Patent Publication Number: US-8525141-B2

Title: Collimator alignment system and method

Description:
BACKGROUND OF THE INVENTION 
     The subject matter disclosed herein relates to single photon emission computed tomography (SPECT), and more particularly to a system and method for aligning collimators with detectors in medical imaging. 
     A wide range of imaging techniques are known and currently in use, particularly for medical diagnostic applications. One such technique, SPECT, relies on the emission of gamma rays during the radioactive decay of a radioisotope (or radionuclide), commonly administered in the form of a radiopharmaceutical agent that can be carried, and in some cases, bound to particular tissues of interest. A SPECT scanner detects the emissions via a gamma camera that typically includes a collimator, a scintillator, and a series of photomultiplier tubes. The collimator allows only emissions in a particular direction to enter into the scintillator. The scintillator converts the gamma radiation into lower energy ultraviolet photons that impact regions (pixels) of the photomultiplier tubes. These, in turn, generate image data related to the quantity of radiation impacting the individual regions. Image reconstruction techniques, such as backprojection, may then be used to construct images of internal structures of the subject based upon this image data. 
     While such systems have proven extremely useful at providing high quality images with good diagnostic value, further refinement is needed. For example, a system may include a gamma camera with two detectors. Each detector uses a collimator to allow only certain emissions. When collimators are attached to the detectors, the collimators need to be aligned with the detectors and each other for proper operation. Furthermore, the alignment position may change due to such things as settling of the floor, temperature changes, floor deviations, and use of collimators on different system. Manual alignment procedures may be performed by trained service personnel to enable the collimators and detectors to be aligned. However, the number of service personnel available to perform alignment procedures may be limited, and the cost for service personnel to perform the alignment procedures on a regular basis may inhibit routine alignment. Therefore, a system that automatically assists in aligning the detectors and collimators may be desirable. 
     BRIEF DESCRIPTION OF THE INVENTION 
     In one embodiment, a system for aligning collimators in an imaging system includes a transmitter coupled to a first detector and configured to transmit a beam, and a receiver coupled to a second detector and configured to receive the beam transmitted from the first detector. The alignment system also includes a cart comprising an alignment device with the cart configured to hold at least two collimators. The system includes a control system configured to align the first and second detectors with the at least two collimators using the alignment device. 
     In another embodiment, a method for aligning collimators in an imaging system includes transmitting a beam via a transmitter coupled to a first detector and receiving the beam via a receiver coupled to a second detector. The alignment method also includes detecting a cart between the first and the second detectors. The cart includes an alignment device and is configured to hold at least two collimators. The method includes adjusting the position of the first and second detectors to be aligned with the alignment device. 
     In a further embodiment, a system for aligning collimators in an imaging system includes a transmitter coupled to a first detector and configured to transmit a laser beam, and a receiver coupled to a second detector and configured to receive the laser beam transmitted from the first detector. The alignment system also includes a cart comprising two collimators and an alignment device with an opening. The system includes a motor configured to move the first and second detectors to an alignment position where the laser beam travels through the opening of the alignment device. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and other features, aspects, and advantages of the present invention will become better understood when the following detailed description is read with reference to the accompanying drawings in which like characters represent like parts throughout the drawings, wherein: 
         FIG. 1  is a diagrammatic representation of an exemplary SPECT imaging system incorporating aspects of the present techniques; 
         FIG. 2  is a graphical representation of an embodiment of a collimator alignment system; 
         FIG. 3  is a top view graphical representation of an embodiment of a collimator alignment system; and 
         FIG. 4  is a flow chart of an embodiment of a method for aligning collimators in an imaging system. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     A diagrammatic representation of an exemplary SPECT imaging system is shown in  FIG. 1 . The system, designated generally by the reference numeral  10 , is designed to produce useful images  12  of a subject  14 . The subject is positioned in a scanner, designated by reference numeral  16  in which a patient support  18  is positioned. The support may be movable within the scanner to allow for imaging of different tissues or anatomies of interest within subject. Prior to image data collection, a radioisotope, such as a radiopharmaceutical substance (sometimes referred to as a radiotracer), is administered to the patient, and may be bound or taken up by particular tissues or organs. Typical radioisotopes include various radioactive forms of elements, although many in SPECT imaging are based upon an isotope of technetium ( 99 Tc) that emits gamma radiation during decay. Various additional substances may be selectively combined with such radioisotopes to target specific areas or tissues of the body. 
     Gamma radiation  20  emitted by the radioisotope is detected by a digital detector or gamma camera  22 . Although illustrated in the figure as a planar device positioned above the patient, in practice the camera may be positioned below the patient, both above and below the patient, and may wrap at least partially around the patient. In general, the gamma camera  22  comprises one or more collimators  24  and a scintillator. The collimator  24  allows gamma radiation emitted only in certain directions (typically perpendicular to the scintillator) to impact the scintillator. The scintillator, which is typically made of a crystalline material, such as sodium iodide (NaI), converts the received gamma radiation to lower energy light energy (e.g., in an ultraviolet range). Photomultiplier tubes  26  then receive this light and generate image data corresponding to photons impacting specific discrete picture element (pixel) regions. 
