WO2025049567A1 - System and method for symmetrical coded aperture imaging for increasing the signal to noise ratio of detected electromagnetic signals - Google Patents

Abstract

Disclosed herein is a system and method for detecting electromagnetic radiation data with increased signal to noise ratio by use of a symmetrical coded aperture. The system includes a symmetrical coded aperture for spatially encoding electromagnetic signal source origins. Detectors record modulated electromagnetic signal, with symmetrical aperture data projections combined to increase signal to noise ratio prior to reconstructing spatially resolved estimates of electromagnetic signal origins for providing useful information about the signal origins or mediums and objects that the signal propagated through.

Description

System and method for symmetrical coded aperture imaging for increasing the signal to noise ratio of detected electromagnetic signals

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to, and the benefit of, U.S. Provisional Application No. 63/579,395, filed on August 29, 2023, titled “System and method for symmetrical coded aperture imaging for increasing the signal to noise ratio of detected electromagnetic signals,” which is incorporated by reference herein in its entirety.

FIELD OF THE INVENTION

[0002] The present invention is generally directed to detecting and imaging electromagnetic radiation.

BACKGROUND

[0003] Coded apertures are a technique used in imaging systems to capture images with high planar spatial resolution, good signal-to-noise ratio, and depth resolution. Coded apertures utilize a patterned mask or aperture that allows electromagnetic radiation to pass through in a specific pattern. The pattern is carefully designed so that the resulting image can be decoded using a mathematical algorithm to recover information about the original imaged object. The use of coded apertures can help to reduce the effects of noise, which can improve the overall quality of the captured image, while they can also be utilized for improved localization of detected signal. Coded apertures are especially useful within imaging systems for high-energy electromagnetic radiation, including X-rays, that cannot be controlled by conventional optical lenses that work for lower energy electromagnetic radiation; however coded apertures can be used for lower-energy electromagnetic radiation including light visible to human eyes.

SUMMARY

[0004] Disclosed herein is a system and method for detecting electromagnetic radiation data with increased signal to noise ratio by use of a symmetrical coded aperture. The system includes a symmetrical coded aperture for spatially encoding electromagnetic signal source origins. Detectors record modulated electromagnetic signal, with symmetrical aperture data projections combined to increase signal to noise ratio prior to reconstructing spatially resolved estimates of electromagnetic signal origins for providing useful information about the signal origins or mediums and objects that the signal propagated through. [0005] In some aspects, a method of imaging using a symmetrical coded aperture to increase signal to noise ratio is disclosed. The method includes: (a) imaging an object of interest with an electromagnetic radiation source, a coded aperture including at least two symmetrical regions, and electromagnetic radiation detector; and (b) digitally aligning and combining detected signals from projected symmetrical coded aperture regions thereby increasing the signal to noise ratio.

[0006] In some aspects, the method further includes determining properties of the object of interest using the combined signals as input for a reconstruction algorithm.

[0007] In some aspects, the reconstruction algorithm is rules based.

[0008] In some aspects, the reconstruction algorithm is machine learned.

[0009] In some aspects, a physics forward model is used in the reconstruction algorithm.

[0010] In some aspects, detector-space elements of the forward model for projected coded aperture symmetrical regions are combined.

[0011] In some aspects, the forward model object-space elements for region(s) of interest are combined.

[0012] In some aspects, the determined object of interest property is a momentum transfer spectra from elastically scattered X-rays.

[0013] In some aspects, the at least two symmetrical regions include rotational symmetry, reflectional symmetry, translational symmetry, or combinations thereof.

[0014] In some aspects, the coded aperture includes at least two and up to 360 symmetrical regions.

[0015] In some aspects, the electromagnetic radiation source illuminates the object of interest in a pencil beam geometry.

[0016] In some aspects, the electromagnetic radiation source illuminates the object of interest in a fan beam geometry.

[0017] In some aspects, the coded aperture includes a spiral pattern.

[0018] In some aspects, the coded aperture includes two or more different symmetrical region patterns.

[0019] In some aspects, the coded aperture includes two or more materials that have differing electromagnetic radiation absorption properties. [0020] In some aspects, the electromagnetic radiation source is an X-ray source.

[0021] In some aspects, the electromagnetic radiation source deposits an absorbed radiation dosage of less than 6 mGy when imaging the object of interest.

[0022] In some aspects, a system for imaging using a symmetrical coded aperture to increase signal to noise ratio is disclosed. The system includes: (a) an electromagnetic radiation source;

(b) a coded aperture including at least two symmetrical regions; and (c) an electromagnetic radiation detector; wherein the coded aperture is placed between an object of interest and the electromagnetic radiation detector.

[0023] In some aspects, the at least two symmetrical regions include rotational symmetry, reflectional symmetry, translational symmetry, or combinations thereof.

[0024] In some aspects, the coded aperture includes at least two and up to 360 symmetrical regions.

[0025] In some aspects, the electromagnetic radiation source illuminates the object of interest in a pencil beam geometry.

[0026] In some aspects, the electromagnetic radiation source illuminates the object of interest in a fan beam geometry.

[0027] In some aspects, the coded aperture includes a spiral pattern.

[0028] In some aspects, the coded aperture includes at least two and up to 360 symmetrical regions.

[0029] In some aspects, the coded aperture includes two or more materials that have differing electromagnetic radiation absorption properties.

[0030] In some aspects, the electromagnetic radiation source is an X-ray source.

[0031] In some aspects, the electromagnetic radiation detector is an X-ray detector.

[0032] In some aspects, the object of interest is a human body.

[0033] In some aspects, the object of interest is a human breast.

BRIEF DESCRIPTION OF THE DRAWINGS

[0034] The embodiments illustrated, described, and discussed herein are illustrative of the present invention. As these embodiments of the present invention are described with reference to illustrations, various modifications, or adaptations of the methods and or specific structures described may become apparent to those skilled in the art. It will be appreciated that modifications and variations are covered by the teachings and within the scope of the appended claims without departing from the spirit and intended scope thereof. All such modifications, adaptations, or variations that rely upon the teachings of the present invention, and through which these teachings have advanced the art, are considered to be within the spirit and scope of the present invention. Hence, these descriptions and drawings should not be considered in a limiting sense, as it is understood that the present invention is in no way limited to only the embodiments illustrated.

