Image Fusion in Multi-layer Flat-panel Imagers

Abstract

An imaging device (200) includes: a first scintillator layer (202) configured to provide a first image signal having a first quantum efficiency and a first spatial resolution; a second scintillator layer (204) configured to provide a second image signal having a second quantum efficiency and a second spatial resolution, wherein the first quantum efficiency is lower than the second quantum efficiency, but the first spatial resolution is higher than the second spatial resolution; and an image combiner (220) configured to combine the first image signal and the second image signal.

Description

[0001] This application is a divisional application of the Chinese invention patent application with an international application date of December 23, 2019, national application number 201980086916.4, and invention name “Image Fusion in Multi-Layer Flat-Plate Imagers”. Technical Field

[0002] The field of the present application relates to medical imaging, and more particularly to imaging devices for providing medical images and methods of processing image signals from such imaging devices. Background Art

[0003] Imaging devices such as X-ray imagers have been used for both diagnostic and therapeutic purposes. One type of X-ray imager is a diagnostic imager configured to operate with a diagnostic radiation source. Another type of X-ray imager is a high detection quantum efficiency (DQE) detector configured for use with a therapeutic radiation source. X-ray imagers can also be configured for use with both diagnostic and therapeutic radiation beams.

[0004] Creating high DQE electronic portal imaging devices (EPIDs) presents significant technical challenges. One approach uses a thick pixelated scintillator array coupled to a matrix of photodiodes. Incoming X-ray photons deposit energy into the scintillator, which then generates optical photons via luminescence. These optical photons, generated with random polarization and direction vectors after the luminescence event, are transmitted throughout the scintillator where they can be reflected, refracted, and scattered beyond the boundaries. Eventually, many photons will cross the boundaries of the scintillator and reach the photodiodes of the EPID. The photodiodes convert the photons into an electrical current for readout and digitization. Although the technology is promising, the performance of current EPIDs may be insufficient.

[0005] EPIDs currently employed in radiotherapy use a standard indirect flat panel design that includes a thin gadolinium oxysulfide (GOS) scintillator. The thickness of the GOS scintillator is typically kept small to maintain spatial resolution. The small thickness of the scintillator and the high energy megavoltage photon beam used in radiotherapy result in a low X-ray absorption rate in the scintillator. The low X-ray absorption rate limits the amount of light generated in the scintillator and subsequently measured by the photodiode matrix. Although the spatial resolution of the resulting digital image remains high, the signal-to-noise ratio (SNR) decreases due to the poor absorption characteristics. Current EPIDs suffer from a low DQE for MV imaging (e.g., ~1.8%). Due to the low contrast, imaging tasks using such low quantum efficiency detectors are not very practical, especially when imaging soft tissue. Creating imaging devices with high DQE in the megavoltage range remains an important issue in radiotherapy.

[0006] One possible approach to improving quantum efficiency (QE) is to try making several identical detection layers for an EPID and then stacking the detection layers on top of each other. An example of such an implementation is to fold several identical detection layers onto each other, with the goal of capturing unabsorbed X-rays in the upper detection layer. While this configuration can increase DQE, manufacturing costs can make this solution impractical. For example, if an EPID has four identical detection layers, the total DQE of the EPID can be increased by up to 4 times compared to a single-layer EPID. Production costs can also increase by up to 4 times, reducing the appeal of higher efficiency. Summary of the Invention

[0007] An imaging device having multiple radiation detection layers is described herein. The imaging device can have a first scintillator layer (e.g., a scintillator based on gadolinium oxysulfide (GOS)) that provides a first image signal and a second scintillator layer (e.g., a glass-based scintillator, such as LKH5 scintillator) that provides a second image signal. The first scintillator layer, together with its associated photodiode, can provide low QE and high spatial resolution for the first image signal (forming a first image), and the second scintillator layer, together with its associated photodiode, can provide high QE and low spatial resolution for the second image signal (forming a second image). Therefore, the first image formed by the first image signal will have a noisy image with higher frequency detail than the second image formed by the second image signal, and the second image will have a blurred image with lower noise than the first image. The first scintillator layer can be thinner than the second scintillator layer.

[0008] The embodiments described herein are not limited to two-layer detector configurations and two-image fusion. The detector may include more than two scintillator layers, which, as a result, will provide multiple digital images that can be combined in the manner described herein. Furthermore, the selection of scintillators described is not limited to GOS and glassy materials. The material and size of the scintillator can be selected such that the X-ray absorption and light output characteristics can produce digital images with inherently different signal-to-noise and resolution characteristics. The scintillator can be made of ceramic, plastic, glass, or any other suitable material that exhibits scintillation properties. Furthermore, the scintillator can be made of transparent or turbid materials and constructed in a pixelated or non-pixelated (flat) form.

[0009] The embodiments described herein teach how to combine two inherently different images (i.e., (1) a high resolution (sharp) and low efficiency (low signal-to-noise ratio) image, and (2) a low resolution (blurred) high efficiency (high signal-to-noise ratio) image) into a "fused" image. To combine the first image signal and the second image signal, several image fusion techniques may be employed in different embodiments. As non-limiting examples, the image fusion techniques may utilize detector imaging characteristics such as modulation transfer function (MTF), noise power spectrum (NPS), DQE, or any combination of the foregoing. In some embodiments, the first image signal and the second image signal may be combined in a manner that maximizes the SNR of the image and / or minimizes spatial resolution loss (which may occur during image fusion).

[0010] In some embodiments, images from multiple layers can be combined via a weighted summation. The weights can depend on spatial frequency, where the weights W(f) are chosen to maximize the SNR of the combined image for all spatial frequencies f. This effectively maximizes the DQE of the combined image (a measure of image quality as a function of spatial frequency). The weights W(f) can be chosen based on the performance of each detector layer, where performance is determined by spatial resolution (related to MTF) and noise (related to NPS). In some cases, the weights can be chosen to maximize the DQE in the combined image. For example, if image n has performance described by DQEn(f) = MTFn2(f) / NPSn(f), then the optimal linear weight for image n is wn(f) = [(MTFn / NPSn) / ∑n(MTFn / NPSn)](f), where the sum is over all images. Therefore, the combined image is: Im′(f) = ∑nwn(f)·Imn(f), where the linear weights give Im′ the highest possible DQE for all frequencies. Each spatial frequency can be selected using a 2D image filter. Using a two-layer (e.g., GOS + glass-based scintillator) example, the predicted MTF and NPS of each of the two images (from the corresponding two scintillators) can be used to determine the optimal linear weights W(f) for each image. These weights produce the desired (e.g., maximum) DQE across all frequencies.

[0011] Some exemplary imaging devices include: a first scintillator layer configured to provide a first image signal having a first quantum efficiency and a first spatial resolution; a second scintillator layer configured to provide a second image signal having a second quantum efficiency and a second spatial resolution, wherein the first quantum efficiency is lower than the second quantum efficiency, but the first spatial resolution is higher than the second spatial resolution; and an image combiner configured to combine the first image signal and the second image signal.

