Patent Grant
9008278
This section is intended to introduce the reader to various aspects of art that may be related to various aspects of the present disclosure, which are described and/or claimed below. This discussion is believed to be helpful in providing the reader with background information to facilitate a better understanding of the various aspects of the present disclosure. Accordingly, it should be understood that these statements are to be read in this light, and not as admissions of prior art.
A variety of diagnostic, laboratory, and other systems (e.g., radiation-based treatment systems) may utilize X-ray tubes as a source of radiation. Typically, the X-ray tube includes a cathode and an anode. An emitter within the cathode may emit a stream of electrons. The anode may include a target that is impacted by the stream of electrons. As a result of this impact, the target may emit radiation. A large portion of the energy deposited into the target by the electron beam produces heat, with another portion of the energy resulting in the production of X-ray radiation. Of the X-ray radiation that is emitted, two types may result: (1) Bremsstrahlung radiation, which is typically emitted toward a subject of interest for treatment or imaging, and (2) characteristic radiation, which is a result of fluorescence from the target atoms and is typically emitted isotropically.
In imaging systems, for example, X-ray tubes are used in projection X-ray systems, fluoroscopy systems, tomosynthesis systems, mammography systems, and computed tomography (CT) systems as a source of X-ray radiation. In these implementations, images are produced by variations in contrast resulting from the different attenuation of X-rays by various materials in the sample or subject. Other techniques, such as diffraction-based phase contrast imaging, may produce images by variations in contrast resulting from differences in the refractive indices of different materials in the subject. Thus, diffraction-based imaging may be used to distinguish between materials having similar X-ray attenuation. While medical X-ray imaging systems typically utilize conventional X-ray tubes, some diffraction-based medical techniques use X-ray sources with higher flux than laboratory-based sources are typically able to provide.
For example, as noted above, during the operation of an X-ray source, the electron beam impacts and deposits energy into the source target, resulting in heat and X-ray radiation. The X-ray flux is, therefore, highly dependent upon the amount of energy that can be deposited into the source target by the electron beam within a given period of time. However, the relatively large amount of heat produced during operation, if not mitigated, can damage the X-ray source (e.g., melt the target). Accordingly, conventional X-ray sources are typically cooled by either rotating or actively cooling the target. However, when rotation is the means of avoiding overheating, the amount of deposited heat is limited by the rotation speed (RPM) and the life of the supporting bearings, this limits the amount of deposited heat and X-ray flux. This also increases the overall volume, and weight of the X-ray source systems. When the target is actively cooled, such cooling generally occurs far from the electron beam impact area, which in turn significantly limits the electron beam power that can be applied to the target. In both situations, the restricted heat removal ability of the cooling methods markedly lowers the overall flux of X-rays that are generated by the X-ray tube.
Certain embodiments commensurate in scope with the originally claimed subject matter are summarized below. These embodiments are not intended to limit the scope of the claimed subject matter, but rather these embodiments are intended only to provide a brief summary of possible embodiments. Indeed, the invention may encompass a variety of forms that may be similar to or different from the embodiments set forth below.
In one embodiment, an X-ray source includes one or more electron emitters configured to emit one or more electron beams; one or more source targets configured to receive the one or more electron beams emitted by the one or more electron emitters and, as a result of receiving the one or more electron beams, to emit X-rays. Each source target includes: a first layer having one or more first materials; and a second layer in thermal communication with the first layer and having one or more second materials, wherein the first layer is positioned closer to the electron emitter than the second layer, the first material layer has a higher overall thermal conductivity than the second layer, and the second layer produces the majority of the X-rays emitted by the source target.
In another embodiment, an X-ray source includes: one or more electron emitters configured to emit one or more electron beams; one or more stationary source targets configured to receive the one or more electron beams produced by the one or more emitters and, as a result of receiving the one or more electron beams, to emit X-rays. Each source target includes: a target layer having one or more target materials; and an electron beam impact area at which the electron beam impinges on the target layer, and wherein the target layer includes a notch disposed about the electron beam impact area.
