Abstract:
A phantom for a nuclear imaging system is provided. In particular, systems and method are provided for a phantom including a pattern plate having a plurality of passages and a plurality of channels sequentially interconnecting each of the plurality of cylindrical cavities.

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
     Not Applicable. 
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH 
     Not Applicable. 
     BACKGROUND 
     The disclosure relates generally to quality assurance (QA) for nuclear imaging systems and, more specifically, to systems and methods for a linearly filled nuclear imaging phantom. 
     Nuclear imaging systems, for example single photon emission computed tomography (SPECT) systems and positron emission tomography (PET) systems, commonly use phantoms for quantifying imaging characteristics and for QA. Regular QA is essential to ensure that the images acquired by the nuclear imaging systems are of proper image quality and accuracy. 
     Typically, the phantoms are filled with a positron emitting radioisotope in fluid (e.g., water) to define a specific geometry which is then scanned by the nuclear imaging system. Various phantom geometries are used to measure specific imaging characteristics (e.g., spatial resolution, sensitivity, attenuation, etc.). One such phantom that is used in clinical and research applications to test the resolution capability of a nuclear imaging system is a Derenzo style phantom. Derenzo style phantoms include six hole patterns which each define a triangular shape and combine to form a hexagonal shape. The same size, or diameter, holes are used within an individual hole pattern, but the size of the holes change from pattern to pattern around the hexagonal shape. Each hole within an individual hole pattern is arranged at a distance that is twice that hole&#39;s diameter from adjacent holes. 
     BRIEF SUMMARY 
     The present disclosure provides a phantom for a nuclear imaging system that is linearly filled with fluid. In particular, the present disclosure provides systems and methods for a phantom having a plurality of passages that are configured to be linearly filled with fluid. 
     In one aspect, the present disclosure provides a phantom for a nuclear imaging system. The phantom includes a pattern plate including a plurality of passages extending through the pattern plate from a first opening on a first side of the pattern plate to a second opening on an opposing second side of the pattern plate. The phantom further includes a plurality of channels arranged on the first side of the pattern plate and the second side of the pattern plate to sequentially interconnect each of the plurality of passages thereby forming a continuous flow path from an inlet passage of the pattern plate to an outlet passage of the pattern plate. 
     In another aspect, the present disclosure provides a phantom for a nuclear imaging system. The phantom includes a pattern plate including a plurality of passages each extending through the pattern plate from a first opening on a first side of the pattern plate to a second opening on an opposing second side of the pattern plate. The phantom further includes a plurality of continuous fluid flow paths arranged on the first side of the pattern plate and the second side of the pattern plate to sequentially interconnect each of the plurality of passages from an inlet passage of the pattern plate to an outlet passage of the pattern plate. 
     In yet another aspect, the present disclosure provides a method of determining an imaging characteristic of a nuclear imaging system using a phantom fillable with a radioisotope doped fluid. The phantom includes a pattern plate and a continuous fluid flow path. The pattern plate includes a plurality of passages arranged in a calibration pattern. The plurality of passages includes an inlet passage and an outlet passage. The continuous fluid flow path sequentially interconnects each of the plurality of passages from the inlet passage to the outlet passage. The method includes furnishing the radioisotope doped fluid to the inlet passage of the pattern plate, filling the plurality of passages in the pattern plate, via the continuous fluid flow path, with a pre-determined volume of the radioisotope doped fluid. The method further includes upon filling the plurality of passages with the pre-determined volume of radioisotope doped fluid, imaging, with the nuclear imaging system, a cross-section of the pattern plate which defines the calibration pattern, and upon imaging the cross-section of the pattern plate which defines the calibration pattern, determining the imaging characteristic of the nuclear imaging system. 