[0012] Optionally, the image combiner is configured to combine the first image signal and the second image signal in a manner that increases the signal-to-noise ratio while reducing loss of spatial resolution.

[0013] Optionally, the image combiner is configured to combine the first image signal and the second image signal based on frequency dependent weighting.

[0014] Optionally, the image combiner is configured to combine the first image signal and the second image signal based on frequency dependent filtering.

[0015] Optionally, the image combiner is configured to combine the first image signal and the second image signal based on noise correlation weighting.

[0016] Optionally, the image combiner is configured to combine the first image signal and the second image signal in the image domain based on noise reduction.

[0017] Optionally, the image combiner is configured to apply a first weighting factor to the first image signal and a second weighting factor to the second image signal.

[0018] Optionally, the first weight factor is between 0.1 and 0.4.

[0019] Optionally, the first weight factor is 0.15.

[0020] Optionally, the first weighting factor has a first value lower than 0.2 for a first frequency or a first frequency range, and has a second value higher than 0.2 for a second frequency higher than the first frequency or for a second frequency range higher than the first frequency range.

[0021] Optionally, the image combiner is configured to combine the first image signal and the second image signal based on a modulation transfer function (MTF).

[0022] Optionally, the image combiner is configured to combine the first image signal and the second image signal based on a noise power spectrum (NPS).

[0023] Optionally, the image combiner is configured to combine the first image signal and the second image signal based on a detection quantum efficiency (DQE).

[0024] Optionally, the first scintillator layer is GOS based.

[0025] Optionally, the second scintillator layer is glass-based.

[0026] Optionally, the first scintillator layer is thinner than the second scintillator layer.

[0027] Optionally, the first scintillator layer and the second scintillator layer are stacked.

[0028] Optionally, the imaging device further includes a third scintillator layer, wherein the first scintillator layer, the second scintillator layer, and the third scintillator layer are stacked.

[0029] Optionally, the imaging device further includes a fourth scintillator layer, wherein the first scintillator layer, the second scintillator layer, and the third scintillator layer are stacked, and the fourth scintillator layer is stacked.

[0030] Optionally, the image combiner is configured to combine a third image signal associated with the third scintillator layer with the first image signal and the second image signal.

[0031] Optionally, the imaging device is configured to provide a detection quantum efficiency of 5% or greater.

[0032] Optionally, the imaging device is configured to provide a detection quantum efficiency of 6.5% or greater.

[0033] Some exemplary imaging methods include: acquiring a first image signal generated by a first scintillator layer, the first image signal having a first quantum efficiency and a first spatial resolution; acquiring a second image signal generated by a second scintillator layer, the second image signal having a second quantum efficiency and a second spatial resolution, wherein the first quantum efficiency is lower than the second quantum efficiency, but the first spatial resolution is higher than the second spatial resolution; and electronically processing the first image signal and the second image by an image combiner to combine the first image signal and the second image signal to form a combined image.

[0034] Some exemplary embodiments include a medium storing a set of instructions, execution of which causes an imaging method to be performed, the imaging method comprising: acquiring a first image signal generated by a first scintillator layer, the first image signal having a first quantum efficiency and a first spatial resolution; acquiring a second image signal generated by a second scintillator layer, the second image signal having a second quantum efficiency and a second spatial resolution, wherein the first quantum efficiency is lower than the second quantum efficiency, but the first spatial resolution is higher than the second spatial resolution; and electronically processing the first image signal and the second image by an image combiner to combine the first image signal and the second image signal to form a combined image.

[0035] Other and further aspects and features will be apparent from a reading of the following detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] The accompanying drawings illustrate the design and utility of the embodiments, wherein similar elements are represented by common reference numerals. These figures are not necessarily drawn to scale. To better understand how the above and other advantages and objectives are achieved, a more detailed description of the embodiments will be provided, which are illustrated in the accompanying drawings. These drawings depict only exemplary embodiments and should not be considered to limit the scope of the claims.

[0037] Figure 1 A radiation system with an imaging device is shown in accordance with some embodiments.

[0038] Figure 2 An imaging device according to some embodiments is shown.

[0039] Figure 3 A method of combining image signals according to some embodiments is shown.

[0040] Figure 4 The relationship between the MTF value and the frequency value is shown.

[0041] Figure 5 The relationship between the MPS value and the frequency value is shown.

[0042] Figure 6 The relationship between DQE value and frequency value is shown.

[0043] Figure 7 The weighting factors are shown as a function of frequency.

[0044] Figure 8 The result of image fusion is shown.

[0045] Figure 9 Image fusion performed using simulation is shown.

[0046] Figure 10 Image fusion performed using simulation is shown.

[0047] Figure 11 A block diagram of a particular machine is shown, in accordance with some embodiments. DETAILED DESCRIPTION

[0048] Various embodiments are described below with reference to the accompanying drawings. It should be noted that these figures are not drawn to scale and that elements having similar structures or functions are represented by similar reference numerals throughout the figures. It should also be noted that the drawings are provided for ease of description of the embodiments only. They are not intended to be an exhaustive description of the invention or to limit the scope of the invention. In addition, the illustrated embodiments do not necessarily have all the aspects or advantages shown. An aspect or advantage described in conjunction with a particular embodiment is not necessarily limited to that embodiment, but may be practiced in any other embodiment, even if not so indicated or even if not so explicitly described.

[0049] Figure 1A radiation system 10 is shown. System 10 is a treatment system that includes a gantry 12, a patient support 14 for supporting a patient 28, and a control system 18 for controlling the operation of gantry 12. Gantry 12 takes the form of an arm, but in other embodiments, gantry 12 can have other forms (such as a ring form, etc.). System 10 also includes a radiation source 20 that projects a radiation beam 26 toward patient 28 while patient 28 is supported on support 14, and a collimator system 22 for controlling the delivery of radiation beam 26. Collimator 22 can be configured to adjust the cross-sectional shape of beam 26. In different embodiments, radiation source 20 can be configured to generate a cone beam, a fan beam, or other type of radiation beam.

[0050] As shown, system 10 also includes an imager 80 located in an operative position relative to source 20 (e.g., beneath support 14). In the illustrated embodiment, radiation source 20 is a therapeutic radiation source that provides therapeutic energy. In this case, imager 80 can acquire images using the therapeutic energy. To acquire images using the therapeutic energy, imager 80 is configured to generate images in response to the radiation having therapeutic energy (e.g., an MV imager). In other embodiments, in addition to being a therapeutic radiation source, radiation source 20 can also be a diagnostic radiation source that provides diagnostic (imaging) energy for imaging purposes. In further embodiments, system 10 can include radiation source 20 and one or more other radiation sources, with radiation source 20 providing therapeutic energy and one or more other radiation sources providing diagnostic energy. In some embodiments, the therapeutic energy is typically 160 kiloelectronvolts (keV) or higher, more typically 1 megaelectronvolt (MeV) or higher, and the diagnostic energy is typically energies below the high energy range, more typically below 160 keV. Furthermore, in some embodiments, the therapeutic energy can be 6 MV or higher (e.g., 25 MV). In other embodiments, therapeutic energy and diagnostic energy can have other energy levels and refer to energy used for therapeutic and diagnostic purposes, respectively. In some embodiments, radiation source 20 is capable of generating X-ray radiation at a plurality of photon energy levels within any range between about 10 keV and about 20 MeV. In other embodiments, radiation source 20 can be configured to generate radiation at other energy ranges.

[0051] In the illustrated embodiment, the control system 18 includes a processing unit 54 (such as a computer processor) coupled to the controller 40. The control system 18 may also include a display 56 for displaying data and an input device 58 (such as a keyboard or mouse) for entering data. The operation of the radiation source 20 and the gantry 12 is controlled by the controller 40, which provides power and timing signals to the radiation source 20 and controls the rotational speed and position of the gantry 12 based on signals received from the processing unit 54. In some cases, the controller 40 may also control the position of the collimator system 22 and the patient support 14. In addition, in some embodiments, the controller 40 can be configured to control the operation of the imager 80. Although the controller 40 is shown as a separate component from the gantry 12 and the processor 54, in alternative embodiments, the controller 40 may be part of the gantry 12 or the processing unit 54.

[0052] In some embodiments, the system 10 can be a treatment system configured to deliver a therapeutic radiation beam to the patient 28 at different gantry angles. During treatment, the source 20 rotates around the patient 28 and delivers the therapeutic radiation beam to the patient 28 from different gantry angles. When the source 20 is at different gantry angles, the collimator 22 is operated to change the shape of the beam to correspond to the shape of the target tissue structure. For example, the collimator 22 can be operated so that the shape of the beam resembles the cross-sectional shape of the target tissue structure. In another example, the collimator 22 can be operated so that different portions of the target tissue structure receive different amounts of radiation (such as in an IMRT procedure).

[0053] In the illustrated embodiment, system 10 further includes an imaging device 150 having an imaging source 152 and an imager 154. Imaging device 150 is configured to acquire one or more images of an internal portion of patient 28. The image(s) acquired by imaging device 150 can be used to position patient 28, monitor the position of patient 28, track targets within patient 28, or any combination thereof. In some cases, imaging device 150 can be configured to acquire images of internal fiducials 90 of patient 28. Internal fiducials 90 can be internal structures within patient 28. In some embodiments, internal structures can move in correspondence with (e.g., synchronously with) the targets of patient 28 to be treated. In such cases, internal structures can be used as surrogates for determining the position and / or motion of targets during treatment of patient 28, and in some cases, surrogate-based motion management can be employed. Thus, internal fiducials 90 can be imaged by imaging device 150 (and / or by radiation source 20 and imager 80) during treatment of patient 28 as a position monitoring system. As non-limiting examples, internal fiducial 90 can be an anatomical surrogate, such as a bone structure, a blood vessel, a natural calcification, or any other item in the body. As described above, imaging device 150 and / or imager 80 can also be used for target tracking and / or patient positioning. In some embodiments, controller 40 can be configured to control the operation of imaging device 150. For example, controller 40 can provide one or more control signals to activate imaging source 152 and / or operate readout and control circuitry in imager 154.

[0054] In some embodiments, imaging device 150 may be an X-ray device. In this case, imaging source 152 comprises a radiation source. In other embodiments, imaging device 150 may have other configurations and may be configured to generate images using other imaging techniques. For example, in other embodiments, imaging device 150 may be an ultrasound imaging device, an MRI device, a tomosynthesis imaging device, or any other type of imaging device. Furthermore, in the above embodiments, imaging device 150 is shown as being integrated with a treatment machine. In other embodiments, imaging device 150 may be a separate device from the treatment machine. Furthermore, in some embodiments, imaging device 150 may be a room-based imaging system or a couch-based imaging system. In either case, imaging device 150 may provide any form of imaging, such as X-ray imaging, ultrasound imaging, MRI, etc. Furthermore, in other embodiments, imaging device 150 may provide in-line imaging, as the imaging device may be configured to acquire images in the same direction as the treatment beam. For example, a dual energy source (integrating treatment source 20 and imaging source 152) may be provided to provide imaging energy for generating images and treatment energy for treating the patient in the same direction. In this case, the imager 154 can replace the imager 80 or can be integrated with the imager 80 to form a hybrid imager that is configured to provide kV and MV imaging. In other embodiments, the imaging device 150 and / or the imaging device 80 can be configured to provide dual energy imaging and any form of energy-resolved imaging to increase the contrast of the x-ray image. For example, a first portion of an image can be generated using a first energy, and a second portion of the same image (e.g., including a more relevant portion of the target) can be generated using a second energy that is higher than the first energy. As a result, the second portion of the image can have a higher contrast than the first portion. However, the total dose involved in generating the entire image can be reduced compared to when the entire image is generated using the second energy.

[0055] Figure 2 FIG. 2 shows an imaging device 200 according to some embodiments. In some embodiments, the imaging device 200 may be implemented as Figure 1 The imaging device 200 includes a first scintillator layer 202 , a second scintillator layer 204 , a first photodiode layer 206 , a second photodiode layer 208 , and an image combiner 220 .

[0056] The first scintillator layer 202 is configured to receive radiation 212 and generate first photons in response to the radiation 212. The radiation 212 may be therapeutic radiation having an energy level sufficient to treat a patient. The first photodiode layer 206 includes a first photodiode element 210 configured to convert the first photons into a first electrical signal for readout by a readout circuit. The first electrical signal may be considered a first image signal forming a first image. The first scintillator layer 202 may be pixelated or non-pixelated.

[0057] The second scintillator layer 204 is configured to receive radiation after having passed through the first scintillator layer 202 and generate a second photon in response to the radiation. The second photodiode layer 208 includes a second photodiode element 212 configured to convert the second photon into a second electrical signal for readout by a readout circuit. The second electrical signal can be considered a second image signal forming the first image. The second scintillator layer 204 can be pixelated or non-pixelated.

[0058] In some embodiments, each photodiode element 210 / 212 may include one or more amorphous silicon (a:Si) detectors. In addition, in some embodiments, the photodiode elements 210 / 212 may be implemented using photodiodes. In this specification, the term "photodiode" refers to one or more circuit elements on a detector pixel that are associated with converting photon energy into an electrical signal. This may include, but is not limited to, (multiple) photodiodes, (multiple) switching transistors, (multiple) amplifying transistors, direct conversion elements, indirect conversion elements, photon counting elements, or combinations thereof. In some embodiments, the signal from each photodiode element 210 / 212 forms a pixel in the image. In other embodiments, a pixel combining circuit (binning circuit) is optionally provided to combine signals from two or more photodiode elements to form each pixel in the image. For example, the pixel combining circuit of the imager 200 may be configured to provide 2×2 pixel combining (binning), 3×3 pixel combining, 4×4 pixel combining, 1×2 pixel combining, 1×4 pixel combining, or pixel combining of another number of pixels. In some embodiments, the pixel combining circuit may be implemented as part of the readout circuit. In some embodiments, the readout circuitry may be communicatively connected to controller 40 or another separate controller for controlling the operation of the readout circuitry. Additionally, in some embodiments, the readout circuitry may be included as part of image combiner 220 or may be communicatively coupled to image combiner 220.

[0059] like Figure 2As shown, image element 210 is secured to first substrate 214, and image element 212 is secured to second substrate 216. In the illustrated embodiment, image element 210 of first photodiode layer 206 is closer to the first side (e.g., top side) of substrate 214 than to the second side (e.g., bottom side) of substrate 214. Additionally, image element 212 of first photodiode layer 208 is closer to the first side (e.g., top side) of substrate 216 than to the second side (e.g., bottom side) of substrate 216. In other embodiments, image element 210 of first photodiode layer 206 is closer to the second side (e.g., bottom side) of substrate 214 than to the first side (e.g., top side) of substrate 214. Additionally, in other embodiments, image element 212 of first photodiode layer 208 is closer to the second side (e.g., bottom side) of substrate 216 than to the first side (e.g., top side) of substrate 216. Substrates 214 and 216 may be made of glass, plastic, or other materials.

[0060] In some embodiments, the first scintillator layer 202 may be GOS-based. For example, the first scintillator layer 202 may be a gadolinium oxysulfide scintillator layer. Furthermore, the second scintillator layer 204 may be glass-based. For example, the scintillator layer 204 may be LKH5 scintillator. Although LKH5 scintillator is used as an example herein, it should be noted that the scintillator layer 204 may be any glass high-density scintillator. Furthermore, in other embodiments, the scintillator layer 204 may not be glass-based. Conversely, in other embodiments, the scintillator layer 204 may be non-glass-based. The scintillator layer 204 may be made of any material as long as the scintillator layer provides a higher absorption rate for X-rays (compared to the scintillator layer 202) and good conversion efficiency (compared to the scintillator layer 202). Such a scintillator may be thicker than the scintillator layer 202 and may produce some blur in the final image.

[0061] like Figure 1 As shown, the first scintillator layer 202 is thinner than the second scintillator layer 204, and the first scintillator layer 202 and the second scintillator layer 204 are arranged relative to each other in a stacked configuration. For example, in some embodiments, the first scintillator layer 202 can have a thickness between 200 μm and 1 mm (e.g., 436 μm), and the second scintillator layer 202 can have a thickness between 1 mm and 5 mm (e.g., 3 mm). In other embodiments, the first scintillator layer 202 and the second scintillator layer 204 can have other thicknesses. In the illustrated embodiment, the first scintillator layer 202 is above the second scintillator layer 204, such that the first scintillator layer 202 receives the radiation 212 before the second scintillator layer 204. In other embodiments, the second scintillator layer 204 can be arranged above the first scintillator layer 202, such that the second scintillator layer 204 receives the radiation 212 before the first scintillator layer 202.

[0062] The image combiner 220 is configured to acquire a first image signal and a second image signal and combine the first image signal and the second image signal to form a combined image. Because the first photodiode layer 206 and the second photodiode layer 208 receive photos from the corresponding scintillator layers 202 and 204, respectively, and generate separate first image signals and second image signals corresponding to the corresponding scintillator layers 202 and 204, the image combiner 220 can process the first image signal and the second image signal separately (e.g., by applying weighting factors, filtering, etc.) before combining the first image signal and the second image signal. In some embodiments, the image combiner 220 can be configured to combine the first image signal and the second image signal in a manner that increases the signal-to-noise ratio while reducing the loss of spatial resolution. In addition, in some embodiments, the image combiner 220 can be configured to combine the first image signal and the second image signal based on frequency-dependent weighting. Alternatively or additionally, the image combiner 220 can be configured to combine the first image signal and the second image signal based on frequency-dependent filtering. Alternatively or additionally, the image combiner 220 can be configured to combine the first image signal and the second image signal based on noise-dependent weighting.

[0063] In some embodiments, the image combiner 220 is configured to apply a first weighting factor to the first image signal and a second weighting factor to the second image signal. For example, the first weighting factor may be between 0.1 and 0.4, and more preferably between 0.12 and 0.2 (e.g., 0.15). The second weighting factor may be a value equal to 1 minus the first weighting factor. In addition, in some embodiments, for a first frequency or a first frequency range, the first weighting factor may have a first value below a threshold, and for a second frequency higher than the first frequency or for a second frequency range higher than the first frequency range, the first weighting factor may have a second value higher than a threshold. The threshold may be between 0.1 and 0.3, and more preferably between 0.15 and 0.25 (such as 0.2).

[0064] In some embodiments, the image combiner 220 can be configured to combine the first image signal and the second image signal based on a modulation transfer function (MTF), a noise power spectrum (NPS), a detection quantum efficiency (DQE), or any combination thereof. As described above, the image combiner 220 can be configured to combine the first image signal and the second image signal based on frequency-dependent weighting and / or filtering. As non-limiting examples, the frequency-dependent weighting and / or filtering can be based on MTF, NPS, DQE, or any combination thereof.

[0065] In addition, in some embodiments, the image combiner 220 can be configured to combine the first image signal and the second image signal based on a noise-dependent weighting factor, which can be estimated by calculating a first-order statistic of the noise in the two images or by iteratively enforcing a regularization constraint (such as the total variation of the output image). In addition, in some embodiments, the image combiner 220 can be configured to combine the first image signal and the second image signal based on a weighting factor, wherein the weighting factor can be frequency-dependent, noise-dependent, or a combination thereof. In addition, in some embodiments, the image combiner 220 is configured to combine the first image signal and the second image signal to maximize the DQE (or SNR) of the combined image. In addition, in some embodiments, the image combiner 220 can be configured to combine the first image signal and the second image signal based on weights that take into account the imaging task (e.g., task transfer function) and / or observer model (e.g., eye filter, human observer, hotel observer, etc.).

[0066] In some embodiments, the image combiner 220 can be configured to combine the first image signal contributed by the first scintillator layer 202 and the second image signal contributed by the second scintillator layer 204 in the frequency domain. In other embodiments, the image combiner 220 can be configured to combine the first image signal and the second image signal in the image domain. For example, the image combiner 220 can be configured to combine the first image signal and the second image signal in the image domain based on noise reduction. In other embodiments, the image combiner 220 can be configured to combine the first image signal and the second image signal in both the frequency domain and the image domain. For example, the image combiner 220 can be configured to perform image fusion in both the frequency domain and the image domain sequentially (e.g., first in the frequency domain, then in the image domain, or vice versa) or simultaneously. In addition, in some embodiments, the image combiner 220 can perform image fusion in the frequency domain by applying various frequency filters that depend on MTF, NPS, DQE, or any combination of the foregoing. Alternatively or additionally, the image combiner 220 may perform image fusion in the image domain based on direct or iterative techniques designed to reduce noise in the fused image and preserve spatial resolution.

