Patent Grant
7366374
The invention relates generally to optics, and more particularly to optic devices used in systems and methods for imaging.
Numerous applications exist that require a focused beam of electromagnetic radiation. For example, energy dispersive X-ray diffraction (EDXRD) may be used to inspect airline baggage for the detection of explosive threats or other contraband. Such EDXRD may suffer a high false positive rate due to weak diffracted X-ray signals. The weakness of the X-ray signals may stem from a variety of origins. First, a portion of the polychromatic X-ray spectrum used in EDXRD is produced by the Bremsstrahlung part of the source spectrum, which is inherently low in intensity. Second, X-ray source collimation may eliminate more than 99.99 percent of the source X-rays incident on the baggage volume under analysis. Third, some of the materials being searched for, e.g., explosives, may not diffract strongly as they are amorphous. Fourth, the diffracting volume may be small. The last two limitations arise from the type of threat materials being searched for in baggage, making all but the second limitation unavoidable. Although discussed in the context of explosives detection, the limitations described above are equally applicable to medical situations.
At lower X-ray energies, such as 60 keV and below, increasing the polychromatic X-ray flux density at the material being inspected has been addressed, for example, by coupling hollow glass polycapillary optics to low powered, sealed tube (stationary anode) X-ray sources. An example of hollow glass polycapillary optics may be found in, for example, U.S. Pat. No. 5,192,869. The glass is the low index of refraction material, and air filling the hollow portions is the high index of refraction material. These types of optics typically do not provide much gain at energy levels above 60 keV, since the difference in the indices of refraction between air and glass, and hence the critical angle for total internal reflection, becomes increasingly small as energy levels approach and surpass 60 keV.
Further, such optics use a concept of total internal reflection to reflect X-rays entering the hollow glass capillaries at appropriate angles back into the hollow capillaries, thereby channeling a solid angle of the source X-rays into collimated or focused beams at the output of the optic. As used herein, the term “collimate” refers to the creation of quasi-parallel beams of electromagnetic (EM) radiation from divergent EM beams. Only about five percent of an EM source's solid angle typically is captured by the input of such known optics.
In addition, the use of air in known optics as one of the materials prevents such optics from being placed within a vacuum. Thus, known optics are limited in their potential uses.
It would thus be desirable for a device that could collect more of the primary electromagnetic radiation from the source and redirect those rays to a desired spot to improve the electromagnetic radiation flux density at that spot.
The invention includes embodiments that relate to an imaging system for imaging an object. The imaging system includes a source of electrons, a target, enclosed within a housing, for emitting X-rays upon being struck by electrons from the source of electrons, a window positioned within a wall of the housing, and an optic device positioned external to the housing and within a pathway of at least a portion of the X-rays. The optic device utilizes total internal reflection to redirect the X-rays at an energy level above about sixty keV.
The invention includes embodiments that relate to an imaging system for imaging an object. The imaging system includes a source of electrons, a target for emitting X-rays upon being struck by electrons from the source of electrons, a vacuum chamber for housing the target, a window between the vacuum chamber and the object, and an optic device positioned within the vacuum chamber and utilizing total internal reflection to redirect the X-rays.
The invention includes embodiments that relate to an imaging system for imaging an object. The imaging system includes at least one source of electrons, at least one target for emitting X-rays upon being struck by electrons from the at least one source of electrons, and an array of optic devices utilizing total internal reflection to redirect the X-rays. The array of optic devices are positioned between the at least one target and the object. Further, either or both of the at least one source of electrons and the at least one target include, respectively, a plurality of sources of electrons and a plurality of targets.
The invention includes embodiments that relate to a method for imaging an object. The method includes placing an object between a source of X-rays and a detector, emitting electrons toward an anode to initiate formation of X-rays, and redirecting the X-rays through an optic device at an energy level above about sixty keV.
The invention includes embodiments that relate to an optic device for transmitting and redirecting X-rays by means of total internal reflection. The optic device includes a non-flat input face, an output face, and at least three conformal solid phase layers between the non-flat input face and the output face. The interfaces between the solid phase layers are gapless and the at least three conformal solid phase layers include at least two X-ray redirection regions.
These and other advantages and features will be more readily understood from the following detailed description of preferred embodiments of the invention that is provided in connection with the accompanying drawings.
