Patent Description:
Imaging devices, such as an x-ray imager, have been used for diagnostic and treatment 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 DQE detector that is configured for use with a treatment radiation source. An x-ray imager may also be configured for use with both diagnostic radiation beam and treatment radiation beam.

Creating a high DQE detector for portal imaging presents a significant technical challenge. One approach uses thick pixilated scintillator arrays that are coupled to an electronic portal imaging device (EPID). Incoming x-ray photons deposit energy into the scintillators which then produce optical photons via luminescence. These optical photons, which originate with random polarizations and direction vectors after the luminescence events, are transported throughout the scintillator during which time they can be reflected, refracted and scattered. Eventually, many photons will cross the boundary between the scintillator and the photodiode array to be absorbed by the EPID's photodiodes and converted into electrical current for readout and digitization. Despite the promise of the technology, performance may be inadequate and a significant manufacturing cost lies in the process of cutting the crystalline scintillators into parallelepipeds and gluing reflective septa between them in order to reduce optical cross talk.

Also, in some cases, an x-ray imager (e.g., a diagnostic x-ray imager or a portal imager) may comprise a scintillator coupled to a photodiode array. X-ray photons deposit energy into the scintillator thereby producing optical photons with random direction and polarization vectors. A percentage of these optical photons will cross the scintillator-photodiode boundary and deposit energy. The photodiodes convert optical photons into electron-hole pairs. After a sufficient amount of charge is collected, signals are read out and digitized to form an image. To achieve a sufficiently high spatial resolution, optical blurring is desired to be minimized. This implies that the photodiode signals associated with a given x-ray photon should be localized in close lateral proximity to where that x-ray photon interacted with the scintillator. A common means of achieving this goal is through the use of pixelated geometries that confine optical photons using reflective septa. Unfortunately, this approach suffers from high manufacturing costs and may not be practical for incorporating into large-area imagers. As similarly discussed, the process of cutting the crystalline scintillators (e.g. CsI, CdWO4, BGO) into parallelepipeds, gluing reflective septa between them, and then assembling the pixels into a complete array, may be very expensive. Another disadvantage of the pixelated geometry is the loss of fill factor (and associated quantum efficiency) due to the finite thickness of the septa.

Also, current amorphous silicon based flat panel imagers for megavoltage radiation suffers from very low x-ray conversion efficiency. Only about <NUM>% of the x-ray photons contribute to an image. In other words, more than <NUM>% of the imaging dose gets lost and will not contribute to the image formation. Approaches that utilize thicker scintillator are either very expensive because the scintillator has to be pixelated or has to exhibit very high imaging performance due to added blurring. <CIT> describes a system and method for a multi-sensor pixel architecture for use in a digital imaging system. The system includes at least one semiconducting layer for absorbing radiation incident on opposite sides of the at least one semiconducting layer. <CIT> describes a radiological image detection apparatus that includes: two scintillators that convert irradiated radiation into lights; and a photodetector arranged between two scintillators, that detects the lights converted by two scintillators as an electric signal. <CIT> describes a radiographic imaging device that has a first scintillating phosphor screen having a first thickness and a second scintillating phosphor screen having a second thickness. A transparent substrate is disposed between the first and second screens.

In an aspect of the invention, there is provided an imaging device in accordance with claim <NUM>.

Optional features are provided in the dependent claims.

An imaging device according to the presently claimed invention includes: a first scintillator layer; an array of detector elements, wherein the array of detector elements comprises a first detector element; and a second scintillator layer configured to receive radiation after the radiation has passed through the first scintillator layer and the array of detector elements, wherein the array of detector elements is located between the first scintillator layer and the second scintillator layer; wherein the first detector element is configured to generate a first electrical signal in response to light from the first scintillator layer, and to generate a second electrical signal in response to light from the second scintillator layer; and wherein the imaging device further comprises: a first electrode located closer to the first scintillator than the second scintillator, and a second electrode situated between the second scintillator and the first detector element, wherein the second electrode is configured to allow the light from the second scintillator layer to reach the first detector element; and optionally: a first neutral density filter located between the first scintillator layer and the first detector element and/or a second neutral density filter located between the second scintillator layer and the first detector element.

Optionally, the first electrode is situated between the first scintillator and the first detector element, and wherein the first electrode is configured to allow light from the first scintillator layer to reach the first detector element.

In the presently claimed invention, the second electrode is made from a non-transparent conductive material but is etched with a pattern to allow light to pass therethrough, or, the second electrode comprises a first opening for allowing the light from the second scintillator layer to pass therethrough.

Optionally, the second electrode has a polygonal pattern.