[0067] In some embodiments, before combining the first image signal and the second image signal, the image combiner 220 can be configured to (1) seal bad pixels and correct the image using dark field (DF) and flat field (FF) data sets, (2) remove scatter from the image (e.g., using polynomial detrending), (3) normalize the images to a common background, (4) register the images with each other, or any combination of the foregoing. In some cases, to seal bad pixels (e.g., due to photodiode failure or poor performance), the image combiner 220 can correct the bad pixels so that the new value of the bad pixel will be similar to that of adjacent pixels. In one implementation, interpolation between adjacent pixels can be performed to determine the new value of the bad pixel. In other embodiments, one or more of the above features can be performed by a module coupled upstream with respect to the image combiner 220.

[0068] In some embodiments, imaging device 200 is configured to provide a detection quantum efficiency (DQE) of 5% or greater, or more preferably, 6.5% or greater.

[0069] Although the imaging device 200 has been described as having two scintillator layers 202, 204 and corresponding two photodiode layers 206, 208, in other embodiments, the imaging device 200 may have more than two scintillator layers and more than two photodiode layers. For example, in some embodiments, the imaging device 200 may further include a third scintillator layer and a corresponding third photodiode layer (for generating a third image signal in response to photons from the third scintillator layer). In this case, the first scintillator layer 202, the second scintillator layer 204, and the third scintillator layer may be stacked. For example, the third scintillator layer and the third photodiode layer may be placed under the second substrate 216. Alternatively, the third scintillator layer and the third photodiode layer may be placed between the first substrate 214 and the second scintillator layer 204. In other embodiments, the third scintillator layer and the third photodiode layer may be placed above the first scintillator layer 202.

[0070] In another embodiment, the imaging device 200 may also include a fourth scintillator layer and a corresponding fourth photodiode layer (for generating a fourth image signal in response to photons from the fourth scintillator layer), wherein the first scintillator layer 202, the second scintillator layer 204, the third scintillator layer are stacked, and the fourth scintillator layer is stacked.

[0071] Figure 3 A method 300 for combining image signals is shown. In some embodiments, the method 300 may be performed by Figure 2The method 300 is performed by the imaging device 200. The method 300 includes acquiring a first image signal generated by a first scintillator layer, the first image signal having a first quantum efficiency and a first spatial resolution (item 302). The method 300 also includes acquiring a second image signal generated by a second scintillator layer (item 304). In the example shown, the second image signal has a second quantum efficiency and a second spatial resolution, wherein the first quantum efficiency is lower than the second quantum efficiency, but the first spatial resolution is higher than the second spatial resolution. The method 300 also includes electronically processing the first image signal and the second image signal by an image combiner to combine the first image signal and the second image signal to form a combined image (item 306).

[0072] In some embodiments, in item 306 , the first image signal and the second image signal are combined in a manner that increases the signal-to-noise ratio while reducing the loss of spatial resolution.

[0073] In some embodiments, in item 306 , the first image signal and the second image signal are combined based on frequency-dependent weighting.

[0074] In some embodiments, in item 306 , the first image signal and the second image signal are combined based on frequency dependent filtering.

[0075] In some embodiments, in item 306 , the first image signal and the second image signal are combined based on noise correlation weighting.

[0076] In some embodiments, in item 306 , the first image signal and the second image signal are combined in the image domain based on noise reduction.

[0077] In some embodiments, in item 306 , the image combiner applies a first weighting factor to the first image signal and a second weighting factor to the second image signal.

[0078] In some embodiments, in method 300, the first weighting factor is between 0.1 and 0.4. In some embodiments, the first weighting factor is 0.15.

[0079] In some embodiments, in method 300 , the first weighting factor has a first value lower than 0.2 for a first frequency or a first frequency range, and has a second value higher than 0.2 for a second frequency higher than the first frequency or for a second frequency range higher than the first frequency range.

[0080] In some embodiments, in item 306 , the first image signal and the second image signal are combined based on the MTF.

[0081] In some embodiments, in item 306 , the first image signal and the second image signal are combined based on the NPS.

[0082] In some embodiments, in item 306 , the first image signal and the second image signal are combined based on DQE.

[0083] In some embodiments, in method 300 , the first scintillator layer is GOS-based.

[0084] In some embodiments, in method 300 , the second scintillator layer is glass-based.

[0085] In some embodiments, in the method 300 , the first scintillator layer is thinner than the second scintillator layer.

[0086] In some embodiments, in method 300 , the first scintillator layer and the second scintillator layer are stacked.

[0087] In some embodiments, method 300 provides a detection quantum efficiency of 5% or greater, or more preferably, a detection quantum efficiency of 6.5% or greater.

[0088] As described above, in some embodiments, combining the first image signal and the second image signal may be performed based on MTF, NPS, DQE, or any combination thereof. Figures 4 to 6 The imaging characteristics of a GOS-based scintillator (which is an example of the first scintillator layer 202) and a glass-based scintillator (which is an example of the second scintillator layer) are shown, and in particular, MTF, NPS, and DQE as a function of frequency or as a function of frequency are shown. In particular, Figure 4 The relationship between the MTF value and the frequency value is shown. Figure 5 The relationship between the MPS value and the frequency value is shown. Figure 6 The relationship between DQE value and frequency value is shown. Figure 4 As shown, the MTF value associated with the first scintillator layer 202 (e.g., a GOS-based scintillator) is generally higher than the MTF value associated with the second scintillator layer 204 (e.g., a glass-based scintillator). This is because, due to the granular structure of the GOS image, the MTF characteristics are very good, i.e., it provides "high" spatial resolution compared to the glass-based image (e.g., LKH5 image). On the other hand, the glass-based image is affected by light blurring and therefore has a "low" spatial resolution. In addition, as Figure 6As shown, the DQE value associated with the first scintillator layer 202 (e.g., a GOS-based scintillator) is lower than the DQE value associated with the second scintillator layer 204 (e.g., a glass-based scintillator). The image combiner 220 can utilize this information when combining the first and second image signals, such that the resulting combined image will have high-resolution features inherited from the first image signal (e.g., higher features than the second image signal), as well as high DQE (or SNR) inherited from the second image signal (e.g., higher DQE than the first image signal). In one embodiment, such image combination can be performed using frequency-dependent filtering or weighting, where the weighting factor (w) is determined by the MTF and NPS characteristic curves. In this case, the MTF determines the frequency-dependent "resolution" of the image, while the NPS curve indicates the amount of noise generated in the system and, in addition, identifies the detection quantum efficiency. For example, the low efficiency and high resolution of the GOS-based scintillator and the high efficiency and low resolution of the glass-based scintillator indicate that it is preferable to use the high-frequency components of the GOS-based scintillator image and the low-frequency components of the glass-based scintillator image during the image fusion process. This means that the GOS-based scintillator image should have a lower weight in the low-frequency region and a higher weight in the high-frequency region, while the remaining "1-w" weight will be applied to the glass-based scintillator image respectively. In some embodiments, the image combiner 220 is configured to combine the first image signal and the second image signal to maximize the DQE (or SNR) of the combined image while maintaining spatial resolution. In one implementation, the first image (first image signal) and the second image (second image signal) can be normalized based on the following formula before being combined (by the image combiner 220 or a normalization unit coupled upstream to the image combiner 220):

