Patent Publication Number: US-2023146608-A1

Title: Nuclear medicine imaging systems and methods having detector heads with two collimators

Description:
BACKGROUND 
     The subject matter disclosed herein relates to medical imaging systems and, more particularly, to radiation detection systems. 
     In nuclear medicine (NM) imaging, such as single photon emission computed tomography (SPECT), radiopharmaceuticals are administered internally to a patient. Detectors (e.g., gamma cameras), typically installed on a gantry, capture the radiation emitted by the radiopharmaceuticals and this information is used, by a computer, to form images. The NM images primarily show physiological function of, for example, the patient or a portion of the patient being imaged. 
     An NM imaging system may be configured as a multi-head imaging system having several individual detectors distributed about the gantry. Each detector (e.g., detector head) may pivot or sweep to provide a range over which the detector may acquire information that is larger than a stationary field of view of the detector. Detectors in nuclear medicine need to absorb x- or gamma-ray photons over a wide energy range. Depending on the application (low/medium energy versus high energy), a different collimator may be utilized for collimation. However, changing out the collimator for each detectors typically involves utilizing a mechanical exchange process to manually replace one collimator utilized with one application with another collimator utilized for another application. Utilization of the mechanical exchange process may be a time consuming process that may take several minutes resulting in down time that hampers workflow (e.g., hospital patient flow). 
     BRIEF DESCRIPTION 
     A summary of certain embodiments disclosed herein is set forth below. It should be understood that these aspects are presented merely to provide the reader with a brief summary of these certain embodiments and that these aspects are not intended to limit the scope of this disclosure. Indeed, this disclosure may encompass a variety of aspects that may not be set forth below. 
     In one embodiment, a radiation detector head assembly is provided. The radiation detector head assembly includes a detector column. The detector column includes a detector having a first surface and a second surface opposite the first surface. The detector column also includes a first collimator disposed over the first surface of the detector configured for use during imaging scans involving radiation in a first energy range. The detector column further includes a second collimator disposed over the second surface of the detector configured for use during imaging scans involving radiation in a second energy range different from the first energy range. 
     In another embodiment, a nuclear medicine multi-head imaging system is provided. The system includes a gantry defining a bore configured to accept an object to be imaged, wherein the gantry is configured to rotate about the bore. The system also includes a plurality of detector units mounted to the gantry and configured to rotate with the gantry around the bore in rotational steps, each detector unit configured to sweep about a corresponding axis and acquire imaging information while sweeping about the corresponding axis. Each detector unit includes a detector head. The detector head includes a detector column. The detector column includes a detector having a first surface and a second surface opposite the first surface. The detector column also includes a first collimator disposed over the first surface of the detector configured for use during imaging scans involving radiation in a first energy range. The detector column further includes a second collimator disposed over the second surface of the detector configured for use during imaging scans involving radiation in a second energy range different from the first energy range. 
     In a further embodiment, a method for changing a collimator in a detector head of a nuclear medicine (NM) multi-head imaging system is provided. The method includes receiving an input to change the collimator in the detector head of the NM multi-head imaging system. The method also includes rotating a detector column from a first position to a second position or a second position to a first position in response to the input, wherein the detector column includes a detector having a first surface and a second surface opposite the first surface, a first collimator disposed over the first surface of the detector configured for use during imaging scans involving radiation in a first energy range, and a second collimator disposed over the second surface of the detector configured for use during imaging scans involving radiation in a second energy range different from the first energy range. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and other features, aspects, and advantages of the present subject matter 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 schematic view of an embodiment of a nuclear imaging system, in accordance with aspects of the disclosed techniques; 
         FIG.  2    is a schematic view of a detector arrangement, in accordance with aspects of the disclosed techniques; 
         FIG.  3    is a schematic view of sweep and acquisition ranges for a detector unit, in accordance with aspects of the disclosed techniques; 
         FIG.  4    is schematic view of an embodiment of a detector head, in accordance with aspects of the disclosed techniques; 
         FIG.  5    is a cross-sectional view of the detector head in  FIG.  4   , in accordance with aspects of the disclosed techniques; 
         FIG.  6    is a schematic view illustrating switching between usage of different collimators within a detector head assembly, in accordance with aspects of the disclosed techniques; 
         FIG.  7    is a flow chart of an embodiment of a method for switching between collimators in a detector head assembly, in accordance with aspects of the disclosed techniques; and 
         FIG.  8    is a schematic view of an imaging system, in accordance with aspects of the disclosed techniques. 
     
    
    
     DETAILED DESCRIPTION 
     One or more specific embodiments will be described below. In an effort to provide a concise description of these embodiments, not all features of an actual implementation are described in the specification. It should be appreciated that in the development of any such actual implementation, as in any engineering or design project, numerous implementation-specific decisions must be made to achieve the developers&#39; specific goals, such as compliance with system-related and business-related constraints, which may vary from one implementation to another. Moreover, it should be appreciated that such a development effort might be complex and time consuming, but would nevertheless be a routine undertaking of design, fabrication, and manufacture for those of ordinary skill having the benefit of this disclosure. 
     When introducing elements of various embodiments of the present subject matter, the articles “a,” “an,” “the,” and “said” are intended to mean that there are one or more of the elements. The terms “comprising,” “including,” and “having” are intended to be inclusive and mean that there may be additional elements other than the listed elements. Furthermore, any numerical examples in the following discussion are intended to be non-limiting, and thus additional numerical values, ranges, and percentages are within the scope of the disclosed embodiments. 
