Abstract:
An X-ray imaging system has an X-ray head containing an x-ray source which emits an X-ray beam. The head is rotatable around a pair of orthogonal axes for orienting the emitted X-ray beam in space. A pair of head angle sensors are located with the X-ray head, each being associated with a different one of the pair of axes for measuring an angle of inclination of the X-ray head dependent on its rotation around its associated axis. A display is operably connected to each head angle sensor through a signal processing unit for providing a graphic displaying of angle information related to each of the measured angles collocated at a single viewing station.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an X-ray imaging system of the nonintegrated type having an X-ray head or radiator containing an X-ray source for generating an X-ray beam, the head being rotatable for orienting the X-ray beam in space, and a planar X-ray imaging device having no mechanical connection with the X-ray head. 
     2. Description of the Prior Art 
     In X-ray examinations of patients it is important for the X-ray beam which is emitted from the X-ray source to strike the X-ray film or other planar imaging device, such as a digital image receiver, at the correct angle after passage through that part of a patient that is to be radiographed, so that the resultant image is un-distorted. To achieve this it is important that the imaging device and X-ray head be properly orientated relative to each other (usually so that a central ray from the X-ray source strikes the imaging device perpendicular to the plane of its imaging surface). A known mobile X-ray imaging system, such as that described in the brochure MOBILETT™ Plus HP “Instructions for Use” of the company Siemens-Elema AB, is used with a film cartridge (or cassette) which has no mechanical connection with the X-ray head. This film cartridge is placed under the patient, often under the mattress on which the patient rests, and an operator is able to rotate the X-ray head around two mutually perpendicular rotational axes until the X-ray source and the cartridge are properly orientated with respect to one another. 
     To facilitate this orienting it is known from the MOBILETT to provide a head angle sensor having a ball, movable in an arcuate ball-race (or groove) and overlaid with a see-through display having angles marked on its surface corresponding to angles of inclination of the head from the horizontal. The actual angle of inclination of the head is indicated by the visual correspondence of ball and an angle mark. This means that in order to achieve an accurate reading of the angle from the display the operator must be standing substantially directly in front of the display. Such an angle sensor is placed on each of two mutually perpendicular outer wall sections of the X-ray head to respectively measure the degree of rotation of the head with respect to the horizontal around each of the two mutually perpendicular rotational axes. In use, an operator measures the angle of inclination (desired angle) of the planar imaging surface to the horizontal around each of a pair of axes corresponding to the rotational axes of the X-ray head and then, with the aid of the angle sensors, inclines the head to the same degree so that the central ray of the X-ray beam is perpendicular to the planar imaging surface of the imaging device. 
     One problem with such an arrangement is that the angle information is displayed at two separate viewing stations, perpendicular to one another. This means that the operator cannot see angle information for both angles of inclination of the X-ray head at the same time and must move around the imaging system to verify each of the angles of inclination of the head. Furthermore the operator must remember the desired angles which only adds to the burden of the operator when setting up the system. 
     As used herein the term “viewing station” means a region of or on the external surface of X-ray imaging system at which one or more displays are situated with the intention to be viewable from a single operator location. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to provide an x-ray imaging system which avoids the above-discussed problem of inclination information being displayed at separate viewing stations which are not simultaneously observable. 
     The above object is achieved in accordance with the principles of the present invention in an x-ray system having an x-ray head containing an x-ray source which emits an x-ray beam, the head being rotatable around a number of axes for orienting the emitted x-ray beam in space, and having a number of head angle sensors located with the x-ray head, respectively for the different axes, which measure an angle of inclination of the x-ray head dependent on the rotation around the associated axis, each head angle sensor being connected to a display for displaying angle information related to the measured angles, and wherein each head angle sensor provides an output signal indicative of the measured angle, the display receiving these output signals and providing a graphic display of the angle information for each head sensor together at a single viewing station. 