     The gamma camera  22  is coupled to system control and processing circuitry  28 . This circuitry may include a number of physical and functional components that cooperate to allow the collection and processing of image data to create the desired images. For example, the circuitry may include raw data processing circuitry  30  that initially receives the data from the gamma camera  22 , and that may perform various filtering, value adjustments, and so forth. Processing circuitry  32  allows for the overall control of the imaging system, and for manipulation of image data. The processing circuitry  32  may also perform calibration functions, correction functions, and so forth on the data. The processing circuitry  32  may also perform image reconstruction functions, such as functions based on known algorithms (e.g., backprojection). Such functions may also be performed in post-processing on local or remote equipment (not shown). The processing circuitry may interact with control circuitry/interface  34  that allows for control of the scanner and its components, including the patient support, camera, and so forth. Moreover, the processing circuitry  32  will be supported by various circuits, such as memory circuitry  36  that may be used to store image data, calibration or correction values, routines performed by the processing circuitry, and so forth. Finally, the processing circuitry may interact with interface circuitry  38  designed to support an operator interface  40 . The operator interface allows for imaging sequences to be commanded, scanner and system settings to be viewed and adjusted, images to be viewed, and so forth. In the illustrated embodiment, the operator interface includes a monitor  42  on which reconstructed images  12  may be viewed. 
     In an institutional setting, the imaging system  10  may be coupled to one of more networks to allow for the transfer of system data to and from the imaging system, as well as to permit transmission and storage of image data and processed images. For example, a local area networks, wide area networks, wireless networks, and so forth may allow for storage of image data on radiology department information systems or on hospital information systems. Such network connections further allow for transmission of image data to remote post-processing systems, physician offices, and so forth. 
     In addition, a collimator cart  44  may be used to transport and store collimators  24 . The cart  44  may also be used to assist installation of collimators  24  onto the gamma camera  22 . Furthermore, the cart  44  may contain features to aid alignment of the collimators  24  to the gamma camera  22  as discussed below in connection with the following figures. 
       FIG. 2  is a graphical representation of an embodiment of a collimator alignment system  46 . A gamma camera  22  and a collimator cart  44  are illustrated. The gamma camera  22  includes a first detector  48  and a second detector  50 , each for detecting gamma radiation. The first detector  48  has a transmitter  52  located adjacent to its radiation detector surface, while the second detector  50  has a receiver  54  located adjacent to its radiation detector surface. The transmitter  52  is configured to transmit a signal to the receiver  54 . The signal may be any type useful to indicate that there is no physical obstruction between the transmitter  52  and the receiver  54 . For example, the signal may be a laser beam transmitted between transmitter  52  and receiver  54 . Therefore, when an object is placed into the path of the laser beam, the object obstructs the laser beam from traveling to the receiver  54 . 
     The receiver  54  may send information to processing and control circuitry connected to the gamma camera  22 . The information may contain data concerning whether the receiver  54  is receiving the signal transmitted from the transmitter  52 . For example, when there is no obstruction between the transmitter  52  and the receiver  54 , the receiver  54  may send information indicating that it is receiving the signal from the transmitter  52 . Conversely, when there is an obstruction between the transmitter  52  and the receiver  54 , the receiver may send information indicating that it is not receiving the signal from the transmitter  52 . As illustrated, the first detector  48  may include a motor  56  or actuator to enable the detectors to move to an alignment position. Likewise, the second detector  50  may include a motor (not shown). 
     The collimator cart  44  includes a frame  58  arranged to hold collimators  24 . The frame  58  is attached to a base  60  that provides support to the frame  58 . In addition, an alignment device  62 , such as a rectangular shaped plate, is attached to the frame  58 . Furthermore, the alignment device  62  has a hole  64  passing through it to enable a signal, such as a laser beam, to be transmitted through the device  62 . Certain embodiments may include an alignment device  62  in the shape of a triangle, circle, oval, square, or other suitable shape. Likewise, although the hole  64  is depicted as being circular, other embodiments may include a hole with any available shape to enables a beam to be transmitted through the hole. The size of the hole  64  may vary depending on the accuracy required for a particular system. 
     The base  60  has front wheels  66  and rear wheels  68  to enable the cart  44  to be moved between locations. The base  60  may also include control circuitry  70  and a motor  72 , i.e., a control system. The control circuitry  70  may be used to control the position of the cart and may control operation of the motor  72 . For example, the control circuitry  70  may cause the cart  44  to move in a horizontal direction  74  by causing the motor  72  to rotate the wheels on the cart  44 . Likewise, the control circuitry  70  may cause the cart  44  to raise or lower the collimators  24  in a vertical direction  76 . 
