Patent Description:
Monochromatic radiation has been used in specialized settings. However, conventional systems for generating monochromatic radiation have been unsuitable for clinical or routine commercial use due to their prohibitive size, cost and/or complexity. For example, monochromatic X-rays can be copiously produced in synchrotron sources utilizing an inefficient Bragg crystal as a filter or using a solid, flat target x-ray fluorescer but these are very large and not practical for routine use in hospitals and clinics.

Monochromatic x-rays may be generated by providing in series a target (also referred to as the anode) that produces broad spectrum radiation in response to an incident electron beam, followed by a fluorescing target that produces monochromatic x-rays in response to incident broad spectrum radiation. The term "broad spectrum radiation" is used herein to describe Bremsstrahlung radiation with or without characteristic emission lines of the anode material. Briefly, the principles of producing monochromatic x-rays via x-ray fluorescence are as follows.

In an x-ray tube electrons are liberated from a heated filament called the cathode and accelerated by a high voltage (e.g., ~<NUM> kV) toward a metal target called the anode as illustrated schematically in <FIG>. The high energy electrons interact with the atoms in the anode. Often an electron with energy E<NUM> comes close to a nucleus in the target and its trajectory is altered by the electromagnetic interaction. In this deflection process, it decelerates toward the nucleus. As it slows to an energy E<NUM>, it emits an X-ray photon with energy E<NUM>-E<NUM>. This radiation is called Bremsstrahlung radiation (braking radiation) and the kinematics are shown in <FIG>.

The energy of the emitted photon can take any value up to the maximum energy of the incident electron, Emax. As the electron is not destroyed it can undergo multiple interactions until it loses all of its energy or combines with an atom in the anode. Initial interactions will vary from minor to major energy changes depending on the actual angle and proximity to the nucleus. As a result, Bremsstrahlung radiation will have a generally continuous spectrum, as shown in <FIG>. The probability of Bremsstrahlung production is proportional to Z<NUM>, where Z is the atomic number of the target material, and the efficiency of production is proportional to Z and the x-ray tube voltage. Note that low energy Bremsstrahlung X-rays are absorbed by the thick target anode as they try to escape from deep inside causing the intensity curve to bend over at the lowest energies, as discussed in further detail below.

While most of the electrons slow down and have their trajectories changed, some will collide with electrons that are bound by an energy, BE, in their respective orbitals or shells that surround the nucleus in the target atom. As shown in <FIG>, these shells are denoted by K, L,M, N, etc. In the collision between the incoming electron and the bound electron, the bound electron will be ejected from the atom if the energy of the incoming electron is greater than BE of the orbiting electron. For example, the impacting electron with energy E > BEK, shown in <FIG>, will eject the K-shell electron leaving a vacancy in the K shell. The resulting excited and ionized atom will de-excite as an electron in an outer orbit will fill the vacancy. During the de-excitation, an X-ray is emitted with an energy equal to the difference between the initial and final energy levels of the electron involved with the de-excitation. Since the energy levels of the orbital shells are unique to each element on the Periodic Chart, the energy of the X-ray identifies the element. The energy will be monoenergetic and the spectrum appears monochromatic rather than a broad continuous band. Here, monochromatic means that the width in energy of the emission line is equal to the natural line width associated with the atomic transition involved. For copper Kα x-rays, the natural line width is about <NUM> eV. For Zr Kα, Mo Kα and Pt Kα, the line widths are approximately, <NUM> eV, <NUM> eV and <NUM> eV, respectively. The complete spectrum from an X-ray tube with a molybdenum target as the anode is shown in <FIG>. The characteristic emission lines unique to the atomic energy levels of molybdenum are shown superimposed on the thick target Bremsstrahlung.

When an x-ray from any type of x-ray source strikes a sample, the x-ray can either be absorbed by an atom or scattered through the material. The process in which an x-ray is absorbed by an atom by transferring all of its energy to an innermost electron is called the photoelectric effect, as illustrated in <FIG>. This occurs when the incident x-ray has more energy than the binding energy of the orbital electron it encounters in a collision. In the interaction the photon ceases to exist imparting all of its energy to the orbital electron. Most of the x-ray energy is required to overcome the binding energy of the orbital electron and the remainder is imparted to the electron upon its ejection leaving a vacancy in the shell. The ejected free electron is called a photoelectron. A photoelectric interaction is most likely to occur when the energy of the incident photon exceeds but is relatively close to the binding energy of the electron it strikes.

As an example, a photoelectric interaction is more likely to occur for a K-shell electron with a binding energy of <NUM> keV when the incident photon is <NUM> keV than if it were <NUM> keV. This is because the photoelectric effect is inversely proportional to approximately the third power of the X-ray energy. This fall-off is interrupted by a sharp rise when the x-ray energy is equal to the binding energy of an electron shell (K, L, M, etc.) in the absorber. The lowest energy at which a vacancy can be created in the particular shell and is referred to as the edge. <FIG> shows the absorption of tin (Sn) as a function of x-ray energy. The absorption is defined on the ordinate axis by its mass attenuation coefficient. The absorption edges corresponding to the binding energies of the L orbitals and the K orbitals are shown by the discontinuous jumps at approximately <NUM> keV and <NUM> keV, respectively. Every element on the Periodic Chart has a similar curve describing its absorption as a function of x-ray energy.

The vacancies in the inner shell of the atom present an unstable condition for the atom. As the atom returns to its stable condition, electrons from the outer shells are transferred to the inner shells and in the process emit a characteristic x-ray whose energy is the difference between the two binding energies of the corresponding shells as described above in the section on Characteristic Line Emission. This photon-induced process of x-ray emission is called X-ray Fluorescence, or XRF. <FIG> shows schematically X-ray fluorescence from the K shell and a typical x-ray fluorescence spectrum from a sample of aluminum is shown in <FIG>. The spectrum is measured with a solid state, photon counting detector whose energy resolution dominates the natural line width of the L-K transition. It is important to note that these monoenergetic emission lines do not sit on top of a background of broad band continuous radiation; rather, the spectrum is Bremsstrahlung free.

<CIT> forms part of the state of the art relative to the present disclosure.

According to a first aspect of the invention, there is provided a carrier as recited in claim <NUM> below.

The dependent claims define particular embodiments of the invention.

Various aspects and embodiments of the disclosed technology will be described with reference to the following figures.

As discussed above, conventional x-ray systems capable of generating monochromatic radiation to produce diagnostic images are typically not suitable for clinical and/or commercial use due to the prohibitively high costs of manufacturing, operating and maintaining such systems and/or because the system footprints are much too large for clinic and hospital use. As a result, research with these systems are limited in application to investigations at and by the relatively few research institutions that have invested in large, complex and expensive equipment.

Cost effective monochromatic x-ray imaging in a clinical setting has been the goal of many physicists and medical professionals for decades, but medical facilities such as hospitals and clinics remain without a viable option for monochromatic x-ray equipment that can be adopted in a clinic for routine diagnostic use.

The inventor has developed methods and apparatus for producing selectable, monochromatic x-radiation over a relatively large field-of-view (FOV). Numerous applications can benefit from such a monochromatic x-ray source, in both the medical and non-medical disciplines. Medical applications include, but are not limited to, imaging of breast tissue, the heart, prostate, thyroid, lung, brain, torso and limbs. Non-medical disciplines include, but are not limited to, non-destructive materials analysis via x-ray absorption, x-ray diffraction and x-ray fluorescence. The inventor has recognized that 2D and 3D X-ray mammography for routine breast cancer screening could immediately benefit from the existence of such a monochromatic source.

According to some embodiments, selectable energies (e.g., up to <NUM> kev) are provided to optimally image different anatomical features. Some embodiments facilitate providing monochromatic x-ray radiation having an intensity that allows for relatively short exposure times, reducing the radiation dose delivered to a patient undergoing imaging. According to some embodiments, relatively high levels of intensity can be maintained using relatively small compact regions from which monochromatic x-ray radiation is emitted, facilitating x-ray imaging at spatial resolutions suitable for high quality imaging (e.g., breast imaging). The ability to generate relatively high intensity monochromatic x-ray radiation from relatively small compact regions facilitates short, low dose imaging at relatively high spatial resolution that, among other benefits, addresses one or more problems of conventional x-ray imaging systems (e.g., by overcoming difficulties in detecting cancerous lesions in thick breast tissue while still maintaining radiation dose levels below the limit set by regulatory authorities, according to some embodiments).

With conventional mammography systems, large (thick) and dense breasts are difficult, if not impossible, to examine at the same level of confidence as smaller, normal density breast tissue. This seriously limits the value of mammography for women with large and/or dense breasts (<NUM>-<NUM>% of the population), a population of women who have a six-fold higher incidence of breast cancer. The detection sensitivity falls from <NUM>% to <NUM>% for women with dense breasts and to <NUM>% for women with extremely dense breasts. Additionally, using conventional x-ray imaging systems (i.e., broadband x-ray imaging systems) false positives and unnecessary biopsies occur at unsatisfactory levels. Techniques described herein facilitate monochromatic x-ray imaging capable of providing a better diagnostic solution for women with large and/or dense breasts who have been chronically undiagnosed, over-screened and are most at risk for breast cancer. Though benefits associated with some embodiments have specific advantages for thick and/or dense breasts, it should be appreciated that techniques provided herein for monochromatic x-ray imaging also provide advantages for screening of breasts of any size and density, as well as providing benefits for other clinical diagnostic applications. For example, techniques described herein facilitate reducing patient radiation dose by a factor of <NUM>-<NUM> depending on tissue density for all patients over conventional x-ray imaging systems currently deployed in clinical settings, allowing for annual and repeat exams while significantly reducing the lifetime radiation exposure of the patient. Additionally, according to some embodiments, screening may be performed without painful compression of the breast in certain circumstances. Moreover, the technology described herein facilitates the manufacture of monochromatic x-ray systems that are relatively low cost, keeping within current cost constraints of broadband x-ray systems currently in use for clinical mammography.

Monochromatic x-ray imaging may be performed with approved contrast agents to further enhance detection of tissue anomalies at a reduced dose. Techniques described herein may be used with three dimensional 3D tomosynthesis at similarly low doses. Monochromatic radiation using techniques described herein may also be used to perform in-situ chemical analysis (e.g., in-situ analysis of the chemical composition of tumors), for example, to improve the chemical analysis techniques described in <CIT> and titled "Methods and Apparatus for Determining Information Regarding Chemical Composition Using X-ray Radiation".

