Adaptive pixel adjustment for spect imaging systems

Abstract

Methods and systems are provided for improving the quality of an image generated by a single photon emission computed tomography (SPECT) imaging system (100, 200). Photons penetrating a protective shield (580) around a detector head (308, 408, 210) of the SPECT system (100, 200) may not be correctly processed by a reconstruction algorithm used to reconstruct an image from a plurality of projection views (701) acquired by the SPECT imaging system (100, 200), thereby generating artifacts (1121, 1112, 730) and reducing the quality of the image. In one embodiment, the artifacts (1121, 1112, 730) may be reduced or eliminated by selectively applying the reconstruction algorithm to a first partial column of pixels (1007, 1012) of the projected views (701) that does not include the artifacts (1121, 1112, 730), and not applying the reconstruction algorithm to a second partial column of pixels (1007, 1012) of the projected views that includes the artifacts (1121, 1112, 730). The number of the second partial pixel columns (1007, 1012) may be based on a sweep angle (550) of a detector (471) that acquires the projected view (701).

Description

Technical Field

[0001] Embodiments of the subject matter disclosed herein relate to improving the image quality of a single photon emission computed tomography (SPECT) imaging system. Background Art

[0002] Nuclear medicine (NM) imaging systems, such as single photon emission computed tomography (SPECT) imaging systems, can be used to diagnose certain conditions of a patient's heart, brain, or other systems. A radioactive substance can be introduced into the patient's body, and the radioactive substance can be absorbed in a target organ or region of the patient's body. The radioactive substance emits photons, and these photons are collimated and detected by a detector subsystem. The detectors of the subsystem can generate output electrical signals, from which a three-dimensional (3D) image can be created, where the 3D image shows the distribution of the radioactive substance in and around the target organ or region. Examining the distribution can help a caregiver diagnose or monitor a patient's condition. For example, the image can be used to diagnose blocked arteries, bone healing, seizures, cancer progression, or other problems.

[0003] The detectors can be configured to detect photons that enter the collimator of the detector from a specified angular range. The detectors can include a shield around the sides of the detector to prevent photons that strike the detector from outside the specified angular range from being detected and counted. However, when using high-energy isotopes, some photons can penetrate the shield and be detected. The penetrating photons can cause artifacts and / or reduce the quality of the reconstructed image. Summary of the Invention

[0004] The present disclosure solves at least one or more of the above problems in part by a method for a single photon emission computed tomography (SPECT) imaging system, the method comprising: acquiring, using the SPECT imaging system, a plurality of projection views of a scanned object, the plurality of projection views including artifacts; configuring a reconstruction algorithm to reconstruct an image based on a first portion of pixels of each of the plurality of projection views and not based on a second portion of pixels of each of the plurality of projection views, the second portion of pixels including the artifacts; using the reconstruction algorithm to reconstruct the image; and displaying the reconstructed image on a display device of the SPECT imaging system and / or storing the reconstructed image in a memory of the SPECT imaging system.

[0005] The above advantages, as well as other advantages and features of the present specification, will be apparent from the following detailed description when considered alone or in conjunction with the accompanying drawings. It should be understood that the above summary is provided to introduce in a simplified form a series of concepts that are further described in the detailed description. This does not mean identifying the key features or essential features of the claimed subject matter, the scope of which is uniquely defined by the claims that follow the detailed description. Additionally, the claimed subject matter is not limited to embodiments that solve any disadvantages mentioned above or in any part of this disclosure. BRIEF DESCRIPTION OF THE DRAWINGS

[0006] Aspects of the present disclosure may be better understood by reading the following detailed description and referring to the accompanying drawings, in which:

[0007] Figure 1A is a schematic block diagram of a nuclear imaging (NM) system according to an embodiment;

[0008] Figure 1B is a schematic block diagram showing a detector unit according to an embodiment;

[0009] Figure 1C is a pictorial illustration of an exemplary detector unit;

[0010] Figure 2A shows a pictorial view of an exemplary multi-headed SPECT imaging system according to one or more embodiments of the present disclosure;

[0011] Figure 2B shows a pictorial view of an exemplary dual-headed SPECT imaging system according to one or more embodiments of the present disclosure;

[0012] Figure 3 shows the orientation of multiple detector units of a multi-headed SPECT system during the scanning of a phantom according to one or more embodiments of the present disclosure;

[0013] Figure 4 shows exemplary collimation of radiation from a phantom by detector units of a multi-headed SPECT system according to one or more embodiments of the present disclosure;

[0014] Figure 5 shows according to one or more embodiments of the present disclosure Figure 4 a radiation penetration shield of a detector unit;

[0015] Figure 6 is a graph showing the relationship between shield penetration and detector angle according to one or more embodiments of the present disclosure;

[0016] Figure 7Shows an exemplary image reconstructed by a SPECT system according to one or more embodiments of the present disclosure, including artifacts caused by radiation penetration;

[0017] Figure 8 Is a flowchart showing an exemplary adaptive pixel zeroing method for removing artifacts from CT images according to one or more embodiments of the present disclosure;

[0018] Figure 9 Is a graph showing adaptive pixel zeroing as a function of the sweep angle of a detector unit according to one or more embodiments of the present disclosure;

[0019] Figure 10 Is a block diagram showing how selected pixels of a projection view can be ignored during image reconstruction using adaptive pixel zeroing to reduce Figure 7 artifacts; and

[0020] Figure 11 Shows an exemplary reconstructed image generated by a SPECT system using adaptive pixel zeroing according to one or more embodiments of the present disclosure.

[0021] The accompanying drawings illustrate specific aspects of the system and method. Together with the following description, the drawings show and explain the structures, methods, and principles described herein. In the drawings, for clarity, the dimensions of components may be enlarged or otherwise modified. Well-known structures, materials, or operations are not shown or described in detail to avoid obscuring aspects of the components, systems, and methods.

[0022] Figure 1B 、 Figure 1C 、 Figure 2A and Figure 2BAn exemplary configuration showing the relative positioning of various components is presented. At least in one example, if elements are shown in direct contact or directly coupled to each other, such elements may be referred to as in direct contact or directly coupled, respectively. Similarly, at least in one example, elements shown adjacent or neighboring each other may be adjacent or neighboring each other, respectively. For example, components placed in coplanar contact with each other may be referred to as being in coplanar contact. As another example, in at least one example, elements positioned so as to be spaced apart from each other and having only space therebetween without other components may be so described. As yet another example, elements shown above / below each other, on opposite sides of each other, or on the left / right sides of each other may be so described relative to each other. Further, as shown in the figure, in at least one example, the topmost element or point of an element may be referred to as the "top" of the component, and the bottommost element or point of an element may be referred to as the "bottom" of the component. As used herein, top / bottom, upper / lower, above / below may be with respect to the vertical axis of the figure and may be used to describe the position of elements in the figure relative to each other. Thus, in one example, an element shown above other elements is vertically positioned above the other elements. As another example, the shapes of the elements depicted in the figure may be referred to as having those shapes (e.g., being circular, straight, planar, curved, rounded, chamfered, angled, etc.). Further, in at least one example, elements shown intersecting each other may be referred to as intersecting elements or intersecting each other. Additionally, in one example, an element shown within another element or shown outside another element may be so described. Detailed Description

[0023] This specification and embodiments of the subject matter disclosed herein relate to methods and systems for a single photon emission computed tomography (SPECT) system. In particular, methods and systems for improving the image quality of images reconstructed using an SPECT system are presented.

[0024] An SPECT system shows the distribution of radioactive material within a patient. A radioactive tracer (e.g., a penetrating radiation source) is administered to the patient, which typically includes a drug labeled with a radionuclide (radioactive pharmaceutical) that emits radiation photons. The radioactive pharmaceutical is designed to be absorbed in a target organ such as the myocardium or other organ or body part of interest. One or more detector arrays may rotate around a gantry within an imaging plane and around the patient, and images are generated from radiation photons at multiple views at different perspectives. Additionally, some SPECT systems may include a detector array having multiple detector heads, where each detector head may rotate or pivot in addition to the gantry rotation. The emitted radiation photons are collimated by a collimator subsystem and detected by a detector subsystem that generates an output electrical signal. The electrical signal is digitized and processed by a computer system to generate an image of the regional distribution of the radiation source in and around the target organ.

[0025] When the detector head rotates and / or pivots, photons emitted by the radiopharmaceutical within the field of view of the detector head (also referred to herein as the detector sweep angle or sweep angle) are focused on the detector elements by the collimator. Photons directed at the detector head outside the field of view may strike one side of the detector head and may not be collimated and detected. One side of the detector head may include a shield for preventing non-collimated photons from being detected. However, when using high-energy isotopes, some photons may penetrate the shield and be detected. The penetrating photons may cause artifacts and / or degrade the quality of the reconstructed image. For example, the reconstruction algorithm used by a SPECT system may misinterpret the penetrating photons and generate artifacts along the contour of the object being scanned. Another effect of the penetrating photons may be that the quality and / or visibility of the internal structure or features of the object being scanned may be reduced.

