Abstract:
An anti-collision method and apparatus for use with a C-arm x-ray imaging machine to prevent damage to the imaging apparatus and injury to patients and health care workers includes a load cell, a differential buffer and integrator, an analog to digital converter, and a microcontroller controlling the motor drive. The present invention also provides a method for controlling the apparatus via a microcontroller and includes the steps of determining whether an up/down switch is actuated, reading and comparing a value with a tabulated value, halting the C-arm if the difference between the tabulated value and the recorded value exceeds a threshold value and reversing the apparatus.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention relates generally to the field of x-ray imaging systems. More specifically, it relates to an anti-collision method and apparatus for use with a C-arm x-ray imaging machine for preventing serious collisions between patients, operators and the equipment itself.  
           [0003]    2. Background of the Invention  
           [0004]    It is frequently desired to conduct an x-ray examination of a patient from several different positions and is often preferable to do so without the need to reposition the patient. Mobile C-arm X-ray diagnostic machines, such as that shown in FIG. 1, have been developed to meet these needs and are now well known in the medical and surgical arts. The C-arm x-ray machine is especially useful in that it is small enough and mobile enough to be present in an operating or exam situation without requiring the physician to repeatedly move or requiring the patient to change positions to obtain a suitable image.  
           [0005]    The term “C-arm” refers to the C-shaped member of the machine that contains an x-ray source and an image receptor mounted on opposing ends of the C-arm such that x-rays emitted by the source are incident on and detected by the image receptor. The source and the image receptor are positioned such that when, for example, a human extremity is interposed between the x-ray source and the image receptor and irradiated with x-rays, the receptor produces data representative of characteristics of the interposed object. The data produced is typically displayed on a monitor and electronically stored.  
           [0006]    The C-arm itself is normally mounted such that it is permitted two degrees of freedom. First, the C-arm track is slidably mounted to the support member so as to be movable in relation to the support member. This permits the x-ray source and image receptor to be moved rotatably about the arc of curvature of the track in the C-arm. The C-arm support member also permits rotation of the C-arm about its axis. Often the support member is in the general shape of an L and is referred to as the L-arm, or yoke. Mobile C-arms have a third degree of freedom in that they are free to move horizontally along the floor and a fourth degree of freedom because the C-arm can be moved both upwardly and downwardly.  
           [0007]    Obviously, a support structure that permits rotation and movement of such a C-arm must be constructed to withstand large torsional, tensile and compressive stresses. It is also desirable to provide a support structure heavy enough and a center of gravity low enough to avoid tipping when the C-arm is raised and rotated, which in some cases causes a dramatic shift in the center of mass of the equipment.  
           [0008]    Additionally, C-arm x-ray equipment must be delicately positioned in order to render the image or images desired by the physician. Unfortunately, the weight of the support structure makes it difficult to position the C-arm. Therefore, it is desirable to design a source of frictional drag between the C-arm and the support member as well as on the C-arm track. It is also desired to provide an electric motor to move the C-arm both up and down due to the weight of the apparatus.  
           [0009]    The delicate nature of the x-ray equipment requires delicate handling. Additionally, patients needing x-rays often require careful handling. In order to make the C-arm x-ray safer for the patient and to reduce the likelihood of damage to the C-arm itself, the device of the present invention provides for an anti-collision alarm and mechanism that stops movement of the C-arm upon contact with an object and then reverses movement of the C-arm to release the force exerted on the object by the machine.  
         SUMMARY OF THE INVENTION  
         [0010]    It is therefore an object of the present invention to provide a method and an apparatus for use with a C-arm x-ray machine that emits a warning when the C-arm has run into an object, such as a patient, a gurney, or other obstacle. It is yet another object of the present invention to provide for such a method and apparatus that stops the C-arm when a part of it runs into an obstacle such that no damage occurs to the obstacle or to the C-arm, and prevents injury to the patient. A further object of the present invention is to provide such a method and apparatus that includes a programmable device in which the threshold of force required to stop the C-arm and sound the alarm may be varied. It is yet another object of the present invention to provide such a method and apparatus that requires relatively few parts, that can be easily manufactured and that can be readily installed on new or existing equipment.  
           [0011]    The device of the present invention has obtained these objects. It provides for a load cell that is mounted at the bottom of the vertical column of the C-arm x-ray machine. This load cell converts the load, or the dynamic change in the load, on the vertical column into an electrical signal. The electronic signal is directed to an electronic circuit that filters and buffers the signal. The filtered signal is directed to a microcontroller. The microcontroller compares the load value with a database of preset load values and can operate to turn off the electric motor that raises and lowers the C-arm if the difference between the force on the load cell and the force expected by the microcontroller is greater than a certain amount. The microcontroller is adjustable such that the amount of force required to stop the motor can be varied. The electronic circuit in the method and apparatus of the present invention then reverses the electric motor to release the force exerted by the machine. Additional objects and advantages of the invention will be set forth in the description that follows. Other objects and advantages may be learned by practice of the invention. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]    [0012]FIGS. 1A and 1B illustrate a C-arm x-ray machine that utilizes the method and apparatus of the present invention.  
