Abstract:
A high resolution magnifying X-ray fluoroscope using a low dose beam includes a scintillator for receiving an X-ray beam and converting the X-ray energy into visible light. The scintillator is in intimate optical contact with a non-demagnifying image intensifier that presents the visible light image through a close-up lens system to an optically magnifying, autofocus, programmable, closed circuit video camera. The fluoroscope is mounted on a moveable frame in a position that is opposed to an X-ray source.

Description:
FIELD OF THE INVENTION 
     The present invention relates to the field of real-time fluoroscopic X-ray imaging, and more particularly to fluoroscopic X-ray imaging at high resolution generated through the use of low dose X-ray beams. 
     BACKGROUND OF THE INVENTION 
     Conventional real-time fluoroscopic X-ray imaging involves directing an X-ray beam through an object to impinge onto a scintillator that converts the X-rays into energy in the visible spectrum. The scintillator is typically a layer of luminescent or phosphorescent material that is capable of generating visible light in response to being stimulated by the X-ray beam. When the X-ray beam passes through portions of the object under examination that are opaque to varying degrees to X-ray wavelengths, e.g. bone or metal, a shadow defining the configuration and position of the opaque portion is formed. The resultant visible light shadow is then typically intensified and reduced in size prior to being transmitted by video means, observed by a technician, and/or recorded. Intensification is conventionally achieved by use of a cesium iodide scintilator demagnifying intensifier tube. Conventional fluoroscopic X-ray imaging systems are used commonly for medical, security and industrial applications. 
     Systems have been developed for converting the X-ray shadow image to a digital signal to conveniently display or record the image or to transmit the image via television. These digital systems commonly utilize a flat panel detector, essentially a planar array of photosensors or CCDs (charge coupled devices) connected to electronic apparatus. One such system is disclosed in U.S. Pat. No. 6,895,077 entitled SYSTEM AND METHOD FOR X-RAY FLUOROSCOPIC IMAGING. The visible light beam created in the scintillator projects to a portion of the array to activate a photosensor receptor that is connected to an output cable. The sum of all the photosensor receptors equates to a total screen picture. To create a moving image, as is common in fluoroscopic imaging for observing internal organs or guiding arthroscopic surgery, the array of photosensors receives a changing image over time and transmits sequential panels of information. As a result, the digital flat panel is analogous to 20 th  century motion picture technology in which an individual frame was exposed, then the film advanced to expose a subsequent frame. By exposing many frames in succession, a live-appearing sequence, or motion picture, was created. Standard motion picture speed captures and displays at a rate of at least 16 frames per second to achieve a realistic motion sequence. In the flat panel X-ray system, a maximum image capture rate of 10 frames per second can be achieved. This capture rate, based on photosensor-digital technology, is insufficient to approach real-time motion viewing that is needed to accurately explore an object or guide an operative procedure. Thus the use of digital imaging is not effective and it is essential to transmit the image in analog format to achieve real-time quality. Digital flat panel imaging devices are neither real-time (i.e. fluoroscopic) nor high resolution (less than 7 lp/mm). 
     As with all imaging formats, image sharpness is a major concern. In the case of visible spectrum converted X-ray imaging, whether medical, security, or industrial, image resolution can be crucial. Image resolution is defined in units of line pairs (a line and a space) per millimeter (lp/mm), that is, the maximum number of line pairs that can be observed in a millimeter of width and distinguished as separate lines. In other words, resolution determines the smallest distinguishable white space between two parallel lines. Prior fluoroscopic X-ray image systems have achieved resolution of up to 5 lp/mm. For acceptable clarity, a resolution of at least 12 lp/mm is needed to visualize small details and comprehend their importance. For example, an X-ray examination of an implanted vascular stent must be sufficiently clear to identify minute problems that occasionally occur. Simply magnifying a small image that is of low resolution will merely provide an unclear larger image. Reducing the size of a large image to intensify the pattern also fails to achieve detail clarity. Early fluoroscopic systems included a scintillator that projected visible light energy to a demagnifying image intensifier which transmitted a smaller image to a camera device. These systems use unacceptably high X-ray dosage, and deliver relatively poor image resolution, on the order of 5 lp/mm or less. 
