Radiation detection system

Abstract

A method for detecting radiation from a source and a radiation detection system embodying the principles of the method are described, comprising the steps of positioning a radiation detector to receive radiation from the source, applying a multiplexing transform to the radiation from the source to create three-dimensional complexity in the pattern of radiation from the source, receiving a plurality of responses, each response to an interaction with 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 in three dimensions of the interaction within the detector, and processing the plurality of responses according to the determined position in three dimensions of each interaction within the detector and deriving inferences therefrom regarding the pattern of radiation from the source.

Description

Technical Field

[0001] The present invention relates to a radiation detection system for detecting radiation from a radiation source, such as a radioactive isotope source, and in particular to a system adapted for detecting radiation from a radiation source that generates a low signal in a detector. The present invention further relates to a method for detecting radiation from such a radiation source.

Background Art

[0002] There is a wide range of scenarios where it may be desirable to obtain more accurate information regarding the radiation emitted from a radiation source and received by a detection system. In particular, there is a wide range of scenarios where it may be desirable to resolve information spatially and / or spectrally, for example, to provide additional information regarding 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 regarding the object under examination.

[0004] An example of such a latter scenario is nuclear medicine imaging, where radiation from a radioactive isotope source is passed through a part of the subject's body and spatially registered information regarding the received radiation by a remote detector is used to obtain information regarding the structure and / or real-time physiological function of that part of the patient's anatomy 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 of resolvable data from a relatively small number of particles of the radiation emitted from the radiation source incident on the detector is consequently reduced, making it more difficult to resolve meaningful information from the background. Such considerations are particularly likely to apply in medical applications where there are clear requirements to minimize the radiation dose received by the subject. Thus, here too, nuclear medicine imaging provides a good example of a technology to which the principle of the present invention can be advantageously applied.

[0006] However, the advantages of the present invention regarding the resolution of higher levels of information from low-level signals generally apply in 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 would be the inspection of nuclear facilities using a portable gamma camera.

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

[0008] An example of an established nuclear medicine imaging technique is SPECT (single-photon emission computed tomography), a nuclear medicine tomography technique using gamma rays. This technique requires, for example, the delivery of a radioactive isotope that emits gamma rays to a patient via the bloodstream. In a typical application, the radioactive isotope is bound to a specific ligand, enabling it to be carried to and bound at the location of interest within the body of the subject being examined.

[0009] The radioactive isotope passes through the tissue of the subject and emits gamma rays that can be detected by a suitable detector, such as a gamma camera. SPECT imaging using a gamma camera acquires a plurality of two-dimensional images, which are then constructed into a three-dimensional data set using standard tomography reconstruction techniques.

[0010] The same principle is adopted in positron emission tomography (PET). In this case, the radioisotope that emits positrons is usually introduced into the body as part of a radioactive ligand. In this case, the emitted positrons are locally annihilated, and the system detects a pair of gamma rays indirectly emitted by this annihilation event.

[0011] Both techniques are particularly powerful and enable not only imaging of relevant parts of the body but also active functional imaging of biological processes.

[0012] A well-known technique for imaging breast tissue, for example, a technique for detecting abnormalities that may lead to early detection of breast cancer, is mammography. In standard mammography, images are created using X-rays. These images are then analyzed for abnormal findings, such as characteristic density masses that may indicate a potential tumor. These patients are then typically referred for further, usually more invasive, tests. Thus, standard mammography is a widely adopted first-stage screening technique.

[0013] 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 that may indicate the potential occurrence of many common tumors, and the discrimination ability of this technique in patients with a high proportion of dense breast tissue is consequently reduced.

[0014] Molecular breast imaging (MBI) is a nuclear medicine imaging technology developed that utilizes many of the above principles of SPECT-type technology. A radioactive isotope source that binds to an appropriate ligand and is positioned within breast tissue is introduced into the subject being examined. To detect the radiation from the source after it has passed through the breast tissue, a suitable system of a small semiconductor-based gamma camera configured generally corresponding to that for more conventional mammograms is used. Since this technology can distinguish between structure and physiological activity, it is particularly effective for detecting early tumors. However, generally, this exposes the patient being examined to a higher total radiation dose, which tends to limit its application as a first-stage screening technology.

[0015] In all nuclear medicine imaging technologies, there is a clear essential condition to keep the radioactivity of the source, and as a result, the radiation dose received by the subject being examined, as low as possible. The low signal collected by the detector as a result poses particular problems in relation to both the detection and resolution of the data.

[0016] The factor that affects the required source signal is the detection efficiency. In particular, in relation to imaging technology, a detection system that can distinguish a plurality of separately addressable detection points or regions in the x and y directions is required to obtain the required x, y resolution. In an imaging system, each point or region may correspond to a pixel in the reconstructed image and is generally also referred to as a pixel on the detector. To achieve an effective x, y resolution in the resulting image, a detection system is required that can distinguish the "pixels" in the x and y directions in a way that allows an effective signal to be obtained individually for each of the separately addressable "pixels" in the x and y directions.