         [0013]    [0013]FIG. 2 is a flow chart summarizing the workflow of the present invention.  
         [0014]    [0014]FIGS. 3A and 3B are diagrams illustrating load curves that may be employed in accordance with the method and apparatus of the present invention. More specifically, FIG. 3A is a tabular example of a Look Up Table (LUT) and FIG. 3B is a graphic example of an LUT.  
         [0015]    [0015]FIG. 4 is a flow chart also summarizing the workflow of the present invention. 
     
    
     DETAILED DESCRIPTION  
       [0016]    The following detailed description is intended to describe the preferred embodiments that are depicted in the figures. It is to be understood that changes could be made to that which is specifically described and shown that would still fall within the scope of the present invention.  
         [0017]    Referring now to the drawings in detail, wherein like numbered elements refer to like elements throughout, FIGS. 1A and 1B depict the basic components of the C-arm x-ray imaging system with which the method and apparatus of the present invention is utilized. In general, the C-arm x-ray imaging machine, generally identified  10 , is comprised of the following components: a support base having a vertically extendable column, a C-arm mounting apparatus providing movement of the C-arm in several directions, the C-arm  100 , an x-ray source  12 , an image receptor  14 , an image processing system, a display and viewing system, a high voltage generator and a control unit.  
         [0018]    The x-ray source  12  preferably comprises an x-ray tube and a high-voltage generator. The high-voltage generator is preferably connected to an adjustable high-voltage power supply capable of generating approximately −70 kV to −120 kV. The x-ray source  12  is generally a scanning beam x-ray in which charged particles are scanned across a target assembly. The x-ray source  12  generally includes a series of deflection coils under the control of a scan generator. High-energy charged particles are generated within a vacuum chamber and then scanned across the target. When the system is operated, the charged particle beam strikes the target and generates x-ray photons. The x-ray photons preferably pass through a collimator and form an x-ray beam. The x-ray beam has an axis that is substantially aligned with the center of the active area of the x-ray detector. The x-ray beam has a vector that is defined by the axis of the x-ray beam in the direction of the x-ray detector assembly. The imaging object generally refers to the patient. X-rays that have passed through the patient are detected and later processed for some form of interpretation.  
         [0019]    The image receptor  14  captures the x-ray photons scanned across the imaging object and converts them to electrical signals. The impulses are then converted to digital data and either stored or directed immediately into a computer for image reconstruction. The imaging process system generally consists of a computer with a software package that reconstructs the image and displays the image on a screen and a device that provides for storage of the image. The display system and the control unit are normally remotely operated. Thus the operator can be shielded from radiation but still perform the x-ray. Alternatively, the entire system can be placed in an examining or operating room so that the health care provider can view images of the patient in real time.  
         [0020]    The mobile C-arm x-ray imaging machine, generally identified  10 , is comprised of a wheeled support base  60 . In a preferred embodiment the support base  60  is a generally rectangular upright body that may be equipped with one or more video monitors and has an upper portion or vertically extendable column  40  with an extendable cross arm  50 . The support base  60  generally features a vertical column  40  used to raise and lower the cross arm  50 . The vertical column  40  raises and lowers the cross arm  50 , which in turn raises and lowers the C-arm apparatus, which is generally comprised of the support arm  30 , the yoke,  20  and the C-arm  100 . The vertical column  40  is generally between the support base  60  and the vertically extendable column  40  and bears the entire weight of the C-arm  100 . The vertical column  40  is generally both raised and lowered using an electric motor (not shown). The extendable cross arm  50  has a first portion  51  slidably mounted within the vertically extendable column  40  and a second end  52  having an aperture in the end of the cross arm  50 . The support base  60  is important to the imaging system  1  in that it provides a platform for the yoke  20  and the C-arm  100 . Therefore, the support base  60  should have a footprint large enough such that the yoke  20  and C-arm  100  are permitted to rotate and can be lifted and lowered without the danger of tipping and/or the support base  60  must be heavy enough to prevent tipping of the C-arm x-ray machine  10 .  