     Image resolution could, theoretically, be enhanced by increasing the intensity or dose of the X-ray beam. However, an increased dose X-ray beam has serious physiological implications both for the patient being examined fluoroscopically and for the medical technician. Thus it is important to reduce X-ray dosage as much as possible. The U.S. Food And Drug Administration monitors radiation relating to the use of fluoroscopic guidance of minimally invasive internal procedures, e.g. angioplasty. The FDA guidelines list time exposures of X-rays that have been shown to cause skin damage resulting from a dose of 2.0 Rads/minute. Longer time at a given radiation dose can cause greater damage, both to the skin and to internal organs. Lower dose rates are deemed to be safer. 
     Therefore, a need exists for a high resolution fluoroscopic X-ray system capable of magnified real-time motion perception and generated from use of a low dose X-ray beam. The invention disclosed below provides such an X-ray fluoroscope. 
     SUMMARY OF THE INVENTION 
     The high resolution real-time X-ray image fluoroscope and system of the present invention includes an X-ray source for penetrating an object with an X-ray beam that is received in a fluoroscope. The X-ray source and fluoroscope are mounted opposite one another on a moveable frame. The fluoroscope has a radioluminescent scintillator optically coupled to a non-demagnifying image intensifier. The intensified image is viewed via a close-up lens device to be focused onto an autofocusing, optically magnifying camera. The closed circuit camera transmits the high resolution, magnified video image to a computer or other viewing or recording device. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention is best understood in conjunction with the accompanying drawing figures in which like elements are identified by similar reference numerals and wherein: 
         FIG. 1  is a diagrammatic side view of the high resolution real-time fluoroscopic X-ray imaging system of the invention in use. 
         FIG. 2  is a diagrammatic side view of the X-ray fluoroscope according to a preferred embodiment of the invention. 
         FIG. 3  is a fluoroscopic image of a stent obtained under clinical conditions of angiography, using conventional X-ray fluoroscopy of the prior art. 
         FIG. 4  is a fluoroscopic image of a stent through a human bone foot phantom as derived from a fluoroscope according to the present invention. 
         FIG. 5  is a fluoroscope optically magnified view of the stent of  FIG. 4  as derived from a fluoroscope according to the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring now to  FIG. 1 , a schematic side elevation view is illustrated of the high resolution, magnifying X-ray fluoroscopic imaging system according to the invention. A subject S is positioned between an X-ray source  10  and a fluoroscope  20  in the path of an X-ray beam XR. X-ray source  10  and fluoroscope  20  are mounted on a common frame  16  to maintain alignment therebetween. X-ray source  10  is a substantially conventional generator and projector of an X-ray beam as is known in the field. X-ray fluoroscope  20  will be described in detail below. Frame  16  is structurally rigid and mounted in a manner to be moveable in the Y and Z directions (see diagram at bottom right) either manually or mechanically. Movement of frame  16 , and resultant movement of X-ray source  10  and X-ray imaging fluoroscope  20 , enables a scanning image of an area of subject S, for example to inspect in real-time the condition of and around an implanted object in subject S, e.g. a vascular stent. The real-time inspection of implanted objects such as stents and imaging of surgical procedures such as catheterization, stent deployment, etc. are major benefits of the present invention. As used herein, real-time involves displaying image movement substantially synchronously with object or camera movement. Frame  16  is additionally able to be rotated in the direction indicated by arrows R around an axis midway between X-ray source  10  and X-ray fluoroscope  20  to inspect an area of subject S at an angle to horizontal. X-ray beam XR from X-ray source  10  passes through subject S and enters X-ray fluoroscope  20  where it is first converted to visible light, intensified without demagnification, optically magnified, and converted to an autofocus video image to exit through a cable C 1  to enter a signal processor, e.g. CPU  12 . In passing through subject S in a location for imaging in real-time a surgical procedure or implanted object, portions of X-ray beam XR are absorbed or blocked by opaque objects, e.g. bones or a dense implant, and other portions of X-ray beam XR pass through translucent portions, creating a shadow image that depicts the shape of the opaque portions. CPU  12  transmits an image via cable C 2  to display  14  or an image recording device (not shown) similarly connected. Display  14  may be located close to X-ray fluoroscope  20  or remote therefrom. Power input to the various operating components of the system is not depicted and understood to be according to the requirements of the individual component. An operator interface  18 , e.g. a keyboard, is connected to CPU  12  via cable C 3  for control of the positioning of frame  16  and the functioning of X-ray source  10  and fluoroscope  20 . An image of a stent is portrayed on display  14  as an implanted object in the body of subject S requiring occasional non-invasive evaluation with high resolution and clarity. 