     The foregoing and other aspects and advantages of the invention will appear from the following description. In the description, reference is made to the accompanying drawings which form a part hereof, and in which there is shown by way of illustration a preferred embodiment of the invention. Such embodiment does not necessarily represent the full scope of the invention, however, and reference is made therefore to the claims and herein for interpreting the scope of the invention. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       The invention will be better understood and features, aspects and advantages other than those set forth above will become apparent when consideration is given to the following detailed description thereof. Such detailed description makes reference to the following drawings. 
         FIG. 1  shows a perspective view of a phantom for a nuclear imaging system according to one embodiment of the present disclosure. 
         FIG. 2  shows an exploded view of the phantom of  FIG. 1 . 
         FIG. 3  shows a cross-sectional view of the phantom of  FIG. 1  taken along line  3 - 3 . 
         FIG. 4  shows a top-perspective view of a pattern plate of the phantom of  FIG. 1 . 
         FIG. 5  shows a bottom-perspective view of a pattern plate of the phantom of  FIG. 1 . 
         FIG. 6  shows a top view of a pattern plate of the phantom of  FIG. 1  with the pattern plate transparent to illustrate a flow path of the pattern plate. 
         FIG. 7  shows a top view of a pattern plate of the phantom of  FIG. 1  with connections between adjacent passages highlighted to illustrate which connections are made on a first side of the pattern plate and which connections are made on a second side of the pattern plate. 
         FIG. 8  shows a perspective view of a first closing plate of the phantom of  FIG. 1  with the first closing plate transparent according to another embodiment of the present disclosure. 
         FIG. 9  shows four PET images of the phantom of  FIG. 1  along a cross-sectional plane with the phantom filled with  52 Mn,  64 Cu,  76 Br, and  124 I. 
     
    
    
     DETAILED DESCRIPTION 
     Currently, nuclear imaging phantoms (e.g., Derenzo style phantoms) include a cylinder having a hole pattern drilled therein and a chamber for receiving the cylinder. The cylinder is placed within the chamber, and the chamber is then filled with a positron emitting radioisotope (e.g.,  52 Mn,  64 Cu,  76 Br,  124 I) in fluid (e.g., water) in an attempt to fill the hole pattern in the cylinder so the phantom can be imaged using a nuclear imaging system. 
     However, several problems exist with these current phantoms designs. For example, when the hole patterns are submerged in the fluid, the smaller holes often do not fill because of the surface tension of the fluid. Incomplete filling of the holes in the phantom leads to air bubbles in the hole pattern thereby making it difficult or impossible to effectively image the phantom. Additionally, the entire chamber of the phantom must be filled with the radioisotope doped fluid. A volume of fluid required to fill the hole pattern is significantly less than a volume of fluid required to fill the chamber. Therefore, the current phantom designs do not utilize (i.e., waste) a significant volume of the radioisotope doped fluid in the chamber. It is well known in the art that the radioisotopes put into these phantoms represent a significant cost to research and clinical institutions and, thus, wasted volume is directly proportional to additional cost. Furthermore, the current phantom designs require a significant dosage (i.e., concentration) of the radioisotope to accompany the large volume of fluid required to fill the chamber. 
     Due to the deficiencies in current nuclear imaging phantom designs, it would be desirable to have a nuclear imaging phantom that is linearly filled with fluid to ensure the hole pattern of the phantom is completely filled with fluid. This would also enable the phantom to utilize only a volume of radioisotope doped fluid necessary to fill the hole pattern. That is, the phantom would not require any radioisotope doped fluid to be wasted, and enable the phantom to utilize a reduced dosage (i.e. concentration) of the radioisotope in the fluid. 
       FIG. 1  shows one non-limiting example of a phantom  10  for a nuclear imaging system (e.g., PET, SPECT, etc.) according to the present disclosure. The phantom  10  includes a first closing plate  12 , a second closing plate  14 , and a pattern plate  16  arranged between the first closing plate  12  and the second closing plate  14 . The first closing plate  12 , the second closing plate  14 , and the pattern plate  16  each define a generally cylindrical shape, and each are fabricated from a material which does not interfere with the nuclear imaging system (e.g., a non-metallic material such as plastic or glass). In other non-limiting examples, the first closing plate  12 , the second closing plate  14 , and/or the pattern plate  16  may define an alternative shape, for example a rectangular or elliptical shape, as desired. 