Conventional monochromatic x-ray sources have previously been developed for purposes other than medical imaging and, as a result, are generally unsuitable for clinical purposes. Specifically, the monochromaticity, intensity, spatial resolution and/or power levels may be insufficient for medical imaging purposes. The inventor has developed techniques for producing monochromatic x-ray radiation suitable for numerous applications, including for clinical purposes such as breast and other tissue imaging, aspects of which are described in further detail below. The inventor recognized that conventional monochromatic x-ray sources emit significant amounts of broadband x-ray radiation in addition to the emitted monochromatic x-ray radiation. As a result, the x-ray radiation emitted from such monochromatic x-ray sources have poor monochromaticity due to the significant amounts of broadband radiation that is also emitted by the source, contaminating the x-ray spectrum.

The inventor has developed techniques for producing x-ray radiation with high degrees of monochromaticity (e.g., as measured by the ratio of monochromatic x-ray radiation to broadband radiation as discussed in further detail below), both in the on-axis direction and off-axis directions over a relatively large field of view. Techniques described herein enable the ability to increase the power of the broadband x-ray source without significantly increasing broadband x-ray radiation contamination (i.e., without substantially reducing monochromaticity). As a result, higher intensity monochromatic x-ray radiation may be produced using increased power levels while maintaining high degrees of monochromaticity.

According to some embodiments, a monochromatic x-ray device is provided that is capable of producing monochromatic x-ray radiation having characteristics (e.g., monochromaticity, intensity, etc.) that enable exposure times of less than <NUM> seconds and, according to some embodiments, exposure times of less than <NUM> seconds for mammography.

According to some embodiments, a monochromatic x-ray device is provided that emits monochromatic x-rays having a high degree of monochromaticity (e.g., at <NUM>% purity or better) over a field of view sufficient to image a target organ (e.g., a breast) in a single exposure to produce an image at a spatial resolution suitable for diagnostics (e.g., a spatial resolution of a <NUM> microns or better).

Following below are more detailed descriptions of various concepts related to, and embodiments of, monochromatic x-ray systems and techniques regarding same. It should be appreciated that the embodiments described herein may be implemented in any of numerous ways. Examples of specific implementations are provided below for illustrative purposes only. It should be appreciated that the embodiments and the features/capabilities provided may be used individually, all together, or in any combination of two or more, as aspects of the technology described herein are not limited in this respect.

<FIG> illustrates a two dimensional (2D) schematic cut of a conventional x-ray apparatus for generating monochromatic x-rays via x-ray fluoresence. The x-ray apparatus illustrated in <FIG> is similar in geometry to the x-ray apparatus illustrated and described in <CIT>, titled "Radiation Source for Generating Essentially Monochromatic X-rays," as well as the monochromatic x-ray source illustrated and described in <NPL>, Advances in Laboratory-based X-ray Sources and Optics II, Ali M. Khounsayr; Carolyn A. MacDonald; Eds. Referring to <FIG>, x-ray apparatus <NUM> comprises a vacuum tube <NUM> that contains a toroidal filament <NUM> that operates as a cathode and primary target <NUM> that operates as an anode of the circuit for generating broadband x-ray radiation. Vacuum tube <NUM> includes a vacuum sealed enclosure formed generally by housing <NUM>, front portion <NUM> (e.g., a copper faceplate) and a window <NUM> (e.g., a beryllium window).

In operation, electrons (e.g., exemplary electrons <NUM>) from filament <NUM> (cathode) are accelerated toward primary target <NUM> (anode) due to the electric field established by a high voltage bias between the cathode and the anode. As the electrons are decelerated by the primary target <NUM>, broadband x-ray radiation <NUM> (i.e., Bremsstrahlung radiation as shown in <FIG>) is produced. Characteristic emission lines unique to the primary target material may also be produced by the electron bombardment of the anode material provided the voltage is large enough to produce photoelectrons. Thus, broadband x-ray radiation (or alternatively broad spectrum radiation) refers to Bremsstrahlung radiation with or without characteristic emission lines of the primary target. The broadband radiation <NUM> emitted from primary target <NUM> is transmitted through window <NUM> of the vacuum enclosure to irradiate secondary target <NUM>. Window <NUM> provides a transmissive portion of the vacuum enclosure made of a material (e.g., beryllium) that generally transmits broadband x-ray radiation generated by primary target <NUM> and blocks electrons from impinging on the secondary target <NUM> (e.g., electrons that scatter off of the primary target) to prevent unwanted Bremststralung radiation from being produced. Window <NUM> may be cup-shaped to accommodate secondary target <NUM> outside the vacuum enclosure, allowing the secondary target to be removed and replaced without breaking the vacuum seal of x-ray tube <NUM>.

In response to incident broadband x-ray radiation from primary target <NUM>, secondary target <NUM> generates, via fluorescence, monochromatic x-ray radiation <NUM> characteristic of the element(s) in the second target. Secondary target <NUM> is conical in shape and made from a material selected so as to produce fluorescent monochromatic x-ray radiation at a desired energy, as discuss in further detail below. Broadband x-ray radiation <NUM> and monochromatic x-ray radiation <NUM> are illustrated schematically in <FIG> to illustrate the general principle of using a primary target and a secondary target to generate monochromatic x-ray radiation via fluorescence. It should be appreciated that broadband and monochromatic x-ray radiation will be emitted in the 4π directions by the primary and secondary targets, respectively. Accordingly, x-ray radiation will be emitted from x-ray tube <NUM> at different angles θ relative to axis <NUM> corresponding to the longitudinal axis through the center of the aperture of x-ray tube <NUM>.

As discussed above, the inventor has recognized that conventional x-ray apparatus for generating monochromatic x-ray radiation (also referred to herein as monochromatic x-ray sources) emit significant amounts of broadband x-ray radiation. That is, though conventional monochromatic sources report the ability to produce monochromatic x-ray radiation, in practice, the monochromaticity of the x-ray radiation emitted by these conventional apparatus is poor (i.e., conventional monochromatic sources exhibit low degrees of monochromaticity. For example, the conventional monochromatic source described in Marfeld, using a source operated at <NUM> kV with a secondary target of tungsten (W), emits monochromatic x-ray radiation that is approximately <NUM>% pure (i.e., the x-ray emission is approximately <NUM>% broadband x-ray radiation). As another example, a conventional monochromatic x-ray source of the general geometry illustrated in <FIG>, operating with a cathode at a negative voltage of -50kV, a primary target made of gold (Au; Z=<NUM>) at ground potential, and a secondary target made of tin (Sn; Z=<NUM>), emits the x-ray spectra illustrated in <FIG> (on-axis) and <FIG> (off-axis). As discussed above, x-ray radiation will be emitted from the x-ray tube at different angles θ relative to the longitudinal axis of the x-ray tube (axis <NUM> illustrated in <FIG>).

Because the on-axis spectrum and the off-axis spectrum play a role in the efficacy of a monochromatic source, both on-axis and off-axis x-ray spectra are shown. In particular, variation in the monochromaticity of x-ray radiation as a function of the viewing angle θ results in non-uniformity in the resulting images. In addition, for medical imaging applications, decreases in monochromaticity (i.e., increases in the relative amount of broadband x-ray radiation) of the x-ray spectra at off-axis angles increases the dose delivered to the patient. Thus, the degree of monochromaticity of both on-axis and off-axis spectra may be an important property of the x-ray emission of an x-ray apparatus. In <FIG>, on-axis refers to a narrow range of angles about the axis of the x-ray tube (less than approximately <NUM> degrees), and off-axis refers to approximately <NUM> degrees off the axis of the x-ray tube. As shown in <FIG> and <FIG>, the x-ray spectrum emitted from the conventional monochromatic x-ray source is not in fact monochromatic and is contaminated with significant amounts of broadband x-ray radiation.

In particular, in addition to the characteristic emission lines of the secondary target (i.e., the monochromatic x-rays emitted via K-shell fluorescence from the tin (Sn) secondary target resulting from transitions from the L and M-shells, labeled as Sn Kα and Sn Kβ in <FIG> and <FIG>, respectively), x-ray spectra 1000a and 1000b shown in <FIG> and <FIG> also include significant amounts of broadband x-ray radiation. Specifically, x-ray spectra 1000a and 1000b include significant peaks at the characteristic emission lines of the primary target (i.e., x-ray radiation at the energies corresponding to K-shell emissions of the gold primary target, labeled as Au Kα and Au Kβ in <FIG> and <FIG>), as well as significant amounts of Bremsstrahlung background. As indicated by arrows <NUM> in <FIG> and <FIG>, the Sn Kα peak is only (approximately) <NUM> times greater than the Bremsstrahlung background in the on-axis direction and approximately <NUM> times greater than the Bremsstrahlung background in the off-axis direction. Thus, it is clear from inspection alone that this conventional monochromatic x-ray source emits x-ray radiation exhibiting strikingly poor monochromaticity, both on and off-axis, as quantified below.

Monochromaticity may be computed based on the ratio of the integrated energy in the characteristic fluorescent emission lines of the secondary target to the total integrated energy of the broadband x-ray radiation. For example, the integrated energy of the low energy broadband x-ray radiation (e.g., the integrated energy of the x-ray spectrum below the Sn Kα peak indicated generally by arrows <NUM> in <FIG> and <FIG>), referred to herein as Plow, and the integrated energy of the high energy broadband x-ray radiation (e.g., the integrated energy of the x-ray spectrum above the Sn Kβ peak indicated generally by arrows <NUM> in <FIG> and <FIG>), referred to herein as Phigh, may be computed. The ratio of the integrated energy of the characteristic K-shell emission lines (referred to herein as Pk, which corresponds to the integrated energy in the Sn Kα and the Sn Kβ emissions in <FIG> and <FIG>) to Plow and Phigh provides a measure of the amount of broadband x-ray radiation relative to the amount of monochromatic x-ray radiation emitted by the x-ray source. In the example of <FIG>, the ratio Pk/Plow is <NUM> and the ratio Pk/Phigh is <NUM>. In the example of <FIG>, the ratio Pk/Plow is <NUM> and the ratio Pk/Phigh is <NUM>. Increasing the ratios Plow and Phigh increases the degree to which the spectral output of the source is monochromatic. As used herein, the monochromaticity, M, of an x-ray spectrum is computed as M = <NUM>/(<NUM>+<NUM>/a +<NUM>/b), where a= Pk/Plow, b=Pk/Phigh. For the on-axis x-ray spectrum in <FIG> produced by the conventional x-ray apparatus, M=<NUM>, and for the off-axis x-ray spectrum in <FIG> produced by the conventional x-ray apparatus, M=<NUM>. As such, the majority of the energy of the x-ray spectrum is broadband x-ray radiation and not monochromatic x-ray radiation.

