Patent Application
20240234076
The disclosure relates generally to Computed Tomography (CT) X-ray systems, and more specifically to a multi-metal patterned anode for CT X-ray systems.
Hyperspectral CT X-ray systems are used in identification and analysis of materials. Unlike conventional systems that measure the total intensity of X-rays, hyperspectral CT X-ray systems can discriminate between X-rays of different energies by using a photon counting detector, which bins detected X-ray photons by energy. This can be useful in applications such as material identification, where different materials being analyzed attenuate or absorb X-rays differently. By analyzing the resulting spectrum, hyperspectral CT X-ray systems can distinguish between different materials.
An illustrative embodiment provides a multi-metal patterned anode for an X-ray detector. The anode comprises a substrate and at least one group of disjointed circular features formed on the substrate, wherein the circular features are made from different metals. The circular features in different groups have different radii, and the circular features in the same group have the same radii. In some example embodiments, each group comprises three circular features, wherein a first circular feature is composed of tungsten, a second circular feature is composed of samarium, and a third circular feature is composed of silver. The plurality of groups of circular features are radially arrayed on the substrate. The area of each group is equal to an area of a circle which encircles the circular features in the group. In some example embodiments, the area of the groups decrease with increasing radial distance from a center of the substrate, and in other example embodiments, the area of the groups increase with increasing radial distance from a center of the substrate. In some example embodiments, the substrate is made of diamond.
Another illustrative embodiment provides a multi-metal patterned anode for an X-ray detector. The anode comprises a diamond substrate and a plurality of groups each comprising three disjointed circular features formed on the diamond substrate. The plurality of groups are radially arrayed on the diamond substrate. Each circular feature is made from a different metal, wherein radii of the groups decrease with increasing radial distance from a center of the diamond substrate.
Another illustrative embodiment provides an X-ray system. The system comprises a cathode configured to emit electrons. The system comprises a multi-metal patterned anode configured to emit X-rays responsive to the electrons striking the anode. The patterned anode comprises a substrate and at least one group of disjointed circular features formed on the substrate, wherein each circular feature is made from a different metal. The system comprises a detector configured to detect the X-rays and generate corresponding electrical signals.
Another illustrative embodiment provides a method of fabricating a multi-metal patterned anode for an X-ray detector. The method comprises applying a layer of photoresist material on a substrate and aligning a photomask with the substrate, wherein the photomask comprises a transparent substrate with at least one group of disjointed circular opaque regions corresponding to desired mask patterns. The method comprises exposing the photoresist layer to ultraviolet (UV) light through the photomask using a photolithography process and developing the photoresist layer to remove either the exposed or unexposed areas of the photoresist. The method comprises depositing metal layers onto the mask patterns on the substrate using a deposition process to form at least one group of circular features on the substrate, wherein the circular features have different metal layers.
The novel features believed characteristic of the illustrative embodiments are set forth in the appended claims. The illustrative embodiments, however, as well as a preferred mode of use, further objectives and features thereof, will best be understood by reference to the following detailed description of an illustrative embodiment of the present disclosure when read in conjunction with the accompanying drawings, wherein:
The illustrative embodiments recognize and take into account one or more different considerations. For example, the illustrative embodiments recognize and take into account that conventional CT X-ray systems generally do not discriminate between X-rays of different energies by identifying energy distribution of the X-rays. As a consequence, conventional CT X-ray systems cannot discriminate well between materials with similar densities and have more beam hardening artifacts.
The illustrative embodiments provide a multi-metal patterned anode for improved spatial resolution of hyperspectral CT X-ray systems. The multi-metal patterned anode can also be used in conventional CT X-ray systems. The multi-metal patterned anode comprises one or more groups or clusters of metal features. The cluster of metal features has a smaller total surface area than the electron beam impinging upon it, thereby minimizing the focal spot of the systems and reducing geometric unsharpness of X-ray beams. In the present disclosure, the term “geometric unsharpness” refers to the loss of definition that is the result of geometric factors of X-ray systems. The factors controlling unsharpness are X-ray source size, source to object distance, and object to detector distance.
The illustrative embodiments provide a multi-metal patterned anode in which the metal features are composed of different metals. Each metal has a characteristic X-ray emission spectrum. When an electron beam is incident on the metal features composed of different metals, the X-rays emitted result in a combined emission spectrum that includes characteristic X-ray peaks of all the metals included in the group or cluster. By including multiple regions of high-intensity X-ray peaks across a wide range of peak energy values, signal-to-noise ratio (SNR) in the regions is improved.
System 100 includes a multi-metal patterned anode 120 which is placed directly in the line of electron beam 116. Multi-metal patterned anode 120 includes a substrate (not illustrated in
Multi-metal patterned anode 120 includes at least one group of disjointed or separated circular features (not illustrated in
System 100 includes power supply 124 configured to apply a DC voltage between cathode 104 and anode 120. Power supply 124 includes first terminal 128 electrically coupled to cathode 104 and includes second terminal 132 electrically coupled to anode 120. Power supply 124, may for example, be a switch mode regulated converter which provides a regulated DC voltage. In some example embodiments, power supply 124 is configured to output a regulated DC voltage in a range of 0V to several hundred KV.
