WO2023141209A1

WO2023141209A1 - X-ray imaging with energy sensitivity

Info

Publication number: WO2023141209A1
Application number: PCT/US2023/011148
Authority: WO
Inventors: Eugene Franklin BARASCH
Original assignee: Sacramento Radiology Services, Inc.
Priority date: 2022-01-19
Filing date: 2023-01-19
Publication date: 2023-07-27

Abstract

An x-ray imaging system including an x-ray source and an energy resolving x-ray detector is provided. The x-ray detector includes a scintillator and a photodetector configured to detect x-rays as a function of both position and energy. The x-ray imaging system is configured to generate energy and/or phase resolved x-ray images. Some embodiments include a scintillator, which converts high-energy photons into UV light, coupled with an array of photodiodes whose output is proportional to the amount of light generated. In some embodiments, the scintillator includes GAGG:Ce ((Gadolinum Aluminum Gallium) Garnet, doped with Cerium). In some embodiments, the x-ray detector is configured to use quantum noise or quantum scatter. The resulting phase contrast imaging and/or energy resolved imaging can create more sharply defined images relative to conventional CT.

Description

X-Ray Imaging with Energy Sensitivity CROSS-REFERENCE TO RELATED APPLICATIONS

[001] This application is a continuation-in part of US non-provisional patent application Ser. No. 17,579,481 filed January 19 2022, which in turn is a continuation-in-part of US non- provisional patent application Ser. No. 16/591,581, filed. October 2, 2019, which in turn claims priority and benefit of US provisional patent application Ser. No. 62/739,954 filed October 2, 2018. The disclosures of which are hereby incorporated herein by reference.

BACKGROUND

[002] Field of the invention:

[003] The application is in the field of x-ray imaging.

[004] Related Art:

[005] The major health concern in radiography, including Computed Tomography, is total accumulated ionizing radiation dosage. Reliable data on medical imaging related radiation exposure and associated health effects is lacking, but it is known that radiation causes cancer from very reliable data on the large population of people exposed to a nearly instantaneous exposure of 10 Rads (.1 Seiverts), the Hiroshima and Nagasaki survivors, but less is known about how this scales to lower accumulated dosages administered over a long span of time which is the typical situation in medical imaging. The functional relation, in mathematical terms, between radiation induced cancer and actual dosage remains unknown.

[006] A prudent approach in the light of this situation is to obtain the required imaging for medical diagnostic purposes with the least amount of radiation exposure. Limiting the gross dosage is the standard approach in this regard but that runs into the problem of quantum mottle which includes graininess in images created by statistical fluctuations in neighboring pixels. These fluctuations are proportional to (N)'¹⁷² and if N is not large enough to drive such fluctuations to ~ 0, the human eye will interpret these fluctuations as variations in gray scale, making the images seem grainy and very hard to interpret.

[007] Traditionally, before the advent of Computed Tomography (CT), chest imaging was strictly a radiographic technique with a wide-angle x-ray beam and single exposure with no change in the angulation of the beam. In contrast, CT uses many narrow-beamed exposures arrayed over 360 degrees. Typical dosages in non-CT radiographic techniques were on the order of .03 m-Seiverts or 30 m-Rads. Digital non-emulsion techniques have driven this down to approximately .015 m-Seiverts or 15 m-Rads. Thus, even low-dose chest CT requires 10 times the amount of x-ray dosage to the patient than does Radiography.

[008] The typical dosage in CT screening for lung cancer was on the order of 1.5 Rads/study. While one can obtain very good images of the lungs themselves with much lower dosage, e.g., at the .60 Rad level, this low dosage makes the chest wall and surrounding tissues so grainy that they become difficult to interpret. Because the legal standard makes a radiologist responsible for everything on every image, the low-dose technique, which may be sufficient for the identification of lung cancer, can mask a cancer in nearby tissue, e.g., in the dome of the liver. [009] A significant shortcoming of traditional imaging techniques is that virtually all x-ray and gamma ray medical imaging has been done using energy blind detectors. Such systems combine (i.e., integrate at each pixel) photons of all energies into a final image without any useful discrimination as to the energy of the photons.

SUMMARY

[0010] Various embodiments include systems and methods of generating energy resolved x-rays. These systems can provide several notable advantages. First, detection of energy resolved x- rays allows for photon phase detection and thereby phase resolved images. Second, detection of energy resolved x-rays allows for improved statistical analysis of the received x-rays, which enables energy dependent smoothing functions and quantum mottle suppression. Third, detection of energy resolved x-rays allows for multi-energy (e.g., dual or tri-energy) techniques, which are desired for tissue identification, without the need for multiple x-ray sources of separate energy and separate detectors.