[0035] FIG. 1 depicts a schematic diagram of a system utilizing electromagnetic signal propagation through an object and coded aperture according to one embodiment described herein.

[0036] FIG. 2 depicts an exemplary flowchart of an embodiment of the method described herein.

[0037] FIG. 3 depicts a schematic illustrating possible variations of coded aperture overall shapes according to one embodiment described herein.

[0038] FIG. 4 depicts a schematic illustrating possible variations of coded aperture opening patterns according to one embodiment described herein.

[0039] FIG. 5 depicts a schematic of coded apertures with various numbers of symmetrical regions according to one embodiment described herein.

[0040] FIG. 6 depicts an illustrative example of a rotated and flipped symmetrical region patterns according to one embodiment described herein.

[0041] FIG. 7 depicts an illustrative example of increased signal to noise ratio from the combination of data from symmetrical regions according to one embodiment described herein.

[0042] FIG. 8 depicts an illustrative example of increased signal to noise ratio from the combination of data from multiple symmetrical region patterns according to an embodiment described herein.

[0043] FIG. 9 depicts a schematic demonstrating combining symmetrical regions for a fan beam illumination geometry according to one embodiment described herein. [0044] FIG. 10 depicts a schematic of combining physics model matrix detector elements for processing symmetry-combined detector data according to one embodiment described herein.

[0045] FIG. 11 depicts a schematic of combining physics model matrix detector elements and region of interest object elements for processing symmetry-combined detector data for a region of interest according to one embodiment described herein.

DETAILED DESCRIPTION

[0046] For the purpose of promoting an understanding of the present disclosure, reference will be made to preferred embodiments and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the disclosure is thereby intended, such alteration and further modifications of the disclosure as illustrated herein, being contemplated as would normally occur to one skilled in the art to which the disclosure relates.

[0047] Articles “a” and “an” are used herein to refer to one or to more than one (i.e., at least one) of the grammatical object of the article. By way of example, “a composite” means at least one composite and can include more than one composite.

[0048] Throughout the specification, the terms “about” and/or “approximately” may be used in conjunction with numerical values and/or ranges. The term “about” is understood to mean those values near to a recited value. For example, “about 40 [units]”may mean within +/- 25% of 40 (e.g., from 30 to 50), within +/- 20%, +/- 15%, +/- 10%, +/- 9%, +/-8 %, +/- 7%, +/- 6%, +/- 5%, +/- 4%, +/- 3%, +/-2 %, +/- 1%, less than +/- 1%, or any other value or range of values therein or there below. Furthermore, the phrases “less than about [a value]” or “greater than about [a value]” should be understood in view of the definition of the term “about” provided herein. The terms “about” and “approximately” may be used interchangeably.

[0049] As used herein, the verb “comprise” as is used in this description and in the claims and its conjugations are used in its non-limiting sense to mean that items following the word are included, but items not specifically mentioned are not excluded.

[0050] Throughout the specification the word “comprising,” or variations such as “comprises” or “comprising,” will be understood to imply the inclusion of a stated element, integer or step, or group of elements, integers, or steps, but not the exclusion of any other element, integer or step, or group of elements, integers or steps. The present disclosure may suitably “comprise,” “consist of,” or “consist essentially of,” the steps, elements, and/or reagents described in the claims. [0051] It is further noted that the claims may be drafted to exclude any optional element. As such, this statement is intended to serve as antecedent basis for use of such exclusive terminology as “solely,” “only,” and the like in connection with the recitation of claim elements, or the use of a “negative” limitation.

[0052] In the descriptions herein, the measured electromagnetic radiation scatter signal and reconstructed spatially resolved scatter spectra are referred to as pertaining to the “X-ray scatter” in certain embodiments, though an X-ray scatter field will, in general, be comprised of both Rayleigh and Compton scatter. The use of the measured scatter signal and reconstructed spatially resolved scatter spectra and similar terminology, particularly the use of the term “diffraction” is not intended to limit the present invention to pertaining to scatter arising from one physical process and not another.

[0053] Unless defined otherwise, all technical and scientific terms used herein have the same meanings as commonly understood by one of ordinary skill in the art to which this disclosure belongs. Preferred methods, devices, and materials are described, although any methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present disclosure. All references cited herein are incorporated by reference in their entirety.

[0054] Coded apertures have been utilized in a wide range of electromagnetic signal detection tasks. For example, coded apertures have been utilized in telescopes for improving origin localization of electromagnetic signals arriving from outer space. Additionally, coded apertures have been utilized in camera systems for enabling gigapixel resolution via improved localization of where detected visible light originated from. As another example, coded apertures have been utilized within X-ray imaging systems, both for compressive computed tomography (CT) transmission imaging as well as for spatially resolved X-ray scatter imaging. While there is wide variety in the energy/wavelengths of these different electromagnetic radiations, the coded aperture functions the same in each of these use cases.

[0055] A coded aperture provides useful spatial information through the unique pattern of the coded aperture. The coded aperture comprises material, often metals, while having patterned openings that allow electromagnetic signals to pass by without interacting with the coded aperture. The material portion of the coded aperture typically absorbs the vast majority of electromagnetic signal that impinges on these regions, effectively blocking this signal from reaching the detecting component of a system being utilized for electromagnetic radiation imaging, while the openings allow their portion of the passing electromagnetic signal to be detected. While blocking signal would typically be viewed as a negative in the design of a signal detection/imaging system, the unique patterns create unique shadows within the detected signals, which when combined with physics models of the system, can be used to provide additional information on the point of origin of the electromagnetic signals. Systems utilizing coded apertures can be described as computational imaging systems, due to the typical use of physics models and algorithms on the detected spatially encoded electromagnetic signals to obtain useful information that can produce enhanced images with higher resolution, improved depth localization, or both.