When a high voltage is applied between cathode 104 and anode 120, a strong electric field is established between cathode 104 and anode 120. As a result, an electric current flows through filament 108, causing it to heat up and emit electrons through a process called thermionic emission. The temperature of filament 108 may be controlled to ensure a consistent emission of electrons. Focusing cup 112 shapes and directs the emitted electrons into electron beam 116 pointed at anode 120. Electron beam 116 accelerates towards anode 120 and collides with anode 120. As a result, the electrons in the beam rapidly decelerate and transfer energy to the atoms of the anode material, resulting in the emission of X-rays 134. Since the substrate material of anode 120 is highly transparent to X-rays, a significant portion of X-rays 134 are created from the circular features of the anode, thus effectively shrinking the focal spot of X-rays 134.
System 100 may include collimator 136 which restricts beams in X-rays 134 to improve spatial coherence. Collimator 136 may include lead plates (not illustrated in
System 100 includes X-ray detector 144 which converts X-rays 134 into an electrical signal or a digital image. In some example embodiments, X-ray detector 144 is an energy resolved photon counting detector that can detect X-ray spectrum.
In some example embodiments, X-ray detector 144 is implemented as a complementary metal-oxide-semiconductor (CMOS) detector. The CMOS detector includes an array of pixels, each consisting of a photodiode and a transistor (not illustrated in
In some example embodiments, X-ray detector 144 is implemented as a Cadmium Telluride (CdTe) photon counting detector. X-ray detector 144 may include an array of pixels, each consisting of a CdTe photodiode along with pulse processing electronics. As photons in X-rays interact with the photodiode, electrical charges are produced which are coupled to the pulse processing electronics, and in response the pulse processing electronics identify and bin the photons according to their energy.
Anode 200 includes at least one group or cluster 220 of disjointed circular features 224, 228 and 232 formed on substrate 204. Although in the illustrative embodiment of
In some example embodiments, circular features 224, 228 and 232 are made from different metals. For example, circular features 224 may be composed of tungsten, circular features 228 may be composed of samarium, and circular features 232 may be composed of silver.
Although in the illustrative embodiment of
In some example embodiments, features 224, 228 and 232 are clustered or placed in close proximity to each other while maintaining a gap between the features. For example, features 224, 228 and 232 may be clustered or placed in close proximity but separated by a 4 μm gap. In other example embodiments, features 224, 228 and 232 may be separated by a gap of less than 1 μm.
In some example embodiments, the area of group 220 is less than the area of an electron beam which is incident on group 220. In the present disclosure, the area of group 220 can be approximated to be equal to an area of the smallest circle which can encircle circular features 224, 228, and 232. In the illustrative embodiment of
When an electron beam strikes group 220, the area contributing to X-ray generation is mostly that of circular features 224, 228232 rather than the total area struck by the beam. Also, different metals have characteristic X-ray emission spectra. As such, X-rays produced by circular features 224, 228 and 232, which are made of different metals, have different spectral characteristics. The spectrum of X-rays generated by anode 200 is the sum of the spectra from each feature in group 220. By including regions of high intensity X-ray peaks generated by circular features 224, 228 and 232 in the spectrum improves SNR in those regions, thus improving image quality.
In some example embodiments, features 220, 224 and 228 have a same width or diameter. For example, features 220, 224 and 228 each may have a width or diameter of 40 μm, 60 μm, 80 μm, or 100 μm. In some example embodiments, features 220, 224, and 228 may have dissimilar diameters or surface areas in order to vary load fractions of X-rays generated.
In the illustrative embodiment of
In some example embodiments, circular features 224, 228 and 232 are made from different metals. For example, circular feature 224 may be composed of tungsten, circular feature 228 may be composed of samarium, and circular feature 232 may be composed of silver. Circular features 224, 228 and 232 are clustered or placed in close proximity to each other while maintaining a gap between the features. For example, features 224, 228 and 232 may be clustered in close proximity but separated by a 4 μm gap. In other example embodiments, circular features 224, 228 and 232 may be separated by a gap of less than 1 μm. In some example embodiments, substrate 204 has a thickness of 300 μm, and features 224, 228 and 232 have a thickness of 2 μm.
In the illustrative embodiment of
In some example embodiments, groups 320-0, 320A-1-320A-6, . . . , and 320E-1-320E-6 are clustered close to the center of anode 300. The location of the clusters relative to the substrate can be dependent on a range of maneuverability of the electron beam in an X-ray tube. In some example embodiments, groups 320-0, 320A-1-320A-6, . . . , and 320F-1-320E-6 are displaced from one another sufficiently so that each group may accommodate an electron beam without the beam overlapping another group.