     The present disclosure provides systems and methods for utilizing at least two collimators within a radiation detector head assembly of a nuclear medicine (NM) multi-head imaging system. In particular, each detector head of the NM multi-head imaging system includes a detector column that includes a semiconductor detector having a first surface that includes a cathode and a second surface that includes pixelated anodes, where a respective collimator is disposed over both the first surface and the second surface of the semiconductor detector. The collimator disposed over the cathode is configured for utilization during an imaging scan involving radiation in a first energy range (e.g., low energy range of approximately 40 to 300 keV) and the collimator disposed over the pixelated anodes is configured for utilization during an imaging scan involving radiation in a second energy range (e.g., high energy range of approximately 250 to 400 keV) different from the first energy range. The first and second energy ranges may partially overlap (e.g., at a high end of the first energy range and a low end of the second energy range) but differ in extent. Rotation about a longitudinal axis (e.g., sweeping axis) of the detector head (e.g., via a motor) enables the collimators to be interchanged between scans or during the same scan (e.g., dual isotopes applications) involving different levels of energy (e.g., low energy versus high energy). The disclosed embodiments enable the automatic interchange between the different collimators to occurs within a matter of seconds (e.g., as opposed to minutes). The interchange occurs completely within the radiation detector head assembly (without having to remove one of the collimators or mounting the collimator to be utilized) and without the utilization of a mechanical (and manual) collimator exchange process. The quick automatic exchange between collimators saves time during the day and avoids downtime for the imaging system, thus, enabling an improved workflow (e.g., hospital patient flow). The disclosed embodiments may also reduce the cost of the imaging system. 
       FIG.  1    provides a schematic view of a NM multi-head imaging system  100  in accordance with various embodiments. Generally, the imaging system  100  is configured to acquire imaging information or data (e.g., photon counts) from an object to be imaged (e.g., a human patient) that has been administered a radiopharmaceutical. The depicted imaging system  100  includes a gantry  110  and a processing unit  120 . 
     The gantry  100  defines a bore  112 . The bore  112  is configured to accept an object to be imaged (e.g., a human patient or portion thereof). As seen in  FIG.  1   , a plurality of detector units  115  are mounted to the gantry  110 . In the illustrated embodiment, each detector unit  115  includes an arm  114  and a head  116 . The arm  114  is configured to articulate the head  116  radially toward and/or away from a center of the bore  112  (and/or in other directions), and the head  116  includes at least one detector, with the head  116  disposed at a radially inward end of the arm  114  and configured to pivot to provide a range of positions from which imaging information is acquired. 
     The detector of the head  116 , for example, may be a semiconductor detector. For example, a semiconductor detector in various embodiments may be constructed using different materials, such as semiconductor materials, including Cadmium Zinc Telluride (CdZnTe), often referred to as CZT, Cadmium Telluride (CdTe), and Silicon (Si), among others. In certain embodiments, the detector of the head  116  may include a scintillator with a silicon photomultiplier (SiPM). The detector may be configured for use with, for example, nuclear medicine (NM) imaging systems such as single photon emission computed tomography (SPECT) imaging systems. 
     In various embodiments, the detector may include an array of pixelated anodes, and may generate different signals depending on the location of where a photon is absorbed in the volume of the detector under a surface if the detector. The absorption of photons from certain voxels corresponding to particular pixelated anodes results in charges generated that may be counted. The counts may be correlated to particular locations and used to reconstruct an image. 
     In various embodiments, each detector unit  115  may define a corresponding view that is oriented toward the center of the bore  112 . Each detector unit  115  in the illustrated embodiment is configured to acquire imaging information over a sweep range corresponding to the view of the given detector unit.  FIG.  2    illustrates a detector arrangement  200  in accordance with various embodiments. The detector units of  FIG.  1   , for example, may be arranged in accordance with aspects of the detector arrangement  200 . In some embodiments, the system  100  further includes a CT (computed tomography) detection unit  140 . The CT detection unit  140  may be centered about the bore  112 . Images acquired using both NM and CT by the system are accordingly naturally registered by the fact that the NM and CT detection units are positioned relative to each other in a known relationship. A patient may be imaged using both CT and NM modalities at the same imaging session, while remaining on the same bed, which may transport the patient along the common NM-CT bore  112 . 
     As seen in  FIG.  2   , the detector arrangement  200  includes detector units  210 ( a ),  210 ( b ),  210 ( c ),  210 ( d ),  210 ( e ),  210 ( f ),  210 ( g ),  210 ( h ),  210 ( i ),  210 ( j ),  210 ( k ),  210 ( l ) disposed about and oriented toward (e.g., a detection or acquisition surface of the detector units, and/or the FOV (Field of View), are oriented toward) an object  202  to be imaged in the center of a bore. Each detector unit of the illustrated embodiment defines a corresponding view that may be oriented toward the center of the bore of the detector arrangement  200  (it may be noted that because each detector unit may be configured to sweep or rotate about an axis, the FOV need not be oriented precisely toward the center of the bore, or centered about the center of the bore, at all times). The view for each detector unit  210 , for example, may be aligned along a central axis of a corresponding arm (e.g., arm  114 ) of the detector unit  210 . In the illustrated embodiment, the detector unit  210 ( a ) defines a corresponding view  220 ( a ), the detector unit  210 ( b ) defines a corresponding view  220 ( b ), the detector unit  210 ( c ) defines a corresponding view  220 ( c ), and so on. The detector units  210  are configured to sweep or pivot (thus sweeping the corresponding FOV&#39;s) over a sweep range (or portion thereof) bounded on either side of a line defined by the corresponding view during acquisition of imaging information. Thus, each detector unit  210  may collect information over a range larger than a field of view defined by a stationary detector unit. It may be noted that, generally, the sweeping range over which a detector may potentially pivot may be larger than the corresponding view during acquisition. In some cameras, the sweeping range that a detector may pivot may be unlimited (e.g., the detector may pivot a full 360 degrees or less), while in some embodiments the sweeping range of a detector may be constrained, for example over 180 degrees (from a −90 degree position to a +90 degree position relative to a position oriented toward the center of the bore). It may be noted that the detector units  210  of  FIG.  2    are mounted to a gantry (e.g., gantry  100  in  FIG.  1   ). The gantry may be rotatable to different positions, with the detector units  210  rotating with the gantry. 