[0017] Any kind of radiation detector, particularly solid detectors widely used in conventional medical imaging applications, is typically characterized by the fact that its efficiency depends on its thickness. While this need not be an obvious relationship, in most cases, the thicker the detector, the higher its efficiency. Typically, the efficiency of solid detectors widely used in conventional medical imaging applications is enhanced by providing an appropriate depth in the z direction, orthogonal to the x and y of the detection surface.

[0018] However, in order to maintain position registration in x and y in a detector having a substantial depth in the z direction, it is necessary to collimate the signals emitted from the source incident on the detector. The quality and usefulness of any image in nuclear medicine imaging technology are critically affected by the collimator structure. It is common to use a collimator such as a parallel hole collimator with a very small divergence angle between the source and the gamma camera or other detector. This collimator creates a registration in the signal between the source and the detector, approaching a one-to-one registration in the x, y plane.

[0019] Therefore, the effective development of devices for technologies embodying nuclear medicine images such as SPECT, PET or MBI is a compromise between the requirements for effective collimation that achieves substantially one-to-one registration in the x and y directions, such as using a parallel hole collimator with a very small divergence angle, the resulting reduction of the signal by the collimator, and the requirement for a radiation source with as low a dose as possible. SUMMARY OF THE INVENTION PROBLEMS TO BE SOLVED BY THE INVENTION

[0020] There is a general desire to provide alternative detection systems and methods that enable resolution of information regarding radiation from low signal sources.

[0021] It is particularly desirable to provide such alternatives that are applicable in nuclear medicine and that can address these opposing considerations in a more effective and efficient manner, providing improved resolution of physiologically relevant data from patients and / or reduced radiation dose levels.

Means for Solving the Problems

[0022] According to the present invention in a first aspect, a method of detecting radiation from a radiation source comprises: positioning a radiation detector to receive radiation from the radiation source; applying multiplex conversion to the radiation from the radiation source to create three-dimensional complexity in the pattern of the radiation from the radiation source; receiving a plurality of responses, each being a response to an interaction with incident radiation occurring within the detector; for each of the plurality of responses, determining characteristics of the interaction, the characteristics including at least a position in three dimensions of the interaction within the detector; processing the plurality of responses according to the determined positions in three dimensions of each interaction within the detector, and therefrom drawing inferences regarding the pattern of the radiation from the radiation source.

[0023] The present invention is distinguished by three steps. converting the incident radiation to add three-dimensional complexity; measuring the complexity in the detector by determining the position in three dimensions of the interaction within the detector for each radiation interaction in the detector; deconvolving the resulting pattern of interactions within the detector to reconstruct an image of the pattern of radiation from the radiation source, thereby enabling inferences to be made about the radiation source from the reconstruction.

[0024] The present invention is clearly characterized over the prior art by the intentional introduction of three-dimensional complexity into the pattern of radiation from a radiation source, the detection of this three-dimensional complexity, and the use of this detected complexity in a processing stage.

[0025] That is, the multiplexed pattern of radiation has three-dimensional complexity introduced not only in the x, y plane of the detector but also in the z direction of the detector, and the detector localizes the respective interactions not only in the x, y plane of the detector but also in the z direction of the detector, and then it is inherent to the present invention to deconvolve this three-dimensional data set to reconstruct a picture of the pattern of radiation from the radiation source.

[0026] It should be understood here that references to multiplexing transformations are to be considered to have the general meaning shown. It is effective in creating complexity in three dimensions in the pattern of radiation from a radiation source when applied to the radiation from the radiation source, and this three-dimensional complexity is utilized in later stages of the present invention by its intentional detection at the detector and also by the use of this detected complexity in a processing stage. No more precise and limited meaning of multiplexing / multiplexing devices that may be technically applicable in specific fields such as telecommunications, data transmission in computer networks, electronics and signal processing, or other technologies should be inferred.

[0027] The function of this multiplexing transformation for retaining more complexity in the data, its intentional detection, and the subsequent analysis of the more complex data can be contrasted with that of a parallel-hole collimator or a similar filter in a conventional imaging device for nuclear medicine tomography imaging, for example.

[0028] In such prior art, the conventionally adopted approach is to limit the complexity of the radiation from the radiation source to two dimensions corresponding to the x and y planes of the detector by means of collimation, and to detect localized interactions, for example, for each pixel, in the x and y planes within the detector. In the prior art approach, the variation of the x and y positions with respect to z is regarded not as a feature to be utilized but as a problem to be eliminated.