The inventor has developed techniques that facilitate generating an x-ray radiation having significantly higher monochromaticity, thus improving characteristics of the x-ray emission from an x-ray device and facilitating improved x-ray imaging. <FIG> illustrates an x-ray device <NUM> incorporating techniques developed by the inventor to improve properties of the x-ray radiation emitted from the device, and <FIG> illustrates a zoomed in view of components of the x-ray device <NUM>, in accordance with some embodiments. X-ray device <NUM> comprises a vacuum tube <NUM> providing a vacuum sealed enclosure for electron optics <NUM> and primary target <NUM> of the x-ray device. The vacuum sealed enclosure is formed substantially by a housing <NUM> (which includes a front portion <NUM>) and an interface or window portion <NUM>. Faceplate <NUM> may be provided to form an outside surface of front portion <NUM>. Faceplate <NUM> may be comprised of material that is generally opaque to broadband x-ray radiation, for example, a high Z material such as lead, tungsten, thick stainless steel, tantalum, rhenium, etc. that prevents at least some broadband x-ray radiation from being emitted from x-ray device <NUM>.

Interface portion <NUM> may be comprised of a generally x-ray transmissive material (e.g., beryllium) to allow broadband x-ray radiation from primary target <NUM> to pass outside the vacuum enclosure to irradiate secondary target <NUM>. In this manner, interface portion <NUM> provides a "window" between the inside and outside the vacuum enclosure through which broadband x-ray radiation may be transmitted and, as result, is also referred to herein as the window or window portion <NUM>. Window portion <NUM> may comprise an inner surface facing the inside of the vacuum enclosure and an outer surface facing the outside of the vacuum enclosure of vacuum tube <NUM> (e.g., inner surface <NUM> and outer surface <NUM> illustrated in <FIG>). Window portion <NUM> may be shaped to form a receptacle (see receptacle <NUM> labeled in <FIG>) configured to hold secondary target carrier <NUM> so that the secondary target (e.g., secondary target <NUM>) is positioned outside the vacuum enclosure at a location where at least some broadband x-ray radiation emitted from primary target <NUM> will impinge on the secondary target. According to some embodiments, carrier <NUM> is removable. By utilizing a removable carrier <NUM>, different secondary targets can be used with x-ray system <NUM> without needing to break the vacuum seal, as discussed in further detail below. However, according to some embodiments, carrier <NUM> is not removable.

The inventor recognized that providing a hybrid interface portion comprising a transmissive portion and a blocking portion facilitates further reducing the amount of broadband x-ray radiation emitted from the x-ray device. For example, <FIG> illustrates an interface portion <NUM>' comprising a transmissive portion 1130a (e.g., a beryllium portion) and a blocking portion 1130b (e.g., a tungsten portion), in accordance with some embodiments. Thus, according to some embodiments, interface portion <NUM>' may comprise a first material below the dashed line in <FIG> and comprise a second material different from the first material above the dashed line. Transmissive portion 1130a and blocking portion 1130b may comprise any respective material suitable for performing intended transmission and absorption function sufficiently, as the aspect are not limited for use with any particular materials.

According to some embodiments, the location of the interface between the transmissive portion and the blocking portion (e.g., the location of the dashed line in <FIG>) approximately corresponds to the location of the interface between the transmissive portion and the blocking portion of the carrier when the carrier is inserted into the receptacle formed by the interface portion. According to some embodiments, the location of the interface between the transmissive portion and the blocking portion (e.g., the location of the dashed line in <FIG>) does not correspond to the location of the interface between the transmissive portion and the blocking portion of the carrier when the carrier is inserted into the receptacle formed by the interface portion. A hybrid interface component is also illustrated in FIG. 28A, discussed in further detail below.

In the embodiment illustrated in <FIG>, secondary target <NUM> has a conical geometry and is made of a material that fluoresces x-rays at desired energies in response to incident broadband x-ray radiation. Secondary target may be made of any suitable material, examples of which include, but are not limited to tin (Sn), silver (Ag), molybdenum (Mo), palladium (Pd), or any other suitable material or combination of materials. <FIG> illustrates the x-ray spectra resulting from irradiating secondary target cones of the four exemplary materials listed above. Secondary target <NUM> provides a small compact region from which monochromatic x-ray radiation can be emitted via fluorescent to provide good spatial resolution, as discussed in further detail below.

The inventor has appreciated that removable carrier <NUM> can be designed to improve characteristics of the x-ray radiation emitted from vacuum tube <NUM> (e.g., to improve the monochromaticity of the x-ray radiation emission). Techniques that improve the monochromaticity also facilitate the ability to generate higher intensity monochromatic x-ray radiation, as discussed in further detail below. In the embodiment illustrated in <FIG>, removable carrier <NUM> comprises a transmissive portion <NUM> that includes material that is generally transmissive to x-ray radiation so that at least some broadband x-ray radiation emitted by primary target <NUM> that passes through window portion <NUM> also passes through transmissive portion <NUM> to irradiate secondary target <NUM>. Transmissive portion <NUM> may include a cylindrical portion 1142a configured to accommodate secondary target <NUM> and may be configured to allow the secondary target to be removed and replaced so that secondary targets of different materials can be used to generate monochromatic x-rays at the different characteristic energies of the respective material, though the aspects are not limited for use with a carrier that allows secondary targets to be interchanged (i.e., removed and replaced). Exemplary materials suitable for transmissive portion <NUM> include, but are not limited to, aluminum, carbon, carbon fiber, boron, boron nitride, beryllium oxide, silicon, silicon nitride, etc..

Carrier <NUM> further comprises a blocking portion <NUM> that includes material that is generally opaque to x-ray radiation (i.e., material that substantially absorbs incident x-ray radiation). Blocking portion <NUM> is configured to absorb at least some of the broadband x-ray radiation that passes through window <NUM> that is not converted by and/or is not incident on the secondary target and/or is configured to absorb at least some of the broadband x-ray radiation that might otherwise escape the vacuum enclosure. In conventional x-rays sources (e.g., conventional x-ray apparatus <NUM> illustrated in <FIG>), significant amounts of broadband x-ray radiation is allowed to be emitted from the apparatus, corrupting the fluorescent x-ray radiation emitted by the secondary target and substantially reducing the monochromaticity of the emitted x-ray radiation. In the embodiments illustrated in <FIG>, <FIG>, <FIG> and <FIG>, the transmissive portion and the blocking portion form a housing configured to accommodate the secondary target.

According to some embodiments, blocking portion <NUM> includes a cylindrical portion 1144a and an annular portion 1144b. Cylindrical portion 1144a allows x-ray radiation fluoresced by the secondary target <NUM> in response to incident broadband x-ray radiation from primary target <NUM> to be transmitted, while absorbing at least some broadband x-ray radiation as discussed above. Annular portion 1144b provides a portion providing increased surface area to absorb additional broadband x-ray radiation that would otherwise be emitted by the x-ray device <NUM>. In the embodiment illustrated in <FIG>, annular portion 1144b is configured to fit snugly within a recess in the front portion of the x-ray tube to generally maximize the amount of broadband x-ray radiation that is absorbed to the extent possible. Annular portion 1144b includes an aperture portion 1144c that corresponds to the aperture through cylindrical portions 1144b and 1142a to allow monochromatic x-ray radiation fluoresced from secondary target <NUM> to be emitted from x-ray device <NUM>, as also shown in <FIG> and <FIG> discussed below. Exemplary materials suitable for blocking portion <NUM> include, but are not limited to, lead, tungsten, tantalum, rhenium, platinum, gold, etc..

In the embodiment illustrated <FIG>, carrier <NUM> is configured so that a portion of the secondary target is contained within blocking portion <NUM>. Specifically, as illustrated in the embodiment shown in <FIG>, the tip of conical secondary target <NUM> extends into cylindrical portion 1144b when the secondary target is inserted into transmissive portion <NUM> of carrier <NUM>. The inventor has appreciated that having a portion of the secondary target contained within blocking portion <NUM> improves characteristics of the monochromatic x-ray radiation emitted from the x-ray device, as discussed in further below. However, according to some embodiments, a secondary target carrier may be configured so that no portion of the secondary target is contained with the blocking portion of the carrier, examples of which are illustrated <FIG> discussed in further detail below. Both configurations of carrier <NUM> (e.g., with and without blocking overlap of the secondary target carrier) provide significant improvements to characteristics of the emitted x-ray radiation (e.g., improved monochromaticity), as discussed in further detail below.

As illustrated in <FIG>, carrier <NUM> (which may be similar or the same as carrier <NUM> illustrated in <FIG>) is configured to be removeable. For example, carrier <NUM> may be removeably inserted into receptacle <NUM> formed by interface component <NUM> (e.g., an interface comprising a transmissive window), for example, by inserting and removing the carrier, respectively, in the directions generally indicated by arrow <NUM>. That is, according to some embodiments, carrier <NUM> is configured as a separate component that can be inserted into and removed from the x-ray device (e.g., by inserting removeable carrier <NUM> into and/or removing the carrier from receptacle <NUM>).

As shown in <FIG>, carrier <NUM> has a proximal end <NUM> configured to be inserted into the x-ray device and a distal end <NUM> from which monochromatic x-ray radiation is emitted via aperture 1244d through the center of carrier <NUM>. In the embodiment illustrated in <FIG>, cylindrical blocking portion 1244a is positioned adjacent to and distally from cylindrical transmissive portion 1242a. Annular blocking portion 1244b is positioned adjacent to and distally from block portion 1244a. As shown, annular blocking portion 1244b has a diameter D that is larger than a diameter d of the cylindrical blocking portion 1244a (and cylindrical transmissive portion 1242a for embodiments in which the two cylindrical portions have approximately the same diameter). The distance from the extremes of the proximal end and the distal end is labeled as height H in <FIG>. The dimensions of carrier <NUM> may depend on the dimensions of the secondary target that the carrier is configured to accommodate. For example, for an exemplary carrier <NUM> configured to accommodate a secondary target having a <NUM> base, diameter d may be approximately <NUM>-<NUM>, diameter D may be approximately <NUM>-<NUM>, and height H may be approximately <NUM>-<NUM>. As another example, for an exemplary carrier <NUM> configured to accommodate a secondary target having a <NUM> base, diameter d may be approximately <NUM>-<NUM>, diameter D may be approximately <NUM>-<NUM>, and height H may be approximately <NUM>-<NUM>. It should be appreciated that the dimensions for the carrier and the secondary target provided are merely exemplary, and can be any suitable value as the aspect are not limited for use with any particular dimension or set of dimensions.

