Emission tomography with generalized time coded aperture imaging

Abstract

For emission tomography, a larger number of emissions are detected. To detect a larger number of emissions and provide better resolution compared to that provided by a parallel aperture collimator, the collimator is replaced by an attenuating object having outer and inner edges. Rather than forcing directivity to be achieved, larger apertures having different shapes may be used to allow for detection of a larger number of emissions. By moving the attenuating object, the difference in shadows on the sensor may be used as a time coded aperture to reconstruct the emission source with higher resolution and sensitivity than where a fixed parallel aperture collimator is used.

Description

Technical Field

[0001] The present embodiment relates to emission tomography, such as single photon emission computed tomography (SPECT), photon emission tomography (PET), or another type of imaging using a gamma camera. High-efficiency tomographic imaging of gamma rays emitted from radioactive isotopes is typically performed using a physical collimator from a discrete spectrum from about 50 keV to <511 keV. These collimators only allow gamma rays to enter the sensor (i.e., parallel hole collimators) in a specified direction to create a projection image (i.e., an image detected by a gamma camera). This process has a trade-off between the high directional accuracy of the collimator and the counting sensitivity. The small directional holes of the collimator block many rays. This low sensitivity results in noisy data, which makes the inverse problem, i.e., tomography, difficult, resulting in artifacts. For tomographic reconstruction, the collimator achieves high directional accuracy at the expense of high sensitivity. Background Art

[0002] Medical emission tomography is used for a variety of specific classes of tasks: 1. Detection of lesions ("detection tasks"), whereby a lesion is an abnormal uptake that is too high or too low compared to what is expected based on anatomy, physiology, and the administered radiopharmaceutical, and 2. Characterization of lesions or uptake patterns through descriptive statistics, such as mean uptake density. In some cases, the ability to resolve spatially is important (spatial resolution), in other cases it is important to resolve the signal in a background of noise, i.e., contrast resolution, and in yet other cases the uptake varies with time ("temporal resolution"). In general, a statistically based criterion is used that separates the signal from the noise with a certain confidence level. The fundamental trade-off between the presence of information ("sensitivity") and direction ("resolution") remains.

[0003] This fundamental trade-off can be influenced by applying or exploiting the auxiliary physical conditions of specific image formation. Contrast and attenuation patterns can be used as information sources, which are obtained by exploiting the physical conditions of specific image formation. Edge encoding has been shown. Time-dependent variable patterns have been considered, such as super-resolution time multiplexing methods. Compressed sensing is used. Further improvements in sensitivity may result in better emission tomography imaging for specific clinical tasks if the use of additional information can more than compensate for the loss of directional information. Summary of the invention

[0004] By way of introduction, the preferred embodiments described below include methods, systems, and sensors for emission tomography. In order to detect a greater number of emissions and / or provide better resolution than that provided by a parallel hole collimator, the collimator is replaced with an attenuating object having outer and inner edges. Rather than forcing directionality, larger holes with different shapes can be used to allow for detection of a greater number of emissions. By moving the attenuating object, the difference in the shadow on the sensor can be used as a time-encoded aperture to reconstruct the emission source with higher resolution and sensitivity than would be possible using a fixed parallel hole collimator. Directional information required for a particular task is acquired based on the moving shadow.

[0005] In a first aspect, an emission tomography system is provided. A sensor is configured to detect the time, position and energy of gamma rays. A movable attenuator has one or more internal through holes. A driver is configured to move the movable attenuator. An image processor is configured to reconstruct the spatial distribution of the emission detected by the sensor when the movable attenuator is in different positions due to movement by the driver. The movable attenuator is between the emission source and the sensor so that the moving shadow of the through hole is projected on the sensor.

[0006] In one embodiment, the sensor is a planar gamma camera. As another example, the planar gamma camera is connected to a gantry configured to place the planar gamma camera at different positions relative to the source for detecting the emission.

[0007] The movable attenuator has various embodiments. According to one embodiment, the movable attenuator is a lead or tungsten object. As another embodiment, the movable attenuator can be moved by translation and / or rotation in three dimensions. In another embodiment, the through hole is a slit. In other embodiments, the through hole has holes of different sizes, shapes and / or angles.

[0008] As another embodiment, the movable attenuator is a rotatable cylinder, wherein the source or sensor is positionable within the rotatable cylinder. The driver is configured to rotate the rotatable cylinder. The movable attenuator may have various shapes, such as a plate.

[0009] In one embodiment, the actuator is configured to rock the movable attenuator and / or oscillate the movable attenuator about a normal to the movable attenuator.Other movements may also be used, for example based on the imaging application.

[0010] In one embodiment, the image processor is configured to form a projection based on the emission, and the reconstruction of the spatial distribution is based on the projection. As an example, the projection is a virtual parallel hole collimator projection, and the reconstruction is an iterative reconstruction using the virtual parallel hole collimator projection according to forward and back projection.

