Abstract:
Methods, systems, and computer-readable mediums are provided that determine the angular orientation of detectors and detector electronic assemblies (“DEAs”). In various embodiments, the orientation of detectors/DEAs (in the ring) is determined with respect to other detectors/DEAs in the ring, the orientation of the detectors/DEAs with respect to a patient bed, or the orientation of the detectors/DEAs with respect to Earth&#39;s gravitational field. In another embodiment, a nuclear medical imaging system has one or more detector units arranged around or that can be swept around a patient bed. Each of the detector units includes an angular orientation-sensing accelerometer. By determining angular orientation of the detector from signals outputted by the accelerometer, the circumferential position of the detector relative to the patient bed can be determined. That information is used in conjunction with information about detected events to construct an image of an organ or tissue mass of interest.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This is a continuation-in-part of U.S. patent application Ser. No. 12/070,751, filed Feb. 21, 2008. 
     
    
     BACKGROUND 
       [0002]    1. Field of the Invention 
         [0003]    Embodiments of the present invention generally relate nuclear imaging and more specifically to systems, methods, apparatuses, and computer-readable mediums for determining the orientation/location of immobile detectors/detector electronic assemblies. 
         [0004]    2. Description of the Related Art 
         [0005]    In PET imaging, for example, positrons are emitted from a radio-pharmaceutically doped organ or tissue mass of interest. The positrons combine with electrons and are annihilated and, in general, two gamma photons which travel in diametrically opposite directions are generated simultaneously upon that annihilation. Opposing crystal detectors, which each scintillate upon being struck by a gamma photon, are used to detect the emitted gamma photons. By identifying the location of each of two essentially simultaneous gamma interactions as evidenced by two essentially simultaneous gamma emissions from a positron annihilation event, a line in space along which the two gamma photons have traveled (a “line of response,” or “LOR”) can be determined, from which the location of the original positron annihilation event can be calculated. The LORs associated with many million annihilation events with the detectors are calculated and “composited” to generate an image of the organ or tissue mass of interest, as is known in the art. 
         [0006]    Conventionally, an array of PET crystal detectors may be arranged circumferentially all the way around a bed on which the patient lies during the scan, with the bed oriented horizontally and the “ring” of detectors oriented in a vertical plane with the bed extending axially through the center of the ring. In such a case, with detectors completely surrounding the patient bed, the detectors remain stationary. (The bed may move longitudinally to image different regions of interest of the patient&#39;s body). 
         [0007]    There are scanning systems where detectors and detector electronic assemblies (“DEAs”) rotate on a gantry, other scanning systems where the detectors and DEAs move intermittently, and yet other systems where the detectors and DEAs remain immobile. 
         [0008]    In systems where the detectors remain immobile (i.e., stationary and not intended to move), it is still necessary to know the position in space of each detector (i.e., by digitally “tagging” or identifying each PET interaction event with its associated detector position) so that the LORs can be constructed. 
         [0009]    Even though the detectors remain stationary, there are times when the scanner system is relocated to a different location and the spatial location of a detector(s) is changed as a result. There are also times when detectors are replaced. These movements result in the detectors/DEAs having a possibly unknown angular orientation and location. 
         [0010]    In general, the detector position can be determined if the angular orientation in space of the detector is known, since each detector around the ring of detectors will have a unique angular orientation. Current schemes set in hardware—usually by use of DIP switches—the circumferential position of each of the acquiring detector&#39;s electronics, thereby providing a basis by means of which individual detector pixels may be encoded. DIP switches are used to determine a detector electronic assembly (“DEA”) location with respect to other detector electronic assemblies and a patient bed. The DIP switches are located on a circuit board of the DEA. DIP switches, however, may require manual setting and can be difficult to access. In addition, DIP switches require time to set and can be easily set to an incorrect setting. 
         [0011]    Other PET imaging systems, on the other hand, use fewer detectors, and the detectors do not completely encircle the patient bed. For example, PET systems are known which use just two opposing detectors that are supported by a gantry, and the detectors are rotated by the gantry, e.g., through 180° each, so as to acquire a full 360° sweep of the patient. Other types of imaging systems such as SPECT imaging systems, as well as others, may use even less detectors, i.e., a single detector, and also acquire a fully swept image by rotating the detector around the patient, e.g., through a full 360°. 