     The first closing plate  12  includes an inlet  18  and an outlet  20 . The inlet  18  is in fluid communication with the outlet  18  via a flow path in the pattern plate  16 , as will be described in detail below. In some non-limiting examples, the inlet  18  and the outlet  20  can be coupled to a fitting (e.g., a Luer lock fitting) to enable the inlet  18  and the outlet  20  to be coupled to a Leur lock syringe. In other non-limiting examples, the inlet  18  and the outlet  20  may be coupled to a tube or a syringe pump device. In any case, the inlet  18  is configured to receive a fluid which is then furnished to the outlet  20  via the flow path in the pattern plate  16 . It should be known that the mechanism used to furnish the fluid from the inlet  18  to the outlet  20  it not meant to be limiting in any way. In other non-limiting examples, one of the inlet  18  and the outlet  20  may be arranged on the first closing plate  12  and the other may be arranged on the second closing plate  14 . 
     The phantom  10  includes a first gasket  22  arranged between the first closing plate  12  and the pattern plate  16 , and a second gasket  24  arranged between the second closing plate  14  and the pattern plate  16 . The first gasket  22  and the second gasket  24  each define a generally cylindrical shape, and are fabricated from a material which does not interfere with the nuclear imaging system (e.g., a non-metallic material such as silicon). The first gasket  22  is configured to provide a seal between the first closing plate  12  the pattern plate  16  to prevent fluid from leaking from the phantom  10  when fluid is furnished from the inlet  18  to the outlet  20 . Similarly, the second gasket  24  is configured to provide a seal between the second closing plate  14  and the pattern plate  16  to prevent fluid from leaking from the phantom  10  when fluid is furnished from the inlet  18  to the outlet  20 . 
     A plurality of fastening elements  26  fasten the pattern plate  16  between the first closing plate  12  and the second closing plate  14 , and compress the first gasket  22  and the second gasket  24 . The fastening elements  26  are fabricated from a material which does not interfere with the nuclear imaging system (e.g., a non-metallic material such as plastic, glass, or glass-filled nylon). The illustrated phantom  10  includes seven fastening elements  26  each in the form of a bolt  28  and a nut  30 . It should be known that the number of fastening elements  26  is not meant to be limiting in any way. That is, the phantom  10  may include more or less than seven fastening elements  26  as long as the pattern plate  16 , the first gasket  22  and the second gasket  24  are sufficiently and uniformly compressed between the first closing plate  12  and the second closing plate  14 . In other non-limiting examples, the fastening elements  26  may be in the form of a clamping device or another compressive mechanism known in the art. 
     Turning to  FIG. 2 , each of the first closing plate  12 , the second closing plate  14 , the pattern plate  16 , the first gasket  22 , and the second gasket  24  include a plurality of fastener apertures  32 . Each of the fastener apertures  32  in the first closing plate  12  are axially aligned with a corresponding fastener aperture  32  in the second closing plate  14 , the pattern plate  16 , the first gasket  22 , and the second gasket  24 . In this way, the fastener apertures  32  combine to form through holes extending from the first closing plate  12  through the second closing plate  14  each for receiving a corresponding one of the bolts  28 . 