[0011] Various embodiments of the invention include an imaging system comprising: an x-ray source, configured to produce x-rays having a range of energies; an x-ray detector including an array of pixels and configured to quantify the energy of detected x-rays, each of the pixels comprising: a scintillation crystal configured to generate ultraviolet light in response to an x-ray, a quantity of the ultraviolet being dependent on an energy of a photon of the x-ray, an ultraviolet sensitive photon detector, the photon detector being configured to generate an electrical signal proportional to the quantity of the ultraviolet light, and electronics configured to quantify the electrical signal, the quantified electrical signal being representative of the energy of the x-ray; and image generation logic configured to generate at least a first image based on a location of each of the pixels within the array and the energies of x-rays detected at each of the pixels. Optionally, the scintillation crystal includes Gadolinum Aluminum Gallium Garnet (GAGG), optionally doped with Cerium. It is anticipated that other scintillators and/or versions of GAGG may be used in alternative embodiments. Optionally, the imaging system further includes a contrast agent to be placed in a subject to be imaged and configured to absorb photons of a selected set of x-ray energies, wherein the image generation logic is configured to generate an image emphasizing or deemphasizing (or otherwise manipulating) photons of the selected set of x-ray frequencies.

[0012] Various embodiments of the invention include a method of producing an x-ray image, the method comprising: generating x-rays using an x-ray source; passing the x-rays through a subject to be imaged; detecting the x-rays using an energy resolved detector, the energy resolved detector having a two-dimensional array of pixels, each of the pixels being configured to determine an energy of each received x-ray photon such that x-ray data representing both two- dimensional position and energy of each x-ray is generated, wherein the energies of the x-rays are sorted into at least 3 energy bins; and generating at least a first image based on the x-ray data. Optionally, the method further comprises applying a smoothing function to the x-ray data, the smoothing function being configured to reduce quantum mottle in the first image and being dependent on the energies of the received x-ray photons; and/or wherein the first image is an energy resolved image in which x-ray photons of a first energy are deemphasized or emphasized relative to photons of a second (or more) energies. The first image may be dependent on and/or modified by the measured photon energy information, optionally within a single exposure. Optionally, the method further comprises selecting photons of an energy absorbed or alternatively not absorbed by a predetermined contrast agent and generating a second image based on emphasizing or deemphasizing or other manipulation of the selected photons. For example, an image may be produced to highlight locations wherein an Iodine contrast agent absorbs photons in a specific energy range.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013] FIG. 1 illustrates use of an energy resolved x-ray imaging system configured to generate an energy resolved x-ray image of a patient, according to various embodiments of the invention. [0014] FIG. 2 illustrates an energy spectrum for an x-ray tube, according to various embodiments of the invention.

[0015] FIG. 3 illustrates a cross-sectional view of a pixel of an energy resolved x-ray detector, according to various embodiments of the invention.

[0016] FIGs. 4A and 4B illustrate isometric and top views of an energy resolved x-ray detector including an array of pixels, according to various embodiments of the invention.

[0017] FIGs. 5A-5C illustrate manipulation of phase resolved x-ray and/or energy resolved data to image a specific tissue, according to various embodiments of the invention.

[0018] FIGs. 6A and 6B illustrate selection of soft tissue data in an energy resolved x-ray, according to various embodiments of the invention.

[0019] FIGs. 7A and 7B illustrate differences between a standard “dual energy” CT system and an energy resolved CT system according to various embodiments of the invention.

[0020] FIGs. 8A and 8B illustrate selection of calcified tissue in a breast x-ray using an energy resolved detector, according to various embodiments of the invention.

[0021] FIG. 9 illustrates a method of generating an image using an energy resolved x-ray detector, according to various embodiments of the invention.

[0022] The figures disclosed herein are generally not to scale.

DETAILED DESCRIPTION

[0023] FIG. 1 illustrates use of an energy resolved X-Ray Imaging System 100 configured to generate an energy resolved x-ray image of a patient, according to various embodiments of the invention. The energy resolved x-ray image is based on x-ray data including both positional (x- y) and energy information. The energy information is optionally embodied in an array of energy bins, each energy associated with a predetermined energy range. Thus, a particular detected x-ray photon may be characterized by at least three values: X, Y and E, where E is represented by a particular energy bin, and X and Y refer to the two-dimensional location of each pixel within an array of detector pixels. Various embodiments may include 2-64 or more energy bins, or any range between 2 and 64 bins. The number of bins is determined in part by the detection electronics. Such electronics can support 128, 256, 512 or 1024 or more bins. [0024] As illustrated in FIG. 1, X-Ray Imaging System 100 includes an X-Ray Source 110 configured to produce x-rays having a range of energies. X-Ray Source 110 may include a wide variety of known x-ray sources, including for example: x-ray tubes, a synchrotron source, radionuclides, and/or any other x-ray sources known in the art. In some embodiments, X-Ray Source 110 is configured to produce x-rays having an X-Ray Spectrum 210 as illustrated in FIG. 2. Such X-Ray Spectrums 210 may include characteristic radiation associated with specific elements, e.g., Iodine.

