Abstract:
A fluoroscopy machine includes an x-ray source and detector mounted in spaced relation to a support arm, an image processor and a display device. The display device includes image optics attached to a head mount wearable by a person, such as a physician or technician. The image displayed by the image optics can be processed by the image processor to present an orientationally accurate image corresponding to the head mount wearer&#39;s field of view. For example, the image can be processed to correct for angle of rotation, translation and/or perspective distortion.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application hereby claims the benefit of provisional application No. 60/144,673 filed Jul. 20, 1999. 
    
    
     BACKGROUND OF THE INVENTION 
     This invention relates generally to fluoroscopic x-ray machines, and in particular to a fluoroscopy machine having a head mounted display for providing a real-time x-ray image to a physician. 
     Early x-ray fluoroscopy machines employed a simple fluorescent screen that could be positioned on one side of a patient opposite an x-ray source. X-rays passing through the patient caused fluorescence of the screen to create an instantaneous or “real-time” x-ray image of the patient. The location of the screen clearly indicated the portion of the patient being imaged and the orientation of the image was, by necessity, always the same as that of the patient. 
     Although this system was simple and intuitive, a relatively high dose of x-rays was needed to produce an image on the fluorescent screen. For this reason, modern fluoroscopy machines have replaced the simple fluorescent screen, usually, with an image intensifier tube coupled to a video camera. The image intensifier tube employs the mechanism of electron multiplication to greatly increase the flux striking the fluorescent screen, significantly reducing the amount of x-ray exposure required. 
     The video camera serves to record the image and provides the additional benefit of permitting the x-ray beam to be positioned without regard to the location of the physician who no longer views the fluorescent screen directly, but instead, views a high resolution CRT-type display placed in a convenient location. In order that the display be easily viewed, it may be placed on a stand independent of the rest of the fluoroscopy machine to be positioned in the best viewing location, or supported on adjustable arms to be moved during the course of the fluoroscopic procedure. Nevertheless, the displays are inherently bulky and relatively difficult to reposition, thus hampering the mobility of the physician. For this reason, multiple displays may be placed at different locations around the patient to accommodate physician movement. 
     By separating the display from the fluorescent screen of the image intensifier, the x-ray image loses its context with the patient. Both the site and orientation of the imaged structure are no longer apparent. For example, the image may often be upside down or in mirror image with respect to the physician&#39;s view of the patient and may rotate as the x-ray beam is repositioned as a result of the geometry of the fluoroscopy machine. 
     While the prior art has addressed the limited problem of image rotation through various means including motors for rotating the video camera with respect to the image intensifier, or by rotating magnetic yokes deflecting the electron beam on the CRT, such systems are imperfect and at best correct only for rotation caused by the movement of the fluoroscopy machine and necessarily fail to account for the movement of the physician which might desirably shift the orientation of the x-ray image. 
     What is needed is a display system that preserves the complete flexibility of x-ray beam orientation and physician location offered by modern fluoroscopy machines while restoring the intuitive relationship between the x-ray image and the patient found in early fluoroscopy machines. 
     BRIEF SUMMARY OF THE INVENTION 
     The present invention employs a head-mounted electronic display, such as has been developed for virtual reality-type systems, to provide a fluoroscopic image in the physician&#39;s changing field of view regardless of movement of the physician. The image may be manipulated according to the relative positions of the physician and the fluoroscopy machine to provide an intuitive relationship between the displayed image and the patient either in rotation, translation or apparent perspective. 
     Specifically, the present invention provides a fluoroscopy machine having an x-ray source producing a beam of x-rays along an axis, and a support arm having a first end attached to the x-ray source and a second end opposite the x-ray source along the axis, the support arm providing a space along the axis between the first and second ends sufficient to accommodate a human patient. An x-ray detector attached to the second end of the arm is positioned to receive the x-rays along the axis and to provide electronic image signals. A head-mounted display provides image optics producing an image from the electronic image signals and viewable by the physician wearing the head mounted display on his or her head. 