[0029] In conventional nuclear medicine imaging, a radioactive isotope administered to a subject is localized in a part of the subject's body. For example, in the case of MBI in breast tissue, radiation from the radiation source is detected by a detector, and is used to reconstruct information about the tissue through which the radiation directly spatially registered in the x and y directions has passed. For example, it is used to construct an image, and in the case of tomography, it is used to construct images of consecutive layers.

[0030] This requires the use of a pixelated detector and the maintenance of a substantially one-to-one registration in the x and y directions between the source radiation and the separately addressable pixels on the detector surface.

[0031] Such pixelated detectors, in which the detector is effectively subdivided into a plurality of detection portions arranged in the detector x and y directions, are of course familiar. The detector can be easily pixelated, for example, by providing discrete subunits, appropriate processing electronics, or a combination of the two.

[0032] The type of radiation detector envisioned for the present invention is typically characterized by the feature that its efficiency depends on its thickness. The efficiency of the detector is usually increased by providing an appropriate depth. Each detection portion or "pixel" of such a detector also follows having a substantial depth in a third orthogonal or z direction. The depth is likely to be such that the depth in the z direction for a given detection portion is several times larger than the lateral extent of the detection portion in x and y (i.e., the "pixel" size in x and y).

[0033] In the conventional systems as described above that attempt to maintain a nearly one-to-one position registration in x and y between the line source and the detector, this can cause problems because deeper levels of particle interactions can register in the "wrong" detection section or pixel, distorting the resulting image.

[0034] Therefore, conventional systems include filters such as collimators between the line source radiation and the detector to create this nearly one-to-one registration in x and y with the pixelated area of the detector. For example, a parallel hole collimator with a very narrow angle aperture is used. This is intended to maintain a substantially monotonic one-to-one position registration in x and y in the radiation pattern as it passes from the line source to the detector.

[0035] The parallel holes are given an aperture with a narrow enough angle to create a substantially one-to-one registration directly between the line source of the detector and the individual pixels. This ensures that any photon detected at any depth within the detector is correctly registered and associated with the pixel on the surface where the interaction occurs. Without this narrow collimation angle, there would be no such consistent registration between the surface interaction and the depth interaction associated with each pixel, and a loss of image resolution would be caused.

[0036] This drawback is that a significant number of photons do not reach the detector. In a typical MBI system, perhaps only 1 out of 10 4 photons is registered. Similar levels are typical of other SPECT-type technologies.

[0037] As a result, much higher sources of radiation are required, and in the case of medical images, as a result, higher radiation doses within the patient's tissue are required to obtain a satisfactory number of photon interactions at the detector to generate an image. Alternatively, by using, for example, holes of larger dimensions to relax the angle through which the collimator passes, the image resolution is lost.

[0038] Thus, in the language of the present invention, the collimator acts on the radiation from the radiation source to convert it, removing the third-dimensional complexity from the pattern of the radiation from the radiation source and creating data that is essentially monotonically and completely registered in x and y at the detector. Correspondingly, in the case of an imaging system at the detector, each pixel at the detector corresponds to and is used by subsequent processing electronics to directly reconstruct the corresponding pixel in the image data set.

[0039] In contrast, the present invention is clearly characterized by intentionally detecting this complexity in three dimensions at the detector, by using multiplexed conversion that intentionally adds a certain degree of complexity in three dimensions to the radiation pattern, by providing a processing module to reconstruct this more complex data and draw additional or alternative inferences regarding the radiation from the radiation source, and by reconstructing information regarding the subject / body from this more complex data when the source radiation has passed through a subject such as a part of a patient's body or has emerged from an object being examined.

[0040] As a result, the present invention takes a very different approach to the obvious contradiction in the prior art between maintaining an appropriate signal / reducing the radiation dose and losing the image contrast. It depends on the following realization. If the depth of each photon interaction, i.e., the z-direction position within the deep detector, can also be resolved to some extent, a dataset is generated in which each photon interaction can be localized to a certain position in all of the x, y, and z coordinates, thereby allowing a speculation to be drawn. The dataset can be deconvolved by an appropriate reconstruction method in an appropriate processing and reconstruction module, thereby eliminating the need to collimate for the purpose of approximately 1-to-1 x, y registration. As a result, the number of photons that are prevented from passing through the filter can be significantly reduced. Therefore, the proportion of photons passing through the filter that are usefully collected and meaningfully processed in the detection module can be significantly increased. A valid set of data can be collected with a detection module having a very low intrinsic radiation source level. For example, in the case of a medical image, a lower radiation dose as a result within the patient's tissue can be obtained.

[0041] Nevertheless, it will be understood that some form of multiplexing transformation is required to add complexity to the pattern of radiation from a radiation source having some functional variation with distance. Without this additional complexity, there would be no pattern in the data regarding the interactions detected by the detector, even if the three-dimensional positional resolution were as envisioned by the present invention. Therefore, some form of multiplexing converter or filter is used to introduce this complexity into the pattern of radiation from the radiation source.