     The first gasket  22  includes a first gasket inlet aperture  34  and a first gasket outlet aperture  36 . The first gasket inlet aperture  34  is axially aligned with the inlet  18  of the first closing plate  12 , and the first gasket outlet  36  is axially aligned with the outlet  20  of the first closing plate  12 . As shown in  FIG. 3 , the inlet  18  defines a generally cylindrical passage in the first closing plate  12  having a first inlet passage  38  and a second inlet passage  40 . The first inlet passage  38  defines a diameter which is greater than a diameter of the second inlet passage  40 . In one non-limiting example, the first inlet passage  38  may include threads for receiving a fitting. In other non-limiting examples, the inlet  18  may define a generally uniform diameter and not include the first inlet passage  38  and the second inlet passage  40 . The first gasket inlet aperture  34  defines a diameter which is substantially equal to the diameter of the second inlet passage  40 . 
     Similar to the inlet  18 , the outlet  20  defines a generally cylindrical passage in the first closing plate  12  having a first outlet passage  42  and a second outlet passage  44 . The first outlet passage  42  defines a diameter which is greater than a diameter of the second outlet passage  44 . In one non-limiting example, the first outlet passage  42  may include threads for receiving a fitting. In other non-limiting examples, the outlet  20  may define a generally uniform diameter and not include the first outlet passage  42  and the second outlet passage  44 . The first gasket outlet aperture  36  defines a diameter which is substantially equal to the diameter of the second outlet passage  44 . 
     With reference to  FIGS. 3-5 , the pattern plate  16  includes a plurality of passages  48  arranged to define a pattern for quantifying an imaging characteristic of the nuclear imagine system, as will be described in detail below. Each of the plurality of passage  48  define a generally cylindrical shape. The plurality of passages  48  are arranged into a plurality of hole pattern groups. In particular, the pattern plate  16  includes a first hole pattern group  50 , a second hole pattern group  51 , a third hole pattern group  52 , a fourth hole pattern group  53 , a fifth hole pattern group  54 , and a sixth hole pattern group  55 . The first hole pattern group  50  includes a first plurality of passages  56  each defining a first diameter. The second hole pattern group  51  includes a second plurality of passages  57  each defining a second diameter. The third hole pattern group  52  includes a third plurality of passages  58  each defining a third diameter. The fourth hole pattern group  53  includes a fourth plurality of passages  59  each defining a fourth diameter. The fifth hole pattern group  54  includes a fifth plurality of passages  60  each defining a fifth diameter. The sixth hole pattern group  55  includes a sixth plurality of passages  61  each defining a sixth diameter. 
     The first, second, third, fourth, fifth, and sixth hole pattern groups  50 ,  51 ,  52 ,  53 ,  54 , and  55  are arranged circumferentially around the pattern plate  16  and each define a generally triangular shape. The first, second, third, fourth, fifth, and sixth hole pattern groups  50 ,  51 ,  52 ,  53 ,  54 , and  55  combine to define a generally hexagonal shape. 
     Each individual passage in the first, second, third, fourth, fifth, and sixth plurality of passages  56 ,  57 ,  58 ,  59 ,  60 , and  61  extend through the pattern plate  16  from a first opening  62  in a first side  63  of the pattern plate  16  to a second opening  64  in an opposing second side  65  of the pattern plate  16 . As shown in  FIGS. 4 and 5 , the first, second third, fourth, fifth, and sixth cavity diameters are all different. The illustrated pattern plate  16  includes gradually decreasing diameters circumferentially around the pattern plate from the first hole pattern group  50  to the sixth hole pattern group  55 . That is, the first diameter is greater than the second diameter, and the second diameter is greater than the third diameter, and so on (the first diameter&gt;the second diameter&gt;the third diameter&gt;the fourth diameter&gt;the fifth diameter&gt;the sixth diameter). Additionally, each individual passage in the first, second, third, forth, fifth, and sixth plurality of passages  56 ,  57 ,  58 ,  59 ,  60 , and  61  are spaced a distance equal to twice the diameter of the individual passage from neighboring passages. That is, each of the passages in the first plurality of passages  56  are spaced a distance equal to twice the first diameter from neighboring passages, and each of the passages in the second plurality of passages  57  are spaced a distance equal to twice the second diameter from neighboring passages, and so on. The above described geometric features of the pattern plate  16  enable the phantom  10  to define a Derenzo style pattern in a cross-sectional plane parallel to and between the first side  63  of the pattern plate  16  and the second side  65  of the pattern plate  16 . 