Next, a thin layer of photoresist material 512 is applied to substrate 504. In some example embodiments, a technique called spin coating is used to apply photoresist material 512 on substrate 504. A desired amount of photoresist material 512 is dropped on substrate 504, and substrate 504 is spun at high speed, causing photoresist material 512 to spread evenly and form a uniform coating.
In some embodiments, a positive photoresist material may be applied and in some other embodiments a negative photoresist material may be applied. If a positive photoresist material is applied, exposure to light makes the photoresist material soluble in a developer solution. The exposed regions are removed, leaving behind a desired mask pattern on substrate 504. If a negative photoresist material is applied, exposure to light makes the photoresist material insoluble in a developer solution. The unexposed regions are washed away, leaving behind the desired mask pattern on substrate 504. In the example process illustrated in
A photomask 520 is used to selectively mask the applied photoresist from light. Photomask 520 may, for example, be a transparent glass plate with patterned opaque regions which mirror a desired pattern to be transferred onto substrate 504. In some example embodiments, the patterned opaque regions may be formed by one or more features 524.
Photomask 520 is aligned with substrate 504 and placed in close contact with photoresist material 512. The photoresist-coated substrate 504 and the aligned photomask 520 are exposed to ultraviolet (UV) light or other light of appropriate wavelengths. When the light passes through the transparent areas of photomask 520, the underlying photoresist material 512 is exposed. The exposed regions become insoluble, while the unexposed regions remain soluble.
A layer of photoresist material is then applied on the substrate (step 608). A technique called spin coating can be used to apply the photoresist material on the diamond. A photomask is aligned with the substrate (step 612). The photomask comprises a transparent substrate with at least one group of disjointed circular opaque regions corresponding to desired mask patterns. The photoresist layer is then exposed to ultraviolet (UV) light using a photolithography process (step 616). Depending on the type of photoresist layer used, a developer solution is used to remove either the exposed or unexposed areas of the photoresist layer (step 620).
Finally, metal layers are deposited on the mask patterns on the substrate using the deposition process to create at least one group of circular features on the substrate (step 624). In some example embodiments, the circular features have different metal layers. The process then ends.
As used herein, the phrase “a number” means one or more. The phrase “at least one of”, when used with a list of items, means different combinations of one or more of the listed items may be used, and only one of each item in the list may be needed. In other words, “at least one of” means any combination of items and number of items may be used from the list, but not all of the items in the list are required. The item may be a particular object, a thing, or a category.
For example, without limitation, “at least one of item A, item B, or item C” may include item A, item A and item B, or item C. This example also may include item A, item B, and item C or item B and item C. Of course, any combinations of these items may be present. In some illustrative examples, “at least one of” may be, for example, without limitation, two of item A; one of item B; and ten of item C; four of item B and seven of item C; or other suitable combinations.
The flowcharts and block diagrams in the different depicted embodiments illustrate the architecture, functionality, and operation of some possible implementations of apparatuses and methods in an illustrative embodiment. In this regard, each block in the flowcharts or block diagrams may represent at least one of a module, a segment, a function, or a portion of an operation or step. For example, one or more of the blocks may be implemented as program code.
In some alternative implementations of an illustrative embodiment, the function or functions noted in the blocks may occur out of the order noted in the figures. For example, in some cases, two blocks shown in succession may be performed substantially concurrently, or the blocks may sometimes be performed in the reverse order, depending upon the functionality involved. Also, other blocks may be added in addition to the illustrated blocks in a flowchart or block diagram.
The description of the different illustrative embodiments has been presented for purposes of illustration and description and is not intended to be exhaustive or limited to the embodiments in the form disclosed. The different illustrative examples describe components that perform actions or operations. In an illustrative embodiment, a component may be configured to perform the action or operation described. For example, the component may have a configuration or design for a structure that provides the component an ability to perform the action or operation that is described in the illustrative examples as being performed by the component. Many modifications and variations will be apparent to those of ordinary skill in the art. Further, different illustrative embodiments may provide different features as compared to other desirable embodiments. The embodiment or embodiments selected are chosen and described in order to best explain the principles of the embodiments, the practical application, and to enable others of ordinary skill in the art to understand the disclosure for various embodiments with various modifications as are suited to the particular use contemplated.
This application claims priority from provisional application No. 63/392,567, filed Jul. 27, 2022, entitled “MULTI-METAL PATTERNED X-RAY TRANSMISSION TARGET AND FABRICATION”, assigned to the present assignee and incorporated herein by reference.
This invention was made with United States Government support under Contract No. DE-NA0003525 between National Technology & Engineering Solutions of Sandia, LLC and the United States Department of Energy. The United States Government has certain rights in this invention.
| Number | Date | Country | |
|---|---|---|---|
| 20240136143 A1 | Apr 2024 | US |
| Number | Date | Country | |
|---|---|---|---|
| 63392567 | Jul 2022 | US |