     By providing angle sensors, such as accelerometers or inclinometers, which each have an output signal dependent on the sensed angles, then respectively associated displays which provide a graphic display of angle information dependent on the output signal can be readily allocated together at a single viewing station, independent of the location of the angle sensors. 
     Preferably, a difference former is provided which generates a signal indicative of a difference between the angle measured by each sensor and a corresponding desired angle of inclination, for example entered by an operator via a user interface such as a keypad or entered automatically from angle sensors at the X-ray imaging device, for supply to and use by the displays to provide a visual indication of the differences. 
    
    
     DESCRIPTION OF THE DRAWINGS 
     FIG. 1 illustrates a known non-integrated X-ray imaging system in use. 
     FIG. 2 illustrates a known mobile X-ray generator together with the pertinent rotational axes for the X-ray head. 
     FIG. 3 is a schematic of the illumination of the X-ray imaging device by an X-ray beam from the X-ray head. 
     FIG. 4 illustrates a known angle sensor used with the X-ray head of FIG.  2 . 
     FIG. 5 illustrates a portion of the X-ray head of FIG. 2 adapted according to the present invention showing internally disposed head angle sensors. 
     FIG. 6 illustrates a display for showing angle information dependent on the outputs of the sensors of FIG. 5 
     FIG. 7 is a block diagram of an embodiment of a non-integrated X-ray imaging system according to the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to FIG. 1, a non-integrated X-ray imaging system  2  is shown having a rotatable X-ray head  4  carried by an arm  6  and a mechanically separate planar X-ray imaging device  8 , such as a film cartridge or a digital imaging array, for recording an image of a patient  10  beneath whom it is located. The imaging device  8  is shown inclined at an angle to the horizontal. The X-ray head  4  contains an X-ray source (not shown) with which an X-ray exposure of the patient  10  can be carried out. A computer system  12  provides a user interface via which information, such as for controlling the duration and energy of an X-ray beam produced by the X-ray source, may be entered into a power supply/control unit  13  of the system  2 , which is responsive to the input to vary the power it supplies to the X-ray head  4 . 
     A mobile X-ray generator  14  is shown in FIG.  2 . This type of generator  14  is usually provided to be rolled to a bed of the patient when an X-ray image is needed. An X-ray head  16  is located at one end of an arm  18  and may be effectively adjusted vertically and horizontally with respect to a control/power supply unit  20  by rotation of the arm  18  about a first pivot axle  22  and a second pivot axle  24 . Importantly for the system according to the present invention the X-ray head  16  is mounted for independent rotation about each of two orthogonal axes X and Y, as shown by the arrows. 
     As is well known in the art and as is shown in FIG. 3, the X-ray head  16  contains an X-ray source, such as an X-ray tube  26  with a collimator  28  in the form of movable diaphragm plates  30  with which a generally rectangular X-ray beam  32  can be generated. The X-ray beam  17  is oriented in centered fashion on a planar, typically rectangular, imaging surface  34  of an imaging device, such as a film cartridge  36  that is arranged on an examination table (or patient bed)  38 . The preferable and most common mutual orientation of the head  16  and imaging surface  34  is illustrated in FIG.  3 . wherein the central ray  40  of the X-ray beam  32  strikes the mid-point  42  of the planar imaging surface  34  perpendicularly to that surface  34 . 
     To aid in the mutual orientation it is known to provide the head  16  of the system of FIG. 2 with head angle sensors, as shown in FIG.  4 . The head  16  is mounted in a cradle  44  by means of a rotational mount  46  for rotation of the head  16  about the axis X. The cradle  44  is itself rotatable about an axle  48  connected to the arm  6  for rotation of the head  16  about the axis Y which is perpendicular to the other axis X. A first known head angle sensor  50 , of the ball type as described with regard to the MOBILETTE system above, is mounted on an external surface of the head  16  at a first viewing station  52  for providing a display of the angle of inclination of the head  16  to the horizontal dependent on rotation about the associated axis X. A second known head angle sensor  54  is mounted on an external surface of the head  16  at a second viewing station  56  to be perpendicular to the first sensor  50  and provides a display of the angle of inclination of the head  16  to the horizontal dependent on rotation about the associated axis Y. As can be seen from the figure an operator cannot read both head angle sensors  50 ,  54  from a single operating location. 
