Structured glass-ceramic scintillators

Abstract

A structured glass-ceramic scintillator (SGCS) and methods of preparing the same are provided. The SGCS comprises a layer comprising a front surface and a back surface. The layer has a plurality of columnar scintillating regions. Each columnar scintillating region comprises a transparent glass-ceramic material. The layer also has a plurality of barrier regions. Each barrier region comprises light-scattering micro- and / or nanocrystals that provide a barrier to light. Neighboring columnar scintillating regions are separated from one another by one of the plurality of barrier regions. An indirect flat panel detector (I-FPD) comprising a SGCS and a readout array are also provided. The readout array comprises thin-film transistor (TFT) switching array and a photodiode pixel array.

Description

[0001] STRUCTURED GLASS-CERAMIC SCINTILLATORS

[0002] PRIORITY

[0003] This application claims benefit of U.S. Provisional Patent Application No. 63 / 655,347 filed with the U.S. Patent and Trademark Office on June 3, 2024, the entire contents of which is incorporated herein by reference.

[0004] TECHNICAL FIELD

[0005] The presently disclosed subject matter relates to structured glass-ceramic scintillators (SGCS), to x-ray imaging systems comprising the SGCS, and to the laser processing of reflective channels into scintillator glasses to create SGCS with increased functionality. For example, in some embodiments, a laser is used to locally crystallize components of an oxyhalide glass matrix in a repeating pattern to create a substantially two-dimensional (2D) array of reflective regions in the glass matrix. The reflective regions provide for thicker materials to be used as intensifier screens for improved radiation capture in digital radiography (DR), while mitigating losses in spatial resolution caused by light spreading, leading to improved efficiency and reduced dose. These improvements can also extend beyond DR, into interventional radiology applications such as cone-beam computed tomography (CBCT) and to improving the contrast of soft tissue at high (MeV) x-ray energies, as in portal imaging for radiation oncology applications.

[0006] OVERVIEW OF THE PRESENTLY DISCLOSED SUBJECT MATTER

[0007] Electronic portal imaging devices (EPIDs), using indirect flat panel detector (LFPD) technology, have become standard in radiation therapy. The x-ray imaging performance of an I- FPD is typically quantified and compared to other detectors according to its detective quantum efficiency (DQE) (1, 2). Unfortunately, the I-FPDs that arecurrently available for portal imaging, typically comprising a terbium-doped gadolinium oxysulfide (GOS) scintillator screen, coupled to a copper buildup plate, have low (~1%) DQE performance at megavoltage (MV) energies (3). There has long been a need for a higher DQE x-ray detector at MV energies. Higher DQE detectors would improve soft tissue contrast resolution in beam’s-eye-view (BEV) imaging applications such as real-time tumor tracking for motion management, (4) and provide for clinically useful mcgavoltagc conc-bcam computed tomography (MV-CBCT) at lower dose (5).

[0008] The presently disclosed subject matter provides a strategy to improve image quality and reduce dose for x-ray imaging applications employing I-FPDs at high energies. According to one aspect, the presently disclosed subject matter provides a novel-structured, glass-based conversion screen that will detect x-rays with MV energies more efficiently. Without being bound to any one theory, such a material incorporated as a conversion layer, coupled with a thin-film transistor (TFT)-based light detector array, can significantly improve the performance of I-FPD systems in portal imaging and MV-CBCT applications (6). The presently disclosed scintillation materials can have thicknesses which are configured to capture a large fraction of otherwise undetected incident radiation, while mitigating light spreading through the use of innovative light-guiding channels, leading to greater DQE. The presently disclosed structured scintillators can serve as practical, low-cost replacements for segmented arrays of individual crystals described in the literature (3-5). The benefits of the presently disclosed subject matter can include, but are not limited to, an order of magnitude increase in DQE over current electronic portal imagers that employ a copper build-up layer and GOS phosphor layer, such as demonstratedin prior studies on thick, segmented crystalline scintillators (3).

[0009] More particularly, according to one aspect of the presently disclosed subject matter, lightchanneling structured glass-ceramic scintillator (SGCS) materials are provided. These materials can be produced through laser processing of oxyhalide or other types of scintillator glasses, as described hereinbelow. In some embodiments, laser pulses (e.g., ultrafast laser pulses), employing a novel (Bessel) beam shape, can be used to induce localized precipitation of lightscattering micro- and / or nanocrystals (e.g., calcium fluoride micro- and / or nanocrystals) within the scintillator glasses in a repeating pattern (7-9). The resultant array of columnar regions with sidewall regions comprising light- scattering micro- and / or nanocrystals can function as optically isolated light guiding channels. The addition of the light-channeling structures can greatly reduce losses in spatial resolution caused by light spreading. In addition, losses in DQE due to depthwise gain variation, “Swank factor” (10), modulation transfer function (MTF) variation, and “Lubberts factor” (11), can be greatly reduced compared to standard granular screens, such as GOS. In some embodiments (e.g., for portal imaging applications), structured screens with thicknesses of about 10 mm to about 40 mm (e.g., 10, 15, 20, 25, 30, 35, or 40 mm) or about 10 mm to about 30 mm and column pitches of about 0.680 to about 1.360 mm (matched to the dimensions of a TFT pixel array intended for use with the structured screen) can be produced. However, other thicknesses and column pitches can be used. In some embodiments, the thickness of the SGCS can be increased to about 40 mm. For instance, in applications using 6 MeV x-rays, a SGCS with a thickness on the order of hundreds of mm could be used. The thickness can also be smaller. For applications involving keV x-rays, a SGCS as thin as about 1 mm can be useful. Thus, in some embodiments, the SGCS can have a thickness of about 1 mm to about 1000 mm. In some embodiments, the SGCS can have a thickness of about 1 mm to about 100 mm. In some embodiments, the SGCS can have a thickness of about 1 mm to about 40 mm. The column pitch can also be altered. Useful column pitches can be between about a few microns to several mm. For example, in some embodiments, column pitch can be about 0.10 mm to about 1.36 mm. In some embodiments, the column pitch can be of use in medical radiography applications involving pixel sizes of about 100 microns.

[0010] In addition, a focused scintillator in which the sidewall projections pass through the x-ray source, can be made. Thus, in some embodiments, a focused SGCS can be provided.

[0011] As described hereinbelow, the light-channeling SGCS materials of the presently disclosed subject matter can be evaluated for use in MV portalimaging applications via various methods. A layer of the SGCS can be aligned with and pressed againsta TFT pixel array of a flat panel imager where the scanning and data-acquisition electronics have beenremoved from the path of the x-ray beam. This imaging system can be exposed to a 6 MV treatment beam from a linear accelerator (LINAC), andmeasurements of MTF and noise power spectrum (NPS) can be made, allowing calculation of the DQE. NPS can be measured, both with and without frame subtraction, providing study of any fixed-pattern noise in the presently disclosed scintillator materials. Radiation hardness measurements can be made. Phantoms can be imaged, including a Las Vegasphantom for contrastdetail and pails of an Alderson Rando phantom for anatomy; these phantoms can reveal potential artifacts and non-uniformities that are not evident from resolution and noise measurements. Finally, since temporal performance is important for MV-CBCT performance, the temporal response can be measured, including afterglow in the glass scintillation pulses and lag in the prototype imaging system. Accordingly, in some embodiments, the presently disclosed subject matter provides a new optical material, a light-channeling glass-ceramic scintillator, for use as an x-ray conversion screen. The presently disclosed scintillator can provide increased performance in MV portal imaging, including improved soft tissue contrast and the enhancement of “beam’ s-eye-view” applications such as real-time motion tracking (4) and can also improve the low-dose performance of MV-CBCT systems (5). Furthermore, additional refinements can lead to improvements in imaging applications using x-rays at kV energies (6) and neutrons (9, 12, 13).

[0012] BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figures la and lb are a pair of schematic diagrams showing differences between (la) conventional thick, transparent x-ray scintillators and (lb) scintillator materials of the presently disclosed subject matter with light-channeling structures. As shown in (la), with thick, transparent x-ray scintillators, there is considerable light spreading that causes blur in the radiographic image. Much of the visible light produced is lost through the sides of the scintillator, due to a process known as “light trapping”, which leads to significant inefficiencies. As shown in (lb), light- scattering structures within the transparent scintillator mitigate issues with light spreading and “light trapping” for greater spatial resolution and efficiency. Note: A thin, reflective coating can optionally be added to the face of the material on the incident x-ray side. The coating can allow light escaping in this direction to be redirected to the detector.