     With continued reference to  FIG.  1   , the depicted processing unit  120  is configured to acquire imaging information or data (e.g., photon counts) via the detector units  115 . In various embodiments the imaging information includes focused imaging information and background imaging information. The focused imaging information corresponds to a focused region, and the background imaging information corresponds to tissues surrounding the focused region. As used herein, both the focused region and surrounding tissue may be used for imaging and/or diagnostic purposes; however, the focused region may be more pertinent or useful for diagnostic purposes, and, accordingly, more imaging information is acquired for the focused region than for the surrounding tissue. An example of a focused region and surrounding tissue is shown in  FIG.  3   . 
       FIG.  3    depicts a focused region and surrounding tissue of an object, or a focused portion and background portion of an image. As seen in  FIG.  3   , the detector unit  300  includes a detector head  310  disposed at an end of a detector arm  308 . In  FIG.  3   , only one detector unit  300  is depicted for ease and clarity of illustration. It may be noted that the detector unit  300  may be part of an arrangement of plural detector heads, such as depicted in  FIGS.  1  and  2   , and that the general principles discussed in connection with the detector unit  300  may be applied to one or more additional detector units of a multi-head camera imaging system. In  FIG.  3   , the detector unit  300  may be used to acquire imaging information (e.g., photon counts) of an object  303  having a focused region  302 . In the illustrated embodiment, the focused region  302  is surrounded by surrounding tissue  322 . The focused region  302 , for example, may be an organ such as the heart or brain (or portion thereof), and may have a substantially larger uptake of an administered radiopharmaceutical than surrounding tissue  322  of the object  303 . For example, in some embodiments, the focused region  302  is the striata of the brain, and the surrounding tissue  322  includes other portions of the brain. A ratio of detected activity between the striata and other portions of the brain may be used in analyzing whether or not a patient has Parkinson&#39;s disease. A central axis  312  of the detector unit  300  passes through a center  304  of the focused region  302  (which is disposed at the center of a bore in the illustrated embodiment). It may be noted that in various embodiments the central axis or center view of the detector need not necessarily pass through the focus center or through the focused region. The central axis  312 , for example, may correspond to a line along the view corresponding to the detector unit  300  when the detector unit  300  is at a midpoint of a range of coverage of the detector unit  300 , and/or may be aligned with a central axis of the detector arm  308  to which the detector head  310  is attached. 
     In the illustrated embodiment, the detector unit  300  is depicted as aligned with the central axis  312 , and may be rotated, pivoted or swept over a sweep range  309  between a first limit  313  and a second limit  314 . In the illustrated embodiment, the first limit  313  and the second limit  314  define a sweep range  309  (or maximum range of coverage) of 180 degrees. In other embodiments, the sweep range  309  and/or relative positions of the first limit  313  and second limit  314  may vary from the depicted arrangement. It may be noted that the sweep range  309  provides more coverage than is required to collect imaging information of the focused region  302  and the surrounding tissue  322 . Thus, if the detector unit  300  is swept over the sweep range  309  during a duration of an imaging acquisition, information that may be not be useful for diagnostic purposes (e.g., information towards the ends of the sweep range  309  that does not include information from either the focused region  302  or the surrounding tissue  322 ) may be collected. The time used to collect the information that is not useful for diagnostic purposes may be more efficiently spent collecting additional information from the focused region  302  and/or the surrounding tissue  322 . Accordingly, in the illustrated embodiment, the detector unit  310  may be controlled (e.g., by processing unit  120 ) to be swept or pivoted over an acquisition range  320  (e.g., a range including the focused region  302  and surrounding tissue  322 ) instead of over the entire sweep range  309  during acquisition of imaging information. 
     As seen in  FIG.  3   , the acquisition range  320  generally corresponds to edges of the surrounding tissue  322 , and is bounded by a first boundary  317  and a second boundary  318 . A focused range  321  is defined within the acquisition range  320  and corresponds to edges of the focused region  302 . The focused range  321  is bounded by a first boundary  315  and a second boundary  316 . Generally, more imaging information is acquired over the focused range  321  than over the background portions  330  of the acquisition range  320  which include the surrounding tissue  322  but not the focused region  302 . Generally, more time is spent acquiring information over the focused range  321  than over the background portions  330 . For example, the detector  310  may be swept at a higher sweep rate over the background portions  330  when acquiring the background imaging information than over the focused range  321  when acquiring the focused imaging information. The first boundary  315  is located at an angle α in clockwise direction from the central axis  312  (and, in the illustrated embodiment, from the center  304 ). The second boundary  316  is located at an angle β in a counterclockwise direction from the central axis  312  (and, in the illustrated embodiment, from the center  304 ). 
     It may be noted the boundaries may not necessarily correspond to a central axis or portion of a field of view of the detector unit, but may correspond to an edge or other portion of the field of view. Further, the acquisition range  320  may be configured in various embodiments to include more or less surrounding tissue beyond the focused region. Further, the acquisition range  320  may include an amount of background or surrounding tissue for a first phase of an acquisition period and omit background or surrounding tissue for a second phase; or omit the acquisition of surrounding tissue altogether (for one or several detector units comprising the system). 