[0042] Unlike a conventional parallel collimator, a multiplexer or filter does not attempt to introduce a monotonic relationship between the order of radiation from a radiation source and the order of radiation at a detector. For example, it is arranged at individual pixels on the detector. It does not attempt to reduce the complexity of the pattern to two dimensions only. Rather, it introduces a resolvable three-dimensional complexity into the radiation detected by the detector, which can be detected by using a detector that detects the depth of interaction and focuses on the mere x, y positions, and can then, in principle, be resolved at the processing stage.

[0043] There is a need for a method of performing a multiplexing transformation on the radiation from a radiation source to create a three-dimensional complexity in the pattern of radiation from the radiation source.

[0044] In a possible embodiment, the multiplexing transformation is performed in that the radiation from the radiation source is passed through a multiplexer or filter configured to generate a three-dimensionally resolvable complexity with respect to the pattern of radiation from the radiation source when the radiation from the radiation source passes through the filter.

[0045] A suitable multiplexing filter may be positionable during use between the radiation source and the detector and may include a discrete structure configured when arranged to generate a three-dimensionally resolvable complexity with respect to the pattern of radiation from the radiation source before the radiation is incident on the detector.

[0046] In addition or alternatively, the multiplexing filter may be combined with the detector and / or the detector may be provided with a detector adapted to perform the multiplexing transformation.

[0047] Such a multiplexing filter is not a monotonic collimator as in the prior art. It does not perform a transformation on the radiation from the radiation source to remove the three-dimensional complexity from the pattern of radiation from the radiation source and create data that is essentially monotonically and completely position-registered in x, y at the detector. It is necessary for the radiation that has undergone the multiplexing transformation to have a certain degree of resolvable complexity, but this resolvable complexity has been shown to have a three-dimensional functional relationship with the source radiation.

[0048] A filter that includes merely a pair of pinholes would be sufficient in the form of a synthetic overlapping conical shape of radiation that provides the required complexity. It is simply sufficient that there is no substantial monotonic correspondence in x and y between the signal incident on the filter and the signal passed by the filter as in the case of a theoretically perfect parallel-hole collimator.

[0049] In contrast, the present invention depends on the realization that when each photon interaction in the detector is positioned not only simply in the x and y coordinates, but also sufficiently in the z coordinate by determining the depth within the detector where the interaction occurs, monotonic collimation is no longer necessary, nor even desirable, and instead, a multiplexing filter that passes a fairly large proportion of the incident photons from the source may be used in combination with appropriate processing and reconstruction modules to deconvolve the three-dimensional data and extract information therefrom.

[0050] According to the present invention, the method includes receiving a plurality of responses to a corresponding plurality of interactions with incident radiation occurring within a detector, and for each such response, determining at least the three-dimensional position within the detector of the interaction.

[0051] For example, the method of the present invention includes the use of a detector adapted or configured to enable an interaction with incident radiation occurring within the detector to be localized to an interaction position within the detector in three dimensions. The method in such a case includes the steps of causing radiation from a source to be incident on such a detector and performing a receiving step and a determining step in response thereto.

[0052] In some embodiments, for example, the present invention includes the use of a detector including a three-dimensional voxel array, and the determination for each of the plurality of responses includes that the characteristics of the interaction, including at least the position of the interaction in three dimensions, locally include the interaction for a particular voxel.

[0053] Preferably, the detector comprises means for localizing interactions within the detector in each of the x and y directions in a plane substantially perpendicular to the direction of the incident radiation, in a direction substantially orthogonal to the x, y plane, and in the z direction including the depth within the detector.

[0054] For example, the radiation detector includes a detection surface divided into a plurality of separately addressable detection portions positioned across the detection surface in each of two orthogonal directions, hereinafter the x and y directions, whereby the interaction of particles of radiation incident from a radiation source in a detection module may be positioned in a detection portion, and the radiation detector is configured such that the interaction of particles of radiation incident from a radiation source in a detection module may be further positioned in the depth in a third orthogonal direction, hereinafter the z direction.

[0055] The method further includes, for example, receiving and processing radiation data from a plurality of successive particle interactions in a detector in a suitable processing module in data communication with the detector, each thereby being positioned in a particular voxel and / or x, y, and z coordinates.

[0056] The principles of the present invention can be applied to various types of radiation from various sources incident on a suitably aligned detector. The radiation preferably includes high-energy radiation such as ionizing radiation, for example, high-energy electromagnetic radiation such as X-rays and / or gamma rays or subatomic particle radiation, and the detector system is correspondingly adapted to detect this type of radiation and detect it in a suitable spectrum.