[0026] Penetrating photons can be prevented by increasing the thickness of the shield. However, the shield may include heavy and / or dense materials, such as lead, and increasing the shield thickness increases the weight and size of the detector. Increasing the detector size may limit the movement of the detector and affect the degree to which the detector can be positioned close to the object being scanned. Increasing the detector weight may increase the cost of the motors used to control the detector and may limit the movement of the detector. Thus, it is desirable to minimize the thickness of the shield and reduce the penetrating photons in a different way.

[0027] To address this problem, systems and methods have been proposed to algorithmically reduce the effect of penetrating radiation during image reconstruction. Specifically, when applying the reconstruction algorithm, a mask may be used to ignore one or more sets of adjacent pixels, such as the pixel columns on one side of each projection. Additionally, for a multi-head detector, since shield penetration is higher in views acquired at large angles and lower in views acquired at small angles, the number of adjacent pixels and / or pixel columns to be ignored may be adaptively selected based on the angle (e.g., the larger the angle, the more pixel columns are ignored).

[0028] Figure 1A is a schematic diagram of an NM imaging system 100 having a plurality of imaging detectors mounted on a gantry. The imaging detectors may be configured to rotate about a fixed pivot. The movement of the imaging detectors is controlled to reduce the likelihood of collisions in the moving imaging detectors or to avoid collisions in the moving imaging detectors and / or reduce the likelihood that one imaging detector obstructs the field of view of another imaging detector. For example, in some embodiments, the NM imaging system provides coordinated swinging or rotational movement of the plurality of imaging detectors or detector heads.

[0029] Specifically, a plurality of imaging detectors 102 are mounted to the gantry 104 and / or a patient support structure (not shown) (e.g., beneath the patient examination table 120), which may define a table support for the patient examination table 120. In the illustrated embodiment, the imaging detectors 102 are configured as a detector array 106 positioned around a subject 110 (e.g., a patient), as Figure 1A shown. The detector array 106 may be directly coupled to the gantry 104 or may be coupled to the gantry via a support member 112 to allow movement of the entire array 106 relative to the gantry 104 (e.g., rotational movement in a clockwise or counterclockwise direction, as Figure 1A shown). Additionally, each of the imaging detectors 102 in the imaging detectors includes a detector unit 114, where at least some of the imaging detectors are mounted to a movable detector carrier 116 extending from the gantry 104 (e.g., a support arm or actuator that may be driven by a motor to cause its movement). For the purposes of this disclosure, the detector unit may also be referred to as a detector head. In some embodiments, the detector carrier 116 allows the detector unit 114 to move toward and away from the subject 110, such as linear movement. Thus, in the illustrated embodiment, the detector array 106 surrounds the subject 110 and may allow linear movement of the detector unit 114, such as linear movement toward or away from the patient examination table 120 in one embodiment. However, other configurations and orientations as well as different types of movement (e.g., lateral or vertical movement relative to the patient examination table 120) as described herein are possible. It should be noted that the movable detector carrier 116 can be any type of support that allows the detector unit 114 to move relative to the support member 112 and / or the gantry 104, which in various embodiments allows the detector unit 114 to move linearly toward and away from the support member 112, such as radially inward and outward, for positioning adjacent the subject 110. For example, as described herein, the detector units 114 can be controlled to move toward or away from the subject 110 independently of each other and, in some embodiments, are capable of rotational, pivoting, or tilting movement.

[0030] Each imaging detector 102 in various embodiments is smaller than a conventional full-body or general imaging detector. A conventional imaging detector can be large enough to image most or all of the width of a patient's body at once and can have a diameter of about 50 cm or more. In contrast, each imaging detector in imaging detector 102 can include one or more detector units 114 that are coupled to corresponding detector carriers 116 and have dimensions of 4 cm to 20 cm and can be formed of cadmium zinc telluride (CZT) wafers or modules. For example, each detector unit 114 in detector unit 114 can have dimensions of 8×8 cm and be composed of a plurality of CZT pixelated modules (not shown). For example, each module can have dimensions of 4×4 cm and have 16×16 = 256 pixels. In some embodiments, each detector unit 114 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 unit 114 having multiple rows of modules.

[0031] It should be understood that the imaging detectors can have different sizes and / or shapes relative to each other, such as square, rectangular, circular, or another shape. The actual field of view (FOV) of each imaging detector in imaging detector 102 can be proportional to the size and shape of the corresponding imaging detector.

[0032] The gantry 104 can be formed with a hole 118 (e.g., an opening or orifice) therethrough, as shown. The patient examination table 120 is configured with a support mechanism, such as a patient support structure, to support and carry a subject 110 within the hole 118 and at one or more of a plurality of viewing positions relative to the imaging detector 102. Alternatively, the gantry 104 can include a plurality of gantry segments (not shown), and each gantry segment can independently move a support member 112 or one or more imaging detectors 102.

[0033] The gantry 104 can also be configured in other shapes, such as a "C" shape, an "H" shape, and an "L" shape, and can rotate around the subject 110. For example, the gantry 104 can be formed as a closed loop or a circle, or formed as an open arc or an arch, which allows easy access to the subject 110 during imaging and facilitates the loading and unloading of the subject 110, as well as alleviates claustrophobia in some subjects 110. For example, in some embodiments, the gantry 104 can be arcuate, and the support member 112 can move along the arc to position the detector unit 114 at different positions along the gantry 104. In some embodiments, the detector unit 114 can also move independently along the gantry 104. For example, in some embodiments, the NM imaging system 100 can be configured with an alternating dual-head configuration of two detector arrays, each detector array including a set of detector units 114. The two detector arrays can be positioned on opposite sides of the open-arched gantry 104, as described below with reference to Figure 2B described.

[0034] Additional imaging detectors (not shown) can be positioned to form a multi-row detector array or an arc or a ring around the subject 110. By positioning the plurality of imaging detectors 102 at a plurality of positions relative to the subject 110, such as along the imaging axis (e.g., the head-to-toe direction of the subject 110), image data specific to a larger FOV can be acquired more quickly.

[0035] Each imaging detector in the imaging detector 102 has a radiation detection surface that points to the subject 110 or the region of interest within the subject 110. The radiation detection surface can be covered or coupled to a collimator 122. The actual FOV of each imaging detector in the imaging detector 102 can be increased, decreased, or relatively unchanged by the type of the collimator 122. In one embodiment, the collimator 122 is a multi-aperture collimator, such as a parallel-hole collimator. However, other types of collimators, such as converging or diverging collimators, can be used optionally or alternatively. Other examples of the collimator 122 include pinhole, parallel-beam converging, diverging fan-beam, converging or diverging conical-beam, multi-aperture converging, multi-aperture converging fan-beam, multi-aperture converging conical-beam, multi-aperture diverging, or other types of collimators.

[0036] Optionally, the multi-aperture collimator can be configured to be pixel registered with the detector units 114, which in one embodiment are CZT detectors. However, other materials can also be used. Registered collimation can increase spatial resolution by forcing photons passing through one aperture to be collected mainly by one pixel. Additionally, registered collimation can increase the sensitivity and energy response of the pixelated detector, because the detector area near the pixel edge or between two adjacent pixels may have reduced sensitivity or reduced energy resolution or other performance degradation. Having collimator septa directly above the pixel edge reduces the chance of photons hitting these performance-degraded locations without reducing the overall probability of photons passing through the collimator.

[0037] The controller unit 130 can control the movement and positioning of the patient examination table 120, the imaging detector 102, the gantry 104, and / or the collimator 122. A series of movements before, during, or between different image acquisitions are set to maintain the actual FOV of each imaging detector in the imaging detector 102, for example, toward or "aimed" at a specific region or area of the subject 110 or along the entire subject 110.

[0038] The controller unit 130 can have a gantry motor controller 132, an examination table controller 134, a detector controller 136, a pivot controller 138, and a collimator controller 140. The controllers 130, 132, 134, 136, 138, 140 can be automatically commanded by the processing unit 150, manually controlled by the operator, or a combination thereof. The gantry motor controller 132 can move the imaging detector 102 relative to the subject 110, for example, individually, in segments or subsets, or simultaneously in a fixed relationship with each other. For example, in some embodiments, the gantry controller 132 can rotate one or more support members in the imaging detector 102 and / or the support member 112 around the subject 110, and the rotation can include movements of less than or up to 180 degrees (or more).

[0039] The examination table controller 134 can move the patient examination table 120 to position the subject 110 relative to the imaging detector 102. For example, the patient examination table 120 can move in the up-down direction, the in-out direction, and the left-right direction. The detector controller 136 can control the movement of each imaging detector in the imaging detector 102 to move it closer to or farther from the surface of the subject 110, such as by controlling the linear translational movement (e.g., sliding or telescoping movement) of the detector carrier 116 toward or away from the subject 110. Optionally, the detector controller 136 can control the movement of the detector carrier 116 to allow coordinated movement of the detector array 106.

