referring to fig1 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 fig2 . 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 fig3 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 fig3 . 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 fig2 with head angle sensors , as shown in fig4 . 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 fig2 has an x - ray head 16 substantially similar to that illustrated in that figure and fig4 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 fig5 . 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 . fig5 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 fig6 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 fig2 . 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 fig6 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 fig7 . considering fig7 an x - ray head 76 , such as that shown in fig2 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 fig7 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 fig7 the display 94 has the two linear arrays 70 , 72 of leds of the type described in connection with fig6 . 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 fig6 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 fig6 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 .
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 .