     Returning to  FIG.  1   , in various embodiments the processing unit  120  includes processing circuitry configured to perform one or more tasks, functions, or steps discussed herein. It may be noted that “processing unit” as used herein is not intended to necessarily be limited to a single processor or computer. For example, the processing unit  120  may include multiple processors, FPGA&#39;s, ASIC&#39;s and/or computers, which may be integrated in a common housing or unit, or which may distributed among various units or housings (e.g., one or more aspects of the processing unit  120  may be disposed onboard one or more detector units, and one or more aspects of the processing unit  120  may be disposed in a separate physical unit or housing). The processing unit  120 , for example, may switch between different collimators (e.g., configured for different energy applications) depending on the energy application, determine acquisition range boundaries for focused and background regions, control the detector heads to acquire desired amounts of focused and background information, and reconstruct an image as discussed herein. It may be noted that operations performed by the processing unit  120  (e.g., operations corresponding to process flows or methods discussed herein, or aspects thereof) may be sufficiently complex that the operations may not be performed by a human being within a reasonable time period. For example, identifying boundaries of acquisition ranges, providing control signals to detector units, reconstructing images, or the like may rely on or utilize computations that may not be completed by a person within a reasonable time period. 
     In the illustrated embodiment, the processing unit  120  includes a reconstruction module  122 , a control module  124 , and a memory  130 . It may be noted that other types, numbers, or combinations of modules may be employed in alternate embodiments, and/or various aspects of modules described herein may be utilized in connection with different modules additionally or alternatively. Generally, the various aspects of the processing unit  120  act individually or cooperatively with other aspects to perform one or more aspects of the methods, steps, or processes discussed herein. 
     In the illustrated embodiment, the depicted reconstruction module  122  is configured to reconstruct an image. The depicted control module  124  is configured to interchange or switch between different collimators (e.g., configured for different energy applications) depending on the energy application. In addition, the depicted control module  124  is configured to control the detector heads  116  to sweep over corresponding acquisition ranges to acquiring focused imaging information and background imaging information. It may be noted that, in various embodiments, aspects of the control module  124  may be distributed among detector units  115 . For example, each detector unit may have a dedicated control module disposed in the head  116  of the detector unit  115 . 
     The memory  130  may include one or more computer readable storage media. The memory  130 , for example, may store information describing previously determined boundaries of acquisition ranges, parameters to be utilized during performance of a scan, parameters to be used for reconstruction or the like. Further, the process flows and/or flowcharts discussed herein (or aspects thereof) may represent one or more sets of instructions that are stored in the memory  130  for direction of operations of the imaging system  100 . 
     It may be noted that while the processing unit  120  is depicted schematically in  FIG.  1    as separate from the detector units  115 , in various embodiments, one or more aspects of the processing unit  120  may be shared with the detector units  115 , associated with the detector units  115 , and/or disposed onboard the detector units  115 . For example, in some embodiments, at least a portion of the processing unit  120  is integrated with at least one of the detector units  115 . 
       FIG.  4    is a schematic view of an example detector head  400  (e.g., having two collimators for different energy applications) and  FIG.  5    is a cross-sectional view (e.g., axial cross section) of the detector head  400 . As seen in  FIG.  5   , the detector head  400  includes a stepper motor  402  that may be utilized to pivot a detector column  404  about its longitudinal axis  406  (e.g., sweeping axis). It may be noted that motors other than stepper motors may be used in various embodiments. The detector head  400  also includes a gear  408  coupling the stepper motor to the column  404 , as well as a slip ring  410  (configured to allow for transfer of signals between the rotating detector column  404  and non-rotating components) and a multiplex board  412 . In the illustrated embodiment, the detector head  400  also includes an air channel  414  configured to provide cooling to components of the detector head  400 . 
     As depicted in  FIG.  5   , the detector column  404  includes a detector  416  (e.g., semiconductor detector such as CZT detector). The detector  416  includes a first surface  418  having a cathode disposed on it and a second surface  420  having pixelated anodes disposed on it. The detector column  404  includes collimators  422 ,  424  disposed over both the first surface  418  and the second surface  420  of the semiconductor device, respectively. The collimator  422  disposed over the cathode is configured for utilization during an imaging scan involving radiation in a first energy range (e.g., low energy range of approximately 40 to 300 keV). The collimator  424  disposed over the pixelated anodes is configured for utilization during an imaging scan involving radiation in a second energy range (e.g., high energy range of approximately 250 to 400 keV) different from the first energy range. The terms “high” and “low” as utilized herein are relative, with high energy meaning an energy higher than another energy and low energy meaning an energy lower than another energy. As noted above, the first and second energy ranges may partially overlap (e.g., at a high end of the first energy range and a low end of the second energy range) but differ in extent. As noted above, the collimators  422 ,  424  may be utilized during the same scan involving dual isotopes (e.g., high and low energy isotopes). 
     The collimators  422 ,  424  each have a respective height  426 ,  428  (e.g., height for the septa). In certain embodiments, the height  428  of the collimator  424  is greater than the height  426  of the collimator  422 . In certain embodiments, the ratio of the height  428  to the height  426  may range from 2:1 to 5:4. For example, the ratio of the height  428  to the height  426  may be 2:1, 3:2, 4:3, 5:4, or another ratio. In certain embodiments, the heights  426 ,  428 , of the collimators  422 ,  424  may be the same. Due to limited space within the detector head  400 , the heights  426 ,  428  of the collimators are limited. In order to avoid degraded spatial resolution due to a limited height collimator and to improve image quality (e.g., due to increased sensitivity, resolution, and/or contrast), sub-pixelation (e.g., either real or virtual sub-pixelation) may be utilized as described in U.S. Pat. No. 10,761,224, entitled “Systems and Methods for Improved Detector Assembly Sizing,” issued on Sep. 1, 2020, and incorporated by reference in its entirety. 
