BEAM DETECTION AND FILTERING NOISE
1. A method of operating a digital radiographic detector that includes a plurality of imaging pixels, the method comprising:
- monitoring output signals of the detector;
detecting positive signals in the output signals;
not detecting negative signals in the output signals; and
determining that the detected positive signals are a result of x-rays impacting the imaging pixels based on said not detecting the negative signals.
A digital radiographic detector outputs positive read out signals that may oscillate. The presence of negative going portions of the read out signals may be used to determine that the detected positive signals are a result of noise, while an absence of the negative going portions may be used to determine that x-rays are impacting the detector.
- 1. A method of operating a digital radiographic detector that includes a plurality of imaging pixels, the method comprising:
monitoring output signals of the detector; detecting positive signals in the output signals; not detecting negative signals in the output signals; and determining that the detected positive signals are a result of x-rays impacting the imaging pixels based on said not detecting the negative signals.
- View Dependent Claims (2, 3, 4, 5, 6)
- 7. A method of operating a digital radiographic detector that includes a plurality of imaging pixels, the method comprising:
monitoring output signals of the detector; detecting positive signals in the output signals; detecting negative signals in the output signals; and determining that the detected positive signals are not caused by x-rays impacting the imaging pixels in the detector based on said detecting the negative signals.
- View Dependent Claims (8, 9, 10, 11, 12)
The subject matter disclosed herein relates to digital radiographic detectors. In particular, to methods and apparatuses for determining a detection of a false x-ray beam start by detecting negative going signals.
A digital radiographic detector outputs positive read out signals that may oscillate. The presence of negative going portions of the read out signals may be used to determine that the detected positive signals are a result of noise, while an absence of the negative going portions may be used to determine that x-rays are impacting the detector. An advantage that may be realized in the practice of some disclosed embodiments of the digital radiographic detector is filtering out false beam detection events.
In one embodiment, output signals of a digital radiographic detector are monitored. Positive signals in the output signals may be detected while negative signals are not detected. An algorithm is used to determine that the detected positive signals are a result of x-rays impacting the imaging pixels based on not detecting the negative signals.
In another embodiment, output signals of a digital radiographic detector are monitored. Positive signals in the output signals may be detected as well as negative signals. An algorithm is used to determine that the detected positive signals are not caused by x-rays impacting the imaging pixels in the detector based on detecting the negative signals.
In another embodiment, read out signals of a digital radiographic detector are monitored. Positive signals as well as negative signals in the read out signals may be absent for a full image frame of data. The full frame of image data is stored based on not detecting positive or negative signals.
This brief description of the invention is intended only to provide a brief overview of subject matter disclosed herein according to one or more illustrative embodiments, and does not serve as a guide to interpreting the claims or to define or limit the scope of the invention, which is defined only by the appended claims. This brief description is provided to introduce an illustrative selection of concepts in a simplified form that are further described below in the detailed description. This brief description is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used as an aid in determining the scope of the claimed subject matter. The claimed subject matter is not limited to implementations that solve any or all disadvantages noted in the background.
So that the manner in which the features of the invention can be understood, a detailed description of the invention may be had by reference to certain embodiments, some of which are illustrated in the accompanying drawings. It is to be noted, however, that the drawings illustrate only certain embodiments of this invention and are therefore not to be considered limiting of its scope, for the scope of the invention encompasses other equally effective embodiments. The drawings are not necessarily to scale, emphasis generally being placed upon illustrating the features of certain embodiments of the invention. In the drawings, like numerals are used to indicate like parts throughout the various views. Thus, for further understanding of the invention, reference can be made to the following detailed description, read in connection with the drawings in which:
This application claims priority to U.S. Patent Application Ser. No. 62/354,900, filed Jun. 27, 2016, in the name of Scott et al., and entitled BEAM DETECT AND NOISE FILTER.
This application is related in certain respects to International Application WO 2016/094503 A1, filed Dec. 9, 2015, in the name of Topfer et al., and entitled BEAM DETECTION WITH CONTINUOUS DETECTOR READOUT, which is incorporated herein by reference in its entirety.
In one exemplary embodiment, the rows of photosensitive cells 22 may be scanned one or more at a time by electronic scanning circuit 28 so that the exposure data from the array 12 may be transmitted to electronic read-out circuit 30. Each photosensitive cell 22 may independently store a charge proportional to an intensity, or energy level, of the attenuated radiographic radiation, or x-rays, received and absorbed in the cell. Thus, each photosensitive cell, when read-out, provides information defining an imaging pixel of a radiographic image 24, e.g. a brightness level or an amount of energy absorbed by the imaging pixel, that may be digitally decoded by image processing electronics 34 and transmitted to the digital monitor 26 for display and for viewing by a user. In some embodiments, each row may be logically divided into a plurality of strips such that each strip, or section, of a row may be read, stored, processed, or a combination thereof, to determine an intensity and polarity of a signal detected therein. Such intensity determinations may be averaged and recorded per row, per strip, per plurality of rows and/or strips, or a combination thereof. An electronic bias circuit 32 may be electrically connected to the two-dimensional detector array 12 to provide a bias voltage to each of the photosensitive cells 22.
