Radiation tomography using generalized time-coded aperture imaging

Abstract

Regarding tomography, more radiation is detected. To detect a large number of radiations and provide better resolution than that provided by a parallel hole collimator, the collimator is replaced by an attenuator having outer and inner edges. Instead of forcing directivity, large holes having different shapes are used to enable detection of more radiation. By operating the attenuator, differences in shadows on the sensor are used as time-coded apertures to reconstruct the radiation source with higher resolution and sensitivity than when a fixed parallel hole collimator is used.

Description

Technical Field

[0001] One aspect of the present invention relates to emission tomography (e.g., single photon emission computed tomography (SPECT), positron emission tomography (PET), or another type of imaging using a gamma camera).

Background Art

[0002] High-efficiency tomography of gamma rays emitted from radioisotopes is typically performed from a discrete spectrum of greater than about 50 keV to less than 511 keV using a physical collimator. This collimator only allows gamma rays to enter the sensor in a specific direction (i.e., a parallel hole collimator) to generate a projection image (i.e., an image detected by a gamma camera). This process involves a trade-off between the high directional accuracy of the collimator and the sensitivity. The small directional holes of the collimator block a lot of radiation. This results in noisy data due to this low sensitivity, which makes tomography difficult as an inverse problem and causes artifacts. For tomography reconstruction, high directional accuracy is achieved with the collimator at a high cost in terms of sensitivity.

[0003] Medical emission tomography is used for various specific categories of tasks: 1. Detecting lesions (the "detection task"), where a lesion is an abnormal accumulation that is too high or too low compared to what is predicted based on anatomy, physiology, and the administered radiopharmaceutical, 2. Characterizing lesions or accumulation patterns by descriptive statistics such as average accumulation density. In some cases, the ability to spatially resolve (spatial resolution) is important, in other cases, resolving the signal in a noisy background, i.e., contrast resolution, is important, and in still other cases, resolving the signal as a temporal accumulation change (the "temporal resolution") is important. Usually, a statistical-based criterion for separating the signal from the noise with a certain level of confidence is used. The fundamental trade-off between direction ("resolution") and presence information ("sensitivity") remains.

[0004] This fundamental compromise can be influenced by imposing or utilizing specific auxiliary physical conditions for image formation. Contrast and attenuation patterns can be used as sources of information derived from utilizing specific physical conditions for image formation. Edge encoding has been proposed. Time-dependent variable patterns, such as super-resolution time multiplexing, are being considered. Compressed sensing is used. If the use of additional information more than compensates for the loss of directional information, further increases in sensitivity may lead to better tomographic imaging for specific clinical tasks. [Overview of the project]

[0005] As a preface, the preferred embodiments described below include methods, systems, and sensors for radiometric tomography. The collimator is replaced by an attenuator having outer and inner edges to detect more radiation and / or provide better resolution than that provided by a parallel-hole collimator. Instead of forcing directivity (directionality), a larger hole with a different shape is used to enable the detection of more radiation. By operating the attenuator, the difference in shading on the sensor is used as a time-coded aperture to reconstruct the radiation source with higher resolution and sensitivity than when using a fixed parallel-hole collimator. Directional information required for a particular task is obtained based on moving shading.

[0006] In a first embodiment, a radiometric 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 drive unit is configured to operate the movable attenuator. An image processor is configured to reconstruct the spatial distribution of radiation detected by the sensor using the movable attenuator, which is in different positions (positions and orientations) due to movement by the drive unit. The movable attenuator is located between the radiation source and the sensor such that the moving shadow of the through-hole is projected onto the sensor.

[0007] In one embodiment, the sensor is a planar gamma camera. In a further example, the planar gamma camera is connected to a gantry configured to position the planar gamma camera at various locations relative to the radiation source for radiation detection.

[0008] Movable attenuators can take various forms. In one form, the movable attenuator is an object made of lead or tungsten. In a further form, the movable attenuator is operable by translation and / or rotation in three dimensions. In another form, the through-hole is a slit. In yet another form, the through-hole has different sizes, shapes, and / or hole angles.

[0009] In a further form, the movable attenuator is a rotatable cylinder, in which case the radiation source or sensor can be placed inside the rotatable cylinder. The drive mechanism is configured to rotate the rotatable cylinder. The movable attenuator can have various shapes, such as plates.

[0010] In one embodiment, the drive device is configured to swing the movable attenuator and / or to oscillate the movable attenuator around a perpendicular (normal) to the movable attenuator. Other movements may be used depending on the imaging application, for example.

[0011] In one embodiment, the image processor is configured to form a projection from radiation, and the reconstruction of the spatial distribution is from that projection. For example, the projection is a virtual parallel-hole collimator projection, and the reconstruction is an iterative reconstruction (sequential reconstruction) using the virtual parallel-hole collimator projection in forward and back projections.

[0012] In a second embodiment, a SPECT method is provided. An attenuator having an inner edge is moved between the patient and the sensor. This moving inner edge forms a time-coded aperture on the sensor. The sensor detects radiation passing from the patient through the attenuator, which is shaded differently on the sensor by the time-coded aperture. The patient's representation is reconstructed from the radiation detected using the time-coded aperture.