         [0012]    These non-fully-encircling systems (PET, SPECT, and others) also rely on knowing the position of the detector in space in order to construct LORs or otherwise generate an image of the patient. In such rotating systems, the detector position in space is typically determined by determining the rotational position of the gantry, which requires geared linkages and/or encoders. “Play” between system components can, however, cause inaccuracies in the detector positions determined by such means. 
         [0013]    Accordingly, improved instrumentalities for determining the position of nuclear imaging detector(s) and DEAs, in a system in which the detectors and DEAs remain immobile (i.e., stationary); and the initial starting position (in rotating systems), is desirable. 
       SUMMARY 
       [0014]    According to various embodiments of the invention, a nuclear medical imaging system has one or more detector units arranged around or that can be swept around a patient bed. Each of the detector units includes an angular orientation-sensing accelerometer. By determining angular orientation of the detector, the circumferential position of the detector relative to the patient bed can be determined That information is used in conjunction with information about detected events to construct an image of an organ or tissue mass of interest. 
         [0015]    In particular, according to one aspect of the invention, a nuclear medical imaging system is provided, which includes at least one detector unit that is sensitive to radiation emitted by a radio-pharmaceutically doped organ or tissue mass of interest; and an angular orientation-sensing member mounted on the detector unit. 
         [0016]    According to another aspect of the invention, a method of encoding scintillation events detected by a radiation detector includes providing an angular orientation value from an angular orientation member associated with the radiation detector, associating the angular orientation value with information concerning a detected scintillation event from the radiation detector, and transmitting the associated information to a processor. 
         [0017]    In another aspect of the invention, a system is provided that includes a plurality of immobile detector electronics assemblies (“DEAs”). The system also includes a plurality of groups of immobile detectors, such that each group is connected to a respective DEA. The system has plurality of accelerometers, such that each accelerometer is connected to a respective DEA. Each accelerometer is adapted to transmit a signal indicative of at least one of an orientation of respective DEA connected thereto with respect to other DEAs, the orientation of the respective DEA with respect to a patient bed, and the orientation of the respective DEA with respect to Earth&#39;s gravitational field. 
         [0018]    In other embodiments of the invention computer-readable mediums and methods are provided which determine the orientation of DEAs and/or detectors. For example, exemplary method receives data from a plurality of accelerometers. The accelerometers can be mounted to the DEAs or to the detectors. Each accelerometer transmits data indicative of the orientation of the device (i.e., the DEAs or detectors) mounted thereto. The transmitted data is compared to predefined location parameters to determine a location of the device (i.e., the DEAs or detectors) mounted thereto. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0019]    So that the manner in which the above recited features of the present invention can be understood in detail, a more particular description of the invention, briefly summarized above, may be had by reference to embodiments, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only typical embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments. 
           [0020]      FIG. 1  is a schematic view of a completely encircling PET detector employing angular orientation accelerometers according to embodiments of the invention; 
           [0021]      FIG. 2  depicts another schematic view of a detector system in accordance with embodiments of the invention; 
           [0022]      FIG. 3  depicts an exemplary look-up table in accordance with embodiments of the invention; 
           [0023]      FIG. 4  depicts an exemplary method in accordance with embodiments of the invention; and 
           [0024]      FIG. 5  depicts an embodiment of a high-level block diagram of a computer architecture used in accordance with aspects disclosed herein. 
       
    
    
       [0025]    To facilitate understanding, identical reference numerals have been used, wherever possible, to designate identical elements that are common to the figures. 
       DETAILED DESCRIPTION 
       [0026]    In the following description, numerous specific details are set forth to provide a more thorough understanding of the invention. As will be apparent to those skilled in the art, however, various changes using different configurations may be made without departing from the scope of the invention. In other instances, well-known features have not been described in order to avoid obscuring the invention. Thus, the invention is not considered limited to the particular illustrative embodiments shown in the specification and all such alternate embodiments are intended to be included in the scope of the appended claims. 