In a further embodiment, an X-ray source includes an emitter assembly having an emitter and one or more electron beam focusing elements. The emitter assembly is configured to emit and focus an electron beam such that the electron beam has an aspect ratio of at least 500:1 at a site of impact. The source also includes a source target configured to receive, at the site of impact, the electron beam and, as a result of receiving the electron beam, to emit X-rays and an X-ray window out of which the X-rays are emitted from the X-ray imaging source.
These and other features, aspects, and advantages of the present disclosure will become better understood when the following detailed description is read with reference to the accompanying drawings in which like characters represent like parts throughout the drawings, wherein:
One or more specific embodiments will be described below. In an effort to provide a concise description of these embodiments, all features of an actual implementation may not be described in the specification. It should be appreciated that in the development of any such actual implementation, as in any engineering or design project, numerous implementation-specific decisions must be made to achieve the developers' specific goals, such as compliance with system-related and business-related constraints, which may vary from one implementation to another. Moreover, it should be appreciated that such a development effort might be complex and time consuming, but would nevertheless be a routine undertaking of design, fabrication, and manufacture for those of ordinary skill having the benefit of this disclosure.
When introducing elements of various embodiments of the present invention, the articles “a,” “an,” “the,” and “said” are intended to mean that there are one or more of the elements. The terms “comprising,” “including,” and “having” are intended to be inclusive and mean that there may be additional elements other than the listed elements. Furthermore, any numerical examples in the following discussion are intended to be non-limiting, and thus additional numerical values, ranges, and percentages are within the scope of the disclosed embodiments.
As noted above, the X-ray flux produced by an X-ray source may depend on the energy and intensity of an electron beam deposited into the source's target. The energy deposited into the target produces, in addition to the X-ray flux, a large amount of heat. Accordingly, during the normal course of operation, a source target is capable of reaching temperatures that, if not tempered, can damage the target. Typically, the temperature rise is managed by either rotating or actively cooling the target. However, such cooling is macroscopic and does not occur immediately adjacent to the electron beam impact area, which in turn substantially limits the overall flux of X-rays produced by the source, potentially making the source unsuitable for certain applications, such as those requiring high X-ray flux densities. Accordingly, it would be desirable if the source could be operated in a substantially continuous basis in a manner that enables the output of high X-ray flux.
The present disclosure provides embodiments of systems including an X-ray source having features configured to reduce thermal buildup in the source. For example, certain of the embodiments disclosed herein include a multilayer source target having one or more layers disposed in thermal communication with a target layer. As discussed herein, a “target layer” is intended to denote a layer that produces the majority of X-rays when the multilayer structure receives an electron beam. The one or more layers that are in thermal communication with the target layer, in accordance with present embodiments, generally have a higher overall thermal conductivity than the target layer. The one or more layers may be disposed between a source of the electron beam and the target layer, or between an X-ray window and the target layer, or both. The one or more layers may generally be referred to as “heat-dissipating” or “heat-spreading” layers, as they are generally configured to dissipate or spread heat away from the target area impinged on by the electron beam to enable enhanced cooling efficiency.
The present disclosure also provides embodiments of an emitter assembly configured to emit and focus an electron beam. The electron beam may be focused in a manner that enables the electron beam to have an aspect ratio when impinging on the source target suitable for particular high flux applications. For example, the aspect ratio, measured by the ratio of orthogonal lines bisecting the width and length of the electron beam when impinging on the source target, may be at least 500:1, such as between 500:1 and 5000:1, between 500:1 and 2500:1, or between 750:1 and 1250:1. Using such an aspect ratio may enable the electron beam to deposit a relatively large amount of energy into a relatively small portion of the target layer, enabling both high flux and faster cooling. Such embodiments are discussed herein below.
Referring to
The subject may, for example, attenuate or refract the incident X rays 16 and produce the projected X-ray radiation 20 impacts a detector 22, which is coupled to a data acquisition system 24. It should be noted that the detector 22, while depicted as a single unit, may include one or more detecting units operating independently or in conjunction with one another. The detector 22 senses the projected X-rays 20 that pass through the subject 18, and generates data representative of the attenuated radiation. The data acquisition system 24, depending on the nature of the data generated at the detector 22, converts the data to digital signals for subsequent processing. Depending on the application, each detector 22 produces an electrical signal that may represent the intensity and/or phase of each projected X-ray beam 20 as it passes through the subject 18.
