Patent Document

CROSS REFERENCE TO RELATED APPLICATION 
     This application is a continuation of U.S. patent application Ser. No. 09/450,031, filed Nov. 24, 1999, U.S. Pat. No. 6,188,501. 
    
    
     BACKGROUND 
     (1) Field of the Invention 
     The invention relates to digital capture of x-ray images. More specifically, the invention relates to capturing of x-ray images from both transmissive film and reflective filmless plates. 
     (2) Background 
     Various scanners for digitizing images from x-ray film are commercially available. For example, Radiographic Digital Imaging of Compton, Calif. produces a lightbox scanner sold under the trademark COBRASCAN® which uses a charge coupled device (CCD) to capture the image contained on a standard x-ray film when the x-ray film is transported past a reading window. 
     While traditional x-ray film has been ubiquitous for decades, more recently, filmless x-rays have been taken using a phosphorescent plate. The phosphorescent plate is reflective and erasable, allowing for repeated reuse. An x-ray impregnates the plate with energy which, when subsequently exposed to a particular excitation, is released, recreating the image. Various companies produce readers for these filmless plates, including Fuji Film Ltd. and Eastman Kodak. Such readers typically employ a flying spot laser and photo multiplier tube. The photo multiplier tube captures the image corresponding to the energy being released by excitation of the flying spot laser. The plate is typically transported by a set of rollers which necessitate that the phosphorescent plate be flexible and, in any case, over time, causes a deleterious effect on the plate, resulting in limited reusability. Additionally, these readers are incapable of digitizing conventional x-ray film. Thus, a radiology department is required to have two separate devices for the digitization of images from the different media types. 
     BRIEF SUMMARY OF THE INVENTION 
     A method and apparatus to permit digital capture of images from both transmissive and reflective media is disclosed. A laser or other source of excitation radiation is coupled to a mounting surface to be in optical communication with a reading window when installed on a scanner. A rear casing is coupled to the mounting surface to engage a housing of a scanner, the housing defining the reading window. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a diagram of the image capture device of one embodiment of the invention. 
     FIG. 2 is a diagram of the image capture system of FIG. 1 transporting a medium. 
     FIG. 3 is a cross-sectional view of a scanning system of one embodiment of the invention. 
     FIG. 4 is a cutaway view showing the digital back of one embodiment of the invention. 
     FIG. 5 is a sectional view showing an image capture camera which captures an image reflected by a mirror from a reading window. 
     FIG. 6 is a top plan cross-sectional view of a system of one embodiment of the invention. 
     FIGS. 7 and 8 show a filmless x-ray cassette which may be used with one embodiment of the invention. 
    