         [0027]      FIG. 1  depicts a PET detector system  10  according to one embodiment of the invention. The system  10  is of the type described above in which a ring of detector units  12  encircles a patient bed  14 . For example, as illustrated, twelve detector units  12  (identified as 0 through 11) may be provided, with each detector unit  12  having a 30° field of view. As is known in the art, each detector unit  12  may include a pixelated detector crystal and may, depending on the specific construction of the unit  12 , include a set of photomultiplier tubes or other photosensors. The detector crystals (and photomultiplier tubes) are designated generally (and collectively) by reference numeral  16 . 
         [0028]    As further illustrated in the  FIG. 1 , each detector unit  12  includes a direct-encoding, DC accelerometer  18  (DEA) (broadly referred to as an angular orientation-sensing member). Such accelerometers are generally known in the field and typically include a pair of orthogonally arranged sensing elements by means of which the angle of inclination of the accelerometer relative to Earth&#39;s gravitational field can be determined. Thus, by measuring the angle of inclination of the detector unit  12 , the location of the detector unit  12  can be determined, and that location information can be tagged to each event detected by the detector unit, for which the information concerning the detector unit is sent to the imaging system processing computer (not illustrated). 
         [0029]    For example, the top detector unit  12  (identified as the 0 detector unit in  FIG. 1 ) has a detector orientation of 180° (facing straight down); thus, any detected event that occurs at the topmost detector unit  0  is tagged with an orientation of 180°. Similarly, for a twelve-unit system as shown, the next detector unit  12  in the clockwise direction (identified as  1  in  FIG. 1 ) will have an orientation of 210°; the next detector unit  2  will have an orientation of 240°; and so on around the detector system. Thus, the detected events from all detector units  12  can be compiled along with the associated detector orientations, and the LORs can be generated by pairing essentially simultaneous events that have associated detector orientations that are 180° apart from each other. 
         [0030]    In an alternative arrangement (not illustrated), only one or two detector units are provided, which do not completely encircle the patient bed but which are swept around the patient as described above. The detector(s) in such an arrangement would also include an orientation-sensing accelerometer, by means of which the position in space of the detector can be determined and hence the angular location of the detector. As above, with such a system (particularly a PET system with two opposing detector units), all detected events can be compiled and paired based on opposing detector locations, together with the actual angular orientation of the opposing detectors in space. 
         [0031]      FIG. 2  depicts another schematic view of a detector system  200  in accordance with embodiments of the invention. The system  200  includes a ring of immobile detector electronics assembly (DEA  202   0 , DEA  202   1 , DEA  202   2 , DEA  202   3 , DEA  202   4 , DEA  202   5 , DEA  202   6 , DEA  202   7 , DEA  202   8 , DEA  202   9 , DEA  202   10 , and DEA  202   11  collectively “DEA units  202 ”). 
         [0032]    Each DEA unit  202  includes a safety ground line  210 , a data/clock lines  212 , and alternating current (“AC”) lines  214 . For simplicity only, only the safety ground line  210 , a data/clock lines  212 , and AC lines  214  for the top most DEA unit  202  are depicted in  FIG. 2  to include lead lines and numbers. 
         [0033]    Illustratively, aspects of the invention are described herein using twelve immobile DEA units  202  that encircle a patient bed  206 . However, that depiction is not intended in any way to limit the scope of the invention. For example, it is appreciated and understood that other embodiments of the invention utilize more than one ring of DEA units  202  and that there can be more or less than twelve DEA units  202  in each ring. 
         [0034]    Each DEA unit  202  acquires data from a group of detectors  204  (group  204   0 , group  204   1 , group  204   2 , group  204   3 , group  204   4 , group  204   5 , group  204   6 , group  204   7 , group  204   8 , group  204   9 , group  204   10 , and group  204   11  (collectively “detectors  204 ”)). The detectors  204  are connected to respective DEA units  202  and provide the field of view (“FOV”) of the DEA unit  202  connected thereto. There are twelve groups of detectors  204  (one group for each DEA unit  202 ). 
