Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
1 DESCRIPTION 2 ~ ~ 9 6 1 6
2
3 "FILMLESS X-RAY APPARATUS AND METHOD OF USING THE SAME"
4
FIELD OF THE INVENTION
6
7 The present invention is directed to apparatus for
8 the direct detection and computer enhancement of X-rays
9 which obviates the need for X-ray film, developers, fixers,
and processing equipment associated with prior art X-ray
11 methods. The inventive apparatus provides faster image
12 processing than conventional methods and requires less
13 exposure for the subject. The inventive method and
14 apparatus has advantages over the new computed radiography
techniques including simplicity and potential for low cost
16 application. This X-ray method and apparatus of the present
17 invention has applications in many fields including airport
18 security systems, industrial quality control, and medicine.
19
BACKGROUND OF THE INVENTION
21
22 For almost eighty years photographic films have
23 been used both to capture and display X-rays for diagnostic
24 purposes. (See Figure 1) . Only in the last ten years have
any alternative methods of X-ray imaging started to appear.
26 Best known of these is the expensive and complicated CAT
27 scan system used in many hospitals. Less well known
28 filmless X-ray systems are now available which use a storage
29 phosphor device to capture the X-ray image. These so called
image plates can be scanned by a laser beam a short time
31 later, causing the image plates to emit light proportional
32 to the intensity of X-rays to which they were previously
33 exposed. Such systems are also complicated and expensive,
34 requiring special laser equipment for the scanning stage.
They have however clearly demonstrated the great advantages
36 of filmless, or digital, X-ray pictures.
37 Digital recorded X-rays are superior to those
38 recorded with photographic film due to the greater dynamic
39 range of the digital recording system. Photographic methods
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1 allow approximately one order of magnitude dynamic range
2 whereas digital methods typically allow four orders of
3 magnitude. This advantage is only realized if the actual
4 capture of the X-ray image is digital. Merely scanning a
previously recorded photographic X-ray will not do. In
6 addition to the inherent advantages of the increased dynamic
7 range, computer image processing techniques provide a wealth
8 of capabilities to study otherwise obscured details within
9 the image. Accordingly, the present invention proposes a
filmless X-ray apparatus and method of using the same which
11 has all the advantages of digitally captured radiography and
12 in addition is mechanically very simple. This allows the
13 apparatus to be made at much lower cost than current
14 systems, making it suitable for installation in many more
locations, e.g. radiology clinics outside of hospitals,
16 veterinary clinics, chiropractic clinics, etc. The
17 inventive apparatus will be a particular boon to remote
18 settlements where "tele-medicine" is practised, such as
19 northern Canada and Alaska, because it allows an X-ray image
signal to be transmitted over phone lines without an
21 unacceptable loss of resolution.
22 Turning to the published prior art, a patent of
23 interest is PCT application W081/03594, filed by Brown et
24 al. This publication discloses an x-ray apparatus
comprising: a source of x-rays for directing x-rays through
26 an object (mail); a fluorescent intensifying screen behind
27 the object, for producing visible light radiation when
28 contacted by the x-rays; a light source for producing
29 visible light radiation as a reference; a movable mirror,
aligned with the screen, for reflecting the visible light
31 radiation and reflecting the x-rays, to separate them, in
32 one mode, and for passing the reference visible light
33 radiation, in the other mode; a video camera for scanning
34 the test and reference visible light images and producing
signals indicative thereof; circuit and computer means for
36 capturing the test image and processing it to measure the
37 amounts of transmission through light and dark areas of the
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1 object and to compare these measurements against the
2 reference measurements to detect the presence of IED's (an
3 explosive device in the envelope).
4 Another patent of interest is U.S. patent
4,063,092 issued to Berdahl. This patent teaches a system
6 involving: an x-ray source for directing x-rays through a
7 biological subject; an electronic image intensifier behind
8 the subject, for amplifying an electrical signal produced by
9 the x-rays and in turn producing visible light radiation; a
lens for collimating the light; a beam splitting mirror
11 which splits the light and directs a portion to a television
12 camera and another portion to a motion picture camera, which
13 is to photograph the image on film. The patent provides a
14 photomultiplier exposure sensing system immediately before
the motion picture camera. Part of the light beam advancing
16 to the camera is directed by a second beam splitter onto an
17 imaging lens, through a mask and to a photomultiplier. The
18 photomultiplier senses the intensity of the light received,
19 determines the correct exposure required for an optimum
photograph and adjusts the x-ray machine in response
21 thereto.
