Helically arranged positron emission tomography detector units

Abstract

A PET imaging system includes a gantry having a patient tunnel, and a first detector unit and a second detector unit housed inside the gantry, each detector unit including a plurality of detector elements in a helical arrangement about an axial axis of the imaging system. Each of the detector elements in the second detector unit is spaced apart from a corresponding detector element in the first detector unit by an axial gap. Each detector element has an axial position. Each of the first and second detector units has its detector elements arranged such that the set of detector elements is positioned such that each detector element in the set is offset from an adjacent detector element in the detector unit, such that a maximum difference between the axial positions of the detector elements in each detector unit is less than or equal to the axial gap.

Description

Background Technology

[0001] Positron emission tomography (PET) is widely used in medical diagnostics. PET allows for the visualization and quantification of metabolic activity in vivo. PET utilizes the special properties of positron emitters and positron annihilation to quantitatively determine the function of organ or cellular regions. Using this technique, an appropriate radiopharmaceutical labeled with a radionuclide is administered to the patient prior to the examination. As they decay, the radionuclide emits a positron, which interacts with an electron shortly afterward, causing what is known as annihilation. This produces two gamma quanta that fly apart in opposite directions (by a 180° offset). These gamma quanta are detected within a specific time window by two opposing PET detector elements (coincidence measurement), resulting in the annihilation site being located on the line connecting the two detector modules.

[0002] Upon detection of a gamma quantum, each detector element generates an event log specifying the time and detection location, i.e., the corresponding detector element. This information is passed to a fast logic unit and compared. If two events coincide within a maximum time interval, it is assumed that a gamma decay process is occurring on the connection line between the two associated detector elements. A tomographic algorithm (i.e., so-called back projection) is used to reconstruct the PET image.

[0003] Detector elements are typically arranged in partial or complete rings, configured to align around the axial axis of the PET system. Due to mechanical constraints, gaps typically exist between adjacent detector rings. These gaps can affect the spatial resolution of the system and the sensitivity of the reconstructed image planes straddled by these gaps.

[0004] U.S. Patent No. 9,599,731, entitled "Positron Emission Tomography and / or Single Photon Emission Tomography Detector," discloses an imaging system comprising a magnetic resonance portion and a PET portion. The PET portion comprises a two-dimensional array of detector tiles. Adjacent tiles along each column are spaced apart by gaps, and adjacent tiles along each row are adjacent to each other and offset from each other by a non-zero distance less than the tile length. Summary of the Invention

[0005] In one aspect, a positron emission tomography (PET) imaging system includes a gantry having a patient receiving tunnel, and a first detector unit and a second detector unit housed within the gantry. The first detector unit includes a plurality of detector elements arranged helically about an axial axis of the PET imaging system. The second detector unit includes a plurality of detector elements arranged helically about the axial axis. Each detector element in the second detector unit is spaced apart from a corresponding detector element in the first detector unit by an axial gap along a direction parallel to the axial axis of the PET imaging system. Each detector element in the first and second detector units has an axial position measured parallel to the axial axis from the entrance of the patient receiving tunnel to the geometric center of the detector element. Both the first and second detector units have their plurality of detector elements, which are arranged such that an assembly of the plurality of detector elements is positioned such that each detector element in the assembly is offset from an adjacent detector element in the detector unit in a direction parallel to the axial axis of the PET imaging system, such that the maximum difference between the axial positions of the detector elements in the detector unit is less than or equal to the axial gap.