         [0035]    Both the DEA units  202  and the detectors  204  remain immobile. 
         [0036]    Included in each DEA unit  202  is a direct-encoding DC accelerometer  208 . For simplicity,  FIG. 2  only depicts DEA unit  202   0  as including an accelerometer  208 . However, it is understood that each of the DEA units  202  includes an accelerometer  208 . 
         [0037]    Each DC accelerometer  208  is broadly referred to as an angular orientation-sensing member. Such accelerometers include a pair of orthogonally arranged sensing elements by which the angle of inclination of the accelerometer relative to Earth&#39;s gravitational field can be determined. Accelerometers are typically used to measure motion (by measuring changes in voltage). However, because the DEA units  202  are immobile/stationary fixed DC voltages from the accelerometers are measured and subsequently used to determine the location of the DEA  202  within the ring. 
         [0038]    Position information (i.e., at least “X-axis” and “Y-axis” data (and optionally “Z-axis” data (e.g., Z-axis data can be used when the accelerometers  208  are mounted on the detectors  204  to provide the location of a ring))) is compared with data stored in memory (e.g., a look-up table). By comparing the acquired position information with the data stored in memory the angle of inclination of the DEA units  202  are determined. Thus, by measuring the angle of inclination of the DEA unit  202 , the location of the DEA unit  202  can be determined, and that location information can be tagged to each event detected by the detector unit, for which the information concerning the detector unit is sent to the imaging system processing computer (not illustrated). 
         [0039]    For example, DEA unit  202   0  has been identified as the top DEA unit (i.e., a DEA unit  202  that is immobile, will always be in the “12 o&#39;clock position” (i.e., will always have an orientation of about 180° with respect to the (i.e., the Earth&#39;s gravitational field) and patient bed  206  and will always be downward facing) with respect to the other DEA units  202  in the gantry. Any event that is detected and received by DEA unit  202   0  is tagged as having come from this top fixed position (again with respect to the other DEA units  202  in the gantry). 
         [0040]    When referring to the top most DEA unit  202  as having an orientation of about 180° it is understood that that reference is taken from a central axis of the DEA unit  202 . When each DEA unit  202  has a field of view of about 30° then the DEA units  202  adjacent to the top most DEA unit  202  are located at 210° and at 150°. 
         [0041]    For example, for a twelve-unit system as shown, the next DEA unit  202   1  in the clockwise direction will have an orientation of 210° with respect to the ground (i.e., the Earth&#39;s gravitational field) and patient bed and other DEA units  202  in the gantry; the next DEA unit  202   2  will have an orientation of 240° with respect to the ground (i.e., the Earth&#39;s gravitational field) and patient bed and other DEA units  202  in the gantry; and so on for all of the DEA units  202  in the scanning system. Thus, the detected events from all DEA units  202  can be compiled along with the associated detector orientations, and the LORs can be generated by pairing essentially simultaneous events that have associated detector orientations that are 180° apart from each other. 
         [0042]    The accelerometer can be located anywhere (e.g., on an electronics board or the detectors  204 ) on the DEA units  202 . 
         [0043]    In various embodiments of the invention, accelerometer-provided DEA location information is compared to position data stored in memory every time the scanning system is turned “on.” One reason for comparing accelerometer-provided DEA locations to position data stored in memory, in those instances when the DEA units  202 /detector(s)  204  remain immobile, is that there are instances when the DEA unit(s)/detectors  204  are just installed or swapped to a different location on the gantry. 
         [0044]    In other embodiments of the invention, a user can manually actuate (through a user interface) a series of computer instructions that compare the accelerometer-provided DEA locations to position data stored in memory and determines the DEA unit locations on the gantry (relative to the patient bed  206  and the other DEA units on the gantry) based upon the results of the comparison. 
         [0045]    In yet other embodiments of the invention, the scanning system periodically (i.e., after expiration of a predetermined time) compares the accelerometer-provided DEA locations to position data stored in memory and determines the DEA unit locations on the gantry (relative to the patient bed  206  and the other DEA units on the gantry) based upon the results of the comparison. 