[0025] Imaging System 100 optionally further includes Phase Selectors 120 A and 120B. Phase Selectors 120 A and 120B are configured for selecting photons of particular phase shifts or having photons of particular phase differences. For example, Phase Selector 120 A may be adjusted to pass photons of a particular phase while Phase Selector 120B is adjusted to pass photons of the same phase or slightly different phases (e.g., 5 degrees different in phase). In this example, the photons that pass both Phase Selector 120A and Phase Selector 120B must have experienced a phase shift of ~5 degrees between the Phase Selectors 120. Specifically, they must have experienced a phase shift through interaction with a Subject 130. In various embodiments, Phase Selectors 120 are configured to distinguish between photons having a few degress of phase difference, e.g., at least 2, 3, 5 or 10 degrees, or any range therebetween.

[0026] Phase Selectors 120 A and 120B may include gratings or other wavelength dependent optics. Typically, at least one of Phase Selectors 120A and 120B include a phase selection adjustment mechanism, such as a mechanical dial, motor (i.e., stepper motor), grating rotator, and/or the like, configured to change the relative phases passed by Phase Selector 120A and 120B, i.e., to pass photons having a selected phase shift. By adjusting this mechanism, it is possible to scan over a range of phase differential (shift) between the relative phase based by Phase Selectors 120 A and 120B.

[0027] X-rays generated by X-Ray Source 110 are passed through a region in which Subject 130 may be placed. Subject 130 may include a patient or other object to be x-rayed. This space may include a structure configured to support Subject 130, such as a platform.

[0028] Subject 130 may absorb and/or change the phase of x-ray photons generated by X-Ray Source 110. For example, photon absorption may be a function of both tissue/material density and photon energy. As such, distinguishing between the absorption of photons of different energies may allow for clearer distinction between tissues/materials of different densities. The phase of x-ray photons may be altered by interaction of x-rays at boundaries between materials of differing densities and/or indices of refraction (at x-ray wavelengths). Thus, adjustment of Phase Selectors 120 A and 120B to detect various changes in phase caused by Subject 130 may be used to detect boundaries between different tissues and/or material types. In a specific example, phase resolved x-ray data may be used to more clearly (relative to non-phased resolved x-ray data) image vascular boundaries or boundaries of tumors. [0029] Imaging System 100 further includes an energy resolving Detector 150. Detector 150 includes an array of pixels and is configured to quantify the energy of detected x-rays. In various embodiments, the array of pixels may be linear or two-dimensional. For example, Detector 150 may include an array of at least 200 x 200, 256 x 256, 512 x 512, or 1024 x 1024 pixels. In various embodiments, Detector 150 includes at least 40k, 64k, 262k, IM, 4M or 8M pixels, or any range therebetween. The array of pixels may be flat or curved. For example, in some embodiments the array of pixels is disposed in a set of flat hexagons, which are in turn disposed to form a curved, e.g., parabolic, shape.

[0030] Imaging System 100 optionally further includes a Filter 140 configured to select a range of energies of x-rays received by Subject 130. Filter 140 may include a bandpass filter or a notch filter. In some embodiments, Filter 140 is configured to pass x-rays of an energy expected from a certain element such as Iodine. For example, Filter 140 may be configured to pass an Iodine peak in the x-ray spectrum illustrated in FIG. 2.

[0031] FIG. 3 illustrates a cross-sectional view of a Pixel 310 as may be included in energy resolved x-ray Detector 150, according to various embodiments of the invention. In typical embodiments, each of Pixel 310 includes at least a Scintillation Crystal 320, an Optical Diode 340 and electronics. Scintillation Crystal 320 is configured to generate ultraviolet light in response to an x-ray. Specifically, when an x-ray strikes Scintillation Crystal 320 ultraviolet and optionally visible light are produced. A quantity of the ultraviolet is dependent on an energy of the detected photon of the x-ray. Higher energy photons produce more light relative to lower energy photons. As used herein, the term “energy resolved” is meant to indicate that the detector is configured to distinguish between x-rays of various energies, and optionally to assign each x-ray photon to one of an array of alternative energy “bins.” For example, each energy bin may represent a 0.1, 0.5, 1 or 2 keV range in energy. In some embodiments, the number of energy bins is selected to include at least 8 or 10 bins to cover fwhm (full-width halfmax) of the x-ray output spectrum of X-Ray Source 110. Alternative numbers of energy bins are discussed elsewhere herein. In some embodiments, Scintillation Crystal 320 includes Gadolinum Aluminum Gallium Garnet (GGAG), optionally doped with Cerium. Fast, bright and/or balanced GGAG may be used in various embodiments. In alternative embodiments, Scintillation Crystal 320 be supplemented or replaced by Cadmium Zinc Telluride (CZT) and/or other scintillators known in the art. For example, some embodiments include CZT disposed between Optical Diode 340 and a layer of GGAG. The GGAG is optionally configured to provide a barrier to moisture.

