Radiation detection system and method

Abstract

A method for processing radiation from a source is described, comprising the steps of: positioning a detector to receive radiation from the source; positioning a collimator between the source and the detector, the collimator having a plurality of apertures; causing radiation from the source to pass through the collimator and be incident on the detector; receiving a plurality of responses, each response to an interaction with the incident radiation occurring within the detector; determining, for each of the plurality of responses, a characteristic of the interaction, the characteristic including at least a position and a depth of the interaction within the detector; and processing the plurality of responses by simultaneously processing the position and depth of interaction data in a manner that accommodates multiplexing effects due to overlapping projected radiation paths from multiple apertures in the collimator at the detector on a detected position on the detector. In particular, a radiation detection system for detecting radiation from a source for implementing the method is also described.

Description

Technical Field

[0001] The present invention relates to a radiation detection system for detecting radiation from a radiation source, such as a radioisotope source, and more particularly to a system adapted for detecting radiation from a source that generates a low signal in a detector. The present invention also relates to a method for detecting radiation from such a source.

Background Art

[0002] There are a wide range of scenarios where it is desirable to obtain more accurate information about the radiation emitted from a radiation source and received by a detection system. In particular, there are a wide range of scenarios where it is desirable to decompose the information, for example, spatially and / or spectrally, to provide additional information about the radiation source and / or the material through which the radiation has passed between the radiation source and the detector.

[0003] Such scenarios include, but are not limited to, scenarios where the radiation source and the detector are intentionally spaced apart and the radiation emitted from a highly active region within a subject is measured by the detector to determine information about the subject.

[0004] Examples of such latter scenarios include nuclear medicine imaging methods. Here, radiation from a radioisotope source is passed through a part of the subject's body, and the spatially recorded information about the radiation received by a remote detector is used to obtain information about the structure and / or real-time physiological function of the anatomical part of the patient and, for example, to construct an image of that structure and / or physiological function. However, the discussion of such applications is by way of example only, and the present invention is not limited to medical or imaging applications.

[0005] The principle of the present invention finds specific applications where the signal from the radiation source is relatively low, and the signal for resolvable data from a relatively small number of particles of radiation emitted from the source incident on the detector is consequently reduced, making it more difficult to separate meaningful information from the background. Such considerations are likely to be particularly relevant in medical applications where there is a clear necessity to minimize the radiation dose received by the subject. Therefore, nuclear medicine imaging again provides a good example of a technique to which the principle of the present invention can be advantageously applied.

[0006] However, the advantages of the present invention related to the resolution of high-level information from low-level signals generally apply to all cases where it is necessary to resolve low signals from a radiation source. An example of a non-medical application where low signals are expected is the inspection of nuclear facilities using a portable gamma camera.

[0007] The advantages of the present invention may arise in situations where image reconstruction is required, or where image reconstruction is unnecessary or undesirable, and can occur in both similar and different ways.

[0008] An established example of nuclear medicine imaging technology is single-photon emission computed tomography (SPECT), a nuclear medicine tomography imaging technique that uses gamma rays. This technique requires the delivery of a radioactive isotope that emits gamma rays to the patient via the bloodstream. In a typical application, the radioactive isotope is bound to a specific ligand, which is then transported to and bound to a target location within the subject's body.

[0009] Radioactive isotopes emit gamma rays, which pass through the subject's tissues and can be detected by a suitable detector, such as a gamma camera. SPECT imaging with a gamma camera acquires multiple two-dimensional images, which are then constructed into a three-dimensional dataset using standard tomography reconstruction techniques. This technique potentially enables not just the imaging of relevant parts of the body, but also the active, functional imaging of biological processes.

[0010] For example, a well-known technique for imaging breast tissue to detect abnormalities that may lead to the early detection of breast cancer is mammography. Standard mammography uses X-rays to create images. These images are analyzed for abnormal findings, particularly for characteristic clusters that may indicate a tumor. These patients are then referred for further, usually more invasive, examinations. Thus, standard mammography is a widely adopted first-stage screening technique.

[0011] However, the response of normal but relatively dense breast tissue to low-energy X-rays may be similar to the response of a type of mass to X-rays that may indicate the potential development of many common tumors, and consequently, the ability of techniques to distinguish patients with a high percentage of dense breast tissue is reduced.

[0012] Molecular breast imaging (MBI) is a developed nuclear medicine imaging technique that utilizes many of the principles described above for SPECT-type techniques. A radioactive isotope source is introduced into the patient, which is then typically bound to a suitable ligand and placed within the breast tissue. A suitable system of a small semiconductor-based gamma camera, with a configuration roughly corresponding to that of a more conventional mammogram, is used to detect the radiation from the source after it has passed through the breast tissue. This technique is particularly effective in detecting early tumors because it can detect physiological activity. However, generally, the patient receives a higher overall radiation dose, which has tended to limit its application as a first-stage screening technique.

[0013] In all nuclear medicine imaging techniques, there is a clear requirement to keep the radioactivity of the radiation source, and consequently the radiation dose received by the patient, as low as possible. As a result, low signals collected by the detector present unique problems in relation to both data detection and resolution.

[0014] A factor affecting the signal from the required radiation source is detection efficiency. Particularly in relation to imaging techniques, a detection system is needed that can distinguish between multiple individually addressable detection points or regions to obtain the required spatial resolution. For example, in the case of a planar detector, the spatial resolution may be in the x and y directions. While two-dimensional (2D) detectors are often used in current practice, detection can also be performed in three dimensions (3D).

[0015] In an imaging system, each point within the detector may correspond to a pixel or voxel in the reconstructed image and may generally be referred to as a pixel on the detector. To achieve effective spatial and, for example, x and y resolution in the resulting image, a detection system is required that distinguishes between pixels in the x and y directions in a manner that allows for obtaining a valid signal individually for each individually addressable "pixel" in the x and y directions.

[0016] Any type of radiation detector, particularly solid-state detectors widely used in conventional medical imaging applications, is typically characterized by the fact that its efficiency depends on its thickness. While there must be a non-trivial relationship, in most cases, the thicker the detector, the higher its efficiency. Traditionally, the efficiency of solid-state detectors widely used in conventional medical imaging applications is increased by providing an appropriate depth in the z-direction or orthogonal to the x and y-directions of the detection surface.

[0017] However, in order to maintain a record of the position in x and y, it is often necessary to collimate the signal emitted from the radiation source incident on the detector. The quality and usefulness of any image in nuclear medicine imaging techniques are severely affected by the collimator structure.

[0018] It is common practice to use a collimator such as a parallel-hole collimator with a very low spread angle between the radiation source and the gamma camera or other detector. This collimator produces a recording that approaches a nearly one-to-one recording in the x,y plane for the signals between the radiation source and the detector. The collimator consists of a number of closely packed parallel holes that allow only a portion of the radiation, nearly perpendicular to the collimator surface, to pass through. As a result, the detector acquires a single orthogonal projection of the radiation source. This image can be used directly in the case of a 2D gamma camera, but for 3D SPECT applications, acquisitions must be repeated from multiple angular positions around the patient to obtain sufficient information for the reconstruction algorithm.