22 Yet another disclosure of interest is European
23 patent application EP-A-0157688 to Klausz which discloses a
24 system for the optimal placement of image enhancing filters.
The subject is exposed to x-ray radiation and the resultant
26 visible light image is passed through an image intensifier
27 to a TV camera. The image is recorded and projected back as
28 visible light onto the subject, typically a medical patient,
29 allowing better positioning and selection of filters to
enhance the image. Once the position is correct and the
31 desired filters are in place, a second x-ray shot is taken
32 to produce the desired image on high-resolution film.
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1 SUMMARY OF THE INVENTION
2
3 In the instant apparatus, X-rays are passed from a
4 conventional X-ray source through a biological subject
(patient) in the usual manner. In most conventional X-ray
6 methods, the film is mounted in a cassette between two
7 layers of fluorescent material. When a short pulse of the
8 X-rays strike the fluorescent material, visible light is
9 produced in proportion to the intensity of the x-ray. This
enhances the photographic effect on the X-ray film. (See
11 U.S. Patents Nos. 2,298,587 and 2,161,058, for example).
12 The present invention employs no film and only one
13 fluorescent layer. A mirror, mounted below the fluorescent
14 layer at an oblique angle, typically 45 degrees, to the path
of the X-ray beam allows the X-rays to pass through the
16 mirror with their path unaltered, but reflects the brief
17 visible light image, created by the passage of X-rays
18 through the fluorescent layer, on a 90 degree path to the X-
19 ray beam, thereby separating the visible light from the X-
rays. This separation is important, because X-rays will
21 destroy most electronic detectors. The 45 degree alignment
22 of the mirror provides an equal path length from the image
23 plane (i.e. the fluorescent screen) to the detector plane
24 regardless of the position on the image plane, thus ensuring
that a part of the image formed on the left of the
26 fluorescent screen will be sharply in focus at the same time
27 as a part from the right side. To minimize scattered
28 radiation, the mirror possesses an aluminum reflective layer
29 on the front, rather than the conventional silver backing,
because aluminum is relatively transparent to X-rays.
31 Behind the reflective aluminum layer and glass substrate,
32 the mirror is coated with lead to absorb X-rays. An optical
33 receiving means, such as a CID (Charge Injection Device)
34 detector, in the form of a video camera disposed at the end
of the 90 degree visible light path, registers the image.
36 The CID video camera is used rather than the generally
37 available CCD cameras because multiple frames may be stacked
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1 with a CID video camera. CCD cameras destroy the captured
2 image while reading it out and so do not allow for image
3 stacking. Without the CID, camera light levels may fall
4 below the usable threshold. While the use of a CID camera
5 is preferred in this device, a CCD camera of sufficient
6 sensitivity could also be used. A photocell detector near
7 the fluorescent screen registers the burst of visible light
8 and initiates capture of the image on the video camera by a
9 frame grabber. A frame grabber is essentially a circuit
board mounted inside a computer which translates a video
11 image into a standard computer graphics file format such as
12 TIFF (Tagged Image File Format) for analysis and enhancement
13 by the computer. This board may be one of any number of
14 commercially available products and will incorporate image
processing software as well as its ability to capture the
16 image. The use of a photocell coordinated frame grabber
17 obviates the need for more expensive techniques now being
18 introduced in the field of computed radiography such as
19 storage phosphors combined with laser scanning.
The whole apparatus, except for the computer, is
21 enclosed in a light proof, lead lined box. The height of
22 the box is determined by the size of the fluorescent screen,
23 as the mirror mounted beneath the fluorescent screen must be
24 of the same size. For example, an 8 inch by 10 inch screen
requires a like sized mirror. With the mirror mounted at 45
26 degrees, the box height is the square root of 32 or
27 approximately 5.65 inches. The length of the box is
28 determined by the focal length of the camera in use. In one
29 example embodiment, a box length of approximately 3 feet is
utilized.