[0032] Optical Diode 340 is an ultraviolet sensitive photon detector (e.g., photodiode) configured to detect the ultraviolet light generated within Scintillation Crystal 320. In response to the ultraviolet light, Optical Diode 340 is configured to generate an electrical signal proportional to the quantity of the ultraviolet light. As such, the electrical signal is also proportional, optionally linearly proportional, to the energy of the detected x-ray photon. In alternative embodiments, Optical Diode 340 may be replaced by an optical transistor or other photoelectric device.

[0033] The electronics of Detector 150 is configured to quantify (e.g., digitize) the electrical signal generated by the Optical Diode 340. The quantified electrical signal is representative of the energy of the detected x-ray. The electronics optionally include Front End Electronics 350 and Back End Electronics 360. Front End Electronics 350 typically includes circuits such as an amplifier. Back End Electronics 360 may include circuits such as a pulse height analyzer or pulse integrator, and memory configured to temporally store a digital result. Typically, each Pixel 310 includes a dedicated Optical Diode 340 and Front End Electronics 350, and optionally a dedicated Back End Electronics 360. In some embodiments each Pixel 310 includes a dedicated Scintillation Crystal 320, although in alternative embodiments, a single Scintillation Crystal 320 is used to convert x-rays into ultraviolet light to be detected by multiple Optical Diodes 340.

[0034] Pixel 310 optionally further includes an Optical Coupling 330 between Scintillation Crystal 320 and Optical Diode 340. Optical Diode 340 and/or associated Front End Electronics 350 are optionally produced in a preconfigured array and then incorporated in Pixel 310. For example, multiple Optical Diodes 340 may be produced in an array on a single silicon substrate, prior to incorporation into an array of Pixels 310.

[0035] Referring again to FIG. 1, Imaging System 100 optionally further includes Image Generation Logic 160. Image Generation Logic 160 is configured to generate images based on a location of each Pixel 310 within an array and also based on the energies of x-rays detected by each Pixel 310. Typically, an image is based on the detection of a large number of x-ray photons, each of which is associated with an X/Y location (e.g., position in two dimensions) and an energy, E. Image Generation Logic 160 includes electronic circuits, hardware, firmware, and/or software stored on a non-transient computer readable medium. For example, in some embodiments, Image Generation Logic 160 includes one or more computing devices including image generation software and an input/output configured to receive energy resolved x-ray data generated by Detector 150.

[0036] In some embodiments, Image Generation Logic 160 is configured to generate at least a second image based on the photons having a different phase shift. Data used to generate such an image may be obtained by detecting x-rays at a first setting of Phase Selectors 120 A and 120B and then detecting x-rays at a second setting of Phase Selectors 120 A and 120B. Differences between the data generated at these two settings may be used, for example, to generate an image highlighting edges of structures within Subject 130.

[0037] In some embodiments, Image Generation Logic 160 is configured to generate a set of images based on photons of different energies, or one or more images wherein x-ray energy is represented by a false color. Optionally, Image Generation Logic 160 includes a user interface wherein a user can select one, two or more energy ranges and manipulate the image data in each energy range independently. For example, a user may select two energy ranges and emphasize or deemphasize photons of different energy in these ranges. This can be accomplished by inverting, subtracting, and/or adding the data in different energy ranges. In a specific example, photons in a higher energy range may be absorbed by more dense material (e.g., a tumor, bone or a calcified lymph node) relative to lower energy photons which are absorbed by less dense materials (e.g., lung tissue, muscle, fatty tissue). By subtracting x-ray data of higher energy x- rays and/or adding x-ray data of lower energy x-rays from an image, details of less dense materials may be made more apparent in a resulting image. This provides a significant clinical benefit.

[0038] The user interface may include features such as: 1) rapidly alternating between images so as to make the difference “flicker” thus highlighting features resulting from the absorption of x- rays of different energy; and/or 2) allowing a user to select energy ranges to be emphasized or deemphasized using a virtual slider bar or dial and, thus, dynamically manipulate the x-ray data to selectively examine and/or search for specific structures. In some embodiments Image Generation Logic 160 includes a neural network and/or a machine learning system configured to automatically process the image data as a function of energy, i.e., as a function of energy quantified in (at least 3, 4, 8, 10, etc.) energy bins as discussed elsewhere herein. An output of this processing may include a composite image in which different structures within Subject 130 are shown at their most distinctive appearance. For example, if an image includes a calcified lymph node, a bone, a tumor, and a fatty breast lump, each of these structures may be most clearly seen at a different specific energy level. A composite image may include the data points representing each of these structures as detected at their optimum x-ray energy, thus producing an optimized image for efficient analysis by a user. A composite image may be generated using (CAD) Computer assisted detection to detect specific objects and then selecting energies to emphasize or deemphasize at which the detected objects are best seen and/or distinguished. [0039] In some embodiments, Image Generation Logic 160 is configured to apply an energy dependent smoothing function to an x-ray image. The smoothing function is optionally configured to reduce quantum mottle in the image. The energy information results in an improved smoothing function because the effect of quantum mottle is energy dependent. An improved smoothing function is applied knowing the energy of the x-ray photons detected by Detector 150. For example, as the energy of x-ray photons are measured, an actual energy spectrum of the received photons can be generated and may be used to provide a best fit through the data, optionally image pixel by image pixel, thus reducing statistical fluctuations. An improved smoothing function means that the Subject 130 may be exposed to a lower overall dose of x-rays to achieve an equilivant image, or an improved image may be obtained at a same dose. For example, knowing an expected energy distribution, it is easy to see variation from that spectrum and thus estimate if a statistically sufficient sample has been obtained. In some embodiments, Image Generation Logic 160 is configured to terminate generation of x-rays from X-Ray Source 110 based on receipt of statistically sufficient data across the energy bins.