An X-ray controller 26 may govern the operation of the X-ray source 14 and/or the data acquisition system 24. The controller 26 may provide power and timing signals to the X-ray source 14 to control the flux of the X-ray radiation 16, and to control or coordinate with the operation of other system features, such as cooling systems for the X-ray source, image analysis hardware, and so on. In embodiments where the system 10 is an imaging system, an image reconstructor 28 (e.g., hardware configured for reconstruction) may receive sampled and digitized X-ray data from the data acquisition system 24 and perform high-speed reconstruction to generate one or more images representative of different attenuation, differential refraction, or a combination thereof, of the subject 18. The images are applied as an input to a processor-based computer 30 that stores the image in a mass storage device 32.
The computer 30 also receives commands and scanning parameters from an operator via a console 34 that has some form of operator interface, such as a keyboard, mouse, voice activated controller, or any other suitable input apparatus. An associated display 40 allows the operator to observe images and other data from the computer 30. The computer 30 uses the operator-supplied commands and parameters to provide control signals and information to the data acquisition system 24 and the X-ray controller 26.
In certain embodiments, the X-ray imaging system 10 may also include certain features that enable the recording of phase information. In particular, in such embodiments, first and second optical elements 36, 38 may be positioned between the X-ray source 14 and the subject 18, and the subject 18 and the detector 22, respectively. The first and second optical elements 36, 38 may independently include any suitable optical element capable of enabling a phase image to be created by causing diffraction in the beam of X-rays 16 and the projected X-ray radiation 20. By way of non-limiting example, the first and second optical elements 36, 38 may include gratings, diffraction crystals, or a combination thereof.
Referring now to
As opposed to sources that use an electron beam that is generally circular in cross-section, one embodiment of the emitter assembly 64 emits and focuses an electron beam with a particular aspect ratio at a point of impact on the source target 80. The aspect ratio is measured as a cross-section of the beam 70, as depicted by section 3-3 orthogonal to an axis 72 of electron flow. In accordance with certain embodiments, the electron beam 70 may have a cross-section with a rectangle shape, a line shape, or an elliptical shape. The general cross-sectional shape of the electron beam 70 may be focused using the beam focusing elements 68, which may include features (e.g., inductive coils) configured to shape the beam 70 using one or more electric, electro-magnetic, or magnetic fields. In essence, these fields serve to shape and steer the electron beam 70.
Returning to
In the illustrated embodiment, the source target 80 may be a multilayer including a top heat-spreading layer 82, which is first impinged by the electron beam 70, a target layer 84, which produces the majority of X-rays 86 emitted by the source 14 when impinged by the electron beam 70, and an X-ray window 88 out of which the X-rays 86 are emitted. In other embodiments, the source target 80 may include more or fewer layers, depending upon the particular implementation. The particular configuration and materials of the multilayer source target 80 are discussed in detail below with respect to
It should be noted that while certain embodiments are discussed in the context of including an emitter that emits a beam toward one focal spot on the target layer 84, that all such embodiments may include, additionally or alternatively, a smaller electron beam emitter that can be raster scanned using electron focusing optics. In other words, the smaller electron beam emitter may be scanned over various regions of the target layer 84, such as scanned over one or more notches, vias, or channels, or over various flat regions, regions having varying thickness, regions having different layer configurations, and so forth.
In the illustrated embodiment, the thermal energy conducted away from the impact area 90 may be directed toward a cooling jacket 92 configured to circulate a cooling fluid (e.g., water, ethylene glycol) or gas about at least a portion of the source target 80. The cooling fluid may be provided by a cooling system 94, which is configured to provide active cooling of the source 14 and, more specifically, the source target 80. The cooling system 94 may include a heat exchanger 96 configured to reject heat from the cooling fluid or gas as it is recycled through the system 94. Additionally or alternatively, the cooling system 94 may flow cool air 98 (e.g., from a fan 100) along an outer perimeter 102 of the window 88. The operation of the cooling system 94 may be controlled, at least in part, by the controller 26. For example, during the course of operation, the cooling system 94 of
As noted above, the electron impact area 90 may define a particular shape, thickness, or aspect ratio on the target 80 to achieve particular characteristics of the emitted X-rays 86.