     The first plurality of passages  50  include an inlet passage  66  and an outlet passage  68 . The inlet passage  66  is axially aligned and in fluid communication with the inlet  18  of the first closing plate  12 . The inlet passage  66  defines a diameter that is substantially equal to the diameter of the second inlet passage  40 . The outlet passage  68  is axially aligned and in fluid communication with the outlet  20  of the first closing plate  12 . The outlet passage  68  defines a diameter that is substantially equal to the diameter of the second outlet passage  44 . 
     The pattern plate  16  includes a plurality of first side channels  70  and a plurality of second side channels  72 . Each of the plurality of first side channels  70  define a channel in the first pattern plate side  62  that connect a pair of the plurality of passages  48 . Each of the plurality of second side channels  72  define a channel in the second patter plate side  64  that connect another pair of the plurality of passages  48 . The plurality of passages  48 , the plurality of first side channels  70 , and the plurality of second side channels  72  combine to define a continuous fluid flow path  74  through the pattern plate  16  that fluidly connects the inlet passage  66  to the outlet passage  68 . 
     Turning to  FIGS. 6 and 7 , the continuous fluid flow path  74  through the pattern plate  16  linearly connects each of the plurality of passages  48  from the inlet passage  66  to the outlet passage  68 . That is, the flow path  74  enables plurality of passages  48  to be filled sequentially and one at a time when fluid is furnished to the inlet  18 . This is accomplished by connecting consecutive pairs of the plurality of passages  48  on alternating sides of the pattern plate  16  via the plurality of first side channels  70  (shown in solid in  FIG. 7 ) and the plurality of second side channels  72  (shown in cross-hatched in  FIG. 7 ). In particular, the pairs of the plurality of passages  48  connected by the first side channels  70  and the second side channels  72  represent a complete set of connections between the inlet passage  66  and the outlet passage  68  and are complementary. In addition, the same two of the plurality of passages  48  should not be connected on both the first side  63  of the pattern plate  16  and the second side  65  of the pattern plate  16  as this would result in a closed off flow path. 
       FIG. 8  shows another non-limiting example of a first closing plate  80  of the phantom  10  according to the present disclosure. The first closing plate  80  of  FIG. 8  is similar to the first closing plate  12  of  FIGS. 1-3  (with similar features identified with like reference numerals) except as described below or is apparent from  FIG. 8 . As shown in  FIG. 8 , the inlet  18  of the first closing plate  12  includes the first inlet passage  38 , the second inlet passage  40 , and an oblique inlet passage  82 . Similarly, the outlet  20  of the first closing plate  12  includes the first outlet passage  42 , the second outlet passage  44 , and an oblique outlet passage  84 . The oblique inlet passage  82  axially offsets the first inlet passage  38  and the second inlet passage  40  (and thereby the inlet passage  66 ), and the oblique outlet passage  84  axially offsets the first outlet passage  42  and the second outlet passage  44  (and thereby the outlet passage  68 ). This enables a distance between the first inlet passage  38  and the first outlet passage  42  in the first closing plate  80  to be greater than a distance between the first inlet passage  38  and the first outlet passage  42  in the first closing plate  12 . 
     One non-limiting example of the operation of the phantom  10  will be described with reference to  FIGS. 1-8 . It should be know that the exemplary advantages of the phantom  10  described herein, or otherwise apparent to one of skill in the art, may be applied to other phantoms designed using the techniques and properties described herein. 