[0013] In one configuration, the damping element is rotated and / or translated in three dimensions. The shading varies depending on the position on the sensor and / or the rotation of the damping element.

[0014] In another form, the inner edges form holes with different shapes, sizes, and / or angles, resulting in corresponding shadows.

[0015] In another form, the holes in the attenuator form edges. The attenuator operates in three dimensions such that the shape and / or size of the holes in the shadows vary over time.

[0016] In yet another form, reconstruction is from the edge response of the shadows. Another form of reconstruction includes constructing projections at separate field angles relative to the patient based on detected radiation and time-coded aperture, and reconstructing from the projections.

[0017] In a third embodiment, a radiometric tomography system is provided. A radiation shield has an inner edge that forms a hole through the radiation shield. A sensor is configured to detect radiation passing through the hole when the radiation shield is in different arrangements relative to the sensor. These different arrangements form a time-coded aperture for the sensor. An image processor is configured to use the time-coded aperture to form a virtual projection from different views of the radiation detected by the sensor, and to reconstruct a representation of the patient from the virtual projection.

[0018] In further forms, the holes may have different sizes, shapes, and / or angles.

[0019] The present invention is defined by its claims, and nothing in this section should be considered to limit the claims. Further aspects and advantages of the present invention are described below in conjunction with preferred embodiments and may be claimed independently or in combination thereafter. [Brief explanation of the drawing]

[0020] The components and the drawings are not necessarily to scale, rather, exaggerations are made for the purpose of explaining the principles of the present invention. Further, in the drawings, like reference numerals indicate corresponding parts throughout the figures. [Figure 1] An embodiment of a tomographic imaging system having a movable attenuator. [Figure 2] Shows different shadows on the sensor by operating an attenuator having a slit. [Figure 3] Shows an example of an attenuator having concentric slit holes. [Figure 4] Shows an example of an attenuator having non-concentric slit holes. [Figure 5] Shows an example of swinging an attenuator for three-dimensional operation. [Figure 6] Shows an example of an attenuator having an offset hole. [Figure 7] Shows an example of the operation of tilting an attenuator. [Figure 8] Shows an embodiment of an attenuator in a cylindrical or hollow form. [Figure 9] Shows an example of the use of edge response for separating radiation source positions. [Figure 10] An example of a graph showing a virtual point spread function related to edge response. [Figure 11] An example of a flowchart of an imaging method of tomographic imaging using edge response.

Embodiments for Carrying Out the Invention

[0021] The non-local pattern of a coded aperture or physical collimator can be used to explore spatial frequencies. In the case of standard SPECT imaging, a regular degenerate pattern (e.g., parallel holes) is used to generate a non-local PSF across the entire field of view (FOV). The result is a strict quality control regarding the uniformity of the collimator and sensor, and an aperture smaller than the original resolution is selected to generate a degenerate response that maximizes the signal-to-noise ratio (SNR) without adding computational load. This approach can be abandoned with the use of a very local response and time-coded varying collimation.

[0022] A tomographic imaging system uses a virtual system resolution restored from generalized time-coded aperture imaging data for imaging discrete or continuous gamma-ray spectra. The concept of time-coded coded apertures is generalized to enable edge-based super-resolution. Edge resolution assuming a known attenuator is used to generate a dataset that takes into account super-resolution, distance measurement, and / or tomographic information. The attenuator provides a coded mask.

[0023] Using edge resolution information and the positive semi-definiteness of the problem, tomographic image formation is provided using the operation of a three-dimensional attenuator with sharp edges. The directivity is extracted from the non-local pattern of the point spread function (PSF) across the entire field of view (FOV) from a coded time-varying aperture pattern based on positive semi-definite data.

[0024] The directivity and holes in the attenuator are separated using the edge response from the time-coded aperture, and the imaging space is expanded by increasing the detected radiation count with long edges. The directivity information is extracted more efficiently than with a fixed parallel hole collimator. In the case of near-field tomography, the shape and operation of the attenuation aperture are designed for each application (e.g., a specific operation pattern of the attenuation aperture body based on the purpose of imaging). The edge response using a movable attenuator with an inner edge is, in a sense, an abstract concept of a multi-focus concept paired with time coding.

[0025] Figure 1 shows an embodiment of a tomography system. A tomography system is a medical imaging device such as a SPECT imaging system. This system is an imaging system for imaging a patient 114 on a bed 104. The tomography system uses edge response with a time-coded aperture by operating an aperture with an internal through-hole to increase sensitivity and sharpen resolution.

[0026] The radiography system includes a gantry 102, a sensor 106, an attenuator 108, a drive unit 112, and an image processor 120. Additional, different, or fewer components may be provided. For example, non-temporary memory is provided for storing detected radiation and / or instructions executed by the processor 120. Another example is the provision of a display for displaying reconstructed images of the patient 114. Another example is the provision of a separate detection processor for binning the detected radiation.

[0027] The gantry 102 is part of the housing. The housing is made of metal, plastic, fiberglass, carbon (e.g., carbon fiber), and / or another material. The housing forms a patient area (e.g., a bore) where the patient is positioned during imaging. The bed 104 can move the patient within the patient area to scan different parts of the patient at different times. In other embodiments, a chair or bed without a housing forming a bore is used, such as when the sensor 106 and attenuator 108 are positioned by one or more robotic arms.