[0011] In a second aspect, a method for SPECT is provided. An attenuating object having an inner edge is moved between a patient and a sensor. The inner edge forms a time-coded aperture on the sensor as the movement proceeds. The sensor detects emissions from the patient that pass through the attenuating object, the attenuating object having a different shadow on the sensor due to the time-coded aperture. A representation of the patient is reconstructed from the detected emissions using the time-coded aperture.

[0012] In one embodiment, the attenuating object is rotated and / or translated in three dimensions. Due to the position on the sensor and / or the rotation of the attenuating object, the shadow may be different.

[0013] As another embodiment, the inner edge forms holes with different shapes, sizes and / or angles to generate corresponding shadows.

[0014] In another embodiment, holes in the attenuating object form said edges.The attenuating object moves in three dimensions such that the shape and / or size of the holes in the shadow are different at different times.

[0015] In yet another embodiment, the reconstruction is based on an edge response of the shadow. As another reconstruction embodiment, the reconstruction includes constructing projections at different viewing angles relative to the patient based on the time-encoded aperture based on the detected emissions, and reconstructing based on the projections.

[0016] In a third aspect, an emission tomography system is provided. A radiation blocker has an inner edge that forms an aperture through the radiation blocker. A sensor is configured to detect radiation passing through the aperture when the radiation blocker is at different positions relative to the sensor, the different positions forming a time-coded aperture of the sensor. An image processor is configured to form virtual projections from different views based on the emissions detected by the sensor using the time-coded aperture, and to reconstruct a representation of a patient based on the virtual projections.

[0017] In another embodiment, the holes have different sizes, shapes and / or angles.

[0018] The present invention is defined by the appended claims, and nothing in this section should be taken as limiting those claims.Other aspects and advantages of the present invention are discussed below in conjunction with the preferred embodiments, and may be claimed later, either independently or in combination. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] The components and drawings are not necessarily drawn to scale, emphasis instead being placed upon illustrating the principles of the present invention. Moreover, in the drawings, like reference numerals designate corresponding parts throughout the different views.

[0020] Figure 1 is an embodiment of an emission tomography system having a movable attenuator;

[0021] Figure 2 The diagram shows different shadows on the sensor caused by moving the attenuator with the gap;

[0022] Figure 3 An exemplary attenuator having concentric slot apertures is illustrated;

[0023] Figure 4 An exemplary attenuator having non-concentric slot apertures is illustrated;

[0024] Figure 5 An example of oscillating the attenuator to move in three dimensions is illustrated;

[0025] Figure 6 An exemplary attenuator having an offset hole is illustrated;

[0026] Figure 7 illustrates exemplary movement of a tilt attenuator;

[0027] Figure 8 One embodiment of the attenuator is illustrated as a cylindrical or hollow form;

[0028] Fig. 9 An example of using edge responses to isolate source locations is illustrated;

[0029] Fig.10 is an example graph of a virtual point spread function showing edge response; and

[0030] Fig.11 is a flow chart of an exemplary embodiment of a method for emission tomography imaging using edge response. DETAILED DESCRIPTION

[0031] Any non-local pattern of a coded aperture or physical collimator can be used to probe spatial frequencies. In classical SPECT imaging, a regular degradation pattern (e.g., parallel holes) is used to create a non-local PSF across the field of view (FOV). The result is a strict quality control of the collimator and sensor uniformity, so that an aperture that is smaller in size than the intrinsic resolution is chosen to produce a degraded response to maximize the signal-to-noise ratio (SNR) without increasing the computational burden. This approach can be abandoned in cases where a very local response and temporal encoding and varying collimation are used.

[0032] Emission tomography systems use the virtual system resolution recovered from generalized time-coded aperture imaging data for imaging of discrete or continuous gamma-ray spectra. The concept of time-coded coded aperture is generalized to enable edge-based super-resolution. The edge resolution of a given known attenuation object is used to create a data set that allows super-resolution, distance estimation, and / or tomographic information. The attenuation object provides a coded mask.

[0033] Using edge resolution information and the semi-positive definiteness of the problem, the movement of a three-dimensional attenuator with sharp edges is used to provide emission tomography image formation. Based on the semi-positive definite data, the directionality is extracted from the non-local pattern of the point spread function (PSF) across the field of view (FOV) according to the encoded time-varying aperture pattern.

[0034] The edge response from the time-encoded aperture is used to isolate the holes in the directionality and attenuation objects to increase the number of detected emissions with larger edge lengths, which expands the image formation space. The directional information is extracted more efficiently than with a fixed parallel hole collimator. For near-field tomography, the shape and movement of the attenuation aperture are designed for the application (e.g., a specific movement pattern of the attenuation aperture object based on the imaging purpose). This edge response using a movable attenuator with an internal edge is somewhat an abstraction of the multi-focus concept paired with time encoding.

[0035] Figure 1 An embodiment of an emission tomography system is shown. The emission tomography system is a medical imager, such as a SPECT imaging system. The system is an imaging system for imaging a patient 114 on a bed 104. The emission tomography system uses edge response using a time-coded aperture, which is achieved by moving the aperture with an internal through hole to increase sensitivity and improve resolution.