[0056] A general depiction of an embodiment of a coded aperture imaging system is shown in FIG 1. FIG. 1 depicts a schematic of a general coded aperture system showing electromagnetic signals interacting with an object before passing through a coded aperture before reaching a detector. The system 100 comprises an electromagnetic signal source 101 that generates propagating electromagnetic signals 102 which can interact with an object of interest 103. The electromagnetic signals 102 interacting with object of interest 103 can redirect or scatter 104. The coded aperture 105 can be positioned between the object of interest 103 and the electromagnetic detector 107. The coded aperture 105 modulates electromagnetic signals 106 before they interact with the electromagnetic detector 107.

[0057] To provide one example of an imaging system and specific electromagnetic signal that utilizes this technology, the signal source 101 can be an X-ray source producing X-rays as the electromagnetic signals 102. The object of interest 103 can be a human body, or more specifically a human breast being analyzed for likelihood of cancerous tissues. When X-rays interact with materials, they can be absorbed, scatter inelastically (Compton Scatter), and/or scatter elastically (Rayleigh scatter), to list a few interactions. It is noted that “elastic” is sometimes used interchangeably with “coherent” in literature when describing Rayleigh X-ray scatter, though the methods and systems described are not limited to only a coherent X-ray source or measurement scenario. In the case of an X-ray scatter imaging system, elastically scattered X-rays are of interest since their momentum transfer spectra provide insightful information into the nanoscale and microscale spacings and characteristic distances, molecular size distributions, and compositions of a material being imaged. Measuring elastically scattered X-rays through in-human breast tissue would have clinical value, given the low precision (20%) of modern mammography systems that result in >1M benign biopsies in the US each year as of 2022. [0058] The coded aperture 105 may comprise materials that absorb X-rays, including but not limited to tungsten, lead, copper, allowing signal to only pass through openings here represented as white rectangles within the coded aperture. The X-rays not attenuated/absorbed 106 by the coded aperture can be detected by an X-ray detector 107, which may comprise standard materials including but not limited to cesium iodide (CsI) and amorphous selenium (a-Se).

[0059] X-ray detectors can come in a variety of forms, including energy-integrating, energydifferentiating, and photon counting. Advanced X-ray detectors can provide better detection efficiency, detecting more of the X-rays that pass through them, allowing for lower patient absorbed radiation dose or better signal to noise ratio (SNR), along with energy-differentiation that can be used to improve scatter localization. These improvements can assist with coded aperture imaging systems, but they are not required for the technology to function in a useful form - therefore the inclusion of advanced detectors is a trade-off between performance and higher cost of the imaging system.

[0060] While use-cases of coded apertures within X-ray scatter imaging systems have been reported elsewhere, the use of symmetrical coded aperture imaging for increasing the signal to noise ratio of detected electromagnetic signals disclosed herein is generalizable to all electromagnetic radiation signals that can be detected within a coded aperture system. Disclosed herein is a new category of coded aperture patterns and the methods for implementing them for improved signal to noise ratios of detected signals. Previously, there have been coded aperture patterns including random ID, random 2D, Fresnel zone plates, optimized random patterns, uniformly redundant arrays, hexagonal uniformly redundant arrays, and modified uniformly redundant arrays, to name a few. The disclosed symmetrical coded aperture patterns have a symmetry relative to the signal propagating through them. In the use-case of X-ray scatter imaging systems, if a pencil beam of X-rays passes through a material of interest, the elastically scattered X-ray signal can have a symmetry about the pencil beam center. The specific symmetry of the elastically scattered X-ray signal about will depend on the material, with amorphous materials and sufficiently small grain crystalline powders generally having uniform intensity distributions about the pencil beam axis, while textured semicrystalline or crystalline materials could have other symmetries in intensity as a function of angle about the pencil beam axis. A coded aperture may have halves, quadrants, or other fractional pie-slices with the same pattern about the center of the pencil beam, providing the same patterned encoding for the elastically scattered X-rays passing through each symmetrical region. After these signals have been detected, during post-processing of the data, the detected signal from symmetrical coded aperture projected regions on the detector can be combined, whether by summation, averaging, or alternative mathematical combination methods, to provide an improvement to the detected signal to noise ratio. In the example of elastic X-ray scatter measurements, where Poisson noise is a dominant factor, effectively increasing the number of measurements will approximately increase the signal to noise ratio by a factor of Number of Measurements. As an example, if the coded aperture contains six symmetrical regions that are combined, this will provide a 2.45 times increase in SNR, which enables a better-quality measurement at a fixed dose and/or allows for obtaining a similar quality measurement at a dose/acquisition time that is 1/2.45 (40.8%) of the reference performance that does not combine symmetrical regions. While this effect increases for any arbitrary number of symmetrical regions, as an example ten regions providing a 3.16 times increase in SNR or 31.6% dose/acquisition time, this will be practically bounded by the symmetrical coded aperture regions requiring sufficient planar area for an effective coding pattern.

[0061] The improvement to signal to noise ratio can be used for improved reconstruction quality (i.e., better reconstructions of spatially resolved X-ray scatter spectra) or be used to lower the radiation dose or exposure time to an object required to obtain sufficient signal for a useful reconstruction, allowing for lower absorbed radiation dose to humans in a medical application or faster scans in a package or airport screening application. Regardless of the application constraints, utilization of symmetrical apertures improves the trade-off space between input signal required and final quality of reconstructed information.