[0019] Therefore, the effective development of instrumentation for nuclear medicine imaging, such as SPECT or MBI, is a compromise between the requirement for effective collimation that substantially completes one-to-one recording in the x,y directions, for example using a parallel-hole collimator with a very low spread angle, resulting in a reduction of the collimator signal, and the requirement for the lowest possible radiation dose source.

[0020] In the field of MBI in particular, there is a wealth of literature on the use of single and dual-plane detectors with moderate breast compression. State-of-the-art commercial systems use, for example, CZT detectors with high-resolution parallel-hole collimators. Good spatial resolution is achieved due to the close approach to the breast. In patients with dense breasts, detection sensitivity is better than conventional mammography, but the radiation dose is higher. Efforts to reduce radiation dose have included the selection of collimators and image filtering to reduce noise / enhance contrast, but these have not achieved sufficient dose reduction to enable the use of MBI as a screening tool.

[0021] For example, it is generally desired to provide alternative detection systems and methods that enable better resolution of radiation information in scenarios such as short-duration measurements from low-intensity sources.

[0022] It is particularly desirable to provide alternative methods that are applicable in nuclear medicine imaging, address these conflicting considerations in a more effective and efficient manner, and can provide improved resolution of physiologically relevant data from patients and / or reduced dose levels with respect to nuclear medicine imaging techniques such as SPECT or MBI.

[0023] For example, the use of multi-aperture collimators with low divergence angles, consisting of pinholes or slits that have virtually no depth in the z-direction, is being explored.

[0024] For example, multi-pinhole collimators have been widely used in preclinical systems where magnification provides high-resolution performance. The concept of using high intrinsic resolution in combination with densely packed pinholes, along with miniaturization as a means of achieving high sensitivity, is not new and offers the additional advantage of enabling compact designs. The development of metal-doped 3D printing has enabled greater design flexibility. A range of alternative collimators were evaluated for MBI, including variable-angle tilted holes (VASH) and slit-slats.

[0025] Limitations in the design of multi-aperture collimators without low spread angles, such as multi-slit collimators and multi-pinhole collimators, are the possible projection overlaps (multiplexing) that can occur, which may result in image artifacts. Conventional approaches are to avoid multiplexing, for example, by separating pinholes, restricting the exposed detector by introducing internal shielding, or using a shutter system to sequentially expose different pinholes, but this can limit the design options. Also, the use of two different opposing collimators has been proposed as a means to overcome multiplexing. The use of multiple acquisition distances (synthetic collimation) has been shown to reduce multiplexing artifacts in preclinical imaging. An approach of iterative inverse multiplexing within the modified MLEM reconstruction has also been proposed. In all cases, the goal is a substantial reduction, or at least a reduction of the multiplexing artifacts that can result therefrom, in the effective removal of the projection overlaps (multiplexing) that can occur with multi-aperture collimators.

Summary of the Invention

Problems to be Solved by the Invention

[0026] The present invention is directed to this multiplexing problem and aims to provide alternative solutions that mitigate some of the effects of such multiplexing and / or use data better when such multiplexing may be present. The present invention is particularly applicable in the context of devices and methods that may be applicable in nuclear medicine imaging for techniques such as SPECT or MBI, which can address the opposing considerations of reducing the dose level and maintaining sufficient signal after collimation loss in order to provide improved resolution and / or reduced radiation dose levels of physiologically relevant data from a patient.

Means for Solving the Problems

[0027] According to the present invention in a first aspect, a method of processing radiation from a line source comprises: positioning at least one detector for receiving radiation from the line source; positioning a collimator between the line source and the detector, the collimator having a plurality of apertures; allowing radiation from the line source to pass through the collimator and impinge on the detector; receiving a plurality of responses, each being a response to an interaction with the incident radiation occurring within the detector; for each of the plurality of responses, determining a characteristic of the interaction, the characteristic including at least the position and depth of the interaction within the detector; <> processing the plurality of responses by simultaneously processing the position and depth of the interaction data in a manner that accommodates the effect of multiplexing due to the overlap of the projected radiation paths from the plurality of apertures within the collimator at the detected positions on the detector.

[0028] Here, when referring to the detector, for each of the plurality of responses, it is applied to a configuration of the detector that effectively receives radiation from the radiation source with a resolution that enables the necessary determination of the characteristic of the interaction, where the characteristic includes at least the position and depth of the interaction within the detector. It will be understood that, in particular, the singular includes the plural. The present invention can be applied to a detection system comprising a configuration of a plurality of individual detectors and / or to a configuration of a single detector defining a plurality of individual detection regions and / or to a configuration of a single detector defining a single continuous detection region that is virtually divided into individually addressable sub-regions.

[0029] In some applications of the present invention, it will be understood that at least one detector is positioned approximately perpendicular to the radiation incidence direction, defining an x, y incidence plane perpendicular to the radiation incidence direction and a z direction corresponding to the depth of the detector, and that the interaction location within the detector may constitute the x position in the case of a linear detector and the x, y positions in the case of an area detector, and that the depth of the interaction within the detector may constitute the z depth.

[0030] In some applications of the present invention, the detector can be pixelated, that is, the detector can be divided into a one- or two-dimensional array of individually addressable subunits which are discrete elements, and / or, for example, into individually addressable regions defined on a surface substantially perpendicular to the direction of radiation incidence, and the location of the interaction within the detector may constitute localization to a particular discretely addressable subunit, and the depth of the interaction within the detector may constitute the depth below the surface of the subunit. The subunits may be discrete physical entities or may be defined substantially digitally, and in this sense, a detection region which may be physically continuous is substantially subdivided, its location determined in x, y, and this determined location is used to assign the interaction to the subunit.

[0031] Here, when referring to such subunits as pixels, unless the context explicitly requires otherwise, it will be understood that this term includes physically discrete pixel subunits, clusters of the same, and subunits defined digitally and virtually as described above.

[0032] The present invention is distinctly characterized from the prior art described above by the use of a collimator having an array of multiple apertures essentially configured to generate overlap between patterns of radiation from different apertures in a manner that tends to generate a multiplexing effect in the detector; the use of a detector having a significant depth to capture this complexity by determining both the location and depth of the interaction within the detector; and the use of this detected complexity in a processing step, for example, to mitigate the contribution of such multiplexing and, preferably, to make further use of the multiplexing to derive further useful inferences.

[0033] In other words, the collimator has a three-dimensional complexity introduced with respect to radiation from a radiation source, where there is not necessarily direct recording between each aperture and a given region on the detector, but instead there may be overlap between each region, which could lead to the possibility of multiplexing.

[0034] This is a consequence of the aperture structure, where each aperture defines a radiation projection zone beyond the aperture exhibiting a non-zero angular spread. For example, in the case of a multi-hole collimator, each hole aperture is configured to define a radiation projection cone beyond the aperture with a positive angular spread. Thus, each aperture is, in effect, an imaging aperture, as understood in imaging techniques, in that at least some complexity from which image information can be resolved is inherently present in the radiation projection from a single aperture. The collimator is further configured so that the resulting radiation projection zones beyond the apertures overlap, producing a multiplexing effect in the detector.