[0036] The emission tomography system includes a gantry 102, a sensor 106, an attenuator 108, a driver 112, and an image processor 120. Additional, different, or fewer components may be provided. For example, a non-transitory memory is provided for storing detected emissions and / or instructions for execution by the processor 120. As another example, a display is provided for displaying a reconstructed image of the patient 114. In another example, a separate detection processor is provided for binning the detected emissions.

[0037] The gantry 102 is part of a housing. The housing is metal, plastic, fiberglass, carbon (e.g., carbon fiber), and / or another material. The housing forms a patient area (e.g., a bore) into which a patient is positioned for imaging. A bed 104 can move the patient within the patient area to scan different portions of the patient at different times. In other embodiments, a chair or bed is used without a housing forming a bore, such as where the sensor 106 and attenuator 108 are positioned by one or more robotic arms.

[0038] The gantry 102 is a motor, sensor, and / or track used to move the sensor 106 relative to the patient 114, e.g., to capture emissions from different angles and / or positions relative to the patient 114. In alternative embodiments, the bed 104 moves without the gantry (e.g., the sensor 106 is fixed within the housing). In still other alternatives, both the sensor 106 and the bed 104 are fixed during imaging.

[0039] The sensor 106 is configured by structure and / or electronics to detect emitted radiation from within the patient 114. The sensor 106 is configured to detect the location, energy, and time of the impact of the gamma ray. The sensor 106 is a detector, such as a SPECT detector or a gamma camera, without a collimator fixed relative to the sensor. Some of the radiation passes through the hole 202 in the interior of the attenuator 108 and / or passes along the edge around the exterior of the attenuator 108. The sensor 106 detects radiation at different known locations relative to the sensor 106 using the attenuator 108. These different locations form a time-encoded aperture for the sensor 106.

[0040] In one embodiment, the sensor 106 is a SPECT sensor having a plurality of pixelated detector cells. For example, the sensor 106 is a gamma camera. The gamma camera includes one or more semiconductor sensors, such as a pixelated sensor with a detection cell. The sensor 106 is made of a room temperature semiconductor sensor. Another example is an array of silicon photon multiplier cells coupled to a scintillator. The sensor 106 forms an array of sensors or pixelated sensor cells. Anode electrodes and cathode electrodes are disposed on opposite surfaces of the sensor 106. The electrodes have the same spacing as the detection cells and are electrically isolated from each other for separate electrical connections to the detection cells of the sensor 106.

[0041] Any material may be used, such as a scintillator, such as NaI, or a direct converter, such as CZT, CdTe, TlBr, and / or another such material suitable for gamma ray imaging. The sensor 106 is produced with wafer fabrication in any thickness, such as about 5-10 mm for CZT. The sensor 106 is square or has a rectangular shape for the emission detection face. Any size may be used, such as about 5x5 cm. Other shapes besides rectangular or square may also be used, such as triangular or hexagonal.

[0042] The sensor 106 is adjacent to the patient area, for example mounted to the movable gantry 102. The sensor 106 is designed and configured to detect gamma emissions, such as emissions from the patient 114. The gamma camera can be a planar camera connected to the gantry 102 or the housing to place the planar gamma camera at different positions relative to the source to detect emissions. For example, the gantry 102 moves the sensor 106 laterally or parallel to the bed 104, and / or rotates the sensor 106 about a longitudinal axis (i.e., around the bed 104). In other embodiments, a mechanical arm or robotic system is used to move the sensor 106. Alternatively, the sensor 106 is fixed to the housing 102 relative to the patient space.

[0043] The attenuator 108 is lead, tungsten or another material that blocks, reflects or absorbs gamma rays from the emission. These gamma rays are diverted or stopped so that rays that intersect the attenuator 108 do not pass from the patient 114 to the sensor 106. The attenuator 108 is a ray blocker.

[0044] Attenuator 108 is a plate or object having a thickness that blocks radiation. Any shape may be provided for the maximum surface, such as a rectangle, hexagon or triangle. The shape forms outer edges, such as sharp edges. These edges may be rounded or shaped according to the amount of rotation and / or translation relative to the patient.

[0045] The attenuator 108 also includes one or more internal through holes 202. Any number of through holes 202 may be provided, such as one, two, dozens, or hundreds. The through holes 202 form internal edges. These edges are sharp edges (eg, flat), but may be rounded or have other shapes.

[0046] The through-holes 202 may have any shape, size, and / or angle. Figure 2 An example is shown where the holes 202 are formed as slits. The holes 202 may be provided in circular, hexagonal, triangular, arc-shaped, and / or other shapes.

[0047] Rather than having holes sized at or below the resolution of sensor 106, the holes are sized to include at least one dimension that is larger than the resolution of sensor 106. For example, slit 202 may extend over tens or hundreds of detector cells along at least one dimension, or over two dimensions.