According to some embodiments, carrier <NUM> may be configured to screw into receptacle <NUM>, for example, by providing threads on carrier <NUM> capable of being hand screwed into cooperating threads within receptacle <NUM>. Alternatively, a releasable mechanical catch may be provided to allow the carrier <NUM> to be held in place and allows the carrier <NUM> to be removed by applying force outward from the receptacle. As another alternative, the closeness of the fit of carrier <NUM> and receptacle <NUM> may be sufficient to hold the carrier in place during operation. For example, friction between the sides of carrier <NUM> and the walls of receptacle <NUM> may be sufficient to hold carrier <NUM> in position so that no additional fastening mechanism is needed. It should be appreciated that any means sufficient to hold carrier <NUM> in position when the carrier is inserted into the receptacle may be used, as the aspects are not limited in this respect.

As discussed above, the inventor has developed a number of carrier configuration that facilitate improved monochromatic x-ray radiation emission. <FIG> illustrate a three-dimensional and a two-dimensional view of a carrier <NUM>, in accordance with some embodiments. The three-dimensional view in <FIG> illustrates carrier <NUM> separated into exemplary constituent parts. In particular, <FIG> illustrates a transmissive portion <NUM> separated from a blocking portion <NUM>. As discussed above, transmissive portion <NUM> may include material that generally transmits broadband x-ray radiation at least at the relevant energies of interest (i.e., material that allows broadband x-ray radiation to pass through the material without substantial absorption at least at the relevant energies of interest, such as aluminum, carbon, carbon fiber, boron, boron nitride, beryllium oxide, silicon, silicon nitride, etc. Blocking portion <NUM>, on the other hand, may include material that is generally opaque to broadband x-ray radiation at least at the relevant energies of interest (i.e., material that substantially absorbs broadband x-ray radiation at least at the relevant energies of interest, such as lead, tungsten, tantalum, rhenium, platinum, gold, etc..

In this way, at least some broadband x-ray radiation emitted by the primary target is allowed to pass through transmissive portion <NUM> to irradiate the secondary target, while at least some broadband x-ray radiation emitted from the primary target (and/or emitted from or scattered by other surfaces of the x-ray tube) is absorbed by blocking portion <NUM> to prevent unwanted broadband x-ray radiation from being emitted from the x-ray device. As a result, carrier <NUM> facilitates providing monochromatic x-ray radiation with reduced contamination by broadband x-ray radiation, significantly improving monochromaticity of the x-ray emission of the x-ray device. In the embodiments illustrated in <FIG>, blocking portion <NUM> includes a cylindrical portion 1344a and annular portion 1344b having a diameter greater than cylindrical portion 1344a to absorb broadband x-ray radiation emitted over a wider range of angles and/or originating from a wider range of locations to improve the monochromaticity of the x-ray radiation emission of the x-ray device.

According to some embodiments, transmissive portion <NUM> and blocking portion <NUM> may be configured to couple together or mate using any of a variety of techniques. For example, the transmissive portion <NUM>, illustrated in the embodiment of <FIG> as a cylindrical segment, may include a mating portion 1343a at one end of the cylindrical segment configured to mate with mating portion 1342b at a corresponding end of cylindrical portion 1344a of blocking portion <NUM>. Mating portion 1343a and 1343b may be sized appropriately and, for example, provided with threads to allow the transmissive portion <NUM> and the blocking portion <NUM> to be mated by screwing the two portion together. Alternatively, mating portion 1343a and 1343b may be sized so that mating portion 1343a slides over mating portion 1343b, or vice versa, to couple the two portions together. It should be appreciated that any mechanism may be used to allow transmissive portion <NUM> and blocking portion <NUM> to be separated and coupled together. According to some embodiments, transmissive portion <NUM> and blocking portion <NUM> are not separable. For example, according to some embodiments, carrier <NUM> may be manufactured as a single component having transmissive portion <NUM> fixedly coupled to blocking portion <NUM> so that the portions are not generally separable from one another as a general matter of course.

Transmissive portion <NUM> may also include portion <NUM> configured to accommodate secondary target <NUM>. For example, one end of transmissive portion <NUM> may be open and sized appropriately so that secondary target <NUM> can be positioned within transmissive portion <NUM> so that, when carrier <NUM> is coupled to the x-ray device (e.g., inserted into a receptacle formed by an interface portion of the vacuum tube, such as a transmissive window or the like), secondary target <NUM> is positioned so that at least some broadband x-ray radiation emitted from the primary target irradiates secondary target <NUM> to cause secondary target to fluoresce monochromatic x-rays at the characteristic energies of the selected material. In this way, different secondary targets <NUM> can be positioned within and/or held by carrier <NUM> so that the energy of the monochromatic x-ray radiation is selectable. According to some embodiments, secondary target <NUM> may include a portion <NUM> that facilitates mating or otherwise coupling secondary target <NUM> to the carrier <NUM>. For example, portions <NUM> and <NUM> may be provide with cooperating threads that allow the secondary target to be screwed into place within the transmissive portion <NUM> of carrier <NUM>. Alternatively, portions <NUM> and <NUM> may be sized so that the secondary target fits snuggly within transmissive portion and is held by the closeness of the fit (e.g., by the friction between the two components) and/or portion <NUM> and/or portion <NUM> may include a mechanical feature that allows the secondary target to held into place. According to some embodiments, a separate cap piece may be included to fit over transmissive portion <NUM> after the secondary target has been inserted into the carrier and/or any other suitable technique may be used to allow secondary target <NUM> to be inserted within and sufficiently held by carrier <NUM>, as the aspects are not limited in this respect.

In the embodiment illustrated in <FIG>, secondary target <NUM> is contained within transmissive portion <NUM>, without overlap with blocking portion <NUM>. That is, the furthest extent of secondary target <NUM> (e.g., the tip of the conical target in the embodiment illustrated in <FIG>) does not extend into cylindrical portion 1344a of the blocking portion (or any other part of the blocking portion). By containing secondary target <NUM> exclusively within the transmissive portion of the carrier, the volume of secondary target <NUM> exposed to broadband x-ray radiation and thus capable of fluorescing monochromatic x-ray radiation may be generally maximized, providing the opportunity to generally optimize the intensity of the monochromatic x-ray radiation produced for a given secondary target and a given set of operating parameters of the x-ray device (e.g., power levels of the x-ray tube, etc.). That is, by increasing the exposed volume of the secondary target, increased monochromatic x-ray intensity may be achieved.

The front view of annular portion 1344b of blocking portion <NUM> illustrated in <FIG> illustrates that annular portion 1344b includes aperture 1344c corresponding to the aperture of cylindrical portion 1344a (and cylindrical portion <NUM>) that allows monochromatic x-rays fluoresced from secondary target <NUM> to be emitted from the x-ray device. Because blocking portion <NUM> is made from a generally opaque material, blocking portion <NUM> will also absorb some monochromatic x-rays fluoresced from the secondary target emitted at off-axis angles greater than some threshold angle, which threshold angle depends on where in the volume of the secondary target the monochromatic x-rays originated. As such, blocking portion <NUM> also operates as a collimator to limit the monochromatic x-rays emitted to a range of angles relative to the axis of the x-ray tube, which in the embodiments in <FIG>, corresponds to the longitudinal axis through the center of carrier <NUM>.

<FIG> illustrates a schematic of carrier <NUM> positioned within an x-ray device (e.g., inserted into a receptacle formed by an interface portion of the vacuum tube, such as exemplary window portions <NUM> and <NUM> illustrated in <FIG> and <FIG>). Portions <NUM> correspond to the front portion of the vacuum tube, conventionally constructed of a material such as copper. In addition, a cover or faceplate <NUM> made of a generally opaque material (e.g., lead, tungsten, tantalum, rhenium, platinum, gold, etc.) is provided having an aperture corresponding to the aperture of carrier <NUM>. Faceplate <NUM> may be optionally included to provide further absorption of broadband x-ray to prevent spurious broadband x-ray radiation from contaminating the x-ray radiation emitted from the x-ray device.

According to some embodiments, exemplary carrier <NUM> may be used to improve monochromatic x-ray emission characteristics. For example, <FIG> and <FIG> illustrate the on-axis x-ray spectrum 1400a and off-axis x-ray spectrum 1400b resulting from the use of carrier <NUM> illustrated in <FIG> and/or 13C. As shown, the resulting x-ray spectrum is significantly improved relative to the on-axis and off-axis x-ray spectra shown in <FIG> and <FIG> that was produced by a conventional x-ray apparatus configured to produce monochromatic x-ray radiation (e.g., conventional x-ray apparatus <NUM> illustrated in <FIG>). As indicated by arrow <NUM> in <FIG>, the on-axis Sn Kα peak is approximately <NUM> times greater than the Bremsstrahlung background, up from approximately <NUM> in the on-axis spectrum illustrated in <FIG>. The off-axis Sn Kα peak is approximately <NUM> times greater than the Bremsstrahlung background as indicated by arrow <NUM> in <FIG>, up from approximately <NUM> in the off-axis spectrum illustrated in <FIG>. In addition, the ratios of Pk (the integrated energy of the characteristic K-shell emission lines, labeled as Sn Kα and Sn Kβ in <FIG> and <FIG>) to Plow (the integrated energy of the low energy x-ray spectrum below the Sn Kα peak, indicated generally by arrows <NUM> in <FIG> and <FIG>) and Phigh (the integrated energy of the high energy spectrum above the Sn Kβ peak, indicated generally by arrows <NUM>) are <NUM> and <NUM>, respectively, for the on-axis spectrum illustrated in <FIG>, up from <NUM> and <NUM> for the on-axis spectrum of <FIG>. The ratios Pk/Plow and Pk/Phigh are <NUM> and <NUM>, respectively, for the off-axis spectrum illustrated in <FIG>, up from <NUM> and <NUM> for the off-axis spectrum of <FIG>. These increased ratios translate to an on-axis monochromaticity of. <NUM>) and an off-axis monochromaticity of. <NUM>), up from an on-axis monochromaticity of. <NUM> and an off-axis monochromaticity of <NUM> for the x-ray spectrum of <FIG> and <FIG>, respectively.