Embodiments of the invention described herein utilize the phenomenon of total internal reflection. Referring to
Referring now to
In one embodiment, the layers making up the multilayer optic 10 may be formed of materials that have varying indices of refraction. For example, layers 15, 19, 23, and 27 may be formed of materials that have a lower index of refraction and a high X-ray absorption. For example, for high energy X-rays, appropriate materials may be chosen from osmium, platinum, gold, or any other suitable elements or compounds having similarly lower refractive indices and high X-ray absorption properties. Further, the core 50 and layers 16, 20, and 24 may be formed of materials having a higher index of refraction and a high X-ray transmission. For example, for high energy X-rays, appropriate materials may be chosen from beryllium, lithium hydride, magnesium, or any other suitable elements or compounds having similarly higher refractive indices and high X-ray transmission properties. The diameter of the core 50 is selected by considering the critical angle for total internal reflection between the higher index of refraction of the core 50 and the lower index of refraction of the layer 15 and the distance between the optic input face and a focal point of a source.
By using alternating lower and higher index of refraction materials with concurrent high and low X-ray absorption properties, respectively, in contiguous layers, the multilayer optic 10 can utilize the principle of total internal reflection of electromagnetic radiation. Specifically, diverging electromagnetic radiation beams 38, 40, and 42 stemming from an electromagnetic radiation source 34 enter the input face 12 and are redirected by the principle of total internal reflection into quasi-parallel beams of photons 44 exiting the output face 14.
Multilayer optics in accordance with embodiments of the invention, such as optic 10, can collect a large solid angle of an X-ray source 34 and redirect photons containing polychromatic energies into quasi-parallel photon beams. “Quasi-parallel” means that diverging beams of photons, such as X-rays, have been collected and focused into beams of electromagnetic radiation or X rays to exit the output face 14 at or below the critical angle θc. This divergence causes the intrinsic source X-ray beam to be larger than the output face 14 of the optic 10 and larger than the quasi-parallel beam of X rays produced by the optic. Alternatively, multilayer optics in accordance with embodiments of the invention may be configured to produce slightly focused, highly focused, slightly diverging, or highly diverging beams. By “slightly focused” is meant that the beam size at the point of interest (i.e., where the diameter of the beam is of concern) is approximately the same as at the output face 14 of the optic 10. By “highly focused” is meant that the beam size at the point of interest is smaller than at the output face 14 of the optic 10. By “slightly diverging” is meant that the beam size is larger than a quasi-parallel beam but smaller than the intrinsic source beam. By “highly diverging” is meant that the beam is the same size or larger than the intrinsic source beam. The phrase “intrinsic source beam” is meant to represent an X-ray beam emitted from the source housing with no optic in the beam.
The composition of materials making up the multilayer optic 10, the macroscopic geometry of the multilayer optic 10, the thickness of the multilayer optic 10, and the number of individual layers determine the angular acceptance range of the multilayer optic 10. The angular acceptance range may be from about 0 steradians up to about 2π steradians of a solid angle of a photon source. For ease of illustration, only a few layers have been illustrated with reference to multilayer optic 10. However, it should be appreciated that any number of layers, including into the hundreds, thousands, or millions of layers, can be fabricated to utilize total internal reflection to form the various types of photon beams listed previously.
Another feature of the multilayer optic 10 is that the core 50 and the layers 16, 20, 24 have photon, or X-ray, redirection regions. For example, layer 16 has a photon redirection region 17 stemming from a center of curvature; layer 20 has a photon redirection region 21 stemming from a second center of curvature; and, layer 24 has a photon redirection region 25 stemming from yet another center of curvature. The photon redirection regions 17, 21, 25 are chosen to allow for the diverging electromagnetic radiation beams 38, 40, and 42 to be made parallel or near parallel to beam 36, or conversely to allow for parallel or converging electromagnetic radiation beams to be made diverging. The minimum photon redirection region is determined by the minimum thickness that would still enable a smooth surface, which is at least two atomic layers, or about ten angstroms. The photon redirection regions 17, 21, 25 each contain redirecting segments. The redirecting segments are chosen such that they each have a constant curvature. The curvature of each redirecting segment may be the same as or different from the curvatures of other redirecting segments. If each of the redirecting segments for a particular photon redirection region is straight, then the radius of curvature is infinite.
By curving the multilayers 16, 20, 24 at the input side of the optic 10, the photons or electromagnetic radiation 38, 40, 42 entering the input face 12 can be redirected into parallel pencil beams 44, thereby increasing the photon flux density at the output face 14 over the photon flux density in the direct source beam at the same distance from the source 34. Depending upon the number of layers in the multilayer optic, there may be a photon density gain for 100 keV photons of as much as 5000 times in the output intensity of electromagnetic radiation from the multilayer optic over the output of conventional pinhole collimators. It should be appreciated that, alternatively, the output face 14 may be formed closer to the input face 12, i.e., positioned prior to the region where the photons are redirected into parallel rays, allowing the input electromagnetic radiation beams 38, 40, 42 to remain somewhat diverging as they exit the output face 14. It should further be appreciated that core 50 and any number of the layers may have no arc of curvature, instead having a cylindrical cross-sectional profile.