[0057] According to a further aspect of the present invention, there is provided a radiation detection system for detecting radiation from a radiation source. The radiation detection system comprises a detector, and a multiplexing converter operating based on the radiation from the radiation source to create a three-dimensional complexity in the pattern of the radiation from the radiation source, and a processing module, wherein the processing module Receiving a plurality of responses that are each a response to an interaction with incident radiation occurring within a detector, For each of the plurality of responses, determining a characteristic of the interaction, the characteristic including at least a position in three dimensions of the interaction within the detector, A processing module operable to process the plurality of responses according to determined positions in three dimensions of each interaction within the detector and therefrom draw inferences regarding a pattern of radiation from a radiation source.

[0058] The system is in particular a system adapted to the performance of the method of the first aspect, and it will be understood that the preferred features of each aspect are applicable to the other also.

[0059] In particular, the multiplexing converter is configured to be operable with respect to radiation from a radiation source and is positionable, for example, to introduce three-dimensional complexity not only in the x, y plane of the detector but also in the z direction of the detector. In particular, the detector is configured to localize each interaction not only in the x, y plane of the detector but also in the z direction of the detector. In particular, the processing module is operable to collect the resulting three-dimensional data set and then deconvolve the same to reconstruct a drawing of the pattern of radiation from the radiation source.

[0060] This function of the multiplexing converter for retaining greater complexity of data, its intentional detection, and the subsequent deconstruction of the more complex data can be contrasted as above with the function of a collimator or similar filter in a conventional imaging device for nuclear medicine tomography imaging.

[0061] By using a multiplexing transducer that intentionally adds a certain degree of three-dimensional complexity to the radiation pattern, and by intentionally detecting this complexity in three dimensions at the detector, a processing module is provided that reconstructs even more complex data and draws additional or alternative inferences regarding the radiation from the source. When the source radiation passes through an object under examination, such as a part of a patient's body, or emerges from the object under examination, information regarding the object / body can be reconstructed from this more complex data at this much lower inherent radiation source level. As a result, for example, in the case of a medical image, a lower radiation dose is brought into the patient's tissue.

[0062] Nevertheless, it will be understood that some form of multiplexing is required to add complexity to the pattern of radiation from a source that has some functional variation with distance. Without this additional complexity, there would be no pattern in the data regarding the interactions detected by the detector, even if the three-dimensional positional decomposition as envisioned by the present invention were achieved.

[0063] In some embodiments, a suitable multiplexing filter may be positionable during use between the source and the detector and may comprise a discrete structure configured when arranged to generate a three-dimensionally resolvable complexity to the pattern of radiation from the source before the radiation is incident on the detector.

[0064] In addition, or alternatively, the multiplexing filter may be combined with the detector and / or the detector may be provided with a detector adapted to perform the multiplexing conversion.

[0065] A filter comprising just a simple pair of pinholes will be sufficient in the form of a synthetic overlapping cone of radiation that provides the required complexity. It is simply sufficient that there is no substantial monotonic correspondence in x, y between the signal incident on the filter and the signal passed by the filter as in the case of a theoretically perfect parallel hole collimator.

[0066] Preferably, the detector is adapted or configured such that an interaction with incident radiation occurring within the detector is localized in three dimensions to an interaction position within the detector.

[0067] For example, in some embodiments, the detector is a voxel detector including an array of three-dimensional voxels. In such cases, for each of a plurality of responses, determining the characteristics of the interaction including at least the position in three dimensions of the interaction comprises localizing the interaction to a particular voxel.

[0068] In some embodiments, the detector comprises means for localizing an interaction within the detector in each of the x and y directions in a plane substantially perpendicular to the direction of the incident radiation, and in a z direction including the depth within the detector in a direction substantially orthogonal to the x, y plane.

[0069] For example, a radiation detector includes a detection surface divided into a plurality of separately addressable detection portions positioned across the detection surface in each of two orthogonal directions, hereinafter the x and y directions, whereby an interaction in a detection module of a particle of radiation incident from a line source may be positioned to a detection portion, and the radiation detector is configured such that an interaction in a detection module of a particle of radiation incident from a line source may further be positioned to a depth in a third orthogonal direction, hereinafter the z direction.

[0070] Ultimately, it is a fundamental and necessary feature of the present invention that the detector is configured to enable determination of the depth of the interaction (i.e., the dimension in the z direction) at which each photon interaction occurs. This may be achieved in any suitable manner by a combination of materials, structural features and processing electronics.