Optionally, the first detector element has a first part configured to generate the first electrical signal in response to the light from the first scintillator layer, and a second part configured to generate the second electrical signal in response to the light from the second scintillator layer.

Optionally, the first part is a top side of the first detector element, and the second part is a bottom side of the first detector element.

Optionally, the first part comprises a first photodiode, and the second part comprises a second photodiode, and wherein the first photodiode and the second photodiode form a side-by-side configuration.

Optionally, the second electrode is at leas partially transparent to light.

Optionally, the second electrode comprises a second opening.

Optionally, the first opening comprises a circular opening, a square opening, a rectangular opening, or a slot.

Optionally, the second electrode has a ring configuration.

Optionally, the second electrode has a grid configuration, and the first opening is one of a plurality of grid holes.

Optionally, the second electrode comprises a chrome layer.

Optionally, the second electrode comprises ITO or another transparent conductor.

Optionally, the first detector element comprises a hardware component, and wherein the second electrode and the hardware component are in a side-by-side configuration.

Optionally, the second electrode comprises a conductor extending along at least a part of a periphery of the second electrode, and one or more optical openings surrounded by the periphery.

Optionally, the hardware component comprises at least a part of a thin-film-transistor (TFT).

Optionally, the second electrode further comprises one or more additional conductors extending within a space that is surrounded by the periphery of the second electrode.

Optionally, the imaging device further includes a substrate, wherein the array of detector elements is secured to the substrate, wherein the substrate has a first side and an opposite second side, the first side being closer to a radiation source than the second side.

Optionally, the array of detector elements is located closer to the first side of the substrate than the second side, or vice versa.

Optionally, a first part of the first detector element is located closer to the first side of the substrate than the second side.

Optionally, the substrate has a thickness that is less than <NUM>.

Optionally, the imaging device further includes a layer of focusing elements located between (<NUM>) the array of detector elements and (<NUM>) the first scintillator layer or the second scintillator layer.

Optionally, the first scintillator layer is non-pixelated, the second scintillator layer is non-pixelated, or both the first and second scintillator layers are non-pixelated.

Optionally, one or both of the first and second scintillator layers are pixelated.

Optionally, the imaging device further includes an optical grid coupled to the first scintillator layer or the second scintillator layer.

Optionally, the imaging device further includes a first optical grid coupled to the first scintillator layer, and a second optical grid coupled to the second scintillator layer.

Optionally, the imaging device further includes a first plate coupled to the first scintillator layer, and a second plate coupled to the second scintillator layer, wherein both the first scintillator layer and the second scintillator layer are between the first and second plates.

Optionally, the imaging device further includes a first neutral density filter located between the first scintillator layer and the first detector element and/or a second neutral density filter located between the second scintillator layer and the first detector element.

Optionally, the first neutral density filter and/or the second neutral density filter is configured to improve a signal-to-noise ratio of the imaging device.

Optionally, a signal-to noise ratio of the imaging device is based on (<NUM>) respective quantum efficiencies (QE1,QE2) of the first and second scintillator layers, (<NUM>) respective detective quantum efficiencies (DQE1,DQE2) of the first and second scintillator layers, (<NUM>) respective optical yields (α1, α2) of the first and second scintillator layers, (<NUM>) optical sensitivities (p<NUM>, p<NUM>) of the first detector element associated with the first and second scintillators respectively, or (<NUM>) a combination of any of the foregoing.

Optionally, the first electrical signal has a first feature value (e1), and the second electrical signal has a second feature value (e2); and wherein min (e1, e2) / max (e1, e2) is larger than a threshold.

Optionally, the first feature value (e1) is a function of quantum efficiency QE1 of the first scintillator layer, optical yield α1 of the first scintillator layer, and optical sensitivity p<NUM> of the first detector element associated with the first scintillator layer; and wherein the second feature value (e2) is a function of quantum efficiency QE2 of the second scintillator layer, optical yield α2 of the second scintillator layer, and optical sensitivity p<NUM> of the first detector element associated with the second scintillator layer.

Optionally, the first feature value (e1) is a function of detective quantum efficiency DQE1 of the first scintillator layer, optical yield α1 of the first scintillator layer, and optical sensitivity p<NUM> of the first detector element associated with the first scintillator layer; and wherein the second feature value (e2) is a function of detective quantum efficiency DQE2 of the second scintillator layer, optical yield α2 of the second scintillator layer, and optical sensitivity p<NUM> of the first detector element associated with the second scintillator layer.

Optionally, the threshold is larger than <NUM>.