[0040] The pivot controller 138 can control the detector unit 114 at the end of the detector carrier 116 and / or the pivoting, rotating, or swinging movement of the detector carrier 116. For example, one or more of the detector unit 114 or the detector carrier 116 can rotate or swing about at least one axis to view the subject 110 from multiple angular orientations. The collimator controller 140 can adjust the position of an adjustable collimator, such as a collimator having adjustable bands (or blades) or an adjustable pinhole.

[0041] It should be noted that the movement of one or more imaging detectors 102 can be in a direction other than strictly axial or radial, and optionally, movement in several directions of movement can be used. In addition, the movement of the imaging detector 102 is coordinated in the various embodiments described herein. Thus, the term "movement controller" can be used to indicate the collective name of all movement controllers. It should be noted that various controllers can be combined. For example, the detector controller 136 and the pivot controller 138 can be combined to provide the different movements described herein.

[0042] As discussed in more detail herein, before acquiring an image of the subject 110 or a portion of the subject 110, the imaging detector 102, the gantry 104, the patient examination table 120, and / or the collimator 122 can be adjusted, such as to a first or initial imaging position and subsequent imaging positions. Each imaging detector 102 can be positioned to image a portion of the subject 110. Alternatively, one or more of the imaging detectors 102 can be not used to acquire data, such as the imaging detectors 102 at the ends of the detector array 106, as Figure 1A shown, these imaging detectors are in an extended position towards the subject 110. The positioning can be done manually by the operator and / or automatically, which can include using other images acquired prior to the current acquisition, such as acquired by another imaging modality, such as CT, MRI, X-ray, PET, or ultrasound. Additionally, the detector unit 114 can be configured to acquire non-NM data, such as x-ray CT data.

[0043] After the imaging detector 102, the gantry 104, the patient examination table 120, and / or the collimator 122 are positioned, one or more images are acquired by one or more of the imaging detectors 102 being used, which can include the pivoting or swinging movement of one or more of the detector units in the detector unit 114, and these detector units can pivot, rotate, or swing to different degrees or between different angular ranges. The image data acquired by each imaging detector 102 can be combined and reconstructed into a synthetic image, which can include a two-dimensional (2D) image, a three-dimensional (3D) volume, or a 3D volume varying over time (4D).

[0044] In one embodiment, the imaging detector 102, gantry 104, patient examination table 120, and / or collimator 122 remain stationary after initial positioning. In another embodiment, the effective field of view of one or more of the imaging detectors can be increased by moving, such as pivoting, rotating, or swinging, one or more of the imaging detectors in the imaging detector 102, rotating the detector array 106 with the gantry 104, adjusting one or more of the collimators in the collimator 122, or moving the patient examination table 120.

[0045] In various embodiments, the data acquisition system (DAS) 160 receives the electrical signal data generated by the imaging detector 102 and converts this data into a digital signal for subsequent processing. In addition to the processing unit 150, an image reconstruction device 162 and a data storage device 164 may also be provided. 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 by hardware, software, and / or shared processing resources, which may be located within or near the imaging system 100 or may be remotely located. Additionally, a user input device 166 may be provided to receive user input (e.g., control commands), and a display 168 for displaying images.

[0046] In addition, a detector position controller 165 is also provided, which can be implemented in hardware, software, or a combination thereof. For example, as Figure 1A shown, the detector position controller 165 may form part of the processing unit 150 or operate in conjunction with the processing unit. In some embodiments, the detector position controller 165 may be a module that operates to control the movement of the imaging detector 102 (including the detector units 114) such that coordinated or synchronized movement is provided as described herein. It should be noted that the movement of multiple imaging detectors 102 and / or detector units 114 may occur at the same time (e.g., simultaneously or in parallel) or at different times (e.g., sequentially or stepwise, such as back and forth between two detector units 114). It should also be understood that when referring to a detector head, such a detector head may include one or more detector modules.

[0047] At least processing unit 150 may be electrically coupled to non - transitory memory 169. Memory 169 may include any known data storage medium. In some embodiments, memory 169 may include components disposed on two or more devices, which may be remotely located and / or configured for coordination of processing. In some embodiments, one or more aspects of memory 169 may include a network - accessible storage device configured in a cloud - computing configuration. Memory 169 may store information for configuring NM imaging system 100. In one example, memory 169 may store a reference or look - up table for selecting, adjusting, and / or configuring a reconstruction algorithm or different algorithms of NM imaging system 100.

[0048] In operation, and as shown, for example, Figure 1B one embodiment includes detector array 106 positioned (e.g., mounted) beneath patient examination table 120. As visible, a plurality of detector units 114a, 114b are positioned in an adjacent arrangement, e.g., along one or more rows beneath patient examination table 120 (it should be noted that only a single row of detector units is shown). In some embodiments, the detector units are aligned along one or more axes that are generally perpendicular to the longitudinal axis of patient examination table 120, which longitudinal axis defines the examination axis (e.g., from the head to the feet of subject 110). However, it should be understood that the detector units may be aligned in different configurations and orientations that may be offset relative to each other, transverse to the longitudinal axis of patient examination table 120, and / or parallel to the longitudinal axis of patient examination table 120. Figure 1B The detector units shown in Figure 1A may each be a non - limiting example of detector unit 114 of Figure 1B Further, detector unit 114a shown in Figure 1B is arranged at an angle relative to the longitudinal axis 115 of the detector unit (which is perpendicular to the longitudinal axis 117 of the patient examination table), and Figure 2B detector unit 114b shown in

[0049] As shown in Figure 1BAs can be seen, each of the detector units 114a, 114b includes a housing 170, which is shown as a circular housing. However, the housings 170 of the detector units 114a, 114b may have different shapes and sizes, such as oval, other curved shapes, etc. The detector units 114a, 114b include a detector support 172 within the housing 170, which may be a frame or other support structure. A detector 174 is coupled to the detector support 172. For example, the detector 174 may include one or more CZT tiles or modules as described herein, which are connected to electronics 176 therein (e.g., output electronics for outputting detected events). Additionally, a collimator 122 is mounted to the front detection surface of the detector 174. Thus, the size and shape of the detector support 172 are configured to have a base and / or walls, for example, to support and hold the components of the detector units 114a, 114b within the housing 170. For example, when the housing rotates, pivots, or swings, the components of the detector units 114a, 114b remain within the housing 170, as described in more detail herein. In the illustrated embodiment, the detector unit 114a is shown in a rotated, pivoted, or swung position, while the detector unit 114b is shown in a non-rotated, non-pivoted, or non-swung position. As can be seen, in the non-rotated, non-pivoted, or non-swung position, the detection surface of the detector is generally parallel to the patient support surface of the patient examination table 120, while in the rotated, pivoted, or swung position, the detection surface of the detector is not parallel to the patient support surface of the patient examination table 120. Various embodiments provide coordinated or synchronized movement of the detector units 114a, 114b, which allows the detector units 114a, 114b to be positioned or packaged in a more closely aligned manner than in conventional systems. For example, in some embodiments, different detector units 114a, 114b (such as adjacent detector units 114) may move to different angular positions along different angular ranges and / or at different speeds.

[0050] It should be noted that the arrangement of the detector units 114 in the detector array 106 may be provided in other parts of the NM imaging system 100, such as at positions along the gantry 104 or as part of the detector array 106. Moreover, it should be noted that in some embodiments, a housing 170 surrounding or enclosing the components within the detector unit 114 is not provided.

[0051] As Figure 1B can be seen, the housings 170 for the detector units 114 are generally circular in shape and are closely adjacent to each other. In this way, the rotation of each detector unit 114 about its individual axis does not physically interfere with adjacent detector units. The circular housings 170 allow a small gap between each detector unit 114 to allow each detector unit to rotate completely during operation of the NM imaging system 100.

[0052] Figure 1C Shows a more detailed view of detector unit 114, including detector 174 positioned behind collimator 122. Collimator 122 includes a plurality of parallel septa 158 that allow photons directed at detector 174 at a vertical or near-vertical angle to strike detector 174, as shown by dashed arrow 160. However, septa 158 prevent photons directed at detector 174 at a non-vertical angle (shown by dashed arrow 161) from striking detector 174.

[0053] Additionally, detector unit 114 may include a protective shield 180 that may surround and / or enclose detector 174. In Figure 1C it, protective shield 180 is depicted on first side 190 and second side 191 of detector unit 114. However, it should be understood that protective shield 180 may surround detector 174 in three dimensions, thereby preventing photons directed at detector 174 from the sides of detector unit 114 from being detected by detector 174, as shown by dashed arrow 163. Protective shield 180 may be made of a heavy or dense material, such as lead. However, when using high-energy isotopes, some photons may penetrate protective shield 180 and be detected and counted by detector 174. Because these penetrating photons are not collimated, they may not be properly processed by the reconstruction algorithm used to reconstruct an image from the projection data acquired by detector unit 114. Thus, penetrating photons may degrade the quality of the reconstructed image, as described in more detail below. Additionally, penetrating photons may cause artifacts in the reconstructed image. By following the Figure 8 method described below, artifacts may be reduced and image quality may be improved.