As discussed with respect to
The emitted X-ray beam 86 has a particular size and shape that is approximately related to the size and shape of the electron beam 70 when incident on the target layer 84. Accordingly, the X-ray beam 86 exits the target 80 from an X-ray emission area 112 that may be predicted based on the size of the impact area 90. As discussed below with respect to
As noted, while the depicted embodiments show a transmission-type arrangement (e.g., with the X-ray beam emitted from an opposing surface of the target) of the electron transmitter and the target, the techniques provided herein may also be implemented in a reflectance-type arrangement. For example, while the illustrated embodiment depicts the main symmetry axis of the x-ray beam 86 as being orthogonal to the source target 80 (e.g., axis 72 is substantially perpendicular to the target 80), in a reflectance arrangement, the angle at which X rays from the target are viewed is frequently acutely angled relative to the perpendicular to the target. This effectively increases the x-ray density in the output beam, while allowing a much larger thermal spot on the target, thereby decreasing the thermal loading of the target.
Alternatively, the electron beam direction 72 can make an acute angle with the normal to the target in a transmission x-ray source. The thickness of the target material may be reduced from the case where the electron beam direction is parallel to the target normal. In the acute angle case, the target may be made thin enough that the length of the oblique electron path through the target may be similar to that of the electron path in the parallel case. By reducing the target thickness in such a way, the self-absorption of X-rays within the target may be reduced and the X-ray flux density may be increased at specific angles, for example perpendicular to the target.
As noted above, the source target 80 may have one or a plurality of layers including at least the top heat spreader 82, the target layer 84, and the X-ray window 88, though these layers may be combined together or other layers may also be included, as discussed below. As generally noted above, the thermal conductivity of the source target 80 may enable an increase in the density of the electron beam 70 on the target 80 without detrimentally affecting the target 80. Indeed, heat dissipating materials, heat-spreading materials, or other microstructural features may be included in the design of the target 80, which collectively enable a relatively higher electron beam flux density on the target 80, resulting in a higher flux density in the X-ray beam 86.
In the illustrated embodiment, the top heat spreader 82 (e.g., a first layer) may include one or more materials (e.g., one or more first materials) that impart a higher overall thermal conductivity to the top heat spreader 82 than the target layer 84, which may include a metal or composite, such as tungsten, molybdenum, europium, samarium, copper, tungsten-rhenium alloy or bilayer, or any other material or combinations of materials that contribute to Bremsstrahlung (i.e., deceleration or braking radiation) when bombarded with electrons. In addition, the top heat spreader 82 may have a higher overall melting point than the target layer 84. Generally, the top heat-spreading layer 82 is configured to conduct heat in a direction away from the position 78 (
In embodiments where the X-ray source 14 is a transmission X-ray source, the X-ray window 88 may be a part of the source target 80, or may be in thermal communication with the source target 80. In the illustrated embodiment, the X-ray window 88 is in thermal communication with the target layer 84. In accordance with present embodiments, the X-ray window 88 may have a relatively high thickness thermal conductivity (i.e., aligned with the axis 72) to enable the X-ray window 88 to dissipate or otherwise conduct thermal energy to its outer perimeter 102, where heat rejection via the cooling system 94 may be facilitated. The X-ray window 88 may have a higher overall thermal conductivity than the target layer 84. The greater the distance from the initial electron impact point, the lower the temperature of the target, resulting in the ability to use x-ray windows having melting points lower than that of the target layer 84. By way of non-limiting example, the window 88 may be beryllium (Be).
It should be noted that the source target 80 may include as little as one layer, but is not limited to a particular number of layers. For example, in certain embodiments, the target layer 84 may act as the X-ray window 88 by separating the vacuum space 62 from the ambient environment around the X-ray source 14, and by serving as the window through which X-rays are emitted. Similarly, in some embodiments, the source target 80 may only include the top heat spreader 82 and the X-ray target 84. The source target 80 may also include one or more heat-spreading layers in addition to the top heat spreader 82.