According to an example useful for understanding, but not forming part of, the presently claimed invention, an imaging device includes: a first scintillator layer; an array of detector elements, wherein the array of detector elements comprises a first detector element; a second scintillator layer, wherein the array of detector elements is located between the first scintillator layer and the second scintillator layer; and optionally a first neutral density filter located between the first scintillator layer and the first detector element and/or a second neutral density filter located between the second scintillator layer and the first detector element; wherein the first detector element is configured to generate a first electrical signal in response to light from the first scintillator layer, and to generate a second electrical signal in response to light from the second scintillator layer.

Optionally, the first electrical signal has a first feature value (e1), and the second electrical signal has a second feature value (e2); and wherein the first neutral density filter and/or the second neutral density filter is configured such that min (e1, e2) / max (e1, e2) is larger than a threshold.

Optionally, the second scintillator layer is configured to receive radiation after it has passed through the array of detector elements.

Optionally, the imaging device further includes a first electrode situated between the first scintillator and the first detector element, wherein the first electrode is configured to allow light from the first scintillator layer to reach the first detector element.

Optionally, the imaging device further includes a second electrode configured to allow the light from the second scintillator layer to reach the first detector element.

Optionally, the second electrode is at least partially transparent to light.

Optionally, the second electrode comprises a first opening for allowing the light from the second scintillator layer to pass therethrough.

Optionally, the hardware component comprises at least a part of a thin-film-transistor (TFT).

Other and further aspects and features will be evident from reading the following detailed description.

The drawings illustrate the design and utility of embodiments, in which similar elements are referred to by common reference numerals. These drawings are not necessarily drawn to scale. In order to better appreciate how the above-recited and other advantages and objects are obtained, a more particular description of the embodiments will be rendered, which are illustrated in the accompanying drawings. These drawings depict only exemplary embodiments and are not therefore to be considered limiting in the scope of the claims.

It should be noted that the figures are not drawn to scale and that elements of similar structures or functions are represented by like reference numerals throughout the figures.

<FIG> illustrates a radiation treatment system <NUM>. The system <NUM> includes an arm gantry <NUM>, a patient support <NUM> for supporting a patient <NUM>, and a control system <NUM> for controlling an operation of the gantry <NUM> and delivery of radiation. The system <NUM> also includes a radiation source <NUM> that projects a beam <NUM> of radiation towards the patient <NUM> while the patient <NUM> is supported on support <NUM>, and a collimator system <NUM> for changing a cross sectional shape of the radiation beam <NUM>. The radiation source <NUM> may be configured to generate a cone beam, a fan beam, or other types of radiation beams in different embodiments. Also, in other embodiments, the source <NUM> may be configured to generate proton beam, electron beam, or photon beam, as a form of radiation for treatment purpose. Also, in other embodiments, the system <NUM> may have other form and/or configuration. For example, in other embodiments, instead of an arm gantry <NUM>, the system <NUM> may have a ring gantry <NUM>.

In the illustrated embodiments, the radiation source <NUM> is a treatment radiation source for providing treatment energy. In other embodiments, in addition to being a treatment radiation source, the radiation source <NUM> can also be a diagnostic radiation source for providing diagnostic energy for imaging purposes. In such cases, the system <NUM> will include an imager, such as the imager <NUM>, located at an operative position relative to the source <NUM> (e.g., under the support <NUM>). In further embodiments, the radiation source <NUM> may be a treatment radiation source for providing treatment energy, wherein the treatment energy may be used to obtain images. In such cases, in order to obtain imaging using treatment energies, the imager <NUM> is configured to generate images in response to radiation having treatment energies (e.g., MV imager). Also, in some embodiments, the imager <NUM> may be a portal imager configured to perform portal imaging. In some embodiments, the treatment energy is generally those energies of <NUM> kilo-electron-volts (keV) or greater, and more typically <NUM> mega-electron-volts (MeV) or greater, and diagnostic energy is generally those energies below the high energy range, and more typically below <NUM> keV. In other embodiments, the treatment energy and the diagnostic energy can have other energy levels. In some embodiments, the radiation source <NUM> is able to generate X-ray radiation at a plurality of photon energy levels. For example, the accelerator may have an energy range from 1MV to <NUM> MV, producing an x-ray having a range from 10kV to <NUM> kV. In other cases, the energy may have a range anywhere between approximately <NUM> keV and approximately <NUM> MeV. In further embodiments, the radiation source <NUM> can be a diagnostic radiation source. In such cases, the system <NUM> may be a diagnostic system with one or more moving parts. In the illustrated embodiments, the radiation source <NUM> is carried by the arm gantry <NUM>. Alternatively, the radiation source <NUM> may be located within a bore (e.g., coupled to a ring gantry).