     A non-integrated X-ray imaging system according to the present invention for example, as illustrated in FIG. 2, has an X-ray head  16  substantially similar to that illustrated in that figure and FIG. 4 except that the angle sensors  50 ,  54  have been removed and replaced with known angle sensors having an electrical signal output indicative of a detected angle of inclination, such as first and second accelerometers or inclinometers  58 ,  60  illustrated schematically in FIG.  5 . These head angle sensors  58 ,  60  are arranged to measure inclinations of the head  16  as occur with rotations around the X and Y axes respectively, to provide functional equivalence with known angle sensors  50 ,  54 . FIG. 5 shows a portion of the X-ray head  16  showing the first and the second head angle sensors  58 ,  60  located internally of the head  16  with their outputs connected to a processing unit  62  which may include the functionality of a difference forming means as described below and which drives a display  64 . The display  64  is here illustrated as a visual display unit such as an LCD unit but may be of the type described below with reference to FIG. 6, and is driven by the processing unit  62  to display angle information dependent on the angles measured by the first and second head angle sensors  58 ,  60 . The display  64  thus acts to present angle information from each of the head angle sensors  58 ,  60  at a single viewing station  66 , which is here shown to be an external wall section of the head  16 . Alternatively, one or both of the processing unit  62  and the display  64  can be located in or on the power/control unit  20  of the imaging system of FIG.  2 . It will be appreciated that the display  64  may also be formed by two displays in a side-by-side arrangement (not shown), one associated with each angle sensor  58 ,  60 , while still being at a single viewing station  66 . 
     A further form of the display  68  is shown in FIG. 6, which is particularly useful for displaying differences between an actual angle of inclination, as measured by a one of the head angle sensors  58 ,  60 , and a corresponding desired angle of inclination, as described in more detail below, to intuitively guide an operator to vary the inclination of the X-ray head  16  to achieve the proper orientation. The display  68  has a first linear array  70  of individually actuable light emitting diodes (LEDs) intersecting with and substantially perpendicular to a second linear array  72  of LEDs. The LED  74  common to each array  70 ,  72  is here arranged to be the middle LED of each of the arrays  70 ,  72 . When the arrays  70 ,  72  are employed to display the differences, this middle LED illuminates to indicate correct alignment (zero angular difference between the head  16  and imaging device). The operation of this display  68  is explained in greater detail below with regard to the non-integrated X-ray imaging system shown in FIG.  7 . 
     Considering FIG. 7, an X-ray head  76 , such as that shown in FIG. 2, contains first and second head angle sensors  78 ,  80  for measuring respective angles of inclination of the head  76  to the horizontal for rotation of the head  76  about respective perpendicular axes X and Y, as described above. The head  16  is operably connected to a power/control unit  82  which provides power to energize an X-ray source (not shown) within the head  16 . An imaging device  84 , such as a digital imaging array or a film cartridge, is also provided in non-mechanical connection with the imaging head  76  so as to be mutually independently orientable. A first imaging angle sensor  86  and a second imaging angle sensor  88  are located with the imaging device  84 , each providing an output signal indicative of the inclination of a planar imaging surface  90  of the imaging device  84  to the horizontal to complement those angles measured by the head angle sensors  78 ,  80 . The angles measured by the imaging angle sensors  86 ,  88  provide desired angles which are to be attained by the X-ray head  76  (as measured by the complementary head angle sensors  58 ,  60 ). Alternatively the imaging angle sensors  86 ,  88  may be mounted on a support which is removably locatable on the imaging device  84 , preferably on or proximal with the planar imaging surface  90 . Such a support may have two orthogonally arranged support bars, one for each imaging sensor  86 ,  88 , which may be located on the imaging device  84  so as to lie substantially parallel with adjacent sides of the planar imaging surface. 