     The detector column  404  includes a radiation shield  430  (e.g., lead shield). In certain embodiments, the radiation shield is an aluminum extrusion having lead. The radiation shield  430  includes a first radiation shield portion  432  and a second radiation shield portion  434  that flank the collimators  422 ,  424 , the detector  416 , and associated electronics. In particular, the radiation shield portions  432 ,  434  extend from adjacent end  436  of the collimator  422  to adjacent end  438  of the collimator  424  in a direction perpendicular to the longitudinal axis  406  (see  FIG.  5   ). The radiation shield portions  432 ,  424  also extend in a direction along the longitudinal axis  406 . In certain embodiments, the collimator  424  enables the detector head  404  to be utilized in imaging applications where a radioactive tracer such as I 131  is utilized. For example with I 131 , the collimator provides adequate collimation for the 364 keV gamma ray and good shielding to reduce eventual contamination from 630 keV into the 364 keV peak (e.g., via limited photopeak charge collection efficiency or patient high energy scattered events). During high energy applications, the thickness of the detector  416  provides some radiation shielding in conjunction with the shielding form the radiation shield  430 . In addition, the peripheral CZT pixels act as a shield and absorb some of the gamma rays. 
     Printed circuit boards  440 ,  442  for electronics (e.g., power boards) are located in respective cavities  444 ,  446  formed between the radiation shield  430 , the collimators  422 ,  424 , and the semiconductor detector  416 . The printed circuit boards  440 ,  442  flank a portion of the collimator  424  and the semiconductor detector  416 . The positioning of the printed circuit boards  440 ,  442  reduces interference due to non-detecting material. In particular, no interfering material is located on the backside (e.g., anode side) to enable gamma ray collection from both the back and front sides of the detector  416 . The printed circuit boards  440 ,  442 , may include dedicated routing blocks and field programmable gate arrays. A printed circuit board  448  including an analog front-end including data channels and ASIC is disposed between the collimator  424  and the semiconductor detector  416 . A heat sink  450  is disposed between the collimator  424  and the printed circuit board  448 . In certain embodiments, the analog-front end associated data channels and ASIC may be located in the same location as the printed circuit boards  440 ,  442  and coupled via flex circuitry. In such an embodiment, no heat sink would be disposed between the collimator  424  and the detector  416 . 
     Returning to  FIG.  4   , the detector head  400  may be rotated about its longitudinal axis  406  as indicated by arrow  452  to position one of the collimators  422 ,  424  for use during an imaging scan (i.e., so that the collimator  422 ,  424  to be used faces the object to be imaged).  FIG.  6    is a schematic view illustrating switching between usage of different collimators within a detector head assembly.  FIG.  6    depicts a single detector unit  115  of an NM multi-head imaging system. The description of the single detector unit  115  applies to the rest of the detector units  115  of the NM multi-head imaging system. The single detector unit  115  is as described above and includes the detector head  400  as described in  FIGS.  4  and  5    having the detector column  404 . The detector column  404  includes the detector  416  disposed between the two collimators  422 ,  424  as described above. The detector unit  116  may move radially in and out as indicated by arrow  454 . In addition, the detector head  404  has a sweep motion as indicated by arrow  456 . In a first position  455  (e.g., for utilization during a low energy application), the collimator  422  is facing the object to be imaged. In a second position  457  (e.g., for utilization during a high energy application or a dual isotopes application), the collimator  424  is facing the object to be imaged. Utilizing the sweep axis degree of freedom, the detector column  404  may be rotated about its longitudinal axis (e.g., longitudinal axis  406  in  FIG.  4   ) approximately 180 degrees (±180 degrees) to change from the first position to the second position or vice versa as depicted in  FIG.  6   . Once the detector head  404  is in the desired position (e.g., first or second position), the detector head  404  may be rotated during an image scan a further approximately 105 degrees (±105 degrees). In total, the detector head  404  may rotated up to approximately 285 degrees (±285 degrees). As noted above, the rotation of the detector head  404  occurs via a motor coupled to the detector head  404 . The interchanging or switching of the collimators  422 ,  424  occurs semi-automatically or automatically (e.g., in response to an input or control signal) without removing the collimator  422 ,  424  from the detector unit  415  and the detector head  400 . In certain embodiments, the interchange or switching may be carried out manually. 
       FIG.  7    is a flow chart of an embodiment of a method  458  for switching between collimators in a detector head assembly of a NM multi-head imaging system. The detector head collimator includes two different collimators configured for different energy applications as described above. One or more steps of the method  458  may be performed by a component of the NM multi-head imaging system (e.g., processing unit  120  in  FIG.  1   ). The method  458  includes receiving a receiving an input (e.g., control signal) to change the collimator in the detector head (block  460 ). The input may be received via an input device of the NM multi-head imaging system. The input may be received in response to selection of a particular imaging scan, a particular radioactive tracer, and a combination thereof. The method  458  also includes rotating (e.g., automatically) the detector column to change the current position of the detector column (e.g., the first position or the second position as described in  FIG.  6   ) to another position (e.g., the second position if initially in the first position or the first position if initially in the second position) if the received input necessitates changing the position of the detector head (block  462 ). The method  458  further includes conducting the scan with the detector column in the desired position (block  464 ). In certain embodiments, switching between the two different collimators may occur during the same scan (e.g., applications involving dual isotopes (e.g., high and low energy isotopes)). 