[0054] Figure 2A is a perspective view of a first embodiment of a nuclear medicine (NM) imaging system 200. NM imaging system 200 includes elements similar or identical to those of NM imaging system 100. It should be noted that Figure 2A the arrangement is provided by way of example for illustrative purposes, and other arrangements may be employed in various embodiments. Figure 2A the NM imaging system 200 of Figure 2AIn [the figure], the vertical axis 292 extends parallel to gravity. However, for other configurations of the NM imaging system, the vertical axis 292 may not extend parallel to gravity. Optionally, the NM imaging system 100 may be positioned adjacent to or in proximity to a computed tomography (CT) imaging system (not shown). The gantry 202 has a discrete housing 203 and is configured to rotate about the longitudinal axis 291 in one or two directions at a rotational speed.

[0055] The NM imaging system 200 also includes a plurality of detector assemblies 206 (e.g., Figure 1A and Figure 1B detector units 114). As shown, the detector assemblies 206 are positioned in an array 208, where the detector assemblies 206 are at least partially distributed around the cavity 204. In the illustrated embodiment, the detector assemblies 206 are evenly circumferentially distributed around the longitudinal axis 291. Each detector assembly 206 in the array 208 includes a movable arm (not shown) and a detector head 210 coupled to the movable arm. The movable arm is configured to move the detector head 210 toward and away from an object within the cavity 204.

[0056] Also shown, the NM imaging system 200 includes a movable examination table 220 (e.g., patient examination table 120). The movable examination table 220 is configured to receive an object (e.g., a patient) and move the object into the cavity 204 along the longitudinal axis 291. In some embodiments, the movable examination table 220 may be movable in one or two directions along the vertical axis 292 and in one or two directions along the horizontal axis 293. Movement along the vertical axis 292 and the horizontal axis 293 may occur simultaneously or in separate movements (e.g., first upward and then translated). As set forth herein, the NM imaging system 200 may move the detector head 210 and the movable examination table 220 such that a series of detector heads 210 are positioned in a dense group adjacent to the object.

[0057] The movable examination table 220 is operatively coupled to one or more motors 212 controlled by one or more processors (not shown). The motors 212 are configured to move the movable examination table 220 to a specified position. For example, the processor may control the motors 212 and the detector assemblies 206 such that the object has a desired position relative to the detector head 210.

[0058] Figure 2B A second embodiment of the NM imaging system 200 having an alternative dual-head configuration 250 is shown. In the dual-head configuration 250, the first head 252 includes a first set of detector units (e.g., Figure 1AThe first head 252 and the second head 254 may be arranged on a gantry 256 (e.g., gantry 104), which may be an open arch gantry. As described above with reference to Figure 1A As described above, the gantry 256 can rotate around a subject positioned on a movable examination table 220 (eg, patient examination table 120). Figure 2B 292, the first head 252 is horizontally aligned above the movable inspection table 220, and the second head 254 is horizontally aligned below the movable inspection table 220. Alternatively, the gantry 256 can be rotated relative to the horizontal axis 293 so that the first head 252 is vertically aligned at a first side 260 of the movable inspection table 220, and the second head 254 is vertically aligned at a second opposite side 262 of the movable inspection table 220. In various embodiments, the first head 252 and the second head 254 can be vertically aligned during calibration of the NM imaging system 100 using a line source, as described below with reference to Figure 5 Described in more detail. The angle between the first head 252 and the second head 254 can be adjusted between 90 degrees and 180 degrees, preferably using conventional means, and / or the distance between the first head 252 and the second head 254 can be adjusted, and the lateral position of each of the first head 252 and the second head 254 (or both together) can be adjusted using conventional mechanical structures. In addition, the movable inspection table 220 can be adjusted upward or downward along the vertical axis 292, for example, to center the subject between the first head 252 and the second head 254. The first head 252 and the second head 254 can also be adjusted upward or downward, for example, along the vertical axis 292 to reduce or increase the distance between either or both of the first head 252 and the second head 254 and the subject.

[0059] Figure 3 A front perspective view of an exemplary configuration of multiple detector heads 308 (e.g., detector units 114) of a SPECT system 300, which may be Figure 1A Non-limiting example of a NM imaging system 100. In the depicted embodiment, the SPECT system 300 is a multi-head configuration such as Figure 2A In other embodiments, the SPECT system can be a dual-head configuration, such as Figure 2B A dual head configuration 250, wherein multiple detector heads can be as Figure 1BDepicted linearly arranged. In the depicted embodiment, a SPECT system is depicted during a scan of a phantom 302 including a high contrast region 304. The high contrast region 304 can be injected with a radioactive tracer that can emit radiation (e.g., photons) detectable by detector elements.

[0060] Each detector head 308 can include a detector array having a plurality of detector elements (e.g., detector 174). Each detector element can generate an electrical signal when a photon is detected by the element, and the electrical signals from the plurality of detector elements can be combined to generate a 3D image of the phantom 302. The detector heads 308 can each be collimated via a collimator 309 such that radiation emitted by the high contrast region 304 and received at an angle perpendicular to the collimator 309 can be detected at the detector elements of the corresponding detector head 308. Each detector head 308 can rotate such that each detector head 308 can sweep over the phantom 302 at a plurality of sweep angles. Each detector head 308 has a field of view 310 at each sweep angle, which is Figure 3 indicated in the figure as the shaded region between two lines extending from the collimator 309 of each detector head 308.

[0061] As each detector head 308 sweeps over the phantom 302, the high contrast region 304 can be within the field of view 310 of some detector heads 308 and outside the field of view 310 of other detector heads 308. When the high contrast region 304 is within the field of view 310 of a detector head 308, photons emitted by the high contrast region 304 can be collimated by the collimator 309 and detected by the detector array of the detector head 308. When the high contrast region 304 is outside the field of view 310 of a detector head 308, photons directed from the high contrast region 304 towards the detector head 308 can be absorbed by the shield (e.g., Figure 1C protective shield 180) of the detector head 308 and not detected at the detector head 308.

[0062] The function of the shield is illustrated by Figure 4 and Figure 5 Illustrated. Turning to Figure 4 Figure 400 shows a detector head 408, which can be Figure 3Non-limiting example of detector head 308. Detector head 408 is shown in a first position relative to a phantom 402 (e.g., phantom 302), which includes various high-contrast regions 403 where a radioactive tracer has been injected. As a result of the injected radioactive tracer, the high-contrast regions 403 may emit photons. In the first position, the high-contrast region 404 (e.g., high-contrast region 304) is within the field of view 410 (e.g., field of view 310) of the detector head 408. The field of view 410 may widen as a function of the distance from the detector head. As a result of being within the field of view 410, photons emitted by the high-contrast region 404 following the trajectory indicated by the dashed arrow 420 may be collimated by the collimator 422 (e.g., Figure 1C collimator 122) of the detector head 408, and the detector 474 of the detector head 408 may detect the photons.

[0063] In contrast, Figure 5 Figure 500 is shown, where the detector head 408 is in a second position relative to the phantom 402. In the second position, the detector head 408 is at a sweep angle 550 relative to the longitudinal axis 590 (e.g., Figure 1B longitudinal axis 115) of the detector head 408. Thus, the high-contrast region 404 is not within the field of view 410. Because the detector head 408 is at a sweep angle 550 relative to the high-contrast region 404, photons following the trajectory indicated by the dashed arrow 420 may strike the detector head 408 at a location 502 on the outer surface of the detector head 408. Accordingly, the photons may be attenuated by the shield 580 (e.g., Figure 1C protective shield 180) of the detector head 408 and may not be detected at the detector 474.

[0064] However, in some cases, a portion of the photons following a trajectory similar to the dashed arrow 420 may penetrate the shield 580 and may not be attenuated by the shield 580. When the photons penetrate the shield 580, the photons may be detected and counted at the detector 474. Further, the number of photons that penetrate the shield 580 may depend on the sweep angle 550. That is, as the sweep angle 550 increases, the number of photons that penetrate the shield 580 may increase, and as the sweep angle 550 decreases, the number of photons that penetrate the shield 580 may decrease.

[0065] Reference Figure 6, the sweep angle graph 600 includes a graph 602 showing how the normalized number of photons counted at the detector head can vary with the sweep angle of the detector head. The normalized photon count is depicted on the vertical axis of graph 600, and the angle of the detector head relative to the incident photons emitted by the radioactive tracer (e.g., the sweep angle 550) is indicated on the horizontal axis of the sweep angle graph 600. The graphical representation 604 of the detector head (e.g., detector heads 308 and 408) shows the orientation of the detector head along the graph 602 at various points of interest.