     As may be appreciated, to install the collimators  24  onto the detectors  48  and  50 , the collimators  24  have to be properly aligned with the detectors. The alignment may be performed manually. However, manual alignment can be difficult and time consuming. Therefore, automatic alignment may be used. The cart  44  may be moved in the horizontal direction  74  toward the gamma camera  22  so that the alignment device  62  is positioned between the transmitter  52  and the receiver  54 . Then the detectors  48  and  50  may be positioned using motors  56 . For example, the motors  56  may move the detectors  48  and  50  in the horizontal direction  74  or in the vertical direction  76  to cause the signal sent from the transmitter  52  to travel through the hole  64  in the alignment device  62 . The detectors  48  and  50  will be aligned with the collimators  24  when the signal travels through the hole  64  and is received by the receiver  54 . The processing and control circuitry of the imaging system may control the motors  56  to move the detectors  48  and  50  to their proper orientation. The motors on the detectors and/or the control circuitry used to control the motors may be considered a control system. The control system may be configured with information about the alignment device  62  such as its dimensions, and the dimensions of the hole  64  to be used by the system to determine if the detectors  48  and  50  are aligned with the alignment device  62 . For example, the control system may use the dimensions of the alignment device  62  to calibrate the distance to move the detectors  48  and  50  relative to a starting position. 
       FIG. 3  is a top view graphical representation of an embodiment of a collimator alignment system  46 . The collimator cart  44  is depicted in a position aligned with the detectors  48  and  50 . Collimators  24  are located on the cart  44  prior to being attached to the detectors  48  and  50 . Like the prior embodiment, the first detector  48  has the transmitter  52 , while the second detector has the receiver  54 . Motors  56  are attached to each of the detectors  48  and  50  to control the detector movement and perform alignment of the detectors to the alignment device  62 . The alignment device  62  is depicted with the hole  64  extending through the device  62 . Furthermore, a beam  78  is illustrated traveling from the transmitter  52 , through a tube  80  mounted in the alignment device  62 , and being received by the receiver  54 . As such, the detectors  48  and  50  are aligned with the collimators  24 . 
     The alignment device  62  may include the tube  80  as illustrated, or in other embodiments may only include the hole  64  extending through the device  62 . As may be appreciated, with the tube  80  extending out of the alignment device  62 , an alignment angle and position may be more precisely reached. For example, the diameter and/or length of the tube  80  may prevent an unacceptable angle deviation between the detectors  48  and  50 , and collimators  24 . 
     To obtain the alignment position, the motors  56  may be controlled by imaging system control circuitry that causes the motors to move the detectors  48  and  50  generally in the vertical direction  76 . As such, the motors  56  may adjust the detectors  48  and  50  up and/or down until the signal  78  is received by the receiver  54 . Likewise, the motors  56  may move the detectors  48  and  50  in a direction  82  or a direction  84  to attain alignment. 
       FIG. 4  is a flow chart of an embodiment of a method for aligning collimators in an imaging system  86 . It should be noted that the steps described below may be completed in any appropriate order. Likewise, some steps described are optional, while other steps may be added. 
     At step  88 , collimators may be placed on a collimator cart to be transported to another location. Then at step  90 , the collimator cart is positioned so that the alignment device is located between the detectors so that the alignment device blocks the signal sent from a transmitter to a receiver. Thus, the receiver may detect that the cart has been positioned between the transmitter and the receiver. Next at step  92 , the imaging system determines whether the alignment device is properly aligned between the detectors, i.e., the detectors are aligned with the collimators. If the detectors are not aligned with the collimators, the position of the detectors is adjusted, per step  94 . The position may be adjusted vertically, horizontally, or any other possible position adjustment. As may be appreciated, other embodiments may cause the collimator cart to move in place of or in conjunction with the detectors for the detectors to be aligned with the collimators. 
     The method then returns to step  92  to determine whether the detectors are aligned with the collimators. If the detectors and collimators are still not aligned, step  94  is repeated until the detectors and collimators are aligned. After the collimators are aligned, the collimators are attached to the detectors per step  96 . Next at step  98 , the collimator cart is removed from the detector area and placed in another location, such as a storage area. 
     It should be understood that the alignment devices and methods described herein may include other configurations, and that the descriptions provided are as examples only. As such, it is contemplated that other embodiments of alignment devices and methods may include: aligning the detectors with each other prior to positioning the alignment device between the detectors, moving only one detector to perform alignment, moving both detectors in a synchronized manner to perform alignment, moving both detectors in an unsynchronized manner to perform alignment, performing alignment by moving the collimator cart without moving the detectors, performing alignment by moving the collimator cart in conjunction with the detectors, and so forth. 
     This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims.