Radiation detector calibration using voltage injection

Abstract

Method for calibrating a direct conversion detector array, the method comprising: Applying a first voltage to a bias electrode (206) of the direct conversion detector array, wherein the bias electrode (206) is placed in a radiation path between an X-ray source (210) and a radiation conversion material (204); Applying a second voltage to the bias electrode (206), wherein the second voltage is different from the first voltage, wherein a difference between the first voltage and the second voltage causes a first electric charge to be generated in the radiation conversion material (204); Measuring the initial electric charge to generate a first measurement; Performing an air scan while X-rays are emitted, generating a second electrical charge within the radiation conversion material (204) due to an interaction of the X-rays with the radiation conversion material (204); Measuring the second electric charge to generate a second measurement; and Comparing the first measurement with the second measurement to identify defects attributable to an element in the radiation path upstream of the radiation conversion material (204).

Description

background

[0001] The present application relates to the field of radiographic examinations and imaging. It finds particular application in the calibration of direct conversion detector arrays and / or flat panel detectors, such as those conventionally included in a computed tomography (CT) scanner, a line scanner, or other radiographic imaging systems (e.g., mammography systems, general radiology systems, etc.).

[0002] Radiography imaging systems are useful for providing information or images of internal aspects of an object under examination. Generally, the object is exposed to radiation, and a two-dimensional image and / or a three-dimensional image is formed based on the radiation absorbed by internal aspects of the object, or instead, on the amount of radiation capable of passing through the object. Typically, very dense aspects of an object absorb more radiation than less dense aspects, and thus, a higher-density aspect, such as a bone, tumor, or weapon, will be visible when surrounded by less dense aspects, such as fatty tissue, muscle, or clothing.

[0003] A radiography imaging system typically includes a detector array and a radiation source. The radiation source is generally configured to emit fan-shaped, conical, wedge-shaped, or otherwise shaped collimated radiation onto an object under examination. The detector array is generally positioned on a diametrically opposite side of the object relative to the radiation source and includes a plurality of pixels that detect radiation incident on the respective pixels. Typically, the pixels are configured to output a substantially continuous analog or digital signal, and when a charge density (e.g., proportional to the detected radiation) is measured by a pixel, the pixel is configured to emit a pulse or change in the respective charge density-indicating signal.The signals emitted by the respective pixels can be converted to the digital domain (if they are not already in the digital domain) and used to generate one or more images of the object showing areas of high radiation transmission and / or low radiation transmission.

[0004] Radiography imaging systems are regularly calibrated to correct for gains, offsets, defect corrections, etc., caused by detector arrays or electronic equipment (e.g., amplifiers, readout devices, etc.). Calibrations are generally performed at the factory before the detector array is attached to other parts of the imaging system. Calibrations are also typically performed during an air scan or a flat-field scan (i.e., a scan in which no object is present and / or an object with known properties is present). During calibration, the detector array emits pulses indicating radiation (e.g., X-rays) that is detected.Since no object is present and / or an object with predetermined / known properties is present, it can be assumed that the pulses generated by the respective pixels have predetermined properties and can be compared with such predetermined properties. Deviations between actual properties of a pulse and predetermined properties of the pulse can be attributed to an error (e.g., an unwanted gain, a defect, etc.), and a correction factor designed to correct the error can be identified. The correction factor can be applied to the pulses generated by the pixel during an examination of an object, for example, to improve the quality of resulting images.

[0005] While the previously mentioned calibration techniques have proven effective in reducing errors and improving the quality of resulting images, there are several limitations / disadvantages of the calibration techniques. For example, factory calibrations are time-consuming because a high number of radiation exposures (e.g., 60 exposures or more) are generally required, for example, to reduce the impact of photon noise. As a result, such a calibration can take two hours or more. Furthermore, because the calibration techniques require the emission of radiation, safety restrictions are imposed. For example, a technician is generally required to monitor the calibration. Thus, a technician's time is used, and the radiation system is unavailable during a period in which the system would typically be in operation.

[0006] The document US 2006 / 0 208 195 A1 relates to systems, methods and devices for calibrating a solid-state X-ray detector.

[0007] The publication US 2010 / 0 183 124 A1 concerns gain calibration and correction methods for digital imaging systems. Summary

[0008] Aspects of the present application address the above-mentioned subject matters and others. According to one aspect, a method for calibrating a direct conversion detector array is provided. The method comprises: applying a first voltage to a bias electrode of the direct conversion detector array, the bias electrode being disposed in a radiation path between an x-ray source and a radiation conversion material; applying a second voltage to the bias electrode, the second voltage being different from the first voltage, a difference between the first voltage and the second voltage causing a first electrical charge to be generated in the radiation conversion material; measuring the first electrical charge to generate a first measurement;Performing an air scan while emitting X-rays, wherein a second electrical charge is generated within the radiation conversion material due to an interaction of the X-rays with the radiation conversion material; measuring the second electrical charge to generate a second measurement; and comparing the first measurement with the second measurement to identify defects attributable to an element in the radiation path upstream of the radiation conversion material.

[0009] The person skilled in the art will also recognize further aspects of the present application upon reading and understanding the attached description. Figures

[0010] The application is illustrated by way of example and not limitation in the figures of the accompanying drawings, in which like reference numerals designate similar elements and in which: Fig. 1 is a schematic block diagram of an exemplary system. Fig. 2 shows a component block diagram of a detector array. Fig. 3 is a circuit diagram of an exemplary pixel and data acquisition component. Fig. 4 is a flowchart illustrating an exemplary method. Fig. 5 is a flowchart illustrating an exemplary method for calibrating a direct conversion detector array. Fig. 6 is an illustration of an exemplary computer-readable medium including processor-executable instructions configured to embody one or more of the provisions set forth herein. Description

[0011] The claimed subject matter will now be described with reference to the drawings, wherein like reference numerals are used to refer to like elements throughout. In the following description, for purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of the claimed subject matter. However, it may be apparent that the claimed subject matter may be practiced without these specific details. In other instances, structures and devices are shown in block diagram form to facilitate description of the claimed subject matter.

[0012] One or more systems and / or techniques for calibrating a direct conversion detector array, or a flat panel detector, of a radiographic imaging system are provided. During calibration of the direct conversion detector array, the voltage applied to a photoconductor, also referred to herein as a direct conversion material (e.g., amorphous selenium), of the direct conversion detector is changed. The change in voltage creates a displacement current in the photoconductor, which generates an electric charge equal to the electric charge generated when radiation strikes the photoconductor. As provided herein, the electric charge or change in charge density generated by the change in voltage can be used to calibrate the direct conversion detector array. In this manner, for example, unit maps and / or gain tables can be generated.Such maps and / or tables can be used to produce a substantially defect-free, uniform image.

[0013] Fig. 1 shows an exemplary system 100. Such an exemplary system 100 may, for example, be used for mammography in a clinic. It will be understood by those skilled in the art that the specific embodiments of the system may depend on the intended functions of the system, and thus, the systems and / or techniques described herein are not intended to be limited by the embodiments of the exemplary system 100. That is, other embodiments known in the art may also be contemplated. For example, in another embodiment, the system may be configured similarly to a computed tomography (CT) scanner used at security checkpoints or in clinics (where the scanner is, for example, shaped like a circular ring and the object to be examined is placed at the center of the circular ring).In another embodiment, the system may, for example, be a line scanner similar to a baggage scanner commonly used at security checkpoints.

[0014] As illustrated, the system 100 typically includes an object inspection device 102 configured to inspect an object (e.g., human tissue, luggage, etc.). One or more images of the inspected object may be displayed, for example, on a monitor of a terminal 108 (e.g., a computer) for human supervision. In this way, aspects of the object that are not visible to the naked eye (e.g., tumors, broken bones, etc.) may be depicted in the one or more images and ultimately detected by a user 126. In another example, where the system is, for example, a baggage scanner at an airport, a dangerous article in a suitcase may be detected based on a scan or examination of the suitcase.

[0015] The object examination device 102 is configured to examine the object to be examined and to transmit the data associated with the examination to other components of the system 100. Among other components, the object examination device 102 includes a radiation source 116 and a detector array 124. The radiation source 116 is configured to emit a fan-shaped, conical, wedge-shaped, and / or other shaped radiation configuration into an examination region 122 of the object examination device 102.

[0016] Aspects (e.g., masses, cancer, weapons, etc.) of the object can cause different amounts of radiation to pass through different parts of the object (e.g., generating high-transmission regions and low-transmission regions within the object). Note that changes in transmission can be used to generate images of an aspect of the object. For example, when human tissue is examined by the object examination device 102, areas of tightly packed (e.g., cancerous) cells may appear more prominent in an image than healthy cells (which may be virtually invisible).

[0017] Radiation passing through the object to be examined (e.g., an object located in the examination area 122) is detected by the detector array 124, which is arranged on a diametrically opposite side of the object from the radiation source 116. As will be described in more detail with respect to Fig. 2, the detector array 124 is a direct conversion detector array. It will be understood by those skilled in the art that a direct conversion detector array is configured to convert radiant energy generated by detected radiation into electrical charge through a direct conversion material, or photoconductor, of the detector array 124. In other words, in a direct conversion detector array, radiation photons interact directly with the direct conversion material (e.g., generating electron-hole pairs) and an electrical charge is generated, which can concentrate at an interface of the direct conversion material (e.g., adjacent pixels of the detector array) to create a net charge density. The direct conversion material may comprise, for example, amorphous selenium, cadmium zinc telluride, silicon, or other direct conversion materials known to those skilled in the art.

[0018] Radiation that passes through highly transmissive / less dense regions of the object may comprise more radiant energy and thus generate a greater electrical charge than radiation that passes through less transmissive / denser regions. Consequently, the electrical charge generated when radiation strikes the detector array is indicative of properties or characteristics of the object. Pixels (e.g., a thin-film transistor (TFT) array) of detector array 124 are configured to detect electrical charge, or a net charge density, generated in a region of the conversion material in close spatial proximity to the pixel and generate a digital or analog signal indicative of the detected charge. It should be noted that in some embodiments, pixels are configured to substantially continuously generate a signal and a pulse, or change in the signal, when electrical charge is detected.In other embodiments, the pixels may be configured not to emit a signal unless and / or until charge is detected.

[0019] It should be noted that an initial voltage is generally applied to the direct conversion material by a power source 112. In this way, an electric field can be generated that is designed to transport the generated electrical charge from the direct conversion material to the pixels. It will be understood by those skilled in the art that the applied initial voltage may depend, for example, on the application of the example system 100 and / or the specifications of the direct conversion detector array 124 (e.g., thickness and / or type of the direct conversion material, etc.). In one example, an initial voltage of 2000 volts is applied to the direct conversion material by the power source 112 (but other voltages may, of course, be applied, such as 10 or 20 volts). The process of applying an initial voltage is generally referred to as biasing the direct conversion material.In other words, a direct conversion material is biased when an initial voltage is applied to the direct conversion material. This initial voltage generally remains constant throughout the examination of an object. Thus, any electrical charge generated by the direct conversion material during the examination is attributable to the detected charge.

[0020] In some embodiments, such as in applications where it is desirable to have the object fixed in a particular orientation for an extended period of time, object supports 118, 120 may be used to maintain the orientation of the object. For example, in a mammography system, the object supports 118, 120 may be used to compress breast tissue to flatten the breast tissue and improve the quality of the resulting image. In other embodiments, the object may be placed on a bed or conveyor belt configured to allow the object, for example, to lie in and / or traverse the examination area 122. A shield 114 may be configured to protect non-examined aspects of the object, such as a person's head, from being exposed to the radiation emitted by the radiation source 116.

[0021] The exemplary system 100 further includes a data acquisition component 104 operatively coupled to the object inspection device 102. The data acquisition component 104 is configured to collect signals, information, and / or data related to the radiation detected by the detector array 124. It should be noted that if the signals emitted by the respective pixels of the detector array 124 are in an analog domain, the data acquisition component 104 may also be configured to convert the signals to the digital domain using analog-to-digital techniques known to those skilled in the art. In one embodiment, the data acquisition component 104 may also be configured to compile the signals and / or the data generated by the respective signals into one or more projections of the object using techniques known to those skilled in the art.

[0022] The exemplary system 100 also includes an image corrector 106 operatively coupled to the data acquisition component 104. The image corrector 106 is configured to correct artifacts, errors, and / or other image degradations in images acquired from the signals. For example, the image corrector 106 may be configured to correct errors in signals caused by the pixels, misalignment of the radiation source and the detector array, defects in the cover of the detector array 124 (e.g., a carbon fiber protective layer, commonly referred to in the art as a bucky cover), etc.

[0023] It will be understood by those skilled in the art that the image corrector 106 generally includes a database of correction factors for respective pixels designed to mitigate errors caused by gains, defects, etc. in the pixels, the direct conversion material, the electronic components of the radiography system 100, etc. Such a database may be referred to by one skilled in the art, for example, as an air table or correction table because the errors are generally determined by an air scan or a flat-field scan (e.g., a scan performed without an object in the examination region 122).It will be understood by those skilled in the art that the terms "air table" and "correction table" herein generally refer to a database of information indicative of defects, non-uniformities, and / or other irregularities in the detector array and / or other electronic components of radiography system 100, and not just those determined when performing an air scan or a flat-field scan. Such a table may, for example, include data indicative of a unit map and / or a gain table that can be used to make corrections.

[0024] As disclosed herein, at least some errors that can conventionally be identified by an air scan or a flat-field scan can be identified using one or more of the techniques and / or systems described herein. Therefore, the term "air table" may be misdescriptive of the database because a conventional air scan need not be performed to identify at least some of the errors associated with the air table. Accordingly, while the term "air table(s)" may be used herein to describe a database containing numerical values ​​for the errors and / or correction factors for correcting the errors, it is understood that such terms are not intended to be limited to mean errors and / or correction factors derived from an air scan or a flat-field scan.It should also be noted that in other embodiments, the data acquisition component 104 may be configured to perform such corrections to the signals or resulting images instead of, or in conjunction with, the image corrector 106.

[0025] The example system 100 also includes a terminal 108 (e.g., a computer) configured to receive the image space data from the image corrector 106. The terminal 108, which may include a monitor, may also be configured to display images of the object to a user 126 (e.g., security personnel, medical personnel, etc.). In this way, the user 126 can examine the image(s) to identify areas of interest within the object(s). In some embodiments, the terminal 108 may also be configured to receive user inputs that may instruct the object inspection device 102 on how to operate and / or may be used to calibrate the object inspection device 102.For example, as described in more detail below, in one embodiment, the terminal 108 may automatically and / or with user input instruct a calibration component 128 when to perform a calibration of the detector array 124.

[0026] The exemplary system 100 also includes a controller 110 operatively coupled to the terminal 108. In one example, the controller 110 is configured to receive user inputs from the terminal 108 and generate commands for the object inspection device 102 indicative of operations to be performed. For example, the user 126 may desire to re-examine the object, and the controller 110 may convert the user inputs into a computer command that instructs the radiation source 116 to emit additional radiation.

[0027] The exemplary system 100 also includes a calibration component 128 operatively coupled to the terminal 108 and configured to perform calibration techniques on the object inspection device, or more specifically, on the detector array 124. As described further below, for example, the calibration component 128 may be configured to specify the voltage for a charge applied to the detector array 124 for calibration purposes. In other embodiments, the calibration component 128 may be configured to determine when a calibration should be performed based on a time elapsed since a previous calibration, a number of examinations since a previous calibration, etc.

[0028] It should be noted that the exemplary system 100 and components of the exemplary system described herein are intended to merely illustrate an exemplary system and are not intended to be construed in a manner that limits the scope of the system and / or the claimed subject matter. For example, the system 100 may include an image restorer configured to convert projection-space data into image-space data, for example, using tomosynthesis. In another embodiment, the exemplary calibration component 128 may be part of a detector array 124. In another embodiment, the power source 112 may be part of an object inspection device 102.Thus, the components of the radiographic imaging system may vary and / or the orientation of the described components may differ from the exemplary system 100 without limiting the scope of the claimed subject matter.

[0029] Fig. Figure 2 illustrates a cross-section of an exemplary conversion detector array 200 (e.g., 124 in the Fig. 1 along line 2-2). As shown, the detector array 200 includes a carbon fiber layer 202, which is designed to protect the detector array from damage and from a radiation source (positioned above the detector array 200) (e.g., 116 in the Fig. 1) to allow emitted radiation to pass through. It should be noted that this layer 202 may be referred to as the buckycover by one skilled in the art. It should also be noted that while the layer 202 is described herein as a carbon fiber layer, other materials having suitable properties (e.g., that can protect other layers from damage, that allow radiation to pass through substantially unhindered, etc.) are also contemplated herein. Furthermore, for example, the buckycover 202 may comprise a combination of two or more materials, one of which may or may not be carbon fiber.

[0030] The detector array 200 also includes a direct conversion material layer, or photoconductor, 204 configured to generate an electric charge in response to radiant energy detected by the direct conversion material. In other words, when radiation photons strike the direct conversion material 204, electron-hole pairs are created, generating an electric charge. As the direct conversion material 204 is biased (as mentioned above and described below), charges begin to drift, generating a current in the direct conversion material 204, and a net charge density is created near an interface of the direct conversion material 204, between the direct conversion material 204 and a detection layer 208 and / or between the direct conversion material 204 and a bias electrode 206. The amount of electric charge generated is a function of the radiant energy detected.In general, higher levels of electrical charge (e.g., producing a higher net charge density) are generated by higher radiation intensity (e.g., a larger dose). Thus, the generated electrical charge indicates the amount of radiation that has passed through the object.

[0031] It should be noted that numerous direct conversion materials are known to those skilled in the art and are contemplated for use herein. For example, the direct conversion material may include amorphous selenium, cadmium zinc telluride (CdZnTe), silicon, and / or other materials that have properties that allow radiant energy to be converted into electrical charge.

[0032] It will be understood by those skilled in the art that in order to generate the current in the direct conversion material 204 and / or to cause the electrical charge to concentrate at an interface of the direct conversion material, the exemplary direct conversion detector array 200 includes a bias electrode 206 configured to apply an initial voltage, or bias, to the direct conversion material 204. In this way, the current drifts, and a net charge density develops at an interface of the direct conversion material 204 near the pixels of the detection layer 208. For example, in one embodiment, the direct conversion material 204 is biased by applying 2000 volts provided by a power source 210 (e.g., 112 in the Fig. 1) to the bias electrode 206.

[0033] As below with respect to Fig. 4-5, the bias electrode 206 can also be used for calibration purposes. For example, in one embodiment, after a bias voltage is applied to the direct conversion material 204 by the bias electrode 206, a second voltage can be applied to the direct conversion material 204 through the bias electrode 206, which can cause a change in a resulting electric field. Such a change in the electric field can cause an electric charge to be generated at an interface of the direct conversion material 204 near the detection layer 208. Thus, the charge density at an interface of the direct conversion material can be (controllably) changed (e.g., similar to a change in charge density caused by incident radiation).