[0089] GOS: LKH5: The image combiner 220 may then perform a frequency-dependent linear combination of the first image and the second image based on the following equation:

[0090] Im3(f)=w(f)·Im1(f)+(1-w(f))·Im2(f)

[0091] MTF3(f)=w(f)MTF1(f)+(1-w(f))MTF2(f)

[0092] NPS3(f)=w 2 (f)NPS1(f)+(1-w(f)) 2 NPS2(f)

[0093] The DQE of the combined image (DQE3) may then be maximized by the image combiner 220 according to the following equation:

[0094] DQE3(f):

[0095] In other embodiments, the image combiner 220 may be configured to combine the first image and the second image by maximizing the SNR of the resulting image based on a Rose noise model. According to the Rose noise model, the SNR may be defined as the product of the contrast-to-noise ratio (CNR) and the square root of the number of pixels N in the region of interest, as follows:

[0096]

[0097] CNR can be measured using the signal (I s ) and background (I b ) intensity and its standard deviation σ s and σ b express:

[0098]

[0099] In some cases, the SNR can be optimized using a figure of merit (FOM) with respect to the integrated dose D delivered to the patient, where the FOM can be defined as:

[0100]

[0101] Figure 7The weighting factors as a function of frequency for the imaging device 200 are shown. As shown, the optimal weight (weighting factor) for the first image signal has different values ​​depending on the frequency value. If a weighting factor of 0.15 is applied to the first image signal contributed by the first scintillator layer 202, the weighting factor provides a good approximation for most of the applicable frequency range (e.g., from 0 to 1.4 mm^-1). Therefore, in some embodiments, the image combiner 220 can be configured to apply a first weighting factor of 0.15 to the first image signal contributed by the first scintillator layer 202, and a second weighting factor of 0.85 (=1-0.15) to the second image signal contributed by the second scintillator layer 204, regardless of the frequency value. In other embodiments, the image combiner 220 can be configured to apply a first weighting factor between 0.1 and 0.4 to the first image signal, and a second weighting factor of 1 minus the first weighting factor to the second image signal. In addition, in other embodiments, the image combiner 220 may be configured to apply a first weighting factor having a first value to a first image signal of a first frequency range, and to apply a first weighting factor having a second value to an image signal of a second frequency range. In this case, the image combiner 220 may also be configured to apply a second weighting factor having a third value (i.e., equal to 1 minus the first value of the first weighting factor) to a second image signal of the first frequency range, and to apply a second weighting factor having a fourth value (i.e., equal to 1 minus the second value of the first weighting factor) to a second image signal of the second frequency range. In some embodiments, the first frequency range may be below a frequency threshold, and the second frequency range may be above the frequency threshold.

[0102] Figure 8 1 shows an exemplary result of image fusion. Image 802 is based on an image signal generated from a GOS-based scintillator (which is an example of the first scintillator layer 202). Image 804 is based on an image signal generated from a glass-based scintillator (which is an example of the second scintillator layer 204). As shown, image 802 has a relatively higher resolution than image 804, but image 802 is generated with a relatively lower quantum efficiency than image 804. Therefore, image 802 has a stronger granular noise structure and a lower SNR than image 804. This is consistent with the Figure 4 The MTF curves for the GOS-based scintillator are consistent with those presented in [1]. That is, the MTF curve produced by the GOS-based scintillator has a slowly decreasing tail in the high-frequency region. The MTF of the glass-based scintillator decreases more rapidly than that of the GOS-based scintillator.

[0103] Image 806 is obtained by taking the average of image 802 and image 804, which is equivalent to applying a weighting factor of 0.5 to image 802, a weighting factor of 0.5 to image 804, and adding them together. Image 808 is obtained by applying a weighting factor of 0.15 to image 802, a weighting factor of 0.85 to image 804, and combining them. Image 810 is obtained by determining optimal weights by preserving an optimal balance between spatial frequency (related to MTF) and noise power reduction (NPS), applying the optimal weights to image 802 and image 804, and combining them. As shown in the figure, applying a weighting factor of 0.15 provides an image fusion result similar to that achieved by optimization. Therefore, both a weighting factor of 0.15 and the optimal weights provide images that retain the high DQE characteristics of the second image (e.g., the image of the glass substrate associated with the second scintillator layer 204), but at the expense of spatial resolution because the MTF is lower than that of a weighting factor of 0.5, but higher than that of the second image alone.

[0104] Figure 9 : The figure shows image fusion performed using simulations performed on phantom and MV beams. The GOS image is based on image signals generated from a GOS-based scintillator (which is an example of the first scintillator layer 202). The LKH5 image is based on image signals generated from an LKH5 scintillator (which is an example of the second scintillator layer 204). As shown in the figure, the GOS image has a relatively higher resolution than the LKH5 image, but the GOS image is generated with a relatively lower quantum efficiency than the LKH5 image. Therefore, the GOS image has a stronger granular noise structure and a lower SNR than the LKH5 image. The GOS+LKH5 image is obtained by averaging the GOS and LKH5 images, which is the same as applying a weighting factor of 0.5 to the GOS image and a weighting factor of 0.5 to the LKH5 image and adding them together. The "0.15*GOS+0.85*LKH5" image is obtained by applying a weighting factor of 0.15 to the GOS image, a weighting factor of 0.85 to the LKH5 image, and combining them. The optimal image is obtained by determining the optimal weights by preserving the optimal balance between spatial frequency (related to MTF) and noise power reduction (NPS), applying the optimal weights to the GOS image and the LKH5 image, and combining them. As shown in the figure, applying a weighting factor of 0.15 provides an image fusion result similar to that achieved by optimization. Therefore, both the weighting factor of 0.15 and the optimal weights provide images that preserve the high DQE characteristics of the second image (e.g., the LKH5 image associated with the second scintillator layer 204), but at the expense of spatial resolution because the MTF is lower than that of the weighting factor of 0.5, but higher than that of the second image alone.