An important feature of this optic 10 is that the layers can be made thin enough and the overall optic length (from input face 12 to output face 14) short enough that photons are redirected through bounces along only one side of a particular layer, for example, layer 24. This is unlike known optics, where the photons bounce off both sides of a particular layer. The fewer number of bounces needed to redirect the photons in this multilayer optic 10 significantly increase the photon transmission efficiency of the optic 10.
Another feature of the multilayer optic 10 is that through fabrication techniques that will be described in detail below, the individual layers can be formed conformally on one another. The conformation of the layers enables the multilayer optic 10 to be utilized in a vacuum environment. Prior art optics utilize air as the higher refractive index material. Such optics cannot be used in vacuum environments. Further, the multilayer optic 10 can be utilized in applications that operate at energy levels above 60 keV, such as, for example, X-ray diffraction, CT medical and industrial imaging, medical and industrial X-ray, and cargo inspection, to name a few. Some of these applications may operate at energy levels as high as 450 keV.
Referring now to
Referring to
Placing a filter at the input or the output faces of the optics in
Referring now to
The shutter apparatus 410 enables the formation of a multilayer optic wherein the individual layers have a photon redirection region. Specifically, as a deposition material is input into the deposition chamber 402 through the inputting apparatus 404, the shutter apparatus 410 moves in a direction A relative to the blank 420. If the speed of the shutter apparatus 410 decreases as it moves in the direction A, an increasing amount of deposition material will contact the blank 420 in the direction A, thereby enabling the formation of a multilayer optic with individual layers having different thicknesses and having photon redirection regions. Control of the movement and velocity of the shutter apparatus 410 may be accomplished electronically with a digital controlling mechanism, such as a microcontroller, microprocessor, or computer. Alternatively, control of the movement may be accomplished manually, or mechanically, such as, pneumatically, hydraulically, or otherwise.
By moving the shutter apparatus 410 along direction A as each deposition material is input through the inputting apparatus 404 into the deposition chamber 402, the individual layers can be deposited upon the blank 420, and a multilayer optic having conformal individual layers, like the multilayer optic 110 shown in
Instead of utilizing a shuttle apparatus 410, it is possible to move at varying speeds the inputting apparatus 404 relative to the blank 420. Further, it is possible to move at varying speeds the blank 420 within the deposition chamber 402 relative to the inputting apparatus 404.
Referring to
Instead of utilizing a shutter apparatus 410, it is possible to move at varying speeds the inputting apparatus 404 relative to the blank 420 while the blank 420 is being rotated by the spindles 505. Further, it is possible to move at varying speeds the spindles 505 and the blank 420 within the deposition chamber 402 relative to the inputting apparatus 404.
It should be appreciated that during the deposition process, the partially formed multilayer optic may be rotated, oscillated, or moved, it may be turned, and it may be subjected to a deposition process whereby the deposition material is deposited at different rates along the axis of the multilayer optic. In this way, multilayer optics can be formed with various configurations and profiles that will allow for a greater amount of electromagnetic radiation to be collected from a source at the input of the optic, parallel or near parallel beams of electromagnetic radiation to be output from the multilayer optic, or the beams of electromagnetic radiation output from the multilayer optic may be shaped into pencil beams, cone beams, fan beams, or curved in an arc, as an example.
Multilayer optics in accordance with embodiments of the invention may be used in various industrial applications. For example, a multilayer optic formed to emit a quasi-parallel beam having a circular cross-section may find utility in X-ray diffraction and backscatter applications, such as non-destructive examination. A multilayer optic formed to emit a slightly focused beam with a circular cross-section may find utility in X-ray diffraction, X-ray fluorescence, medical diagnostic or interventional treatments, and non-destructive examination applications. Multilayer optics formed to emit a highly focused beam having a circular cross-section may find utility in X-ray fluorescence; medical diagnostic or interventional treatments of, for example, small tumors; and, non-destructive examination applications. Multilayer optics formed to emit a slightly diverging beam having a circular cross-section may find utility in computed tomography and X-ray diagnostic system applications. Multilayer optics formed to emit a highly diverging beam having a circular cross-section may find utility in non-destructive examination applications requiring an increased field-of-view, and in medical diagnostic or interventional imaging and treatments requiring an increased field-of-view, such as the imaging and treatment of large tumors.
One example of the utility of multilayer optics formed to emit a variety of beam shapes is in medical interventional treatments, such as treatment of tumors, where the optic shape is determined by the tumor shape. Such multilayer optics would allow X rays to be focused onto the tumor without irradiating nearby healthy tissue, providing targeted treatment with a minimum of damage to surrounding healthy tissue.