[0034] Electric charge, or a net charge density, developed at an interface of the direct conversion material 204 near the detection layer 208 (e.g., a TFT array, a complementary metal oxide semiconductor (CMOS) array, and / or another pixelated array) is detected by one or more pixels of the detection layer 208 of the detector array 200. Generally, those pixels that are in close spatial proximity to the position at which the radiation impinges on the detector array 200 detect the electric charge, and other pixels do not. Thus, the trajectory of the radiation can be determined by drawing an imaginary line from the focal point of a radiation source (when radiation was emitted) to the pixels that detected the electric charge.It is obvious to those skilled in the art that identifying the trajectory is crucial for some reconstruction techniques, such as tomography, which attempt to reconstruct a 3D image of the object from a multitude of two-dimensional projections.

[0035] Fig. Figure 3 illustrates an exemplary circuit diagram 300 of a thin film transistor 302 and other components that may be, for example, part of the pixel and / or part of a data acquisition component (e.g., 104 in the Fig. 1). The electrical charge generated by a direct conversion material layer by incident radiation (e.g. 204 in the Fig. 2) and / or is generated at an interface of the direct conversion material by changing the voltage applied to the direct conversion material (e.g. by a bias electrode 206 in the Fig. 2) is received at input 304. It will be understood by those skilled in the art that thin-film transistor 302 includes a storage capacitor 306 and a switch 308. Storage capacitor 306 is configured to store a charge while switch 308 is open. When switch 308 is closed, the charge stored in storage capacitor 306 flows through the switch and into an integrator 310, or charge amplifier, operatively coupled to the switch. Integrator 310 is configured to convert the charge to a voltage and output the voltage to a readout device 312, operatively coupled to integrator 310. Readout device 312 is configured to perform a sample and hold and convert the analog signal to the digital domain.A capacitor 314, operatively coupled to the integrator 310, is designed, among other things, to reduce or attenuate reverse current flow.

[0036] It is pointed out that the Fig. 3 is merely an example, and other circuit diagrams known to those skilled in the art are also contemplated. For example, in another example, the integrator 310 may be part of the pixel 302. In another example, the circuitry of the pixel 302 and / or the data acquisition component may differ from the example circuitry.

[0037] Fig. 4 illustrates an exemplary method 400. The exemplary method 400 begins at 402 and a charge generated by a photoconductor (e.g., amorphous selenium), or a direct conversion material, of a direct conversion detector array is detected at 404. The electrical charge indicates a change in a voltage applied to the photoconductor (e.g., by a bias electrode 206 in the Fig. 2). For example, in one embodiment, a first voltage, which may be, for example, ground or zero voltage, is applied to bias the photoconductor during a first time interval, and a second voltage different from the first voltage is applied to the photoconductor during a second time interval subsequent to the first time interval.

[0038] It should be noted that the amount of charge may vary according to the initial applied voltage, the type and / or thickness of the photoconductive material, gain settings of the detector array, etc. For example, in one embodiment, the change in voltage may equal a low exposure dose of radiation (e.g., a change of about 10 V or more). In another embodiment, the change in voltage may equal a high exposure dose of radiation (e.g., a change of about 100 V or more). It should also be noted that the term "change" as used herein may refer to an increase or a decrease in the applied voltage. For example, in one embodiment, the initial applied voltage is 2000 V and the second applied voltage is 2010 V, resulting in a voltage change of plus 10 V.In another embodiment, the second applied voltage is 1990 V, resulting in a voltage change of minus 10 V.

[0039] In one embodiment, the detected electrical charge, or change in charge density, is used to calibrate the detector array. For example, the detected electrical change can be used to generate a unit map, a gain table, and / or another calibration table known to those skilled in the art (e.g., air table / correction table). In this way, the detected electrical change can be used to, for example, detect at least one of non-uniformity in the photoconductor, defects in the photoconductor, gains in an amplifier (e.g., 310 in the Fig. 3), enhancements in a pixel and / or defects in a detection layer (e.g. 208 in the Fig. 2) to calibrate. In this way, correction factors that can be applied to signals and / or data output by the detector array or data acquisition components during an examination can be calculated without performing an air scan or a flat-field scan (which requires the emission of radiation), and can be performed, for example, on-site or off-site at a production facility. In other words, defects and / or errors in the direct conversion material layer (e.g., 204 in the Fig. 2) a detector array (e.g. 200 in the Fig. 2) and / or components of the system following the direct conversion material are identified without radiation emission. It is noted that for some calibration procedures, such as misalignment of the focal point, defects in radiation filters and / or defects in the bucky cover (e.g. 202 in the Fig. 2) to detect, for example, it is still necessary that radiation is emitted.

[0040] The exemplary method 400 ends at 406.