[0066] At a sweep angle of 0°, the detector head is aligned with the trajectory of the photons (e.g., trajectory 420), and the normalized number of photon counts is the highest, meaning close to 100. During the first portion 610 of graph 602, as the sweep angle increases from 0° to 10°, the normalized number of photon counts decreases as the incident photons move out of the field of view of the detector head. During the second portion 612 of graph 602, as the sweep angle increases from 10° to approximately 40°, the normalized number of photon counts remains low because fewer photons are collimated and detected at the detector head. However, during the third portion 614 of graph 602, as the sweep angle of the detector head increases from 45° to approximately 90°, the normalized number of photon counts increases. The increase in photon counts as the sweep angle approaches 90° is due to photons striking one side of the detector head and penetrating the shield of the detector head. Photons that penetrate the shield of the detector head can generate artifacts in the projection views acquired by the detector head and generally degrade the quality of the images reconstructed from the projection views, as described above.

[0067] Figure 7Image 700 shows multiple projection views 701 of a phantom (e.g., phantom 302 / 402) obtained from a detector head (e.g., detector head 408) within a sweep angle range from -50° to 50°. The projection views 701 are cascaded to facilitate comparison between the projection views. In other words, the first projection view 702 among the multiple projection views at the leftmost side of image 700 corresponds to a sweep angle of -50°, and the last projection view 704 among the multiple projection views at the rightmost side of image 700 corresponds to a sweep angle of 50°, with the projection views obtained at 2° increments being displayed in between. Projection view 706 corresponds to a sweep angle of 0°, where the field of view of the detector head is aligned with the high contrast region 750 (e.g., high contrast region 404) of the phantom. Thus, the high contrast region 750 in the object being scanned is most clearly visible in projection view 706. The high contrast region 750 is less clearly visible in the adjacent projection view 705 (where the detector head is at a sweep angle of -2°) and in the adjacent projection view 707 (where the detector head is at a sweep angle of 2°). As the sweep angle decreases towards -50° and increases towards 50°, the visibility of the high contrast region 750 decreases. At the first projection view 702 and the second projection view 704, the high contrast region 750 is not visible because at sweep angles of -50° and 50°, the high contrast region 750 of the phantom is outside the field of view of the detector head.

[0068] However, artifacts 730 including vertical penetration of photon counting are visible in the first portion 722 of image 700, and these artifacts increase as the sweep angle decreases to -50°. Similar artifacts 732 are also visible in the second portion 724 of image 700, and these artifacts increase as the sweep angle increases to 50°. Artifacts 730 and 732 are not visible in the third central portion 720 of image 700, where the sweep angle is the smallest and the high contrast region is within the field of view of the detector head. Artifacts 730 and 732 can be generated by photons detected after penetrating the shield of the detector head, as described above with reference to Figures 3 - 5 . The intensity with which artifacts 730 and 732 increase as the sweep angle increases in the positive or negative direction can be explained by Figure 6 sweep angle graph 600.

[0069] Furthermore, artifacts 730 and 732 are located at one side of the corresponding projection views. That is, artifact 730 appears at the right side 703 of projection view 704, and artifact 732 appears at the left side 710 of projection view 702. More generally, artifact 730 can appear at the right side of the projection views obtained when the sweep angle is negative, and at the left side of the projection views obtained when the sweep angle is positive.

[0070] Artifacts 730 and 732 in the wider sweep angle projection view 701 of image 700 can result in corresponding artifacts in the image reconstructed from the projection views. For example, the corresponding artifacts may be visible at the contour of the phantom in the reconstructed image, as Figure 9 shown. However, since artifacts 730 and 732 appear at the sides of the respective projection views (e.g., within the pixel columns located at the sides), when reconstructing an image from multiple projection views 701, artifacts 730 and 732 can be advantageously reduced or removed by selectively ignoring one or more side pixel columns of the multiple projection views 701. Selective ignoring can be achieved by pixel zeroing, as described in more detail below.

[0071] In some embodiments, the number of side pixel columns to be selectively ignored can be predefined. In other embodiments, the number of side pixel columns to be selectively ignored can vary within the projection view. In at least one embodiment, the number of side pixel columns to be selectively ignored can be selected as a function of the sweep angle of the corresponding detector head, where the number of side pixel columns to be selectively ignored increases as the sweep angle increases. Pixel zeroing can be performed according to methods such as Figure 8 method 800, etc. to reduce or remove artifacts 730 and 732.

[0072] It should be understood that although the examples and embodiments described herein relate to selectively ignoring pixel columns, in other embodiments, other adjacent pixel groups can be selectively ignored without departing from the scope of the present disclosure. In other words, in some embodiments, the pixels to be selectively ignored may not be in a linear profile (such as a column). For example, a circular profile or a different shape can be used, where pixels outside or inside the circular profile or different shape can be selectively ignored.

[0073] Now referring to Figure 8 , method 800 is shown, which is used to improve the quality of CT images reconstructed using a SPECT system by reducing artifacts generated in the projection views acquired by the SPECT system, such as the SPECT system Figure 1A NM imaging system 100 or other embodiments of the SPECT system described herein, and these artifacts are the result of photons not being collimated at the detector head of the SPECT system but being detected after passing through the shield located around the side portion of the detector head. Method 800 can be executed by the control unit of the SPECT system (such as Figure 1A control unit 130). Regarding the multi-head SPECT embodiment (e.g., Figure 2A)Describe method 800, in which multiple detector heads are arranged in a gantry (e.g., gantry 104), which can rotate around a bed or examination table on which a subject is placed for scanning. However, it should be understood that method 800 can be applied to a dual-head SPECT implementation, in which the detector heads are arranged linearly as described with reference to Figure 1B and Figure 2B .

[0074] Method 800 begins at 802, where method 800 includes scanning an object using a SPECT system. The object being scanned can be a patient of the SPECT system, or a phantom, or a different object being scanned. The object being scanned can include a radioactive tracer that can emit photons that can be detected by the detectors of the SPECT system. When scanning, as the detector heads of the SPECT system rotate around the object being scanned and sweep across the object being scanned, a plurality of projection views (e.g., Figure 7 projection view 701) are generated. Thus, each projection view can be acquired by the detector heads at a corresponding sweep angle within the sweep angle range of the detector heads. In one example, the range of sweep angles can include angles from 0° to 50° in the positive and negative directions, as shown in Figure 7 .

[0075] At 804, method 800 includes determining, for each projection view, a first portion of pixels that can be used by the reconstruction algorithm of the SPECT system to reconstruct the image volume, and a second portion of pixels including projection data that cannot be used by the reconstruction algorithm to reconstruct the image volume. In other words, the reconstruction algorithm can be configured to reconstruct an image based on the first portion of the projection data and ignore the second portion of the projection data, where the second portion can include artifacts as described above with reference to Figure 7 . For the purposes of the present disclosure, ignoring the second portion of pixels or pixel columns means ignoring (e.g., not considering) the projection data of the second portion of pixels or pixel columns. Ignoring pixel data or pixel columns can be achieved using a pixel zeroing process, as described in more detail below. The second portion of pixels to be ignored by the reconstruction algorithm can include pixels located in one or more pixel columns of the projection view. The pixel columns can be located at one side of the projection view.

[0076] In some embodiments, not all pixels in a pixel column can be ignored. For example, the reconstruction algorithm can selectively ignore the first portion of pixels in a pixel column, and the reconstruction algorithm can not ignore the second portion of pixels in the pixel column. For example, every other pixel in a pixel column can be selectively ignored, or every two pixels in a pixel column can be selectively ignored, or the pixels in the pixel column to be ignored can be selected in a different manner. As another example, the reconstruction algorithm can selectively ignore one or more pixel segments within a pixel column. As yet another example, pixel segments inside or outside a defined shape can be selectively ignored.

[0077] In some embodiments, for all projection views, the second portion of pixels to be selectively ignored by the reconstruction algorithm may be fixed (e.g., the same). For example, the reconstruction algorithm may not be applied to one column of pixels of each of the plurality of projection views, or two columns of pixels of each of the plurality of projection views, or six columns of each of the plurality of projection views, or a different number of columns of pixels. The number of columns of pixels (and / or pixels) to be ignored by the reconstruction algorithm may be predefined and stored in the memory of the SPECT system (e.g., Figure 1A the memory 169).

[0078] In other embodiments, the second portion of pixels to be selectively ignored by the reconstruction algorithm may not be the same for all projection views. For example, a first number of columns of pixels of a first set of projection views may be selectively ignored; a second number of columns of pixels of a second set of projection views may be selectively ignored; a third number of columns of pixels of a third set of projection views may be selectively ignored; and so on. Additionally, the number of columns of pixels to be selectively ignored may be determined based on the sweep angle of the detector of the projection view. For example, a first number of columns of pixels of a first projection view acquired by the detector at a first sweep angle may be ignored; a second number of columns of pixels of a second projection view acquired by the detector at a second sweep angle may be ignored; a third number of columns of pixels of a third projection view acquired by the detector at a third sweep angle may be ignored; and so on. The first number, the second number, the third number, etc. may be stored in a look-up table in the memory of the SPECT system.