[0035] Furthermore, a feature of embodiments of the present invention is that the detector localizes each interaction not only in the detector x,y plane but also in the depth of the detector interaction, i.e., in the z direction. This dataset, including the depth of interaction and the x,y positions, is then used to reconstruct a photograph of the radiation pattern from the source in a manner that accepts and, for example, mitigates the multiplexing effect. That is, the method of the present invention is characterized by using a collimator having multiple apertures having overlapping projected radiation zones, accepting the resulting multiplexing effect in the raw data of the interaction positions in x,y, but using the depth of interaction in z to accept and, for example, mitigate the contribution of such multiplexing, and preferably making further use of the multiplexing to derive further useful inferences.

[0036] In some embodiments, the method comprises the steps of processing a collected dataset including the determined location and depth of each interaction in the detector, and generating a modified dataset therefrom which data for the modified location of each interaction includes, for example, data that localizes each interaction in the pixel and / or in the x,y directions, as defined above, in a manner that adapts to the effects of multiplexing due to the overlap of paths of projected radiation from multiple apertures in the collimator in the detector at the apparent location where the interaction is localized in the input dataset.

[0037] In some embodiments, the method includes the steps of reducing the effects of multiplexing and substantially eliminating the effects of multiplexing from the modified dataset, for example.

[0038] In a preferred embodiment, where data may be used to reconstruct one or more images, the present invention further includes, for example, the steps of using the depth of interaction to accept multiplexing effects in the reconstructed image(s) to improve image quality, and reducing artifacts in the reconstructed image(s).

[0039] In contrast, in typical prior art, the conventional approach is to mitigate, and ideally substantially eliminate, overlap during the acquisition phase by proper hardware configuration, such as proper collimation configuration, and pixelation that maintains a monotonous record of interactions localized and detected at the pixel level. In typical prior art approaches, multiplexing, i.e., variations in x and y positions along with z, is not seen as an acceptable, and even usable, feature in the raw detected interaction dataset, but rather as a problem to be minimized or eliminated from the raw detected interaction dataset by completely minimizing or eliminating overlap during the acquisition phase.

[0040] In conventional techniques, the collimation system is intended to maintain a substantially monotonous one-to-one positional record of x and y in the radiation pattern as it passes from the source to the detector.

[0041] The drawback of this is that a significant number of photons do not reach the detector. In a typical MBI system, perhaps 10 4 Only about one instance is recorded per photon. Similar levels are typical for other SPECT-type techniques.

[0042] As a result, a much higher signal source of radiation, and in the case of medical imaging, a higher dose of radiation to the patient's tissue, is required, and a satisfactory number of photon interactions must be obtained in the detector to produce an image. For example, an alternative to mitigate the angle through which the collimator passes, such as by using a larger hole, will result in a loss of resolution in the image.

[0043] In contrast, the present invention is clearly characterized by the collection of inherently multiplexed interaction data, including the depth of the interaction data, rather than the elimination of multiplexing in the hardware at the acquisition stage, and by providing processing steps to reconstruct this more complex data with respect to radiation from a source and derive additional or alternative inferences, in order to accept the multiplexing effect and, for example, to mitigate it, or to make further use of multiplexing to derive additionally useful inferences at will.

[0044] As a result, the present invention takes a fundamental approach to the obvious conflict in the prior art between maintaining a suitable signal / reducing dose and losing image contrast. It is possible to generate a dataset in which each photon interaction can be localized to some extent in all x, y, and z coordinates, if the depth of each photon interaction, i.e., the position in the z direction within a deep detector, can also be resolved to some extent. This can be inferred, but it depends on the reality that it can be deconvolved by a suitable reconstruction method in a suitable processing and reconstruction module, which may eliminate the need for collimation and pixelation for the purpose of recording nearly one-to-one x, y, and as a result, the number of photons prevented from passing through the filter can be significantly reduced, and therefore the proportion of photons that pass through the filter can be significantly increased, so that they can be usefully collected and processed meaningfully in the detection module. An effective set of data can be collected from much lower intrinsic source levels of radioactivity, and, for example, from lower resulting radiation doses to patient tissue in the case of medical imaging.

[0045] According to the present invention, the method comprises the step of using a collimator having multiple apertures that do not have a minimized spread angle. Particularly preferred is that the collimator is not a parallel hole collimator, but a parallel hole collimator designed for a minimized spread angle, or even other collimators; however, multiplexing cannot be ruled out in all situations, and the principle of the method of the present invention can be used accordingly.

[0046] In this embodiment, the collimator may have a one-dimensional or two-dimensional array of multiple apertures that do not have a minimized divergence angle. Each aperture may be configured such that, for example, each aperture defines the portion from which radiation emerges, by referring to, for example, a short length and / or divergence profile of the direction of the emerging radiation, and radiation passing through the aperture tends to have a non-zero divergence angle at emergence. A preferred divergence angle may be at least 15 degrees.

[0047] In some embodiments, the method includes the step of using a collimator having an array of slits, for example, a slit-slat arrangement. In other embodiments, the method includes the step of using a collimator having a one-dimensional or two-dimensional array of pinholes. In such cases, the slits or pinholes may be equivalent or different in configuration, and may be evenly spaced or at different intervals. Other arrangements and configurations of multiple apertures are possible.

[0048] According to the present invention, the method comprises the steps of receiving a plurality of responses to a plurality of corresponding interactions with incident radiation occurring within the detector, and determining, for each of such responses, at least the location of the interaction within the detector and the depth of the interaction.

[0049] For example, the method of the present invention involves the use of a detector adapted or configured to enable the interaction with incident radiation generated within the detector to be localized in three dimensions at the interaction location within the detector. In such a case, the method comprises the steps of incidentally injecting radiation from a source into such a detector and, accordingly, performing the receiving step and the determining step.

[0050] For example, in some embodiments, the present invention involves the use of a detector comprising a three-dimensional voxel array, wherein for each of the plurality of responses, the step of determining the characteristics of the interaction, including the location of the interaction in at least three dimensions, includes the step of localizing the interaction to a specific voxel.

[0051] In some embodiments, the detector includes means for localizing the interactions within the detector in the x and y directions with respect to the direction of the incident radiation and the z direction, which includes the depth within the detector in a plane that is substantially perpendicular to the x and y planes.

[0052] For example, a radiation detector has a detection surface that is divided into multiple individually addressable detection portions that are spatially defined across the detection surface in each of two orthogonal directions (hereinafter referred to as the x-direction and the y-direction), thereby allowing the interaction of radiation particles incident from the source in the detection module to be spatially localized to the detection portion. The radiation detector has depth in a third orthogonal direction (hereinafter referred to as the z-direction), and the radiation detector is configured such that the interaction of radiation particles incident from the source in the detection module can be further localized in depth in the z-direction.

[0053] This method further comprises, for example, the steps of receiving radiation data from a series of particle interactions in a radiation detector using a suitable processing module that is communicating with a radiation detector, and processing the data so that each is localized to a specific voxel and / or x, y, z coordinates.

