Abstract:
A collimator handling system for partially or fully automating the task of replacing and storing collimators in nuclear imaging systems. A collimator server stores a set of different collimators in stacked drawers which may be automatically extracted into the detector. The reduction in time spent on these tasks reduces cost and increases throughput. Furthermore, the automation of handling heavy lead (or like) collimators increases technician safety,

Description:
BACKGROUND  
       [0001]     The invention relates to nuclear medicine imaging systems, and more particularly relates to collimators used with gamma cameras in the detectors of nuclear medicine imaging systems. In its most immediate sense, the invention relates to a method and apparatus for the transfer, removal, mounting and storage of collimators in nuclear medicine imaging systems.  
         [0002]     Nuclear medicine imaging assesses the radionuclide distribution within a patient after the in vivo administration of radiopharmaceuticals. Imaging systems that assess radionuclide distribution include radiation detectors and acquisition electronics. The imaging systems detect x-ray or gamma ray photons derived from the administered radionuclides. Single photon emission imaging and coincidence imaging are two forms of nuclear medicine imaging that are currently in common use. In single photon emission imaging, the radionuclide itself directly emits the radiation to be assessed. For example, in Single Photon Emission Computed Tomography (SPECT), y-emitting radionuclides such as  99m Tc,  123 I,  67 Ga and  111 In may be part of the administered radiopharmaceutical.  
         [0003]     Detectors used in such single photon emission imaging often use collimators placed between the patient and the gamma ray camera of the detector. The purpose is to eliminate all photons but those photons traveling in a desired direction. For example, a parallel hole collimator eliminates photons traveling in all directions except those almost perpendicular to the surface of the detector. The energy of emitted photons as well as their location of origin may then be accumulated until a satisfactory image is obtained.  
         [0004]     Coincidence imaging eliminates the need for such a collimator by relying on the detection of two photons at different detectors at nearly the same time. An example of coincidence imaging in current clinical use is Positron Emission Tomography (PET).  
         [0005]     Radiation detectors used in nuclear medicine imaging need to absorb x- or gamma-ray photons in an energy range typically between 1 keV and several MeV. These imaging photons are the photons either directly emitted or resulting from radionuclides within a patient. In order to stop imaging photons of these energies with a collimator in SPECT imaging, a material with a high density and a high atomic number (Z) is necessary. Lead is the most common material used for collimators, but other materials such as tungsten may also be used.  
         [0006]     Radiation detectors for SPECT imaging systems often have the ability to use collimators which may be mounted or removed from the system detectors. These “mountable” detectors are useful because a collimator with a different geometry may yield higher quality images in different situations. Being able to “swap in” a collimator with a specific geometry is thus highly advantageous.  
         [0007]     As mentioned above, collimators need to be made of a material with a high density and a high atomic number in order to effectively stop imaging photons. These materials, such as lead, are very heavy. For example, a typical lead collimator may weigh on the order of several hundred kilograms. This high weight creates many problems for the effective and efficient imaging of patients when collimators which are mountable are in use. One problem is the risk of damage to either the gamma camera system within the detector, or even damage the collimator itself, when physically removing or mounting the collimator into the detector. Another problem is the risk of injury to the medical technician performing the mounting or removal of the collimator. Another problem is the time required to remove an old collimator and mount a new one in a detector. These procedures time increase the set up time for a patient scan, and reduce the throughput of patients of an imaging system, a determining factor in the profitability of an imaging system. In addition, transferring a collimator from a storage location to the imaging system may also increase the set up time for a patient scan. Another problem is that bulky and heavy collimators often require additional floor space for storage. Another problem is that removing and mounting collimators often requires that components of an imaging system, such as a patient handling system, be moved from their standard operating position. This also increase the time required for patient setup.  
         [0008]     Various attempts have been made to address the above problems. However, none of the currently available solutions adequately address the problems of using mountable collimators. Their remains a need in the nuclear medicine imaging art for systems and methods of reducing the danger, time, space, and expense of using modular collimators. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]     The above description, as well as further objects, features and advantages of the present invention will be more fully understood with reference to the following detailed description of the preferred embodiments, when taken in conjunction with the accompanying drawings, wherein:  
         [0010]      FIG. 1  is a side view of an embodiment of the present invention implemented a nuclear medicine imaging system.  
         [0011]      FIG. 2  shows an enlarged side view of a the embodiment of  FIG. 1 .  
         [0012]      FIG. 3  is a flow chart for the procedure of removing a collimator using the embodiment of the present invention shown in  FIG. 1 .  
         [0013]      FIG. 4  is a flow chart for the procedure of mounting a collimator using the embodiment of the present invention shown in  FIG. 1 .  
         [0014]      FIG. 5  shows another embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION  
       [0015]      FIG. 1  shows a nuclear medicine imaging system  2  illustrating one embodiment of the present invention. The imaging system  2  includes a gantry  4 , a rail  6 , a detector  8 , and a patient handling system  10 . The detector  8  includes a collimator slot  12  and a gamma camera  14 . The collimator slot is filled with a first collimator  16 . The gantry  4  is capable of rotating the detector  8  around the center line of the gantry  4 , and the rail  6  allows the detector  8  to moved toward and away from the center line of gantry  4 .  