[0028] The gantry 102 is a motor, sensor, and / or track that moves the sensor 106 relative to the patient 114, for example, to capture radiation from different angles and / or positions relative to the patient 114. In an alternative embodiment, the bed 104 moves without a gantry (for example, the sensor 106 is fixed within a housing). In yet another alternative embodiment, both the sensor 106 and the bed 104 are fixed during imaging.

[0029] Sensor 106 consists of a structure and / or electronic equipment for detecting radiation from radiation within patient 114. Sensor 106 is configured to detect the location, energy, and time of gamma ray collisions. Sensor 106 is a detector such as a SPECT detector or gamma camera and does not require a collimator fixed to the sensor. A portion of the radiation passes through the inner hole 202 of the attenuator 108 and / or along the outer edge around the attenuator 108. Sensor 106 detects radiation using the attenuator 108 in different known arrangements relative to sensor 106. These different arrangements form a time-coded aperture relative to sensor 106.

[0030] In one embodiment, sensor 106 is a SPECT sensor having a number of pixelated detector cells. For example, sensor 106 is a gamma camera. The gamma camera includes one or more semiconductor sensors, such as pixelated sensors having detection cells. Sensor 106 consists of room-temperature semiconductor sensors. In another example, it is an array of silicon photon multiplier cells coupled to a scintillator. Sensor 106 forms an array of sensors or pixelated sensor cells. Anode and cathode electrodes are provided on both sides of sensor 106. These electrodes have the same pitch as the detection cells and are electrically isolated from each other for separate electrical connections of sensor 106 to the detection cells.

[0031] Any material can be used, such as a scintillator like NaI, or a direct converter like CZT, CdTe, TlBr, and / or other similar materials suitable for gamma-ray imaging. Sensor 106 is manufactured by wafer fabrication of any thickness, such as about 5-10 mm in the case of CZT. Sensor 106 has a radiating detection surface that is either square or rectangular. Any size can be used, such as about 5 cm x 5 cm. Shapes other than rectangles or squares, such as triangles or hexagons, may also be used.

[0032] Sensor 106 is adjacent to the patient area, for example, by being mounted on a movable gantry 102. Sensor 106 is designed and configured to detect gamma radiation, such as radiation from the patient 114. This gamma camera is a planar camera connected to the gantry 102 or housing, and the planar gamma camera is positioned at different locations relative to the radiation source to detect the radiation. For example, the gantry 102 moves sensor 106 laterally or parallel to the bed 104 and / or rotates sensor 106 around its longitudinal axis (i.e., around the bed 104). In other embodiments, a robotic arm or system is used to move sensor 106. Alternatively, sensor 106 is fixed to the housing 102 relative to the patient space.

[0033] The attenuator 108 is made of lead, tungsten, or other material that blocks, reflects, or absorbs gamma rays from radiation. Gamma rays are redirected or stopped so that radiation crossing the attenuator 108 does not pass from patient 114 to sensor 106. The attenuator 108 is a radiation shield.

[0034] The attenuator 108 is a plate or object with a thickness that blocks radiation. Any shape, such as a rectangle, hexagon, or triangle, is provided on the maximum surface area. This shape forms an outer edge, such as a sharp edge. The edge is rounded or shaped depending on the amount of rotational and / or translational motion relative to the patient.

[0035] The attenuator 108 also includes one or more internal through-holes 202. Any number of through-holes 202 are provided, such as one, two, tens, or hundreds. The through-holes 202 form an internal edge. This edge is a sharp edge (e.g., flat / planar), but may have other shapes, such as being rounded.

[0036] The through-hole 202 may have any shape, size, and / or angle. Figure 2 shows an example where the hole 202 is formed as a slit. The hole 202 may be circular, hexagonal, triangular, curved, and / or other shapes.

[0037] Rather than having a hole with a size equal to or less than the resolution of sensor 106, the hole is sized to include at least one dimension greater than the resolution of sensor 106. For example, the slit 202 extends across tens or hundreds of detector cells along at least one dimension or across two dimensions.

[0038] The hole 202 has an inner edge perpendicular to the maximum surface of the attenuator 108 (for example, perpendicular to the sensor 106 when the maximum surface is parallel to the detection surface). The edge may be at a different angle to block or allow radiation to pass in a directional manner. Figure 1 shows two holes 202 with two different angles (i.e., the inner edges are at different angles with respect to the maximum surface and / or detection surface of the sensor 106). Each portion of the edge formed for a given hole 202 has the same or different angles, such as having a trapezoidal shape in cross-section.

[0039] The holes 202 of the attenuator may have the same or different shapes, sizes, edge angles, and / or orientations. For example, all holes 202 may have the same size, shape, edge angle, and edge orientation. Another example is when each hole 202 has a different size, shape, orientation, and / or angle from at least one other hole 202. Figure 2 shows three holes 202, each having a different size and / or shape. One hole 202 is tilted in the plane of the attenuator 108 relative to the other holes 202, showing a different orientation. Figure 3 shows an example where the holes 202 are concentric rings or slits with different widths. Figure 4 shows an example where the holes 202 are non-concentric rings or slits with different widths and different center positions on their widest faces. Figure 6 shows an example where the holes 202 are rectangular slits and each hole 202 overlaps or intersects. Different sizes, orientations, and / or thicknesses may be used.