[0040] In various embodiments, the suppression of quantum mottle dramatically increases the quality of a standard chest Radiograph and all radiography by digitizing each photon, one at a time, by using a detector that can count and record the position and energy of every photon (x- ray or gamma ray). This is very useful, for not only standard medical imaging, but also for advanced imaging using phase contrast techniques. Phase contrast techniques can provide images that are even sharper than those available in CT using a radiographic technique and the energy of each photon is helpful in determining the photon phase or phase shift. The technique is based on noting which photons interact with the edges of objects and are, thus, delayed (phase shifted) on their way to the detector, and since photons travel as waves, such delayed photons are of a different phase than other photons. Phase contrast imaging can obviate the need for CT in many cases, which has many advantages besides the promise of a lower radiation dosage as computed to CT.

[0041] FIGs. 4A and 4B illustrate isometric and top views of an energy resolved x-ray detector including a Pixel Array 410, according to various embodiments of the invention. Scintillation Crystal 320 is optionally grown on an x-ray transparent Substrate 420. The Scintillator Crystals 320 of each Pixel 310 may be combined in a single crystal. Alternatively, a Barrier 430 may be disposed between the Scintillation Crystals 320 of each Pixel 310. Barrier 430 is typically grown along with the Scintillation Crystal 320, and may include, for example, a metal or a region of the crystal that has been grown slightly differently to create a variation in index of refraction at ultraviolet and/or x-ray frequencies, e.g., annealed or doped differently. Barrier 430 is configured to prevent ultraviolet and/or x-rays from traveling between the Scintillation Crystals 320. Since the number of photons generated by the scintillator is proportional to the x-ray energy absorbed, the same energy resolution can be achieved over a wide range of scintillator thicknesses.

[0042] FIGs. 5A-5C illustrate manipulation of phase resolved and/or energy resolved x-ray data to image a specific tissue, according to various embodiments of the invention. FIG. 5A is a conceptual drawing of a Tissue 510 including a Vein 520. Edges of the vein may be distinguished by an x-ray phase shift, and/or the vein may be distinguished by a contrast agent. In FIG. 5B the x-ray data has been manipulated to emphasize the Tissue 510 and deemphasize the Vein 520. In FIG. 5C the x-ray data has been manipulated to emphasize the Vein 520 and deemphasize the Tissue 510.

[0043] FIGs. 6A and 6B illustrate selection of soft tissue data in an energy resolved x-ray, according to various embodiments of the invention. In FIG. 6 A dense Bone Structures 610 are distinguished. Such structures may more clearly be seen in data collected from higher energy x-rays. In FIG. 6B a Soft Tissue Structure 620 is distinguished. Such structures may more clearly be seen in data collected from relatively lower energy x-rays. As noted herein, a user may choose to emphasize or deemphasize such different structures in energy resolved images (images manipulated based on detected x-ray energy).

[0044] FIGs. 7A and 7B illustrate differences between a standard “dual-energy” CT (computed tomography) System 710 (such as may be found in the prior art) and an Energy Resolved CT System 760, according to various embodiments of the invention. In a Dual-Energy CT System 710 two x-ray sources are used: a High Energy X-Ray Source 720 and a Low Energy X-ray Source 730. Each of these are preconfigured to provide x-rays within different energy ranges. The two x-ray sources are optionally mounted on a Gantry 740 configured to move the x-ray sources so as to generate CT data. X-rays from both sources are directed at Subject 130, optionally disposed on a Platform 755. The x-rays from each source are detected by a separate (energy blind) X-Ray Detector 735.

[0045] This Dual -Energy CT System 710 has some advantages. For example, dual-energy CT identifies calcium and ossification far better and more accurately than standard CT. However, Dual -Energy CT System 710 has a number of disadvantages. Such systems require two detectors, two x-ray sources and a much more expensive CT machine (in part due to a stronger Gantry 740) that takes two separate but simultaneous images of the subject with the two x-ray sources and the two detectors separated by -90° from one another. The two x-ray sources are set at widely different tube energies producing very poor energy selection between the two tubes/detector systems and these separate images are “subtracted” to get better identification of calcium and ossified nodules. The subject gets a double dose of x-ray radiation and the energy of each x-ray source is fixed at the time the data is collected. There are only two sets (“bins”) of energy data, each associated with a separate data set. This technique increases the dose to the patient by approximately a factor of two and the energy selection/differentiation is poor since the detectors are actually energy blind.