Each of the bias circuit 32, the scanning circuit 28, and the read-out circuit 30, may communicate with an acquisition control and image processing unit 34 over a connected cable 33 (wired), or the DR detector 40 and the acquisition control and image processing unit 34 may be equipped with a wireless transmitter and receiver to transmit radiographic image data wirelessly 35 to the acquisition control and image processing unit 34, or to transmit and receive program instructions or other commands. The acquisition control and image processing unit 34 may include a processor and electronic memory (not shown) to control operations of the DR detector 40 as described herein, including control of circuits 28, 30, and 32, for example, by use of programmed instructions, and to store and process image data. The acquisition control and image processing unit 34 may also be used to control activation of the x-ray source 14 during a radiographic exposure, controlling an x-ray tube electric current magnitude, and thus the fluence of x-rays in x-ray beam 16, and/or the x-ray tube voltage, and thus the energy level of the x-rays in x-ray beam 16. The acquisition control and image processing unit 34 may also receive instructions or commands transmitted from the DR detector 40.
A portion or all of the acquisition control and image processing unit 34 functions and hardware may reside in or be duplicated in the detector 40 in an on-board processing system 36 which may include a processor and electronic memory to control operations of the DR detector 40 as described herein, including control of circuits 28, 30, and 32, by use of programmed instructions, and to store and process image data similar to the functions of acquisition control and image processing system 34. The image processing system 36 may perform image acquisition and image disposition functions as described herein. The image processing system 36 may control image transmission and image processing and image correction on board the detector 40 based on instructions stored on-board processing system 36 or based on instructions or other commands transmitted from the acquisition control and image processing unit 34. The image processing system 36 may transmit corrected digital image data therefrom. Alternatively, acquisition control and image processing unit 34 may receive raw image data from the detector 40 and process the image data and store it, or it may store raw unprocessed image data in local memory, or in remotely accessible memory.
With regard to a direct detection embodiment of DR detector 40, the photosensitive cells 22 may each include a sensing element sensitive to x-rays, i.e. it absorbs x-rays and generates an amount of charge carriers in proportion to a magnitude of the absorbed x-ray energy. A switching element may be configured to be selectively activated to read out the charge level of a corresponding x-ray sensing element. With regard to an indirect detection embodiment of DR detector 40, photosensitive cells 22 may each include a sensing element sensitive to light rays in the visible spectrum, i.e. it absorbs light rays and generates an amount of charge carriers in proportion to a magnitude of the absorbed light energy, and a switching element that is selectively activated to read the charge level of the corresponding sensing element. A scintillator, or wavelength converter, may be disposed over the light sensitive sensing elements to convert incident x-ray radiographic energy to visible light energy. Thus, in the embodiments disclosed herein, it should be noted that the DR detector 40 (or DR detector 300 in
Examples of sensing elements used in sensing array 12 include various types of photoelectric conversion devices (e.g., photosensors) such as photodiodes (P-N or PIN diodes), photo-capacitors (MIS), photo-transistors or photoconductors. Examples of switching elements used for signal read-out include a-Si TFTs, oxide TFTs, MOS transistors, bipolar transistors and other p-n junction components.
Incident x-rays, or x-ray photons, 16 are converted to optical photons, or light rays, by a scintillator, which light rays are subsequently converted to electron-hole pairs, or charges, upon impacting the a-Si:H n-i-p photodiodes 270. In one embodiment, an exemplary detector cell 222, which may be equivalently referred to herein as a pixel, may include a photodiode 270 having its anode electrically connected to a bias line 285 and its cathode electrically connected to the drain (D) of TFT 271. The bias reference voltage line 232 can control a bias voltage of the photodiodes 270 at each of the detector cells 222. The charge capacity of each of the photodiodes 270 is a function of its bias voltage and its capacitance. In general, a reverse bias voltage, e.g. a negative voltage, may be applied to the bias lines 285 to create an electric field (and hence a depletion region) across the pn junction of each of the photodiodes 270 to enhance its collection efficiency for the charges generated by incident light rays. The image signal represented by the array of photosensor cells 212 may be integrated by the photodiodes while their associated TFTs 271 are held in a non-conducting (off) state, for example, by maintaining the gate lines 283 at a negative voltage via the gate driver circuits 228. The photosensor cell array 212 may be read out by sequentially switching rows of the TFTs 271 to a conducting (on) state by means of the gate driver circuits 228. When a row of the pixels 22 is switched to a conducting state, for example by applying a positive voltage to the corresponding gate line 283, collected charge from the photodiode in those pixels may be transferred along data lines 284 and integrated by the external charge amplifier circuits 286. The row may then be switched back to a non-conducting state, and the process is repeated for each row until the entire array of photosensor cells 212 has been read out. The integrated signal outputs are transferred from the external charge amplifiers 286 to an analog-to-digital converter (ADC) 288 using a parallel-to-serial converter, such as multiplexer 287, which together comprise read-out circuit 230.
