layers of droplets, forming a vertical pool, without excessive lateral spreading. In one embodiment the substrate is thick cellulose blotting paper, over 1/8" thick and preferably 3/16" thick. In an other embodiment, shown in FIG. 5, the substrate is a honeycomb structure formed in joined capillary tubes with the alignment of the tube axis being perpendicular to the plane of the substrate. The ink will be deposited in the tubes and the attenuation will depend upon how many droplets are deposited in each tube. Preferably there are sufficient droplets to form a "gray scale" of at least 30 degrees of attenuation, from zero to 100%, each degree being 3.33% of the scale. The honeycomb is flexible and may be re-used by cleaning out the ink. The substrate is small, for example, an inch square (2.54 cm) and is formed into imaginary discrete areas (pixels), preferably a grid of equal-sized squares. There are at least 32.times.32=pixels, i.e., each pixel is 1/32-inch square (0.079 cm); however, the substrate may be a 64.times.64 grid. Preferably the ink is a dispersant liquid system in which finely powdered metal is held suspended in a carrier fluid, for example, the metal may be 17%, by weight, of the liquid system. The metals are preferably selected from the group consisting of lead, barium, cadmium, calcium, cesium and lithium. Preferably the metal particles are less than 3 microns in diameter. Each droplet of the dispersant, i.e., a single layer, provides a 13% attenation of the X-rays. An organic carrier, such as methyl ethyl ketone, is used to transport the metal particles. The ink does not dry, or clog the ink jet device, and stays liquid for 2-4 weeks. Alternatively, the ink is of neutral Ph and is a solvent system in which the solute is a metal compound. The metal is selected from the group of barium, cadmium, calcium, cesium and lithium. The solvent system does not give as much attenuation per droplet as the dispersant system; for example, each droplet attenuates 1% to 2% of the X-rays. To abtain, for example, a 40% attenuation, it is necessary, with a 1% attenuation per drop system, to deposit 40 layers on each pixel. Suitable metal compounds (solute) and their solvents are shown below in the order of their attenuation, with the highest listed first. ______________________________________ Single Layer No. of Layers Thickness For Dynamic Compound Solvent (.mu.m) Range = 20 ______________________________________ barium bromide hot water .85 636 barium iodide cold water .92 364 cesium fluoride cold water 1.69 281 cesium iodide hot water .94 416 cadmium iodide MeOH .95 356 calcium iodide hot water 1.86 282 cobalt(ii) iodide hot water 1.53 249 lithium iodide MeOH 1.78 308 ______________________________________ In general, solvent system jet inks contain a dye, a solvent blend, a resinous component and an electrolyte in an amount effective to achieve desired drop deflection characteristics. The ink components must be in carefully balanced proportion to achieve successful operation. The effective amount of electrolyte will vary, depending on the original resisitivity of the ink and on the resistivity desired.