[0054] According to the present invention, the method includes a step of deriving an inference regarding the pattern of radiation from a radiation source. In particular, the inference can be derived by simultaneously processing the position and depth of interaction data in a manner that is adapted to the apparent position on the detector, for example, the multiplexing effect due to the overlap of projected paths from multiple apertures in the collimator in a detector on a pixel where phase radiation interaction occurs.

[0055] In some embodiments, the method is applied as a method for collecting radiation data after it has passed through a subject, for example, for imaging a subject, and the system is used as a system for collecting radiation data after it has passed through a subject.

[0056] In such cases, this method further... A step of positioning the subject between the radiation source and the collimator, The steps include: irradiating the subject with radiation from a radiation source, The method includes the step of passing at least a portion of the radiation emanating from there through a filter and directing it into a detection module.

[0057] Each of the consecutive particle interactions collected in the detection module after passing through the subject is localized, for example, to x, y, and z coordinates.

[0058] According to the general principles of the present invention, the method comprises the steps of receiving a plurality of responses to a plurality of corresponding interactions with incident radiation generated in the detector, and determining, for each such response, at least the location of the interaction and the depth of the interaction within the detector.

[0059] In some embodiments, this method The steps include determining an input dataset that includes the determined location and depth of each interaction within the detector, The process includes processing the input dataset and generating a modified dataset from the input dataset that includes at least data including the location of each interaction modified in a manner that adapts to the multiplexing effect due to the overlap of the projected radiation paths from the plurality of apertures.

[0060] In some embodiments, the method includes the step of generating an image dataset. In a possible embodiment, an input dataset for the interaction of a series of particles is processed to generate an image dataset. The method may further include the steps of generating an image and optionally further displaying the image.

[0061] In this embodiment, the method includes the step of simultaneously processing the location and depth of interaction data in order to reduce multiplexing artifacts in the resulting imaging dataset or image in a manner that is adaptable to the multiplexing effect due to the overlap of the paths of the projected radiation from multiple apertures in a collimator in a detector at an apparent location, for example, on a pixel where the interaction occurs.

[0062] In some embodiments, the method is applied as a medical examination and, for example, a medical imaging method, where the subject is a part of the subject's body, for example, a human subject or a non-human animal subject.

[0063] In some embodiments, the method includes the step of generating an image dataset and, for example, an image by tomography reconstruction. In such cases, the reconstructed dataset referred to above may include a tomography image dataset or, for example, a portion thereof representing an image layer.

[0064] In this embodiment, the method includes, for example, a step of simultaneously processing the location and depth of interaction data in a manner that adapts to the effects of multiplexing on a reconstructed tomographic image dataset in order to reduce multiplexing artifacts in the reconstructed tomographic images.

[0065] This method may further include the step of displaying tomographic images.

[0066] In general, tomographic reconstruction involves constructing an image from radiation data from a source collected at a detector by converting raw data into a 3D image dataset in the form of a dataset of radiation interaction responses attributable to radiation from the source incident at the detector. Reconstructing data from a limited number of projection angles and directions is often called tomosynthesis.

[0067] In its broadest sense when applied to tomography reconstruction, the present invention comprises the steps of: adapting to potential multiplexing effects in raw data by processing a collected dataset of radiation interaction responses according to both the determined location and depth of each interaction within the detector; and using the latter to adapt to the multiplexing effects in the former, thereby mitigating, for example, the multiplexing effects in the resulting image dataset.

[0068] For example, an appropriate tomography reconstruction methodology based on known tomography reconstruction methodologies may be used in conjunction with modifications according to the principles of the present invention. In some embodiments, a maximum likelihood expectation maximization (ML-EM) image reconstruction method can be used. In some embodiments, this method may be combined with an ordered subset algorithm (OS-EM). In other embodiments, a penalty image reconstruction method, such as a one-step rate method or a more advanced optimization method, can be used.

[0069] In some embodiments, an input dataset containing the determined location and depth of each interaction within the detector is processed, and a corrected dataset is generated before subsequent tomographic reconstruction, taking into account both the determined location and depth of each interaction to adapt to the effects of multiplexing. In some embodiments, an input dataset containing the determined location and depth of each interaction within the detector is processed, taking into account both the determined location and depth of each interaction to adapt to the effects of multiplexing, and a corrected dataset is generated simultaneously with tomographic reconstruction. In some embodiments, an input dataset is processed, and a corrected dataset is generated both before and during tomographic reconstruction, taking into account both the determined location and depth of each interaction to adapt to the effects of multiplexing.

[0070] Therefore, in this embodiment, the method is The steps include determining an input dataset that includes the determined location and depth of each interaction within the detector, The method includes the step of processing the input dataset to adapt to the effects of multiplexing and generating a modified dataset before and / or during subsequent tomography reconstruction.

[0071] In some embodiments, some or all of the above steps are repeated.

[0072] For example, in some embodiments, the process includes image reconstruction, thereby incorporating the multiplexing effect into the system matrix used in the iterative reconstruction process. In other embodiments, the process includes a separate iterative demultiplexing procedure performed in projection space before the final image reconstruction using conventional image reconstruction. In yet another embodiment, these principles can be combined in an iterative manner and / or used alternately.

[0073] As discussed herein, multiplexing consists of overlapping projections from different apertures within the detector volume. The optimal demultiplexing procedure may depend on the amount of multiplexing at different depths within the detector volume.

[0074] Possible embodiments of the demultiplexing procedure are: The steps include dividing the depth of the detector volume into a finite number of different depths of the interaction layer (defined physically or virtually), A step of estimating a virtual 2D non-multiplexed projection of layers at each depth by applying an algorithm that performs data conversion between a 2D data format and a 3D data format, wherein the step involves introducing multiplexing. The method comprises any or all of the following steps: generating a set of demultiplexed projections by considering different degrees of multiplexing at each depth of the interaction layer.

[0075] The inverse multiplexed data may be determined in either a selected DOI plane within the detector or any desired virtual detector plane.

[0076] In some embodiments, the estimation step may include the steps of: estimating a virtual two-dimensional non-multiplexed projection for each depth layer; and applying an iterative ML-EM algorithm, wherein during the steps, the data is transformed by forward and backward projections between the two-dimensional data format and the three-dimensional data format.

[0077] In some embodiments, demultiplexed projection is used to generate a three-dimensional solution, for example, a three-dimensional image dataset.

[0078] In all such cases, the present invention is particularly distinguished by the use of a measured depth of interaction data, which can be useful in adapting to overlap in a detector, for example, overlap across multiple pixels on a detector, and enabling a reduction of the resulting image artifact. This is presented as an alternative to the prior art approach that attempts to reduce image artifacts by directly reducing overlap in the detector. According to the principle of the present invention, if the depth of each interaction can be determined to some extent, it is possible to generate a dataset in which each photon interaction can be localized to some extent in all x, y, and z coordinates, and artifacts in the generated image can be reduced without requiring a collimator that is rigidly configured to avoid overlap between projections from adjacent apertures.