The source target 80 may be fabricated using any suitable technique, such as suitable semiconductor manufacturing techniques including vapor deposition such as chemical vapor deposition (CVD), sputtering, atomic layer deposition, chemical plating, ion implantation, or additive manufacturing, and so on. However, due to the variance in materials utilized to achieve the particular thermal conductivity desired for the source target 80, certain transition materials may be utilized between each layer to facilitate thermal and mechanical bridging of the layers. For example, carbon-based materials may be thermally conductive via phonon travel (i.e., elastic vibrations in the material's lattice), while metallic materials may be thermally conductive via the metal's loosely bound valence electrons. These dissimilar modes of thermal conductance can sometimes prevent suitable thermal conductance between layers. In addition, materials having dissimilar coefficients of thermal expansion may not necessarily be compatible with one another. Accordingly, in such situations, it may be desirable to provide a transition material that prevents thermal resistance between the layers of the source target 80 while also allowing for thermal expansion. Example embodiments of such configurations are discussed below with respect to
It should be noted that for the embodiments depicted in
To bridge the top heat-spreading layer 82 and the target layer 84, the transition layer 120 includes, by way of example, a compositional gradient. The compositional gradient serves to gradually transition from at least one material 122 of the one or more materials of the top heat-spreading layer 82 and into one or more transition materials 124. The compositional gradient also serves to gradually transition from the one or more transition materials 124 and into at least one material 126 of the target layer 84. In one embodiment, the one or more transition materials 124 may be selected so as to prevent high thermal resistance between the top heat-spreading layer 82 and the target layer 84, and also to enable a degree of mechanical deformability to account for the coefficients of thermal expansion of the top heat-spreading layer 82 and the target layer 84. In a general sense, the transition layer 120 enables thermal communication between the top heat-spreading layer 82 and the target layer 84, such that the top heat-spreading layer 82 and the target layer 84, even though they are separated by one or more layers, may nevertheless be in thermal communication. It should be noted, however, that embodiments where the heat-spreading layers and the target layer 84 are in direct thermal communication (i.e., are directly and physically coupled to one another) are also presently contemplated.
Returning to the example noted above where the target layer 84 includes copper and the top heat-spreading layer 82 includes a carbon-based material, the embodiment of the source target 80 depicted in
While it may be desirable to provide the transition layer 120 as a single layer that is capable of accommodating the thermal coefficients of expansion and preventing thermal bonding resistance between the top heat-spreading layer 82 and the target layer 84, in other embodiments, this may be accomplished using two or more transition layers, as depicted in
While any configuration for the first and second transition layers 130, 132 is presently contemplated, it may be desirable for the first transition layer 130 to account for the coefficient of thermal expansion of the top heat-spreading layer 82 and the target layer 84, while the second transition layer 132 is configured to prevent thermal bonding resistance between the top heat-spreading layer 82 and the target layer 84. For example, the first transition layer 130 may be chosen to have a coefficient of thermal expansion value that is between that of the top heat-spreading layer 82 and the target layer 84, and the second transition layer 132 may be chosen to have a thermal conductivity that is between that of the top heat-spreading layer 82 and the target layer 84. Further, it should be noted that the first and second transition layers 130 and 132 may include materials having similar modes of thermal conductivity. For example, in embodiments where the top heat-spreading layer 82 conducts thermal energy by phonon travel, the first transition layer 130 may include materials whose main mode of thermal conductivity is also phonon travel but may also include materials whose main mode of thermal conductivity is via metallic valence electrons. Similarly, in embodiments where the target layer 84 conducts thermal energy via electrons, the second transition layer 132 may include materials whose main mode of thermal conductivity is also via electrons but may also include materials whose main mode of thermal conductivity is via phonons.
By way of non-limiting example, the top heat-spreading layer 82 may be a carbon based material such as HOPG, diamond, diamond-like carbon (DLC), graphite, or any combination thereof, and the target layer 84 may be tungsten or molybdenum. In this example, the first and second transition layers 130, 132 may independently include copper, silver, silver-diamond, tungsten, tungsten carbide, molybdenum, molybdenum carbide, or any combination thereof.