[0006] On the other hand, a detector unit for a positron emission tomography (PET) imaging system having a gantry with a patient receiving tunnel, the detector unit comprising a plurality of detector elements arranged in a helical configuration, the plurality of detector elements being configured to be positioned about an axial axis of the PET imaging system. When the detector unit is mounted in the PET imaging system, each detector element has an axial position measured parallel to the axial axis of the PET imaging system from the entrance of the patient receiving tunnel to the geometric center of the detector element. The plurality of detector elements are arranged such that an assembly of the plurality of detector elements is positioned such that each detector element in the assembly is offset from an adjacent detector element in a direction parallel to the axial axis of the PET imaging system, such that when the detector unit and a second detector unit are mounted in the PET imaging system, the maximum difference between the axial positions of the detector elements in the detector unit is less than or equal to the axial gap between each of the plurality of detector elements and a corresponding detector element in the second detector unit. Attached Figure Description

[0007] The features of the embodiments described herein will be more fully disclosed in the following detailed description, which will be attached. Figure 1 For consideration, in the attached figures, similar numbers refer to similar parts.

[0008] Figure 1 A schematic diagram of a PET imaging system is shown.

[0009] Figure 2 It shows Figure 1 A schematic cross-sectional view of a PET imaging system, wherein the cross-section is obtained through one of the detector units with the patient positioned within the detector tunnel.

[0010] Figure 3 shows a schematic diagram of a subset of detector units in a prior art PET imaging system according to an embodiment described herein.

[0011] Figure 4 A schematic diagram of a detector unit of a PET imaging system according to an embodiment described herein is shown, wherein the detector unit is shown in a plan view for ease of visualization.

[0012] Figure 5 A schematic diagram of a detector unit of a PET imaging system according to another embodiment described herein is shown, wherein the detector unit is shown in a plan view for ease of visualization. Detailed Implementation

[0013] This description of exemplary embodiments is intended to be read in conjunction with the accompanying drawings, which are considered an integral part of the entire written description. The drawings are not necessarily drawn to scale, and for clarity and brevity, some features may be exaggerated to scale or in a schematic manner. In this description, related terms such as “horizontal,” “vertical,” “up,” “down,” “top,” and “bottom,” and their derivatives (e.g., “horizontally,” “downward,” “upward,” etc.) should be interpreted as referring to the orientation as described subsequently or as shown in the drawings discussed. These related terms are for the convenience of description and are generally not intended to require a specific orientation. Terms including “inward” relative to “outward,” “longitudinal” relative to “lateral,” etc., are to be interpreted relative to each other, or, where appropriate, relative to an axis of elongation or axis of rotation or center of rotation. Terms relating to attachment, coupling, etc. (such as “connected” and “interconnected”) refer to relationships in which structures are directly or indirectly fixed or attached to each other by means of intervening structures and movable or rigid attachments or relationships, unless otherwise explicitly described. The term "operably connected" refers to an attachment, coupling, or connection that allows related structures to operate as intended by means of the relationship.

[0014] The imaging system described herein includes detector elements arranged in a helical pattern. This helical arrangement of the detector elements provides a configuration in which the axial gap between the axially aligned detector elements is circumferentially offset. Therefore, artifacts and discontinuities in the images produced using the imaging system are reduced.

[0015] Figure 1An imaging system 100, such as a PET imaging system, is shown, including a PET scanner gantry 102. In some embodiments, the imaging system 100 further includes other imaging modalities, such as, for example, a CT scanner or an MRI scanner. According to one embodiment described herein, the PET scanner gantry 102 houses a plurality of detector units 104, each detector unit 104 being arranged helically in a circumferential direction (i.e., transaxial direction) surrounding a patient receiving tunnel 106. Each of the detector units 104 may be supported by the gantry 102. The patient receiving tunnel 106 defines an axial axis A oriented substantially parallel to the spatial direction Z. The tunnel 106 has an entrance 107 through which a patient 112 may be introduced into the tunnel 106.

[0016] Figure 2 A cross-sectional view of the PET scanner gantry 102 of the imaging system 100 is shown. This cross-section is obtained through one of the detector units 104 housed within the gantry 102. Arranged within the patient receiving tunnel 106 is a patient bed 110 on which the patient 112 can be positioned. The patient's torso and arms are... Figure 2 It is shown in the cross-section.