[0046] In contrast with Dual -Energy CT System 710, Energy Resolved CT System 760 (See FIG. 7B) requires only a single X-Ray Source 770 and a single energy sensitive/selective detector, such as X-ray Detector 150. X-Ray Source 770 is optionally an embodiment of X- Ray Source 110. In fact, in some embodiments, existing CT systems can be retrofitted with X- Ray Detector 150 to be converted to energy resolved systems. These systems can then benefit from multi-energy data and energy-based data manipulation as described herein, with a single image and lower dosages than standard Dual -Energy CT System 710. One gets “dual energy” or “multi-energy” by just segregating the energy spectrum of photons into high and low (or 3 or more) energy bins.

[0047] FIGs. 8A and 8B illustrate selection of calcified tissue in a breast x-ray using an energy resolved detector, according to various embodiments of the invention. In FIG. 8A a Breast Image 810 includes an x-ray signal resulting from both structures within the breast and from Soft Tissue 830 of the breast. In FIG. 8B a Breast Image 840 includes deemphasis of x-ray (signal) data of an energy that would be absorbed by the soft tissue and emphasis of x-ray data of an energy that would be absorbed by the structures within the breast, e.g., Calcified Tissue 850 and/or a Tumor 860.

[0048] It is known that dual energy CT is useful in tissue identification. This is important in the case of cancer therapy. For instance, one major way of monitoring the progress of cancer and cancer therapy is to monitor metastases to lymph nodes. Effective therapy destroys the metastatic cancer in lymph nodes. In the case of complete eradication of the cancer from the lymph nodes, the lymph node does not usually completely involute, it calcifies. The lymph node itself dies. This is called a “granuloma”. A grain (i.e. calcium) containing nodule. Distinguishing between cancerous and calcified lymph nodes can be accomplished using Detector 150 to generate energy and/or phase resolved images as discussed herein.

[0049] FIG. 9 illustrates a method of generating an image using an energy resolved x-ray detector, according to various embodiments of the invention. The steps illustrated in FIG. 9 are optionally performed in alternative orders, as well as concurrently, and may be performed using X-Ray Imaging System 100 discussed elsewhere herein.

[0050] In a Generate X-Rays Step 910, an x-ray source, such as X-Ray Source 110, is used to generate x-rays. The generated x-rays may have an energy distribution as illustrated in FIG. 2. In some embodiments, Generate X-Rays Step 910 is automatically terminated once a statistically relevant number of x-rays have been detected in multiple energy bins.

[0051] In a Pass X-Rays Step 920, the generated x-rays are passed through a subject to be examined, e.g., Subject 130. The subject may be any subject for which x-ray imaging is currently practiced, including, for example, a person, an animal, artifacts, historical items, assembled or manufactured materials, a geological sample, etc. The subject may include a contrast agent, for example barium or iodine may be used as a contrast agent in medical applications. Within the subject the x-rays may be attenuated, absorbed, phase altered, scattered, etc.

[0052] In a Detect X-Rays Step 930, the x-rays having passed through the subject are detected using an energy resolved detector, such as Detector 150. The energy resolved detector is configured to determine an energy for each received x-ray photon. The energy resolved detector optionally includes a two-dimensional array of pixels, e.g., an array of Pixel 310, such that x-ray data representing both two-dimensional position and energy of each x-ray is generated. In typically embodiments, the energy resolved detector is configured to sort the x-rays into at least 2, 3, 4, 8, 10, 16, 32 or 64 energy bins, or any range therebetween.

[0053] In an Optional Detect Phase Step 940, a phase shift of each received x-ray photon is detected. The phase shift is optionally detected by setting Phase Selectors 120 in different configurations so as to pass photons of particular phase differences, (e.g., approximately 0, 2, 4, 5, or 6 degrees). X-ray data may be obtained at one, two or multiple settings of Phase Selectors 120 (each setting being configured for x-rays of a different phase shift to reach the detector). As noted elsewhere herein, a phase shift may result from interaction of an x-ray at an edge within the subject. Detect Phase Step 940 is optionally performed contemporaneously with Detect X- Rays Step 930. In some embodiments, detection of edges is used to distinguish between structures having cancerous and non-cancerous shapes.

[0054] In a Generate Image Step 950, one or more images are generated based on the x-ray data generated in Detect X-Rays Step 930. The generated images may include, for example, an image based on x-rays of a particular x-ray energy or energy range, an image based on x-rays of a particular phase shift or range of phase shift, and/or an image where x-ray data is emphasized and/or deemphasized as a function of energy and/or phase. For example, an “energy resolved” image may be generated by subtracting data associated with one energy from a data set or from data associated with a second energy. An image may be generated by subtracting data associated with one phase shift from data associated with a second phase shift. In a more specific example, data of an energy that would be absorbed by a contrast agent is emphasized relative to data of an energy that would not be absorbed by the contrast agent. In another example, data showing a phase shift is emphasized relative to data having no or minimal phase shift.