[0105] Figure 10 Another image fusion performed using simulations performed on phantom and MV beams is shown. The GOS image is based on image signals generated from a GOS-based scintillator (which is an example of the first scintillator layer 202). The LKH5 image is based on image signals generated from an LKH5 scintillator (which is an example of the second scintillator layer 204). As shown in the figure, the GOS image has a relatively higher resolution than the LKH5 image, but the GOS image is generated with a relatively lower quantum efficiency than the LKH5 image. Therefore, the GOS image has a stronger granular noise structure and a lower SNR than the LKH5 image. The GOS+LKH5 image is obtained by averaging the GOS and LKH5 images, which is the same as applying a weighting factor of 0.5 to the GOS image, a weighting factor of 0.5 to the LKH5 image, and adding them together. The "0.15*GOS+0.85*LKH5" image is obtained by applying a weighting factor of 0.15 to the GOS image, a weighting factor of 0.85 to the LKH5 image, and combining them. The optimal image is obtained by determining the optimal weights by preserving the optimal balance between spatial frequency (related to MTF) and noise power reduction (NPS), applying the optimal weights to the GOS image and the LKH5 image, and combining them. As shown in the figure, applying a weighting factor of 0.15 provides an image fusion result similar to that achieved by optimization. Therefore, both the weighting factor of 0.15 and the optimal weights provide images that preserve the high DQE characteristics of the second image (e.g., the LKH5 image associated with the second scintillator layer 204), but at the expense of spatial resolution because the MTF is lower than that of the weighting factor of 0.5, but higher than that of the second image alone.

[0106] In some embodiments, the combined images achieved using the image fusion techniques described herein provide better soft tissue visualization than when only a thick glass-based scintillator layer is used. In addition, in some embodiments, the combined images achieved using the image fusion techniques described herein are better able to detect smaller (high frequency) features than when only a thick glass-based scintillator layer is used (as in current EPID imagers). In other embodiments, the combined images achieved using the image fusion techniques described herein achieve better noise reduction and edge enhancement than when only a thick glass-based scintillator layer is used (as in current EPID imagers). In addition, in some embodiments, the image fusion techniques described herein provide lower dose MV imaging than when current EPID imagers are used. In some embodiments, the image fusion techniques described herein can be performed during treatment, for example, for soft tissue visualization, patient positioning, etc.

[0107] In some embodiments, the first scintillator layer 202 and the second scintillator layer 204 can be configured to provide a detection quantum efficiency (DQE) of at least 5%. One exemplary configuration that provides such a 5% DQE can utilize a 436 μm thick GOS-based scintillator and a 3 mm thick glass-based scintillator, where the GOS-based scintillator will produce a DQE of approximately 1.8% and the glass-based scintillator will produce a DQE of approximately 3.8%. The thickness and efficiency of the glass-based scintillator are not limited to the values ​​discussed and can have higher or lower values ​​in other embodiments. DQE is a measure of the combined effects of the signal (related to image contrast) and noise performance of an imaging system. In some cases, DQE can be expressed as a function of spatial frequency. In other embodiments, DQE can be improved to achieve higher values, such as 6.5% or greater. For example, in other embodiments, the thickness of the first scintillator layer 202 and / or the thickness of the second scintillator layer can be increased. Furthermore, in some embodiments, the imaging device 200 can include additional scintillator layer(s) to provide a higher DQE, as described above.

[0108] In some embodiments, the first scintillator layer 202 and the second scintillator layer 204 provide a higher DQE than a single-layer EPID (which may only have a DQE of 1.8%). Furthermore, in some embodiments, the first scintillator layer 202 and the second scintillator layer 204 can be configured to provide a higher DQE than a four-layer design having four layers of GOS-based detectors. Thus, the two-layer design reduces system complexity and associated costs.

[0109] In some embodiments, a product is provided that includes a medium storing a set of instructions. Execution of the instructions causes an imaging method to be performed. The imaging method includes acquiring a first image signal generated by a first scintillator layer, the first image signal having a first quantum efficiency and a first spatial resolution; acquiring a second image signal generated by a second scintillator layer, the second image signal having a second quantum efficiency and a second spatial resolution, wherein the first quantum efficiency is lower than the second quantum efficiency but the first spatial resolution is higher than the second spatial resolution; and electronically processing the first image signal and the second image signal by an image combiner to combine the first image signal and the second image signal to form a combined image.

[0110] Exemplary Machine

[0111] Figure 11 is a block diagram illustrating an embodiment of a specific machine 1600 that can be used to implement various features described herein. In some embodiments, the specific machine 1600 can be considered an example of a processing system. In some embodiments, the processing system 1600 can be used to implement Figure 5The processing unit 54 of the imaging device 200 may also be used to implement controls for controlling the operation of the imaging device 200 and / or controls for controlling the operation of the treatment machine. In further embodiments, the processing system 1600 may be used to implement components of the imaging device 200, such as an image combiner of the imaging device 200.

[0112] The processing system 1600 includes a bus 1602 or other communication mechanism for communicating information, and a processor 1604 coupled to the bus 1602 for processing information. The processor system 1600 also includes a main memory 1606, such as a random access memory (RAM) or other dynamic storage device, coupled to the bus 1602 for storing information and instructions to be executed by the processor 1604. The main memory 1606 may also be used to store temporary variables or other intermediate information during execution of instructions to be executed by the processor 1604. The processor system 1600 also includes a read-only memory (ROM) 1608 or other static storage device coupled to the bus 1602 for storing static information and instructions for the processor 1604. A data storage device 1610, such as a magnetic disk, solid-state drive, or optical disk, is provided and coupled to the bus 1602 for storing information and instructions.

[0113] The processor system 1600 can be coupled to a display 167 (such as a flat-panel display) via a bus 1602 for displaying information to a user. An input device 1614, including alphanumeric and other keys, is coupled to the bus 1602 for communicating information and command selections to the processor 1604. Another type of user input device is a cursor control 1616, such as a mouse, trackball, or cursor direction keys, for communicating directional information and command selections to the processor 1604 and for controlling cursor movement on the display 167. This input device typically has two degrees of freedom in two axes, a first axis (e.g., x) and a second axis (e.g., y), to allow the device to specify a position in a plane.

[0114] In some embodiments, the processor system 1600 can be used to perform the various functions described herein. According to some embodiments, this use is provided by the processor system 1600 in response to the processor 1604 executing one or more sequences of one or more instructions contained in the main memory 1606. Those skilled in the art will know how to prepare such instructions based on the functions and methods described herein. Such instructions can be read into the main memory 1606 from another processor-readable medium (such as a storage device 1610). The execution of the instruction sequence contained in the main memory 1606 causes the processor 1604 to perform the processing steps described herein. One or more processors of a multi-processing arrangement can also be used to execute the instruction sequence contained in the main memory 1606. In alternative embodiments, hard-wired circuitry can be used instead of software instructions or in combination with software instructions to implement the various embodiments described herein. Therefore, the embodiments are not limited to any specific combination of hardware circuitry and software.

[0115] As used herein, the term "processor-readable medium" refers to any medium that participates in providing instructions to processor 1604 for execution. Such media may take a variety of forms, including, but not limited to, non-volatile media, volatile media, and transmission media. Non-volatile media include, for example, optical, solid-state, or magnetic disks, such as storage device 1610. Non-volatile media may be considered an example of non-transitory media. Volatile media include dynamic memory, such as main memory 1606. Volatile media may be considered an example of non-transitory media. Transmission media include coaxial cables, copper wire, and fiber optics, including the wires that comprise bus 1602. Transmission media may also take the form of acoustic or light waves, such as those generated during radio wave and infrared data communications.