[0071] For example, detectors can be fabricated from materials that inherently enable extraction of the depth of interaction information, such as a bulk crystalline cadmium telluride type solid state semiconductor detector. The material constituting the semiconductor detector is selected from, for example, cadmium telluride, cadmium zinc telluride (CZT), cadmium manganese telluride (CMT), and alloys thereof, for example, crystalline Cd where a + b < 1 and a and / or b may be 0 1-(a+b) Mn a Zn b Te. Bulk single crystal detectors may be particularly preferred. Advantageously, this type of detector is effective in that it is inherently adapted for determination of the depth of interaction with respect to an incident radiation event. Advantageously, this type of detector exhibits high sensitivity to X-rays and gamma rays over a wide spectral range and has better energy resolution than scintillation detectors, thus providing the possibility of utilizing the principles of the present invention in a wide range of scenarios and with a wide range of radiation sources.

[0072] In addition, or alternatively, the detector may include a plurality of discrete layers in the z-direction of a suitable detector material. For example, a multi-layer scintillator detector may be suitable for implementation of the present invention.

[0073] A major advantage of the present invention is the ability to derive additional information from a set of photon interactions resolved in three dimensions into x, y, and z coordinates, if necessary for imaging, provided that appropriate reconstruction techniques are followed, resulting in a significant reduction in signal loss when passing through a filter compared to simple collimation. As a result, the present invention is particularly suitable for information extraction in any scenario where the source is a low-signal source. This may be a characteristic inherent to the source or, for example, a desirable characteristic of the source in a medical application.

[0074] A multiplexing filter suitable for the performance of the present invention includes any device that differentially passes only a portion of the radiation incident on an orientation-registered base to create a pattern that is at least partially a function of position in the X and Y coordinates, creating some registration between x and y in the radiation emitted from the source and x and y at the detector, but not designed to produce a substantially one-to-one registration in x and y.

[0075] For example, the multiplexing filter may be a collimator, but not a collimator having a monotonic approximate design registration between x and y during irradiation generated from the source and x and y at the detector. Suitable collimators can include, for example, one-dimensional or two-dimensional arrays of apertures such as pinhole arrays, and arrays of parallel holes and slits having a relatively wide angular tolerance.

[0076] Other multiplexing filters may include appropriately coated optics.

[0077] Most simply, even a pair of pinholes can introduce a useful level of complexity, and an example of a multiplexing filter based on such a simple principle is discussed below in this specification by way of illustration. However, any suitable design that introduces some degree of three-dimensional complexity into the radiation pattern from the source when passing through the filter and does not result in a substantial monotonic correspondence in x and y between the signal from the source incident on the filter and the signal passed by the filter can be appropriately combined with suitable deconvolution techniques within the processing module to derive useful information from the more complex data received and collected by the detection module. A suitable design of the multiplexing filter will readily combine with suitable deconvolution techniques to solve a particular problem. In either case, the use of deconvolved data may be required for image reconstruction, and image reconstruction may be unnecessary or undesirable.

[0078] In a possible embodiment, this method is applied as a method for collecting radiation data after passing through a subject, for example, as a method for imaging a subject, and this system is adapted to be used as a system for collecting radiation data after passing through a subject.

[0079] In such a case, this method includes the steps of placing the subject between the radiation source and the multiplexing filter, and additionally includes the steps of causing the radiation from the radiation source to be incident on the subject, passing at least a part of the generated radiation through the filter, and causing it to be incident on the detection module.

[0080] Each of a plurality of consecutive particle interactions collected by the detection module after passing through the subject is positioned in x, y, and z coordinates.

[0081] In a possible embodiment, the data for a plurality of consecutive particle interactions positioned as such is processed to generate an image data set. This method can further include the steps of generating an image and, optionally, further displaying the image. The system can further include an image generation module for generating an image and an image display device. This method can further include the step of generating consecutive images as tomographic reconstruction. The system may further include a tomographic reconstruction module to achieve a similar effect.

[0082] In a preferred embodiment, this method is applied as a method for medical examination, for example, as a medical image, and the subject is a part of the body of the subject.

[0083] Furthermore, or alternatively, the data for a plurality of consecutive particle interactions to be positioned may be processed to triangulate the position of the underlying tissue in the subject.

Brief Description of the Drawings

[0084] Next, the present invention will be described as an example with reference to FIGS. 1 to 7 of the accompanying drawings.

[0085]

Figure 1

Figure 2

Figure 3

Figure 4

DETAILED DESCRIPTION OF THE INVENTION

[0086] FIG. 1 shows the principle often referred to as multiple pinhole image multiplexing and shows a pinhole collimator used to project an image from a radiation source onto a detector plane. In the simplest case, even a pair of pinholes can introduce useful complexity, and the principle will be described herein by way of example.

[0087] Each pinhole will create a partial image of the subject on the detector plane with possible overlap of their images depending on the distance between the pinholes and their geometric shapes. The reconstruction of the complete subject image from the detector data will consist of bringing together all the individual images created by each pinhole with appropriate adjustment of the shift and projection angle.