     It is one object of the invention to provide a fluoroscopy machine allowing complete freedom of movement by the physician without the need for multiple display systems or complex gimbaled or articulated display supports. The head-mounted display ensures that the x-ray image is always in the physician&#39;s field of view. 
     The image optics may produce an opaque image blocking the receipt of light through the image from the physician&#39;s field of view, or may be transparent to permit the passage of light through the image. 
     Thus, it is another object of the invention to provide hands free viewing of both the image and other areas of the physician&#39;s field of view. When an opaque image is selected it may be displaced from the center of the field of view so as to be visible by eye movement alone. 
     The fluoroscopy machine may include an input representing an angle of rotation and may further include image processing electronics for rotating the image to the angle of rotation. The input may be the relative angular displacement between the physician&#39;s field of view and a reference fixed with respect to the fluoroscopy machine or the patient. 
     Thus, it is another object of the invention to provide automatic correction of the image rotation to comport with the viewpoint of the physician as the physician moves with respect to either the fluoroscopy machine or the patient. 
     The fluoroscopy machine may include an input representing a translation, and may include further, an image processor for translating the image within the field of view of the physician based on that input. The input may be the relative displacement between the physician&#39;s field of view and a reference fixed with respect to the fluoroscopy machine or the patient. 
     Thus, it is another object of the invention to allow the image to be electronically “attached” to the patient or the fluoroscopy machine so as to provide an intuitive reference frame between the image and patient or fluoroscopy machine. 
     The fluoroscopy machine may include an input representing a skewing, and may further include an image processor skewing of the image as a function of the input. The input may be a relative displacement and orientation between the physician&#39;s field of view and a predetermined image plane fixed with respect to the image intensifier or the patient. 
     Thus, it is another object of the invention to impose perspective effects on the image so that the image is not only attached to a reference point in the real world, but appears to conform to a reference plane as well so as to provide an “x-ray vision” type display. 
     The foregoing and other objects and advantages of the invention will appear from the following description. In this description, reference is made to the accompanying drawings which form a part hereof and in which there is shown by way of illustration the preferred embodiment of the invention. Such embodiment does not necessarily represent the full scope of the invention, however, and reference must be made therefore to the claims for interpreting the scope of the invention. 
    
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
     FIG. 1 is a perspective view of a compact fluoroscopy machine as may be viewed by a physician, showing an x-ray source projecting x-rays toward an image intensifier, the latter covered, in part, by a patient&#39;s hand and further showing the projection of an x-ray image produced by the fluoroscopy machine in fixed location above the image intensifier as is possible with the present invention; 
     FIG. 2 is a block diagram of a fluoroscopy machine similar to that of FIG. 1 but including a patient support, and further showing three, three-dimensional tracking devices fixed to the x-ray source and used by an image processor, the patient support and a head-mounted display to be worn by the physician; 
     FIG. 3 is a simplified representation of the head-mounted display of FIG. 2 employing opaque display optics positioned at the edge of the physician&#39;s field of view; 
     FIG. 4 is a figure similar to that of FIG. 3 showing an alternative head-mounted display employing transparent display optics centered within the physician&#39;s field of view; 
     FIG. 5 is a depiction of the physician&#39;s field of view when the image provided by the head mounted display is fixed with respect to the physician&#39;s field of view; 
     FIG. 6 is a figure similar to that of FIG. 5 where the image provided by the head mounted display is manipulation so as to appear attached to a fixed reference object; 
     FIG. 7 is a flowchart showing the principal steps performed by the image processor of FIG. 2 in producing the image of FIG. 6; 
     FIG. 8 is a schematic perspective representation of a physician and a fluoroscopy machine showing relevant measurements for rotational correction of the image of FIG. 5; and 
     FIG. 9 is a schematic perspective representation of a perspective correction employed in the generation of the image of FIG.  6 . 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring now to FIG. 1, a fluoroscopy machine  10  includes an x-ray source  12 , being an x-ray tube of conventional design, attached at a first end of a C-arm  14  to project x-rays along an axis  16  bisecting the circle of the C-arm  14 . A second end of the C-arm  14  supports an image intensifier/camera unit  18  positioned to receive x-rays along the axis  16  while providing a gap between the x-ray source  12  and the image intensifier/camera unit  18  to receive a patient. 