     Embodiments described herein may be implemented in medical imaging systems, such as, for example, SPECT and SPECT-CT. Various methods and/or systems (and/or aspects thereof) described herein may be implemented using a medical imaging system. For example,  FIG.  8    is a schematic illustration of a NM imaging system  1000  having a plurality of imaging detector head assemblies mounted on a gantry (which may be mounted, for example, in rows, in an iris shape, or other configurations, such as a configuration in which the movable detector carriers  1016  are aligned radially toward the patient-body  1010 ). It should be noted that the arrangement of  FIG.  8    is provided by way of example for illustrative purposes, and that other arrangements (e.g., detector arrangements) may be employed in various embodiments. In the illustrated example, a plurality of imaging detectors  1002  are mounted to a gantry  1004 . In the illustrated embodiment, the imaging detectors  1002  are configured as two separate detector arrays  1006  and  1008  coupled to the gantry  1004  above and below a subject  1010  (e.g., a patient), as viewed in  FIG.  8   . The detector arrays  1006  and  1008  may be coupled directly to the gantry  1004 , or may be coupled via support members  1012  to the gantry  1004  to allow movement of the entire arrays  1006  and/or  1008  relative to the gantry  1004  (e.g., transverse translating movement in the left or right direction as viewed by arrow T in  FIG.  8   ). Additionally, each of the imaging detectors  1002  includes a detector unit  1014 , at least some of which are mounted to a movable detector carrier  1016  (e.g., a support arm or actuator that may be driven by a motor to cause movement thereof) that extends from the gantry  1004 . In some embodiments, the detector carriers  1016  allow movement of the detector units  1014  towards and away from the subject  1010 , such as linearly. Thus, in the illustrated embodiment the detector arrays  1006  and  1008  are mounted in parallel above and below the subject  1010  and allow linear movement of the detector units  1014  in one direction (indicated by the arrow L), illustrated as perpendicular to the support member  1012  (that are coupled generally horizontally on the gantry  1004 ). However, other configurations and orientations are possible as described herein. It should be noted that the movable detector carrier  1016  may be any type of support that allows movement of the detector units  1014  relative to the support member  1012  and/or gantry  1004 , which in various embodiments allows the detector units  1014  to move linearly towards and away from the support member  1012 . 
     Each of the imaging detectors  1002  in various embodiments is smaller than a conventional whole body or general purpose imaging detector. A conventional imaging detector may be large enough to image most or all of a width of a patient&#39;s body at one time and may have a diameter or a larger dimension of approximately 50 cm or more. In contrast, each of the imaging detectors  1002  may include one or more detector units  1014  coupled to a respective detector carrier  1016  and having dimensions of, for example, 4 cm to 20 cm and may be formed of Cadmium Zinc Telluride (CZT) tiles or modules. For example, each of the detector units  1014  may be 8×8 cm in size and be composed of a plurality of CZT pixelated modules (not shown). For example, each module may be 4×4 cm in size and have 16×16=256 pixels (pixelated anodes). In some embodiments, each detector unit  1014  includes a plurality of modules, such as an array of 1×7 modules. However, different configurations and array sizes are contemplated including, for example, detector units  1014  having multiple rows of modules. 
     It should be understood that the imaging detectors  1002  may be different sizes and/or shapes with respect to each other, such as square, rectangular, circular or other shape. An actual field of view (FOV) of each of the imaging detectors  1002  may be directly proportional to the size and shape of the respective imaging detector. 
     The gantry  1004  may be formed with an aperture  1018  (e.g., opening or bore) therethrough as illustrated. A patient table  1020 , such as a patient bed, is configured with a support mechanism (not shown) to support and carry the subject  1010  in one or more of a plurality of viewing positions within the aperture  1018  and relative to the imaging detectors  1002 . Alternatively, the gantry  1004  may comprise a plurality of gantry segments (not shown), each of which may independently move a support member  1012  or one or more of the imaging detectors  1002 . 
     The gantry  1004  may also be configured in other shapes, such as a “C”, “H” and “L”, for example, and may be rotatable about the subject  1010 . For example, the gantry  1004  may be formed as a closed ring or circle, or as an open arc or arch which allows the subject  1010  to be easily accessed while imaging and facilitates loading and unloading of the subject  1010 , as well as reducing claustrophobia in some subjects  1010 . 
     Additional imaging detectors (not shown) may be positioned to form rows of detector arrays or an arc or ring around the subject  1010 . By positioning multiple imaging detectors  1002  at multiple positions with respect to the subject  1010 , such as along an imaging axis (e.g., head to toe direction of the subject  1010 ) image data specific for a larger FOV may be acquired more quickly. 
     Each of the imaging detectors  1002  has a radiation detection face, which is directed towards the subject  1010  or a region of interest within the subject. 
     The collimators  1022  (and detectors) in  FIG.  8    are depicted for ease of illustration as single collimators in each detector head. As noted above, in certain embodiments, each detector unit  1014  (or detector head) includes a detector column that be rotated between two different collimators configured for two different energy applications (e.g., high energy versus low energy). Optionally, for embodiments employing one or more parallel-hole collimators, multi-bore collimators may be constructed to be registered or semi-registered with pixels of the detector units  1014 , which in one embodiment are CZT detectors. However, other materials may be used. Registered collimation may improve spatial resolution by forcing photons going through one bore to be collected primarily by one pixel. Additionally, registered collimation may improve sensitivity and energy response of pixelated detectors as detector area near the edges of a pixel or in-between two adjacent pixels may have reduced sensitivity or decreased energy resolution or other performance degradation. Having collimator septa directly above the edges of pixels reduces the chance of a photon impinging at these degraded-performance locations, without decreasing the overall probability of a photon passing through the collimator. 