[0079] Further, in some embodiments, adaptive pixel zeroing may be used to dynamically and / or adaptively determine the number of pixels and / or columns of pixels of the second portion of pixels to be ignored as a function of the sweep angle of the associated detector. The function may be represented using a look-up table stored in the memory of the SPECT system, or the function may be stored in the memory of the SPECT system. For example, at optional step 806, method 800 may include determining the sweep angle of each projection view and then determining the number of pixels and / or columns of pixels of the second portion of pixels to be selectively ignored as a function of the sweep angle. For example, the sweep angle may be the input to the function, and the output of the function may be the number of pixels and / or columns of pixels of the second portion of pixels to be selectively ignored.

[0080] Briefly refer to Figure 9, shows a graph 900 that includes a curve 902 of an exemplary step function that is used to calculate the number of pixel columns to be ignored by a reconstruction algorithm when reconstructing an image from projection views acquired by a detector at different sweep angles. The number of pixel columns to be ignored for each projection view is shown on the vertical axis of graph 900, and the sweep angle of the detector acquiring the projection view is shown on the horizontal axis of graph 900. According to curve 902, between a sweep angle of -15° and a sweep angle of 15°, the first part of the pixels of the projection views used by the reconstruction algorithm to reconstruct the image may include all the pixels of the projection views, and no pixel columns may be ignored by the reconstruction algorithm. At sweep angles from -15° to 15°, photons emitted from the object being scanned may be within the field of view of the detector (e.g., corresponding to Figure 7 portion 720 of image 700), and no artifacts may be generated in the projection views.

[0081] Between a sweep angle of -15° and a sweep angle of -45°, the number of pixel columns to be ignored by the reconstruction algorithm linearly increases from one to eight because an increasing number of photons emitted from the object being scanned are outside the field of view of the detector, and some of these photons may penetrate the detector shield and cause artifacts in the projection views (e.g., corresponding to portion 722 of image 700). For example, at a sweep angle of -20°, the reconstruction algorithm may ignore three pixel columns; at a sweep angle of -30°, the reconstruction algorithm may ignore four pixel columns; at a sweep angle of -40°, the reconstruction algorithm may ignore seven pixel columns; and so on.

[0082] Between a sweep angle of 15° and a sweep angle of 45°, the number of pixel columns to be ignored by the reconstruction algorithm also linearly increases from one to eight because an increasing number of photons emitted from the object being scanned are outside the field of view of the detector, and some of these photons may penetrate the detector shield and cause artifacts in the projection views (e.g., corresponding to portion 724 of image 700). For example, at a sweep angle of 20°, the reconstruction algorithm may ignore three pixel columns; at a sweep angle of 30°, the reconstruction algorithm may ignore four pixel columns; at a sweep angle of 40°, the reconstruction algorithm may ignore seven pixel columns; and so on.

[0083] In this way, the step function shown by curve 902 indicates the number of pixel columns to be ignored by the reconstruction algorithm during image reconstruction to eliminate artifacts generated by penetrating photons. Additionally, depending on the sweep angle, the pixel columns to be ignored may be selected from one side of the projection view. In particular, the number of pixel columns to be ignored may be the adjacent pixel columns at the side of the projection view closest to 0°. For example, referring to Figure 7For the image 700, for the negative sweep angle in the portion 722, the number of pixel columns to be ignored in the projection view 701 can be located on the right side of the corresponding projection view. For the positive sweep angle in the portion 724, the number of pixel columns to be ignored in the projection view 701 can be located on the left side of the corresponding projection view.

[0084] Return to Figure 8 , at 808, the method 800 includes generating a mask based on the pixels or pixel columns to be selectively ignored to be applied to each projection view during image reconstruction. The mask can be used to zero out pixels, where the pixel data of one or more projection views is converted to a value of 0 or a value very close to 0, such that the pixel data is ignored by the reconstruction algorithm or has a very small (e.g., negligible) contribution in the calculations of the reconstruction algorithm. In various embodiments, the mask can be a matrix of weight values to be multiplied by the corresponding number of pixels of the projection view, where the weight value is 1.0 (if the corresponding pixel is to be used by the reconstruction algorithm) or 0.0 (if the corresponding pixel is ignored and not used by the reconstruction algorithm). The matrix can be a two-dimensional (2D) matrix, where the length is equal to the pixel length of the projection view and the width is equal to the pixel width of the projection view. In some environments, values such as 0.000001 can be used instead of 0.0.

[0085] For example, in one embodiment, the projection view has a length of 279 pixels and a width of 39 pixels. Thus, the projection view includes 39 pixel columns, where each pixel column includes 279 pixels. The mask can include a 2D matrix of weight values with a length of 279 and a width of 39, such that each weight value of the mask can correspond to (e.g., multiply) the corresponding pixel of the projection view.

[0086] Figure 10 FIG. 1000 shows a mask diagram, which includes a depiction of an exemplary projection view 1001 and a mask that can be applied to the projection view 1001. For simplicity, in the depicted embodiment, the projection view 1001 includes 10 pixel columns, where each pixel column includes 10 pixels. In other embodiments, the projection view 1001 can include a different number of pixel columns (e.g., 39) and / or a different number of pixels per column (e.g., 279). Each pixel can be defined by a pixel intensity value, for example, from 0.0 to 1.0, where 0.0 is black and 1.0 is white.

[0087] The mask map 1000 includes a first mask 1004 that can be applied to the projection view 1001. The first mask 1004 is a 10x10 matrix of weight values, where each weight value corresponds to a pixel of the projection view 1001. When the first mask 1004 is applied to the projection view 1001, each weight value of the first mask 1004 can be multiplied by the corresponding pixel intensity value of the projection view 1001. Thus, the first weight value 1005 of the first mask 1004 can be multiplied by the pixel intensity value of the first pixel 1002 of the projection view 1001. Since the first weight value 1005 is 0.0, the result of multiplying the first weight value 1005 by the pixel intensity value of the first pixel 1002 is that the pixel intensity value of the first pixel 1002 becomes 0.0. As a result of the pixel intensity value being 0.0, when reconstructing the image volume based on the projection view 1001, the reconstruction algorithm can ignore the pixel 1002. That is, the calculation performed according to the reconstruction algorithm will not include the original pixel intensity value of the pixel 1002.

[0088] Conversely, the second weight value 1006 of the first mask 1004 can be multiplied by the pixel intensity value of the second pixel 1009 of the projection view 1001. Since the second weight value 1006 is 1.0, the result of multiplying the second weight value 1006 by the pixel intensity value of the second pixel 1009 is that the pixel intensity value of the second pixel 1009 remains unchanged. As a result of the pixel intensity value remaining unchanged, when reconstructing the image volume based on the projection view 1001, the reconstruction algorithm may not ignore the second pixel 1009. That is, the calculation performed according to the reconstruction algorithm will include the pixel intensity value of the second pixel 1009.

[0089] The first mask 1004 includes a first column 1011 with a weight value of 0.0, where the other columns of the first mask 1004 have weight values of 1.0. Thus, applying the first mask 1004 to the projection view 1001 produces an adjusted projection view 1010, where the pixel intensity values of the first pixel column 1007 are zeroed out by the first mask 1004. As a result of zeroing out the pixel intensity values of the first pixel column 1007, the pixels of the first pixel column 1007 can be ignored by the reconstruction algorithm during image reconstruction, while the pixel intensity values of the pixels of the other pixel columns of the projection view 1001 can be used by the reconstruction algorithm to create the image volume.

[0090] Mask diagram 1000 includes a second mask 1020 applicable to the projection view 1001, which can be used to zero out the pixel intensity values of both the first pixel column 1007 and the second column 1012 of the projection view 1001. The second mask 1020 includes a first column 1022 with a weight value of 0.0 and a second column 1024 with a weight value of 0.0, and the remaining columns have a weight value of 1.0. Applying the second mask 1020 to the projection view 1001 results in an adjusted projection view 1026, where the pixels of both the first pixel column 1007 and the second column 1012 of the adjusted projection view 1026 can be ignored by the reconstruction algorithm during image reconstruction, and the pixel intensity values of the pixels in the other pixel columns of the adjusted projection view 1026 can be used by the reconstruction algorithm to create an image volume. In this way, different masks can be configured such that when applied to a projection view, various pixel columns of the projection view are ignored by the reconstruction algorithm. In some embodiments, for each projection view, the same mask can be used to ignore the same number of pixel columns, while in other embodiments, different masks can be generated for different pixel columns based on the sweep angle of the associated detector (e.g., adaptive pixel zeroing).