[0079] In a further embodiment of the present invention, a radiation detection system for detecting radiation from a radiation source is provided. A radiation detection system for detecting radiation from a radiation source, wherein the radiation detection system is Radiation detector and A collimator that can be positioned between the radiation source and the detector during use, wherein the collimator has a plurality of apertures, An operable processing module, wherein the processing module is Each of these responses is a response to the interaction with the incident radiation generated within the detector, For each of the plurality of responses, the characteristics of the interaction are determined, and the characteristics include at least the position and depth of the interaction within the detector. The system includes a processing module that processes the multiple responses according to the determined position and depth of each interaction by simultaneously processing the position and depth of interaction data in a manner that adapts to the multiplexing effect due to the overlap of projected radiation paths from multiple apertures in the collimator of the detector at the detected position on the detector.

[0080] Particularly preferably, the system is a system adapted to perform the method of the first aspect of the present invention.

[0081] Accordingly, in the embodiments, the processing module is operable to perform any appropriate combination of one or more of the determining steps or the processing steps of the method of the present invention as defined herein.

[0082] In one embodiment, the detector is adapted or configured to enable the interaction with incident radiation occurring within the detector to be localized to at least the location and depth of the interaction within the detector.

[0083] The system is particularly suited to the performance of the method of the first embodiment, and it will be understood that the preferred features of each embodiment are applicable to the other.

[0084] In particular, the system's processing module is operable to perform any of the steps of the method of the first aspect of the present invention, and / or the system may further include additional modules, such as an imaging module, which is operable to perform any of the steps of the method of the first aspect of the present invention.

[0085] In exemplary embodiments, the detector has an x,y plane and a z direction of the detector orthogonal thereto, and the processing module is operable to localize each interaction to a position in the x,y plane of the detector and to the depth of the interaction in the z direction of the detector. In some embodiments, the detector is adapted or configured to allow interaction with incident radiation generated within the detector and to enable such localization.

[0086] In the exemplary embodiments, the detector is pixelated into a plurality of individually addressable detector subunits, as defined above, and the processing module is operable to localize each interaction to a specific subunit and the depth of the interaction within it. In some embodiments, the detector is adapted or configured to allow interaction with incident radiation generated within the detector and to enable such localization.

[0087] In embodiments, the collimator may have a one-dimensional array or a two-dimensional array of multiple apertures. The apertures may be configured such that, for example, the radiation passing through the aperture tends to have a non-zero divergence angle at emergence, with reference to the short length and / or divergence profile of the direction of the emerging radiation. A preferred divergence angle may be at least 15 degrees.

[0088] In some embodiments, the collimator comprises multiple slits, for example, in a slit-slat arrangement. In other embodiments, the collimator comprises a two-dimensional array of pinholes. Other arrangements of multiple divergent apertures may also be considered.

[0089] In some embodiments, the detector is adapted or configured to allow the interaction with incident radiation generated within the detector to be localized to the location of the interaction within the detector in three dimensions.

[0090] For example, in some embodiments, the detector is a voxel detector comprising a three-dimensional voxel array. In such cases, for each of the plurality of responses, the step of determining the characteristics of the interaction, including the location of the interaction in at least three dimensions, includes the step of localizing the interaction to a specific voxel.

[0091] In some embodiments, the detector includes means for localizing interactions within the detector with respect to the x and y directions in a plane substantially perpendicular to the direction of the incident radiation, and with respect to the z direction, including the depth within the detector, in a direction substantially orthogonal to the x,y plane.

[0092] For example, the detector has a detection surface divided into multiple separately addressable detection parts that are positionally defined across the detection surface in each of two orthogonal directions, hereinafter referred to as the x-direction and the y-direction, thereby allowing the interaction of radiation particles incident from the source in the detection module to be positionally localized to the detection parts, and the radiation detector is configured to further positionally localize the interaction of radiation particles incident from the source in the detection module to a depth in the z-direction, a third orthogonal direction.

[0093] Therefore, the detector is configured to allow determination of the interaction depth (i.e., the dimension in the z-direction) at which each photon interaction occurs. This can be achieved in any suitable way through a combination of materials, structural features, and processing electronics.

[0094] For example, the detector may be fabricated from a material that inherently enables the extraction of information about the depth of interaction, such as a bulk crystalline cadmium telluride type solid semiconductor detector. The material constituting the semiconductor detector includes, for example, semiconductor detector materials selected from cadmium telluride, zinc cadmium telluride (CZT), manganese cadmium telluride (CMT), and their alloys, for example, crystalline Cd where a+b < 1 and a and / or b may be zero. 1-(a+b) Mn a Zn b Contains Te. Bulk single-crystal detectors are sometimes particularly preferred.

[0095] Additionally or alternatively, the detector may include multiple discrete layers in the z direction of a suitable detector material. For example, a multilayer scintillator detector may be suitable for carrying out the present invention.

[0096] In some embodiments, the method comprises the steps of generating an image and optionally displaying the image. The system may further comprise an image generation module for generating the image and an image display device. The method may further comprise the step of generating a series of images as tomography reconstruction. The system may further comprise a tomography reconstruction module that can influence them.

[0097] In some embodiments, the images are tomographic images, and the image generation module includes a tomographic image reconstruction module that generates a series of images as a tomographic reconstruction, for example, utilizing the 3D of the detected events to account for the uncertainty of the source of radioactivity. Optionally, this may be done directly within the reconstruction or as a pre-processing step. Optionally, a hybrid approach may be used, such as the hybrid method explored below.

[0098] In some embodiments, the image is an estimated activity distribution for a selected surface and is suitable for verifying system operation, and the image generation module includes a backprojection that takes into account the uncertainty of the origin of radioactivity as a preprocessing step, utilizing the 3D position of the detected events.

[0099] Other desirable features of the system in the second embodiment can be understood by analogy from the discussion of the method in the first embodiment, and vice versa. [Brief explanation of the drawing]

[0100] The present invention will be described below with reference to Figures 1 to 11 of the attached drawings.

[0101] [Figure 1] An example of a conventional multiple pinhole system is shown, in which the detection areas are spaced apart to avoid redundancy. [Figure 2]This demonstrates an alternative system for multi-pinhole detectors with a stationary high-resolution detector and low magnification. It also demonstrates an alternative multi-pinhole system with a stationary high-resolution detector and low magnification. [Figure 3] This demonstrates the principle of multiplexing pinhole projections. [Figure 4] This is a schematic flowchart illustrating an exemplary method for tomographic reconstruction of multiplexed data according to the principles of the present invention. [Figure 5] This is a schematic diagram of the method shown in Figure 4, which is applied to a detector with depth information resolution. [Figure 6] The following shows specific embodiments of the examples. [Figure 7] The following shows specific embodiments of the examples. [Figure 8] The following shows specific embodiments of the examples. [Figure 9] The following shows specific embodiments of the examples. [Figure 10] The following shows specific embodiments of the examples. [Figure 11] The following shows specific embodiments of the examples. [Modes for carrying out the invention]

[0102] Figure 1 shows an embodiment of a prior art multiple pinhole system in which the detection regions are spaced apart to avoid overlap. A pinhole collimator 6 is shown projecting from the object 2 onto a detector 8 having large detection regions or pixels defined to be spaced far enough apart to avoid overlap.