[0041] Fig. 5 illustrates an exemplary method 500 for calibrating a direct conversion detector array, such as that shown in Fig. 2. The method begins at 502 and a first power source (e.g., 208 in the Fig. 2) is used to apply a first voltage to a photoconductor of the direct conversion detector array at 504. As previously described, the first voltage may be configured to bias the photoconductor so that if and / or when it detects radiation, an electrical charge may be generated from the change in voltage caused by incident radiation.

[0042] At 506, a second power source is used to apply a second voltage to the photoconductor. The second voltage is different from the first voltage and causes a first electrical charge to be generated at an interface of a photoconductor adjacent to a pixel (e.g., a TFT array). In other words, the voltage change between the first voltage and the second voltage causes a first electrical charge to be generated and / or causes a change in the net charge density at an interface of the photoconductor. It should be noted that the applied voltage change may be a function of, for example, the type and / or thickness of the photoconductor, the type of calibration performed, and / or the gain settings of the detector. It should also be noted that a net charge density (e.g., indicative of the amount of electrical charge generated) is a function of the voltage change.For example, a change in voltage of 100 V can cause a larger net charge density to be generated than a voltage change of, say, 10 V.

[0043] It should be noted that while the terms first power source and second power source are used herein, the terms "first" and "second" are not intended to necessarily be interpreted as two different power sources. That is, in one embodiment, the first power source and the second power source may be the same power source. In another embodiment, the first power source and the second power source may be different power sources. Thus, the terms "first power source" and "second power source" are intended to be used broadly herein to mean one power source or two or more different power sources.

[0044] At 508, the first electrical charge, or other net charge density, is detected. Generally, the electrical charge is detected by pixels of a detection layer region (e.g., 208) of the detector array. For example, the pixels of a thin-film transistor array (e.g., 302 in the Fig. 3) in one embodiment, configured to collect electrical charge generated at an interface of the photoconductor located in close spatial proximity to the respective pixels. It should be noted that in other embodiments, the detector array may comprise other types of pixelated arrays. For example, in another embodiment, the detector array may comprise a Complementary Metal Oxide Semiconductor (CMOS) array. Generally, the pixels of the pixelated array are regularly configured to release the electrical charge, and a signal, or a pulse in a uniformly emitted signal, is generated indicative of the generated electrical charge.

[0045] At 510, the detected first electrical charge is used to calibrate the detector array. That is, the first electrical charge is used to identify errors in the detector array, amplifiers, readout devices, etc., and / or to identify correction factors that can correct such errors. For example, in one embodiment, the detected first electrical charge can be used to generate a unit map, a gain table, and / or another air table that can be used to correct signals / pulses generated by respective pixels during an examination of an object. In other words, the detected electrical charge can be used to calibrate at least one of non-uniformity in the photoconductor, defects in the photoconductor, gains in the pixels, gains in other electronic components of the system, such as amplifiers (e.g., 310 in the Fig. 3), etc. In this way, for example, air tables or correction tables (which are usually generated using air scans or flat-field scans) can be generated without emitting radiation.

[0046] In one embodiment, the operations may be repeated multiple times to refine the calibration and / or ensure the accuracy of the calibration. For example, the second power source may be used to reapply the second voltage to the photoconductor (e.g., once the photoconductor has returned to the first voltage state), and electrical charge generated by the difference between the first voltage and the second voltage may be detected and compared with data generated by the first electrical charge. In this way, the accuracy of correction factors applied to signals and / or data during an examination of an object may be improved, so that additional errors (which further degrade the image quality of the resulting image) are not introduced into the signals and / or data due to inaccurate correction factors.

[0047] In another embodiment, a third power source (which may, for example, be different from the first and second power sources or one of the first and second power sources) is used to apply a third voltage to the photoconductor. The third voltage is different from the first and second voltages. Furthermore, the difference between at least one of the first voltage and third voltage and the second voltage and the third voltage causes a second electrical charge to be generated. In other words, the third voltage may be applied while the second voltage is applied (for example, causing the second electrical charge to be the difference between the second and third voltages) or may be applied while the first voltage is applied but not the second voltage (for example, causing the second electrical charge to be the difference between the first and third voltages).In other words, when three or more voltages are applied, the voltages may be applied in a pulse mode, where the photoconductor returns to a base voltage (e.g., the first voltage) between voltage changes, or in a staircase mode, where the photoconductor does not return to a base voltage until another voltage is applied. That is, in a staircase mode, after a second voltage is applied (and a first electrical charge is generated), a third voltage is applied (and a second electrical charge is generated) before the photoconductor returns to a base voltage (e.g., a first voltage). It will be understood by those skilled in the art that, for example, whether a pulse mode or a staircase mode is used for applying the voltages may be a function of the photoconductor used in the detector array.For example, if the detector array includes a photoconductor with a high leakage current and / or if the system is in a low frame rate mode, a pulse mode method may be more suitable than a staircase mode method. Conversely, if the detector array includes a photoconductor with a low leakage current and / or if the system is in a high frame rate mode, a staircase mode method may be more suitable than a pulse mode method.