[0062] The method of utilizing symmetrical coded apertures for increasing signal to noise ratio is depicted in FIG. 2. In method 200, an electromagnetic signal is emitted from an electromagnetic signal source 201. The electromagnetic signals interact with an object of interest 202, which results in scattered electromagnetic signals containing object information. Electromagnetic signals pass through the symmetrical coded aperture placed between the object of interest and the detector, while other electromagnetic signals are blocked by the symmetrical coded aperture 203. The electromagnetic signals that pass through the symmetrical coded aperture are detected by the electromagnetic detector 204. After electromagnetic signal detection 204, post-acquisition processing combines detected electromagnetic signals that passed through symmetrical coded aperture regions to increase signal to noise ratio 205. A reconstruction algorithm predicts the spatial origin of detected electromagnetic signals 206. [0063] For reconstruction algorithms operating on the detected electromagnetic signals, it will be known to those skilled in the art that these algorithms can utilize physics-forward models that account for the physics of electromagnetic radiations interacting with mediums or objects that they pass through before detection. These physics forward models often take the form of matrices, where different dimensions (i.e., rows vs columns) can represent each of the detectors pixels vs each object space spatial/angular point. These physics models can be used along with algorithms based on iterative deblurring or maximum likelihood estimation to reconstruct the origins and interaction dynamics of the coded aperture encoded electromagnetic signals that have been detected by the system. As an example of an iterative deblurring algorithm, a physics forward model, as it relates to a measured signal and original material property is shown below: y = H * f (1)

Where is the detected signal, in this case one that has passed through a symmetrical coded aperture,/ is the property of the imaged medium or object, and His the physics forward model that models the known physics and geometries impacting how a given medium or object property would present in ay detected signal. When a detected signal and physics forward model are known, one method for reconstructing the medium or object property /is a Bayesian- based iterative deblurring algorithm. One form this algorithm can take is shown below:

Where /+i is a new iteration’s estimate of the medium or object property,/ is the prior iteration’s estimate of the medium or object property, H^T is the transpose of the physics forward model, and all other symbols are as previously defined. During the first iteration of this algorithm, the initial estimate of / can be approximated as:

This iterative deblurring algorithm can run until a predetermined number of iterations have occurred, until a desired quality or stability in estimated /is achieved, or alternate termination conditions are met. Non-iterative reconstruction algorithms, including but not limited to, filtered back projection, radon transforms, and direct image reconstruction, can also be utilized with symmetrical coded apertures. [0064] It should be noted that when building the physics forward model, H, for the disclosed system and method, the coded aperture pattern is factored into the understanding of how any given signal in f would present in the detected data

[0065] While the prior examples of reconstruction algorithms can be described as rules-based, it is also possible to utilize reconstruction algorithms that leverage artificial intelligence including machine learning, where the reconstruction process operates differently, may have black-box components (i.e., not easily human-interpretable), and may entirely skip reconstructing known physical parameters and may learn to make predictions on a medium or object properties based on the detected encoded electromagnetic signals. These types of machine learned reconstruction algorithms could utilize components or entire architectures of commonly used Al models, including but not limited to, shallow or convolutional neural networks, generative adversarial networks, support vector machines, and linear or non-linear regressions. We would describe this type of algorithm as a machine learned reconstruction algorithm, and this type of algorithm would still benefit from the implementation of symmetrical coded apertures that increase the signal to noise ratio of the data the reconstruction algorithm is operating on. To provide examples, not intended to be limiting, on medium or object properties that can be reconstructed by rules-based or artificial intelligence applications for a region of interest, in the example of X- rays, this can be the momentum transfer spectra of individual voxels imaged; in astronomy applications the reconstructed property can be electromagnetic wave origins in space; in medical applications the reconstructed property can be the probability of a disease, including but not limited to cancer, cirrhosis, or Alzheimer’s.

[0066] Before discussing the symmetrical coded aperture in detail, it is worth describing the physical properties and characteristics of coded apertures in general. As shown in FIG. 3, coded apertures can be created with any arbitrary overall shape. The left panel of FIG. 3 shows a square aperture, the center panel shows a rectangle aperture, and the right panel shows a circular aperture. These are exemplary illustrations. A rectangular coded aperture can be useful if the electromagnetic radiation interacting with a medium/object is illuminating via a fan-beam geometry. For the examples shown in the left and central panels of FIG. 3, a central opening within the coded aperture allows primary electromagnetic radiation to pass through, while providing symmetrical encoding on the left and right side of the illuminated material. A circular coded aperture can be useful in the implementation of an electromagnetic radiation pencil beam geometry, where all signal is originating from a central point and the radius of the circle should be designed to encode the maximum extent required, while a square in contrast would have wasted comers that extend beyond the needed radius and provide no useful encoding. It is contemplated that any of a circular, square, rectangular, or other regularly shaped coded aperture are suitable shapes of the aperture, the choice of shape may be dependent on code design choices, radiation source and shape, and/or limitations of equipment.

[0067] Beyond the ability to be developed in arbitrary overall shapes that can have utility in various applications, coded apertures can come in a variety of patterns, some of which have been previously mentioned. FIG. 4 depicts how coded aperture patterns can come in a range of styles and patterns. The left panel of FIG. 4 shows a coded aperture with a random 2D pattern, the center panel shows a coded aperture with concentric circle patterns, while the right panel shows spiral patterns. Any design that would partially obstruct electromagnetic signals can be used as a coded aperture pattern. Random 2D patterns can help with localization of electromagnetic signal within a plane parallel to the coded aperture or detector, while concentric rings can provide information on electromagnetic radiation for discrete angles of propagation. Spiral patterns, if designed carefully, can allow for unique detection of angularly scattered electromagnetic radiation without allowing these propagating signals to overlap at the detector, thus reducing the degree of multiplexing within the computation imaging system. Note that structural bars shown in the central and right panels of FIG. 4 can be added to a coded aperture to enable the manufacturability of the coded aperture.