[0017] like Figure 2 As shown, each detector unit 104 includes a plurality of detector elements 114 (e.g., scintillation detectors) arranged outside the patient receiving tunnel 106. Each detector unit 104 may further include an avalanche photodiode array (APD) in front of a lutetium oxyorthosilicate (LSO) crystal array and an electrical amplifier circuit (AMP). However, the imaging system 100 described herein is not limited to detector units 104 having an APD photodiode array in front of an LSO crystal array, and other types of photodiodes, crystals, and devices may be used equivalently for detection purposes. Furthermore, detector units 104 may include detector electronics, including an electrical amplifier circuit (not shown) and other electronic components.

[0018] Figure 3 shows a schematic perspective view of a subset of detector units P104 in a typical prior art imaging system. In the prior art system, detector elements P114 in a given detector unit P104 are arranged in a ring. In the ring configuration, each detector element P114 in a given detector unit P104 is aligned with the other detector elements P114 in the same detector unit P104 in the transverse (i.e., circumferential) direction. In other words, each of the detector elements P114 in the detector unit P104 has the same axial position—for example, measured from the entrance 107 of the tunnel 106.

[0019] Additionally, in a direction parallel to the axial axis A of the imaging system 100, there is an axial gap G between each detector unit P104. Therefore, gap G exists between each detector element P114 in the detector unit P104 and adjacent detector elements P114 in adjacent detector units P104. The gap G exists due to mechanical constraints preventing detector units P104 from directly colliding with each other. As shown in Figure 3, the gaps between adjacent detector elements P114 create continuous gaps around the perimeter of the patient receiving tunnel P106. These continuous gaps can create discontinuities in images produced using this prior art system, particularly for image planes spanning these gaps.

[0020] An example of a novel configuration of detector element 114 in detector unit 104 according to this disclosure is shown in... Figure 4 The image is shown in the middle. Figure 4 A schematic diagram showing a flattened detailed view of adjacent segments of the detector unit 104 of the imaging system 100 described herein. Figure 4 The detector unit 104 is shown as if it were being observed from inside the patient tunnel 106. It should be understood that... Figure 4 The detector units 104 shown are schematic and are presented in an enlarged view for illustrative purposes. Therefore, their size is not proportional to the patient 112 shown in the figure. It should also be noted that only a subset of the detector elements 114 is shown. As illustrated, in some embodiments of the detector units 104 of this disclosure, the set of PET detector elements 114 (i.e., one or more detector elements 114) in a given detector unit 104 is sequentially displaced in the axial direction relative to other PET detector elements 114 in the same detector unit 104. This displacement of the detector elements 114 creates a helical arrangement of the detector elements 114.

[0021] The spatial relationship between the two detector units 104 is described in more detail below. It should be understood that the described spatial relationship applies to all detector units 104 in the PET scanner gantry 102. The imaging system 100 may include a first detector unit 104a containing a first set 114a of detector elements and a second detector unit 104b containing a second set 114b of detector elements. For illustrative purposes, detector elements 114 in each detector unit 104 are referred to as 114x-1 to 114x-n, where x indicates a detector unit to which the detector element is a part, and n is the total number of detector elements in each of the detector units 104. Thus, for example, the detector elements in the second detector unit 104b will be referred to as 114b-1 to 114b-n.

[0022] An axial gap G exists between each detector element 114a of the first detector unit 104a and its corresponding detector element 114b of the second detector unit 104b, wherein the corresponding detector element 114b is the detector element 114b adjacent to the detector element 114a in the first detector unit 104a. In other words, the corresponding detector element 114b is linearly aligned with the associated detector element 114a parallel to the axial axis A of the imaging system 100. For example, there is an axial gap G between the first detector element 114a-1 and the second detector element 114b-1. The axial gap G may be due to mechanical or other constraints preventing direct contact between the detector elements 114. In some embodiments, the axial gap G is approximately equal to the crystal pitch of the detector elements 114. In some embodiments, the axial gap G between each of the detector elements 114a in the first detector unit 104a and its corresponding detector element 114b in the second detector unit 104b is equal (or uniform) for each detector element; however, this is not necessary, and the axial gap G can vary. As described above, in existing PET scanners, these axial gaps can cause spatial resolution problems and may lead to image artifacts and discontinuities. This is especially true in systems where the axial spacing of the detector crystals in detector element 114 has been reduced to such that the axial gap G is approximately the same as the axial spacing of the detector crystals in detector element 114.