[0088] Overlap on a partial image is usually referred to as multiplexing. It is typically regarded as an image defect or at least an image artifact to be adjusted. Naturally, the larger the multiplexing area, the larger the resulting reconstructed subject image artifact. There are difficult limits to achieving maximum efficiency when trying to increase the efficiency of the collimator (i.e., trying to increase the number of photons reaching the detector).

[0089] However, when using a multiplexing filter to apply a pinhole collimator in the system and method of the present invention, allowing a certain amount of multiplexing will enable obtaining data not only about the x, y positions on the plane of the detection surface but also about the depth of interaction in the z direction of the detector, even when a detector that enables obtaining data about the depth of interaction in the z direction of the detector is used, and will also enable increasing further efficiency.

[0090] The multiplexing filter does not attempt to introduce a monotonic relationship between the order of radiation from the radiation source and the order of radiation of the individual rays positioned at the individual pixels on the detector, as is the case with conventional parallel hole collimators. The radiation passing through the multiplexing filter needs to have a certain resolvable complexity. In an embodiment, the overlapping conical shape of the radiation provides the required complexity.

[0091] The present invention then utilizes data obtained about the depth of interaction in the z direction of the detector in addition to data regarding interactions in the x, y plane of the detection surface. A detector that can essentially do this is preferred.

[0092] In one embodiment, a thick bulk semiconductor detector of cadmium zinc telluride (CZT) is used. Such detectors essentially enable determination of the depth of photon interaction in the z-direction as well as the position within a particular pixel in x and y. However, the present invention is not limited to such detectors. Such semiconductor detectors can be replaced with any "depth-sensing" or "3D position-sensing" detector structure, for example, including a scintillator detector module consisting of several layers to provide some degree of depth sensing.

[0093] Embodiments utilize the thickness of the semiconductor detector to obtain a certain separation between images from adjacent pinholes.

[0094] Figure 2 shows the absorption probability of photons incident at various angles on a 7 mm thick CZT detector. The angles are calculated with respect to the vertical direction. Figure 3 shows the ratio of those probabilities normalized to the absorption probability of photons incident at an angle = 0°. For example, for photons incident at an angle = 45°, it can be seen that the probability of being absorbed within the first 0.5 mm of the detector is 35% higher compared to photons incident perpendicularly to the detector. For the same photons, there will be approximately twice as many photons incident perpendicularly that are absorbed in the second half of the detector.

[0095] Appropriate processing and reconstruction modules are used to deconvolve the 3D interaction data and extract information accordingly, for example, to reconstruct an image. Since the x and y positions of the interaction in the detector (z is the dimension along the thickness of the detector) are also used in image reconstruction, this method can use the 3D position of the interaction in multi-pinhole collimator image reconstruction to reduce image artifacts due to multiplexing on the image. This can improve the efficiency of the collimator, potentially improve the efficiency of image reconstruction for low signal sources, and / or enable satisfactory imaging from reduced signal sources. Preferably, this principle is applied to medical images and, for example, molecular breast images, ultimately reducing the patient's dose.

[0096] This is a major advantage of the present invention. If the depth of each photon interaction, i.e., the z - direction position within the deep detector, can be resolved to some extent, a dataset is generated in which each photon interaction can be positioned to some extent in all of the x, y, and z coordinates, from which inferences are drawn and the dataset can be de - convolved by an appropriate reconstruction method. Instead of a parallel - hole collimator, a filter as in the embodiment can significantly reduce the number of photons that are prevented from passing through the filter, and thus can significantly increase the proportion of photons that pass through the filter and are usefully collected and meaningfully processed in the detection module. An effective set of data can be collected with a detection module having a very low intrinsic radiation source level. For example, in the case of medical imaging, a lower radiation dose as a result within the patient's tissue is obtained.

[0097] The above is only an example. The principles of the present invention can be applied to develop an appropriate design of a collimator or other multiplexing filter in combination with appropriate de - convolution techniques to solve a particular problem, both in cases where the use of de - convolved data for image reconstruction may be required and in cases where image reconstruction is unnecessary or undesirable.

[0098] In particular, the pinholes do not need to be identical, and multiplexing collimators with structures other than pinholes are conceivable. Other multiplexing filters based on similar principles include simple pinhole arrays as well as other arrays of parallel holes and slits, and one - dimensional or two - dimensional arrays of apertures having a relatively wide acceptance angle can be used.

[0099] The collimator is considered to dynamically change its characteristics, such as a hole profile, during measurement. This can lead to a situation where data in the detector may not be collected simultaneously, for example, when the collimator dynamically changes the acceptance of the angles of photons passing through it and then the final image is reconstructed using the entire data set or even multiple data sets collected in different configurations.

[0100] Another configuration for controlling multiplexing in multiple pinhole collimation can be considered as being as shown in FIG. 4. The general principle is to stagger detectors including detector arrays such that each (or several) collimator pinhole irradiates only a sub - array of the detection portion.