[0014] Figures 2a and 2b are a pair of schematic drawings showing aspects of the presently disclosed structured scintillator material. (2a) shows a wireframe representation of a focused, lightchanneling x-ray conversion screen, indicating the arrangement of the individual light-channeling columnar structures when the material is viewed from the front or back surface. (2b) shows a simplified cross section of the focused screen integrated with an I-FPD (note: not to scale). The source-to-detector distance isgreatly reduced to illustrate basic channel shape. While Figures 2a and 2b show a focused screen, the non-focused screens can also be useful.

[0015] Figures 3a and3b are a pair of schematic drawings showing (3a) a step in the process of preparing the presently disclosed scintillator material wherein laser pulses are directed at a glass scintillator layer positioned on a support stage, and (b) a grid resulting from the laser-induced crystallization of light-scattering micro- and / or nanocrystals when the laser pulses are translated in the glass scintillator material in a predetermined grid pattern. The crystals form the sidewalls (darker grey areas, with thicknesses on the order of microns) of the light guiding channels.

[0016] Figure 4A is a schematic diagram showing a cross section of an exemplary structured glassceramic scintillator (SGCS) of the presently disclosed subject matter where regions of lightscattering centers (i.e., light-scattering micro- and / or nanocrystals, hexagons) form barriers between transparent scintillating regions comprising luminescent centers (circles).

[0017] Figure 4B is a schematic diagram showing a cross section of an exemplary structured glassceramic scintillator (SGCS) similar to that shown in Figure 4A, but also including sensitizers (starshape).

[0018] Figure 4C is a schematic diagram showing a cross section of an exemplary structured glassceramic scintillator (SGCS) similar to that shown in Figure 4A, where the light-scattering centers can also act as luminescent centers (octagons).

[0019] Figure 4D is a schematic diagram showing a cross section of an exemplary structured glassceramic scintillator (SGCS) similar to that shown in Figure 4C, where the light- scattering / luminescent centers (octagons) further include sensitizers (circles).

[0020] Figure 5A is a schematic diagram showing elements of an exemplary single screen configuration of an imaging system including a structured glass-ceramic scintillator (SGCS) of the presently disclosed subject matter. The SGCS is attached to a thin-film transistor (TFT, shown in the figure as “switching elements”) and a photodiode pixel array (shown in the figure as “photosensitive storage elements”) on the incident x-ray side (front irradiation). An optional reflective optical backing can be attached externally to the SGCS.

[0021] Figure 5B is a schematic diagram showing elements of an exemplary single-screen configuration of an imaging system including a structured glass-ceramic scintillator (SGCS) of the presently disclosed subject matter. The SGCS can be attached to a thin-film transistor (TFT, shown in the figure as “switching elements”) and a photodiode pixel array (shown in the figure as “photosensitive storage elements”) opposite the incident x-ray side (back irradiation). An optional reflective optical backing can be attached externally to the SGCS. The configuration shown in Figure 5B corresponds to the configuration shown in Figure 5A, where the x-rays are incident from the opposite direction in use.

[0022] Figure 5C is a schematic diagram showing elements of an exemplary dual-screen configuration of an imaging system including a structured glass-ceramic scintillator (SGCS) of the presently disclosed subject matter. Two SGCSs are attached to a thin-film transistor (TFT, shown in the figure as “switching elements”) and a bidirectional photodiode pixel array (shown in the figure as “photosensitive storage elements”), one on each side. One SGCS serves as the substrate for the TFT and photodiode pixel array. An optional reflective optical backing may be attached externally to the SGCSs.

[0023] Figure 5D is a schematic diagram showing elements of an exemplary configuration of an imaging system including a structured glass-ceramic scintillator (SGCS) of the presently disclosed subject matter. One SGCS is attached to a thin-film transistor (TFT, shown in the figure as “switching elements”) and a bidirectional photodiode pixel array (shown in the figure as “photosensitive storage elements”) opposite to the incident x-ray side (back irradiation), while another scintillator material is attached on the incident x-ray side (front irradiation). The SGCS serves as the substrate for the TFT and photodiode pixel array. An optional reflective optical backing can be attached externally to the SGCS. An optional reflective or absorptive optical backing can be attached externally to the other scintillator material. In use, x-rays can also be incident from the opposite direction.

[0024] Figure 5E is a schematic diagram showing elements of an exemplary configuration of an imaging system including a structured glass-ceramic scintillator (SGCS) of the presently disclosed subject matter. One SGCS is attached to a thin-film transistor (TFT, shown in the figure as “switching elements”) and a bidirectional photodiode pixel array (shown in the figure as “photosensitive storage elements”) opposite to the incident x-ray side (back irradiation), while another scintillator material is attached on the incident x-ray side (front irradiation). The SGCS serves as the substrate for the bidirectional TFT and photodiode pixel array. An additional scintillator material is attached to the SGCS opposite the incident x-ray side. An optional reflective or absorptive optical backing can be attached externally to either of the other scintillator materials. In use, x-rays can also be incident from the other direction.

[0025] Figure 5F is a schematic diagram showing elements of an exemplary configuration of an imaging system including a structured glass-ceramic scintillator (SGCS) of the presently disclosed subject matter. Two SGCSs are attached to a thin-film transistor (TFT, shown in the figure as “switching elements”) and a bidirectional photodiode pixel array (shown in the figure as “photosensitive storage elements”), one on each side. One SGCS serves as the substrate for the bidirectional TFT and photodiode pixel array. Additional scintillator materials are attached to the SGCSs. An optional reflective or absorptive optical backing can be attached externally to either of the other scintillator materials.

[0026] Figure 5G is a schematic diagram showing elements of an exemplary configuration of an imaging system including a structured glass-ceramic scintillator (SGCS) of the presently disclosed subject matter. The SGCS is attached to a thin-film transistor (TFT, shown in the figure as “switching elements”) and a photodiode pixel array (shown in the figure as “photosensitive storage elements”) on the incident x-ray side (front irradiation). Readout arrays are deposited on a glass substrate. An additional scintillator material is attached to the SGCS on the incident x-ray side. An optional reflective or absorptive optical backing can be attached externally to the other scintillator material.

[0027] Figure 5H is a schematic diagram showing elements of an exemplary dual screen configuration of an imaging system including a structured glass-ceramic scintillator (SGCS) of the presently disclosed subject matter. The SGCS is attached to a thin-film transistor (TFT, shown in the figure as “switching elements”) and a photodiode pixel array (shown in the figure as “photosensitive storage elements”) opposite to the incident x-ray side (back irradiation). The readout arrays are deposited on a glass substrate. An additional scintillator material is attached to the SGCS opposite the incident x-ray side. An optional reflective or absorptive optical backing can be attached externally to the other scintillator material. The configuration of Figure 5H corresponds to the configuration of Figure 5G, where the x-rays are incident from the opposite direction in use.

[0028] Figure 6 is a graph showing a series of ramps and soaks for an exemplary heat treatment.

[0029] Figures 7a and 7b are a pair of schematic drawings showing (7a), an experimental I-FPD apparatus of the presently disclosed subject matter; and (7b) a cross section of the apparatus. The apparatus can be used in either a front- or back irradiation configuration.

[0030] Figure 8 illustrates DSC scans at a rate of 1 K per minute for the glass samples containing: (a) 14%, 16%, (c) 18%, (d) 20%, (e) 22%, (f) 24%, (g) 26%, and (h) 28% LaF3.

[0031] Figure 9 illustrates DSC scans at a rate of 1 K per minute for the glass samples containing: (a) 14% CaFo and (b) 14% LaF? crystalline precursor material.

[0032] Figure 10a illustrates a Sample SGCS020 showing laser-induced arrays and Figure 10b is a micrograph of the individual structures (appealing as black dots) found in the Sample SGCS020 arrays demonstrating 20 pm spacing. Note: The regular rectangular array is rotated ~45° in the image.

[0033] Figure 11 illustrates a line array produced by laser processing Sample SGCS027. Note: A blurred reflection of the array can be seen on the backside of the sample.

[0034] REPRESENTATIVE EMBODIMENTS

[0035] The indirect flat panel detector (I-FPD) is the predominant technology currently in use for digital x-ray imaging. High x-ray energies are required for certain applications, such as chest radiography, where 80-120 kVp tube voltages are typical. With portal imaging, the energies are even greater, often exceeding 1 MeV (14, 15). Unfortunately, performance, as measured by detective quantum efficiency (DQE), declines rapidly with increasing x-ray energies when imaging with indirect flat panel detectors (I-FPDs) (16). The highest-performingl-FPDs have relatively poor DQE (-50%) in applications requiring energies of 80 keV or greater (16). The situation at MeV energies is even worse, with electronic portal imaging devices (EPIDs) employing a GOS phosphor plate and a copper buildup layer having a DQE of -1% with a 6 MV beam (3). A higher-DQE MV detector could improve soft tissue contrastresolution in beam’ s-eye- view (BEV) imaging applications such as real-time tumor tracking for motion management, (4) and enable clinically useful MV cone-beam computed tomography (MV-CBCT) at lower dose (5).

[0036] I-FPDs employ a scintillating x-ray conversion screen, which converts x-ray radiation into visible light to be detected by an array of photosensors. Granular or powder screens typically consist of a plastic substrate, a fine layer of phosphor material encapsulated in an optically- transparent plastic matrix, and a thin, optically transparent protective outer layer. Currently, GOS is the most commonly used powder phosphor, due to excellent x-ray attenuation, high conversion gain (number of light quanta released on average per absorbed x-ray), and a principalemission wavelength which is well-matched to the sensitivity of a-Si:H photosensors (550 nm). The thickness has a large effect upon performance, with thicker screens having greater x-ray interaction efficiency at the expense of spatial resolution (17). However, the thickest GOS screen typically used in diagnostic radiology (Lanex Fast Back, 134 mg- cm"2) has only -2% quantum efficiency at 6 MV, leading to a DQE of -1% when it isused as a conversion screen at that energy (3). To overcome limitations in DQE, a number of different approaches investigating higher- DQE detectors for MV imaging have been undertaken (4, 18, 19). In recent year’s, the most successful of these approaches has been the use of arrays of thick, segmented crystalline scintillator arrays comprising individual crystal blocks separated by opaque or reflective septal walls (3-5, 20). A number of scintillator materials have been tried, including CsLTl, Bi4Ge3O12 (BGO), CdWO4, and ZnW04; DQE values ranging from 10 to 25 times that of a conventional MV I-FPD have been demonstrated in laboratory tests. However, the manufacturing process for these arrays is difficult, involving cutting and polishing of the individual scintillation blocks, and gluing together the arrays with the septal walls, and the crystalline materials themselves can be costly and hard to work with. Even with care in assembly, there can be errors in the alignment of the individual blocks of the array.

[0037] Other scintillator materials, such as glass and plastics, have been employed as conversion screens in certain, high-energy x-ray applications (21). However, their poor conversion efficiency requires a relatively thick cross-section to achieve brightness comparable to that of powder scintillators. The required thickness increases blurring of the image and negatively impacts the spatial resolution of the system (22). In addition, much of the scintillation light produced in transparent materials escapes through the sides due to the phenomenon known as light trapping (see Figure la). Attempts to mitigate blurring in thick glass scintillators, by producing them as fiber optic face plates have been unsuccessful due to many factors, including the following: inability to be produced as an array in a scale suitable for radiography, pixel size limited by drawing capability and structural properties of individual fibers, limited fill factor due to cladding thickness, and limitations on glass compositions that can be successfully drawn into fibers (23).

[0038] A recent paper (24) has studied the use of a scintillating glass to replace the crystalline blocks used in the segmented- array approach for MV imaging. The glass is based on a scintillating formulation developed at the Lockheed Marlin company. A large sheet was cut and polished into individual 1.51 mm square blocks, and an array wasglued together with septal walls of aluminized Mylar. The modulation transfer function (MTF) was found to be inferior to the conventional GOS detector (because of the large pixel size), but a significant (8x) improvement in DQE was found.

[0039] According to one aspect of the presently disclosed subject matter, novel light-channeling, glass-ceramic scintillator materials, also referred to herein as SGCSs, are provided.The presently disclosed SGCSs can be prepared with a laser, which can be used to locally nucleate and grow micro- and / or nanocrystals within a scintillator glass in a repeating pattern that surrounds internal sides of each individual light-channeling element with a light-scattering barrier that mitigates the spread of light between adjacent detector pixels (see Figure lb). These light-channeling, glassceramic scintillator materials can provide for the use of thicker cross sections in conversion screens for improved radiation capture with MV x-rays, while, at the same time, mitigating losses in spatial resolution caused by light spreading, leading to improved DQE and reduced dose requirements. Additionally, it is possible to make the walls of these arrays “focused”, i.e. pointed toward the focal spot of the x-ray source (see Figures 2a and 2b), in order to avoid image blurring due to x-rays crossing multiple channels (parallax errors); to date, there has been no demonstration of a focused 2D array using the segmented crystal approach. Compared to the sectioning and reassembling of individual scintillation blocks, the presently disclosed preparation method is distinctively practical, having the ability to produce large-area detector arrays with pixel sizes that canbe made as small as required for different applications. Furthermore, because the scintillator glass is not cut and instead remains continuous, structural integrity is maintained.

[0040] Accordingly, the presently disclosed subject matter provides a new, realistic path forward for the development of high-performance MV x-ray conversion screens. Importantly, both the glass scintillator material and the laser technology to be employed in the construction of the structures can be customized, depending upon the intended application. The presently disclosed scintillator screens can have a profound effect upon portal imaging, MV-CBCT, and other MV x-ray applications that employ an I-FPD.

[0041] As used herein, the term “glass -ceramic” refers to a composite material comprising at least one amorphous and at least one crystalline phase. The presently disclosed SGCSs comprises a scintillating glass-ceramic (i.e., a material comprising luminescent centers) and discrete regions comprising light- scattering centers, where the light- scattering centers comprise light- scattering micro- and / or nano-crystals. The regions of light- scattering centers can include crystals of the same composition or a combination of crystals having different compositions. The light- scattering centers can comprise crystals of approximately the same size or combinations of crystals of different sizes. The luminescent centers can include chemical moieties of the same composition or a combination of moieties of different compositions. In some embodiments, the luminescent centers can comprise crystals (e.g., micro- and / or nanocrystals). In some embodiments, the SGCS can also be doped with a sensitizer.

[0042] The SGCS can be prepared from a precursor glass matrix material that comprises both the luminescent centers and light-scattering centers (or precursors thereof). The glass matrix material can be a material that remains stable, without undergoing devitrification, while hosting both the luminescent centers and light-scattering centers. The glass matrix material can also be stable under the expected operating conditions including, but not limited to, use in a flat panel imaging system. The glass matrix material can also comprise a composition containing desired precursor crystalline elements that are thermally stable enough to precipitate crystallites.

[0043] The glass matrix material can have a high degree of transparency at the wavelength or wavelengths of light expected to be emitted from the luminescent centers, thus preventing or reducing self-absorption. A low phonon energy matrix can be used to increase scintillation efficiency by reducing nonradiative return via multi-phonon energy transfer. In some embodiments, the glass matrix material can also serve as a substrate for flat panel detector electronics, such as a photosensor array. In some embodiments, the matrix material and the SGCS prepared therefrom can have the necessary thermal and mechanical properties, such as, but not limited to, glass transition temperature, crystallization temperature, melting point, elastic modulus, strength, hardness, and impact resistance. In some embodiments, the glass matrix can be based on a composition such as, but not limited to, a halide, an oxide, an oxyhalide, a borate, a telluride, a chalcogenide, a phosphate, a germanate, a silicate, a fluorosilicate, an aluminosilicate, a ^-quartz, a P-spodumenephosphate, and a cordierite.

[0044] The term “luminescent center” as used herein can refer to an intentional imperfection in a material, added in a controlled manner, which gives rise to luminescence when excited by appropriate radiation. Luminescent centers can also be referred to as “activators” (intentionally added to a glass matrix or crystal). Thus, luminescent centers can include elements, ions, or compounds which convert incident radiation into light that can be easily detected, for example, by a flat panel detector (e.g., UV, visible, or infrared light). In some embodiments, the emission spectrum of the luminescent centers can match the quantum efficiency curve of a photosensitive array for increased efficiency.

[0045] There are many chemical moieties or combinations of moieties that can act as luminescent centers, such as, but not limited to, ions from the first and second row of the transition metals (Z (atomic number)=22-30 and 40-48), the rare earth metals (Z=21 , 39, and 57-71 ), the actinides (Z=89-103) or ns2type activators (Z=31, 32, 49-51, 79, and 81-83). Crystalline materials can also serve as the source of emission (luminescent centers). The crystals can be intrinsic or extrinsic scintillators. A combination of scintillating crystals and other materials can also be used for improved light output.

[0046] In an exemplary SGCS, the luminescent centers can be Tb3+ions and the scintillating glass ceramic matrix can comprise Tb2C>3. The percentage of Tb20 in the matrix can be varied depending upon the intended application of the SGCS. In some embodiments, the percentage of Tb2<D3 can be about 6% by weight or mole percentage basis, depending on the composition of the matrix or SGCS as a whole.

[0047] As described hereinabove, the presently disclosed SGCS includes light- scattering centers in addition to the luminescent centers. The term “light- scattering center” as used herein refers to an intentional imperfection in a transparent material, added in a controlled manner, which results in the elastic scattering of light. As described hereinabove, it has been found according to one aspect of the presently disclosed subject matter that preparing a SGCS with regions of lightscattering centers that form barriers between individual columnar transparent scintillating regions can provide enhanced detection efficiency for imaging systems, e.g., both with single-screen configurations and dual-screen configurations. The presence of banner regions of light-scattering centers (e.g., light- scattering micro- and / or nanocrystals) can prevent “light-trapping” of the emission in an imaging system, e.g., situations where a significant portion of the light emitted by luminescent centers is incident at an interface between a scintillating medium and an external medium at an angle greater than the critical angle, resulting in total internal reflection (TIR). The “trapped” light exits the sides of the scintillating medium or is self-absorbed, without being detected, reducing the efficiency of the scintillator / detector system. The critical angle, 0C, is defined by the following equation:

[0048] 9c = sin'1(n2 / ni) where m is the refractive index of the scintillator medium and U2 is the refractive index of the external medium.

[0049] In some embodiments, the presence of the regions of light-scattering centers can redirect light emitted by the luminescent centers to travel within a columnar scintillating region, reducing the “trapping” effect and resulting in increased emission of light that can be detected by a photosensor array.

[0050] Figures la and lb show the difference in the amount of light making it to a detector (e.g., a photosensor array) in a system with structured scintillating material versus an unstructured material. Fig. la shows light paths within an unstructured scintillating medium, whereas Figure lb shows an exemplary SGCS of the presently disclosed subject matter. A larger percentage of the emission is coupled out to the detector, without excessive light spreading, with the structured scintillator. In the figures, the light paths are shown with arrows. The incident radiation is shown with the longer arrow. The detector is on the opposite side of the incident radiation.

[0051] Some examples of crystals that can be precipitated, for instance, within an oxyhalide matrix, or other glass systems, include the following: PbWO4, Yb2TeO6, PbTeO4, TeO2, CdF3, PbF2, BaF2, BaCl2, Bal2, BaBr2, CaF2, SrCl2, LaF3, Na, YF4, YLiF4, GdF3, and TbF3. However, additional oxide, halide, or other types of crystals may be used in the barrier regions of the presently disclosed SGCS (or a combination of different types of crystals can be used). The chemicals, either chemical composition or quantity, required for synthesis should not be detrimental to the formation of precursor glass, i.e. must allow glass formation and not facilitate unwanted crystallization. Oxyhalide glass ceramics also can have a high degree of transparency depending upon crystallite size, which can be controlled via heat- treatment parameters. In an aspect of the disclosure, the crystals should be of a size large enough to enable light scattering at the scintillation emission wavelengths. In some embodiments, the crystals can be larger than about 10 nm. In some embodiments, the size of the crystals can be a function of the scintillation emission wavelengths. In some embodiments, the size of the crystals can be greater than about 1 pm. Thus, the light- scattering crystals can be nanocrystals, microcrystals, or mixtures thereof.

[0052] In some embodiments, the scintillating glass ceramic matrix can further comprise one or more sensitizers. The one or more sensitizers can be selected from ns2type ions and lanthanide ions. Exemplary sensitizers include, but are not limited to, Gd3+and / or Ce3+.

[0053] In some embodiments, the presently disclosed subject matter provides a SGCS, wherein the SGCS comprises a plurality of columnar scintillating regions comprising a transparent glassceramic material, wherein the plurality of columnar scintillating regions are separated from one another by banner regions comprising light- scattering micro- and / or nanocrystals. Either or both of the columnar scintillating regions and the barrier regions can comprise luminescent centers and / or sensitizers. In some embodiments, the SGCS comprises a layer (e.g., a substantially planar layer) comprising a front surface and a back surface, wherein said layer comprises: (a) a plurality of columnar scintillating regions, wherein each of the plurality of columnar scintillating regions extends from the front surface of the layer to the back surface of the layer, and wherein each of the plurality of columnar scintillating regions comprises a transparent glass-ceramic material; and (b) a plurality of barrier regions, wherein each of the plurality of barrier regions comprises lightscattering micro- and / or nanocrystals that provide a barrier to light; and wherein neighboring columnar scintillating regions are separated by one of the plurality of banner regions. The columnar scintillating regions can be arranged in any suitable pattern, including both regular and irregular patterns. Thus, the plurality of columnar scintillating regions can be arranged in a tessellation (e.g., a regular or irre ular grid) when viewed in two dimensions from the front or back surface of the SGCS, as defined by a framework formed by the barrier regions.

[0054] The individual columnar scintillating regions can have any suitable cross-sectional shape, e.g., circle, oval, triangle, square, pentagon, hexagon, octagon, or other polygon, or any suitable cross-sectional size. In some embodiments, each individual columnar’ scintillating region has the same cross-sectional size and / or cross-sectional shape. In some embodiments, the plurality of columnar scintillating regions comprises individual columnar- scintillating regions of different size and / or cross-sectional shape. The size and / or shape of the columnar scintillating regions can be designed to be compatible with a photodiode pixel array intended for use with the SGCS in a particular detection scheme (e.g., imaging system).

[0055] In some embodiments, each of the plurality of columnar scintillating regions has at least three sides, said at least three sides comprising: (a) two exterior sides comprising two opposing sides of each columnar scintillating region, wherein a first exterior side forms part of the front surface of the SGCS and wherein a second exterior side forms part of the back surface of the SGCS; and (b) at least one interior side, wherein each of the at least one interior side is in contact with at least one of the plurality of barrier regions. In some embodiments, each of the plurality of columnar scintillating regions has three, four, five, or six interior sides, and a cross section of each of the plurality of columnar scintillating regions has a shape selected from a triangle, a square, a rectangle, a pentagon, a hexagon, or other polygon. In some embodiments, the columnar scintillating regions of the SGCS are arranged in a regular grid or honeycomb pattern. Figure 4A shows a schematic diagram of a portion of a SGCS of the presently disclosed subject matter where light-scattering centers 15 arc shown by hexagons and luminescent centers 10 by circles. More particularly, Figure 4A shows a cross section of an SGCS where two barrier regions (one near the top and the other at the bottom of the diagram) of light-scattering centers 15 are positioned on either side of a columnar’ scintillating region. Light (solid line) emitted from one of luminescent centers 10 encounters one of light-scattering centers 15 and is scattered (dashed line) along a path back across the columnar scintillating region to encounter another of the lightscattering centers 15 and is then scattered along a path further along the columnar’ scintillating region.

[0056] Figure 4B shows an embodiment where the SGCS further comprises sensitizers 20, shown as a star- shape. The term “sensitizer” as used herein refers to an ion capable of transferring its excitation energy to a neighboring activator, inducing an excited state, resulting in luminescence. In some embodiments, the presence of a sensitizer can improve luminescent efficiency. The energy transfer from the sensitizer 20 to one of the luminescent centers 10 is indicated by the dotted line. Exemplary sensitizers include ns2ions, such as Sb3+and Bi3+; lanthanides, such as Ce3+, Pr3+, Eu2+, Gd3+, Tm3+, and Yb3+, or other ions capable of transferring energy from an excited state to an activator. In some embodiments, the selection of sensitizer can increase x-ray absorption of the scintillating material for increased scintillation efficiency, through increased density and increased average atomic number.

[0057] Any combination of different sensitizing materials can be used. The sensitizer ions, in the form in which they are added to the composition, should be selected so as not to be detrimental to the formation of a precursor glass, e.g., they can allow for glass formation and do not facilitate undesired crystallization, which could unfavorably alter the scintillator’s transparency and / or negatively affect the efficiency of the luminescent centers.

[0058] In some embodiments, the same moiety serves as both a luminescent center and a lightscattering center. See Figure 4C, where combination luminescent and light-scattering centers 15A are shown as octagons. Crystals can be either intrinsic or extrinsic scintillator materials. For example, halide crystals can be used as both luminescent centers 10 and light- scattering centers 15 in ceramics used in x-ray conversion. There is a strong affinity of rare earth ions for halide anions, so that they can be easily incorporated as an activator material. The low phonon energy of the halide crystals makes for an efficient host for improved scintillation efficiency. For example, certain crystals, such as the halide crystals described above, doped or undoped with an activator, such as Eu2+, can serve as both scattering centers and luminescent centers, for example BaCh:Eu2+and BaCh; other, non-halide crystals, such Y3AI5O12, ZmSiCU, and PbWCE could also serve as both luminescent and scatterings centers. Sensitizers 20 can also be used with the luminescent / scattering centers 15A in the SGCS as shown in Fig. 4D.

[0059] In an aspect of the disclosure, the SGCS has sufficient density, such as about 3.0 g em-3, and appropriate elemental composition to provide efficient absorption of incident radiation. The composition of the SGCS can be tuned for a particular type of incident radiation. In some embodiments, the SGCS comprises a high-Z element. A high-Z element used herein refers to any element with an atomic number greater than or equal to 64.

[0060] According to another aspect of the presently disclosed subject matter, the presently disclosed SGCSs can be combined in an imaging apparatus, e.g., an I-FPD system, and used in imaging methods, e.g., in MV imaging. The x-ray conversion screens can be tested, for example, using a I-FPD apparatus as disclosed herein underMeV (6 MV) imaging conditions, using a medical linear accelerator (LINAC) source. The improvements in spatial resolution, sensitivity, and the DQE of the systems can be assessed. Exemplary configurations of single- and dual-screen imaging systems are shown in Figures 5A-5H. In some embodiments, the presently disclosed subject matter provides an imaging system comprising a SGCS as described hereinabove and further comprising a readout array, wherein the readout array comprises thin-film transistor (TFT) switching array and a photodiode pixel array, optionally wherein the readout array further comprises a glass substrate.

[0061] In some embodiments, the presently disclosed subject matter provides a method of producing an SGCS. In some embodiments, the method includes laser processing of x-ray conversion screens. Laser processing parameters and the chemical composition of the scintillator glass can be varied.

[0062] As noted hereinabove, according to the presently disclosed subject matter, a laser is used to locally nucleate and grow light-scattering micro- and / or nanocrystals within the scintillator glasses along a grid (see Figures 3a and 3b) or other repeating pattern (e.g., a honeycomb or other tessellation) to create light-channeling arrays in scintillator glasses. Laser-induced crystallization in glasses can be used with a wide variety of glass compositions (25-29). The laser irradiation causes localized heating, resulting in controlled crystallization with precise spatial positioning. Ultrafast laser pulses suppress thermal diffusion and accordingly confine high repetition rate, heat- induccd changes to very narrow regions around the laser focal volume. However, forming the grid of light- scattering micro- and / or nanocrystalsby tracing a focused Gaussian laser beam throughout the volume of a thick scintillator glass can be time-consuming and can suffer from the effects of spherical aberration that change laser focal spot size and shape, thus distorting the focal intensity distribution (30, 31). In some embodiments, according to the presently disclosed subject matter, an expedited and aberration-insensitive tracing of the light- scattering grid can be achieved by focusing a Gaussian laser beam through an axicon lens to form a Bessel beam with a long axial depth extending hundreds of micrometers inside the glass (30, 32). In some embodiments, structured screens with thicknesses of 10-30 mm and column pitches of 0.68 and 1.36 mm, matched to the dimensions of the TFT pixel array, with sizes appropriate for image quality testing, can be produced. Other thicknesses and column pitches are also contemplated. In some embodiments, column pitch can be about 0.10 mm to about 1.36 mm. In addition, in some embodiments, a focused scintillator can be produced.

[0063] Although its focal length can extend several hundreds of microns, the Bessel beam cannot modify material throughout thicknesses of glass substrates that exceed the extent of the Bessel beam’s focus for a given axial (Z) focal position. However, it is possible to stitch overlapping Bessel-beam foci axially in Z-layers as well as laterally, to create a three-dimensional grid pattern throughout the bulk of the glass substrate. This is accomplished layer-wise by starting with the focus positioned at the bottom surface (where the top surface is the incident surface), tracing the desired grid pattern, and then following the same lateral grid pattern after translating a significant percentage of the Bessel-beam focal extent in Z towards the top surface, so that the newly positioned focal region contiguously overlaps with the previous layer. The process is repeated until the grid has been scribed throughout the entire substrate thickness. Beginning the layering process from the bottom surface avoids focal disruption by already -modified substrate material.

[0064] In some embodiments, the glass matrix for use in the presently disclosed SGCS is an oxyhalide glass. In some embodiments, the oxyhalide glass can have a composition of 34.OB2O3- 23.0Li20-6.0Tb203-5.0Si02-22.0CaF2-10.0GdF3 on a mole percentage basis or similar. Laser- induced crystallization has been shown in oxyhalide glasses in the literature, with the differences in bonding (covalent foroxygen and ionic for halides) aiding phase separation (27, 28). In some embodiments, the scintillator glass is based upon a composition developed by Applebee et al. (e.g., 56.7B2O3-25.8Li2O-2.5(2LiF)-15BaCl2:Eu2+0.005-0.5 mol % EuCb 4 mol% SiO2(33, 34). These glass systems have many favorable properties, including low phonon energy for increased scintillation efficiency, and the ability to host a large percentage of rare earth elements (35-37). The transparency of the oxyhalide matrix limits self-absorption of the emission (38). Gadolinium is a well-known sensitizer and increases the x-ray absorption of the glass (36, 39). Trivalent terbium is a bright scintillator with a favorable emission spectrum that is well- suited for the photodiodes in flat panel detectors (40, 41). Laser-induced precipitation of calcium fluoride has been reported in the literature (7, 28); these precipitated calcium fluoride crystals can serve as light-scattering centers and constitute the barrier regions in the SGCS materials. In addition, calcium fluoride is a known scintillator, meaning that its presence will not overtly affect the x-ray sensitivity of each pixel, i.e., it will not constitute “dead space” (42, 43); if prudent, the brightness of calcium fluoride can be enhanced through europium doping (9). The glass composition can be adjusted as needed to facilitate controlled localized crystallization.

[0065] In some embodiments, the scintillator glasses can be made using melt-quench methods. The raw powders can be prepared, for example, in an argon atmosphere glovebox (MBraun Labmaster SP) and heated within a platinum crucible inside an attached tube furnace (MTI OTF- 1200X) to avoid contamination. In some embodiments, the molten glass can be poured into a temperature-controlled mold to allow the glass to quickly solidify and then cool slowly to room temperature to avoid thermal shock.

[0066] Basic characterization of the as-made glass can be performed to inform the laser-induced crystallization process. Thermal properties including glass transition and crystallization temperature can be determined via differential scanning calorimetry (Nctzsch 200 F3 Maia DSC). Transmission properties can be determined by spectrophotometry (GenTech Scientific TU-1901 double beam ultraviolet / visible light spectrophotometer). Density, composition, and data for elemental media from NIST can be used to determine the x-ray attenuation coefficient for each sample at relevant energies.

[0067] In some embodiments, ultrafast laser pulses are used to induce highly localized nucleation and growth of light- scattering calcium fluoride crystals within the glass matrix in a repeating 2D pattern. In some embodiments, samples can be laser-processed using a Coherent RegA 9000 Ti:Sapphire amplified femtosecond laser emitting 5 pJ, 160 fs, 790 nm pulses at rates up to 250 kHz. Different optical microscope objectives, with numerical aperture values ranging from 0.2 to 0.8, can be considered for focusing a Gaussian laser beam inside the glass matrix. If needed, the energy per pulse can be reduced using a neutral density filter, and the pulse repetition rate can be reduced electronically, to limit excessive heat accumulation effects along the laser traced path. In some embodiments, samples can be prepared using the 20 W Amplitude Systemes TANGERINE laser emitting 100 pJ, 0.3-10 ps, 1030 nm pulses at rates up to 0.2-2 MHz; second harmonic generation (SHG) 515 nm radiation can also be used. These higher energy pulses can be shaped into a Bessel-beam with a 1 pm wide, 500 pm long central lobe to enable expedited laser processing (32). In some embodiments, pulse duration and repetition rate can be adjusted electronically to limit excessive heat accumulation effects along the laser-traced pattern, allowing for precision control of barrier wall thickness. For both Gaussian and Bessel beams, dynamic exposure to the ultrafast laser radiation can be performed by translating the focused laser radiation inside the glass substrate at different speeds, in the about 10 to about 1000 pm / s range. In some embodiments, optical design software (e.g., ZEMAX OpticStudio optical design software) can be used to estimate the variation of spherical aberration of the laser focus with sample depth (44). In some embodiments, dynamic aberration correction can be carried out using a spatial light modulator (45-47).