In the illustrated embodiments, the control system <NUM> includes a processing unit <NUM>, such as a processor, coupled to a control <NUM>. The control system <NUM> may also include a monitor <NUM> for displaying data and an input device <NUM>, such as a keyboard or a mouse, for inputting data. The operation of the radiation source <NUM> and the gantry <NUM> are controlled by the control <NUM>, which provides power and timing signals to the radiation source <NUM>, and controls a rotational speed and position of the gantry <NUM>, based on signals received from the processing unit <NUM>. Although the control <NUM> is shown as a separate component from the gantry <NUM> and the processing unit <NUM>, in alternative embodiments, the control <NUM> can be a part of the gantry <NUM> or the processing unit <NUM>.

In some embodiments, the system <NUM> may be a treatment system configured to deliver treatment radiation beam towards the patient <NUM> at different gantry angles. During a treatment procedure, the source <NUM> rotates around the patient <NUM> and delivers treatment radiation beam from different gantry angles towards the patient <NUM>. While the source <NUM> is at different gantry angles, the collimator <NUM> is operated to change the shape of the beam to correspond with a shape of the target tissue structure. For example, the collimator <NUM> may be operated so that the shape of the beam is similar to a cross sectional shape of the target tissue structure. In another example, the collimator <NUM> may be operated so that different portions of the target tissue structure receive different amount of radiation (as in an IMRT procedure).

The imager <NUM> may have different configurations in different embodiments. <FIG> illustrates an imaging device <NUM> in accordance with the presently claimed invention. The imaging device <NUM> may be used to implement the imager <NUM> in some embodiments. As shown in the figure, the imaging device <NUM> includes a first scintillator layer <NUM>, and an array of detector elements <NUM>. In some embodiments, each detector element <NUM> may include one or more amorphous silicon (a:Si) detector. The imaging device <NUM> also includes a second scintillator layer <NUM>. As shown in the figure, the array of detector elements <NUM> is located between the first scintillator layer <NUM> and the second scintillator layer <NUM>. The second scintillator layer <NUM> is configured to receive radiation after it has passed through the array of detector elements <NUM>. The imaging device <NUM> also includes electrodes <NUM>, <NUM> coupled to respective ones of the detector elements <NUM>. Each detector element <NUM> is configured to generate a first electrical signal in response to light from the first scintillator layer <NUM>, and to generate a second electrical signal in response to light from the second scintillator layer <NUM>.

In the illustrated embodiments, each detector element <NUM> has a first electrode <NUM> electrically coupled thereto, and a second electrode <NUM> coupled thereto. The first electrode <NUM> and the second electrode <NUM> are on opposite sides of the detector element <NUM>, and are configured to receive opposite charge of an electron-hole pair generated in the detector element <NUM> in response to detected light. In the presently claimed invention, the second electrode <NUM> has a configuration for allowing the light from the second scintillator layer <NUM> to reach the detector element <NUM>. Also, in some embodiments, the first electrode <NUM> also has a configuration for allowing light from first scintillator layer <NUM> to reach the detector element <NUM>. In some embodiments, the detector element <NUM> may be implemented using a photodiode. Also, in some embodiments, the electrodes <NUM>, <NUM> may be considered as parts of the photodiode, or as terminals that are separately coupled to the photodiode.

In the presently claimed invention, the detector element <NUM> has a first part configured to generate a first electrical signal in response to the light from the first scintillator layer <NUM>, and a second part configured to generate a second electrical signal in response to the light from the second scintillator layer <NUM>. In some cases, the first part <NUM> is a top side <NUM> of the detector element <NUM>, and the second part <NUM> is a bottom side <NUM> of the detector element <NUM> (<FIG>). In other cases, the first part <NUM> and the second part <NUM> may form a side-by-side configuration (<FIG>).

Also, in some embodiments, the first part may comprise a first photodiode element, and the second part may comprise a second photodiode element. In this specification, the term "photodiode element" refers to one or more electrical circuit element(s) on a detector pixel that are associated with converting photon energy into electrical signals. This can include, but is not limited to, photodiode(s), switching transistor(s), amplification transistor(s), direct conversion element, or a combination thereof. The first scintillator layer <NUM> and the second scintillator layer <NUM> are configured to receive radiation and generate photons in response to the radiation. The first photodiode element is configured to generate electrical signals in response to the photons provided from the first scintillator layer <NUM>, and the second photodiode element is configured to generate electrical signals in response to photons provided from the second scintillator layer <NUM>. The electrical signals are then read out and digitized to form an image. In some embodiments, a circuit is provided to combine the signals from the first and second photodiode elements for each detector element <NUM> to form each pixel in the image.