A number of alternative configurations for emitters or distributed sources may be, of course, envisioned. For example, it is envisioned that a plurality of electron sources, a plurality of transmission targets, and/or a plurality of reflection targets may be incorporated into a configuration that utilizes one or more optic devices, such as the optic devices 10. For example, a configuration that includes multiple electron sources with either a single reflection target or a single transmission target, a configuration that includes multiple electron sources with multiple transmission or reflection targets, and a configuration that includes a single electron source swept across a single target are envisioned as being coupled to one or more optic devices, such as the optic devices 10.
Moreover, the individual X-ray sources in the distributed source may emit various types and shapes of X-ray beams. These may include, for example, fan-shaped beams, cone-shaped beams, and beams of various cross-sectional geometries. Similarly, the various components comprising the distributed X-ray source may also vary. In one embodiment, for example, a cold cathode emitter is envisioned which will be housed in a vacuum housing. A stationary anode is then situated in the housing and spaced apart from the emitter. This type of arrangement generally corresponds to the diagrammatical illustration of
A multilayer optic, such as the multilayer optic 10 is incorporated within the system 800. The alternating lower and higher index of refraction materials in contiguous layers of a multilayer optic 10 utilize the principle of total internal reflection to collect a large solid angle of X-rays from the target 724 and redirect them into X-ray beams 734 exiting the output face 14 of the optic 10. The multilayer optic 10 can be formed to output any desired beam. The multilayer optic 10 can be positioned exterior or interior to the window 748. The multilayer optic 10 is shown in both locations in
The multilayer optic 10 may be formed in such a way as to produce a limited cone beam of X-rays, such as the beams of photons 734 shown in
It should be appreciated that multiple optic devices, such as the multilayer optics 10, may be used in conjunction with multiple focal spots or a single focal spot on a single target. By focal spots is meant the spot on the target where the electron beam hits the target and X-rays are generated. For example, and with specific reference to
Each of the multilayer optics 10 in the array 760 provides a means of utilizing a higher percentage of the available X-ray flux from each of the X-ray beams 725, and redirecting them into a stack (discrete or continuous) of parallel reduced cone beams 734. The result is a higher X-ray flux utilization than without the optic array 760. Although described in terms of multilayer optics 10, it should be appreciated that the array 760 may include a plurality of multilayer optics 110, 210, or 310.
There are a number of targeted field-of-view applications that utilize only a portion of a source X-ray cone. Examples include radiographic imaging, non-destructive testing, computed tomography, X-ray diffraction, and X-ray diagnostic systems. Such targeted field-of-view applications using a portion of the source X-ray cone benefit from the increased flux delivery provided by embodiments of the multilayer optics described herein. Further, in applications where the X-ray flux density is currently sufficient, an increased flux density from the multilayer optics would allow X-ray sources in such applications to operate at lower power. This leads to reduced target loading, which increases the reliability of the source and decreases the overall cost of the system.
There are a number of medical applications, such as 3D-conformal radiotherapy (3D-CRT) or intensity-modulated radiotherapy (IMRT), that would benefit greatly from the increased radiation flux produced by the multilayer optics. Additionally, many medical applications may benefit from the ability of the optic devices to focus the radiation into odd-shaped restricted volumes of space. The main goal in these types of radiotherapy treatments is to develop a technique that spares normal tissue while allowing dose escalation at the treatment site. The multilayer optic, with its ability to focus X rays and its flexibility in focusing these X rays into a wide variety of shaped beams, would permit tuning of the X-ray beam to the shape of the disease site and minimize radiation of surrounding healthy tissue. Similarly, in interventional radiotherapy where images are used to guide the positioning of the X-ray beam to the disease site, which then may or may not be treated with the radiation beam, the multilayer optic would be of great benefit by providing maximal radiation flux while minimizing the amount of irradiated healthy tissue.
While the invention has been described in detail in connection with only a limited number of embodiments, it should be readily understood that the invention is not limited to such disclosed embodiments. Rather, the invention can be modified to incorporate any number of variations, alterations, substitutions or equivalent arrangements not heretofore described, but which are commensurate with the spirit and scope of the invention. For example, while embodiments have been described in terms that may initially connote singularity, such as, for example, a source of electrons or a target, it should be appreciated that multiple components may be utilized. Further, while the embodiments of the invention described with specific reference to
| Number | Name | Date | Kind |
|---|---|---|---|
| 5192869 | Kumakhov | Mar 1993 | A |
| 5604353 | Gibson et al. | Feb 1997 | A |
| 5744813 | Kumakhov | Apr 1998 | A |
| 6504901 | Loxley et al. | Jan 2003 | B1 |
| 6504902 | Iwasaki et al. | Jan 2003 | B2 |
| 6934359 | Chen et al. | Aug 2005 | B2 |
| 7006741 | Yu | Feb 2006 | B1 |
| 20060093086 | Gallagher | May 2006 | A1 |