[0068] Coded apertures can be manufactured by computer numerical control (CNC) machines, photochemical etching, metal filament 3D printing, or metal-doped resin 3D printing, to list a few non-limiting examples of manufacturing methods. These coded apertures can be constructed out of one material, or multiple materials. If multiple materials are utilized in the design of a coded aperture for regions that will interact with electromagnetic radiation, they can be selected such that their absorption of or interactions with the signal are different so that the different material regions provide different information that can be added to physics forward models, for example, to improve the reconstruction process. Different materials could be used for different symmetrical regions, or individual symmetrical regions can be comprised of a combination of materials, whether alloys or layered combinations. This type of multi -material coded aperture can provide energy-dependent information that can enable energy discrimination within an electromagnetic radiation imaging system even without the use of an energy discriminating detector. [0069] Having described coded apertures in general, we will now discuss features and implementations of the disclosed invented symmetrical coded apertures. As shown in FIG. 5, symmetrical coded apertures can have any arbitrary n-number of subregions. The left panel of FIG. 5 shows a coded aperture with two symmetrical halves (i.e., 2 subregions), the center panel shows a coded aperture comprised of 4 symmetrical pattern quadrants (i.e., 4 subregions), and the right panel shows a coded aperture with 6 symmetrical pie-slice spiral regions (i.e., 6 subregions). Note that in a coded aperture with symmetry and a spiral pattern, as shown in the right panel of FIG 5., several spiral patterns or a single spiral pattern regularly shifted by some angle about a pencil beam axis can be used to most efficiently utilize the plane of the coded aperture for coding, to ensure sufficient coverage of all scatter angles from the material or object, to reduce multiplexing of scatter on the detector (particularly useful for a source with a relatively broad energy spectrum, such as is used in mammography or CT), and to improve manufacturability of the coded aperture.

[0070] A symmetrical coded aperture may comprise an unlimited number of symmetrical regions, but eventually there is a diminishing return in the increase to signal to noise ratio given the ceiling set by all detected electromagnetic photons and that more symmetrical regions equates to smaller spatial areas to encode, which results in less of an ability for the coded aperture individual symmetrical regions to provide meaningful spatial encoding. It is for this reason that we note a useful symmetrical coded aperture will have some maximum number of useful symmetrical regions that depends on the particular system and measurement (source power, irradiation time, location of detector, location of object, location of material of interest, volume of material of interest being irradiated, size of aperture, size of aperture features, detector pixel size, detector efficiency, detector noise properties, etc.). The symmetric coded aperture has at least two symmetrical regions, which may be used for a pencil beam or fan beam electromagnetic radiation illumination geometry. Note that as shown in FIG. 5, the symmetrical regions can have reflective or mirror symmetry (as shown in the left panel), rotational or radial symmetry (as shown in the central and right panel), or even translational symmetry with elements being translated to how the symmetrical regions are positioned on an overall coded aperture design.

[0071] On the note of rotating and reflecting symmetrical patterns within a coded aperture, it is possible to do both operations in a single design. FIG. 6 depicts how, even if a pattern is rotated and reflected relative to central origin, post-processing could realign the symmetrical regions to combine all six slices to achieve a signal to noise ratio increase. Reflection, rotational, and translational movement of the symmetrical regions can be used in any combination for any number of sub-segments, the utilization of all methods can be implemented with the intent to improve the symmetrical coded aperture manufacturability.

[0072] In demonstration of the symmetrical coded aperture technology, FIG. 7 shows real scattered X-ray data passing through a symmetrical coded aperture with spiral patterns and the achievable increase in signal to noise ratio. The left panel of FIG. 7 shows the symmetrical coded aperture pattern, while the central panel shows scattered X-rays generated by an X-ray pencil beam passing through 5mm of water. The right panel of FIG. 7 shows the post-processing rotation and summation of all symmetrical projected coded aperture regions, achieved by any common rotational computation about the central pencil beam point to match and sum corresponding symmetrical region pixel data with corresponding pixel data in all other symmetrical regions, which enables an increased signal to noise ratio that will provide better input into reconstruction algorithms for estimating properties or identifying materials that the electromagnetic radiation interacted with.

[0073] This same concept of increasing signal to noise ratio can be applied with coded apertures with multiple patterns - multiple patterns coded apertures may also be a novel concept or invention disclosed here. FIG. 8 left panel depicts a coded aperture with two sub-patterns, spiral and 2D random, that could be utilized in a single coded aperture if one pattern provides superior depth information encoding while the other pattern provides superior planar information encoding. Unlike FIG. 7, the central panel of FIG. 8 is simulated scattered X-rays not real measurements, but the right panel demonstrates how in simulation, the concept of combining symmetrical regions even when multiple patterns are present can still provide an increase in signal to noise ratio. Symmetrical coded apertures pursuing this type of design will have to be analyzed to quantify if the performance gained by multiple encoding patterns is worth the reduction in identical symmetrical regions that can be combined, as in this case only a 3x combination occurs due to the two patterns covering a larger area of encoding, in contrast to the 6x combination shown in FIG. 7 with only one pattern for combining.

[0074] While FIGs. 4-8 show symmetrical coded apertures based around a central point geometry that would be expected if the electromagnetic radiation is illuminating a medium or object via a pencil beam geometry, it should be noted that the symmetrical coded aperture design can work for fan beam geometries as well, albeit restricted to only two symmetrical regions and therefore only combining signal from those two regions. FIG. 9 depicts on the left panel a symmetrical rectangular coded aperture where each half is a reflection of the other, providing symmetry along the fan beam extent. The central panel of FIG. 9 presents synthetic X- ray scatter passing through the coded aperture, where the pattern on the left and right would be expected to mirror each other, with the right panel of FIG. 9 demonstrating the increase in signal to noise ratio that can be achieved by flipping and summing both detector halves together in post-processing. While fan beam geometries are limited to only two symmetrical regions being possible on a symmetrical coded aperture due to the nature of different fan locations passing through different materials, this invention still enables the ability to reduce exposure time and radiation dose by 29.3% (1 - 1 /2) while potentially achieving the performance previously possible without a symmetrical coded aperture, assuming there is sufficient coding and material information present in the half-space of the scatter signal.