[0040] Providing an inner edge offers many opportunities to depict the directivity from the radiation source to the sensor 106. Providing different sizes, shapes, and / or angles offers a lot of information regarding the depiction. The larger and / or more numerous the holes 202, the more radiation can be collected, increasing sensitivity.

[0041] In principle, any three-dimensional (3D) collimation can be used. Different shapes, sizes, edge angles, orientations, and / or combinations of the holes 202 provide different processing (i.e., reconstruction) efficiencies. For example, the holes 202 of the attenuator 108 in Figure 6 are an efficient pattern for mapping to a rectangular form factor having 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 a plate with mutually orthogonal slits ("slit-slats"), and instead of moving the sensor with the collimator to obtain different field angles, a movement pattern can be created on the sensor's detection plane simply by moving the "slits" in front of the "slats".

[0042] Figure 8 shows another embodiment of the attenuator 108. This attenuator 108 is a hollow cylinder with slits as holes 202. Although shown as parallel slits of the same size and shape, holes of various orientations, sizes, shapes, or edge angles may be used. Hole shapes other than cylinders, such as cubic shapes, may also be used. The sensor 106 or radiation source (e.g., patient 114) is positioned inside the cylindrical attenuator 108. The cylinder 108 rotates around the radiation source or sensor 106 to provide relative motion with respect to the sensor 106. When the sensor 106 is inside the attenuator 108, external (ecto) tomography with a small footprint is provided, and the sensor 106 and attenuator 108 can be robotically controlled to move around the patient or fixed relative to the patient without a large housing and bore (i.e., the patient is seated in a chair or lying in a bed).

[0043] Referring again to Figure 1, the drive unit 112 is a motor such as a servo, electric motor, air compressor, actuator, hydraulic pump, or other motor that can apply force to the damper 108. Gear mechanisms, pulleys, guides, clutches, rack and pinion, tubes, and / or other mechanisms transmit force from the motor, for example, rotational force from an electric motor, to the damper 108. The drive unit 112 consists of control and mechanical connections for operating the movable damper 108. The drive unit 112 is an encoding drive unit because it encodes the aperture. The drive unit 112 positions the damper 108 in a known arrangement and / or in a known operation. This encoding provides the positional relationship between the damper 108 and the sensor 106.

[0044] In one embodiment, the drive unit 112 is part of a robot arm. The robot arm positions and operates the attenuator 108. In other embodiments, the attenuator 108 is connected to a guide or gear mechanism to operate repeatedly under control. The drive unit 112 is configured to operate the attenuator 108 between the sensor 106 and the patient 114 (i.e., the radiator) along with the inner edge and, if possible, the outer edge from the hole 202.

[0045] The drive unit 112 operates the attenuator 108 with any degree of freedom, for example, 1 to 6 degrees of freedom. In one embodiment, this operation is three-dimensional, such as 3 rotational degrees of freedom, 3 translational degrees of freedom, or 3 rotational degrees of freedom and 3 translational degrees of freedom, respectively.

[0046] Figure 2 shows several examples. The shading 200 of the attenuator 108 on sensor 106 is shown. The three holes 202 and the outer edge result in the shading 200 on sensor 106 in this example. If the attenuator 108 is larger than sensor 106, the shading will include the holes 202 (i.e., the inner edge) but will not include all or any of the outer edges.

[0047] The shading 200 shown in the upper left figure is such that the maximum surface area of ​​the attenuator 108 is parallel to the sensor surface of the sensor 106 (i.e., their perpendiculars are parallel to each other and perpendicular to the plane of the paper). The attenuator 108 can be rotated around the perpendicular to its center or shifted (offset) to a different position. The upper right figure shows the rotation or change in orientation of the attenuator 108 and shading 200 around their centers, and a slight translation to the left. The lower left figure shows the shading 200 translated to different positions in the vertical and slightly horizontal dimensions. The lower right figure shows the shading 200 as a result of tilting the attenuator 108 around a horizontal axis on the paper such that one edge is closer to the sensor 106 than the opposite edge. In the shading 200 resulting from this tilt around the horizontal axis, the slit by the hole 202 is narrower when viewed from the perpendicular to the sensor surface. Other operations or combinations of operations may be provided.

[0048] Figure 8 shows the rotational motion of the cylinder formed by the damper 108. The drive unit 112 rotates the damper 108 around a central axis or an offset axis, moving the shadow from the hole 202 relative to the sensor 106. The sensor 106 may be made to move such as translating along the axis of the cylinder and / or tilting around an axis perpendicular to the axis of the cylinder.

[0049] Figure 7 shows the tilting operation of the attenuator 108. The attenuator 108, which has a Hall 202, is tilted for the cosine alpha effect. The attenuator 108 rotates around a central axis parallel to the largest surface of the attenuator. Other axes of rotation may be used. The attenuator 108 may be rotated to provide oscillation. The attenuator 108 may be rotated periodically with further oscillation in the opposite direction.