[0091] Return to Figure 8 , at 810, method 800 includes reconstructing an image (e.g., an image volume) from projection views acquired during a scan, where a corresponding mask can be applied to the projection views to reduce artifacts generated by photons penetrating the detector shield. In particular, the mask can be applied based on the sweep angle of the detector associated with the projection view, using a look-up table and / or a function such as Figure 9 the function shown. Various methods can be used to ignore pixels or entire views during the reconstruction process. Iterative reconstruction algorithms such as ordered subset expectation maximization (OSEM) or block sequential regularization expectation maximization (BSREM) can be used, or different reconstruction algorithms can be used. In various embodiments, the reconstruction algorithm can include a pixel weight input corresponding to a weight matrix for each pixel. Before or during reconstruction, each pixel weight can be multiplied by the corresponding pixel value. Thus, pixels assigned a pixel weight of 0 or a very low pixel weight (e.g., close to 0) can be ignored by the reconstruction algorithm (e.g., can have a negligible contribution). Pixel weights can be assigned based on various factors such as view acquisition time and / or other correction methods.

[0092] At 812, method 800 includes on a display device of the SPECT system (e.g., Figure 1AThe reconstructed image is displayed on the display device 168), and method 800 ends. Additionally or alternatively, the reconstructed image can be stored in the memory of the SPECT system (e.g., memory 169 and / or data storage device 164). When the reconstructed image is displayed on the display device, artifacts present in the projection views acquired by the SPECT system may not appear in the reconstructed image, and the quality of the reconstructed image can be improved.

[0093] Figure 11 Table 1100 shows six examples of reconstructed images generated by a SPECT system from a phantom 1103, where pixel zeroing is advantageously used to configure the reconstruction algorithm of the SPECT system to ignore the pixels of the projection views including artifacts. Phantom 1103 includes 6 high-contrast regions of different sizes and located at different positions within the phantom 1103, shown in black in the image, and these high-contrast regions include radioactive tracers that emit photons detectable by the SPECT system.

[0094] Table 1100 includes three columns. The first column 1106 shows the reconstructed images without using pixel zeroing in image reconstruction. The second column 1107 shows the reconstructed images using non-adaptive pixel zeroing, where the reconstruction algorithm ignores six pixel columns of each projection view including artifacts. The third column 1108 shows the reconstructed images using adaptive pixel zeroing, where according to functions such as Figure 9 functions depicted in, etc., the reconstruction algorithm ignores from one to eight different numbers of pixel columns of each projection view including artifacts.

[0095] Table 1100 includes two rows. The first row 1102 shows the transverse axis (TX) view of the reconstructed image, and the second row 1104 shows the coronal plane view of the reconstructed image, where the coronal plane view is generated using maximum intensity projection (MIP).

[0096] In the first column 1106, the first transverse axis image 1110 without using pixel zeroing is shown. The transverse axis image 1110 shows five of the six high-contrast regions, but the smallest high-contrast region 1113 is not visible. Additionally, the second smallest high-contrast region 1111 is blurred and not displayed in high contrast. Artifacts 1112 caused by penetrating photons are visible around the contour of the phantom 1103. Similarly, the first MIP image 1120 shows artifacts 1121 (at one side of the MIP image 1120) and 1122 (striped).

[0097] In the second column 1107, the second transverse axis image 1114 is shown, where non-adaptive pixel zeroing is used, and six pixel columns are used as described above with reference to Figure 10The reconstruction algorithm of the described mask is ignored. Compared with the first transverse image 1110, all six high-contrast regions are visible in the transverse image 1114, but the smallest high-contrast region 1113 is blurred. The contrast of the second smallest high-contrast region 1111 increases, but it is still blurred. The artifact 1112 is not visible around the contour of the phantom 1103, although it still exists. Therefore, as a result of non-adaptive pixel zeroing, the quality of the second transverse image 1114 is higher than that of the first transverse image 1110. The second MIP image 1124 similarly shows a reduced visibility of the artifacts 1121 and 1122 relative to the first MIP image 1120.

[0098] In the third column 1108, the third transverse image 1116 is shown, in which adaptive pixel zeroing is used according to a function such as the function plotted in Figure 9 For example, a smaller number of pixel columns can be zeroed at a lower detector sweep angle, and a larger number of pixel columns can be zeroed at a higher detector sweep angle, where the number of pixel columns to be zeroed ranges from one to eight. In the third transverse image 1116, all six high-contrast regions are visible, and the contrast of the smallest high-contrast region 1113 and the second smallest high-contrast region 1111 increases relative to the first transverse image 1110 and the second transverse image 1114. The artifact 1112 around the contour of the phantom 1103 is almost completely eliminated. Therefore, as a result of adaptive pixel zeroing, the quality of the third transverse image 1116 is higher than that of both the second transverse image 1114 and the first transverse image 1110. The third MIP image 1126 shows a similar reduction in the visibility of the artifacts 1121 and 1122 relative to the first MIP image 1120 and the second MIP image 1124.

[0099] Accordingly, a method for removing artifacts caused by photons penetrating a detector shield from an image reconstructed by a SPECT system is disclosed. Since the artifacts appear at one side of a projection view acquired by the SPECT system, the artifacts in the reconstructed image can be reduced or eliminated by: configuring a reconstruction algorithm to reconstruct the image based on a first portion of pixels that do not include the artifacts of each projection view and ignoring a second portion of pixels that include the artifacts of the projection view. The second portion of pixels may include one or more adjacent pixel columns located at one side of the projection view. The size of the second portion of pixels to be ignored (e.g., the number of pixel columns) may depend on the sweep angle of the detector that acquires the projection view. At a low sweep angle close to 0°, the artifacts caused by penetrating photons may not appear in the projection view, and no pixel columns may be ignored. As the sweep angle increases away from 0° and the size of the artifacts increases, the reconstruction algorithm may be configured to ignore an increasing number of pixel columns. The number of pixel columns to be ignored may be determined as a function of the detector sweep angle, e.g., a step function that may be represented in a look-up table of the SPECT system. The reconstruction algorithm may be configured to ignore the pixel columns by applying a mask to some or all of the projection views used to reconstruct the image to convert the pixel intensity values of the pixels in the pixel columns to 0, such that the pixel columns do not contribute to the generation of the reconstructed image. In this way, the reconstructed image may not include artifacts, and the overall quality of the reconstructed image may be improved. By improving the overall quality of the reconstructed image, a radiologist can detect abnormalities in the reconstructed image more quickly and effectively, and the diagnosis of the radiologist can be more accurate, thus improving patient treatment. The technical effect of configuring the reconstruction algorithm of the SPECT system to ignore a portion of pixels of a projection view when reconstructing the image is that artifacts caused by non-collimated photons penetrating the detector shield can be reduced, thereby generating a higher-quality reconstructed image.

[0100] The present disclosure also provides support for a method for a single photon emission computed tomography (SPECT) imaging system, the method comprising: using the SPECT imaging system to acquire a plurality of projection views of a scanned object, the plurality of projection views including artifacts; configuring a reconstruction algorithm to reconstruct an image based on a first portion of pixels of each of the plurality of projection views and not based on a second portion of pixels of each of the plurality of projection views, the second portion of pixels including the artifacts; using the reconstruction algorithm to reconstruct the image; and displaying the reconstructed image on a display device of the SPECT imaging system and / or storing the reconstructed image in a memory of the SPECT imaging system. In a first example of the method, the SPECT imaging system is a multi-head SPECT imaging system including a plurality of detector heads arranged on a gantry around the scanned object, and the plurality of projection views include projection views acquired at different sweep angles of each detector head. In a second example of the method, optionally including the first example, configuring the reconstruction algorithm to reconstruct the image based on the first portion of pixels and not based on the second portion of pixels further includes applying a mask to the projection views when applying the reconstruction algorithm to cause the reconstruction algorithm to ignore the second portion of pixels of the projection views, wherein the mask is a weight matrix to be multiplied by each pixel of the projection views, the weight matrix including a weight of 1.0 for pixels to be used by the reconstruction algorithm and a weight of 0.0 for pixels to be ignored by the reconstruction algorithm. In a third example of the method, optionally including one or both of the first example and the second example, the second portion of pixels to be ignored by the reconstruction algorithm includes one or more pixel columns. In a fourth example of the method, optionally including one or more or each of the first example to the third example, the projection data of the second portion of pixels to be ignored by the reconstruction algorithm includes projection data of pixels outside or inside a defined shape. In a fifth example of the method, optionally including one or more or each of the first example to the fourth example, for the plurality of projection views, the number of the one or more pixel columns to be ignored by the reconstruction algorithm is fixed. In a sixth example of the method, optionally including one or more or each of the first example to the fifth example, the number of the one or more pixel columns to be ignored by the reconstruction algorithm varies among the plurality of projection views. In a seventh example of the method, optionally including one or more or each of the first example to the sixth example, the number of the one or more pixel columns of the projection views to be ignored by the reconstruction algorithm varies as a function of the sweep angle of the detector acquiring the projection views. In an eighth example of the method, optionally including one or more or each of the first example to the seventh example, the number of the one or more pixel columns to be ignored is retrieved from a look-up table stored in the memory of the SPECT imaging system.In a ninth example of the method, optionally including one or more or each of the first example to the eighth example, these artifacts are generated by photons that penetrate the shield of the detector of the SPECT imaging system. In a tenth example of the method, optionally including one or more or each of the first example to the ninth example, under a first condition, wherein the reconstruction algorithm is not configured to reconstruct the image based on the first partial pixels of each projection view of the plurality of projection views and not based on the second partial pixels of each projection view of the plurality of projection views, and these artifacts are visible in the reconstructed image; and under a second condition, wherein the reconstruction algorithm is configured to reconstruct the image based on the first partial pixels of each projection view of the plurality of projection views and not based on the second partial pixels of each projection view of the plurality of projection views, and these artifacts are not visible in the reconstructed image.