Using any one or a combination of these approaches, embodiments of the source target 80 having any number and combination of layers may be produced. For example, in
To enable the bottom heat-spreading layer 140 to conduct thermal energy in this manner, the bottom heat-spreading layer 140 may include any one or a combination of the materials described above for the top heat-spreading layer 82, such as the materials set forth in Table 1. However, it should be noted that the bottom heat-spreading layer 140 material may be the same or different than that of the top heat-spreading layer 82. Thus, the bottom heat-spreading layer 140, independent of the top heat-spreading layer 82, may include HOPG, diamond, sputtered carbon, DLC, or the like, and/or metal-based materials such as beryllium oxide, silicon carbide, aluminum nitride, silicon nitride, alumina, copper-molybdenum, aluminum silicon carbide, OFHC, or any combination thereof. Additionally, the bottom heat-spreading layer 140 may be provided as a part of the source target 80 using the approaches described above with respect to
As noted, the bottom heat-spreading layer 140 may desirably conduct thermal energy longitudinally and laterally away from the electron beam impact area 90. Indeed, in certain embodiments, the overall thermal conductivity of the bottom heat-spreading layer 140 may be sufficient to draw thermal energy to the X-ray window 88 which, as noted above, may have a relatively high thickness (i.e., longitudinal) conductivity so as to dissipate the thermal energy to the outside environment.
In some embodiments, the bottom heat-spreading layer 140 may incorporate the X-ray window 88. That is, in such embodiments, the bottom heat-spreading layer 140 may include one or more materials that are suitable to act as an X-ray window material. Accordingly, the bottom heat-spreading layer 140 may, in these embodiments, include diamond, beryllium oxide, or other window materials having a relatively high thermal conductivity. However, it should be noted that the bottom heat-spreading layer 140 may, in some embodiments, have a thickness that is greater than a traditional X-ray window to enable the bottom heat-spreading layer 140 to not only serve as the X-ray window 88, but also to enable the bottom heat-spreading layer 140 to serve as a heat sink for the target layer 84. In certain embodiments, the bottom heat-spreading layer 140 may have a thickness 146 that is greater than or equal to a thickness 148 of the target layer 84. The top heat-spreading layer 82 may also have a thickness 150 that is greater than or equal to the thickness 148 of the target layer 84 to enable the top heat-spreading layer to serve as a heat sink for the target layer 84.
In some embodiments, the source target 80 may utilize a particular combination of materials to allow a higher electron beam flux to impact it, thereby achieving a higher X-ray flux. Indeed, it is now recognized that particular material combinations may be desirable to achieve certain levels of X-ray flux. By way of example, it is now recognized that the combination of diamond for the top heat-spreading layer 82, tungsten for the target layer 84, and diamond for the bottom heat-spreading layer 140 and/or X-ray window 88 may enable an increase in the X-ray beam flux produced by the X-ray source by approximately one order of magnitude.
It will be appreciated upon reference to
It should be noted that the electrically conductive coating 152 may generally have any thickness—including thicknesses that are substantially equal to or greater than the thicknesses of other source target layers. However, in some embodiments, the thickness of the metallic coating 152 may be significantly smaller than the thickness of the other source target layers. Indeed, the material and thickness of the conductive coating 152 may be such that minimal electron beam energy is lost in the coating 152 and substantially no X-rays or an insignificant amount of X-rays are produced in the coating 152, thereby substantially not affecting the intended operation of the X-ray source 14. By way of example, the conductive coating 152 may include copper (Cu), aluminum (Al), or any combination thereof. In one embodiment, the Cu and Al thicknesses would be as thin as 1 nm and as thick as 1 μm.
In addition to or in lieu of certain of the layers disclosed herein, the source target 80 may include one or more microstructural features configured to enable enhanced thermal energy dissipation, which may ultimately enable a higher electron beam flux and a concomitant increase in X-ray beam flux.