[0023] like Figure 4 As shown in the embodiment of the PET scanner 102 described herein, in each of the detector units 104, the detector element 114 is axially displaced such that the detector elements 114a-1…114a-n of the first detector unit 104a are not circumferentially (or transversely) aligned with the axial gap G between the detector elements 114b-1…114b-n of the second detector unit 104b. For example, the axial gap G between detector elements 114a-1 and 114b-1 is not aligned with the axial gap G between detector elements 114a-2 and 114b-2. By arranging the detector elements 114 in each detector unit 104 in this way, the spatial resolution and image artifact problems described above with respect to prior art systems can be reduced or eliminated.

[0024] The arrangement of detector elements 114 will be described using the first detector unit 104a as an example. Figure 4As shown, the set of detector elements 114 of the first detector unit 104a is positioned such that each detector element 114a in the set is offset from its adjacent detector element 114a in a direction parallel to the axial axis A of the imaging system 100. Although Figure 4 An embodiment is shown in which each detector element 114a is in a set of detector elements that are shifted relative to adjacent detector elements; however, it should be understood that this is not necessary. For example, in other embodiments, every three detector elements 114a are shifted relative to their adjacent detector elements. Alternatively, the set of shifted detector elements may include every four detector elements, every five detector elements, etc. Figure 4 As shown, each detector element in the set of offset detector elements is displaced by an offset distance 116 from its adjacent detector element in the first detector unit 104a along a direction parallel to the axial axis A of the PET scanner 102 (e.g., detector element 114a-2 is displaced relative to detector element 114a-1). Preferably, each of the detector elements 114a in the set of offset detector elements is displaced in the same axial direction (i.e., detector elements 114a do not alternate back and forth). Figure 4 As shown, each of the second detector elements 114a can be offset from its adjacent second detector element 114a by the same offset distance 116 (i.e., the offset distance 116 is uniform). In other embodiments, the offset distance 116 may vary (e.g., the offset distance 116 between detector element 114a-1 and detector element 114a-2 may be different from the offset distance 116 between detector element 114a-2 and detector element 114a-3). Due to the displacement of the detector elements 114a, the detector elements 114a of the first detector unit 104a have different axial positions 118 (e.g., as measured from the entrance 107 of the tunnel 106 to the geometric center of the detector unit 114a). For example, the axial position 118a-n of detector element 114a-n may be different from the axial position 118a-1 of detector element 114a-1. It should be understood that although a single detector unit 104a has been described with reference to it for illustrative purposes, one or more of the detector units 104 of the PET scanner 102 may have a shifted arrangement of the detector elements 114 described herein. In a preferred embodiment, all detector units 104 of the PET scanner 102 have a shifted arrangement of the detector elements 114 described herein.