         [0046]    In further embodiments of the invention, the scanning system initiates a series of computer instructions to determine the location of each DEA unit  202  when another program is initiated (e.g., a diagnostic program). 
         [0047]    In an alternative arrangement (not illustrated), DEA units  202  unit(s) are provided, which do not completely encircle the patient bed but which are swept around the patient. In this alternative arrangement, the DEA units  202 /detectors  204  do not remain immobile/stationary. When more than one DEA unit  202  is provided in the ring each DEA unit  202  has a DEA unit  202  positioned 180° (i.e., oppositely) thereto on the ring. The detector(s)  204 /DEA unit  202  in such an arrangement would also include an orientation-sensing accelerometer, by means of which the position in space of the detector  204 /DEA unit  202  can be determined and hence the angular location of the detectors  204 /DEA unit  202 . As with such a system (e.g., a PET system with two opposing detector units), all detected events can be compiled and paired based on opposing detector locations, together with the actual angular orientation of the opposing detectors in space. For example, in a ring having six DEA units  202  (which will begin scanning at predefined positions (e.g., three adjacent DEA units  202  positioned at 330°, 0°, and 30°; and three adjacent DEA units  202  positioned at 150°, 180°, 210°)). When the scanning system is turned “on,” the DEA units  202 /detectors(s)  204  are stationary and the accelerometers  208  transmit data indicative of the location of the DEA units  202 /detector(s)  204 . The received data is compared to the predefined locations stored in memory. In various embodiments of the invention, the received data is used to reposition the DEA units  202 /detectors(s)  204  to the appropriate angular orientation. In other embodiments of the invention, the data received from the accelerometers  208  is used to replace the predefined locations and is stored in memory. 
         [0048]      FIG. 3  depicts an exemplary look-up table  300  in accordance with embodiments of the invention. Although look-up table  300  is depicted as having addresses to accommodate twelve DEA units  202  that depiction is for illustrative purposes only and not intended in any way to limit the scope of the invention. The look-up table  300  includes position data addresses ( 302   0 ,  302   1 ,  302   2 ,  302   3 ,  302   4 ,  302   5 ,  302   6 ,  302   7 ,  302   8 ,  302   9 ,  302   10 , and  302   11  (collectively “position data addresses  302 ”) for storing position data. 
         [0049]    Position data is a pre-defined location parameter(s) that identifies locations for the DEA unit  202 . For example, when the scanning system includes twelve DEA units  202  it follows that each of the DEA units  202  has a specific location in the ring (i.e., the DEA units  202  are incrementally spread around the ring). As such, there should be a DEA unit  202  located at each of “12:00 o&#39;clock position” (i.e., facing straight down and at 180°) clockwise through to the “11 o&#39;clock position.” These positions (i.e., the 12 o&#39;clock position clockwise through 11 o&#39;clock position) are stored in data addresses  302 . 
         [0050]    As explained above, position information (e.g., at least “X-axis” and “Y-axis” data (and optionally “Z-axis” data)) is received from each of the DEA units  202 . This position information, from the DEA units  202 , is compared to the position data stored in addresses  302  to determine which DEA unit  202  to associate with each data address  302 . The resulting association (of the respective DEA units  202  to data addresses  302 ) is stored in the look-up table  300  (in addresses  304   0 ,  304   1 ,  304   2 ,  304   3 ,  304   4 ,  304   5 ,  304   6 ,  304   7 ,  304   8 ,  304   9 ,  304   10 , and  304   11  (collectively “addresses  304 ”)). 