         [0021]    [0021]FIGS. 2 and 4 are schematic summaries of the workflow of the method and apparatus of the present invention. From rest, the C-arm  100  is activated to move the vertical column  40  either up or down  161 . A microcontroller  140  is provided and the microcontroller  140  reads the analog to digital converter  130  and compares it with the value in a Look Up Table  162  (or “LUT”). The microcontroller  140  then determines whether the difference between the value reported and the value in the LUT is greater than the allowable, or threshold, value  163 . If it is not, the process continues the up or down movement  161 . If the threshold  163  is met or exceeded, the C-arm  100  is halted  164 , an audio alarm, or buzzer, is sounded  165  and the motor M is reversed  165  incrementally and then stopped  165 .  
         [0022]    As shown in FIG. 2, the method and device of the present invention provide for a load cell  110  mounted at some point along the bottom of the vertical column  40 . The load cell  110  is capable of sensing the proportional change of the resistivity of the material of the vertical column  40  and emits an electronic signal proportional to that change.  
         [0023]    The electronic signal is directed from the load cell  110  to a differential buffer and an integrator  120  to isolate and filter the signal. The filtered signal is then routed to an analog to digital converter  130 . The analog to digital converter  130  is often part of a microcontroller  140 , as shown in FIG. 2.  
         [0024]    The microcontroller  140  effectively reads the output from the analog to digital converter  130  and compares it with reference values in an LUT, such as the one shown in FIG. 3A. If the difference between the output of the load cell  110  is larger than the reference value in the LUT, the microcontroller  140  sends a signal to the motor drive  150  that stops the motor drive  150  and sends a signal to a buzzer  160 , which alerts the operator to the potential problem. It is often advantageous to program the microcontroller  140  to operate the motor drive  150  in the reverse direction to alleviate the force on the obstacle as well as the force on the C-arm  100 .  
         [0025]    The LUTs are created by operating the C-arm  100  over its full range of motion in the absence of obstacles and recording the values at different heights. It is preferred to have four sets of LUTs, one for upward motion of the C-arm  100 , one for downward motion of the C-arm  100 . The other two LUTs are designed to be used when the C-arm  100  is activated for initial movement of the C-arm  100  in both the upward and downward directions. The weight and weight distribution of the C-arm  100  combine to create a spike in the load recorded by the load cell  1   10  during the initial movement of the C-arm  100 . During an initial jerk, the input value is compared with an LUT specifically designed for either upward or downward jerks. Obviously, this spike is not related to an encounter with an obstacle and the inventors do not wish for the C-arm  100  to reverse itself at that point of operation.  
         [0026]    An LUT is nothing more than an index of the position of the vertical column  40  as measured by a multi-turn potentiometer and a gear assembly versus the amount of force recorded by the load cell  110  converted to digital. A baseline value is first established for each position along the vertical column  40 . Baseline values are then established by starting movement of the C-arm  100  in both upward and downward directions at each point along the vertical column&#39;s  40  range of motion. The amount of force required before the motor drive  150  is reversed can be varied, depending on the desired sensitivity of the system.  
         [0027]    [0027]FIGS. 3A and 3B are simple examples of LUTs. Each table describes the load on the load cell  110  in the absence of external force over the range of vertical motion of the column  40 . As can be observed from the figures, the load varies over the range of the vertically extendable column  40 . Two more sets of LUTs are necessary in the preferred embodiment. Those LUTs would account for the larger forces encountered when the C-arm  100  is initially moved.  
         [0028]    It is to be understood that the invention is not limited to the embodiments set forth herein but that the invention may be carried out in other ways without departure from the spirit of this invention.  
         [0029]    Parts List:  
         [0030]    [0030] 10  C-arm x-ray imaging system  
         [0031]    [0031] 12  x-ray source  
         [0032]    [0032] 14  image receptor  
         [0033]    [0033] 20  yoke  
         [0034]    [0034] 30  support arm  
         [0035]    [0035] 40  vertical column  
         [0036]    [0036] 50  cross arm  
         [0037]    [0037] 51  first end of the cross arm  
         [0038]    [0038] 52  second end of the cross arm  
         [0039]    [0039] 60  support base  
         [0040]    [0040] 100  C-arm  
         [0041]    [0041] 110  load cell  
         [0042]    [0042] 120  differential buffer and integrator  
         [0043]    [0043] 130  analog to digital converter  
         [0044]    [0044] 140  microcontroller  
         [0045]    [0045] 150  motor drive  
         [0046]    [0046] 160  buzzer, audio alarm  
         [0047]    [0047] 161  process step—determining whether the up/down switch is actuated  
         [0048]    [0048] 162  process step—read value and compare with the Look Up Table (LUT) value  
         [0049]    [0049] 163  process step—is difference greater than the threshold value  
         [0050]    [0050] 164  process step—C-arm is halted  
         [0051]    [0051] 165  process step—motor reversed, buzzer sounds