[0068] In some embodiments, focused scintillators can be formed with the help of atilt stage. The inclination of each line of the light- sc altering grid, calculated as a function of the desired focal distance of the scintillator, can be used to calculate the corresponding angle of incidence of the Bessel beam using Snell’s law of refraction. For each line of the light- scattering grid, the correct angle of incidence of the Bessel beam can be set via tilt stage during laser processing.

[0069] In some embodiments, the SGCSs can be characterized to understand the relationships between processing parameters and material properties, leading to improved process control. The crystalline phase can be verified by a variety of methods known in the art, including, but not limited to, x-ray diffraction (XRD), electron diffraction spectroscopy (EDS), and phosphorimetry via the characteristic emission of calcium fluoride. In some embodiments, phosphorimetry can confirm emissionfrom trivalent terbium. In some embodiments, the 2D dimensions of the arrays can be verified by brightfield, darkfield, and / or differentialinterference contrast (DIC) optical microscopy. In some embodiments, the size, distribution, and morphology of the crystallites can be determined by optical or electron microscopy. In some embodiments, the presently disclosed light-channeling SGCSs can be performance-tested in imaging applications and relationships between processing parameters and material properties of the structured glass-ceramic scintillators can be determined. The understanding of these relationships, along with performance feedback, can provide for customization of these materials for each x-ray conversion screen application. If desired, additional glass and glass-ceramic scintillator materials can be produced based upon other matrices (48-53).

[0070] The laser-processed glass can possibly become stressed after the calcium fluoride crystals form. In addition, in some embodiments, it can be desirable to alter the size distribution of said crystals in order to modify their light-scattering function. In some embodiments, these issues can be modified by post heat treatments. The heat treatments can include, for instance, one or more ramps (heating or cooling at a prescribed rate) and soaks (also known as isothermals or dwells) at a particular temperature. The parameters can be based upon the results of thermal analysis techniques, such as differential scanning calorimetry, or trial- and-error, or a combination of the two. Figure 6 shows an exemplary heat treatment comprising a series of ramps and soaks.

[0071] Rather than precipitate crystals, in some embodiments, the laser system can be used to create an array of defects in the glass material, which can serve as nucleation sites and can result in an array of crystalline regions upon subsequent heat treatment. These heat treatments can include one or more ramps and soaks. The parameters can be based upon the results of thermal analysis techniques, such as differential scanning calorimetry, or trial-and-error, or a combination of the two.

[0072] Non-negligible CaF2 nucleation and growth by exposure to sidelobes of the Bessel beam can affect the point spread function of the individual light-channeling elements and can set a lower limit to the size of the pixel formed. However, because crystallization is thermally-induced rather than optically-induced, crystallization does not necessarily occur at the sidelobes. In some embodiments, Bessel-beam laser processing can be performed using laser energy pulse values that minimize CaF2 nucleation and growth caused by sidelobes.

[0073] According to an aspect of the presently disclosed subject matter, the light-channeling SGCSs can be evaluated as lower-cost, focusable replacements for segmented crystalline scintillators in megavoltage imaging applications. In some embodiments, the area-averaged brightness of SGCS can be measured separately using previous methods (6). Based on experience with similarly formulated glasses developed for keV imaging (6), an average conversion gain of 4000-5000 photons / McV or greater can be expected, which can be more than sufficient to avoid problems with secondary quantum noise. It is also desirable that the conversion gain be sufficient to overcome electronic pixel readout noise, at the doses to be used. In some embodiments, X-ray emission spectra can also be measured.

[0074] In some embodiments, studies can be performed to assess the radiation hardness of the SGCSs. Briefly, glass samples can be placed in the beam path of a linear accelerator and exposed to doses up to 5 Mrad. Transmission can be measured before and after exposure, with a spectrophotometer. Sensitivity can be measured before and after exposure, using an I-FPD apparatus. If a change in transmission (discoloration) is noted, the issue can be mitigated via compositional changes and / or optical bleaching (54).

[0075] In some embodiments, a medical linear accelerator (LINAC) at 6 MV can be used as the source, for the imaging performance measurements. A custom modular I-FPD apparatus (which allows for both front and back x-ray irradiation), where the scanning and data acquisition electronics have been moved out of the path of the x-ray beam, and which has been employed in previous studies (6, 16) can be used. A schematic diagram of an exemplary I-FPD apparatus for use in assessing SGCSs is shown in Figures 7a and 7b. SGCSs of the presently disclosed subject matter can bealigned with the gate and data lines of the TFT array and pressed against the I-FPD using the compression foam, as shown in Figure 7b. Fine alignment adjustment can be done using flat- fieldimages.

[0076] The readout timing of the I-FPD can be synchronized with the timing of the x-ray pulses produced by the LINAC, in order to achieve delivery of a constant number of LINAC pulses per image frame (e.g., 1-4), and to enable the readout of several consecutive frames for lag measurements.

[0077] In some embodiments, SGCSs can be produced with two different pixel pitches (0.68 and 1.36 mm), corresponding to 8 x 8 and 16 x 16 binning of the I-FPD pixels, to study the effect on measured MTF and overall image quality. The effect of thickness on measured DQE can be determined using samples with thicknesses of 10, 20, and 30 mm. In addition, at least one focused array can be tested to demonstrate the effect of focusing on MTF and overall image quality. The effect of back versus front x-ray irradiation on image quality can also be studied. This effect has been shown to be substantial for kV imaging (16) but has not typically been studied for MV imaging.

[0078] In some embodiments, large-area signal response versus x-ray exposure (sensitivity) can be measured, as well as MTF and NNPS (normalized noise power spectrum). In view of the intended application, the scintillator structures can have pixel pitches of 0.68 and 1.36 mm, so the sampling requirements for MTF and NPS (noise power spectrum) are relaxed compared to previous work on diagnostic imaging at kV energies. Methods developed previously for these measurements (6, 16, 55) can be used. Without being bound to any one theory, the line spread function (LSF) is expected to be a rectangular function of width equal to the column width, with additional spreading effects due to light spreading between the columns. The LSF can be measured directly by using a slit source aligned with the pixel walls and sampling the LSF at the pitch of the I-FPD (85 pm). The MTF is taken as the modulus of the fast Fourier transform of the LSF.

[0079] At the same x-ray exposure level used for the MTF results, the NNPS can be measured. The noise measurements can be done using a large number of pairs of flood images. A 64 x 64-pixel region of interest (RO I) can be taken from each image and offset and gain-corrected for variations in the pixel response of the I-FPD. The ROIs can be further corrected (linearized), based on the x- ray system response curve (above). Before Fourier analysis, signal differences can be formed by pixelwise subtracting the signals from two successive frames. This can have the effect of subtracting any fixed pattern noise from the DQE results. 2D Fourier transforms can be performed on the corrected and linearized ROI signal difference data, and these can be used to calculate ID NPS curves. The NPS can then be divided by the square of the average signal output (and an additional factor of two to account for the doubling of variance in the frame subtraction process) to obtain the NNPS. Given this data, the DQE can be obtained. These results can be compared to published data for the MTF, NPS, and DQE of commercial EPIDs (e.g. AS-1200) (56), other segmented array imagers (3-5), and multi-layer EPIDs (20).

[0080] In addition, in some embodiments, the flat-field noise power at low and high exposure levels can be measured, allowing study of spatially varying detector response (structure noise). In some embodiments, imaging can be performed using a Las Vegas phantom for contrast-detail and parts of an Alderson Rando phantom for anatomy, which can reveal potential artifacts and non-uniformities that would not be evident from resolution and noise measurements. Since temporal performance is important for MV-CBCT performance, measurement of the temporal response, including afterglow in the glass scintillation pulses and lag in the prototype imaging system, can be assessed.

[0081] Performance results can be used for customizing of the scintillator materials for megavoltage imaging applications. Without being bound to any one theory, the presently disclosed subject matter provides an order of magnitude improvement in DQE over that obtained in conventional megavoltage detectors comprising a copper plate and GOS phosphor screen. This can improve the visualization of soft tissue in radiotherapy imaging using the treatment beam.

[0082] The presently disclosed subject matter can reach comparable performance to other segmented array imagers in the literature (3-5, 20). The upper limit to DQE(O) is defined by the scintillator’s x-ray quantum efficiency (QE). The average photon cncrgyat 6 MV is ~1.5 MeV (57). The presently disclosed glass has a linear attenuation coefficient of 0.196 cm’1at this energy (assuming p = 4 g / cm3and omitting coherent scatter), which corresponds to 18, 33, 45, and 54% QE at 10, 20, 30, and 40mm thicknesses. Without being bound to any one theory, lower DQE(0) than this theoretical maximum is expected due to Swank noise (10). This noise has been discussed previously (58, 59). Based on these figures, the DQE(0) can be about 0.3-0.5 times its QE, which corresponds to about 5-27% DQE(0) for 10-40 mm thickness. This is approximately a 5-to-27-fold improvement over current commercial EPIDs. Accordingly, as a conservative estimate, the presently disclosed subject matter can, in some embodiments, provide DQE(0) > 10% at 6 MV, which is an order of magnitude improvement overpresent electronic portal imagers employing a copper build-up layer and GOS phosphor layer. For MTF, an MTF(0.5 cy / mm) > 0.3 can be achieved due to the potential for focused arrays with relatively small pixels.