[0050] Figure 5 shows the oscillation of the attenuator 108. The attenuator 108 is oscillated around the perpendicular to the attenuator 108. This oscillation is along another axis that is either parallel to or not parallel to the perpendicular. The attenuator 108 is oscillated as a plate with holes 202 so that the perpendicular vector precesses (like a mortar and pestle) at a certain opening angle and frequency ω.

[0051] Other operations and / or combinations of operations may be provided. The operation is performed at any frequency, speed, and / or range. The operation can be modified, such as by changing the speed, frequency, or range. The operation may be continuous or it may operate in a step function. For example, the attenuator 108 is held in a predetermined position for a period of time, for example, 5 minutes, and then moved to another position, where the attenuator 108 is held for the same or a different period of time. Any number of steps or scattered holding positions can be used, such as 2, tens, or hundreds. Any holding time can be used, such as a few seconds or a few minutes. The operation is used to generate a strong, locally changing pattern that explores spatial frequencies.

[0052] The image processor 120 in Figure 1 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 any other currently known or future-developed device for processing radiation information and / or reconstructing an image based on detected radiation (e.g., position, energy, and / or time of incident radiation). The image processor 120 is one device, multiple devices, or a network. In the case of two or more devices, parallel processing or sequential partitioning processing may be used. Each device constituting the image processor 120 performs a separate function, for example, one processor controls the operation of the attenuator 108, and another processor forms a projection from the detected radiation (i.e., position, energy, and / or time) and time-coded aperture and performs reconstruction from the projection. In one embodiment, the image processor 120 is a control processor or other processor in a medical imaging system. In another embodiment, the image processor 120 is part of a separate workstation, server, or computer.

[0053] The image processor 120 operates according to stored instructions for performing various processes described herein, such as processes 1106, 1108, and / or 1110 of the method shown in Figure 11. The image processor 120 is comprised of software, firmware, and / or hardware to perform each process.

[0054] The image processor 120 is configured to reconstruct the object from the detected radiation. The location, time, and energy of the radiation are used to reconstruct the object. The spatial distribution of radiation sources, such as radiopharmaceuticals, within the patient 114 is reconstructed. The image processor 120 reconstructs the spatial distribution of radiation sources detected by the sensor 106, which has a movable attenuator 108 that is positioned differently by operation by the drive unit 112.

[0055] The attenuator 108 operates between the radiation source and the sensor 106, generating a local pattern (i.e., shading 200) over time, and this time-coded aperture is used to determine the directivity in reconstruction. The operational shading 200 of the hole 202 projected onto the sensor 106 is used for reconstruction.

[0056] Figure 9 shows an example based on the outer edge of the attenuator 108. The same principle applies to the inner edge. Having multiple edges allows more information to be obtained about a given arrangement of the attenuator 108 relative to the sensor 106.

[0057] The radiation source 900 emits radiation at different times. The attenuator 108 is in different positions relative to the sensor 106 at those different times. Due to the different positions of the attenuator 108, the position of the radiation source 900 is resolved based on the position of the edge of the attenuator 108 and the position of detection on the sensor 106. Triangulation and time-coded aperture provide the position of the radiation source 900 in three dimensions. The shading, determined by the shape and moment of the attenuator 108 (assuming a known deformation of a rigid or non-rigid body), represents the directivity.

[0058] Triangulation is possible because the detection position by sensor 106 and the arrangement of attenuator 108 are known. Even if the position of attenuator 108 is unknown, if its shape and operation are known, the set of shadows 200 is sufficient to determine the position of radiation source 900. Since numerous radiations are emitted from various radiation sources, tomography is used rather than attempting to resolve each radiation source individually. Statistics may be constrained to optimization for reconstructing radiation source 900 by tomography. Optimization includes the aforementioned auxiliary conditions and solves the Maximum Information Question (MIQ), in which case directivity is extracted from the non-local pattern of the PSF across the entire field-of-view coded time-varying aperture pattern based on semi-definite detection event data.

[0059] The image processor 120 is configured to perform reconstruction. Detected radiation has time and location. Energy information is included, for example, to filter the radiation to a specific energy or energy range. Optimization is applied to minimize the difference between the detected radiation and the distribution of radiation sources that would be giving rise to the radiation. Optimization includes forward and back projections between the radiation or sensor space and the object or image space. The projection includes a system model. The system model includes time-coded apertures (e.g., the position and orientation of the attenuator 108 relative to the sensor 106). The physical properties of the local pattern (shading 200) are part of the system model. The point spread function determined by the time-coded aperture is used in reconstruction. By iterative optimization, the difference is minimized until a reconstruction of the object's pixels or voxels results. Various optimizations can be used, such as the various optimizations used in SPECT.

[0060] Reconstruction may be performed by other means. In one embodiment, the image processor 120 forms a virtual projection from separate views. A representation of patient 114 (i.e., the distribution of radiation sources in patient 114) is reconstructed from the virtual projection. The virtual projection is formed from radiation detected by sensor 106 using time-coded aperture. Radiation data is riving, resampled, and / or collected with respect to different angles or views to form the projection. The projection is formed from radiation, and the reconstruction of the spatial distribution is from the projection.