[0055] In some embodiments, Generate Image Step 950 includes automated generation of an image using computer assisted detection (CAD). For example, a machine learning system may be trained for manipulating data of different x-ray energies so as to automatically highlight specific structures within the subject. Further, Generate Image Step 950 may include generation of a composite image in which different regions of the image are manipulated in different ways. For example, a first part of the image may be manipulated to emphasize a first structure while a second part of the image may be manipulated to emphasize a second structure, the structures optionally having different characteristics related to x-ray interaction. In some embodiments, Generate Image Step 950 includes addition of false color to an image based on energy and/or phase shift of detected x-rays.

[0056] In some embodiments, Generate Image Step 950 includes a user manipulating a control, such as a virtual dial or slider bar, to dynamically select energies and/or a phase shift to be used in manipulating the x-ray data used to generate an image. For example, a user may select x-ray energies to be emphasized and/or deemphasized using a control and then observe resulting images in real-time. Such selection may be from 1, 2, 3, 4, 8, 10, 16, 32 or 64 energy bins, or more, or any range therebetween.

[0057] In some embodiments, Generate Image Step 950 includes generation of a sequence of images. This sequence may be a sequence over time, for example, a series of x-ray images generated at different times to observe changes in a subject. An example of such changes may include perfusion of a contrast agent through a person’s organ. Alternatively, this sequence may be a sequence of images emphasizing different x-ray energies and/or phase shifts.

[0058] In an optional Smooth Step 960, one or more smoothing functions are applied to the x-ray data generated in Detect X-Rays Step 930. A smoothing function can optionally be dependent on the energies of detected x-rays and/or dependent on statistics of photons detected at specific energies. For example, an amount of smoothing may be dependent on a number of x-ray photons detected within particular energy bins. Different amounts of smoothing may be applied to x-ray data in one energy range relative to one or more other energy ranges. A smoothing function applied in Smooth Step 960 is optionally configured to reduce quantum mottle in the first image, while optionally being dependent on the energies of the received x-ray photons. Smooth Step 960 is optionally a part of Generate Image Step 950.

[0059] In an optional Identify Step 970, an image generated in Generate Image Step 950 is used to identify a structure within the subject. The structure is optionally distinguished (e.g., emphasized or deemphasized) within the image based on x-ray energy and/or phase shift.

Some structures may be identified using a machine learning system or other computer assisted detection. In some embodiments, Image Generation Logic 160 is configured for a user to request automatic selection of objects within the subject having specific characteristics. For example, a user may request automatic identification of objects having densities characteristic of calcified tissue and/or having densities characteristic of cancers. In one example, a user may request that a narrow range of energies absorbed by a specific contrast agent (such as at the k- edge of Iodine) be emphasized in a first image, while other energies are deemphasized. This highlights the contrast agent. Data collected in the same x-ray exposure can be manipulated to emphasize surrounding tissue in a second image. The combination of first and second images provides unique clinical information (both highlighting a specific structure and showing its position relative to other tissues), optionally in a single x-ray exposure.

[0060] Several embodiments are specifically illustrated and/or described herein. However, it will be appreciated that modifications and variations are covered by the above teachings and within the scope of the appended claims without departing from the spirit and intended scope thereof. For example, the energy resolved detector described herein may be used as a nuclear camera to detect a radioactive tracer and/or contrast agent within a subject or material. In such cases, an image may be produced by comparing detected signal at an energy the tracer emits or the contrast agent absorbs, to a detected signal at a different energy. At these different energies, X-Ray Imaging System 100 can produce two images (from data obtained at the same time/x-ray exposure), one with and one without the enhancement of the tracer/contrast agent. These images can be subtracted from each other using Image Generation Logic 160 to produce an enhanced image.

[0061] The embodiments 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. 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.

[0062] Computing systems and/or logic referred to herein can comprise an integrated circuit, a microprocessor, a personal computer, a server, a distributed computing system, a communication device, a network device, or the like, and various combinations of the same. A computing system or logic may also comprise volatile and/or non-volatile memory such as random access memory (RAM), dynamic random access memory (DRAM), static random access memory (SRAM), magnetic media, optical media, nano-media, a hard drive, a compact disk, a digital versatile disc (DVD), optical circuits, and/or other devices configured for storing analog or digital information, such as in a database. A computer-readable medium, as used herein, expressly excludes paper. Computer-implemented steps of the methods noted herein can comprise a set of instructions stored on a computer-readable medium that when executed cause the computing system to perform the steps. A computing system programmed to perform particular functions pursuant to instructions from program software is a special purpose computing system for performing those particular functions. Data that is manipulated by a special purpose computing system while performing those particular functions is at least electronically saved in buffers of the computing system, physically changing the special purpose computing system from one state to the next with each change to the stored data.