[0083] In some embodiments of the presently disclosed subject matter, while concurrently functioning as a scintillator, the structured glass-ceramic scintillator can eliminate or greatly reduce radiation damage to materials and / or equipment when the structured glass-ceramic scintillator is placed between the radiation source and the materials and / or equipment.

[0084] In some embodiments of the presently disclosed subject matter, localized non-crystalline defects produced by laser processing may also act as light scattering centers and may therefore also be used to construct light-guiding arrays. The resulting amorphous materials would have the same functionality and serve the same purpose as structured glass-ceramic scintillators previously described. The localized non-crystalline defects may vary from the surrounding glass matrix by composition and / or density.

[0085] By way of example with regard to composition, but without limitation, “high laser intensity in the focal volume induces nonlinear absorption of the laser energy by the material via multiphoton, tunneling, and avalanche ionization. If sufficient laser energy is deposited, permanent structural changes are produced inside a glassy material at the location of the laser focus.” Madhar NA, Varma KBR. Spinodal Decomposition in Tellurite-Based Glasses Induced by Excimer Laser Irradiation. Journal of the American Ceramic Society. 2009;92(l l):2609-15. doi: https: / / doi.Org / 10.l l l l / j.1551-2916.2009.03269.x. By way of example with regard to composition, but without limitation, “amorphous phase separation (APS) causes an initially homogeneous single-phase glass to separate into two or more phases of different compositions. The Gibbs free energy of the system with two or more distinct phases has to be lower than that of the system with one single homogeneous phase. The degree of interconnectivity of the two glass phases depends on the nature of the phase separation mechanism. This process can occur by a nucleation and growth process (which gives isolated spherical particles) or by spinodal decomposition where an interconnected structure is obtained.” Lizzi F, Goutaudier C, Attik N, Jackson P, Campbell I, Mokbel I, Grosgogeat B, Villat C. Ion release characterization in phase separated borosilicate glass powders. Journal of Non-Crystalline Solids. 2020;534: 119934. doi: https: / / doi.Org / 10.1016 / j.jnoncrysol.2020.119934.

[0086] By way of example with regard to density, but without limitation, within the affected zone, localized heating may relieve intrinsic stresses, found in the glass matrix, which were produced during the melt-quench process used for synthesizing the glass. Conversely, the localized heating may induce stress concentrations within the glass matrix. These differences in stress between the affected area and the remainder of the glass matrix can result in a difference in density between the two. Stress is related to dimensional changes, also known as strain, via the elastic modulus; for a given mass quantity of material, any volumetric change will result in a density change, as well. The amorphous phase separation, mentioned above, can also result in local differences in density.

[0087] In some embodiments of the presently disclosed subject matter, the choice of crystalline precursor material in the glass, for example LaF-, versus CaF , can greatly affect the stability of the glass, which can be verified using differential scanning calorimetry. These precursors are also discussed elsewhere herein. In some embodiments of the presently disclosed subject matter, the amount of crystalline precursor material in the glass, can alter the crystallization temperature of the glass. This amount can be tailored to produce high quality glass samples, free of crystalline defects, with relatively low crystallization temperatures for improved laser processing ability. By way of elaboration and not limitation, a study was performed where eight terbium-doped borosilicate glass samples were synthesized according to the following composition, on a mole percentage basis, with x being 14, 16, 18, 20, 22, 24, 26 and 28:

[0088] (56-x)B2O3+ 5SiO2+ 10GdF3+ 6TbF3+ 23Li2O + xLaF3

[0089] The amount of LaF3precursor material in the glass had a clear affect on both the glass transition onset temperature (Tg) and the onset of crystallization (Tx), shown in Figure 8. Figure 8 shows DSC scans at a rate of 1 K per minute for the glass samples containing: (a) 14%, 16%, (c) 18%, (d) 20%, (e) 22%, (f) 24%, (g) 26%, and (h) 28% LaF3.

[0090] The Txis important as it affects the laser processing parameters required to induce crystallization in the glass material. A decreased Txmay indicate improved manufacturability, because lesser pulse energy and / or a decreased number of pulses may be necessary to produce the crystalline arrays.

[0091] The difference between Txand Tg(Tx- Tg) is one measure of glass stability (see Table 1). Smaller temperature differences are indicative of less stable glasses. Less stable glasses can be undesirable as the glass can spontaneously crystallize during synthesis, as was the case for the sample containing 28% LaF3; controlled crystallization is needed for this application. The thermal properties of the glass can be tailored by altering the amount of LaF3(or other crystalline precursor) in the composition to yield a balance between stability and improved manufacturability.

[0092] T The choice of crystalline precursor can also affect the thermal properties of the glass. Two tcrbium-dopcd borosilicate glass samples with the following compositions were compared:

[0093] 47B2O3+ 5SiO2+ 10GdF3+ lTbF3+ 23Li2O + 14CaF2and

[0094] 47B2O3+ 5SiO2+ 10GdF3+ lTbF3+ 23Li2O + 14LaF3

[0095] As shown in Figure 9, both Txand Tgare affected by the choice of crystalline precursor. Figure 9 shows DSC scans at a rate of 1 K per minute for the glass samples containing: (a) 14% CaF2and (b) 14% LaF3crystalline precursor material.

[0096] LASER PROCESSING

[0097] Beam Characteristics for Both Tests

[0098] Beam Shape: Bessel

[0099] Beam Diameter: Approximately 1 pm

[0100] Axial Length: 500 pm

[0101] Wavelength: 1030 nm

[0102] Pulse Rate: 100 kHz

[0103] Beam Polarization: Circular

[0104] Laser Parameters and Characteristics of Structures found in Sample SGCS020

[0105] Sub-Array Size: 1.5 mm x 1.5 mm

[0106] Spacing between Sub-Arrays: 1.25 mm spacing in X and Y

[0107] Spacing between Exposures within Arrays: 20 pm in X and Y

[0108] Settle Time: 50 ms settle time between movement and pulse firing

[0109] Exposure Conditions: 1 ps / 20 pJ, 2 ps / 22 pj, or 5 ps / 25 pJ (column-wise)

[0110] Pulses per Row: 100, 1000, or 10,000

[0111] Figure 10a illustrates a Sample SGCS020 showing laser-induced arrays and Figure 10b illustrates a micrograph of the individual structures (appealing as black dots) found in the Sample SGCS020 arrays demonstrating 20 pm spacing. Note: The regular rectangular array is rotated -45° in the image. Laser Parameters and Characteristics of Structures found in Sample SGCS027

[0112] Line Array Size: 2 mm long (X) x 1 mm wide (Y)

[0113] Spacing in Y Direction: 5 pm

[0114] Translation Velocity in X Direction: 1000 m / s

[0115] Pulse Length: 2 ps

[0116] Burst: 3-pulse burst (25 ns sub-pulse separations)

[0117] Pulse Energy: 35 pJ

[0118] Figure 11 illustrates a line array produced by laser processing Sample SGCS027. Note: A blurred reflection of the array can be seen on the backside of the sample.

[0119] Definitions

[0120] While the following terms are believed to be well-understood by one of ordinary skill in the ait, the following definitions are set forth to facilitate explanation of the presently disclosed subject matter.

[0121] Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood to one of ordinary skill in the ail to which the presently disclosed subject matter belongs.

[0122] Following long-standing patent law convention, the terms “a”, “an”, and “the” refer to “one or more” when used in this application, including the claims.

[0123] The term “and / or” when used in describing two or more items or conditions, refers to situations where all named items or conditions are present or applicable, or to situations wherein only one (or less than all) of the items or conditions is present or applicable.

[0124] The use of the term “or” in the claims is used to mean “and / or” unless explicitly indicated to refer to alternatives only or the alternatives are mutually exclusive, although the disclosure supports a definition that refers to only alternatives and “and / or.” As used herein “another” can mean at least a second or more.

[0125] The term “comprising”, which is synonymous with “including,” “containing,” or “characterized by” is inclusive or open-ended and does not exclude additional, unrecited elements or method steps. “Comprising” is a term of art used in claim language which means that the named elements arc essential, but other elements can be added and still form a construct within the scope of the claim.