     A processing unit  92 , such as a programmable microprocessor, is located within the power/control unit  82  and is arranged to receive signals from all sensors  78 ,  80 ,  86 ,  88  representative of the angles measured by each of the sensors  78 ,  80 ,  86 ,  88  and to form a difference between the desired angles measured by the imaging angle sensors  86 ,  88  and respective angles measured by the complementary head angle sensors  78 ,  80 . A signal indicative of this difference for rotation of the head around each of the X and Y rotational axes provides a drive signal to a display  94  which is located either on the head  76  or the power/control unit  82  at a single viewing station. The display  94  responds to the drive signal by providing a visual display related to the thus formed differences. As also shown in FIG. 7 a user input device  84 , such as a keypad or keyboard (with or without an associated display) is also provided, via which an operator may provide the desired angles, measured manually in a known manner, as an alternative to having the display  94  provided with imaging angle sensors  86 ,  88 . 
     In the embodiment of FIG. 7 the display  94  has the two linear arrays  70 ,  72  of LEDs of the type described in connection with FIG.  6 . The array  72  is here associated with “Y-differences”, for rotation of the head  76  around the Y axis. This is the output from the second imaging angle sensor  88  minus that from the second head angle sensor  80 . The array  70  is here associated with “X-differences”, for rotation of the head  76  around the X axis. This is the output from the first imaging angle sensor  86  minus that from the first head angle sensor  78 . 
     The processing unit  92  is programmed to form an X-difference and selectively activates one LED  98  in the LED array  70 , the location of which one LED  98  is dependent on this X-difference. In this example the processor  92  operates to cause an individual LED  98  in the LED array  70  to illuminate, selected according to the rules: 
     (a) For absolute values of X-differences greater than 10 degrees each LED of the array  70  represents a variation of 10 degrees from the desired angle (represented by the central LED  74 ). 
     (b) For absolute values of X-difference less than 10 degrees each LED of the array  70  represents a variation of 1 degrees from the desired angle. 
     Thus as, shown in FIG. 6 the processor  92  has formed an X-difference with an absolute value of either 2 degrees or of between 20 to 29 degrees. The processing unit  92  also is programmed to form a Y-difference and selectively illuminates one LED,  100 , in the LED array  72 , the location of which one LED  100  is dependent on this Y-difference. In this example the processor  92  operates to illuminate an individual LED in the LED array  72  according to the rules, suitably amended for reference to the Y-difference, set out above for illuminating an individual LED in the array  70 , dependent on the X-difference. 
     Thus as, shown in FIG. 6 the processor  92  has formed a Y-difference with an absolute value of either 4 degrees or of between 40 to 49 degrees. 
     The processing unit  92  is further programmed to utilize the signs of the X- and Y-differences respectively determine on which side of the central LED  74  the individual LED will be illuminated. 
     It will be appreciated by those skilled in the art that the resolution of the display can be readily adjusted to suit the particular application and the resolution of the angle sensors  78 ,  80 ,  86 ,  88  used. It will be further appreciated that the individual LED arrays  70 ,  72  may be readily replaced by a visual display unit driven to display individual segements each corresponding to an individual LED of the arrays  70 ,  72 , which segments may be higlighted in a manner corresponding to the activation of an individual LED  98 ,  100  in each of the respective arrays  70 ,  72 . 
     The common LED  74  can be operated by the processor  92  to blink until both desired angles have been attained by the X-ray head  76 , at which time the illumination will become constant. This blinking provides a enhanced visual warning to the operator that the orientation of the head  76  is incorrect. 
     Although modifications and changes may be suggested by those skilled in the art, it is the intention of the inventors to embody within the patent warranted hereon all changes and modifications as reasonably and properly come within the scope of their contribution to the art.