     The C-arm  14  is supported by a collar  20  to slide therein, which in turn is supported to be easily positioned around several axes by gimble assembly  24 . Collar  20  and gimble assembly  24  may instrumented so as to provide electronic signals indicating the orientation and location of the axis  16 . 
     Referring also to FIG. 2, the electronic signals from the collar and gimble assembly  24  and other mechanical position signals relating to the position of the axis  16  as may be understood in the art, may be provided to an image processor  26  whereby the relative orientation of axis  16  with respect to a stationary reference may be calculated. 
     Alternatively or in addition, a three-dimensional tracking antenna  28  may be attached to the x-ray source  12  (or any mechanical element fixed with respect to the x-ray source  12 ) so as to provide identical information about the position of axis  16 . In the present example, the three-dimensional tracking antenna  28  is of a type currently used in virtual reality systems and employs a stationary three-dimensional tracking receiver  30  which may detect and quantify movements of the antenna  28 . Such tracking systems are commercially available from Polhemus of Colchester, Vt. under the tradename INSIDETRAK and from Ascension Technology Corporation of Burlington, Vt. under the tradename FLOCK OF BIRDS. Such systems desirably provide real-time measurements of six degrees of freedom of antenna  28  in x, y and z of Cartesian coordinates and in azimuth, elevation, and roll. 
     Additional antennas  32  and  36  may be used to allow the three-dimensional tracking receiver  30  to also monitor the relative position of other objects. In particular antenna  32  attached to a patient support  34  or alternatively to the patient his or herself may be used to track the position of the patient. Similarly, antenna  36  attached to a head-mounted display  40  or otherwise to the head of the physician, may be used to track the location of the physician and in particular the direction of the physician&#39;s gaze. 
     The three-dimensional tracking receiver  30  is connected to an image processor  26  so that the location and orientation of the fluoroscopy machine  10 , patient  17 , and the physician&#39;s gaze may be used to modify an x-ray image obtained by the fluoroscopy machine  10  and provided to the physician via the head-mounted display  40  as will be discussed below. Image processor  26  may be associated with a general purpose processor used for control of the fluoroscopy machine  10 . 
     A conventional display  42  is also connected to image processor  26  to receive an image signal as processed by image processor  26  or unprocessed directly from the image intensifier/camera unit  18 . 
     Referring now to FIG. 3, the head-mounted display  40  provides display optics  46  positioned in fixed relationship to the physician&#39;s field of view  48  as held by glasses-like frame  44 . The display optics are constructed such that a virtual image  50  is formed having an apparent location in space several feet in front of the physician. Binocular or monocular head mounted displays may be used with the present invention. 
     In a first version, display optics  46  subtend only a portion of the field of view  48  displaced from the center of the field of view  48 . Thus, the physician may view a real object  52  near the center of his or her field of view, then by shifting his or her eyes to the edge of the field of view  48 , view the virtual image  50 . The display optics  46  may in this case be opaque, that is blocking of light from beyond the display optics  46  within that portion of the field of view subtended. 
     Referring to FIG. 4 in a second embodiment, the display optics  46  subtend a substantial portion, if not all, of the field of view  48  but are transparent so as to allow light from real object  52  to pass through the display optics  46  so that the virtual image  50 ′ appears semi-transparent and superimposed on real object  52 . In both cases, the antenna  36  may be attached to the glasses-like frame  44  so as to provide the indication of the orientation of the gaze of the physician. 
     Head mounted displays are commercially available from a number of sources including Virtual Research Systems, Inc. of Santa Clara, Calif. under the tradename of i-glasses and Kaiser Electro-Optics Inc. of Carlsbad, Calif. under the tradename of Proview. 