31 Broadly stated then, the invention involves a
32 filmless x-ray apparatus for medical diagnostic imaging
33 comprising an x-ray source (1) for directing x-rays through
34 a subject (2), a fluorescent intensifying screen (3) behind
the subject for producing visible light radiation when
36 contacted by the x-rays, an oblique mirror (6) behind the
37 screen for reflecting the visible light radiation and
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1 separating it from the x-rays, an optical receiving means
2 (7) and controlling/processing means (8,9), characterized
3 by: an x-ray source for directing a short pulse of x-rays
4 through a biological subject; a screen for producing a pulse
of visible light radiation which is in the form of a visible
6 image; an optical receiving means, positioned in the path of
7 the reflected visible light radiation, for receiving the
8 pulse and producing a first signal indicative of the
9 received image; means (10) for sensing the first incidence
of the emission of the pulse of light radiation by the
11 screen; and controlling/processing means, connected to
12 receive the first signal and to be activated by the sensing
13 means, for capturing the first signal in response to
14 activation by the sensing means, producing a digital
representation of the captured image and producing the
16 digitized image on a viewable screen.
17 Experiments have shown that the image is captured
18 in the time taken to register a single frame of video,
19 typically 1/60 of a second. As photographic methods in
radiology normally require exposures of 1/10 to 1 second,
21 the method of the present invention allows for either a
22 multiplicity of images to be captured in the same time
23 period or for the radiation exposure to be greatly reduced.
24 If the multiplicity of images is used, they may then be
stacked together. The signal, or desirable part of the
26 picture, will be increased by the number of pictures
27 stacked. Any random noise however will increase only by the
28 square root of the number of pictures stacked. This yields
29 a signal to noise ratio improvement multiplier equal to the
square root of the number of pictures stacked. If, for
31 example, four pictures of the same subject are stacked
32 together, the signal to noise ratio will improve by a factor
33 of two.
34 In current methods, an effect known as "heeling"
causes a variation of intensity from one end of the X-ray
36 image to the other due to the angle at which the X-rays are
37 emitted from the focal spot of the X-ray machine. This
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1 heeling effect must be allowed for in examining X-ray films.
2 In the inventive method, the heeling effect may be
3 electronically processed out at the image enhancement stage.
4 If a subject (patient) moves during exposure, as
is common in veterinary medicine, the radiograph is useless
6 for diagnostic purposes using current methods. In the
7 method of the present invention, image processing software
8 allows for the removal of blur caused by linear motion. A
9 computer image can therefore be corrected, rather than
repeating the exposure. This saves time and reduces patient
11 exposure in medical applications.
12 While an image obtained with a single video camera
13 may be adequate for most purposes, inevitably some
14 applications will require a higher resolution. To this end,
a second embodiment of the invention uses not one, but many
16 video cameras. As suitable video cameras are commercially
17 available which measure only one or two inches in size, it
18 is feasible to mount as many as are required along a back
19 plane of a light proof box housing the imaging apparatus.
The desired resolution may then be obtained by forming a
21 composite of all the captured images, each of which will
22 have the same detailed spatial resolution.
23 These and various other advantages and features of
24 novelty which characterize the invention are pointed out
with particularity in the claims annexed hereto and forming
26 a part hereof. However, for a better understanding of the
27 invention, its advantages, and the objects obtained by its
28 use, reference should be made to the drawings which form a
29 further part hereof, and to the accompanying descriptive
matter, in which there is illustrated and described
31 preferred embodiments of the invention.
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1 BRIEF DESCRIPTION OF THE DRAWINGS
2
3 Figure 1 is a block diagram illustrating prior art
4 film type X-ray apparatus.
Figure 2 is a block diagram diagrammatically
6 illustrating a filmless X-ray apparatus according to a first
7 embodiment of the present invention.
8 Figure 3 is an exploded side elevational view of a
9 mirror component of the filmless X-ray apparatus of the
present invention.
11 Figure 4 is a diagrammatic side elevational view
12 illustrating the housing, fluorescent screen, mirror and
13 video camera components of the filmless X-ray apparatus of
14 the present invention.