     A controller unit  1030  may control the movement and positioning of the patient table  1020 , imaging detectors  1002  (which may be configured as one or more arms), gantry  1004  and/or the collimators  1022  (that move with the imaging detectors  1002  in various embodiments, being coupled thereto). A range of motion before or during an acquisition, or between different image acquisitions, is set to maintain the actual FOV of each of the imaging detectors  1002  directed, for example, towards or “aimed at” a particular area or region of the subject  1010  or along the entire subject  1010 . The motion may be a combined or complex motion in multiple directions simultaneously, concurrently, or sequentially. 
     The controller unit  1030  may have a gantry motor controller  1032 , table controller  1034 , detector controller  1036 , pivot controller  1038 , and collimator controller  1040 . The controllers  1030 ,  1032 ,  1034 ,  1036 ,  1038 , and  1040  may be automatically commanded by a processing unit  1050 , manually controlled by an operator, or a combination thereof. The gantry motor controller  1032  may move the imaging detectors  1002  with respect to the subject  1010 , for example, individually, in segments or subsets, or simultaneously in a fixed relationship to one another. For example, in some embodiments, the gantry controller  1032  may cause the imaging detectors  1002  and/or support members  1012  to move relative to or rotate about the subject  1010 , which may include motion of less than or up to 180 degrees (or more). 
     The table controller  1034  may move the patient table  1020  to position the subject  1010  relative to the imaging detectors  1002 . The patient table  1020  may be moved in up-down directions, in-out directions, and right-left directions, for example. The detector controller  1036  may control movement of each of the imaging detectors  1002  to move together as a group or individually. The detector controller  1036  also may control movement of the imaging detectors  1002  in some embodiments to move closer to and farther from a surface of the subject  1010 , such as by controlling translating movement of the detector carriers  1016  linearly towards or away from the subject  1010  (e.g., sliding or telescoping movement). Optionally, the detector controller  1036  may control movement of the detector carriers  1016  to allow movement of the detector array  1006  or  1008 . For example, the detector controller  1036  may control lateral movement of the detector carriers  1016  illustrated by the T arrow. In various embodiments, the detector controller  1036  may control the detector carriers  1016  or the support members  1012  to move in different lateral directions. Detector controller  1036  may control the swiveling motion of detectors  1002  together with their collimators  1022 . In some embodiments, detectors  1002  and collimators  1022  may swivel or rotate around an axis. 
     The pivot controller  1038  may control pivoting or rotating movement of the detector units  1014  at ends of the detector carriers  1016  and/or pivoting or rotating movement of the detector carrier  1016 . For example, one or more of the detector units  1014  or detector carriers  1016  may be rotated about at least one axis to view the subject  1010  from a plurality of angular orientations to acquire, for example, 3D image data in a 3D SPECT or 3D imaging mode of operation. The collimator controller  1040  may rotate a detector column between two different collimators configured for two different energy applications (e.g., high energy versus low energy). 
     It should be noted that motion of one or more imaging detectors  1002  may be in directions other than strictly axially or radially, and motions in several motion directions may be used in various embodiment. Therefore, the term “motion controller” may be used to indicate a collective name for all motion controllers. It should be noted that the various controllers may be combined, for example, the detector controller  1036  and pivot controller  1038  may be combined to provide the different movements described herein. 
     Prior to acquiring an image of the subject  1010  or a portion of the subject  1010 , the imaging detectors  1002 , gantry  1004 , patient table  1020  and/or collimators  1022  may be adjusted, such as to first or initial imaging positions, as well as subsequent imaging positions. The imaging detectors  1002  may each be positioned to image a portion of the subject  1010 . Alternatively, for example in a case of a small size subject  1010 , one or more of the imaging detectors  1002  may not be used to acquire data, such as the imaging detectors  1002  at ends of the detector array  1006  and  1008 , which as illustrated in  FIG.  8    are in a retracted position away from the subject  1010 . Positioning may be accomplished manually by the operator and/or automatically, which may include using, for example, image information such as other images acquired before the current acquisition, such as by another imaging modality such as X-ray Computed Tomography (CT), MRI, X-Ray, PET or ultrasound. In some embodiments, the additional information for positioning, such as the other images, may be acquired by the same system, such as in a hybrid system (e.g., a SPECT/CT system). Additionally, the detector units  1014  may be configured to acquire non-NM data, such as X-ray CT data. In some embodiments, a multi-modality imaging system may be provided, for example, to allow performing NM or SPECT imaging, as well as X-ray CT imaging, which may include a dual-modality or gantry design as described in more detail herein. 
     After the imaging detectors  1002 , gantry  1004 , patient table  1020 , and/or collimators  1022  are positioned, one or more images, such as three-dimensional (3D) SPECT images are acquired using one or more of the imaging detectors  1002 , which may include using a combined motion that reduces or minimizes spacing between detector units  1014 . The image data acquired by each imaging detector  1002  may be combined and reconstructed into a composite image or 3D images in various embodiments. 
     In one embodiment, at least one of detector arrays  1006  and/or  1008 , gantry  1004 , patient table  1020 , and/or collimators  1022  are moved after being initially positioned, which includes individual movement of one or more of the detector units  1014  (e.g., combined lateral and pivoting movement) together with the swiveling motion of detectors  1002 . For example, at least one of detector arrays  1006  and/or  1008  may be moved laterally while pivoted. Thus, in various embodiments, a plurality of small sized detectors, such as the detector units  1014  may be used for 3D imaging, such as when moving or sweeping the detector units  1014  in combination with other movements. 