This digital image information may be subsequently processed by image processing system 34 or 36 to yield a digital image which may then be digitally stored, transmitted, or immediately displayed on monitor 26, or it may be displayed at a later time by accessing digital electronic on-board memory, memory in the acquisition control & image processing 34, or remote memory such as in a network storage location containing the stored image. The flat panel DR detector 40 having an imaging array as described with reference to
With reference to
In one embodiment, a detector'"'"'s imaging array and electronic circuits may be monitored and evaluated based on various design considerations. These may include required signal thresholds, duration of timing windows, and magnitude or amount of deviations or excursions from a preset value, as will be described herein. A detector'"'"'s imaging array may be evaluated per designated sections of the array, which evaluations may be combined into a full image frame evaluation in order to determine how to disposition a full frame of image data. If the evaluation indicates that a noise event has been detected during a capture of a frame of image data, the design parameters may be consulted to determine how to disposition the full frame of image data. In one embodiment, it may be determined beforehand that a frame of image data will be discarded if a noise event has been detected and a beam-on event has not been detected. In one embodiment, it may be determined beforehand that a frame of image data will be saved as an offset image, or a correction image, if a noise even has not been detected and a beam-on event has not occurred. Two or more of such detected offset images may be detected and combined into one offset image; or a weighted average offset image may be calculated, using two or more of such offset images, and stored for image correction purposes. In one embodiment, it may be determined beforehand that a frame of image data will be saved as an exposure image (diagnostic) even if a noise event has been detected (or not), so long as a legitimate beam-on event has also occurred during a capture of such a frame of image data. These preselected disposition parameters may be embodied in on-board software that programmably controls image handling operations in the DR detector.
The methods described herein may be useful to determine whether an x-ray beam, e.g., a “beam-on” event, impacting the pixels of the detector 500 has occurred by monitoring the detector'"'"'s read-out circuitry for the presence of negative going signals. In one embodiment, the methods described herein may be useful to detect a collimated x-ray beam impacting the detector to capture a radiographic image of an object using only a fraction of the total number of pixels in the image frame of DR detector 500 due to the collimation. In order to detect an x-ray beam collimated onto a small area of the detector, which area may appear anywhere in the array of imaging pixels, the methods disclosed hereunder may be performed to process a portion, or the entire array, of imaging pixels. Thus, while the description hereunder may refer to processing a window 502 of imaging pixels, or consecutive horizontal windows 506 of imaging pixels, the method described herein may be performed such that all the imaging pixels in the DR detector 500 are thereby processed. In one embodiment, all the rows of the detector'"'"'s imaging pixels are continuously processed frame by frame, even if a beam on event does not occur, according to the methods described herein, until a beam-on event is detected, whereafter the methods may be at least temporarily halted while further standard radiographic image capture processing continues in the detector and/or a beam off detection procedure is initiated.
In one exemplary embodiment of the methods disclosed herein, the detector read-out circuitry is monitored for negative going output signals after positive going output signals are detected. Such negative going signals are typically caused by noise sources, and may be identified by their positive-negative (+/−) oscillation. If such a negative signal is detected within a preset time window after a positive signal is detected, the positive signal detection may be programmably classified as a noise signal, or a non-x-ray signal, and may be ignored for the purpose of indicating a beam-on event (no legitimate x-ray beam-on detection). The usefulness of this method stems from the fact that x-rays impacting imaging pixels in the detector do not cause negative going oscillating signals in the detector circuitry.
With reference to
A first exemplary positive signal intensity mean 601 detected in one strip of pixels of the array 500, as illustrated, does not reach a positive intensity +threshold, e.g., a preselected (preprogrammed) value of 20 as designated by the bottom border of the dashed line rectangle 610. The intensity value units (e.g. voltages) and thresholds may be arbitrarily chosen according to desired design considerations. In one embodiment, because the measured positive signal mean 601 does not reach the +threshold it may be ignored for purposes of classifying the positive signal mean 601 as a detected positive signal. As described herein, a positive signal mean above the +threshold is classified as a detected positive signal and may be used to start, i.e., be designated as a first strip, in a logically defined sample window 502. A next vertically consecutive strip of the array 500 is detected to have a positive signal mean 602 because it exceeds the preselected +threshold. In one embodiment, in order to start a logically defined and monitored sample window 502, a minimum preselected number of detected positive signals may be required, such as a number between one (1) and twelve (12), for example. The preselected count of detected positive signals may also be required to be consecutive signals or a cumulative number. If the +threshold required minimum number is preset at one (1), then the detection of the positive signal mean 602 will logically start a monitoring window. The monitoring window size is defined by a preselected number of vertically consecutive strips of pixels. The strips in this exemplary logically defined window are thereafter monitored to detect negative going signals therein.