This significant improvement in monochromaticity facilitates acquiring x-ray images that are more uniform, have better spatial resolution and that deliver significantly less x-ray radiation dose to the patient in medical imaging applications. For example, in the case of mammography, the x-ray radiation spectrum illustrated in <FIG> and <FIG> would deliver four times the mean glandular dose to normal thickness and density breast tissue than would be delivered by the x-ray radiation spectrum illustrated in <FIG> and <FIG>. <FIG> illustrates the field of view of the conventional x-ray source used to generate the x-ray spectrum illustrated in <FIG> and <FIG> along with the field of view of the x-ray device used to generate the x-ray spectrum illustrated in <FIG> and <FIG>. The full width at half maximum (FWHM) of the conventional x-ray apparatus is approximately <NUM> degrees, while the FWHM of the improved x-ray device is approximately <NUM> degrees. Accordingly, although the field of view is reduced via exemplary carrier <NUM>, the resulting field of view is more than sufficient to image an organ such as the breast in a single exposure at compact source detector distances (e.g., approximately <NUM>), but with increased uniformity and spatial resolution and decreased radiation dose, allowing for significantly improved and safer x-ray imaging. <FIG> illustrates the integrated power ratios for the low and high energy x-ray radiation (Pk/Plow and Pk/PHigh) as a function of the viewing angle θ and <FIG> illustrates the monochromaticity of the x-ray radiation for the conventional x-ray apparatus (1560a, 1560b and <NUM>) and the improved x-ray apparatus using exemplary carrier <NUM> (1570a, 1570b and <NUM>). As shown by plots 1570a, 1570b and <NUM>, monochromaticity decreases as a function of viewing angle. Using carrier <NUM>, monochromatic x-ray radiation is emitted having a monochromaticity of at least. <NUM> across a <NUM> degree field of view and a monochromaticity of at least. <NUM> across a <NUM> degree field of view about the longitudinal axis. As shown by plots 1560a, 1560b and <NUM>, monochromaticity of the conventional x-ray apparatus is extremely poor across all viewing angles (i.e., less than. <NUM> across the entire field of view).

The inventor has appreciated that further improvements to aspects of the monochromaticity of x-ray radiation emitted from an x-ray tube may be improved by modifying the geometry of the secondary target carrier. According to some embodiments, monochromaticity may be dramatically improved, in particular, for off-axis x-ray radiation. For example, the inventor recognized that by modifying the carrier so that a portion of the secondary target is within a blocking portion of the carrier, the monochromaticity of x-ray radiation emitted by an x-ray device may be improved, particularly with respect to off-axis x-ray radiation. <FIG> illustrate a three-dimensional and a two-dimensional view of a carrier <NUM>, in accordance with some embodiments. Exemplary carrier <NUM> may include similar parts to carrier <NUM>, including a transmissive portion <NUM> to accommodate secondary target <NUM>, and a blocking portion <NUM> (which may include a cylindrical portion 1744a and annular portion 1744b with an aperture 1744c through the center), as shown in <FIG>.

However, in the embodiment illustrated in <FIG>, carrier <NUM> is configured so that, when secondary target <NUM> is positioned within transmissive portion <NUM>, a portion of secondary target <NUM> extends into blocking portion <NUM>. In particular, blocking portion includes an overlap portion 1744d that overlaps part of secondary target <NUM> so that at least some of the secondary target is contained within blocking portion <NUM>. According to some embodiments, overlap portion 1744d extends over between approximately. <NUM> and <NUM> of the secondary target. According to some embodiments, overlap portion 1744d extends over between approximately <NUM> and <NUM> of the secondary target. According to some embodiments, overlap portion 1744d extends over approximately <NUM> of the secondary target. According to some embodiments, overlap portion 1744d extends over less than. <NUM>, and in some embodiments, overlap portion 1744d extends over greater than <NUM>. The amount of overlap will depend in part on the size and geometry of the secondary target, the carrier and the x-ray device. <FIG> illustrates carrier <NUM> positioned within an x-ray device (e.g., inserted in a receptacle formed at the interface of the vacuum tube), with a faceplate <NUM> provided over front portion <NUM> of a vacuum tube (e.g., vacuum tube <NUM> illustrated in <FIG>).

According to some embodiments, exemplary carrier <NUM> may be used to further improve monochromatic x-ray emission characteristics. For example, <FIG> and <FIG> illustrate the on-axis x-ray spectrum 1800a and off-axis x-ray spectrum 1800b resulting from the use of carrier <NUM> illustrated in <FIG>. As shown, the resulting x-ray spectrum are significantly improved relative to the on-axis and off-axis x-ray spectrum produced the conventional x-ray apparatus shown in <FIG> and <FIG>, as well as exhibiting improved characteristics relative to the x-ray spectra produced using exemplary carrier <NUM> illustrated in <FIG>. As indicated by arrow <NUM> in <FIG>, the on-axis Sn Kα peak is <NUM> times greater than the Bremsstrahlung background, compared to <NUM> for the on-axis spectrum in <FIG> and <NUM> for the on-axis spectrum illustrated in <FIG>. As indicated by arrow <NUM> in <FIG>, the off-axis Sn Kα peak is <NUM> times greater than the Bremsstrahlung background, compared to <NUM> for the off-axis spectrum in <FIG> and <NUM> for the off-axis spectrum illustrated in <FIG>.

The ratios of Pk (the integrated energy of the characteristic K-shell emission lines, labeled as Sn Kα and Sn Kβ in <FIG> and <FIG>) to Plow (the integrated energy of the low energy x-ray spectrum below the Sn Kα peak, indicated generally by arrows <NUM> in <FIG> and <FIG>) and Phigh (the integrated energy of the high energy spectrum above the Sn Kβ peak, , indicated generally by arrows <NUM>) are <NUM> and <NUM>, respectively, for the on-axis spectrum illustrated in <FIG>, compared to <NUM> and <NUM> for the on-axis spectrum of <FIG> and <NUM> and <NUM> for the on-axis spectrum of <FIG>. The ratios Pk/Plow and Pk/Phigh are <NUM> and <NUM>, respectively, for the off-axis spectrum of <FIG>, compared to <NUM> and <NUM>, respectively, for the off-axis spectrum illustrated in <FIG> and <NUM> and <NUM> for the off-axis spectrum of <FIG>. These increased ratios translate to an on-axis monochromaticity of. <NUM>) and an off-axis monochromaticity of. <NUM>), compared to an on-axis monochromaticity of. <NUM>) for x-ray spectrum of <FIG> and an off-axis monochromaticity of. <NUM>) for the x-ray spectrum of <FIG>, and an on-axis monochromaticity of. <NUM> and an off-axis monochromaticity of <NUM> for the x-ray spectra of <FIG> and <FIG>, respectively.

Referring again to <FIG> and <FIG>, the stars indicate the on-axis and off-axis low energy ratio (1580a) and high energy ratio (1580b), as well as the on-axis and off-axis monochromaticity (<NUM>), respectively, of the x-ray radiation emitted using exemplary carrier <NUM>. As shown, the x-ray radiation exhibits essentially the same characteristics on-axis and <NUM> degrees off-axis. Accordingly, while exemplary carrier <NUM> improves both on-axis and off-axis monochromaticity, use of the exemplary carrier illustrate in <FIG> exhibits a substantial increase in the off-axis monochromaticity, providing substantial benefits to x-ray imaging using monochromatic x-rays, for example, by improving uniformity, reducing dose and enabling the use of higher x-ray tube voltages to increase the mononchromatic intensity to improve the spatial resolution and ability differentiate small density variations (e.g., small tissue anomalies such as micro-calcifications in breast material), as discussed in further detail below. Using carrier <NUM>, monochromatic x-ray radiation is emitted having a monochromaticity of at least. <NUM> across a <NUM> degree field of view and a monochromaticity of at least. <NUM> across a <NUM> degree field of view about the longitudinal axis.

It should be appreciated that the exemplary carrier described herein may be configured to be a removable housing or may be integrated into the x-ray device. For example, one or more aspects of the exemplary carriers described herein may integrated, built-in or otherwise made part an x-ray device, for example, as fixed components, as the aspects are not limited in this respect.

As is well known, the intensity of monochromatic x-ray emission may be increased by increasing the cathode-anode voltage (e.g., the voltage potential between filament <NUM> and primary target <NUM> illustrated in <FIG>) and/or by increasing the filament current which, in turn, increases the emission current of electrons emitted by the filament, the latter technique of which provides limited control as it is highly dependent on the properties of the cathode. The relationship between x-ray radiation intensity, cathode-anode voltage and emission current is shown in <FIG>, which plots x-ray intensity, produced using a silver (Ag) secondary target and a source-detector distance of <NUM>, against emission current at a number of different cathode-anode voltages using two different secondary target geometries (i.e., an Ag cone having a <NUM> diameter base and an Ag cone having a <NUM> diameter base).

Conventionally, the cathode-anode voltage was selected to be approximately twice that of the energy of the characteristic emission line of the desired monochromatic x-ray radiation to be fluoresced by the secondary target as a balance between producing sufficient high energy broadband x-ray radiation above the absorption edge capable of inducing x-ray fluorescence in the secondary target to produce adequate monochromatic x-ray intensity, and producing excess high energy broadband x-ray radiation that contaminates the desired monochromatic x-ray radiation. For example, for an Ag secondary target, a cathode-anode potential of <NUM> kV (e.g., the electron optics would be set at -<NUM> kV) would conventionally be selected to ensure sufficient high energy broadband x-rays are produced above the K-edge of silver (<NUM> keV) as illustrated in <FIG> to produce the <NUM> keV Ag K monochromatic x-ray radiation shown in <FIG> (bottom left). Similarly, for a Sn secondary target, a cathode-anode potential of <NUM> kV would conventionally be selected to ensure sufficient high energy broadband x-rays are produced above the K-edge of tin (<NUM> keV) as illustrated in <FIG> to produce the <NUM> keV Sn K monochromatic x-ray radiation shown in <FIG> (bottom right). This factor of two limit on the cathode-anode voltage was conventionally followed to limit the high energy contamination of the monochromatic x-rays emitted from the x-ray apparatus.

The inventor has recognized that the techniques described herein permit the factor of two limit to be eliminated, allowing high cathode-anode voltages to be used to increase mononchromatic x-ray intensity without significantly increasing broadband x-ray radiation contamination (i.e., without substantial decreases in monochromaticity). In particular, techniques for blocking broadband x-ray radiation, including the exemplary secondary target carriers developed by the inventors can be used to produce high intensity monochromatic radiation while maintaining excellent monochromaticity. For example, <FIG> illustrates the on-axis monochromaticity 2200a and the off-axis monochromaticity 2200b for a number of cathode-anode voltages (primary voltage) with a Sn secondary target using exemplary carrier <NUM> developed by the inventor. Similarly, <FIG> illustrates the on-axis monochromaticity 2300a and the off-axis monochromaticity 2300b for a number of cathode-anode voltages (primary voltage) with an Ag secondary target using exemplary carrier <NUM> developed by the inventor. As shown, a high degree of monochromaticity is maintained across the illustrated range of high voltages, varying by only <NUM>% over the range illustrated. Thus, higher voltages can be used to increase the monochromatic x-ray intensity (e.g., along the lines shown in <FIG>) without substantially impacting monochromaticity. For example, monochromatic x-ray radiation of over <NUM>% purity (M ><NUM>) can be generated using a primary voltage up to and exceeding <NUM> KeV, significantly increasing the monochromatic x-ray intensity.