[0048] Similar to the first electric charge, the second electric charge is transferred through the detection layer (e.g. 208 in the Fig. 2) and can be used to calibrate the detector array and / or other components downstream of the detector array. For example, in one embodiment, errors generated by components of the detector array and / or correction factors for correcting the errors can be identified using both the first electrical charge and the second electrical charge. In this way, the errors and / or correction factors can be identified, for example, using more data points (e.g., causing the accuracy of the identifications to be improved relative to a single data point).

[0049] The exemplary method 500 ends at 512.

[0050] Another embodiment involves a computer-readable medium comprising processor-executable instructions configured to implement one or more of the techniques presented herein. An exemplary computer-readable medium that may be devised in this manner is described in Fig. 6, wherein the implementation 600 comprises a computer-readable medium 602 (e.g., a flash drive, a CD-R, DVD-R, or a hard disk of a hard disk storage device) on which computer-readable data 604 is encoded. This computer-readable data, in turn, comprises a set of computer instructions configured to operate according to one or more of the principles set forth herein. In such an embodiment 600, the processor-executable instructions 606 may, for example, be configured to perform a method 608, such as the exemplary methods 400 of Fig. 4 and / or 500 of the Fig. 5. In another such embodiment, the processor-executable instructions may be configured, for example, to implement a system such as at least a portion of the exemplary system 100 of the Fig. 1. Many such computer-readable media can be devised by one skilled in the art that are adapted to operate in accordance with one or more of the techniques presented herein.

[0051] Those skilled in the art will appreciate that there are numerous advantages to the systems and / or techniques disclosed herein. For example, because calibration can be performed without emitting radiation, the methods disclosed herein can be performed programmatically or automatically. In other words, for example, a computer program can automatically determine a calibration to be performed after, for example, a predetermined time has elapsed and / or a predetermined number of tests have been performed. Thus, a technician, who is commonly required to monitor the calibration of a system during radiation exposure, is not necessarily required to monitor the calibration. Furthermore, because calibration can be performed programmatically, it can be performed during downtimes when the system is typically not in use, for example, in the middle of the night.

[0052] The systems and / or techniques described herein also facilitate a faster calibration procedure. While a conventional calibration procedure (using radiation) may require a large number of radiation exposures (e.g., 60 exposures or more) to reduce the influence of photon noise and may therefore take up to two or more hours to complete, a calibration procedure using the techniques described herein may take significantly less time, at least in part because the number of exposures (e.g., changes in voltage and / or radiation exposures) can be reduced and the length of time between exposures can be shortened. For example, the calibration procedure may be completed in five minutes, but generally will not take more than thirty minutes.Furthermore, in one embodiment, fewer than thirty images are generated (compared to the at least sixty typically generated during calibration).

[0053] Furthermore, since the voltage is applied to the photoconductor, defects attributable to the photoconductor, the pixelated array, and / or other electronic devices downstream of the photoconductor can be decoupled from defects attributable to the buckycover, radiation filters, etc. In other words, in ordinary calibration procedures (e.g., when radiation is emitted), it is difficult to determine whether the errors are caused by the radiation filters, the buckycover, the photoconductor, the pixelated array, etc., since there is no measurement of the error upstream of the readout device (e.g., 312 in the Fig.3). Using the techniques disclosed herein, it can be determined whether the errors / defects occur in parts of the system preceding the photoconductor or in parts of the system following and including the photoconductor, since errors / defects that occur in parts of the system following and including the photoconductor will appear in data acquired by techniques and / or systems disclosed herein. Errors / defects that occur in data acquired by air scans or flat-field scans, but not in data acquired by calibration techniques disclosed herein, can be attributed to parts of the system preceding the photoconductor.

[0054] Furthermore, as used herein, the terms "example" and / or "exemplary" serve as an example, instance, or illustration. Any aspect, design, etc. described herein as an "example" and / or "exemplary" is not necessarily to be construed as advantageous over other aspects, designs, etc. Use of these terms is intended rather to present present concepts in a concrete manner. As used in this application, the term "or" is intended to mean an inclusive "or" rather than an exclusive "or." Unless otherwise described or clearly evident from the context, "X uses A or B" is intended to mean any of the naturally inclusive permutations. That is, if X uses A; X uses B; or X uses both A and B, then "X uses A or B" is satisfied in each of the foregoing cases.In addition, the articles "a" or "an" as used in this application and the appended claims may generally be interpreted to mean "one or more" unless otherwise described or it is clearly evident from the context that they are directed to a singular form.

