Abstract:
A self-aligning collimator for a radiation imaging device that is secured and aligned through the use of a plurality of small magnets. The collimator allows for the rapid exchange, removal, or addition of collimators for the radiation imaging device without the need for tools. The accompanying method discloses the use of magnets and accompanying magnetic fields to align and secure collimators in a radiation imaging assembly.

Description:
The United States of America may have certain rights to this invention under Management and Operating Contract No. DE-AC05-84ER 40150 from the Department of Energy. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to a device and method for attaching one or more collimators in a radiation imaging system. 
     BACKGROUND OF THE INVENTION 
     Medical imaging through the use of radionuclides has become a critical component in the diagnosis and treatment of many diseases and conditions. A device, such as a gamma camera, can be used to detect radiation emitted from radioisotopes. These types of devices are often used by physicians within a sterile surgical field. 
     One or more collimators are typically employed in such a device in order to facilitate the desired imaging. A collimator can be used to reduce stray or unwanted radiation so that it does not reach the detector portion of the imaging device. Stray or scattered radiation, e.g., radiation that is not travelling parallel from the imaged area, may significantly impair the resolution of the device. 
     In certain types of radiation imaging, it is necessary to frequently change collimators. Collimators may be changed for several reasons, including adapting the radiation imager to a different energy, changing its resolution or count rate, or changing the angle of view. 
     A surgeon may have the desire to initially operate the gamma camera at a rapid speed, with low resolution, as he begins the process of localizing a target area. In such cases, the gamma camera might be operated with simply one collimator attached. Once the surgeon approaches a suspect lesion, he may wish to increase the resolution of the device. He may then add one or more additional collimators until the desired resolution is achieved. 
     In traditional assemblies, the collimators are retained by screws within flanges. With intraoperative radiation imagers, the devices are usually operated within a disposable sheath or sleeve in order to maintain the integrity of the sterile field. The use of a sleeve is a preferred method of operation as sterilization of the entire gamma camera assembly is more problematic due to the numerous surfaces and crevices on the assembly. If a different collimator is required, the device must be removed from the sterile field, the collimator changed using tools, the device inserted in a new sterile sheath, and then returned to the sterile field. This method of exchange is time-intensive and may result in a disruption of the surgical procedure. The use of screws/flanges has further drawbacks in that it requires an inert area within the collimator structure that in some cases inhibits the optimum use of the collimator. 
     It is therefore preferable to have a collimator that can be easily and quickly changed. It is further desirable to have a device and method which insures the accurate and precise positioning of the collimators in the assembled radiation imager. 
     OBJECT OF THE INVENTION 
     It is an object of the invention to provide a collimator design and a method of attachment which permits a user to rapidly and effectively exchange, add, or remove collimators from a radiation imaging device, particularly one that is being used inter-operatively. 
     SUMMARY OF THE INVENTION 
     The present invention discloses a self-aligning collimator that is secured to other collimators on a radiation imaging device through the use of a plurality of small magnets. The magnets allow a user to rapidly exchange collimators. The disclosed collimator uses the magnetic field of the magnets in order to guide the collimators into an appropriate axial alignment and to insure proper rotational orientation. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of a gamma camera assembly. 
         FIG. 2  shows the bottom ( 2   a ) and top ( 2   b ) of a base collimator. 
         FIG. 3  shows a perspective view of an additional collimator: front ( 3   a ) and back ( 3   b ). 
         FIG. 4  is a plane top view of an additional collimator. 
         FIG. 5  is a side view of a preferred embodiment of a gamma camera assembly with attached collimators. 
         FIG. 6  is a side view of an alternate embodiment of a gamma camera assembly with attached collimators. 
     
    
    