         [0051]    In various embodiments, the look-up table  300  optionally includes addresses (e.g., addresses  306   0 ,  306   1 ,  306   2 ,  306   3 ,  306   4 ,  306   5 ,  306   6 ,  306   7 ,  306   8 ,  306   9 ,  306   10 , and  306   11  for storing X-axis data; addresses  308   0 ,  308   1 ,  308   2 ,  308   3 ,  308   4 ,  308   5 ,  308   6 ,  308   7 ,  308   8 ,  308   9 ,  308   10 , and  308   11  for storing Y-axis data; and/or addresses  310   0 ,  310   1 ,  310   2 ,  310   3 ,  310   4 ,  310   5 ,  310   6 ,  310   7 ,  310   8 ,  310   9 ,  310   10 , and  310   11  for storing Z-axis data) for also storing the position information received from the DEA units  302 . 
         [0052]      FIG. 4  depicts an exemplary method  400  in accordance with embodiments of the invention. The method  400  determines the location of DEA units  202 . The method  400  begins at step  402  and proceeds to step  404 . 
         [0053]    At step  404 , position information is received from the accelerometers regarding the locations of the DEA units  202 . Thereafter, the method  400  proceeds to step  406 . 
         [0054]    At step  406 , the position information is compared to predefined location parameters stored in memory. Thereafter, the method  400  proceeds to step  408 . 
         [0055]    At step  408 , the results of the comparison in step  406 , is used to determine the location of the DEA units  202  and store the determination in memory. After step  408 , the method  400  proceeds to and ends at step  410 . 
         [0056]    In various embodiments of the invention, the method  400  includes optional step  412 . At optional step  412 , the scanning device is turned “on” and in response thereto, the method  400  proceeds to step  402 . Step  402  operates as described above. 
         [0057]    In yet other embodiments of the invention, the method  400  includes optional step  414 . At optional step  414 , the position information from the accelerometer  208  is stored in memory (e.g., look-up table  300 ). Thereafter, the method  400  proceeds to and ends at step  410 . 
         [0058]      FIG. 5  depicts an embodiment of a high-level block diagram of a general-purpose computer architecture  500  for determining the angular orientation/location of each DEA unit  202  in relation to the other DEA units  202 , a patient bed  206 , and the ground (i.e., the Earth&#39;s gravitational field). For example, the general-purpose computer  500  is suitable for use in performing method  400  (depicted in  FIG. 4 ). The general-purpose computer of  FIG. 5  includes a processor  510  as well as a memory  504  for storing control programs and the like. In various embodiments, memory  504  also includes programs  512  (e.g., depicted as a “DEA orientation/location”) for determining the angular orientation/location of each DEA unit  202  in a scanner system) for performing the embodiments described herein. The processor  510  cooperates with conventional support circuitry  508  such as power supplies, clock circuits, cache memory and the like as well as circuits that assist in executing the software routines  506  stored in the memory  504 . As such, it is contemplated that some of the process steps discussed herein as software processes can be loaded from a storage device (e.g., an optical drive, floppy drive, disk drive, etc.) and implemented within the memory  504  and operated by the processor  510 . Thus, various steps and methods of the present invention can be stored on a computer readable medium. The general-purpose computer  500  also contains input-output circuitry  502  that forms an interface between the various functional elements communicating with the general-purpose computer  500 . 
         [0059]    Although  FIG. 5  depicts a general-purpose computer  500  that is programmed to perform various control functions in accordance with the present invention, the term computer is not limited to just those integrated circuits referred to in the art as computers, but broadly refers to computers, processors, microcontrollers, microcomputers, programmable logic controllers, application specific integrated circuits, and other programmable circuits, and these terms are used interchangeably herein. In addition, although one general-purpose computer  500  is depicted, that depiction is for brevity on. It is appreciated that each of the methods described herein can be utilized in separate computers. 
         [0060]    Although embodiments of the invention have been described herein as including the accelerometers  208  mounted within the DEA units  202  those descriptions are not intended in any way to limit the scope of the invention. It is appreciated that in other embodiments of the invention the accelerometers  208  are mounted inside/on the detectors  204 . 
         [0061]    The invention having been thus described, it will apparent to those skilled in the art that the same may be varied in many ways without departing from the spirit and scope of the invention. For example, other imaging technologies besides PET and SPECT may benefit from the invention. Any and all such modifications are intended to be included within the scope of the following claims. 
         [0062]    While the foregoing is directed to embodiments of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.