[0048] The aperture 202 may have inner edges at right angles to the largest surface of the attenuator 108 (eg, at right angles to the sensor 106, where the largest surface is parallel to the detection surface). These edges may also be at other angles, such as to directionally block or allow emission. Figure 1 Two holes 202 are shown at two different angles (ie, the inner edge has different angles to the largest surface and / or detection face of the sensor 106). Different portions of the edge formed for a given hole 202 may have the same or different angles, such as a cross-section having a trapezoidal shape.

[0049] The holes 202 of the attenuator have the same or different shapes, sizes, edge angles and / or orientations. For example, all holes 202 have the same size, shape, edge angles and edge orientations. As another example, different holes 202 have different sizes, shapes, orientations and / or angles than at least one other hole 202. Figure 2 Three apertures 202 are shown, each having a different size and / or shape. One aperture 202 is angled within the plane of the attenuator 108 relative to the other apertures 202, thereby providing different orientations. Figure 3 An example is shown where the apertures 202 are concentric rings or slots having different widths. Figure 4 An example is shown where the holes 202 are non-concentric rings or slots having different widths and different center locations on the largest face. Figure 6 An example is shown where the apertures 202 are rectangular slots, where different apertures 202 overlap or intersect. Different sizes, orientations, and / or thicknesses may be used.

[0050] By providing an inner edge, more opportunities are provided to characterize the direction from the source to the sensor 106. By providing different sizes, shapes and / or angles, more information can be provided for characterization. Larger and / or more apertures 202 result in more emissions being collected, thereby increasing sensitivity.

[0051] In principle, any three-dimensional (3D) collimation may be used. Different shapes, sizes, edge angles, orientations, and / or combinations of holes 202 may provide different processing (ie, reconstruction) efficiencies. For example, Figure 6 The holes 202 of the attenuator 108 can be an efficient pattern to map into a rectangular form factor with the same aspect ratio as the sensor 106. Any 3D collimator shape can be created by stacking 2D shapes. For example, a rectangular hole collimator can be created by plates with slits perpendicular to each other ("slit slats"), and instead of moving the sensor with the collimator to obtain different viewing angles, simply move the "slits" in front of the "slats", creating a moving pattern on the detection plane of the sensor.

[0052] Figure 8 Another embodiment of an attenuator 108 is shown. The attenuator 108 is a hollow cylinder having a slit for the hole 202. Although shown as parallel slits of the same size and shape, holes of different orientations, sizes, shapes, or edge angles may also be used. Other hollow shapes other than cylinders may also be used, such as a rectangular parallelepiped shape. The sensor 106 or source (e.g., patient 114) is located within the cylindrical attenuator 108. The cylinder 108 can be rotated about the source or sensor 106 to provide movement relative to the sensor 106. With the sensor 106 within the attenuator 108, ecto tomography can be provided with a small footprint, allowing the sensor 106 and attenuator 108 to be moved around the patient robotically or fixed relative to the patient without the need for a large housing and hole (i.e., the patient can be sitting in a chair or lying in their bed).

[0053] Reference again Figure 1 , the driver 112 is a motor, such as a servo system, an electric motor, a pneumatic compressor, an actuator, a hydraulic pump, or another motor for applying force to the attenuator 108. Gears, pulleys, guides, clutches, racks and pinions, tubes, and / or other mechanisms transmit force from a motor, such as a rotational force from an electric motor, to the attenuator 108. The driver 112 is configured to move the movable attenuator 108 through control and mechanical connections. The driver 112 encodes the aperture and is therefore an encoded driver. The driver 112 positions the attenuator 108 at a known position and / or with a known movement. This encoding provides a positional relationship between the attenuator 108 and the sensor 106.

[0054] In one embodiment, the actuator 112 is part of a robotic arm. The robotic arm positions and moves the attenuator 108. In other embodiments, the attenuator 108 is connected to a guide or gear so as to be repeatedly moved in a controlled manner. The actuator 112 is configured to move the attenuator 108 with the inner edge and possibly the outer edge of the hole 202 between the sensor 106 and the patient 114 (i.e., the projectile object).

[0055] The driver 112 moves the attenuator 108 in any degree of freedom, such as one to six degrees of freedom. In one embodiment, the movement is in three dimensions, such as three rotational degrees of freedom, three translational degrees of freedom, or any three rotational degrees of freedom and translational degrees of freedom.

[0056] Figure 2 Some examples are shown. A shadow 200 of the attenuator 108 on the sensor 106 is shown. In this example, three holes 202 and the outer edge create the shadow 200 on the sensor 106. In the case where the attenuator 108 is larger than the sensor 106, then the shadow will include the holes 202 (i.e., the inner edge), but not all or any of the outer edges.

[0057] The upper left figure shows the shadow 200, where the largest surface of the attenuator 108 is parallel to the sensor face of the sensor 106 (i.e., the normals of both are parallel to each other and perpendicular to the page). The attenuator 108 can be rotated about a normal centered on the attenuator 108 or offset to another position. The upper right shows a rotation or orientation change about the center of the attenuator 108 and the shadow 200 and a slight translation to the left. The lower left shows the shadow 200 translated to different positions along the vertical dimension and slightly along the horizontal dimension. The lower right shows the shadow 200 produced by tilting the attenuator 108 about a horizontal axis on the page, so that one edge is closer to the sensor 106 than the opposite edge. As a result of this tilting about the horizontal axis, the shadow 200 includes a narrower gap from the hole 202 when viewed from the normal direction of the sensor face. Other movements or combinations of movements may also be provided.