[0103] Each pinhole 4 within the collimator 6 will create at least a partial image of the target 2 on the detector surface 8. Reconstructing the entire target image from the detector data will consist of combining information from all the individual images created by each pinhole 4.

[0104] In this type of arrangement, the overlap of partial images, generally referred to herein as multiplexing, tends to introduce artifacts into the entire target image. Naturally, the larger the multiplexed area, the larger the resulting artifacts in the reconstructed target image. In the system of the example shown, the spacing of the detection areas or pixels, and the spacing of the pinholes, are selected so that each detection area or pixel corresponding to a pinhole in the collimator is essentially discrete, thereby avoiding overlap and preventing the generation of image artifacts in the reconstruction of the entire target image.

[0105] Figure 2 shows an alternative system with a stationary high-resolution detector and a multi-pinhole collimator arrangement 16b with low magnification. The collimator 16 projects from the object 12 to the corresponding detector 18. This system would seek to utilize a higher-resolution detector to employ lower magnification while maintaining the expected resolution. In other words, the number of pinholes can be significantly increased without having to enlarge the detector surface. The resulting multi-pinhole configuration can not only help improve image quality parameters but also lead to the ability to acquire 3D images without requiring separate acquisitions from multiple directions.

[0106] A standard method for designing multi-pinhole collimation is to ensure there is no overlap between the projections of individual pinholes. While increasing pinhole density may be advantageous for other reasons, it introduces overlapping regions, and the consequences must be addressed. When projections from adjacent pinholes overlap, a region is created on the detector that records events originating from two or more pinholes. Since it is impossible to know the actual source of the events, this introduces extra ambiguity into the detected signal. Depending on the overall system design, the reconstruction method used, and the nature of the source distribution itself, this uncertainty can lead to serious artifacts in the reconstructed 3D image.

[0107] The present invention utilizes data obtained on the depth of interaction in the z-direction of the detector, in addition to data on the interaction in the x,y planes of the detection surface, to mitigate this effect and eliminate artifacts. This is discussed with reference to Figure 3, for example, but in the context of multi-pinhole collimation, a similar principle would be applicable to other suitable arrays of apertures. There are other collimator configurations that can be used in the same way, such as "slit-slat" or "fan beam". They can provide angular sampling as well as multi-pinhole collimators, and therefore the same image reconstruction principle described below can be applied.

[0108] The detector needs to collect the depth of the interaction data. A detector that can do this in essence is preferred, and in one embodiment, a thick bulk semiconductor detector of zinc cadmium telluride (CZT) is used. Such a detector essentially allows for the determination of the depth of the photon interaction in the z direction and its position within a particular pixel in x, y. However, the present invention is not limited to such detectors. Such a semiconductor detector can be replaced by any “depth-sensing” or “3D position-sensing” detector structure, which includes, for example, a multi-layer scintillator detector module to provide some kind of depth sensing.

[0109] The embodiment utilizes the thickness of a semiconductor detector to acquire interaction depth (DOI) data, enabling constant separation between images from adjacent pinholes. The inherent depth resolution of the detector in the effect means that we have multiple independent detection layers. The pinhole projections may overlap in each detection layer, but the amount of overlap will differ, and the different parts of the overlap will cause overlap problems. This variation in overlap in the DOI layer provides additional information for the reconstruction process, which can ultimately resolve ambiguity from multiplexing, and this is key to artifact-free imaging.

[0110] Figure 3 illustrates the principle of pinhole projection multiplexing. The amount and position of overlap differ for each detection layer. This is utilized by the method of the present invention.

[0111] In general principle, the present invention includes a multi-aperture collimator not configured to avoid overlap between projections from adjacent apertures, a detector having a 3D position of interaction functions, and a reconstruction method. The collimator is configured to project at least two overlapping projections onto the detector, and the detector records radiation in multiple depth layers. A reconstructed image with reduced artifacts, and ideally artifact-free, is provided by a reconstruction algorithm using multilayer projection data.

[0112] The reconstruction algorithm may be a conventional algorithm capable of handling multilayer data, or the reconstruction algorithm may incorporate a novel demultiplexing step, as illustrated by the following embodiments and with reference to Figure 4, a schematic flowchart illustrating an exemplary method of tomographic reconstruction of multiplexed data according to the principles of the present invention.

[0113] Tomography reconstruction of multiplexed data can follow different paths, including iterative reconstruction using ML-EM, OS-EM, or more recent algorithms incorporating normalization. • Direct reconstruction in which the multiplexing (MX) effect is incorporated into the system matrix (SM) used in the iterative reconstruction process. (Option A) • Perform separate, iterative demultiplexing procedures in projection space before the final image reconstruction using conventional image reconstruction. (Option B) Options A and B can be combined with the output from reconstruction using demultiplexed data by initializing direct reconstruction. (Option C) • An alternating scheme between demultiplexing and reconstruction, where the previous image is used as initialization or normalization for the next step. (Option D) • Hybrid method: Reconfiguration that includes updates using both demultiplexed and multiplexed projections, in combination with options A and B above. (Option E)

[0114] The optimal algorithm (in terms of image quality relative to a given computational cost) will depend on the amount of multiplexing in different layers. The selection of the algorithm and its parameters can be done based on simulation data.

[0115] In an exemplary method embodying the principle of the present invention, multiplexing (MX) consists of the overlap of projections from different pinholes within the detector volume (upper half of Figure 5).

[0116] During the demultiplexing procedure, projection data from different pinholes is processed separately (lower half of Figure 5). • An iterative ML-EM algorithm is used to estimate a virtual 2D projection without multiplexing (MX). During this process, the data is transformed by forward and reverse projections (FP / BP) between 2D and 3D data formats, and multiplexing (MX) is introduced. • Automatically considers different multiplexing (MX) degrees in different DOI layers to derive a stable solution.

[0117] Multiplexed FP / BP operations can be performed by adding counts within the overlap / multiplexed regions and are very fast. In more sophisticated implementations, FP / BP can also take into account the resolution characteristics and / or pinhole penetration effects of each detector layer.

[0118] This is presented merely as an example. The key to the present invention is the use of detectors having intrinsic or constructed DOI layers, as shown in Figure 5. If the depth of each photon interaction, i.e., its position in the z direction within a deep detector, can also be determined to some extent, it is possible to create a dataset in which each photon interaction can be localized to some degree in all x, y, and z coordinates. Artifacts can be reduced in the generated image without requiring a collimator that is rigidly configured to avoid overlap between projections from adjacent apertures.

[0119] Possible advantages include the ability to collect effective datasets at the detector with much lower intrinsic source levels of radioactivity, and, for example in medical imaging, lower radiation doses to patient tissues.

[0120] The following are specific examples of algorithms. ·Demultiplexing The acquired multiplexed 3D projection data can be demultiplexed using an algorithm that involves the use of a 2D virtual data plane at a selected location relative to the physical detector. The demultiplexing algorithm can be described by the following steps, which are repeated for a number of iterations.