Claims

1. Positioning a detector to receive radiation from a radiation source; Applying multiplexing conversion to the radiation from the radiation source to create three-dimensional complexity in the pattern of the radiation from the radiation source; Receiving a plurality of responses, each being a response to an interaction with incident radiation occurring within the detector; For each of the plurality of responses, determining a characteristic of the interaction, the characteristic including at least a position in three dimensions of the interaction within the detector; Processing the plurality of responses according to the determined positions in three dimensions of each interaction within the detector, from which inferring about the pattern of the radiation from the radiation source. A method for detecting radiation from a radiation source, comprising:

2. The detector has an x, y plane of the detector and a z direction orthogonal thereto, The step of applying the multiplexing conversion includes introducing three-dimensional complexity not only in the x, y plane of the detector but also in the z direction of the detector, The method includes localizing each interaction not only in the x, y plane of the detector but also in the z direction of the detector. The method according to claim 1.

3. The multiplexing conversion acts on the radiation from the radiation source and adds complexity having a functional variation according to distance to the pattern of the radiation from the radiation source. The method according to claim 1 or claim 2.

4. The multiplexing conversion does not act on the radiation from the radiation source to generate a monotonic relationship in the x, y plane between the order of the radiation from the radiation source and the order of the radiation at the position of the detector. The method according to any one of claims 1 to 3.

5. The multiplexing conversion is performed at a point where the radiation from the radiation source is passed through a multiplexing filter configured to generate three-dimensionally resolvable complexity in the pattern of the radiation from the radiation source when the radiation from the radiation source passes through the multiplexing filter. The method according to any one of claims 1 to 4.

6. The multiplexing filter has a discrete structure and is disposed between the radiation source and the detector, and is configured to generate three-dimensionally resolvable complexity with respect to the pattern of the radiation from the radiation source before the radiation is incident on the detector. The method according to claim 5.

7. The multiplexing filter is combined with the detector. The method according to claim 5 or claim 6. Claim 8 The multiplexing transformation is the method according to any one of claims 1 to 7, performed by the detector, in that the detector is adapted to perform the multiplexing transformation. Claim 9 The method according to any one of claims 1 to 8, including the use of a detector adapted or configured to enable the interaction with the incident radiation occurring within the detector to be positioned in three dimensions at the interaction position within the detector. Claim 10 The method according to claim 9, including the use of a detector comprising a three-dimensional voxel array, wherein the determination for each of the plurality of responses includes localizing the interaction with a particular voxel, the characteristics of the interaction including at least the position in three dimensions of the interaction. Claim 11 A radiation detection system for detecting radiation from a radiation source, the radiation detection system comprising: a detector; a multiplexer operating based on the radiation from the radiation source to create a three-dimensional complexity in the pattern of the radiation from the radiation source; a processing module, the processing module receiving a plurality of responses each being a response to an interaction with incident radiation occurring within the detector, determining, for each of the plurality of responses, characteristics of the interaction, the characteristics including at least the position in three dimensions of the interaction within the detector, and being operable to process the plurality of responses according to the determined positions in three dimensions of each interaction within the detector and therefrom draw inferences regarding the pattern of the radiation from the radiation source. Claim 12 The detector has an x, y plane of the detector and a z direction of the detector orthogonal thereto, The system according to claim 11, wherein the multiplexer is configured to be operable with respect to the radiation from the radiation source and is positionable to be operable to introduce a three-dimensional complexity not only in the x, y plane of the detector but also in the z direction of the detector. Claim 13 The system according to claim 11 or claim 12, wherein the multiplexer operates on the radiation from the radiation source and adds a complexity having a functional variation according to distance to the pattern of the radiation from the radiation source. Claim 14 The multiplexing converter of any one of claims 11 to 13, which does not operate on the radiation from the line source, to generate a monotonic relationship in the x, y plane between the order of the radiation from the line source and the order of the radiation at the position of the detector.

15. The system according to any one of claims 11 to 14, wherein the multiplexing converter comprises an array of pinholes.

16. The detector of any one of claims 11 to 15, which is adapted or configured to enable localizing the interaction with the incident radiation occurring within the detector in three dimensions at an interaction position within the detector.

17. The system according to any one of claims 11 to 16, wherein the detector is a voxel detector comprising a three-dimensional voxel array.

18. The system according to any one of claims 11 to 17, wherein the detector is a semiconductor detector.

19. The semiconductor detector includes a semiconductor detector material selected from cadmium telluride, cadmium zinc telluride (CZT), cadmium manganese telluride (CMT), and alloys thereof, and a crystalline Cd where a + b < 1 and a and / or b may be 0 1-(a+b) Mn a Zn b Te, the system according to claim 18.

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