[0058] Figure 8 The rotational motion of the cylinder formed by the attenuator 108 is shown. The driver 112 rotates the attenuator 108 about a central axis or an offset axis to move the shadow from the aperture 202 relative to the sensor 106. The sensor 106 may also be moved, such as translated along the axis of the cylinder and / or tilted about an axis perpendicular to the axis of the cylinder.

[0059] Figure 7The tilting motion of the attenuator 108 is shown. The attenuator 108 with the hole 202 is tilted for the cosine alpha effect. The attenuator 108 is rotated about a central axis parallel to the largest surface of the attenuator. Other axes of rotation may also be used. The attenuator 108 may be rotated to provide a rocking motion. The attenuator 108 may be cyclically rotated in the opposite direction to further rock.

[0060] Figure 5 A wobbling attenuator 108 is shown. The attenuator 108 wobbles about a normal to the attenuator 108. The wobbling may be along other axes, parallel or non-parallel to the normal. As a plate with a hole 202, the attenuator 108 wobbles so that the normal vector precesses at a certain opening angle and frequency ω.

[0061] Other motions and / or combinations of motions may be provided. The motion has any frequency, speed and / or range. A change in motion may be provided, such as changing speed, frequency or range. The motion may be continuous or may be operated as a step function. For example, the attenuator 108 is held at a given position for a period of time, such as 5 minutes, and then moved to another position where the attenuator 108 is held for the same or different time period. Any number of steps or any number of discrete holding positions may be used, such as two, tens or hundreds. Any holding time may be used, such as a few seconds or minutes. The motion is used to create a strong local variation pattern that detects spatial frequency.

[0062] Figure 1 The image processor 120 is a general purpose processor, an artificial intelligence processor or accelerator, a tensor processor, a digital signal processor, a graphics processing unit, an application specific integrated circuit, a field programmable gate array, a digital circuit, an analog circuit, a combination thereof, or another now known or later developed device for processing emission information and / or reconstructing an image based on detected emissions (e.g., the location, energy, and / or time of incident radiation). The image processor 120 is a single device, a plurality of devices, or a network. For more than one device, parallel or sequential processing partitioning may be used. The different devices that make up the image processor 120 may perform different functions, such as one processor for controlling the movement of the attenuator 108 and another processor for forming projections based on detected emissions (i.e., location, energy, and / or time) and a time-encoded aperture and for reconstructing based on the projections. In one embodiment, the image processor 120 is a control processor or other processor of the medical imaging system. In other embodiments, the image processor 120 is part of a separate workstation, server, or computer.

[0063] The image processor 120 operates according to stored instructions to perform various actions described herein, such as Fig.11The image processor 120 is configured by software, firmware and / or hardware to perform these actions.

[0064] The image processor 120 is configured to reconstruct an object from the detected emissions. The location, time, and energy of the emissions are used to reconstruct the object. The spatial distribution of the emission source, such as a radiopharmaceutical in the patient 114, is reconstructed. The image processor 120 reconstructs the spatial distribution of the emission source detected by the sensor 106, wherein the movable attenuator 108 is in different positions due to movement by the driver 112.

[0065] The time-encoded aperture is used to determine directionality in the reconstruction, since the attenuator 108 generates local patterns (ie, shadows 200) at different times due to the movement between the emission source and the sensor 106. The moving shadows 200 cast by the apertures 202 on the sensor 106 are used in the reconstruction.

[0066] Fig. 9 An example based on the outer edge of the attenuator 108 is shown. The same principle applies to the inner edge. By having multiple edges, more information can be obtained for a given position of the attenuator 108 relative to the sensor 106.

[0067] Source 900 emits at different times. Attenuator 108 is at different positions relative to sensor 106 at these different times. Due to the different positions of attenuator 108, the position of source 900 can be resolved based on the position of the edge of attenuator 108 and the detection position on sensor 106. Triangulation and time-coded aperture provide the position of source 900 in three dimensions. Shadows determined by the shape and timing of attenuator 108 (assumed to be a known variation of a rigid body or non-rigid body) indicate directionality.

[0068] The known detection position of the sensor 106 and the position of the attenuator 108 allow triangulation. If the position of the attenuator 108 is unknown but the shape and movement are known, then the collection of shadows 200 is sufficient to determine the location of the source 900. Since many emissions from various sources occur, tomography is used rather than trying to resolve each source individually. Statistics can constrain the optimization to tomographically reconstructing the source 900. The optimization includes the auxiliary conditions mentioned above and solves the maximum information problem (MIQ), where directionality is extracted from the non-local pattern of the PSF encoding the time-varying aperture pattern across the field of view based on semi-positive definite detection event data.