     In operation, the phantom  10  is used to quantify a resolution capability of the nuclear imaging system. To accomplish this, the phantom  10  is first filled with a radioisotope doped fluid. The inlet  18  of the first closing plate  12  is connected to a fluid source (e.g., a tube, a syringe, a syringe pump, etc.). A volume required to fill the continuous fluid flow path  74  with fluid can be determined either experimentally (e.g., using a predetermined volume of fluid) or theoretically (e.g., calculating the volume based on the first, second, third, fourth, fifth, and sixth diameters and a depth of the plurality of first side channels  70  and the plurality of second side channels  72 ). Since the volume required to fill the continuous fluid flow path  74  is known, the fluid source can provide an exact pre-determined volume of radioisotope doped fluid to the inlet  18 . Once the fluid source furnishes the radioisotope fluid to the inlet  18 , the fluid linearly follows the continuous fluid flow path  74  thereby filling each of the passages  48  one at a time from the inlet passage  66  to the outlet passage  68 . In this way, the phantom  10  does not require any wasted or additional expensive radioisotope doped fluid to fill the plurality of passages  48 . Additionally, a reduced volume required to fill the continuous fluid flow path  74  (when compared to current phantom designs) enables the phantom  10  to utilize a reduced dosage (i.e., concentration) of the radioisotope in the fluid. 
     Once the plurality of passages  48  are all filled with the radioisotope doped fluid, the nuclear imaging system can acquire an image of the phantom  10  along a cross-sectional plane parallel to and between the first side  63  and the second side  65  of the pattern plate  16 . Because of the Derenzo style pattern defined by this cross-section, the resultant image can be used to determine the resolution capability of the nuclear imaging system. 
     It should be known that the pattern plate  16  of the phantom  10  may be designed to define an alternative pattern or shape to test another imaging characteristic of the nuclear imaging system. Also, the linearly fillable properties provided by the phantom  10  may be applied to patterns, shapes, or other phantoms to reduce wasted or unused radioisotope doped fluid. It should also be know that since the flow path  74  is continuous, the inlet  18  and outlet  20  are interchangeable. That is, fluid may be provided to the outlet  20  and flow to the inlet  18 , if desired. Alternatively or additionally, the inlet passage  66  and the outlet passage  68  can be chosen to be any two of the plurality of passages  48 , and the continuous fluid flow path  74  can be adjusted accordingly by the plurality of first side channels  70  and the plurality of second side channels  72 . Alternatively or additionally, the phantom  10  can be scaled to define a desired size for the nuclear imaging system in which it is used. 
     EXAMPLES 
     The phantom  10  was imaged along the cross-section plane parallel to and between the first side  63  and the second side  65  of the pattern plate  16 . The phantom  10  was imaged using a UWCCC Siemens Inveon MicroPET/CT scanner with the continuous fluid flow path  74  of the phantom  10  filled using four different radioisotopes (i.e.,  52 Mn,  64 Cu,  76 Br,  124 I) doped into water. The resultant images are shown in  FIG. 9 . Image  90  of  FIG. 9  was acquired with the continuous fluid flow path  74  of the phantom  10  filled with  52 Mn, image  92  of  FIG. 9  was acquired with the continuous fluid flow path  74  of the phantom  10  filled with  64 Cu, image  94  of  FIG. 9  was acquired with the continuous fluid flow path  74  of the phantom  10  filled with  76 Br, and image  96  of  FIG. 9  was acquired with the continuous fluid flow path  74  of the phantom  10  filled with  124 I. As shown by images  90 ,  92 ,  94 , and  96  of  FIG. 9 , the phantom  10  successfully provides a Derenzo style pattern for the MicroPET/CT scanner to image, and determine a resolution capability of the MicroPET/CT scanner for the four different radioisotopes. 
     Thus, while the invention has been described above in connection with particular embodiments and examples, the invention is not necessarily so limited, and that numerous other embodiments, examples, uses, modifications and departures from the embodiments, examples and uses are intended to be encompassed by the claims attached hereto. The entire disclosure of each patent and publication cited herein is incorporated by reference, as if each such patent or publication were individually incorporated by reference herein.