[0101] The present disclosure also provides support for a single photon emission computed tomography (SPECT) imaging system, the SPECT imaging system including: a plurality of detector heads, each detector head including a shield disposed around the detector of the detector head; a controller including instructions stored in a memory of the SPECT imaging system, the instructions when executed causing the controller to: acquire a plurality of projection views of a scanned object using the SPECT imaging system; partially or completely remove artifacts generated in one or more of the plurality of projection views, the artifacts caused by photons penetrating the shield; apply a reconstruction algorithm to the plurality of projection views to reconstruct an image; and display the reconstructed image on a display device of the SPECT imaging system and / or store the reconstructed image in the memory. In a first example of the system, additional instructions are stored in the memory, the instructions when executed causing the controller to apply a mask to the one or more projection views during image reconstruction to cause the reconstruction algorithm to ignore one or more pixel columns of the one or more projection views that include the artifacts, wherein the mask is a weight matrix to be multiplied by each pixel of the projection view, the weight matrix including a weight of 1.0 for pixels to be considered by the reconstruction algorithm and a weight of 0.0 or a weight close to 0.0 for pixels to be ignored by the reconstruction algorithm. In a second example of the system, optionally including the first example, the one or more ignored pixel columns are adjacent pixel columns located at one side of the projection view. In a third example of the system, optionally including one or both of the first example and the second example, for the one or more projection views, the number of the one or more ignored pixel columns is fixed. In a fourth example of the system, optionally including one or more or each of the first example to the third example, the number of the one or more ignored pixel columns of the projection view varies as a function of a sweep angle of a detector that acquires the projection view. In a fifth example of the system, optionally including one or more or each of the first example to the fourth example, the number of the one or more ignored pixel columns is between one and eight. In a sixth example of the system, optionally including one or more or each of the first example to the fifth example, as a result of partially or completely removing the artifacts generated in the one or more projection views, the image quality of the reconstructed image is improved.

[0102] The present disclosure also provides support for a method for improving the quality of images generated by a single photon emission computed tomography (SPECT) imaging system, the method comprising: acquiring, using the SPECT imaging system, a plurality of projection views of a scanned object; determining a number of pixel columns of one or more of the plurality of projection views in which an artifact is visible, the artifact being a result of photons penetrating a shield of a detector of the SPECT imaging system; applying a mask to the one or more projection views to convert pixel intensity values of these pixel columns to 0; applying a reconstruction algorithm to the plurality of projection views to reconstruct an image that does not include the artifact; and displaying the reconstructed image on a display device of the SPECT imaging system and / or storing the reconstructed image in a memory of the SPECT imaging system. In a first example of the method, the number of pixel columns in the projection views of the plurality of projection views is based on a detector sweep angle of the projection views.

[0103] When introducing elements of various embodiments of the present disclosure, the articles "a", "an", and "the" are intended to mean that there is one or more of such elements. The terms "first", "second", etc. do not denote any order, quantity, or importance, but are used to distinguish one element from another. The terms "comprising", "including", and "having" are intended to be inclusive and mean that additional elements may exist in addition to the listed elements. As used herein, terms such as "connected to", "coupled to", etc., an object (e.g., a material, an element, a structure, a component, etc.) may be connected to or coupled to another object, regardless of whether the one object is directly connected or coupled to the other object, or whether there is one or more intervening objects between the one object and the other object. Further, it should be understood that references to "one embodiment" or "an embodiment" of the present disclosure are not intended to be construed as excluding the existence of additional embodiments that also incorporate the recited features.

[0104] In addition to any previously indicated modifications, those skilled in the art can devise many other variations and alternative arrangements without departing from the substance and scope of this specification, and the appended claims are intended to cover such modifications and arrangements. Thus, although the information has been described specifically and in detail above in connection with what is presently considered to be the most practical and preferred aspects, it will be apparent to those of ordinary skill in the art that many modifications can be made without departing from the principles and concepts set forth herein, including but not limited to form, function, mode of operation, and use. Also, as used herein, in all respects, the examples and embodiments are intended to be illustrative only and should not be construed as limiting in any way.

Claims

1. A method (800) for a single photon emission computed tomography (SPECT) imaging system, the method (800) comprising: Obtaining, using the SPECT imaging system, a plurality of projection views (802) of a scanned object, the plurality of projection views including artifacts; Configuring a reconstruction algorithm to reconstruct an image based on projection data of a first portion of pixels of each of the plurality of projection views and to ignore projection data of a second portion of pixels of each of the plurality of projection views, the second portion of pixels including the artifacts; Using the reconstruction algorithm to reconstruct an image (810); and Displaying the reconstructed image on a display device of the SPECT imaging system and / or storing the reconstructed image in a memory of the SPECT imaging system (812).

2. The method (800) according to claim 1, wherein the SPECT imaging system is a multi-head SPECT imaging system including a plurality of detector heads arranged on a gantry around the scanned object, and the plurality of projection views include projection views obtained at different sweep angles of each detector head.

3. The method (800) according to claim 1, wherein configuring the reconstruction algorithm to reconstruct the image based on the projection data of the first portion of pixels and to ignore the projection data of the second portion of pixels further comprises applying a mask to the projection views (808) when applying the reconstruction algorithm, wherein the mask is a weight matrix to be multiplied by each pixel of the projection views, the weight matrix including a weight of 1.0 for pixels to be used by the reconstruction algorithm and a weight of 0.0 or a weight close to 0.0 for pixels to be ignored by the reconstruction algorithm.

4. The method (800) according to claim 1, wherein the projection data of the second portion of pixels to be ignored by the reconstruction algorithm includes projection data included in one or more pixel columns located at one side of the projection views.

5. The method (800) according to claim 1, wherein the projection data of the second portion of pixels to be ignored by the reconstruction algorithm includes projection data of pixels outside or inside a defined shape.

6. The method (800) according to claim 4, wherein for the plurality of projection views, the number of the one or more pixel columns to be ignored by the reconstruction algorithm is fixed.

7. The method (800) according to claim 4, wherein the number of the one or more pixel columns to be ignored by the reconstruction algorithm varies among the plurality of projection views.

8. The method (800) according to claim 7, wherein the number of the one or more pixel columns of the projection views including projection data to be ignored by the reconstruction algorithm varies as a function of the sweep angle of the detector obtaining the projection views.

9. The method (800) according to claim 4, wherein the number of the one or more pixel columns including projection data to be ignored is retrieved from a look-up table stored in the memory of the SPECT imaging system.

10. The method (800) according to claim 1, wherein the artifact is generated by photons that penetrate a shield of a detector of the SPECT imaging system.

11. The method (800) according to claim 1, wherein the artifact is invisible in the reconstructed image.

12. A single photon emission computed tomography (SPECT) imaging system (200, 100), the SPECT imaging system comprising: a plurality of detector heads (308, 408, 210), each detector head (308, 408, 210) including a shield (580) disposed around a detector (174, 474) of the detector head (308, 408, 210); a controller, the controller including instructions stored in a memory (169) of the SPECT imaging system (200, 100), the instructions when executed causing the controller to: acquire a plurality of projection views (701) of a scanned object using the SPECT imaging system (200, 100); partially or completely remove artifacts (1121, 1112, 730) generated in one or more of the plurality of projection views (701), the artifacts (1121, 1112, 730) being caused by photons that penetrate the shield (580); apply a reconstruction algorithm to the plurality of projection views (701) to reconstruct an image (700); and display the reconstructed image (1114, 1116) on a display device (168) of the SPECT imaging system (200, 100) and / or store the reconstructed image (1114, 1116) in the memory (169).

13. The SPECT imaging system (200, 100) according to claim 12, wherein additional instructions are stored in the memory (169), the additional instructions when executed causing the controller to: apply a mask (1004, 1020) to the one or more projection views (701) during image reconstruction to cause the reconstruction algorithm to ignore one or more pixel columns (1007, 1012) of the one or more projection views (701) that include the artifacts (1121, 1112, 730), wherein the mask is a weight matrix to be multiplied by each pixel (1002) of the projection view (701), the weight matrix including a weight of 1.0 for pixels to be considered by the reconstruction algorithm and a weight of 0.0 for pixels to be ignored by the reconstruction algorithm.

14. The SPECT imaging system (200, 100) according to claim 13, wherein the one or more ignored pixel columns (1007, 1012) are adjacent pixel columns located at one side of the projection view (701).

15. The SPECT imaging system (200, 100) according to claim 13, wherein for the one or more projection views (701), the number of the one or more ignored pixel columns (1007, 1012) is fixed.

Images