     Referring now to FIG. 5, in a first mode of operation of the present invention, a virtual image  50  is displayed to the physician by the head mounted display  40 , displaced to the side of the field of view  48 . This image  50  may be essentially the same as that displayed by display  42  and may include no or little image processing. As a result of the physical linking of the display optics  46  (not shown in FIG. 5) to the physician&#39;s head, the image  50  floats fixed within the field of view  48  regardless of motion of the physician. By so displacing the virtual image  50  from the center of the field of view  50 , the physician&#39;s view of the patient  17  is not obstructed and yet the image  50  is always viewable. 
     In a second embodiment, the image  50  may be processed by the image processor  26  based on input from the three-dimensional tracking receiver  30 . In particular, the rotational orientation of the image  50  may be adjusted so that as the physician moves about the patient  17  or as the fluoroscopy machine  10  moves with respect to the patient  17 , the image  50  retains rotational linkage with respect to the patient  17  preventing an inversion such as might complicate interventional procedures if the rotated image  50  were relied upon. 
     Referring now to FIGS. 7 and 8, in such a system, after each frame of video from the image intensifier/camera unit  18  is acquired, as indicated by process block  53 , a determination is made as to the relative orientation of the fluoroscopy machine  10  with respect to the physician using antenna  36  and  28  or alternatively, the electrical signals from the collar  20  and gimble assembly  24  described above. Generally, the physician  45  will have a field of view  56  whose angle  60  that may be determined from antenna  36  as a rotation about an imaginary inferior/superior physician axis  58 , the latter normally near vertical. This angle  60  may be compared to a similar angle  61  about axis  16  of the fluoroscopy machine  10  and the difference, corrected for divergence angle α between the physician axis  58  and the x-ray axis  16  according to the sine of α. Thus, if the x-ray axis  16  and physician axis  58  are both vertical, rotation of the physician&#39;s head will cause equal rotation of the image  50 . In this way, as the physician walks about the patient, for example, the image will rotate so as to present an intuitive orientation to the physician. 
     The step of computing this rotation is shown in FIG. 7, process block  62 , and the display of the given frame is shown by process block  64 . This process of blocks  54 ,  62  and  64  may be repeated as additional frames of x-ray image data are acquired so as to create an essentially real-time correction of the image  50 . 
     Referring now to FIG. 6, the rotation correction described with respect to FIG. 5, may be augmented by a translation correction and skew correction so as to essentially “attach” the image  50  to an actual object, such as the patient  17 . In this way, the location and perspective of the image  50 ′ can closely match that image that would have been obtained with the fluorescent screen of early fluoroscopy machines placed in the same location. For this purpose, a head-mounted display  40  with transparent display optics  46 , such as the type described with respect to FIG. 4, is used. 
     Referring to FIGS. 7 and 9 in the embodiment of FIG. 6, first both the relative angle and the relative location between the physician and the fluoroscopy machine  10  may be obtained at process block  54 . A determination of the relative position between the physician and the fluoroscopy machine  10  is obtained simply by subtracting their individual locations with respect to the stationary three-dimensional tracking receiver  30 . 
     Next the location of the image plane  66  must be decided. This may be done by user input by the use of a fourth antenna (not shown) or as a predetermined location with respect to the fluoroscopy machine  10  or the patient  17  using antennas  28  and  32 , respectively. For example, an image plane  66  may be established with respect to the fluoroscopy machine  10  independent of the location of the patient  17 . Referring to FIG. 1, for example, the image plane  66  may be positioned perpendicular to axis  16  approximately midway between the x-ray source  12  and image intensifier/camera unit  18 . In this way, the image plane  66  is intersected by the axis  16  providing a highly intuitive localization of the image plane  66 . 
     After a determination of the relative positions, two manipulations of the image are necessary to affix it to a structure such as the fluoroscopy machine  10 . The first is a translation of the image  50  within the field of view  48  and the second is a perspective skewing of the image  50  so as to accommodate the distortion implicit in a possibly oblique image plane  66 . Such manipulation of an image to fit a polygon of known orientation is well understood in the art of texture mapping. 
     The above description has been that of a preferred embodiment of the invention. It will occur to those that practice the art that many modifications may be made without departing from the spirit and scope of the invention. In order to apprise the public of various embodiments that may fall within the scope of the invention the following claims are made.