[0061] The virtual PSF is reconstructed by measuring the edge response (shading 200) of the attenuator 108 on the sensor 106. Time coding is extended from small movements in front of the sensor 106 to arbitrary movements of multiple apertures (one or more holes of shape and / or size 202), which generate different patterns on the sensor 106 for each stationary view. For example, tilting, rotating, and / or shifting a plate with slits in front of the sensor 106 can generate k distinct patterns. If the movements are known, it is also known that the patient 114 did not change during the stay (quasi-stationary, at a sampling time determined by the required contrast, noise, etc.), and the virtual PSF is constructed. The virtual PSF mimics a non-local, good-resolution PSF. The virtual PSF is based on the following inversion: JPEG0007871426000001.jpg15134 Here, Sigma1(σ1) and Sigma2(σ2) define Gaussian curves, ERF is an error function based on a Gaussian integral, and Mu(μ) is a linear attenuation coefficient. Figure 10 shows an example plot of a virtual PSF. The PSF determines directivity by modeling sharp edges.

[0062] In one embodiment, the projection is formed as a virtual parallel-hole collimator projection. The detected radiation and time-coded apertures are used to determine a projection with common directivity for each of the different views of patient 114. Adding a convolutional PSF of the Heaviside function (Gaussian with σ1, σ2 in the example of Figure 10) results in the reconstruction of a regular parallel-hole collimator quasiplanar projection at the field of view angle. The same is repeated at different field of view angles until the Orlov, Tuy, and Nyquist tomography conditions are met. A set of projected views is reconstructed, as if obtained from a collimator with a much larger aperture but very high resolution. Resolution is increased because the directivity is based on edge response. Greater sensitivity is provided because the aperture (hole 202) is larger than that of a parallel-hole collimator. Tomography-suitable projections other than parallel-hole collimator projections can be formed. Field of view angle requirements can be relaxed while still meeting the tomography conditions.

[0063] The image processor 120 uses projections for iterative reconstruction. For example, a virtual parallel-hole collimator projection is reconstructed using forward and back projections. To perform reconstruction from projections, either currently known or future-developed tomography or SPECT reconstruction can be used. The projection represents a directional count from a gamma camera, provided as if a collimator had been used. SPECT iterative reconstruction is performed using a virtual PSF.

[0064] This embodiment of reconstruction uses a two-step process. First, a virtual projection (e.g., a virtual parallel-hole collimator projection image) is reconstructed. Second, reconstruction is performed on that virtual projection. In the first step, the generated local patterns can be reconstructed into virtual non-local image formation. Artificial intelligence (AI) (e.g., machine learning models such as deep learning models) can be used to form projections from radiative data. Time-coded apertures are used as input to the AI ​​with radiative data, or the AI ​​is trained on known time-coded apertures and therefore only radiative data is input. The AI ​​outputs one or more projections. Choquet integrals can be used to model the complex decision-making process of the observer, thereby optimizing the image formation design.

[0065] Figure 11 shows an embodiment of a flowchart for a radiation tomography (e.g., SPECT) method. A time-coded aperture is formed by operating attenuators and / or sensors relative to each other. By providing a hole in the attenuator, much information is provided for edge response measurements. Because the direction is not very restricted, reconstruction uses a stepwise approach in which a virtual projection is formed, and then the object or image is reconstructed from the virtual projection. In another reconstruction approach, optimization is used that uses the time-coded aperture as part of a system model.

[0066] This method is performed by a radiometric tomography imaging device or system, such as a SPECT system. A motor operates an attenuator, and a sensor detects radiation using attenuators located at different positions relative to the sensor. An image processor reconstructs the detected radiation and time-coded apertures (e.g., patterns from the attenuator shadows). The image processor generates a reconstructed image of the target, which is displayed on a display device or screen. Other components may be used to perform and / or assist in any part of the process.

[0067] Each process is executed in the order shown (i.e., from top to bottom, or in numerical order) or in any other order. Processes 1102 and 1104 are executed iteratively for any number of cycles, such as activating the attenuator, then performing detection, then activating it and performing detection again. Process 1104 can be executed first, followed by the activation of the attenuator in process 1102, and vice versa.

[0068] Additional, different, or fewer processes may also be provided. For example, these may include processes for moving sensors, positioning patients, and / or rendering three dimensions from the reconstructed volume distribution. In another example, the display process 1112 may not be performed, and for example, the image or reconstruction may be stored in or transferred for storage in a radiology report, electronic patient medical record, or picture archiving system (PACS).

[0069] In process 1102, an attenuator (e.g., an attenuator or radiation shield) is operated. The attenuator has an inner edge. The attenuator is operated between the patient and the sensor. With or without an outer edge, the inner edge forms a time-coded aperture on the sensor due to the operation. The pattern or shadow from the attenuator is shifted two or more times to provide the time-coded aperture. This operation results in the inner edge and, if present, the outer edge from the hole having different positions, shapes, sizes, orientations, and / or angles (see Figure 2).

[0070] The motion involves rotation and / or translation along one or more dimensions (e.g., three). Motion involving three-dimensional translation or rotation increases the diversity of shading. Motion involving both rotation and translation in three dimensions further increases diversity. Shifting or changing one or more holes adds diversity to the shading. Moving the sensor also contributes to increasing diversity. The shape and / or size of the holes in the shading on the sensor varies over time.