The via or channel 170 may have any suitable geometry, including any suitable size and/or shape. In certain embodiments, the particular geometry of the via or channel 170 may depend on the size and/or shape of the electron beam 70 and, more specifically, on the geometry of the electron beam impact area 90. For example, in embodiments where the electron beam 70 has an extreme aspect ratio (e.g., between 500:1 and 5000:1 as noted above) and is linear or rectangular in shape, the via or channel 170 may have a similar shape. That is, the via or channel 170 may be a rectangular channel similar in shape to the geometry provided in
Similarly, in embodiments where the electron beam 70 has a circular or elliptical cross-section, the electron beam impact area 90 will have a correspondingly circular or elliptical geometry. Thus, the via or channel 170 may be a via having a particular radius that is substantially equal to the radius of the electron beam impact area, and may be larger than the radius of the electron beam impact area (e.g., between approximately 1% and 100% larger). The via or channel 170 may also have a particular radius that is smaller than the radius of the electron beam impact in situations, which can be used to reduce, for example, non-uniformities in the electron beam.
While the via or channel 170 is illustrated in
The notch 180, as depicted, has a size that may be smaller than the electron beam cross-section to reduce the size of the electron beam impact area to a specific desired dimension. That is, the notch 180 may act as an electron beam impact area defining aperture. In another embodiment, the notch 180 has a size that is at least substantially equal to, or greater than a size of the electron beam impact area 90. For example, a width 182 of the notch 180 is at least equal to or greater than the width 174 of the electron beam impact area 90. The notch 180, as noted above, may have any geometry suitable for enabling the electron beam 70 to traverse in an area defined by the notch 180. In some embodiments, the notch 180 may act to restrict the electron beam 70 into the electron beam impact area.
As noted above, the notch 180 does not span the entire thickness 148 of the target layer 84. Rather, the target layer 84 has a first thickness outside of the notch 180 corresponding to the entire thickness 148 of the target layer 84, and a second thickness 186 at (i.e., underneath) the notch 180. While the ratio of the first thickness to the second thickness may be any ratio, in certain embodiments it is desirable for the first thickness (i.e., the thickness 148 of the target layer 84) to be larger than the second thickness 186, such as between approximately 50% larger and 10,000% larger than the second thickness 186. By way of non-limiting example, the first thickness (i.e., the thickness 148 of the target layer 84) may be at least 10% larger than the second thickness 186. In some embodiments, the first thickness (i.e., the thickness 148 of the target layer 84) may be between 2 and 100, 5 and 50, 10 and 25 times the second thickness 186. By way of non-limiting example, the first thickness may be approximately 1 mm and the second thickness 186 may be approximately 10 microns.
In some embodiments it may be desirable for the first thickness to be at least two orders of magnitude greater than the second thickness 186. Such a ratio may be desirable to ensure that a sufficient amount of each of the one or more materials of the target layer 84 is present in an area 188 outside of the notch 180 to enable the area 188 to act as a heat sink for dissipating heat away from the electron beam impact area 90.
As noted above, the X-ray source 14 is not limited to any particular number of vias, channels, notches, emitters, electron beams, and so on. Indeed, in some embodiments, more than one electron beam may be utilized to produce more than one focused X-ray beam. Examples of such embodiments are depicted in
In
The illustrated source 14 may also include a plurality of X-ray beam focusing elements 200, each of which collects and focuses a respective group of X-rays emitted from the source target 80. For example, because the source target 80 emits X-rays in a fan or cone shape, the focusing elements 200 may focus the beams into a plurality of substantially parallel X-ray beams 202 to be emitted toward a subject of interest. By way of non-limiting example, the X-ray beam focusing elements may be total external reflection polycapillary optics, multilayer diffractive optics, multilayer reflecting optics, total internal reflection multilayer optics, refractive replicated optics.
In addition to the change to the emitter 66, the embodiment of the source target 80 does not include a separate X-ray window from the bottom heat-spreading layer 140. Again, the bottom heat-spreading layer 140 may have a sufficient overall thermal conductivity, melting point, and X-ray transmissivity that it may serve as the X-ray window for the X-ray source 14.
It should be noted that the embodiments of the multilayer target structure are not limited to having only one top heat spreader, or only one of any particular layer for facilitating thermal conductance away from areas that are impacted by an electron beam. Indeed, many such layers may be utilized to facilitate cooling of the target 80.
The target 80 of
The two window layers of the target 80 include the window layer 88 which, as noted above, is transparent to X-rays and may also act as a bottom heat spreader. The target 80 also includes the set of second window elements 232 described above with respect to
This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples and combinations that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims.
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