[0069] The image processor 120 is configured to reconstruct. The detected emission has a time and a position. Energy information may be included, for example, for filtering the emission to a specific energy or energy range. Optimization is applied to minimize the difference between the detected emission and the distribution of the source that will cause the emission. The optimization includes forward and backward projections between the emission or sensor space and the object or image space. These projections include a system model. The system model includes a time-coded aperture (e.g., the position and orientation of the attenuator 108 relative to the sensor 106). The physics of the local pattern (shadow 200) may be part of the system model. The point spread function determined due to the time-coded aperture can be used in the reconstruction. By iterative optimization, the difference is minimized until a reconstruction through the pixels or voxels of the object is produced. Various optimizations can be used, such as different optimizations used for SPECT.

[0070] Reconstruction may be performed in other ways. In one embodiment, the image processor 120 forms virtual projections from different views. A representation of the patient 114 (i.e., the distribution of sources within the patient 114) is reconstructed from these virtual projections. These virtual projections are formed from the emissions detected by the sensor 106 using a time-encoded aperture. The emission data is re-binned, re-sampled, and / or collected for different angles or views to form the projections. The projections are formed from the emissions, and the reconstruction of the spatial distribution is from these projections.

[0071] The virtual PSF is recovered by measuring the edge response of the attenuator 108 on the sensor 106 (shadow 200). The time encoding is extended from only a small movement in front of the sensor 106 to any movement of a large number of apertures (one or more shapes and / or sizes of holes 202), which produces a different pattern at each static view on the sensor 106. For example, a plate with a slit can be tilted, rotated and / or moved in front of the sensor 106, thereby forming k different patterns. Since the motion is known and it is also known that the patient 114 does not change during the dwell time (quasi-stable, where the sampling time is determined by the required contrast, noise, etc.), a virtual PSF is constructed. This virtual PSF simulates a non-local better resolution PSF. The virtual PSF relies on the following inversion:

[0072] 1 / 2(Sqrt[1 / \[Sigma]1^2]\[Sigma]1+Sqrt[1 / \[Sigma]2^2]\[Sigma]2+

[0073] Erf[(y-\[Mu]) / (Sqrt[2]\[Sigma]1)]+ERF[(y-\[Mu]) / (Sqrt[2]\[Sigma]2)]).

[0074] Where sigma 1 and 2 define the Gaussian curve, ERF is the error function based on the integration of the Gaussian distribution, and mu is the linear attenuation coefficient. Fig.10 An example graph of a virtual PSF is shown. The PSF models sharp edges to determine directionality.

[0075] In one embodiment, the projections are formed as virtual parallel hole collimator projections. The detected emission and time coded apertures are used to determine projections with common directionality for each different view relative to the patient 114. As a convolution PSF ( Fig.10 The result of the Gaussian distribution with sigma1, sigma2 in the example of ) is restored to a quasi-planar projection of a conventional parallel hole collimator at a viewing angle. The same operation is repeated at different viewing angles until the tomography conditions of Orlov, Tuy and Nyquist are met. A set of projection views as if produced by a very high resolution collimator is restored, but with a much larger aperture. Since the directionality is based on the edge response, the resolution may be higher. Since the aperture (hole 202) is larger than that of a parallel hole collimator, a higher sensitivity is provided. Other projections suitable for tomography can be formed in addition to the parallel hole collimator projection. The viewing angle requirements can be relaxed while still meeting the tomography conditions.

[0076] The image processor 120 uses the projections for iterative reconstruction. For example, forward and reverse projections are used to reconstruct virtual parallel hole collimator projections. Any emission tomography or SPECT reconstruction now known or later developed can be used to reconstruct from the projections. These projections represent the direction counts from the gamma camera as if provided by the collimator. SPECT iterative reconstruction is performed using a virtual PSF.

[0077] This reconstruction embodiment uses a two-step process. First, a virtual projection (e.g., a virtual parallel hole collimator projection image) is restored. Second, reconstruction is performed on the virtual projection. For the first step, the local pattern created can be restored as a virtual non-local image formation. Artificial intelligence (AI) (e.g., a machine learning model, such as a deep learning model) can be used to form a projection based on the emission data. The time-coded aperture can be used as an input to the AI ​​together with the emission data, or the AI ​​can be trained for a known time-coded aperture, thus inputting separate emission data. The AI ​​outputs one or more projections. The Choquet integral can be used to model the complex decision-making process of the observer and thereby optimize the image formation design.

[0078] Fig.11One embodiment of a flow chart of a method for emission tomography (e.g., SPECT) is shown. By moving the attenuator and / or the sensor relative to each other, a time-coded aperture is formed. By including holes in the attenuator, more information is provided for edge response measurements. Since the directions are less restricted, reconstruction uses a staged approach in which virtual projections are formed and then the object or image is reconstructed from the virtual projections. In another reconstruction method, optimization can be used that uses the time-coded aperture as part of the system model.