The “logic” discussed herein is explicitly defined to include hardware, firmware or software stored on a non-transient computer readable medium, or any combinations thereof. This logic may be implemented in an electronic and/or digital device (e.g., a circuit) to produce a special purpose computing system. Any of the systems discussed herein optionally include a microprocessor, including electronic and/or optical circuits, configured to execute any combination of the logic discussed herein. The methods discussed herein optionally include execution of the logic by said microprocessor.

Claims

CLAIMS What is claimed is:

1. An imaging system comprising: an x-ray source, configured to produce x-rays having a range of energies; an x-ray detector including an array of pixels and configured to quantify the energy of detected x-rays, each of the pixels comprising: a scintillation crystal configured to generate ultraviolet light in response to an x- ray, a quantity of the ultraviolet being dependent on an energy of a photon of the x-ray, an ultraviolet sensitive photon detector, the photon detector being configured to generate an electrical signal proportional to the quantity of the ultraviolet light, and electronics configured to quantify the electrical signal, the quantified electrical signal being representative of the energy of the x-ray; and image generation logic configured to generate at least a first image based on a location of each of the pixels within the array and the energies of x-rays detected at each of the pixels.

2. The system of claim 1, further comprising an optical coupling layer disposed between the scintillation crystal and the photon detector.

3. The system of any one of the preceding claims, further comprising a contrast agent configured to absorb photons of a selected set of x-ray energies, wherein the image generation logic is configured to generate an image emphasizing or deemphasizing photons of the selected set of x- ray frequencies.

4. The system of any one of the preceding claims, wherein the scintillation crystal includes Gadolinum Aluminum Gallium Garnet, doped with Cerium.

5. The system any one of the preceding claims, further comprising a set of phase filters configured to select a phase shift of x-ray photons detected by the photon detector, so as to distinguish between photons of the x-rays of different phase.

6. The system of any one of the preceding claims, wherein the photon detector is configured to produce an electrical signal linearly proportional to the energy of the photon.

7. The system of any one of the preceding claims, further comprising an optical barrier disposed between the scintillation crystals of each of the array of pixels, the optical barrier being configured to prevent light from traveling between the scintillation crystals.

8. The system of any one of the preceding claims, wherein the array of pixels includes at least 40,000 pixels.

9. The system of any one of the preceding claims, wherein the photon detector includes an optical diode.

10. The system of any one of the preceding claims, wherein the electronics include a front-end preamplifier and a pulse height detector.

11. The system of any one of the preceding claims, wherein the image generation logic is configured to generate at least a second image based on photons of different phase shift.

12. The system of any one of the preceding claims, wherein the image generation logic is configured to generate at least a second image based on photons of different energies.

13. The system of any one of the preceding claims, wherein the image generation logic configured to generate images emphasizing or deemphasizing photons as a function of their energy.

14. The system of any one of the preceding claims, wherein the image generation logic is configured for a user to select which photons to emphasize or deemphasize as a function of their energy, the selection being from an array of energies including at least 3, 4, 8, 10, 16 or 32 energy bins.

15. The system of any one of the preceding claims, wherein the image generation logic is configured to apply an energy dependent smoothing function to the first image.

16. The system of any one of the preceding claims, further comprising a gantry configured to move the x-ray detector, wherein the imaging system is configured to generate CT (computed tomography) images.

17. A method of producing an x-ray image, the method comprising: generating x-rays using an x-ray source; passing the x-rays through a subject to be imaged; detecting the x-rays using an energy resolved detector, the energy resolved detector having a two-dimensional array of pixels, each of the pixels being configured to determine an energy of each received x-ray photon such that x-ray data representing both two-dimensional position and energy of each x-ray is generated, wherein the energies of the x-rays are sorted into at least 2 energy bins; and generating at least a first image based on the x-ray data.

18. The method of any one of the preceding claims, further comprising detecting a phase shift of each received x-ray photon.

19. The method of any one of the preceding claims, wherein the first image is a phase contrast image generated by deemphasizing or emphasizing photons of one phase shift relative to photons of another phase shift.

20. The method of any one of the preceding claims, further comprising applying a smoothing function to the x-ray data, the smoothing function being configured to reduce quantum mottle in the first image and being dependent on the energies of the received x-ray photons.

21. The method of any one of the preceding claims, wherein the first image is an energy resolved image in which x-ray photons of a first energy are deemphasized or emphasized relative to photons of a second energy.

22. The method of any one of the preceding claims, further comprising selecting the first energy and second energy from at least the four energy bins.

23. The method of any one of the preceding claims, further comprising generating a second image based on the x-ray data, the second image being an energy resolved image in which photons of the second energy are deemphasized or emphasized relative to the first energy.

24. The method of any one of the preceding claims, further comprising automatically identifying structure within the subject using the first image, the structure being distinguished in the first image based on x-ray energy.

25. The method of any one of the preceding claims, further comprising selecting photons of an energy absorbed or not absorbed by a predetermined contrast agent and generating a second image based on emphasizing or deemphasizing or manipulation of the selected photons.