[0055] Furthermore, although the disclosure has been shown and described with respect to one or more implementations, variations and modifications may occur to those skilled in the art based on a reading and understanding of this description and the accompanying drawings. The disclosure includes all such modifications and variations and is limited only by the scope of the following claims. With particular regard to the various functions performed by the components described above (e.g., elements, devices, etc.), the terms used to describe such components, unless otherwise described, are intended to correspond to any component that performs the described function of the described components (e.g.,that is, functionally equivalent), although not structurally equivalent to the disclosed structure performing the function in the exemplary implementations of the disclosure shown herein. Moreover, while a particular feature has been disclosed with respect to only one of the various implementations, such feature may be combined with one or more other features of the other implementations as may be desired and advantageous for any given or particular application. Furthermore, to the extent that the terms "include," "have," "has," "with," or variations thereof are used in either the Detailed Description or the claims, such terms are intended to be inclusive in a manner similar to the term "comprising."

Claims

[1] A method for calibrating a direct conversion detector array, the method comprising: Applying a first voltage to a bias electrode (206) of the direct conversion detector array, the bias electrode (206) being disposed in a radiation path between an x-ray source (210) and a radiation conversion material (204); Applying a second voltage to the bias electrode (206), the second voltage being different from the first voltage, a difference between the first voltage and the second voltage causing a first electrical charge to be generated in the radiation conversion material (204); measuring the first electrical charge to produce a first measurement; performing an air scan while emitting X-rays, wherein a second electrical charge is generated within the radiation conversion material (204) due to an interaction of the X-rays with the radiation conversion material (204); measuring the second electrical charge to produce a second measurement; and Comparing the first measurement with the second measurement to identify defects attributable to an element in the radiation path upstream of the radiation conversion material (204). [2] The method of claim 1, comprising: correcting a non-uniformity in the radiation conversion material (204). [3] A method according to claim 1, comprising: programmatically applying the first voltage to the bias electrode (206); programmatically applying the second voltage to the bias electrode (206); programmatically detecting the first electrical charge; and programmatically using the detected first electrical charge to calibrate the detector array. [4] The method of claim 1, comprising: generating a defect map using the first measurement. [5] Method comprising: Generating a first electrical charge in a radiation conversion material (204) by varying a voltage applied to the radiation conversion material (204) through a bias electrode (206) arranged in a radiation path between an x-ray source (210) and the radiation conversion material (204); Storing the first electrical charge in a capacitor (306); Converting the first electrical charge stored in the capacitor (306) into a voltage signal; Generating a first measurement, the first measurement indicative of the first electrical charge stored in the capacitor (306) using the voltage signal; performing an air scan while emitting X-rays, wherein a second electrical charge is generated within the radiation conversion material (204) due to an interaction of the X-rays with the radiation conversion material (204); measuring the second electrical charge to produce a second measurement; and Comparing the first measurement with the second measurement to identify defects attributable to an element in the radiation path upstream of the radiation conversion material (204). [6] The method of claim 5, wherein the radiation conversion material (204) comprises cadmium zinc telluride. [7] The method of claim 6, comprising: generating a defect map of the radiation conversion material (204) using the first measurement. [8] The method of claim 6, comprising: correcting a non-uniformity in the radiation conversion material (204). [9] The method of claim 5, wherein converting comprises selectively coupling the capacitor (306) to an integrator (310). [10] A method according to claim 9, wherein the voltage is varied by at least 10 V. [11] The method of claim 5, wherein the radiation conversion material (204) comprises amorphous selenium. [12] A method according to claim 5, comprising: Correcting at least one of: gain in a pixel of the direct conversion detector array comprising the radiation conversion material (204), a defect in the pixel, or gain in an amplifier using the first measurement. [13] The method of claim 5, wherein the first electrical voltage is not generated by the detected X-radiation. [14] A method for calibrating a direct conversion detector array, comprising: Applying a first voltage to a bias electrode (206) of the direct conversion detector array, the bias electrode (206) being arranged in a radiation path between an x-ray source (210) and the radiation conversion material (204); Applying a second voltage to the bias electrode (206), the second voltage being different from the first voltage, a difference between the first voltage and the second voltage causing a first electrical charge to be generated in the radiation conversion material (204) of the direct conversion detector array; measuring the first electrical charge to produce a first measurement; performing an air scan while emitting X-rays, wherein a second electrical charge is generated within the radiation conversion material (204) due to an interaction of the X-rays with the radiation conversion material (204); measuring the second electrical charge to produce a second measurement; Calibrating the direct conversion detector array using the first measurement to correct one or more defects in the radiation conversion material (204); and Comparing the first measurement with the second measurement to identify defects attributable to an element in the radiation path upstream of the radiation conversion material (204). [15] A method according to claim 14, comprising: Correcting a gain in a pixel of the direct conversion detector array, a defect in the pixel, a defect in the radiation conversion material (204), or a gain in an amplifier. [16] A method according to claim 14, comprising: Applying a third voltage to the bias electrode (206), the third voltage being different from the first voltage and the second voltage, a difference between the third voltage and at least one of the first voltage and the second voltage causing a third electrical charge to be generated; Measuring the third electrical charge to produce a third measurement; and Calibrate the direct conversion detector array using the third measurement.

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