[0079] The method is implemented by an emission tomography imager or system (e.g., a SPECT system). A motor moves the attenuator, and a sensor detects emission using the attenuator at different positions relative to the sensor. An image processor reconstructs based on the detected emission and a time-coded aperture (e.g., a pattern of shadows from the attenuator). The image processor generates an image of the reconstructed object, which is displayed by a display device or screen. Other components may be used to perform and / or assist in any of the actions.

[0080] These actions are performed in the order shown (i.e., from top to bottom or in numerical order) or in another order. Actions 1102 and 1104 are performed iteratively, such as moving the attenuator, then detecting, then moving, detecting, and so on, for any number of cycles. Action 1104 may be performed first, and then the attenuator is moved in action 1102, or vice versa.

[0081] Additional, different, or fewer actions may be provided. For example, actions for moving a sensor, positioning a patient, and / or three-dimensional rendering according to a reconstructed volume distribution may be included. As another example, display action 1112 is not performed, such as where the image or reconstruction is stored or transmitted for storage in a radiology report, an electronic patient medical record, or a picture archiving and communication system (PACS).

[0082] In act 1102, an attenuating object (e.g., an attenuator or a radiation blocker) is moved. The attenuating object has an inner edge. The object is moved between the patient and the sensor. Due to the movement, the inner edge with or without the outer edge forms a time-encoded aperture on the sensor. The pattern or shadow from the attenuating object is moved two or more times, thereby providing a time-encoded aperture. The movement causes the inner edge and any outer edge from the aperture to have different positions, shapes, sizes, orientations, and / or angles (see Figure 2 ).

[0083] The motion is rotation and / or translation in one or more (e.g., three) dimensions. Movement by translation or rotation in three dimensions allows for more variation in the shadow. Movement with both rotation and translation around three dimensions creates even more variation. Where one or more holes may move or change, additional variation in the shadow is provided. Furthermore, moving the sensor may also contribute further variation. The shape and / or size of the hole in the shadow on the sensor may be different at different times.

[0084] The movement may be by translation and / or rotation in a plane parallel to the detection surface of the sensor. The movement may be translation, tilt or swing outward from the plane. In another embodiment, the movement is a rotation of the attenuated object around the sensor.

[0085] In act 1104, the sensor detects emissions from the patient. Some emissions pass through the sensor. Other emissions are blocked by the attenuator. Other emissions pass through the attenuator, such as through the exterior or through a hole, to the sensor. The attenuator casts a shadow on the sensor based on the emissions.

[0086] Detection is performed with the attenuator in a given position. Then, detection is performed with the attenuator in a different position. Any detection period can be used. The energy, time and position on the sensor of each detected emission are used to identify the detection event. When multiple emissions occur, counts at different positions on the sensor are performed for a given attenuator position.

[0087] Since the detected emissions are only incident rays that pass through the attenuator, different shadows are produced by the attenuator at different positions. The detected events reflect these shadows, allowing edge responses. Due to internal edges, a greater number of events are detected and more edges are provided to determine the directionality due to edge responses. The time-coded aperture and corresponding detection events are recorded for each position of the aperture formed by the attenuator. Based on the detection by the sensor, the movement of the attenuating object results in different shadows on the sensor. Due to the movement of action 1102, the orientation and / or position of the attenuating object relative to the sensor is different at different times.

[0088] In act 1106, the image processor reconstructs a representation of the patient from the detected emissions using a time-encoded aperture. The edge response of the shadow is used to determine or limit the directionality in the optimization. The edges limit the angles to a certain range of angles. By having edges at different locations relative to the sensor at different times, the edge response indicates the location of the source based on the detected location on the sensor. The representation is reconstructed from the edge response of the shadow of the attenuated object on the sensor.

[0089] In one embodiment, an optimization is used where shadows or time coded apertures are part of the system model. The spatial distribution of sources within the patient is solved using detected events from different times and the time coded aperture.

[0090] In another embodiment, a two-stage approach represented by actions 1108 and 1110 is used. In action 1108, projections at different viewing angles relative to the patient are constructed. These projections are constructed based on the detected emissions and based on the time-encoded aperture. For example, a virtual PSF is created by using an integral of a Gaussian model. Given a known non-negative condition, the virtual PSF from different directions is determined by ray tracing and careful recording of signal changes. In action 1110, the projections are used as samples or bin counts from the sensor at different views. An iterative optimization is performed using the projections as input. The iterative optimization solves for the spatial distribution of those sources based on the projections of the emissions from those sources.

[0091] In act 1112, an image is generated from the reconstruction. The spatial distribution represents the distribution of the sources in a plane or volume. The representation is reformatted for display as an image for a two-dimensional display. For a two-dimensional representation, the scan conversion is reformatted to the resolution and / or dynamic range of the display. For a three-dimensional representation, the voxels are rendered as a two-dimensional image, for example using volume or surface rendering.

[0092] The resulting image is displayed on a display screen. The physician can view the location and / or intensity of radiopharmaceutical uptake by the patient's tissue. Hot spots or hot spot locations indicate the function of the tissue, allowing the physician to identify areas of dysfunction or concern for diagnosis and / or treatment.