     In various embodiments, a data acquisition system (DAS)  1060  receives electrical signal data produced by the imaging detectors  1002  and converts this data into digital signals for subsequent processing. However, in various embodiments, digital signals are generated by the imaging detectors  1002 . An image reconstruction device  1062  (which may be a processing device or computer) and a data storage device  1064  may be provided in addition to the processing unit  1050 . It should be noted that one or more functions related to one or more of data acquisition, motion control, data processing and image reconstruction may be accomplished through hardware, software and/or by shared processing resources, which may be located within or near the imaging system  1000 , or may be located remotely. Additionally, a user input device  1066  may be provided to receive user inputs (e.g., control commands), as well as a display  1068  for displaying images. DAS  1060  receives the acquired images from detectors  1002  together with the corresponding lateral, vertical, rotational and swiveling coordinates of gantry  1004 , support members  1012 , detector units  1014 , detector carriers  1016 , and detectors  1002  for accurate reconstruction of an image including 3D images and their slices. 
     It should be noted that the particular arrangement of components (e.g., the number, types, placement, or the like) of the illustrated embodiments may be modified in various alternate embodiments, and/or one or more aspects of illustrated embodiments may be combined with one or more aspects of other illustrated embodiments. For example, in various embodiments, different numbers of a given module or unit may be employed, a different type or types of a given module or unit may be employed, a number of modules or units (or aspects thereof) may be combined, a given module or unit may be divided into plural modules (or sub-modules) or units (or sub-units), one or more aspects of one or more modules may be shared between modules, a given module or unit may be added, or a given module or unit may be omitted. 
     As used herein, a structure, limitation, or element that is “configured to” perform a task or operation is particularly structurally formed, constructed, or adapted in a manner corresponding to the task or operation. For purposes of clarity and the avoidance of doubt, an object that is merely capable of being modified to perform the task or operation is not “configured to” perform the task or operation as used herein. Instead, the use of “configured to” as used herein denotes structural adaptations or characteristics, and denotes structural requirements of any structure, limitation, or element that is described as being “configured to” perform the task or operation. For example, a processing unit, processor, or computer that is “configured to” perform a task or operation may be understood as being particularly structured to perform the task or operation (e.g., having one or more programs or instructions stored thereon or used in conjunction therewith tailored or intended to perform the task or operation, and/or having an arrangement of processing circuitry tailored or intended to perform the task or operation). For the purposes of clarity and the avoidance of doubt, a general purpose computer (which may become “configured to” perform the task or operation if appropriately programmed) is not “configured to” perform a task or operation unless or until specifically programmed or structurally modified to perform the task or operation. 
     As used herein, the term “computer,” “processor,” or “module” may include any processor-based or microprocessor-based system including systems using microcontrollers, reduced instruction set computers (RISC), application specific integrated circuits (ASICs), logic circuits, and any other circuit or processor capable of executing the functions described herein. The above examples are exemplary only, and are thus not intended to limit in any way the definition and/or meaning of the term “computer,” “processor,” or “module.” 
     The computer or processor executes a set of instructions that are stored in one or more storage elements, in order to process input data. The storage elements may also store data or other information as desired or needed. The storage element may be in the form of an information source or a physical memory element within a processing machine. 
     The set of instructions may include various commands that instruct the computer or processor as a processing machine to perform specific operations such as the methods and processes of the various embodiments. The set of instructions may be in the form of a software program. The software may be in various forms such as system software or application software. Further, the software may be in the form of a collection of separate programs or modules, a program module within a larger program or a portion of a program module. The software also may include modular programming in the form of object-oriented programming. The processing of input data by the processing machine may be in response to operator commands, or in response to results of previous processing, or in response to a request made by another processing machine. 
     As used herein, the terms “software” and “firmware” may include any computer program stored in memory for execution by a computer, including RAM memory, ROM memory, EPROM memory, EEPROM memory, and non-volatile RAM (NVRAM) memory. The above memory types are exemplary only, and are thus not limiting as to the types of memory usable for storage of a computer program. 
     Technical effects of the disclosed subject matter include a radiation detector head assembly of a NM multi-head imaging system that includes two collimators (each specifically configured for use with different energy applications such as high and low energy applications). The disclosed embodiments enable the automatic interchange between the different collimators to occurs within a matter of seconds (e.g., as opposed to minutes). The interchange occurs completely within the radiation detector head assembly (without having to remove one of the detectors) and without the utilization of a mechanical (and manual) collimator exchange process. The quick automatic exchange between collimators saves time during the day and avoids downtime for the imaging system, thus, enabling an improved workflow (e.g., hospital patient flow). The disclosed embodiments may also reduce the cost of the imaging system. 
     The techniques presented and claimed herein are referenced and applied to material objects and concrete examples of a practical nature that demonstrably improve the present technical field and, as such, are not abstract, intangible or purely theoretical. Further, if any claims appended to the end of this specification contain one or more elements designated as “means for [perform]ing [a function] . . . ” or “step for [perform]ing [a function] . . . ”, it is intended that such elements are to be interpreted under 35 U.S.C. 112(f). However, for any claims containing elements designated in any other manner, it is intended that such elements are not to be interpreted under 35 U.S.C. 112(f). 
     This written description uses examples to disclose the present subject matter, including the best mode, and also to enable any person skilled in the art to practice the subject matter, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the subject matter 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.