According to some embodiments, a primary voltage (e.g., a cathode-anode voltage potential, such as the voltage potential between filament <NUM> and primary target <NUM> of x-ray tube <NUM> illustrated in <FIG>) greater than two times the energy of the desired monochromatic x-ray radiation fluoresced from a given target is used to generate monochromatic x-ray radiation. According to some embodiments, a primary voltage greater than or equal to approximately two times and less than or equal to approximately three times the energy of the desired monochromatic x-ray radiation fluoresced from a given target is used to generate monochromatic x-ray radiation. According to some embodiments, a primary voltage greater than or equal to approximately three times and less than or equal to approximately four times the energy of the desired monochromatic x-ray radiation fluoresced from a given target is used to generate monochromatic x-ray radiation. According to some embodiments, a primary voltage greater than or equal to approximately four times and less than or equal to approximately five times the energy of the desired monochromatic x-ray radiation fluoresced from a given target is used to generate monochromatic x-ray radiation. According to some embodiments, a primary voltage greater than or equal to five times greater the energy of the desired monochromatic x-ray radiation fluoresced from a given target is used to generate monochromatic x-ray radiation. In each case, x-ray radiation having monochromaticity of greater than or equal to. <NUM>, on and off axis across the field of view may be achieved, though it should be appreciated that achieving those levels of monochromaticity is not a requirement.

The inventor has recognized the geometry of the x-ray tube may contribute to broadband x-ray radiation contamination. The inventor has appreciated that the electron optics of an x-ray tube may be improved to further reduce the amount of broadband x-ray radiation that is generated that could potentially contaminate the monochromatic x-rays emitted from an x-ray device. Referring again to <FIG>, x-ray device <NUM> includes electron optics <NUM> configured to generate electrons that impinge on primary target <NUM> to produce broadband x-ray radiation. The inventor has developed electron optics geometry configured to reduce and/or eliminate bombardment of surfaces other than the primary target within the vacuum enclosure. This geometry also reduces and/or eliminates parasitic heating of other surfaces that would have to be removed via additional cooling in conventional systems.

As an example, the geometry of electron optics <NUM> is configured to reduce and/or eliminate bombardment of window portion <NUM> and/or other surfaces within vacuum tube <NUM> to prevent unwanted broadband x-ray radiation from being generated and potentially emitted from the x-ray tube to degrade the monochromaticity of the emitted x-ray radiation spectrum. In the embodiment illustrated in <FIG>, electron optics <NUM> comprises a filament <NUM>, which may be generally toroidal in shape, and guides <NUM>, <NUM> and/or <NUM> positioned on the inside and outside of the toroidal filament <NUM>. For example, guides <NUM>, <NUM>, <NUM> may be positioned concentrically with the toroidal filament <NUM> (e.g., an inner guide <NUM> positioned within the filament torus and an outer guides <NUM> and <NUM> positioned around the filament torus) to provide walls on either side of filament <NUM> to prevent at least some electrons from impinging on surfaces other than primary target <NUM>, as discussed in further detail below.

According to some embodiments, electronic optics <NUM> is configured to operate at a high negative voltage (e.g., 40kV, 50kV, 60kV, 70kV, 80kV, 90kV or more). That is, filament <NUM>, inner guide <NUM> and outer guides <NUM>, <NUM> may all be provided at a high negative potential during operation of the device. As such, in these embodiments, primary target <NUM> may be provided at a ground potential so that electrons emitted from filament <NUM> are accelerated toward primary target <NUM>. However, the other components and surfaces of x-ray tube within the vacuum enclosure are typically also at ground potential. As a result, electrons will also accelerate toward and strike other surfaces of x-ray tube <NUM>, for example, the transmissive interface between the inside and outside of the vacuum enclosure (e.g., window <NUM> in <FIG>). Using conventional electron optics, this bombardment of unintended surfaces produces broadband x-ray radiation that contributes to the unwanted broadband spectrum emitted from the x-ray device and causes undesirable heating of the x-ray tube. The inventor appreciated that this undesirable bombardment of surfaces other than primary target <NUM> may be reduced and/or eliminated using inner guide <NUM> and outer guides <NUM> and/or <NUM> that provide a more restricted path for electrons emitted by filament <NUM>.

According to some embodiments, guides <NUM>-<NUM> are cylindrical in shape and are arranged concentrically to provide a restricted path for electrons emitted by filament <NUM> that guides the electrons towards primary target <NUM> to prevent at least some unwanted bombardment of other surfaces within the vacuum enclosure (e.g., reducing and/or eliminating electron bombardment of window portion <NUM>). However, it should be appreciated that the guides used in any given implementation may be of any suitable shape, as the aspects are not limited in this respect. According to some embodiments, guides <NUM>, <NUM> and/or <NUM> comprise copper, however, any suitable material that is electrically conducting (and preferably non-magnetic) may be used such as stainless steel, titanium, etc. It should be appreciated that any number of guides may be used. For example, an inner guide may be used in conjunction with a single outer guide (e.g., either guide <NUM> or <NUM>) to provide a pair guides, one on the inner side of the cathode and one on the outer side of the cathode. As another example, a single inner guide may be provided to prevent at least some unwanted electrons from bombarding the interface between the inside and outside of the vacuum tube (e.g., window portion <NUM> in <FIG>), or a single outer guide may be provide to prevent at least some unwanted electrons from bombarding other internal surface of the vacuum tube provides. Additionally, more than three guides may be used to restrict the path of electrons to the primary target to reduce and/or eliminate unwanted bombardment of surfaces within the vacuum enclosure, as the aspects are not limited in this respect.

<FIG> illustrate a cross-section of a monochromatic x-ray source <NUM> with improved electron optics, in accordance with some embodiments. In the embodiment illustrated, there is a <NUM> kV is the potential between the cathode and the anode. Specifically, a tungsten toroidal cathode <NUM> is bias at -<NUM> kV and a gold-coated tungsten primary target <NUM> is at a ground potential. A copper inner guide <NUM> and an outer copper guides <NUM> and <NUM> are also provided at -<NUM> kV to guide electrons emitted from the cathode to prevent at least some electrons from striking surfaces other than primary target <NUM> to reduce the amount of spurious broadband x-ray radiation. Monochromatic x-ray source <NUM> uses a silver secondary target <NUM> and a beryllium interface component <NUM>. <FIG> illustrates the electron trajectories between the toroidal cathode and the primary target when the monochromatic x-ray source <NUM> is operated. <FIG> illustrate the locus of points where the electrons strike primary target <NUM>, demonstrating that the guides prevent electrons from striking the interface component <NUM> in this configuration. <FIG> illustrates a monochromatic x-ray source including a hybrid interface component having transmissive portion of beryllium and a blocking portion of tungsten that produces monochromatic x-ray radiation of <NUM>% purity (M= <NUM>) when combined with other techniques described herein (e.g., using the exemplary carriers described herein). <FIG> illustrates an alternative configuration in which the cathode is moved further away from the primary target, resulting in divergent electron trajectories and reduced monochromaticity.

The monochromatic x-ray sources described herein are capable of providing relatively high intensity monochromatic x-ray radiation having a high degree of monochromaticity, allowing for relatively short exposure times that reduce the radiation dose delivered to a patient undergoing imaging while obtaining images with high signal-to-noise ratio. Provided below are results obtained using techniques described herein in the context of mammography. These results are provided to illustrate the significant improvements that are obtainable using one or more techniques described herein, however, the results are provided as examples as the aspects are not limited for use in mammography, nor are the results obtained requirements on any of the embodiments described herein.

<FIG> illustrates a mammographic phantom (CIRS Model 011a) <NUM> used to test aspects of the performance of the monochromatic x-ray device developed by the inventor incorporating techniques described herein. Phantom <NUM> includes a number of individual features of varying size and having different absorption properties, as illustrated by the internal view of phantom <NUM> illustrated in <FIG>. <FIG> highlights some of the embedded features of phantom <NUM>, including the linear array of <NUM> blocks, each <NUM> thick and each having a composition simulating different densities of breast tissue. The left most block simulates <NUM>% glandular breast tissue, the right most, <NUM>% adipose (fat) tissue and the other three have a mix of glandular and adipose with ratios ranging from <NUM>:<NUM> ( glandular : adipose) to <NUM>:<NUM> to <NUM>:<NUM>. All <NUM> blocks are embedded in the phantom made from a <NUM>:<NUM> glandular to adipose mix. The total thickness of the phantom is <NUM>.

<FIG> also shows a schematic description of the imaging process in one dimension as the x-ray beam enters the phantom, passes through the blocks and the phantom on their way to the imaging detector where the transmitted x-ray intensity, is converted into an integrated value of Gray counts. (The intensity in this case is the sum of the x-ray energies reaching each detector pixel. The electronics in each pixel convert this energy sum into a number between <NUM> and <NUM>, where <NUM> represents the maximum energy sum allowable before the electronics saturate. The number resulting from this digital conversion is termed a Gray count).

The data shown by the red horizontal line in a) of <FIG> is the x-ray intensity, B, measured through the background <NUM>:<NUM> glandular-adipose mixture. The data shown by the black curve is the x-ray intensity, W, transmitted through the <NUM>:<NUM> mix and the <NUM> blocks. The varying step sizes represent different amounts of x-ray absorption in the blocks due to their different compositions. Plot b) in <FIG> defines the signal, S, as W-B and plot c) of <FIG> defines the contrast as S/B. The figure of merit that is best used to determine the detectability of an imaging system is the Signal-to-Noise Ratio, SNR. For the discussion here, the SNR is defined as S/noise, where the noise is the standard deviation of the fluctuations in the background intensity shown in plot a) of <FIG>. Images produced using techniques described herein and may with <NUM> keV x-rays and <NUM> keV x-rays and presented herein and compared to the SNR values with those from a commercial broad band x-ray mammography machine.

Radiation exposure in mammographic examinations is highly regulated by the Mammography Quality Standards Act (MQSA) enacted in <NUM> by the U. The MQSA sets a limit of <NUM> milliGray (mGy) for the mean glandular dose (mgd) in a screening mammogram; a Gray is a joule/kilogram. This <NUM> mGy limit has important ramifications for the operation of commercial mammography machines, as discussed in further detail below. Breast tissue is composed of glandular and adipose (fatty) tissue. The density of glandular tissue (ρ = <NUM> gm/cm-<NUM>) is not very different from the density of adipose tissue (ρ = <NUM> gm/cm-<NUM>) which means that choosing the best monochromatic x-ray energy to optimize the SNR does not depend significantly on the type of breast tissue. Instead, the choice of monochromatic energy for optimal imaging depends primarily on breast thickness. A thin breast will attenuate fewer x-rays than a thick breast, thereby allowing a more significant fraction of the x-rays to reach the detector. This leads to a higher quality image and a higher SNR value. These considerations provide the major rationale for requiring breast compression during mammography examinations with a conventional, commercial mammography machine.