In the presently claimed invention, the electrode <NUM> is at least partially transparent to light. In some cases, the electrode <NUM> may comprise a first opening <NUM> for allowing the light from the second scintillator layer <NUM> to pass therethrough (<FIG>). Also, in some embodiments, the electrode <NUM> may comprise multiple openings (e.g., a first opening and a second opening) for allowing light from the second scintillator layer <NUM> to pass therethrough. The first opening may comprise a circular opening, a square opening, a rectangular opening, or a slot. In some embodiments, the electrode <NUM> may have a ring configuration (<FIG>). In further embodiments, the electrode <NUM> may have a grid configuration, and the opening <NUM> is one of a plurality of grid holes (<FIG>). In some embodiments, the electrode <NUM> may have a shape that accommodates component(s) of the detector element <NUM>, such as that shown in <FIG>. As shown in the figure, the electrode <NUM> has a substantially square shape that accommodates component(s) <NUM> of the detector element <NUM> at the corner or side(s) of the electrode <NUM>. The component(s) <NUM> may be photodiode, or hardware component(s) (such as at least a part of a thin-film-transistor (TFT), trace, wire, circuit, etc.). In other embodiments, the electrode <NUM> may have a rectangular shape, a circular shape, a hexagonal shape, or other customized shapes. The electrode <NUM> is positioned next to the component(s) <NUM> of the detector element <NUM> in a side-by-side configuration, and defines the opening <NUM> for allowing light to travel therethrough. In some embodiments, the opening <NUM> may be a space without any material. In other embodiments, the opening <NUM> may be filled or covered by an optically transparent material, which may or may not be electrically conductive. In the illustrated embodiments, the electrode <NUM> has a conductor <NUM> (e.g., a wire or trace) extending around a perimeter of the electrode <NUM>. In other embodiments, the conductor <NUM> may not extend completely around the perimeter of the electrode <NUM>, and may instead extend partially around the perimeter to define an open-loop for the electrode <NUM>. Also, in other embodiments, the electrode <NUM> may include additional conductor(s) <NUM> in the space defined by the perimeter of the electrode <NUM> (<FIG>). As shown in the embodiment of <FIG>, the electrode <NUM> has additional conductors <NUM> extending in the same direction within the perimeter of the electrode <NUM>. Such configuration defines a plurality of openings <NUM> (e.g., slots) for allowing light to travel therethrough. In other embodiments, the electrode <NUM> may include additional conductors extending in other directions (such as in a horizontal direction to form a grid of holes with the vertical conductors <NUM>).

It should be noted that the term "opening" (such as the opening <NUM>) may refer to a space without any material that allows light to travel therethrough, or may refer to a material that has at least some optical transparency for allowing light to travel through the material.

Also, in other embodiments, the electrode <NUM> may be made from a non-transparent conductive material, but is etched with a pattern to allow light to pass therethrough. For example, the electrode may have a polygonal pattern, or any customized pattern, that is etched to allow light to pass therethrough.

In any of the embodiments described herein, the electrode <NUM> may comprise a chrome layer. Also, in some embodiments, the electrode <NUM> may comprise Indium tin oxide (ITO), or another transparent conductor.

Returning to <FIG>, the imaging device <NUM> further includes a glass substrate <NUM>, wherein the array of detector elements <NUM> is secured to the glass substrate <NUM>. In the illustrated embodiments, the glass substrate <NUM> has a first side <NUM> and an opposite second side <NUM>, wherein the first side <NUM> is closer to a radiation source than the second side <NUM>. The glass substrate <NUM> may have a thickness that is less than <NUM>, and more preferably less than <NUM>, and even more preferably less than <NUM>. Also, in some embodiments, the substrate <NUM> that is greater than <NUM>, or greater than <NUM>. In other embodiments, the glass substrate <NUM> may have a thickness that is greater than <NUM>. In some embodiments, the array of detector elements <NUM> is located closer to the first side <NUM> of the glass substrate <NUM> than the second side <NUM>. It has been discovered that any blurring effect (due to light traveling from the second scintillator layer <NUM> through the glass substrate <NUM> to reach the detector elements <NUM>) is minimal, or does not significantly degrade image quality. Accordingly, the imaging device <NUM> does not need to have any optical filter coupled between the second scintillator layer <NUM> and the glass substrate <NUM> to improve image resolution. However, if improvement is needed, the imaging device <NUM> may include such optical filter, or may utilize a kernel-based algorithm to improve resolution of the image generated by the imaging device <NUM>.