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[0121] Image merging A simple image of the activity distribution can be generated from inversely multiplexed projection data using a weighted summation process.

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[0122] Image reconstruction Based on data obtained through multiplexing or demultiplexing (either 2D or 3D) using ML-EM [Shepp & Vardi 1982], various approaches can be used to obtain the final image.

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[0123] Furthermore, these various processing steps can be performed alternately. An exemplary embodiment would alternate between several iterations of demultiplexing, several iterations of reconstructing the demultiplexed data, and several iterations of reconstructing the unmultiplexed data. It may be advantageous for these steps to include information from the other steps. A particular embodiment would involve a demultiplexing step in which the demultiplexing data must be close to the unmultiplexed projection of the previously obtained image estimation, which is a disadvantage. Another embodiment would be one in which there is no alternation, but the above steps are performed sequentially using the demultiplexed data as initialization for the final reconstruction. The final option is to combine the demultiplexing of the projections with their direct use in the system matrix, and to combine them within the updates in the reconstruction algorithm. Thus, the updates are based on both the ratio of the unmultiplexed estimated projection to the demultiplexed raw data, and the ratio of the estimated multiplexed projection to the raw data.

[0124] Detailed discussion of the approach in the examples The following provides a discussion of novel approaches to the reconstruction of highly multiplexed data for use in fixed-dose molecular breast tomosynthesis according to the principles of the present invention. These are intended to address the problems surrounding multiplexing (MX) that introduce ambiguity regarding the incident direction of detected gamma photons. We have developed various novel approaches to address this problem by performing demultiplexing either before or during DOI-assisted image reconstruction. By optimizing the system geometry, we have shown that it is possible to obtain a gain of 2x in effective sensitivity compared to systems without multiplexing.

[0125] The applicant has developed a fixed tomosynthesis system for MBl based on a CZT detector with DOI and MPH collimation. The basic idea is that by using multiple pinholes, multiplexing becomes possible, resulting in higher sensitivity and improved sampling. Multiplexing introduces some ambiguity regarding the incident direction of detected gamma photons, which can lead to artifacts in the reconstructed image. However, it has been shown in the past that artifact-free images can be obtained by combining multiplexed and unmultiplexed data. DOI information has the potential to provide data with a variable amount of multiplexing and therefore can assist in demultiplexing.

[0126] To optimize system performance, various design configurations in a multi-parameter space were investigated. Furthermore, a novel demultiplexing approach applicable to projection data before reconstruction was developed. Here, this approach was compared with direct reconstruction, which incorporates multiplexing into the system matrix, similar to the hybrid approach.

[0127] Materials and methods Data generation The exemplary system consists of two planar CZT detector arrays positioned opposite each other (Figure 6 shows the complete system geometry (left) and a magnified blow-up of the corner region showing the multiplexing (right)). We assume mild breast compression with an average thickness of 6 cm. The authors performed simulations for a 16x16 cm detector size with a 1x1 mm pixel size and for DOI estimation in a 1 mm layer. For system optimization, the following parameters were investigated: number of pinholes, pinhole aperture size, pinhole aperture angle, and collimator-detector distance.

[0128] First, the parameter space was narrowed down using analytical calculations of the contrast-to-noise ratio (CNR). Next, analytical simulations were performed to generate projection data corresponding to a phantom containing one layer of spherical damage in each of the four quadrants of 36 spheres. The diameter of the spheres was 6 mm, and the ratio of spheres to background was 5, 10, 15, and 20 in the four quadrants, respectively. The simulation was also performed with the four layers of spheres spaced 15 mm apart. The simulation was as follows: 99m This was a 10-minute patient scan following a 150 MBq Tc-MIBI injection. The background radioactivity concentration was estimated at 760 Bq / mL.

[0129] Demultiplexing and reconstruction This algorithm consists of iterative steps in which data is projected forward and backward between a virtual 2D plane representing each pinhole and a block of 3D detectors (Figure 7 shows the forward transformation process in the inverse multiplexing algorithm; the virtual plane is projected (FP) onto the multilayer detector block and then merged with multiplexing (MX)).

[0130] This demultiplexing method differs from conventional implementations in that it is completely independent of the tomography reconstruction process.

[0131] Three different approaches were employed for tomography reconstruction: 1) a one-step direct image reconstruction incorporating multiplexing into the system matrix [Option A], 2) a two-step demultiplexing applied to projection data before tomography reconstruction [Option B], and 3) a combination of the two methods. In each iteration, the image was updated using the average of correction factors obtained from the multiplexed and demultiplexed data [Option E] (Figure 8 shows a schematic of the hybrid reconstruction algorithm, where correction factors are calculated based on both the multiplexed and demultiplexed data). For reconstruction, a prior MAP algorithm obtained by distance-dependent smoothing for resolution equalization was used.

[0132] Here, we compare three approaches regarding contrast and noise. We also compare the results with images reconstructed from ideal projection data for the same geometric shape but without multiplexing (which is practically impossible).

[0133] result The target-to-background ratio (TBR) was calculated for spheres within a single-layer phantom, and the coefficient of variation was calculated in a uniform region away from the spherical surface. Figure 9 shows TBR vs. CoV curves for different MPH configurations of 8x8 to 16x16 pinholes per head, with separations of 10-16, 18, and 20 mm. The solid line with a circle represents the case without ideal (but unattainable) multiplexing, while the dashed line with a circle represents different reconstruction approaches for multiplexed data. The dotted line connects the points for the same pinhole separation. The 8x8 configuration with 20 mm spacing corresponds to the case without actual multiplexing. The graph resembles a "bow and arrow," with the "arrow" corresponding to the ideal no-multiplexing situation, and the other three curves corresponding to different reconstruction approaches. Starting from the no-multiplexing case on the right side of the graph, initially all three curves move more or less in the same direction as the ideal curve. These then appear to hit an invisible barrier and bounce back in different directions due to unresolved multiplexing or noise amplification. Along this "invisible barrier," there are multiple solutions, which are essentially equivalent but have different bias-to-noise trade-off relationships. The "bow" intersects the "arrow" at a point corresponding to a pinhole separation of ~14.3 mm. Compared to the case without multiplexing, this represents an effective increase in sensitivity (20 / 14.3). 2 This corresponds to an increase in pinhole density due to a coefficient of approximately 2.

[0134] An MPH configuration with 14x14 pinholes spaced 12 mm apart was selected for further evaluation. Reconstructed images are shown in Figure 10 for different reconstruction approaches. Reconstructed images (transverse, coronal, and sagittal) are shown in the 14x14 pinhole configuration (12 mm separation) with different reconstruction approaches: a) ideal case with no multiplexing, b) one-step, c) two-step, and d) hybrid reconstruction.

[0135] Figure 11 shows TBR vs. CoV curves for different reconstruction approaches in single-layer and multi-layer phantoms. BR vs. CoV curves for different iteration counts (1-8) are shown for reconstruction approaches in single-layer (top) and multi-layer (bottom) phantoms. The curve without multiplexing is always optimal because it represents the ideal case without multiplexing, which is practically impossible. It can be seen that the best approach differs for the two phantoms (apart from the ideal case without multiplexing), being 1 step for the single-layer phantom and 2 steps for the multi-layer phantom. In both cases, the results of the hybrid method fall between the other two, representing a good compromise.