In the example of
Continuing with the example of
The +threshold and −threshold detections are monitored and measured in the array of imaging pixels 500 using fixed preset processing window sizes 502 to process all the imaging pixels in the array 500. Row dispositions cover an entire row k in the array 500 and so require the results of horizontally consecutive window dispositions that all include the row being dispositioned. Thus, the row dispositions require processing coordination using the inputs from consecutive horizontal windows 506 that span the entire row and provide detection information for each portion of the row, i.e., each strip. In one embodiment, a positive signal mean for a particular strip in any of the windows 506 is logically ORed with the strips in other windows 506 corresponding to the particular row, so that a positive detection for a strip in one or more windows of the group of five windows 506 corresponding to a particular row will result in a positive detection classification for that particular row. This example is illustrated in
With regard to the Frame Classification table of
The Current Frame Disposition table of
As will be appreciated by one skilled in the art, aspects of the present invention may be embodied as a system, method, or computer program product. Accordingly, aspects of the present invention may take the form of an entirely hardcoded hardware embodiment, an entirely software embodiment (including firmware, on-board resident software, micro-code, etc.), or an embodiment combining software and hardware aspects that may all generally be referred to herein as a “processor”, “circuit,” “circuitry,” “module,” “processing unit,” and/or “processing system.” Furthermore, aspects of the present invention may take the form of a computer program product embodied in one or more computer readable medium(s), such as electronic memory having computer readable program code embodied thereon.
Any combination of one or more computer readable medium(s) may be utilized. The computer readable medium may be a computer readable signal medium or a computer readable storage medium. A computer readable storage medium may be, for example, but not limited to, an electronic, magnetic, optical, electromagnetic, infrared, or semiconductor system, apparatus, or device, or any suitable combination of the foregoing. More specific examples (a non-exhaustive list) of the computer readable storage medium would include the following: an electrical connection having one or more wires, a portable computer diskette, a hard disk, a random access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or Flash memory), an optical fiber, a portable compact disc read-only memory (CD-ROM), an optical storage device, a magnetic storage device, or any suitable combination of the foregoing. In the context of this document, a computer readable storage medium may be any tangible medium that can contain, or store a program for use by or in connection with an instruction execution system, apparatus, or device.
Program code and/or executable instructions embodied on a computer readable medium may be transmitted using any appropriate medium, including but not limited to wireless, wireline, optical fiber cable, RF, etc., or any suitable combination of the foregoing.
Computer program code for carrying out operations for aspects of the present invention may be written in any combination of one or more programming languages, including an object oriented programming language such as Java, Smalltalk, C++ or the like and conventional procedural programming languages, such as the “C” programming language or similar programming languages. The program code may execute entirely on the user'"'"'s computer (device), partly on the user'"'"'s computer, as a stand-alone software package, partly on the user'"'"'s computer and partly on a remote computer or entirely on the remote computer or server. In the latter scenario, the remote computer may be connected to the user'"'"'s computer through any type of network, including a local area network (LAN) or a wide area network (WAN), or the connection may be made to an external computer (for example, through the Internet using an Internet Service Provider).
Aspects of the present invention are described herein with reference to flowchart illustrations and/or block diagrams of methods, apparatus (systems) and computer program products according to embodiments of the invention. It will be understood that each block of the flowchart illustrations and/or block diagrams, and combinations of blocks in the flowchart illustrations and/or block diagrams, can be implemented by computer program instructions. These computer program instructions may be provided to a processor of a general purpose computer, special purpose computer, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, create means for implementing the functions/acts specified in the flowchart and/or block diagram block or blocks.
These computer program instructions may also be stored in a computer readable medium that can direct a computer, other programmable data processing apparatus, or other devices to function in a particular manner, such that the instructions stored in the computer readable medium produce an article of manufacture including instructions which implement the function/act specified in the flowchart and/or block diagram block or blocks.
The computer program instructions may also be loaded onto a computer, other programmable data processing apparatus, or other devices to cause a series of operational steps to be performed on the computer, other programmable apparatus or other devices to produce a computer implemented process such that the instructions which execute on the computer or other programmable apparatus provide processes for implementing the functions/acts specified in the flowchart and/or block diagram block or blocks.
This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal language of the claims.