In other embodiments, the substrate <NUM> may be made from other materials that are different from glass. For example, in other embodiments, the substrate <NUM> may be made from plastic.

In other embodiments, the array of detector elements <NUM> is located closer to the second side <NUM> of the glass substrate <NUM> than the first side <NUM>. This configuration is advantageous because the detector elements <NUM> are in close proximity to the scintillator layer <NUM>, so that photons leaving the scintillator layer <NUM> can be immediately received by the detector elements <NUM>.

Also, in some embodiments, a first part of the first detector element <NUM> is located closer to the first side <NUM> of the glass substrate <NUM> than the second side <NUM>, and a second part of the first detector element <NUM> is located closer to the second side <NUM> of the glass substrate <NUM> than the first side <NUM>. In other embodiments, both the first part and the second part of the detector element <NUM> may be located closer to the first side <NUM> of the glass substrate <NUM> than the second side <NUM>. In further embodiments, both the first part and the second part of the detector element <NUM> may be located closer to the second side <NUM> of the glass substrate <NUM> than the first side <NUM>.

The scintillator layers <NUM>, <NUM> may be selectively chosen to fit the required imaging tasks. For example, the first scintillator layer <NUM> may be copper and Lanex™, while the second scintillator layer <NUM> may be CdWO<NUM>, Csl, or BGO, or vice versa. Also, in some embodiments, GOS with a copper build-up plate may be used for the first scintillator layer <NUM>, the second scintillator layer <NUM>, or both. When implemented in the second scintillator layer <NUM>, the build-up plate may be positioned below the GOS. Scintillator options that are suitable for the first scintillator layer <NUM> and/or second scintillator layer <NUM> include, but are not limited to, LKH-<NUM>, CdWO4, CsI, with or without build-up plate. The first scintillator layer <NUM> and the second scintillator layer <NUM> may be the same or different.

In some embodiments, the first scintillator layer <NUM> may be non-pixelated, the second scintillator layer <NUM> may be non-pixelated, or both the first and second scintillator layers <NUM>, <NUM> may be non-pixelated. In other embodiments, one or both of the first and second scintillator layers <NUM>, <NUM> may be pixelated.

During use of the imaging device <NUM>, the imaging device <NUM> is positioned so that the first scintillator layer <NUM> receives radiation from the radiation source before the second scintillator layer <NUM>. The first scintillator layer <NUM> receives the radiation, and generates photons in response to the received radiation. The photons are detected by the detector elements <NUM>, which generate electrical signals (imaging signals) in response to the detected photons from the first scintillator layer <NUM>. Some of the radiation is not absorbed by the first scintillator layer <NUM>, and passes through the detector elements <NUM> and the glass substrate <NUM>, and reaches the second scintillator layer <NUM>. The second scintillator layer <NUM> receives the radiation and generates photons in response to the received radiation. The photons from the second scintillator layer <NUM> travel backward towards the direction of the radiation, and reach the detector elements <NUM>. The detector elements <NUM> generate electrical signals (imaging signals) in response to the photons detected by the respective detector elements <NUM>. Thus, each detector element <NUM> generates two electrical signals based on photons from the first and second scintillator layers <NUM>, <NUM>. The two electrical signals from each detector element <NUM> are combined, e.g., via a circuit, to form an image signal for a pixel of an image. The imaging signals may be transmitted to a device, such as a processor for determining an image based on the imaging signals, and/or to a medium for storage.

In order for each detector element <NUM> to be able to detect photons coming from both the first scintillator layer <NUM> and the second scintillator layer <NUM>, the detector element <NUM> needs to be able to detect photons coming from two opposite directions. In some embodiments, the detector element <NUM> has a photodiode that is configured to detect photons coming from two opposite directions. Alternatively, the detector element <NUM> may have a first photodiode for detecting photons from the first scintillator layer <NUM>, and a second photodiode for detecting photons from the second scintillator layer <NUM>. The first and second photodiodes may be disposed on the top and bottom sides, respectively, of the detector element <NUM>. Thus, in this embodiment, there are two photodiodes for each pixel, with one of them being upside down. Also, in order for the photons from the second scintillator layer <NUM> to reach the detector element <NUM>, the electrode <NUM> is configured to allow light to pass therethrough. For example, the electrode <NUM> may have one or more opening(s) (like those shown in <FIG>) for allowing light to pass therethrough to reach the detector element <NUM>. Alternatively, or additionally, the electrode <NUM> may be made from ITO or a combination of ITO with other material, so that the electrode <NUM> is at least partially transparent. Also, alternatively or additionally, the electrode <NUM> may be implemented using a thin chrome layer.