[0025] Axially displaced each of the detector elements 114 in detector unit 104 is not necessary, and other configurations can be used. In one embodiment, such as Figure 5 As shown, each of the detector elements 114 in the set of offset detector elements is a member of a group of n consecutive detector elements 114, wherein each of the n consecutive detector elements in the corresponding group has the same axial position (e.g., detector elements 114a-1 and 114a-2 have the same axial position 118a-1). Each group of n consecutive detector elements 114 in detector unit 104 is offset by an offset distance (e.g., Figure 5 The offset distance 116 shown is offset from the detector element 114 adjacent to that group in the corresponding detector unit 104. It should be understood that each member of the set of offset detector elements can be a member of a different group of n consecutive detector elements. For example, in Figure 5 In the illustrated embodiment, the first detector unit 104a can be arranged as a group of two detector elements 114a, wherein each group of the two detector elements 114a is offset from the adjacent group of the two detector elements 114a. Although Figure 5 The illustration shows two detector elements 114a in each group of consecutive detector elements; however, it should be understood that each group may include other numbers of detector elements 114a (e.g., three detector elements, four detector elements, etc.). Furthermore, the offset distance 116 between detector elements 114b does not need to be uniform. For example, in some embodiments, the offset distance 116 between different detector elements 114a may be different at different cross-sectional positions. Again, it should be understood that although described with reference to a single detector unit 104a for illustrative purposes, one or more of the detector units 104 of the PET scanner 102 may have the features described herein and... Figure 5 The diagram illustrates the shifted arrangement of detector elements 114. In a preferred embodiment, all detector units 104 of the PET scanner 102 have the features described herein and... Figure 5 The detector element 114 is shown in the diagram in a shifted arrangement.

[0026] In some embodiments, the sum of offset distances 116 of the detector elements 114 in detector unit 104 (e.g., the sum of offset distances 116 between each detector element 114a and its adjacent detector element 114a) is less than or equal to the axial gap G between detector elements 114 (e.g., between detector element 114a-1 and detector element 114b-1). In other words, the maximum difference between the axial positions of the detector elements 114 in detector unit 104 (e.g., as measured from the entrance 107 of the tunnel 106 of the PET scanner 102 to the geometric center of the detector element 114) is less than, equal to, or not greater than the gap G. For example, the difference between the axial positions 118a-n of detector elements 114a-n and the axial position 118a-1 of detector element 114a-1 is less than or equal to the gap G. Therefore, the gap G between any second detector element 114b and its corresponding first detector element 114a is "filled" by one or more detector elements 114a in the first detector unit 104a. In other words, the gap G between each pair of the first 114a and the second 114b detector elements is staggered or offset in a direction parallel to the axial axis A, so that the PET scanner 102 does not have a continuous gap extending in the transverse direction, which may cause artifacts and other problems with spatial resolution. Furthermore, the arrangement of the detector elements 114 disclosed herein can be used to improve axial sampling of the imaging system 100 because the detector elements 114 are positioned at different axial locations within the gantry 102.

[0027] For example, in an embodiment where each of the detector elements (e.g., detector element 114a-2) is offset from its adjacent detector element (e.g., detector element 114a-1) by a uniform or equal offset distance 116, the uniform offset distance 116 (i.e., the offset distance between a detector element and its adjacent detector element) may be less than or equal to:

[0028] Uniform offset distance ≤ G / N

[0029] Where N is the number of detector elements 114 in detector unit 104, and G is the axial gap between detector elements 114 in detector unit 104 and corresponding detector elements 114b in adjacent detector units 104 (e.g., between detector elements 114a-1 and detector elements 114b-1).

[0030] In one embodiment, each detector unit 104 includes 40 detector elements 114, and the axial clearance G is equal to 4 mm. For this embodiment, the axial offset distance 116 is equal to 0.1 mm.

[0031] In addition to eliminating or reducing artifacts and discontinuities in images, the spiral detector unit 104 described herein can also be used in long-axis field-of-view systems with minimal image quality degradation. The spiral arrangement of the detector unit 104 can also reduce the number of detector elements 114 required for a given axial field of view.

[0032] It will be understood that the foregoing description is a description of exemplary embodiments of the present invention, and the present invention is not limited to the specific forms shown. Modifications may be made to the design and arrangement of the elements without departing from the scope of the present invention.