Imaging experiments were conducted the industry-standard phantom illustrated in <FIG>, which has a thickness of <NUM> and is representative of a typical breast under compression. Phantom <NUM> has a uniform distribution of glandular-to-adipose tissue mixture of <NUM>:<NUM>. The SNR and mean glandular dose are discussed in detail below for CIRS phantom images obtained with monochromatic energies of <NUM> keV and <NUM> keV. Experiments were also conducted with a double phantom, as illustrated in <FIG>, to simulate a thick breast under compression with a thickness of <NUM>. The double phantom also has a uniform distribution of glandular-to-adipose tissue mixture of <NUM>:<NUM>. The SNR and mean glandular dose are presented for the double phantom using a monochromatic energy of <NUM> keV. The high SNR obtained on this model of a thick breast demonstrates that monochromatic x-rays can be used to examine women with reduced compression or no compression at all, since, typically, a compressed breast of <NUM> thickness is equivalent to an uncompressed breast of <NUM>-<NUM> thickness, as discussed in further detail below.

The experiments demonstrate that the mean glandular dose for the monochromatic measurements is always lower than that of the commercial machine for the same SNR. Stated in another way, the SNR for the monochromatic measurements is significantly higher than that of the commercial machines for the same mean glandular dose. Thus, monochromatic X-ray mammography provides a major advance over conventional broadband X-ray mammographic methods and has significant implications for diagnosing breast lesions in all women, and especially in those with thick or dense breast tissue. Dense breasts are characterized by non-uniform distributions of glandular tissue; this non-uniformity or variability introduces artifacts in the image and makes it more difficult to discern lesions. The increased SNR that monochromatic imaging provides makes it easier to see lesions in the presence of the inherent tissue variability in dense breasts, as discussed in further detail below.

<FIG> illustrates images of phantom <NUM> obtained from a monochromatic x-ray source described herein using monochromatic Ag K (<NUM> keV) and Sn K (<NUM> keV) x-rays and an image from a conventional commercial mammography machine that uses broad band emission, along with respective histograms through the soft tissue blocks. The image from the commercial machine is shown in (a) of <FIG>. The SNR for the <NUM>% glandular block is <NUM> and the mean glandular dose (mgd) is <NUM> mGy (<NUM> Gy = <NUM> joule/kgm). Image (b) in <FIG> illustrates a monochromatic image using <NUM> keV x-rays and image (c) in <FIG> was obtained with <NUM> keV X-rays. The mean glandular doses for the <NUM>% glandular block measured with <NUM> keV is <NUM> mGy and that measured with 25keV is <NUM> mGy, and the SNR values are <NUM> for both energies. To achieve the same SNR as the commercial machine, the monochromatic system using <NUM> keV delivers a dose that is <NUM> times lower and using <NUM> keV delivers a dose that is <NUM> times lower.

The dose reduction provided by the monochromatic X-ray technology offers significantly better diagnostic detectability than the conventional broad band system because the SNR can be increased by factors of <NUM> to <NUM> times while remaining well below the regulatatory dose limit of <NUM> mGy for screening. For example, the SNR value for the <NUM> keV images would be <NUM> at the same dose delivered by the commercial machine (<NUM> mGy) and <NUM> for a dose of <NUM> mGy. Similarly, using the <NUM> keV energy, the SNR values would be <NUM> and <NUM> for mean glandular doses of <NUM> mGy and <NUM> mGy, respectively. This significantly enhanced range in SNR has enormous advantages for diagnosing women with dense breast tissue. As mentioned earlier, such tissue is very non-uniform and, unlike the uniform properties of the phantoms and women with normal density tissue, the variability in glandular distribution in dense breast introduces artifacts and image noise, thereby making it more difficult to discern lesions. The higher SNR provided by techniques describe herein can overcome these problems.

The monochromatic x-ray device incorporating the techniques described herein used to produce the images displayed here is comparable in size and footprint of a commercial broadband x-ray mammography system, producing for the first time low dose, high SNR, uniform images of a mammographic phantom using monochromatic x-rays with a degree of monochromaticity of <NUM>%. In fact, conventional monochromatic x-ray apparatus do not even approach these levels of monochromaticity.

To simulate thick breast mammography, a model for thick breast tissue was created by placing two phantoms on top of each other (total thickness <NUM>), the <NUM>-<NUM> ACR Mammography Accreditation Phantom (<NUM>) placed on top of the CIRS Model 011A phantom (<NUM>), as shown in <FIG>. For this series of experiments, <NUM> keV x-rays were selected to optimize the transmission while maintaining good contrast in the soft tissue represented by the <NUM> array of blocks embedded on the CIRS phantom. The images for the <NUM> keV monochromatic x-rays are compared to the images obtained from the same commercial broad band mammography machine used in the previous experiment. The resulting images are displayed in <FIG>, along with the histograms of the contrast through the soft tissue blocks.

The image quality for the thick breast tissue is superior to anything obtainable with current commercial broad band systems. The dose delivered by the commercial machine is <NUM> mGy and only achieves a SNR of <NUM> in the <NUM>% glandular block. The monochromatic image in <FIG> has a SNR=<NUM> for a dose of <NUM> mGy. The dose required for the commercial broad band X-ray system to reach a SNR of <NUM>, the accepted value of radiologists for successful detection in thinner <NUM> thick tissue would be <NUM> mGy, <NUM> times higher than the commercial dose used to image normal density breast tissue (<NUM> mGy). This is prohibitively high and unsafe for screening and <NUM> times higher than the regulated MQSA screening limit. On the other hand, the required dose from the monochromatic system to achieve a SNR = <NUM> is only <NUM> mGy, <NUM> times lower than that required by the commercial machine. The dose required using monochromatic x-rays is safe, more than <NUM> times lower than the regulatory limit, and still <NUM> times lower than the dose for normal thickness, <NUM> breasts using the commercial broad band x-ray mammography machine. Comparing the monochromatic X-ray and the commercial broad band X-ray machines at close to the maximum allowed exposure (<NUM>. 75mGy), the monochromatic technology provides <NUM> times higher SNR. The above discussion is summarized schematically in <FIG>.

The measurements on the <NUM> thick breast phantom show that the monochromatic techniques described herein facilitate elimination of breast compression during mammography screening. A <NUM> compressed breast could be as thick at <NUM> when uncompressed. Whereas the commercial machine loses sensitivity as the breast thickness increases because it cannot increase the dose high enough to maintain the SNR and still remain below the regulated dose limit, the monochromatic x-ray system very easily provides the necessary SNR. As an example, of a monochromatic mammography procedure, a woman may lie prone on a clinic table designed to allow her breasts to extend through cutouts in the table. The monochromatic x-ray system may be designed to direct the x-rays parallel to the underside of the table. The table also facilitates improved radiation shielding for the patient by incorporating a layer of lead on the underside of the table's horizontal surface.

The inventor has recognized that the spatial resolution of the geometry of the monochromatic x-ray device described herein is excellent for mammographic applications. According to some embodiments, the monochromatic x-ray system has a source-to-detector distance of <NUM>, a secondary target cone with a <NUM> base diameter and <NUM> height, and an imaging detector of amorphous silicon with pixel sizes of <NUM> microns. This exemplary monochromatic x-ray device using the techniques described herein can easily resolve microcalicifications with diameters of <NUM> - <NUM> microns in the CIRS and ACR phantoms. <FIG> and <FIG> illustrate images and associated histograms obtained using this exemplary monochromatic x-ray radiation device compared to images obtained using the same commercial device. The microcalcifications measured in the double ACR-CIRS phantom (stacked <NUM> and <NUM> phantoms) experiments described earlier using the monochromatic <NUM> keV x-ray lines have a SNR that is <NUM>% higher than the SNR for the commercial machine and its mean glandular dose (mgd) is <NUM> times lower for these images. If one were to make the monochromatic SNR the same as that measured in the commercial machine, then the monochromatic mean glandular does (mgd) would be another factor of <NUM> times smaller for a total of <NUM> times lower.

Simple geometric considerations indicate that the effective projected spot size of the secondary cone is <NUM>- <NUM>. <FIG> illustrates histograms of the measured intensity scans through line-pair targets that are embedded in the CIRS phantom. The spacing of the line-par targets ranges from <NUM> lines per mm up to <NUM> lines per mm. The top four histograms show that the scans for <NUM> keV, <NUM> keV, <NUM> keV and <NUM> keV energies using a <NUM> secondary cone described briefly above can discern alternating intensity structure up to <NUM> lines per mm which is consistent with a spatial resolution FWHM of <NUM> microns. The <NUM> keV energy can still discern structure at <NUM> lines per mm. The bottom histogram in <FIG> is an intensity scan through the same line-pair ensemble using a commonly used commercial broad band mammography system. The commercial system's ability to discern structure fails beyond <NUM> lines per mm. This performance is consistent with the system's modulation transfer function (MTF), a property commonly used to describe the spatial frequency response of an imaging system or a component. It is defined as the contrast at a given spatial frequency relative to low frequencies and is shown in <FIG>. The value of <NUM> at <NUM> lines/mm is comparable to other systems with direct detector systems and better than flat panel detectors.

According to some embodiments, the exemplary monochromatic system described herein was operated with up to <NUM> watts in a continuous mode, i.e., the primary anode is water-cooled, the high voltage and filament current are on continously and images are obtained using a timer-controlled, mechanical shutter. The x-ray flux data in <FIG> together with the phantom images shown in <FIG> and <FIG> provide scaling guidelines for the power required to obtain a desired signal to noise for a specific exposure time in breast tissue of different compression thicknesses. Using a secondary material of Ag, <NUM> and <NUM> cone assemblies are compared for a compressed thickness of <NUM> and <NUM>:<NUM> glandular-adipose mix) in <FIG>. The power requirements for a compressed thickness of <NUM> (<NUM>:<NUM> glandular-adipose mix) as defined by experiments described above are compared in <FIG> for the <NUM>, <NUM> cones made from Sn.

The results indicate that a SNR of <NUM> obtained in a measurement of the <NUM>% glandular block embedded in the CIRS phantom of normal breast density compressed to <NUM> can be achieved in a <NUM> second exposure expending <NUM> kW of power in the primary using the <NUM> cone (<FIG> top); <NUM> kW are needed if one uses the <NUM> cone (<FIG> bottom). In both of these cases, the source-to-detector (S-D) is <NUM>. If <NUM> sec are required, <NUM> kW are needed if an <NUM> cone is used or a <NUM> cone can be used at a source-to-detector (S-D) distance of <NUM> instead of <NUM>. Since the spatial resolution dependence is linear with S-D, then moving the <NUM> cone closer to the sample will only degrade the spatial resolution by <NUM> times, but it will still be better than the <NUM> cone at <NUM>. In general, there is a trade-off between spatial resolution and exposure time that will determine whether the <NUM> or <NUM> embodiments at the two source-to-detector distances best suit an application. This data serves as guides for designing monochromatic x-ray sources and do not exclude the possibilities for a variety of other target sizes and source-to-detector distances.