     DETAILED DESCRIPTION 
     The present invention discloses a device and method for securing and aligning collimators to a radiation imaging assembly such as a gamma camera. In many common applications, multiple collimators are used in the imaging device. These collimators are stacked on top of one another in a particular alignment and orientation. When stacking collimators in such a fashion, it is essential to maintain their position relative to both one another and the radiation imaging assembly. The present invention facilitates the replacement, addition, or removal of such additional collimators on the imaging assembly. 
     In operation, a radiation imaging device such as the gamma camera  100  depicted in  FIG. 1 , may utilize one or more collimators  105  and  110 . A base collimator  105  is secured to the gamma camera  100  through the use of a bayonet-type mount or similar structure as seen in  FIG. 2   a . In a preferred embodiment, the base collimator  105  includes a first portion of a bayonet mount  115 . The gamma camera base includes a second portion of the bayonet mount, i.e., slots, designed to receive and secure the first portion of the mount. The bayonet mount may be made of brass or any other suitable material. 
     Additional or extra collimators may then be easily added to the gamma camera assembly and base collimator through the use of magnets. Referring now to  FIG. 3   a , each additional collimator disk  120  incorporates four magnets  125  of appropriate strength. When an additional collimator disk is to be attached, each such magnet is subsequently attached to a corresponding magnet on the additional collimator disk. Accordingly, four pairs of magnets are used to secure and align the collimator disks. 
     Each magnet  125  is embedded at a pre-determined location in the collimator disk  120 . Therefore, each magnet  125  is essentially flush with the top  130  and bottom  135  surfaces of the collimator, as shown in  FIGS. 3   a  and  3   b . Further, each magnet  125  would be located such that each would be in alignment with magnets of additional collimator disks that may be positioned above or below a particular disk.  FIG. 4  shows a plan view of an additional collimator disk  120 . 
     Each collimator disk beyond the base disk  105  must be precisely aligned with the gamma camera  100  and other collimator disks. In traditional collimator arrangements, e.g., where mounting screws are used, the collimator disks must be physically moved into proper alignment so as to permit the installation of the screws. 
     In the preferred embodiment of the invention shown in  FIG. 5 , the magnetic field of the magnets  125 , rather than hand placement, is used for alignment. The magnetic field of the magnets  125  serves to axially align the collimators within acceptable limits. As an example, if the collimator placement on the assembly is off by ¼ mm, the magnetic field will pull the collimator into proper axial alignment at a 0, 0 (x, y) coordinate position relative to the collimators and radiation imaging assembly. The magnets  125  are mounted in holes in the collimator body. 
     In an alternate embodiment, shown in  FIG. 6 , the magnets  135  are not flush with the collimator surfaces. In this alternate embodiment, each magnet  135  is positioned within the hole such that the bottom portion of the magnet projects outward from the bottom side of the collimator surface for a short distance. This positioning also results in the creation of a small aperture or depression  140  on the top surface of the collimator. The aperture or depression  140  on the top surface of the collimator then serves to receive the magnet  135  extension from an additional collimator if further stacking is desired. 
     In such an embodiment, the magnets  135 , in essence, also act as dowels. Each collimator disk  145 ,  150 ,  155  is then axially aligned and further secured by placing the protruding portion of the magnets  135  in the appropriate corresponding aperture on another respective collimator disk. 
     Rotational orientation of the collimators is also critical in the imaging assembly. Proper rotational orientation can be achieved in more than one fashion. In the preferred embodiment, the rotational alignment is achieved through a particular arrangement of the polarity of the magnets. As mentioned earlier, four pair of magnets may be used. In such case, the respective poles of the pairs of magnets are oriented as north/south and south/north. As a result of the foregoing arrangement, if two collimators are placed together such that they are rotated 180 degrees out of alignment, the two collimators will not remain secured together and will simply fall apart. In order to rectify that problem, the user will have to spin one of the collimators around to the correct alignment, i.e., until the correct pairs are aligned up, and they will lock on. 
     In an alternate embodiment, one pair of the magnets is installed a few degrees out of alignment. In this alternate embodiment, if a user attempts to place a collimator disk in an incorrect rotational alignment, the magnets will force the disk noticeably out of axially alignment and a user would be alerted as to the improper rotational positioning. 
     When used inter-operatively, the addition, removal, or substitution of collimators may be accomplished while the gamma camera remains in the sterile surgical field and the device is still retained within the sleeve. A user can actually leave or stack additional collimator disks in the sleeve—at a location further up the sleeve. The additional collimator disks can then be slipped into place as necessary. Once the additional collimator disk is placed somewhat near the proper positioning, it will simply click into place. The magnetic field will insure proper alignment and will further secure the additional collimator without the need for removal of the device from the sheath or the use of tools. 
     In addition, the elimination of the mounting screws and flanges serves to provide smoother surfaces on the gamma camera device. Smoother surfaces are preferable in order to reduce the likelihood of retaining bacteria or other such contamination on the exterior of the device. 
     While the invention has been described in reference to certain preferred embodiments, it will be readily apparent to one of ordinary skill in the art that certain modifications or variations may be made to the system without departing from the scope of invention claimed below and described in the foregoing specification.