[0075] Beyond the visual representation of symmetrical coded aperture patterns and symmetrical detected electromagnetic signals, the disclosed method of utilizing symmetrical coded apertures can be supported by utilizing the symmetry within the reconstruction process. FIG. 10 presents a schematic diagram of how symmetrical coded apertures can be used along with physics forward models of a system for improved reconstructions. In the simplified schematic embodiment shown in FIG. 10, the electromagnetic detector array is composed of Pixels 1-8. This representation assumes a fan beam illumination geometry; thus the symmetry line is drawn between the left Pixels 1-4 and right Pixels 5-8 similar to the symmetry shown in FIG. 9. The Forward Model of System presents a forward model where rows 1-8 represent detector Pixels 1-8, as the first sub-index of values V, while the columns 1-8 represent object voxels 1-8 that were illuminated by the electromagnetic signal and are marked as the second sub-index of values of V. The physics model would be constructed accounting for the geometry and physics of the system and would represent how a signal originating from a known location in object space would be detected. Since it is known that Pixels 1 & 5, 2 & 6, 3 & 7, and 4 & 8 will have symmetrical data, their detector rows can be combined, in FIG. 10 this is shown as a summation operation in the far-right panel marked “Detector Symmetry Summed Forward Model of System”, but it could also be an averaging or other mathematical combination operation. This combination is represented by the first sub-index for detector space denoting which prior forward model rows have been combined (ex. 1+5 is marking that former rows 1 & 5 have been summed to form this new physics model row). It is useful to combine these rows, and not just assume them to be equivalent, in instances where the medium or object that electromagnetic signals propagated through is not uniform. To provide an explicit example, imagine a fan beam of X-rays passing through a human body, while the scattered X-rays at their point of origin will have symmetry perpendicular to the fan beam extent, if they pass through different organs or bones before detection, there will be variability on the left vs right side detected signal that impacts the symmetry assumption. While this case is extreme, the effects would be more minor in an imaging application such as mammography, where the dispersion of fat and glandular tissue throughout a breast might semi-impact the symmetry assumption, but combining the physics models rows would support averaging out this effect and still provide the signal to noise ratio increase. As an example of how this process would occur in the prior example of an iterative deblurring algorithm (equation 1), the detected signal from the electromagnetic detector array would be ; by summing the two symmetrical regions, the length of a ID array representing y would be cut in half, while the remaining values would be the summed symmetrical points. The forward model of the system would be H, a 2D matrix; by summing the symmetrical detector space rows, the row dimension would also be cut in half. Given the example iterative deblurring algorithm in equations 1-3, y and H would still have matching dimensional lengths for required matrix multiplications and would still output the full- length the reconstructed property of the imaged medium or object for every individual object voxel.

[0076] In pursuit of even further improvements to signal to noise ratio and/or reductions to exposure times and radiation dose deposited to imaged objects, FIG. 11 demonstrates another technique that can be combined with the symmetrical coded aperture system and method to further aggregate detected electromagnetic signals in the reconstruction process. FIG. 11 presents the same symmetrical detector case as shown in FIG. 10 but introduces the concept of a region of interest within object space shown to the right of “Forward Model of System”. Now object voxels 1-8 are depicted, while a region of interest for voxels 4-5 are marked in black. To provide an example, this could occur in X-ray scatter imaging in mammography, if a technologist, radiologist, or Al algorithm operating on mammography data noted a concerning mass that should potentially be flagged for biopsy to learn if it is benign or malignant. If the approximate extent of the mass is known or selected within a user interface, the reconstruction algorithm could further combine (sum in this example) the columns representing these object space voxels. The far-right panel of FIG. 11 presents both the combination of combining detector space rows based on symmetrical coded aperture illuminations, along with combining object space columns, especially for the new central column with second sub-index “4+5” that will now aggregate these concerning voxels within the reconstruction process. The “Detector Symmetry Summed + Object ROI Voxel Summed Forward Model of System” would allow for an even greater increase in signal to noise ratio or reduction of exposure time or radiation dose, given that signal originating from multiple object space voxels will now be combined for a single property reconstruction - in the example of elastic X-ray scatter, a single momentum transfer spectrum that could be used for identifying a material or differentiating cancer from benign tissue.

[0077] As an example of how this process would occur in the prior example of an iterative deblurring algorithm (equation 1), the detected signal from the electromagnetic detector array would be ; by summing the two symmetrical regions, the length of a ID array representing y would be cut in half, while the remaining values would be the summed symmetrical points. The forward model of the system would be H. a 2D matrix; by summing the symmetrical detector space rows, the row dimension would also be cut in half. By summing the corresponding H columns for the sub-region of interest, the column dimension will be reduced to a width of 3 in this example. Given the example iterative deblurring algorithm (equation 1), y and H would still have matching dimensional lengths for required matrix multiplications, and the additional reduction in the H column will reduce the length of the estimated providing in this example the aggregate reconstructed property of the imaged medium or object for the three object voxel regions of voxels 1-3, voxels 4-5, and voxels 6-8. It should be noted that a single operation is used to sum the rows for detector space symmetry and to sum the columns for mass/object space of the sub-region of interest.

[0078] Unlike symmetrical coded apertures that will have a fixed design resulting in a locked-in signal to noise ratio boost, combining the object space region of interest will mean that for larger regions of interest, a greater increase to signal to noise ratio or greater decrease to exposure time and dose will be achieved. To quantify this, say a symmetrical coded aperture is used with six symmetrical regions. If this method shown in FIG. 11 was used to investigate say a 3mm suspicious mass, with object space voxels being 1mm, this would provide a 3 times ( 6 + 3) aggregation advantage, or 66.7% reduction in dose and time. If instead the same technique was used on a 12mm suspicious mass (example based on average breast tumor size), it would provide a 4.2 times ( 6 + 12) aggregation advantage, or 76.4% reduction in dose and time. Symmetrical coded apertures offer a new advancement that will enable electromagnetic radiation imaging applications to achieve faster sufficient data acquisition, higher resolution, and lower dose, thus enabling new imaging technologies that can further scientific discovery and protection of human health. [0079] Specific embodiments of the disclosed method and system are provided below, followed by additional information on components that can be included within a symmetric coded aperture system.

[0080] In one embodiment, a method of imaging using a symmetrical coded aperture to increase signal to noise ratio is disclosed. The method comprises imaging an object of interest with an electromagnetic radiation source, a coded aperture with symmetrical regions, and electromagnetic radiation detector. The method further comprises digitally aligning and combining detected signals from projected symmetrical coded aperture regions thereby increasing the signal to noise ratio.