    
     DETAILED DESCRIPTION 
     FIG. 1 is a diagram of the image capture device of one embodiment of the invention. Lightbox and dual scanner unit  10  includes a housing  12  that defines a translucent viewing surface  14  and a reading window (not shown). The unit  10  is mounted vertically such that reading of media occurs in a vertical plane. This vertical mounting also reduces the likelihood of dust contamination on the internal optics of the unit  10 . In one embodiment, the viewing surface is illuminated from within by a pair of fluorescent tubes mounted within the housing  12 . In an alternative embodiment, camera  30  is replaced with a photo multiplier tube (PMT). In such embodiment, an optical wave guide may be used between the PMT and the reading window. ISAs and PMT are generically referred to as “sensors” herein. A digital camera  30  which includes an image sensing array (ISA), such as a charge coupled device (CCD) or a complementary metal oxide semi-conductor (CMOS) device is disposed within the housing  12 . A digital back  16  contains a laser  40  that is described in further detail below. Switch  22  may be a multi-positional switch which selects a mode of operation, including lightbox only, transmissive scan, or reflective scan. Alternatively, switch  22  may merely turn the power to the system on, while mode selection is software driven or provided by another switch, button or keypad. 
     A bar clip  18  is used to hold a medium to be scanned. In this instance, the medium may be a transmissive traditional x-ray film, or a reflective phosphorescent plate. It is desirable that the bar clip be offset from viewing window  14  such that media hanging in the bar clip is not in surface contact with the window. This avoids frictional degradation of the film or plate. Lightcover  20  covers a vertically mounted fluorescent tube which provides the backlight source for scanning transmissive media. This backlight source is disposed a displacement from the reading window (not shown) such that when a transmissive medium is transported by the transport mechanism past the reading window, the light source shines through the transmissive media permitting the sensor to scan the image line by line. The transport mechanism in one embodiment of the invention includes a stepper motor and a rack-and-pinion drive which drives at the bar clip during scanning. 
     FIG. 2 is a diagram of the image capture system of FIG. 1 transporting a medium. The media  50  is retained in bar clip  18  and transported under the scanning light source past the reading window. In the shown embodiment during scanning, the bar clip will transport the media from left to right between the reading window and the backlighting source and then return the media to be disposed over the viewing surface  14 . 
     FIG. 3 is a cross-sectional view of a scanning system of one embodiment of the invention. The backlight  21  for reading of transmissive media is revealed in this cross-sectional view. Backlight  21  is mounted vertically under lightcover  20  a displacement from reading window  34  which permits the transport mechanism  18  to transport media  50  between the reading window  34  and the light  21 . Reading mirror  32  and the laser redirection mirror  48  are also shown. 
     FIG. 4 is a cutaway view showing the digital back of one embodiment of the invention. A mounting surface  42  is coupled to a rear casing  52 . A laser  40  is mounted on the mounting surface  42 . The mounting surface  42  defines a optically transmissive window  58  which permits the laser  40  to be in optical communication with a reading window. A mirror  48  is mounted on the mounting surface  42  and reflects the laser light incident thereon through the optically transmissive window  58  and on through the reading window (not shown). 
     Because of the energy density required to excite typical existing phosphorescent plates to release the image stored thereon, the number of options for laser  40  are possible. One option is to have the laser be a twenty watt laser. With a twenty watt laser, using a simple mask, a line of laser light can be created and reflected by mirror  48  to excite the plate directly. In one embodiment, the line created has a width of fifty microns. Embodiments using a twenty watt laser tend to be quite expensive. Alternatively, a scan pattern may be created by a scan pattern creator  46 . The scan pattern should be created at a speed much faster than the response time of the ISA such that the ISA “sees” the scan pattern as a unit. In such embodiment, laser  40  may be a continuous spot laser and the scan pattern creator  46  may be a piezo electric mirror or a rotating prism driven by motor  44 . In this manner of relatively low wattage, continuous spot lasers can be used to create a line by rotating the mirror or prism back and forth rapidly at a rate higher than the response rate of the ISA, thereby exciting a continuous line on the phosphorescent plate and allowing line-by-line capture of the image by the ISA. 
     For example, laser  40  may be a diode laser at a 680 nm wavelength with a spot size of fifty microns. The pattern generated for excitation of lines of a typical phosphorescent plate is a fourteen inch line with a power density of ten mW/spot. This then dictates the wattage of the laser and the rate of rotation of the scan pattern generator. In some embodiments, such as those using PMT, laser  40  may be a flying spot laser. 
     FIG. 5 is a sectional view showing image capture camera  30  which captures an image reflected by reading mirror  32  from reading window  34 . A pair of horizontally mounted fluorescent tubes  31  illuminates viewing surface  14  from within the housing  12 . As previously noted, all of these components are mounted within housing  12 . The reading mirror  34  ensures optical communication between the camera  30  and any media passing over a reading window. 
     FIG. 6 is a top plan cross-sectional view of a system of one embodiment of the invention. Digital back  16  couples to housing  12  to form an enclosure that prevents contaminants from entering. In one embodiment, the digital back is desired to provide an easy retrofit for existing COBRASCAN® scanners. 
     The laser  40  focuses its beam on scan pattern creator  46  which directs the pattern created, which in one embodiment is a line, onto mirror  48 . Mirror  48  is at an angle to the pattern creator  46  such that the created line of laser light is directed by mirror  48  at an angle past reading mirror  32  through reading window  34 . Reading mirror  32  is positioned at a 45° degree angle to both camera  30  and reading window  34  such that it reflects a line of the image just beyond the exposure to laser light. In this manner, if the medium transported is a phosphorescent plate, released energy signature corresponding to an image is stored by the camera  30 . If the medium is an x-ray film or other transmissive medium, it is backlit by the light source in light source cover  20  and that image is captured by camera  30 . Notably, if the medium is transmissive, the line of laser light will pass through and the coefficient of reflection is such that it will not be reflected to the mirror  32  and captured by the camera  30 . Accordingly, operating the laser while scanning transmissive media results in no significant degradation of the images captured. Thus, in one embodiment of the invention, media images are simultaneously backlit and exposed to laser light. In such cases, the system need not know what mode it is operating in. The sensor merely captures the image reflected by reading mirror  32  without regard to whether the media is transmissive or reflective. 
     FIGS. 7 and 8 show a filmless x-ray cassette which may be used with one embodiment of the invention. The cassette includes a casing  100  having a cover  102  which slidably engages the casing  100  and is held by a pair of continuous springs  104  such that it is exposed when the cover is open. The cover is provided with a lip  106 . When the cassette is held by the bar clip of one embodiment of the invention, the lip  106  hooks over the left end of the housing. Then as the cassette is transported in front of the viewing window, the cover slides off by virtue of the action of the transport mechanism and having the lip hooked on the left edge of the housing, thereby exposing the phosphorescent plate  150  inside. As the transport mechanism returns to its pre-scan position, the continuous springs pull the cover into a retracted position. In this manner, the contact with the phosphorescent plate is minimized such that the useful life is vastly increased. 
     In one embodiment, the light source for the viewing surface is selected to have a wavelength that causes the plate to be erased. In such an embodiment, if the continuous springs are omitted, the plate will be scanned and erased in a single cycle. In such an embodiment, the cassette is opened by the action of the transport mechanism but requires manual closing after erasure in the return position. Notably, no contact with the plate is required even in this embodiment. 
     In the foregoing specification, the invention has been described with reference to specific embodiments thereof. It will, however, be evident that various modifications and changes can be made thereto without departing from the broader spirit and scope of the invention as set forth in the appended claims. The specification and drawings are, accordingly, to be regarded in an illustrative rather than a restrictive sense. Therefore, the scope of the invention should be limited only by the appended claims.

Technology Category: 5