Figure 5 is a block diagram depicting a back plane
16 of a light proof box component of a filmless X-ray apparatus
17 according to a second embodiment of the invention.
18
19 DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
21 As shown in Figure 1, a prior art film type X-ray
22 apparatus typically includes an X-ray source 1, which
23 directs X-rays X toward and through a subject 2, for example
24 a human, animal, or luggage at an airport security device.
The X-rays subsequently pass through a fluorescent
26 intensifying screen 3, for the purpose of producing light
27 radiation in the spectrum which can be recorded on a
28 photographic film plate 4. The photographic film 4 is
29 typically sandwiched between a first fluorescent
intensifying screen 3 and a second fluorescent intensifying
31 screen 5 which includes a lead backing for preventing the
32 harmful emission of X-ray radiation.
33 According to a first embodiment of the present
34 invention, illustrated in Figures 2 and 4, a conventional X-
ray source 1 emits a pulse of X-rays X toward and through a
36 subject 2. The X-rays travel through the subject 2 and a
37 conventional fluorescent intensifying screen 3. One
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1 suitable type of fluorescent intensifying screen is sold
2 under the designation DUPONT CRONEX QUANTA III (TM) and
3 distributed by Medtec Marketing Ltd., of Calgary, Alberta,
4 Canada, and many other sources. As a result of passage
through fluorescent screen 3, X-rays and a visible component
6 of the light spectrum, indicated by the arrows designated
7 X+L, impinge upon a mirror 6 disposed at a 45 degree
g included angle relative to the plane of the screen 3.
g As shown in Figure 3, the preferred mirror 6 for
use in the present invention comprises a front surface
11 coated by an aluminum "silvering" layer 11 on a glass
12 substrate 12 provided with a lead backing layer 13.
13 After being reflected by the mirror 6, the visible
14 component of radiation L is directed toward a CID video
camera. One suitable conventional form of CID video camera
16 for use in the present invention is available from CIDTEC of
17 Liverpool, New York, U.S.A. under the designation CIDTEC
lg model no. CID3710D solid state monochrome video camera. The
19 X-ray component of the radiation is not reflected by the
mirror 6, but is rather absorbed by the lead backing 13 of
21 the mirror 6 (Figure 3), or by a lead lining 17 within a
22 light tight housing 14. The video signal produced by the
23 video camera 7 is directed by a conventional video coaxial
24 cable 16 or other suitable connector to a frame grabber
circuit 8 operably connected to a computer 9, for example an
26 IBM compatible PC type computer. One example commercially
27 available frame grabber circuit is available from DataCube
28 of Peabody, Massachusetts, U.S.A., under the designation
29 DataCube QVC-423 and associated suitable image processing
software is available from Sun Microsystems of Mountain
31 View, California, U.S.A., under the designation SunVision.
32 Alternative example image processing software is available
33 under the designation Aldus PhotoStyler (TM) in most retail
34 computer software stores.
In order to initiate and control the frame grabber
36 to capture an image from the video camera 7, a photocell 10
37 is positioned behind the fluorescent intensifying screen 3
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1 and is operably connected to activate the fame grabber 8
2 upon emission of visible spectrum light from the screen 3
3 which impinges upon the photocell 10. Suitable conventional
4 control circuits may be utilized in association with the
5 frame grabber 8 to control the capture of single or multiple
6 images from the video camera 7 disposed on the back plane 15
7 of the housing 14.
g Figure 5 illustrates a modified back plane 15'
9 according to a second embodiment of the present invention,
10 in which a plurality of video cameras 7A, 7B, 7C, 7D, 7E,
11 7F, 7G, 7H, 7I, and 7J are mounted for the purpose of
12 capturing multiple images to achieve enhanced resolution.
13 It is to be understood, however, that even though
14 numerous characteristics and advantages of the present
invention have been set forth in the foregoing description,
16 together with details of the structure and function of the
17 invention, the disclosure is illustrative only, and changes
18 may be made in detail, especially in matters of shape, size
19 and arrangement of parts within the principles of the
invention to the full extent indicated by the broad general
21 meaning of the terms in which the appended claims are
22 expressed.