[0071] The motion may be due to translation and / or rotation in a plane parallel to the sensor's detection surface. The motion may be translation, tilt, or oscillation outside of that plane. In another embodiment, the motion is the rotation of a damping body around the sensor.

[0072] In process 1104, the sensor detects radiation from the patient. Some radiation passes through the sensor. Other radiation is blocked by an attenuator. Other radiation passes through the attenuator, for example, through the outside or through holes, and reaches the sensor. The attenuator projects a shadow onto the sensor based on the radiation.

[0073] Detection is performed using attenuators in a predetermined configuration. Next, detection is performed using attenuators in a different configuration. An arbitrary period is used for detection. The energy, time, and location on the sensor for each detected radiation are used to identify the detection event. Counts at different locations on the sensor are performed with respect to the given attenuator configuration when many radiations occur.

[0074] Since the detected radiation is only the incident radiation passing through the attenuator, different shadows arise from the attenuator at different positions. The detected events reflect these shadows, enabling edge response. Numerous events are detected by the inner edge, and further edges are provided to determine the directivity by the edge response. For each position of the aperture formed by the attenuator, a time-coded aperture and the corresponding detected event are recorded. The operation of the attenuator results in different shadows on the sensor based on detection by the sensor. The orientation and / or position of the attenuator relative to the sensor varies over time according to the operation of process 1102.

[0075] In process 1106, the image processor uses a time-coded aperture to reconstruct a representation of the patient from the detected radiation. The edge response of the shadow is used to determine or limit the directivity in optimization. The edge limits the angle to a range of angles. By having the edge at a different position relative to the sensor at each time step, the edge response indicates the location of the radiation source based on the detected position on the sensor. The representation is reconstructed from the edge response of the shadow of the attenuator on the sensor.

[0076] In one embodiment, optimization is used when the shadow or time-coded aperture is part of the system model. Events and time-coded apertures detected from different time points are used to solve the spatial distribution of radiation sources in the patient.

[0077] In another embodiment, a two-step approach represented by processes 1108 and 1110 is used. In process 1108, projections are constructed for the patient at different field angles. The projections are constructed from detected radiation based on time-coded apertures. For example, a virtual PSF is created by integration using a Gaussian model. Virtual PSFs from different directions are determined by ray tracing and accurate recording of signal changes, under known non-negativity conditions. In process 1110, the projections are used as samples or binned counts from the sensor at different views. Iterative optimization is performed with the projections as input. Iterative optimization solves the spatial distribution of the radiation source from the projections based on radiation from the radiation source.

[0078] In process 1112, an image is generated from the reconstruction. The spatial distribution represents the distribution of radiation sources in a plane or volume. The representation is reformatted to be displayed as an image on a two-dimensional display. In the case of a two-dimensional representation, the reformatting scan is converted to the resolution and / or dynamic range of the display. In the case of a three-dimensional representation, the voxels are rendered into a two-dimensional image, for example, by using volume or surface rendering.

[0079] The resulting image is displayed on a screen. The physician can see the location and / or intensity of radiopharmaceutical uptake by the patient's tissue. The hotspots or locations represent tissue function, allowing the physician to identify areas of dysfunction or impairment that may be subject to diagnosis and / or treatment.

[0080] Instead of using a sensor with a fixed collimator, which is moved to detect from different angles, the relative movement of an attenuator to the sensor provides a pattern change in addition to the signal change. The attenuator projects a shadow onto the sensor. As the attenuator operates in known ways (e.g., translation, rotation, and / or deformation), the shadow of the attenuator on the sensor changes, generating a changing shadow pattern on the sensor. By including multiple holes and / or edges of different known sizes, shapes, and angles, many radiations pass through the attenuator, along with additional information arising from the edges. The radiation pattern is estimated by viewing from different directions toward the radiation source and collecting information from different shadows. More signal and resulting information is used, along with known aperture coding, to solve the distribution of radiators within the radiation source (patient). Instead of observing through a collimator that only shows what is in front and rotating the sensor and collimator together to capture a wider field of view, the sensor remains stationary and captures information by the movement of the attenuator.

[0081] Although the present invention has been described with reference to various embodiments, many changes and modifications can be made without departing from the scope of the invention. Therefore, the above detailed description should be understood as illustrative rather than limiting, and it should be understood that the spirit and scope of the invention are intended to be defined by the claims, including all equivalents.

Claims

1. A radiometric tomography system, A sensor configured to detect the position, energy, and time of a gamma-ray collision, A movable attenuator that is movable relative to the sensor, A drive device configured to operate the aforementioned movable damper, The image processor is configured to reconstruct the spatial distribution of radiation detected by the sensor using the movable attenuators which are arranged in different configurations by the operation of the drive device, The movable attenuator has a two-dimensional shape that provides an outer edge to the detection surface of the sensor, and one or more through holes that provide an inner edge. The movable attenuator is positioned between the radiation source and the sensor such that the moving shadow of the through-hole is projected onto the sensor. Radiation tomography system wherein the movable attenuator is operable by translation of the cutoff surface of the movable attenuator with respect to the detection surface of the sensor, rotation of the cutoff surface of the movable attenuator about a rotation axis perpendicular to the cutoff surface, inclination of the cutoff surface perpendicular to the detection surface perpendicular of the sensor, oscillation of the cutoff surface with respect to the detection surface, and / or precession of the cutoff surface perpendicular.