[0093] Instead of using a sensor with a fixed collimator, the combination can be moved to detect from different angles, providing relative motion of the attenuator relative to the sensor and even pattern changes. The attenuator casts a shadow on the sensor. Since the attenuator moves in a known manner (e.g., translates, rotates, and / or deforms), the shadow of the attenuator on the sensor changes, resulting in a changing shadow pattern on the sensor. By including multiple holes and / or edges with different known sizes, shapes, and angles, many emissions pass through the attenuator, and additional information is generated by the edges. The emission pattern can be inferred by observing from different directions toward the source and also collecting information from different shadows. More signals and the resulting information are used together with the known aperture encoding to solve the distribution of emitters in the source (patient). Instead of capturing more viewing angles by looking at the collimator only in front and rotating the sensor and collimator together, the sensor can remain stationary to capture information due to the movement of the attenuator.

[0094] Although the present invention has been described above by reference to various embodiments, many changes and modifications may be made without departing from the scope of the present invention. Therefore, the foregoing detailed description is intended to be regarded as illustrative rather than restrictive, and it is to be understood that the appended claims, including all equivalent forms, are intended to define the spirit and scope of the present invention.

Claims

1. An emission tomography system, comprising: a sensor configured to detect the position, energy, and timing of an impact of a gamma ray; a movable attenuator having one or more internal through holes, the movable attenuator being movable relative to the sensor; a driver configured to move the movable attenuator; as well as An image processor configured to reconstruct the spatial distribution of the emission detected by the sensor when the movable attenuator is in different positions due to movement by the actuator, the movable attenuator being between the source of the emission and the sensor so that the moving shadow of the through-hole is projected on the sensor.

2. The emission tomography system according to claim 1, wherein: The sensor comprises a planar gamma camera.

3. The emission tomography system according to claim 2, wherein: The planar gamma camera is connected to a gantry configured to place the planar gamma camera at different positions relative to the source for detecting the emissions.

4. The emission tomography system according to claim 1, wherein: The movable attenuator comprises a lead or tungsten object.

5. The emission tomography system according to claim 1, wherein: The movable attenuator can be moved by translation and / or rotation in three dimensions.

6. The emission tomography system according to claim 1, wherein: The through hole includes a slit.

7. The emission tomography system according to claim 1, wherein: The through holes include holes of different sizes, shapes and / or angles.

8. The emission tomography system according to claim 1, wherein: The movable attenuator comprises a rotatable cylinder, wherein the source or the sensor is positionable within the rotatable cylinder, and the driver is configured to rotate the rotatable cylinder.

9. The emission tomography system according to claim 1, wherein: The driver is configured to rock the movable attenuator.

10. The emission tomography system according to claim 1, wherein: The driver is configured to oscillate the movable attenuator about a normal to the movable attenuator.

11. The emission tomography system according to claim 1, wherein: The image processor is configured to form projections from the emissions, and the reconstruction of the spatial distribution is from the projections.

12. The emission tomography system according to claim 11, wherein: The projections are virtual parallel-hole collimator projections, and wherein the reconstruction is an iterative reconstruction using the virtual parallel-hole collimator projections as forward and backward projections.

13. A method for single photon emission computed tomography (SPECT), the method comprising: moving an attenuating object having an inner edge between the patient and the sensor, the inner edge forming a time-encoded aperture on the sensor as the object is moved; detecting, by the sensor, emissions from the patient that pass through the attenuating object, the attenuating object having a different shadow on the sensor due to the time-encoded aperture; as well as A representation of the patient is reconstructed from the detected emissions using the time encoding aperture.

14. The method according to claim 13, wherein: Moving the attenuating object includes rotating and / or translating in three dimensions, and wherein detecting includes detecting using shadows that differ due to a position on the sensor and / or a rotation of the attenuating object.

15. The method according to claim 13, wherein: Moving the attenuating object includes moving with holes having different shapes, sizes and / or angles formed in the inner edge.

16. The method according to claim 13, wherein: The hole in the attenuating object forms the edge, and wherein moving comprises moving in three dimensions such that the shape and / or size of the hole in the shadow is different at different times.

17. The method according to claim 13, wherein: The reconstruction comprises recovering a virtual point spread function from the edge response of the shadow.

18. The method according to claim 13, wherein: Reconstructing includes constructing projections at different viewing angles relative to the patient from the detected emissions and based on the time encoding aperture, and reconstructing from the projections.

19. An emission tomography system comprising: a radiation blocker having an inner edge defining an aperture therethrough; a sensor configured to detect radiation passing through the aperture with the radiation blocker at different positions relative to the sensor, the different positions forming a time-encoded aperture of the sensor; as well as An image processor is configured to form virtual projections from different views from the emissions detected by the sensor using the time-encoded aperture, and to reconstruct a representation of the patient from the virtual projections.

20. The emission tomography system of claim 19, wherein: The holes have different sizes, shapes and / or angles.

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