[0116] Common forms of processor-readable media include, for example, a floppy disk, a hard disk, magnetic tape or any other magnetic medium, a CD-ROM, any other optical medium, any other physical medium with a pattern of holes, RAM, PROM and EPROM, FLASH-EPROM, a solid-state disk, any other memory chip or cartridge, the carrier wave described below, or any other medium from which a processor can read.

[0117] Various forms of processor-readable media may be involved in carrying one or more sequences of one or more instructions to processor 1604 for execution. For example, the instructions may initially be carried on a magnetic disk or solid-state drive of a remote computer. The remote computer may load the instructions into its dynamic memory and send the instructions over a network (such as the Internet). Processing system 1600 may receive data on a network line. Bus 1602 transfers the data to main memory 1606, from which processor 1604 retrieves and executes the instructions. The instructions received by main memory 1606 may optionally be stored on storage device 1610 before or after execution by processor 1604.

[0118] The processing system 1600 also includes a communication interface 1618 coupled to the bus 1602. The communication interface 1618 provides a bidirectional data communication coupling to a network link 1620 connected to a local network 1622. For example, the communication interface 1618 can be a local area network (LAN) card for providing a data communication connection to a compatible LAN. A wireless link can also be implemented. In any such implementation, the communication interface 1618 sends and receives electrical, electromagnetic, or optical signals that carry data streams representing various types of information.

[0119] The network link 1620 typically provides data communication to other devices through one or more networks. For example, the network link 1620 can provide a connection to a host 1624 or a device 1626 (such as a radiation beam source and / or imaging device or a switch operatively coupled to the radiation beam source and / or imaging device) through a local network 1622. The data stream transmitted through the network link 1620 may include electrical, electromagnetic, or optical signals. The signals through the various networks and the signals on the network link 1620 and through the communication interface 1618 (which carry data to and from the processing system 1600) are exemplary forms of carrier waves for transporting information. The processing system 1600 can send messages and receive data, including program code, through the network(s), network link 1620, and communication interface 1618.

[0120] Although specific embodiments have been shown and described, it should be understood that this is not intended to limit the claimed invention to the preferred embodiments, and that various changes and modifications are apparent to those skilled in the art without departing from the spirit and scope of the claimed invention. Accordingly, the specification and drawings are to be regarded as illustrative rather than restrictive. The claimed invention is intended to encompass alternatives, modifications, and equivalents.

Claims

1. An imaging device comprising: a first scintillator layer configured to provide first photons having a first quantum efficiency, the first photons being used to generate a first image signal for a first image, the first image having a first spatial resolution; a second scintillator layer configured to provide second photons having a second quantum efficiency, the second photons being used to generate a second image signal for a second image, the second image having a second spatial resolution, wherein the first quantum efficiency is lower than the second quantum efficiency and the first spatial resolution is higher than the second spatial resolution, wherein the first scintillator layer comprises a first scintillator material and the second scintillator layer comprises a second scintillator material different from the first scintillator material; as well as An image combiner is configured to determine an output image based on the first image signal and the second image signal. 2 . The imaging device of claim 1 , wherein the image combiner is configured to determine the output image based on the first image signal and the second image signal in a manner that increases a signal-to-noise ratio while reducing a loss of spatial resolution. 3 . The imaging apparatus according to claim 1 , wherein the image combiner is configured to combine the first image signal and the second image signal based on frequency-dependent weighting. 4 . The imaging device according to claim 1 , wherein the image combiner is configured to combine the first image signal and the second image signal based on frequency dependent filtering. 5 . The imaging apparatus according to claim 1 , wherein the image combiner is configured to combine the first image signal and the second image signal based on noise correlation weighting. 6 . The imaging device of claim 1 , wherein the image combiner is configured to combine the first image signal and the second image signal in an image domain based on noise reduction. 7 . The imaging apparatus according to claim 1 , wherein the image combiner is configured to apply a first weighting factor to the first image signal and a second weighting factor to the second image signal. The imaging device according to claim 7 , wherein the first weighting factor is between 0.1 and 0.

4.

9. The imaging device according to claim 7, wherein the first weighting factor has a first value lower than 0.2 for a first frequency or a first frequency range, and has a second value higher than 0.2 for a second frequency higher than the first frequency or for a second frequency range higher than the first frequency range. 10 . The imaging apparatus of claim 1 , wherein the image combiner is configured to combine the first image signal and the second image signal based on a modulation transfer function (MTF). 11 . The imaging apparatus of claim 1 , wherein the image combiner is configured to combine the first image signal and the second image signal based on a noise power spectrum (NPS). 12 . The imaging device of claim 1 , wherein the image combiner is configured to combine the first image signal and the second image signal based on a detection quantum efficiency (DQE). 13 . The imaging device of claim 1 , wherein the first scintillator layer is GOS-based, and wherein the second scintillator layer is glass-based. 14 . The imaging device according to claim 1 , wherein the first scintillator layer and the second scintillator layer are stacked. 15 . The imaging device according to claim 1 , further comprising a third scintillator layer, wherein the first scintillator layer, the second scintillator layer, and the third scintillator layer are stacked. 16 . The imaging device according to claim 15 , further comprising a fourth scintillator layer, wherein the first scintillator layer, the second scintillator layer, and the third scintillator layer are stacked, and the fourth scintillator layer is stacked. 17 . The imaging device of claim 15 , wherein the image combiner is configured to determine the output image based on the first image signal, the second image signal, and a third image signal associated with the third scintillator layer.

18. The imaging device of claim 1, wherein the imaging device is configured to provide a detection quantum efficiency of 5% or greater.

19. An imaging method comprising: acquiring a first image signal associated with a first photon generated by the first scintillator layer, the first image signal being generated with a first quantum efficiency and forming a first image having a first spatial resolution; acquiring a second image signal associated with a second photon generated by a second scintillator layer, the second image signal generated with a second quantum efficiency, and forming a second image having a second spatial resolution, wherein the first quantum efficiency is lower than the second quantum efficiency and the first spatial resolution is higher than the second spatial resolution, wherein the first scintillator layer includes a first scintillator material and the second scintillator layer includes a second scintillator material different from the first scintillator material; as well as The first image signal and the second image signal are electronically processed to form an output image.

20. An article of manufacture having a medium storing a set of instructions, execution of which causes an imaging method to be performed, the imaging method comprising: acquiring a first image signal associated with a first photon generated by the first scintillator layer, the first image signal being generated with a first quantum efficiency and forming a first image having a first spatial resolution; acquiring a second image signal associated with a second photon generated by a second scintillator layer, the second image signal generated with a second quantum efficiency, and forming a second image having a second spatial resolution, wherein the first quantum efficiency is lower than the second quantum efficiency and the first spatial resolution is higher than the second spatial resolution, wherein the first scintillator layer includes a first scintillator material and the second scintillator layer includes a second scintillator material different from the first scintillator material; as well as The first image signal and the second image signal are electronically processed to form an output image.

Images