         [0016]     The patient handling system  10  includes a collimator server  18  integrated into the patient handling system  10 . The collimator server  18  may have a number of different forms. In this particular embodiment, it includes a number of drawers  20 . Each drawer may contain a single collimator, or may be empty.  
         [0017]      FIG. 2  shows an enlarged view of the embodiment of the present invention of  FIG. 1 . wherein like numbers indicate like components, the collimator server  18  and the detector  8  are shown in detail. The first drawer  22  is shown empty. The first drawer  22  has a front  24 . The second drawer  26  has a front  28 . It contains a second collimator  30 . The first drawer  22  is shown aligned with the collimator slot  12 .  
         [0018]      FIG. 3  is a flow chart of the steps necessary to remove first collimator  16  from collimator slot  12 . In step  32  the collimator slot  12  of detector  8  is aligned with the empty first drawer  22  of collimator server  18 . This alignment occurs in both rotation (around gantry  4 ) and translation (along rail  6 ). In step  34 , the front  24  of the drawer  22  opens. In step  36 , the first collimator  16  is unclamped from the detector  8 . In step  38 , the first collimator  16  is lifted from collimator slot  12  into drawer  22 . In step  40  the front  24  of drawer  22  is closed.  
         [0019]      FIG. 4  is a flow chart of the steps necessary to mount the second collimator  24  into collimator slot  12 . In step  42  the collimator slot  12  is aligned with second drawer  26 . If this is performed directly after step  40 , only translation of detector  8  along rail  6  will be necessary, Otherwise, both rotation and translation will be necessary. In step  44 , the front  28  of drawer  26  opens. In step  46  the second collimator  30  is lifted from the second drawer  26  onto collimator slot  12 . In step  48  the front  28  of second drawer  26  closes. In step  50 , the second collimator  30  is clamped into the collimator slot  12 .  
         [0020]     The above steps do not assume manual or automatic function. Each step could be performed manually, triggered manually, or performed automatically at the request of a program. Thus either procedure can either be manual, automatic or (likely) having both manual and automatic aspects. Note that if a step is performed manually, an additional step by the imaging system&#39;s control system is necessary to check to see if and when that step is performed. For example, if in step  44  the drawer  28  is opened manually, there should be a step  49  of the control system of the nuclear medicine imaging system  2  sensing the drawer  28  has been opened. This allows any automatic functions and fail safes to remain coordinated.  
         [0021]     The exact mechanical mechanism for the lifting of the first collimator  16  in step  38  or the second collimator  30  in step  46  is an implementation detail well understood by those skilled in the art. Both hydraulic and electro-mechanical systems could be used to implement the lifting of collimators.  
         [0022]     The above system and methods are easily applicable systems with two or more detectors. The above delineated steps would be repeated with appropriate checks.  
         [0023]     The above system and methods provide for the swapping of a number of collimators for a single detector. The number of collimators would be limited to the number of drawers in the collimator server  18 . The embodiment of the present invention addresses many of the problems mentioned hereinabove. The chance of damaging the collimator, the detector, and of injuring the medical technician in such a controlled system is substantially reduced. The time required to both mount and remove a collimator from a detector is substantially reduced, improving patient throughput. The amount of additional floor space needed for mounting and removing collimators is substantially minimized by integrating the collimator server  18  with the patient handling system  10 . Additionally, integrating the collimator server  18  into the patient handling system  10  allows the mounting or removing of collimators without moving components the nuclear medicine imaging system out of standard operating positions.  
         [0024]     Another embodiment of the present invention is shown in  FIG. 5 . Note that like numbers represent like components. The nuclear medicine imaging system  52  is shown with collimator cart  54 . The collimator cart  54  supplements the collimator server  18  by allowing other collimators to be mounted onto the detector  8  which are not currently loaded in the collimator  18 . The collimator cart  54  is has wheels  56  for ease of transport of heavy collimators. Collimator cart  54  is docked from a side of patient handling system  10 .  FIG. 5  shows the drawers  58  of collimator cart  54  are positioned above the patient handling system  10 . The detector  8  is aligned as above in step  32 . This precision alignment is possible because docking aligner  60  forces the rigid cart into a fixed, known position. The front  62  of drawers  58  are positioned toward the gantry  4 . In all other ways the method of removing and mounting collimators is the same.  
         [0025]     The collimator cart  56  allows for storage of collimators in a space efficient manner. Collimator cart  56  also allows the transport of collimators in a time efficient, space efficient, and safe manner. The docking ability of collimator cart  56  allows use of same advantages of mounting and removal as discussed for collimator server  18 .  
         [0026]     A further advantage of the collimator cart  56  may be realized in yet another embodiment of the present invention.  FIG. 6  shows collimator cart  56  docking from the other side of patient handling system  10  such that the fronts  62  of drawers  58  face away from the gantry and towards the front of collimator server  18 . This allows from the direct transfer of collimators from the collimator cart  56  to the collimator server  18 .  
         [0027]     As these and other variations and combinations of the features discussed above can be utilized, the foregoing description of the preferred embodiments should be taken by way of illustration rather than by limitation of the invention set forth in the claims.