The above embodiments illustrate a reverse geometry, which is advantageous because it increases the number of photons that are detected by the detector elements <NUM>. Also, by adding a second scintillator layer <NUM>, the conversion efficiency of the imaging device <NUM> is improved. In addition, the above approach of using scintillator layers on opposite sides of the detector elements <NUM> reduces artifacts significantly and does not add significant cost. Furthermore, the above multi-scintillator layers approach is advantageous over an imaging device that utilizes thick non-pixelated scintillator or thick pixelated scintillator. A thick scintillator layer without pixelation will blur the signal and as a consequence, will degrade image resolution. In addition to the blurring, the generated light at the upper part of a thick scintillator layer has to travel a long distance and gets much more attenuated, than the light generated at the lower part of the thick scintillator. Hence, the efficiency does not scale with the thickness. The above approach of using two scintillator layers can be viewed as splitting a thick scintillator layer into two layers, and placing the two scintillator layers on opposite sides of the detector elements <NUM>. This reduces blurring and because the light has to travel a shorter distance, it reduces unwanted light attenuation. Also, thick pixelated scintillators will address the light scattering issue in the thick non-pixelated scintillator as described above, but manufacturing a large area pixelated scintillator is very expensive. Adding a second scintillator layer <NUM> below the detector elements <NUM> only adds the cost of a relatively inexpensive second scintillator layer <NUM>. In some embodiments, the substrate <NUM> is configured to have a thinner thickness that reduces a distance light has to travel from the scintillator layer <NUM> to the detector elements <NUM>, thereby reducing blurring effect.

In any of the embodiments described herein, the imaging device <NUM> may not need any optical grid between the first scintillator layer <NUM> and the detector elements <NUM>, and may also not need any optical grid between the second scintillator layer <NUM> and the detector elements <NUM>. In other embodiments, the imaging device <NUM> may optionally further include an optical grid coupled between the first scintillator layer <NUM> and the detector elements <NUM>, and/or an optical grid coupled between the second scintillator layer <NUM> and the detector elements <NUM>. The optical grid is configured to allow "on-angle" light generated by the second scintillator <NUM> to be transmitted towards the detector elements <NUM>, while blocking the "off-angle" light.

In some embodiments, the imaging device <NUM> may further include a layer <NUM> of focusing elements located between the array of detector elements <NUM> and the second scintillator layer <NUM> (<FIG>). The layer <NUM> of focusing elements is configured to direct light generated by the second scintillator <NUM> to reach the detector elements <NUM>, thereby improving the resolution of the image. The layer <NUM> of focusing elements may comprise a fiber optic array, a brightness enhancement film (BEF), an optical grid, an optical filter, or any optical device that is capable of channeling optical rays (e.g., using Fresnel refraction and/or reflection). In other embodiments, the focusing elements are not needed, and the imaging device <NUM> does not include the focusing elements between the detector elements <NUM> and the second scintillator layer <NUM>.

In some embodiments, the imaging device <NUM> may optionally further include a first plate <NUM> coupled to the first scintillator layer <NUM>, and a second plate <NUM> coupled to the second scintillator layer <NUM>, wherein both the first scintillator layer <NUM> and the second scintillator layer <NUM> are between the first and second plates300, <NUM>.

During use, radiation may interact with the first plate <NUM> and the second plate <NUM> (in addition to the first and second scintillator layers <NUM>, <NUM>) to create photons for detection by the detector elements <NUM>.

One consideration in maximizing signal-to-noise ratio (SNR) is equalizing the signals from the first and second scintillator layers <NUM>, <NUM>. Signal detection theory dictates that the electron signal amplitude from each side's scintillator (after conversion of the optical signal by the photodiode) should be proportional to that side's scintillator's detective quantum efficiency (DQE). For example, if the same scintillator with the same thickness is used for the top and bottom sides, but the photodiode efficiency on the bottom side is, for example, ½ of the efficiency of the top side, then a ½x neutral density filter may be put between the top scintillator and the detector elements <NUM> to equalize the signals, or to at least bring them closer to each other. Alternatively, different scintillators with different optical yields may be used on the top and bottom sides.