[0126] As used herein, the phrase “consisting of’ excludes any element, step, or ingredient not specified in the claim. When the phrase “consists of’ appears in a clause of the body of a claim, rather than immediately following the preamble, it limits only the element set forth in that clause; other elements are not excluded from the claim as a whole.

[0127] As used herein, the phrase “consisting essentially of’ limits the scope of a claim to the specified materials or steps, plus those that do not materially affect the basic and novel characteristic(s) of the claimed subject matter.

[0128] With respect to the terms “comprising”, “consisting of’, and “consisting essentially of’, where one of these three terms is used herein, the presently disclosed and claimed subject matter can include the use of either of the other two terms.

[0129] Unless otherwise indicated, all numbers expressing quantities of time, temperature, light output, atomic (at) or mole (mol) percentage (%), and so forth used in the specification and claims are to be understood as being modified in all instances by the term “about”. Accordingly, unless indicated to the contrary, the numerical parameters set forth in this specification and attached claims are approximations that can vary depending upon the desired properties sought to be obtained by the presently disclosed subject matter.

[0130] As used herein, the term “about”, when referring to a value is meant to encompass variations of in one example ±20% or ±10%, in another example ±5%, in another example ±1%, and in still another example ±0.1% from the specified amount, as such variations are appropriate to perform the disclosed methods.

[0131] Numerical ranges recited herein by endpoints include all numbers and fractions subsumed within that range (e.g. 1 to 5 includes 1, 1.5, 2, 2.75, 3, 3.90, 4, 4.24, and 5). Similarly, numerical ranges recited herein by endpoints include subranges subsumed within that range (e.g. 1 to 5 includes 1-1.5, 1.5-2, 2-2.75, 2.75-3, 3-3.90, 3.90-4, 4-4.24, 4.24-5, 2-5, 3-5, 1-4, and 2-4).

[0132] The term “scintillator” refers to a material that emits light (e.g., visible light) in response to excitation by ionizing radiation (e.g., x-ray, a, |3, or y radiation). REFERENCES

[0133] All references listed herein, including but not limited to all patents, patent applications and publications thereof, scientific journal articles, conference papers, and books, are incorporated herein by reference in their entireties to the extent that they supplement, explain, provide a background for, or teach methodology, techniques, and / or compositions employed herein.

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[0167] It will be understood that various details of the presently disclosed subject matter may be changed without departing from the scope of the presently disclosed subject matter. Furthermore, the foregoing description is for the purpose of illustration only, and not for the purpose of limitation.

Claims

What is claimed is:

1. A structured glass-ceramic scintillator (SGCS), wherein the SGCS comprises a layer comprising a front surface and a back surface, wherein said layer comprises:(a) a plurality of columnar scintillating regions, wherein each of the plurality of columnar scintillating regions comprises a transparent glass-ceramic material; and(b) a plurality of bander regions, wherein each of the plurality of banier regions comprises light-scattering micro- and / or nanocrystals that provide a barrier to light; and wherein neighboring columnar scintillating regions are separated from one another by one of the plurality of banier regions.

2. The SGCS of claim 1, wherein the plurality of columnar scintillating regions is arranged in a regular pattern defined by the plurality of barrier regions.

3. The SGCS of claim 1 or claim 2, wherein each of the plurality of columnar scintillating regions has at least three sides, said at least three sides comprising: two exterior sides comprising two opposing sides of each columnar scintillating region, wherein a first exterior side forms part of the front surface of the SGCS and wherein a second exterior side forms part of the back surface of the SGCS; and at least one interior side, wherein each of the at least one interior side is in contact with at least one of the plurality of barrier regions.

4. The SGCS of claim 3, wherein each of the plurality of columnar scintillating regions has three, four, five, or six interior sides, and a cross-section of each of the plurality of columnar scintillating regions has a shape selected from a triangle, a square, a rectangle, a pentagon, a hexagon, or another polygon.

5. The SGCS of any one of claims 1-4, wherein the SGCS has a thickness of about 1 millimeter (mm) to about 100 mm.

6. The SGCS of any one of claims 1-5, wherein each columnar scintillating region has a column pitch of about 0.10 mm to about 1.36 mm.

7. The SGCS of any one of claims 1-6, wherein the SGCS is a focused SGCS.

8. The SGCS of any one of claims 1-7, wherein the transparent glass-ceramic material comprises a glass matrix selected from the group consisting of a halide, an oxide, an oxyhalide, a telluride, a chalcogenide, a phosphate, a germanate, a silicate, a fluorosilicate, an aluminosilicate, P-quartz, |3-spodumenephosphate, and a cordierite.

9. The SGCS of claim 8, wherein the transparent glass-ceramic material comprises an oxyhalide, optionally wherein the oxyhalide comprises boron oxide (B2O3), lithium oxide (LioO), terbium (III) oxide (TbsOa), silicon dioxide (SiO ), calcium fluoride (CaFa), lanthanum fluoride (LaFa), and / or gadolinium fluoride (GdFri; further optionally wherein the glass material comprises B2O3:Li2O:Tb2O3:SiO2:CaF2:GdF3 in a molar percentage ratio of about 34.0:23.0:6.0:5.0:22.0:10.0.

10. The SGCS of any one of claims 1-9, wherein the light- scattering micro- and / or nanocrystals comprise calcium fluoride micro- and / or nanocrystals.

11. The SGCS of any one of claims 1-10, wherein the barrier region has a thickness of about a 1 nanometer (nm) to about 100 micrometers (pm),12. The SGCS of any one of claims 1-11, wherein the SGCS is for use in digital x-ray imaging, optionally in an indirect flat panel detector (I-FPD), further optionally wherein the I-FPD is for use in portal imaging, megavoltage cone-beam computed tomography (MV-CBCT), or another megavoltage (MV) x-ray application.

13. An indirect flat panel detector (I-FPD) comprising the SGCS of any one of claims 1-2, and further comprising a readout array, wherein the readout array comprises thin-film transistor (TFT)switching array and a photodiode pixel array, optionally wherein the readout array further comprises a glass substrate.

14. A method of preparing a SGCS of any one of claims 1-12, wherein the method comprises:(a) providing a layer of a scintillator glass, optionally an oxyhalide scintillator glass; and(b) forming regions of micro- and / or nanocrystals in the layer from (a) by translating laser pulses, optionally about 0.1 picosecond (ps) to about 10 ps laser pulses, inside the layer from (a) in a predetermined pattern, thereby inducing nucleation and crystal growth in select regions of the layer that correspond to the predetermined pattern.

15. The method of claim 14, wherein step (b) is performed by focusing a Gaussian laser beam though an axicon lens to form a Bessel beam with a long axial length extending inside the layer from (a).

16. The method of claim 15, wherein the Bessel beam has a central lobe that is about 1 micrometer (pm) wide and about 500 pm long.

17. The method of any one of claims 14-16, wherein the laser pulses comprise about 500 to about 1100 nanometer (nm) pulses at rates of about 0.02 to about 2.0 megahertz (MHz).

18. The method of any one of claims 14-17, wherein the laser pulses are translated in the predetermined pattern inside the glass at a speed of about 10 micrometer per second (pm / s) to about 1000 pm / s.

19. The method of any one of claims 14-18, wherein step (a) comprises preparing the layer of the scintillator glass, optionally wherein the preparing comprises doping a scintillator glass with a sensitizer.

20. The method of claim 19, wherein the preparing comprises mixing raw powders of scintillator glass precursors in a predetermined ratio to provide mixed raw powders; heating themixed raw powders to provide a molten glass; and pouring the molten glass into a mold, optionally a temperature-controlled mold.

21. The method of any one of claims 14-20, wherein the method further comprises performing a heat treatment following step (b) to alter the size distribution of the micro- and / or nanocrystals.

22. A method of performing digital x-ray imaging using a lower x-ray dose and / or with greater detective quantum efficiency (DQE) than conventional digital x-ray imaging, wherein the method comprises use of a SGCS of any one of claims 1-12 or the I-FPD of claim 13.

23. A method of preparing a SGCS of any one of claims 1-12, wherein the method comprises:(a) providing a layer of a scintillator glass, optionally an oxyhalide scintillator glass;(b) forming regions of defects in the layer from (a) by translating laser pulses, optionally about 0.1 picosecond (ps) to about 10 ps laser pulses, inside the layer from (a) in a predetermined pattern; and(c) nucleating and growing micro- and / or nanocrystals in the regions of defects by performing a heat treatment.

Images