Claims

1. A positron emission tomography (PET) imaging system, comprising: A stand with a patient receiving tunnel; A first detector unit and a second detector unit are housed within the gantry, wherein the first detector unit includes a plurality of detector elements arranged helically around the axial axis of the PET imaging system, and wherein the second detector unit includes a plurality of detector elements arranged helically around the axial axis of the PET imaging system. Each of the detector elements in the second detector unit is spaced apart from the corresponding detector element in the first detector unit by an axial gap along a direction parallel to the axial axis of the PET imaging system. Each detector element in the first and second detector units has an axial position measured parallel to the axial axis from the entrance of the patient receiving tunnel to the geometric center of the detector element, and Each of the first detector unit and the second detector unit includes a plurality of detector elements, the plurality of detector elements being arranged such that the set of the plurality of detector elements is positioned such that each detector element in the set is offset from an adjacent detector element in the detector unit in a direction parallel to the axial axis of the PET imaging system, such that the maximum difference between the axial positions of the detector elements in each detector unit is less than or equal to the axial gap.

2. The system of claim 1, wherein each detector element in the first detector unit and the second detector unit is offset from the adjacent detector element in the corresponding detector unit in a direction parallel to the axial axis.

3. The system of claim 2, wherein each detector element in the first detector unit and the second detector unit is offset from its adjacent detector element in the corresponding detector unit by a uniform offset distance.

4. The system of claim 3, wherein the axial gap between each of the plurality of detector elements in the second detector unit and the corresponding detector element in the first detector unit is uniform.

5. The system of claim 4, wherein the uniform offset distance is equal to G / N, where G is the axial clearance and N is the number of detector elements in each detector unit.

6. The system of claim 4, wherein the axial clearance is 4 mm.

7. The system of claim 1, wherein each detector element in the set of detector elements is a member of a corresponding group of n consecutive detector elements, wherein each of the n consecutive detector elements in the corresponding group has the same axial position, and wherein each group is offset from the detector elements adjacent to the group in the corresponding detector unit by an offset distance.

8. The system of claim 7, wherein each group of n consecutive detector elements is offset from the detector elements adjacent to the group by a uniform offset distance.

9. The system of claim 1, wherein the axial gap is approximately the same as the axial crystal spacing of the detector element.

10. The system of claim 1, wherein each of the first detector unit and the second detector unit comprises 40 detector elements.

11. The system of claim 1, wherein a plurality of detector elements in the first detector unit and a plurality of detector elements in the second detector unit form a helix around the axial axis of the PET imaging system.

12. A detector unit for a positron emission tomography (PET) imaging system, the PET imaging system having a gantry having a patient receiving tunnel, the detector unit comprising: The system employs a plurality of detector elements arranged in a spiral configuration, the plurality of detector elements being arranged around the axial axis of the PET imaging system; When the detector units are mounted in the PET imaging system, each detector element has an axial position parallel to the axial axis of the PET imaging system, measured from the entrance of the patient receiving tunnel to the geometric center of the detector element. The plurality of detector elements are arranged such that the set of the plurality of detector elements is positioned such that each detector element in the set is offset from an adjacent detector element in a direction parallel to the axial axis of the PET imaging system, such that when the detector unit and the second detector unit are mounted in the PET imaging system, the maximum difference between the axial positions of the detector elements is less than or equal to the axial gap between each of the plurality of detector elements and the corresponding detector element in the second detector unit.

13. The detector unit of claim 12, wherein each of the detector elements is offset from its adjacent detector element in a direction parallel to the axial axis, and wherein each of the detector elements is offset from its adjacent detector element by a uniform offset distance.

14. The detector unit of claim 13, wherein the uniform offset distance is equal to G / N, where G is the axial gap and N is the number of detector elements in the detector unit.

15. The detector unit of claim 12, wherein each detector element in the set of detector elements is a member of a corresponding group of n consecutive detector elements, wherein each of the n consecutive detector elements in the corresponding group has the same axial position, and wherein each group is offset from the detector elements of the adjacent group in the corresponding detector unit by an offset distance.

Images