[0081] In one embodiment, the method further comprises determining properties of the object of interest using the combined signals as input for a reconstruction algorithm.

[0082] In one embodiment of the symmetrical coded aperture reconstruction method described herein, the reconstruction algorithm is rules based.

[0083] In one embodiment of the symmetrical coded aperture reconstruction method described herein, the reconstruction algorithm is machine learned.

[0084] In one embodiment of the symmetrical coded aperture reconstruction method described herein, a physics forward model is used in the reconstruction algorithm.

[0085] In one embodiment of the symmetrical coded aperture reconstruction method described herein, detector-space elements of the forward model for projected coded aperture symmetrical regions are combined.

[0086] In one embodiment of the symmetrical coded aperture reconstruction method described herein, the forward model object-space elements for sub-region(s) of interest are combined.

[0087] In one embodiment of the symmetrical coded aperture reconstruction method described herein, the determined object of interest property is a momentum transfer spectra from elastically scattered X-rays.

[0088] In one embodiment of the symmetrical coded aperture reconstruction method described herein, the at least two symmetrical regions comprise rotational symmetry, reflectional symmetry, translational symmetry, or combinations thereof. In one embodiment of the symmetrical coded aperture reconstruction method described herein, the coded aperture comprises at least two and up to 360 symmetrical regions. [0089] In one embodiment of the symmetrical coded aperture reconstruction method described herein, the electromagnetic radiation source illuminates the object of interest in a pencil beam geometry.

[0090] In one embodiment of the symmetrical coded aperture reconstruction method described herein, the electromagnetic radiation source illuminates the object of interest in a fan beam geometry.

[0091] In one embodiment of the symmetrical coded aperture reconstruction method described herein, the coded aperture comprises a spiral pattern.

[0092] In one embodiment of the symmetrical coded aperture reconstruction method described herein, the coded aperture comprises two or more different symmetrical region patterns.

[0093] In one embodiment of the symmetrical coded aperture reconstruction method described herein,

[0094] In one embodiment of the symmetrical coded aperture reconstruction method described herein, the coded aperture comprises two or more materials that have differing electromagnetic radiation absorption properties.

[0095] In one embodiment of the symmetrical coded aperture reconstruction method described herein, the electromagnetic radiation source is an X-ray source.

[0096] In one embodiment of the symmetrical coded aperture reconstruction method described herein, the electromagnetic radiation source deposits an absorbed radiation dosage of less than 6 mGy when imaging the object of interest.

[0097] In one embodiment, a system for imaging using a symmetrical coded aperture to increase signal to noise ratio is disclosed. The system comprises an electromagnetic radiation source, a coded aperture with symmetrical regions placed between an object of interest and the electromagnetic radiation detector, and an electromagnetic radiation detector.

[0098] In one embodiment of the symmetrical coded aperture system described herein, the coded aperture symmetrical region patterns have at least one of rotational, reflectional, translational symmetry, or combinations thereof.

[0099] In one embodiment of the symmetrical coded aperture system described herein, the coded aperture comprises at least 2 and up to 360 symmetrical regions. [0100] In one embodiment of the symmetrical coded aperture system described herein, the electromagnetic radiation source is illuminating the object of interest in a pencil beam geometry.

[0101] In one embodiment of the symmetrical coded aperture system described herein, the electromagnetic radiation source is illuminating the object of interest in a fan beam geometry.

[0102] In one embodiment of the symmetrical coded aperture system described herein, the coded aperture pattern is spiral.

[0103] In one embodiment of the symmetrical coded aperture system described herein, the coded aperture comprises at least 2 and up to 360 symmetrical regions.

[0104] In one embodiment of the symmetrical coded aperture system described herein, the coded aperture regions are composed of 2 or more materials that have differing electromagnetic radiation absorption properties.

[0105] In one embodiment of the symmetrical coded aperture system described herein, the electromagnetic radiation source is an X-ray source.

[0106] In one embodiment of the symmetrical coded aperture system described herein, the electromagnetic radiation detector is an X-ray detector.

[0107] In one embodiment of the symmetrical coded aperture system described herein, the object of interest is a human body.

[0108] In one embodiment of the symmetrical coded aperture system described herein, the object of interest is a human breast.

[0109] The symmetrical coded aperture system described herein may further include controllable electronics. In one embodiment, the symmetrical coded aperture device includes components such as a processor, a system memory having a random-access memory (RAM) and a read-only memory (ROM), an 12C sensor, a system bus that couples the memory to the processor. The processor manages the overall operations of the symmetrical coded aperture system. The processor is any controller, microcontroller, or microprocessor that is capable of processing program instructions. In one embodiment, the control electronics includes at least one antenna, which enables the symmetrical coded aperture system to send information to at least one remote device and/or receive information from at least one remote device. The at least one antenna provides wireless communications, standards-based or non-standards-based including but not limited to, radiofrequency (RF), Wi-Fi, Bluetooth, Zigbee, near field communication (NFC), 3G, 4G, and/or 5G Cellular or other similar communication methods. As a further example, the processor may be a general-purpose microprocessor (e.g., a central processing (CPU)), a graphics processing unit (GPU), a microcontroller, a Digital Signal Processor (DSP), an Application Specific Integrated Circuit (ASIC), a Field Programmable Gate Array (FPGA), a Programmable Logic Device (PLD), a controller, a state machine, agate or transistor logic, discrete hardware components or any other suitable entity or combinations thereof that can perform calculations, process instructions for execution, and/or other manipulations of information.

[0110] Any combination of one or more computer-readable medium(s) may be utilized with the symmetrical coded aperture system described herein. The computer-readable medium may be a computer readable signal medium or a computer-readable storage medium (including, but not limited to, non-transitory computer-readable storage media). A computer-readable storage medium may be, for example, but not limited to, an electronic, magnetic, optical, electromagnetic, infrared, or semiconductor system, apparatus, or device, or any suitable combination of the foregoing. More specific examples (a non-exhaustive list) of the computer- readable storage medium would include the following: an electrical connection having one or more wires, a portable computer diskette, a hard disk, a random access memory (RAM), a readonly memory (ROM), an erasable programmable read-only memory (EPROM or Flash memory), an optical fiber, a portable compact disc read-only memory (CD-ROM), an optical storage device, a magnetic storage device, or any suitable combination of the foregoing. In the context of this document, a computer-readable storage medium may be any tangible medium that can contain or store a program for use by or in connection with an instruction execution system, apparatus, or device.