Claims

1. A method for processing radiation from a radiation source, The steps include positioning a detector to receive radiation from the aforementioned radiation source, A step of positioning a collimator between the radiation source and the detector, wherein the collimator has a plurality of apertures, The steps include: causing radiation from the radiation source to pass through the collimator and enter the detector; The steps include receiving a plurality of responses, each of which is a response to interaction with incident radiation generated within the detector, A step of determining the characteristics of the interaction for each of the plurality of responses, wherein the characteristics include at least the location and depth of the interaction within the detector. The process includes processing the multiple responses by simultaneously processing the position and depth of the interaction data in a manner that adapts to the multiplexing effect due to the overlap of projected radiation paths from multiple apertures in the collimator at the detected position on the detector. The image dataset is generated by tomography reconstruction, which involves processing multiple consecutive particle interaction data, and the method is as follows: To reduce multiplexing artifacts in reconstructed tomography images, the method includes a step of processing the location and depth of interaction data in a manner that adapts to the effect of multiplexing on the reconstructed tomography image dataset. Processing to adapt the effects of the multiplexing to the reconstructed tomography image dataset is performed by a demultiplexing procedure. The steps include dividing the depth of the detector volume into a finite number of different depths of the interaction layer, A step of estimating a virtual two-dimensional, non-multiplexed projection of layers at each depth, and applying an algorithm to perform data conversion between a two-dimensional data format and a three-dimensional data format, wherein multiplexing is introduced in this step. A method characterized by comprising any or all of the following steps: generating a set of demultiplexed projections by considering different degrees of multiplexing at each depth of the interaction layer.

2. The steps include determining an input dataset that includes the determined location and depth of each interaction within the detector, The method according to claim 1, comprising the step of processing the input dataset to adapt to the effects of the multiplexing, thereby generating a modified dataset that includes at least data including the location of each interaction modified in a manner that adapts to the effects of multiplexing due to the overlap of the paths of the projected radiation from the plurality of apertures, before or as part of the tomographic reconstruction.

3. The aforementioned estimation step is, The steps include: estimating a virtual two-dimensional, non-multiplexed projection for each depth of the layer; The method according to claim 1 or 2, comprising the step of applying an iterative ML-EM algorithm, wherein during the step, the data is transformed by forward and backward projections between the two-dimensional data format and the three-dimensional data format.

4. The detector has an x, y plane and a z direction of the detector that is orthogonal thereto. The method according to any one of claims 1 to 3, further comprising the step of localizing each interaction to a position in the x,y plane of the detector and to the depth of the interaction in the z direction of the detector.

5. The detector is pixelated into a plurality of individually addressable detector subunits, The method according to any one of claims 1 to 4, further comprising the step of localizing each interaction to a specific subunit and the depth of the interaction therein.

6. The collimator is A pinhole array and The method according to any one of claims 1 to 5, comprising one or more arrays of slits.

7. The method according to any one of claims 1 to 6, comprising the use of a detector adapted or configured to enable three-dimensional localization of the interaction with incident radiation generated within the detector to the interaction location within the detector.

8. A method comprising the use of a detector comprising a three-dimensional voxel array, wherein the step of determining the characteristics of the interaction, including at least three-dimensional location of the interaction, for each of the plurality of responses, comprises the step of localizing the interaction to a specific voxel, according to claim 7.

9. A radiation detection system for detecting radiation from a radiation source, wherein the radiation detection system is Radiation detector and A collimator that can be positioned between the radiation source and the detector during use, wherein the collimator has a plurality of apertures, An operable processing module, wherein the processing module is Each of these responses is a response to the interaction with the incident radiation generated within the detector, For each of the plurality of responses, the characteristics of the interaction are determined, and the characteristics include at least the position and depth of the interaction within the detector. The system includes a processing module that processes the multiple responses according to the determined position and depth of each interaction by simultaneously processing the position and depth of interaction data in a manner that adapts to the multiplexing effect due to the overlap of projected radiation paths from multiple apertures in the collimator of the detector at the detected position on the detector, The method generates an image by processing a series of consecutive particle interaction data through tomography reconstruction, and the method is as follows: To reduce multiplexing artifacts in reconstructed tomography images, the method includes a step of processing the location and depth of interaction data in a manner that adapts to the effect of multiplexing on the reconstructed tomography image dataset. Processing to adapt the effects of the multiplexing to the reconstructed tomography image dataset is performed by a demultiplexing procedure. The steps include dividing the depth of the detector volume into a finite number of different depths of the interaction layer, A step of estimating a virtual two-dimensional, non-multiplexed projection of layers at each depth, and applying an algorithm to perform data conversion between a two-dimensional data format and a three-dimensional data format, wherein multiplexing is introduced in this step. A radiation detection system characterized by having any or all of the following steps: generating a demultiplexed projection set by considering different degrees of multiplexing at each depth of the interaction layer.

10. The system according to claim 9, wherein the processing module is further operable to perform one or more of the determining steps or processing steps described in any one of claims 1 to 3.

11. The system according to claim 9 or 10, wherein the detector is adapted or configured to enable the interaction with incident radiation generated within the detector to be localized to at least the position and depth of the interaction within the detector.

12. The detector has an x, y plane and a z direction of the detector that is orthogonal thereto. The system according to any one of claims 9 to 11, wherein the processing module is operable to localize each interaction to a position in the x,y plane of the detector and to the depth of the interaction in the z direction of the detector.

13. The detector is pixelated into a plurality of individually addressable detector subunits, The system according to any one of claims 9 to 12, wherein the processing module is operable to localize each interaction to a specific subunit and the depth of the interaction therein.

14. The collimator is A pinhole array and The system according to any one of claims 9 to 13, comprising one or more arrays of slits.

15. The system according to any one of claims 9 to 14, wherein the detector is a voxel detector comprising a three-dimensional voxel array.

16. The system according to any one of claims 9 to 15, wherein the detector is a semiconductor detector.

17. The system according to claim 16, wherein the semiconductor detector comprises a semiconductor detector material selected from cadmium telluride, zinc cadmium telluride (CZT), manganese cadmium telluride (CMT), and alloys thereof.

18. The semiconductor detector is a crystalline Cd where a+b < 1 and a and / or b may be zero. １－（a＋b） Mn a Zn b The system according to claim 17, including Te.

19. The system according to any one of claims 9 to 18, further comprising an image generation module for generating images.

20. The system according to claim 19, wherein the image is a tomographic image, and the image generation module comprises a tomographic image reconstruction module that uses the 3D position of the detected event to generate a series of images as a tomographic reconstruction that takes into account the uncertainty of the source of radioactivity.

21. The system according to claim 19 or 20, wherein the image is an estimated activity distribution for a selected target surface and is suitable for verifying system operation, and the image generation module includes backprojection that takes into account uncertainty about the origin of radioactivity as a preprocessing step, utilizing the 3D position of the detected events.

Images