2. The radiation tomography system according to claim 1, wherein the sensor includes a planar gamma camera.

3. The tomography system according to claim 2, wherein the planar gamma camera is connected to a gantry configured to position the planar gamma camera at a different location relative to the radiation source in order to detect the radiation.

4. The radiometric tomography system according to claim 1, wherein the movable attenuator includes an object made of lead or tungsten.

5. The tomography system according to claim 1, wherein the through-hole includes a slit.

6. The radiometric tomography system according to claim 1, wherein there are multiple through-holes, and any one of the through-holes has a different size, shape, and / or angle from the other through-holes.

7. The radiation tomography system according to claim 1, wherein the image processor is configured to form a projection from the radiation, and the reconstruction of the spatial distribution is from the projection.

8. The tomography system according to claim 7, wherein the projection is a virtual parallel-hole collimator projection, and the reconstruction is an iterative reconstruction using the virtual parallel-hole collimator projection in forward and back projections.

9. A single-photon emission computed tomography (SPECT) method, An attenuator having an outer edge and an inner edge is operated between the patient and the sensor, and the operating inner edge forms a time-coded aperture on the sensor. The sensor detects radiation from the patient that passes through the attenuator, which provides different shadows on the sensor due to the time-coded aperture. This includes reconstructing a representation of the patient from the detected radiation using the time-coded aperture, The damping body is operated by the following methods: translation of the damping body's blocking surface with respect to the sensor's detection surface; rotation of the damping body about a perpendicular line to the blocking surface as the axis of rotation; inclination of the blocking surface's perpendicular line with respect to the sensor's detection surface; oscillation of the blocking surface with respect to the detection surface; and / or precession of the blocking surface's perpendicular line.

10. The method according to claim 9, wherein detecting the radiation includes detecting it using different shadows resulting from the operation of the attenuator.

11. The method according to claim 9, wherein the damping body has a plurality of inner edges, and any one of the inner edges has a different shape, size, and / or angle from the other inner edges.

12. The hole in the damper forms the inner edge, The method according to claim 9, wherein the shape and / or size of the hole in the shadow differs over time due to the operation of the attenuator.

13. The method according to claim 9, wherein reconstructing the representation includes reconstructing a virtual point spread function from the edge response of the shading.

14. The method according to claim 9, wherein reconstructing the representation includes constructing a projection for the patient at different field angles based on the time-coded aperture from the detected radiation, and reconstructing from the projection.

15. A radiometric tomography system, A radiation shield having an outer edge and an inner edge, The inner edge is provided by a hole that penetrates the radiation shield. A sensor configured to detect radiation passing through the aforementioned hole, The radiation shield is arranged differently with respect to the sensor, and this different arrangement forms a time-coding aperture with respect to the sensor. The image processor is configured to form a virtual projection from different views of radiation detected by the sensor using the time-coded aperture, and to reconstruct a representation of the patient from the virtual projection, Radiation tomography system wherein the radiation shield can be positioned differently relative to the sensor by translation of the shielding surface of the radiation shield with respect to the detection surface of the sensor, rotation of the radiation shield with respect to the perpendicular line of the shielding surface as the axis of rotation, inclination of the perpendicular line of the shielding surface with respect to the perpendicular line of the detection surface of the sensor, oscillation of the shielding surface with respect to the detection surface, and / or precession of the perpendicular line of the shielding surface.

16. The radiometric tomography system according to claim 15, wherein there are multiple holes, and any one of the holes has a different size, shape, and / or angle from the other holes.

17. A radiometric tomography system, A sensor configured to detect the position, energy, and time of a gamma-ray collision, An attenuator having an outer edge and a through hole providing one or more inner edges, which is positioned relative to the sensor, The image processor is configured to reconstruct the spatial distribution of the radiation detected by the sensor using an attenuator located between the radiation source and the sensor such that the shadow of the through-hole is projected onto the sensor, Radiation tomography system wherein the attenuator is positioned relative to the sensor by translation of the attenuator's shielding surface relative to the sensor's detection surface, rotation of the attenuator's shielding surface about a rotation axis perpendicular to the sensor's shielding surface, inclination of the shielding surface's shielding surface perpendicular to the sensor's detection surface perpendicular, oscillation of the shielding surface relative to the detection surface, and / or precession of the shielding surface's shielding surface perpendicular.

18. The radiation tomography system according to claim 17, wherein the sensor includes a planar gamma camera, the planar gamma camera being connected to a gantry configured to position the planar gamma camera at a different location relative to the radiation source in order to detect the radiation.

19. The tomography system according to claim 17, wherein the attenuator includes an object made of lead or tungsten.

20. The tomography system according to claim 17, wherein the through-holes include slits and / or holes of different sizes, shapes and / or angles.

21. The radiometric tomography system according to claim 17, wherein the image processor is configured to form a projection from the radiation, and the reconstruction of the spatial distribution is from the projection.

22. The tomography system according to claim 21, wherein the projection is a virtual parallel-hole collimator projection, and the reconstruction is an iterative reconstruction using the virtual parallel-hole collimator projection in forward and back projections.

Images