     Referring now to  FIG. 2 , X-ray fluoroscope  20  is depicted schematically to show internal components in detail. A housing  22  encloses and supports the components comprising X-ray fluoroscope  20 . At least the window portion  26  of housing  22  is transparent to X-ray. X-ray beam XR passes through window portion  26  to impinge on scintillator  24 , being in the form of a thin sheet or coating of radioluminescent phosphor, for example CsI or Gd 2 O 2 S. Scintillator  24  converts the impinging X-ray input radiation frequency into a visible light frequency for further processing and image projection. Scintillator  24  is positioned and maintained in intimate optical contact with the input end of a non-demagnifying image intensifier  28  to maximize transmission integrity. Scintillator  24  may be formed by directly depositing the selected phosphor on the input of image intensifier  28  or by adhering a formed phosphor sheet scintillator to the image intensifier input. Alternatively, a phosphor is deposited, or a phosphor sheet is adhered, onto a fiber optic plate or taper  30  that is in intimate optical contact with image intensifier  28 . Image intensifier  28  is of the type able to increase the energy of visible light transmitted therethrough by electronic or electrostatic means while maintaining a constant image size. A specific type of non-demagnifying image intensifier that is satisfactory to the objects of the invention is known as a microchannel plate, characteristically a thin plate of conductive glass with a large number of very small apertures, on the order of 10 μm in diameter. The apertures, or microchannels, are coated to cause a single incoming light ray impacting the side wall to divide multiple times, adding photons and thus intensifying the energy level of the light ray projected therefrom. An available non-demagnifying microchannel plate image intensifier is capable of projecting an image with a resolution on the order of 25-28 lp/mm. 
     Referring further to  FIG. 2 , the intensified, non-demagnified image next passes through a close-up lens system  32  capable of focusing and transmitting the image received from proximally located image intensifier  28  to a camera  36 . Camera  36  generates a video signal representing the image which is transmitted via cable C 1  to an output device. Camera  36  is a compact programmable, autofocus block camera having an optical magnification multiplier of 10× and a digital zoom of 4×, equal to a total magnification capability of 40×. It is noted that optical magnification retains details and clarity to attain a desired level of resolution. A camera adequate to the requirements of the present invention is Model FCB-1X Series by Sony Corporation. 
     Referring now to  FIG. 3 , a fluoroscopic image of an implanted stent as viewed through a human subject chest is shown as a typical example of results achieved using fluoroscopic equipment known in the prior art. The stent is barely discernible, but no details are perceptible. The X-ray dose employed to obtain this fluoroscopic image is in the range of 2000 mRad/minute, a potentially toxic dose. 
     Referring now to  FIG. 4 , a fluoroscopic image of a stent viewed by use of the invention X-ray fluoroscope through a human foot phantom is shown. A foot phantom is a model foot for use in evaluating X-ray equipment and methods. The stent appears well defined. The X-ray dose used is only 10 mRad/hour, or 0.17 mRad/minute, significantly less than the dose rate delivered when using the prior art equipment. 
     The fluoroscopic image shown in  FIG. 5  is the result of magnifying the image of  FIG. 4 . In  FIG. 5 , the stent is clearly displayed large enough to determine any problem areas by visual examination. This degree of detail and magnification clearly indicates a highly resolved image. 
     While the description above discloses preferred embodiments of the present invention, it is contemplated that numerous variations of the invention are possible and are considered to be within the scope of the claims that follow.