[OHl] A computer-readable signal medium may include a propagated data signal with computer-readable program code embodied therein, for example, in baseband or as part of a carrier wave. Such a propagated signal may take any of a variety of forms, including, but not limited to, electro-magnetic, optical, or any suitable combination thereof. A computer-readable signal medium may be any computer-readable medium that is not a computer readable storage medium and that can communicate, propagate, or transport a program for use by or in connection with an instruction execution system, apparatus, or device.

[0112] In one or more exemplary aspects, the instructions may be implemented in hardware, software, firmware, or any combinations thereof. A computer readable medium may provide volatile or non-volatile storage for one or more sets of instructions, such as operating systems, data structures, program modules, applications, or other data embodying any one or more of the methodologies or functions described herein. The computer readable medium may include the memory, the processor, and/or the storage media and may be a single medium or multiple media (e.g., a centralized or distributed computer system) that stores the one or more sets of instructions. Non-transitory computer readable media includes all computer readable media, with the sole exception being a transitory, propagating signal per se. The instructions may further be transmitted or received over the network via the network interface unit as communication media, which may include a modulated data signal such as a carrier wave or other transport mechanism and includes any delivery media. The term "modulated data signal" means a signal that has one or more of its characteristics changed or set in a manner as to encode information in the signal.

[0113] The corresponding structures, materials, acts, and equivalents of all means or step plus function elements in the claims below are intended to include any structure, material, or act for performing the function in combination with other claimed elements as specifically claimed. The description of the symmetrical coded aperture system described herein has been presented for purposes of illustration and description but is not intended to be exhaustive or limited to the invention in the form disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the invention. The embodiment was chosen and described in order to best explain the principles of the invention and the practical application, and to enable others of ordinary skill in the art to understand the invention for various embodiments with various modifications as are suited to the particular use contemplated.

[0114] The descriptions of the various embodiments of the symmetrical coded aperture system described herein have been presented for purposes of illustration but are not intended to be exhaustive or limited to the embodiments disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the described embodiments. The terminology used herein was chosen to best explain the principles of the embodiments, the practical application or technical improvement over technologies found in the marketplace, or to enable others of ordinary skill in the art to understand the embodiments disclosed herein.

Claims

1. A method of imaging using a symmetrical coded aperture to increase signal to noise ratio, the method comprising: a. imaging an object of interest with an electromagnetic radiation source, a coded aperture comprising at least two symmetrical regions, and electromagnetic radiation detector; and b. digitally aligning and combining detected signals from projected symmetrical coded aperture regions thereby increasing the signal to noise ratio.

2. The method of claim 1, further comprising determining properties of the object of interest using the combined signals as input for a reconstruction algorithm.

3. The method of claim 2, wherein the reconstruction algorithm is rules based.

4. The method of claim 2, wherein the reconstruction algorithm is machine learned.

5. The method of claim 2, wherein a physics forward model is used in the reconstruction algorithm.

6. The method of claim 5, wherein detector-space elements of the forward model for projected coded aperture symmetrical regions are combined.

7. The method of claim 6, wherein the forward model object-space elements for region(s) of interest are combined.

8. The method of claim 2, wherein the determined object of interest property is a momentum transfer spectra from elastically scattered X-rays.

9. The method of claim 1, wherein the at least two symmetrical regions comprise rotational symmetry, reflectional symmetry, translational symmetry, or combinations thereof.

10. The method of claim 1, wherein the coded aperture comprises at least two and up to 360 symmetrical regions.

11. The method of claim 1, wherein the electromagnetic radiation source illuminates the object of interest in a pencil beam geometry.

12. The method of claim 1, wherein the electromagnetic radiation source illuminates the object of interest in a fan beam geometry.

13. The method of claim 1, wherein the coded aperture comprises a spiral pattern.

14. The method of claim 1, wherein the coded aperture comprises two or more different symmetrical region patterns.

15. The method of claim 1, wherein the coded aperture comprises two or more materials that have differing electromagnetic radiation absorption properties.

16. The method of claim 1, wherein the electromagnetic radiation source is an X-ray source.

17. The method of claim 16, wherein the electromagnetic radiation source deposits an absorbed radiation dosage of less than 6 mGy when imaging the object of interest.

18. A system for imaging using a symmetrical coded aperture to increase signal to noise ratio, the system comprising: a. an electromagnetic radiation source; b. a coded aperture comprising at least two symmetrical regions; and c. an electromagnetic radiation detector; wherein the coded aperture is placed between an object of interest and the electromagnetic radiation detector.

19. The system of claim 18, wherein the at least two symmetrical regions comprise rotational symmetry, reflectional symmetry, translational symmetry, or combinations thereof.

20. The system of claim 18, wherein the coded aperture comprises at least two and up to 360 symmetrical regions.

21. The system of claim 18, wherein the electromagnetic radiation source illuminates the object of interest in a pencil beam geometry.

22. The system of claim 18, wherein the electromagnetic radiation source illuminates the object of interest in a fan beam geometry.

23. The system of claim 18, wherein the coded aperture comprises a spiral pattern.

24. The system of claim 18, wherein the coded aperture comprises at least two and up to 360 symmetrical regions.

25. The system of claim 18, wherein the coded aperture comprises two or more materials that have differing electromagnetic radiation absorption properties.

26. The system of claim 18, wherein the electromagnetic radiation source is an X-ray source.

27. The system of claim 18, wherein the electromagnetic radiation detector is an X-ray detector.

28. The system of claim 18, wherein the object of interest is a human body.

29. The system of claim 18, wherein the object of interest is a human breast.