In some embodiments, the first electrical signal (generated based on light from the first scintillator layer <NUM>) may have a first feature value (e1), and the second electrical signal (generated based on light from the second scintillator layer <NUM>) may have a second feature value (e2). The first and second feature values may be first and second electron signal amplitudes, respectively. The ratio, min (e1, e2) / max (e1, e2), may be larger than a threshold. For examples, the threshold may be larger than <NUM>, larger than <NUM>, larger than <NUM>, etc. In any of the examples, the threshold may be less than or equal to <NUM>. In some embodiments, such ratio may be achieved to be below the prescribed threshold by selecting the appropriate materials and thicknesses for the first and second scintillator layers <NUM>, <NUM>. In other embodiments, the imaging device <NUM> may optionally further include a first neutral density filter located between the first scintillator layer <NUM> and the first detector element, and/or a second neutral density filter located between the second scintillator layer <NUM> and the first detector element. The first neutral density filter and/or the second neutral density filter may be configured to improve a signal-to-noise ratio of the imaging device. For example, the first neutral density filter and/or the second neutral density filter may be configured such that min (e1, e2) / max (e1, e2) is larger than a threshold.

In some embodiments, a signal-to noise ratio of the imaging device <NUM> is based on (<NUM>) respective quantum efficiencies (QE1,QE2) of the first and second scintillator layers <NUM>, <NUM>, (<NUM>) respective detective quantum efficiencies (DQE1,DQE2) of the first and second scintillator layers <NUM>, <NUM>, (<NUM>) respective optical yields (α1, α2) of the first and second scintillator layers <NUM>, <NUM>, (<NUM>) optical sensitivities (p1, p2) of the detector element(s) associated with the first and second scintillators respectively <NUM>, <NUM>, or (<NUM>) a combination of any of the foregoing.

Also, in some embodiments, the first feature value (e1) may be a function of quantum efficiency QE1 of the first scintillator layer <NUM>, optical yield α1 of the first scintillator layer <NUM>, and optical sensitivity p<NUM> of the detector element(s) associated with the first scintillator layer <NUM>. Also, the second feature value (e2) may be a function of quantum efficiency QE2 of the second scintillator layer <NUM>, optical yield α2 of the second scintillator layer <NUM>, and optical sensitivity p2 of detector element(s) associated with the second scintillator layer <NUM>.

In other embodiments, the first feature value (e1) may be a function of detective quantum efficiency DQE1 of the first scintillator layer, optical yield α1 of the first scintillator layer, and optical sensitivity p<NUM> of the detector element(s) associated with the first scintillator layer. Also, the second feature value (e2) may be a function of detective quantum efficiency DQE2 of the second scintillator layer, optical yield α2 of the second scintillator layer, and optical sensitivity p<NUM> of the detector element(s) associated with the second scintillator layer.

It should be noted that the term "first scintillator layer" and the term "second scintillator layer" need not refer to the top scintillator layer and the bottom scintillator layer, respectively. For example, in other cases, the first scintillator layer may refer to the bottom scintillator layer, and the second scintillator layer may refer to the top scintillator layer.

It should be noted that the embodiments of the imaging device <NUM> described herein are not limited to portal imagers, and that any of the embodiments of the imaging device <NUM> described herein may be used with diagnostic radiation beam. The imaging device <NUM> may be a part of a treatment machine, a part of an imaging machine, or both.

In the above embodiments, various features have been described with reference to medical imaging. In other embodiments, any or all of the features described herein may be implemented for security applications. For example, in some embodiments, any of the imaging devices <NUM> described herein may be employed for cargo screening.

Claim 1:
An imaging device (<NUM>), comprising:
a first scintillator layer (<NUM>);
an array of detector elements (<NUM>), wherein the array of detector elements (<NUM>) comprises a first detector element (<NUM>); and
a second scintillator layer (<NUM>) configured to receive radiation after the radiation has passed through the first scintillator layer (<NUM>) and the array of detector elements (<NUM>), wherein the array of detector elements (<NUM>) is located between the first scintillator layer (<NUM>) and the second scintillator layer (<NUM>);
wherein the first detector element (<NUM>) is configured to generate a first electrical signal in response to light from the first scintillator layer (<NUM>), and to generate a second electrical signal in response to light from the second scintillator layer (<NUM>); and
wherein the imaging device (<NUM>) further comprises:
a first electrode (<NUM>) located closer to the first scintillator (<NUM>) than the second scintillator (<NUM>), and a second electrode (<NUM>) situated between the second scintillator (<NUM>) and the first detector element (<NUM>), wherein the second electrode (<NUM>) is configured to allow the light from the second scintillator layer (<NUM>) to reach the first detector element (<NUM>);
characterized in that:
the second electrode (<NUM>) is made from a non-transparent conductive material but is etched with a pattern to allow light to pass therethrough; or
the second electrode (<NUM>) comprises a first opening for allowing the light from the second scintillator layer (<NUM>) to pass therethrough.