For thick breast tissue compressed to <NUM>, the dependency of the SNR on power is shown in <FIG>. A <NUM> sec exposure can produce a SNR of <NUM> at <NUM> kW using a <NUM> Sn cone at a source-to-detector distance of <NUM> or with a <NUM> cone at <NUM>. Conventional broad band commercial mammography systems would have to deliver a <NUM> mGy dose to achieve this same SNR whereas the monochromatic system at <NUM> keV would only deliver <NUM> mGy, a factor of <NUM> times lower and still <NUM> times lower than the conventional dose of <NUM> mGy delivered by a commercial machine in screening women with normal density breast tissue compressed to <NUM>.

The inventor has recognized that maximizing the monochromatic X-ray intensity in a compact X-ray generator may be important for applications in medical imaging. Increased intensity allows shorter exposures which reduce motion artifacts and increase patient comfort. Alternatively, increased intensity can be used to provide increased SNR to enable the detection of less obvious features. There are three basic ways to increase the monochromatic flux: <NUM>) maximizing fluorescence efficiency through the geometry of the target, <NUM>) enhance the total power input on the primary in a steady state mode and <NUM>) increase the total power input on the primary in a pulsed mode.

To increase the power and further decrease the exposure times, power levels of 10kW - <NUM> kW may be used. For example, an electron beam in high power commercial medical x-ray tubes (i.e., broadband x-ray tubes) has approximately a 1x7mm fan shape as it strikes an anode that is rotating at <NUM>,<NUM> rpm. Since the anode is at a steep angle to the electron beam, the projected spot size in the long direction as seen by the viewer is reduced to about <NUM>. For an exposure of <NUM> sec, once can consider the entire annulus swept out by the fan beam as the incident surface for electron bombardment. For a <NUM> diameter anode, this track length is <NUM>, so the total incident anode surface area is about <NUM><NUM>. For the monochromatic system using a conical anode with a <NUM> diameter and a truncated height of <NUM>, the total area of incidence for the electrons is <NUM><NUM>. Therefore, it should be straightforward to make a <NUM> sec exposure at a power level that is <NUM>% of the power of strong medical sources without damaging the anode material; <NUM> kW is a typical power of the highest power medical sources. Assuming a very conservative value that is <NUM>% of the highest power, an anode made of a composite material operating at 50kW should be achievable for short exposures. This is more power than is needed for thick and/or dense breast diagnostics but offers significant flexibility if reducing the effective size of the secondary cone becomes a priority.

A one second exposure at 50kW generates 50kJ of heat on the anode. If the anode is tungsten, the specific heat is <NUM> J/g/K. To keep the temperature below <NUM>° C in order not to deform or melt the anode, the anode mass needs to be at least <NUM> gm. An anode of copper coated with a thick layer of gold would only have to be <NUM> gm. These parameters can be increased by at least <NUM> - <NUM> times without seriously changing the size or footprint of the source. For repeat exposures or for longer exposures, the anode in this system can be actively cooled whereas the rotating anode system has to rely on anode mass for heat storage and inefficient cooling through a slip-ring and slow radiative transfer of heat out of the vacuum vessel. The monochromatic x-ray systems described above can be actively cooled with water.

According to some embodiments, the primary anode material can be chosen to maximize the fluorescent intensity from the secondary. In the tests to date, the material of the primary has been either tungsten (W) or gold (Au). They emit characteristic K emission lines at <NUM> keV and <NUM> keV, respectively. These energies are relatively high compared to the absorption edges of silver (Ag; <NUM> keV) or tin (Sn; <NUM> keV) thereby making them somewhat less effective in inducing x-ray fluorescence in the Ag or Sn secondary targets. These lines may not even be excited if the primary voltage is lower than <NUM> keV. In this situation only the Bremsstrahlung induces the fluorescence. Primary material can be chosen with characteristic lines that are much closer in energy to the absorption edges of the secondary, thereby increasing the probablility of x-ray fluorescence. For example, elements of barium, lanthanum, cerium, samarium or compounds containing these elements may be used as long as they can be formed into the appropriate shape. All have melting points above <NUM>. If one desires to enhance production of monochromatic lines above <NUM> keV in the most efficient way, higher Z elements are needed. For example, depleted uranium may be used ( K line =<NUM> keV) to effectively induce x-ray fluorescence in Au (absorption edge =<NUM> keV). Operating the primary at <NUM> kV, the Bremsstrahlung plus characteristic uranium K lines could produce monochromatic Au lines for thorasic/chest imaging, cranial imaging or non-destructive industrial materials analysis.

For many x-ray imaging applications including mammography, the x-ray detector is an imaging array that integrates the energies of the absorbed photons. All spectroscopic information is lost. If a spectroscopic imager is available for a particular situation, the secondary target could be a composite of multiple materials. Simultaneous spectroscopic imaging could be performed at a minimum of two energies to determine material properties of the sample. Even if an imaging detector with spectral capability were available for use with a broad-band source used in a conventional x-ray mammography system for the purpose of determining the chemical composition of a suspicious lesion, the use of the spectroscopic imager would not reduce the dose to the tissue (or generically the sample) because the broad band source delivers a higher dose to the sample than the monochromatic spectrum.

Contrast-enhanced mammography using monochromatic x-ray radiation is superior to using the broad band x-ray emission. It can significantly increase the image detail by selectively absorbing the monochromatic X-rays at lower doses. The selective X-ray absorption of a targeted contrast agent would also facilitate highly targeted therapeutic X-ray treatment of breast tumors. In the contrast enhanced digital mammographic imaging conducted to date with broad band x-ray emission from conventional x-ray tubes, users try to take advantage of the increased absorption in the agent, such as iodine, by adjusting the filtering and increasing the electron accelerating voltage to produce sufficient x-ray fluence above the <NUM> keV K absorption edge of iodine. <FIG> shows the mass absorption curves for iodine as a function of x-ray energy. The discontinuous jumps are the L and K absorption edges. The contrast media will offer greater absorption properties if the broad band spectra from conventional sources span an energy range that incorporates these edges. As a result, detectability should improve.

Monochromatic radiation used in the mammographic system discussed here offers many more options for contrast-enhanced imaging. Ordinarily, one can select a fluorescent target to produce a monochromatic energy that just exceeds the iodine absorption edge. In this sense, the monochromatic x-ray emission from the tube is tuned to the absorption characteristics of the contrast agent. To further improve the sensitivity, two separate fluorescent secondary targets may be chosen that will emit monochromatic X-rays with energies that are below and above the absorption edge of the contrast agent. The difference in absorption obtained above and below the edge can further improve the image contrast by effectively removing effects from neighboring tissue where the contrast agent did not accumulate. Note that the majority of x-ray imaging detectors currently used in mammography do not have the energy resolution to discriminate between these two energies if they irradiate the detector simultaneously; these two measurements must be done separately with two different fluorescent targets in succession. This is surely a possibility and is incorporated in our system.

Since the contrast agent enhances the x-ray absorption relative to the surrounding tissue, it is not necessary to select a monochromatic energy above the K edge to maximize absorption. For example, <FIG> shows that the absorption coefficient for the Pd Kα <NUM> keV energy, which is below the K edge, is comparable to the absorption coefficient of the Nd Kα <NUM> keV energy which is above the K edge. As long as the atoms of the contrast agent are sufficiently heavier (atomic number, Z > <NUM>) than the those in the surrounding tissue ( C, O, N, P, S; Z < <NUM> and trace amounts of Fe, Ni, Zn, etc., Z < <NUM>), the monochromatic x-ray technique increases the potential choices for contrast agents in the future. The secondary targets of Pd, Ag and Sn are perfect options for this application. Using monochromatic energies below the absorption edge of iodine, for example, takes better advantage of the quantum absorption efficiency of a typical mammographic imaging detector. The absorption at <NUM> keV (above the iodine edge) is about <NUM> times lower than at <NUM> keV (below the edge). The lower energy may also prove to have better detectability in the surrounding tissue simultaneously. <FIG> shows a linear set of <NUM> drops of Oxilan <NUM>, an approved iodine contrast agent manufactured by Guerbet superimposed on the the ACR phantom. The amount of iodine in each of the drops ~<NUM> iodine.

Having thus described several aspects and embodiments of the technology set forth in the disclosure, it is to be appreciated that various alterations, modifications, and improvements will readily occur to those skilled in the art. For example, those of ordinary skill in the art will readily envision a variety of other means and/or structures for performing the function and/or obtaining the results and/or one or more of the advantages described herein, and each of such variations and/or modifications is deemed to be within the scope of the embodiments described herein. In addition, any combination of two or more features, systems, articles, materials, kits, and/or methods described herein, if such features, systems, articles, materials, kits, and/or methods are not mutually inconsistent, is included within the scope of the present disclosure.

Claim 1:
A carrier (<NUM>) configured for use with a broadband x-ray source comprising an electron source and a primary target (<NUM>) arranged to receive electrons from the electron source to produce broadband x-ray radiation in response to electrons impinging on the primary target (<NUM>), the carrier (<NUM>) comprising:
a housing (<NUM>) configured to be removably coupled to the broadband x-ray source and configured to accommodate a secondary target (<NUM>) capable of producing monochromatic x-ray radiation in response to incident broadband x-ray radiation, the housing (<NUM>) comprising:
a transmissive portion (<NUM>) configured to allow broadband x-ray radiation to be transmitted to the secondary target (<NUM>) when present, and
a blocking portion (<NUM>) configured to absorb broadband x-ray radiation,
wherein the housing (<NUM>) is configured such that, when the secondary target (<NUM>) is accommodated within the housing (<NUM>), at least a first portion of the secondary target (<NUM>) is positioned within the transmissive portion (<NUM>) of the housing (<NUM>) and a second portion of the secondary target (<NUM>) is positioned within the blocking portion (<NUM>) of the housing (<NUM>),
wherein the transmissive portion (<NUM>) comprises a first cylindrical portion (1142a) configured to accommodate the secondary target (<NUM>) and the blocking portion (<NUM>) comprises a second cylindrical portion (1144a) configured to overlap the second portion of the secondary target (<NUM>) when the first cylindrical portion (1142a) accommodates the secondary target (<NUM>), and
wherein the secondary target (<NUM>) is conical.