Patent Description:
Scattered radiation is known to degrade image quality in diagnostic x-ray imaging. Traditional methods of reducing scatter include collimation, utilizing an air-gap, and/or utilizing an anti-scatter grid. Best practices in radiography prescribe collimation on every exam and, while this is helpful, it is not completely sufficient due to scatter that occurs within the subject. Likewise, air-gap techniques are helpful, but are not practical at the bedside. Anti-scatter grids are the most popular means of reducing x-ray scatter in portable imaging, but they present challenges to radiographers such as positioning and alignment. Image processing tools, such as SmartGrid from Carestream Health, Inc. , have been developed to compensate for the effects of x-ray scatter in a radiographic image, and produces results comparable to those of a physical anti-scatter grid. The SmartGrid algorithm estimates the scatter distribution and removes it from the radiographic image, resulting in an image with improved contrast. Many physical factors affect scatter: the energy spectrum of the x-ray beam, thickness and material composition of the subject being imaged, and collimation, for example. The SmartGrid algorithm accommodates these variables automatically and so its use results in image quality that approximates anti-scatter grid visual performance.

A scatter removal algorithm is an enhancement algorithm that improves radiographic image contrast by suppressing scatter in the image. The fundamental method includes developing a scatter distribution image, which is a representation of the scatter contained in the radiographic image, and then subtracting it from the original input image. The scatter distribution image is developed using information from the image in both linear exposure space as well as attenuation space, which is a log transformation of the linear data. Segmentation is done to focus the development of the scatter field on relevant anatomical data and is used to compute the mean linear exposure of the input image. Parameters used to estimate scatter are determined. These include the scatter-to-primary ratio (SPR) and a curvature parameter used to control perturbation of the scatter distribution as the scatter field is developed. The scatter distribution image is computed based upon the default assumption that every object exposed by x-rays has a basic (default) scatter distribution that is characterized by a certain level of energy and scatter intensity variation across the whole object field of view. Adaptive updating of the scatter intensity across the entire object field of view is performed in a repetitive fashion based upon the SPR parameter for a prescribed number of iterations.

Reference is made to <CIT> disclosing an X-ray imaging apparatus with an X-ray generation means for emitting X-rays, and an X-ray detector on which a grid selected from a plurality of different types of grids is removably mountable. The X-ray detector includes an automatic exposure control (AEC) detector for detecting the quantity of X-rays received and for outputting a signal based on the detected quantity and a control means for controlling the X-ray generation means and the AEC detector. The control means controls the X-ray generation means based on the signal output from the AEC detector, and the AEC detector using correction data to correct an exposure detection element forming a part of the AEC detector.

Further, <CIT> discloses a method for processing a radiography image derived from an X-ray radiation passing through an object, and a radiography system for performing such method. The method comprises a step of estimating, based on the radiography image, a scatter signal present in the radiography image, a step of calculating, based on the estimated scatter signal, a scatter removal signal indicative of a scattered radiation removable from the X-ray radiation passing through the object by a reference anti-scatter device, and a step of correcting the radiography image based on the scatter removal signal.

Scatter removal processing has demonstrated that equivalent radiographic image quality can be achieved without using an anti-scatter grid at a dose level comparable to that when an anti-scatter grid is used. Compensating the anti-scatter grid bucky factor can be easily performed with portable imaging where the exposure level is determined manually by the operator. However, for a radiographic system with AEC, the exposure level of the detector to the x-ray beam is preconfigured generically by programming an AEC trigger level. When a radiographic image is captured without an anti-scatter grid the AEC will be triggered more quickly, as compared to the same exposure with an anti-scatter grid, at a lower x-ray exposure level to the subject. This automatically applied lower exposure level to the subject does not allow a scatter removal algorithm to fully realize its benefit. To overcome this issue, whenever a scatter removal algorithm is to be used, either without a grid or with a low ratio grid, the AEC will be preconfigured at a higher trigger level to ensure enough primary exposure is delivered to the subject as if a high ratio grid is used in the x-ray beam path.

A radiographic imaging system uses an automatic exposure control device configured at a default shut-off threshold. If the radiographic imaging system includes a processor programmed to process the image by executing a scatter removal algorithm thereupon, the shut-off threshold of the AEC is increased prior to capturing the radiographic image.

In accordance with the present invention, a radiographic imaging system and a method as set forth in the independent claims, respectively, is provided. Further embodiments of the invention are inter alia disclosed in the dependent claims. In one embodiment, a radiographic imaging system includes an x-ray source, an x-ray detector, and an automatic exposure control (AEC) device coupled to the x-ray source. The AEC is configured to trigger a shutdown of the x-ray source when the AEC receives an amount of x-ray energy that satisfies a preset threshold. A processing system may receive a request to execute a program for removing x-ray scatter in the captured radiographic image and, in response, the processing system increases the preset threshold for triggering the AEC.

In another embodiment, a method of capturing and processing a radiographic image of a subject includes positioning an x-ray source and an x-ray detector about a subject to be radiographically imaged. A default threshold is preset in an AEC device configured to terminate x-ray emission from the x-ray source. In response to a request for using a scatter removal algorithm, the preset default threshold of the AEC is increased prior to capturing the radiographic image of the subject.

The summary descriptions above are not meant to describe individual separate embodiments whose elements are not interchangeable. In fact, many of the elements described as related to a particular embodiment can be used together with, and possibly interchanged with, elements of other described embodiments. Many changes and modifications may be made within the scope of the appended claims.

This brief description 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 below are intended to be drawn neither to any precise scale with respect to relative size, angular relationship, relative position, or timing relationship, nor to any combinational relationship with respect to interchangeability, substitution, or representation of a required implementation, 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:.

<FIG> is a perspective view of a digital radiographic (DR) imaging system <NUM> that may include a generally curved or planar DR detector <NUM> (shown in a planar embodiment and without a housing for clarity of description), an x-ray source <NUM> configured to generate radiographic energy (x-ray radiation), and a digital monitor, or electronic display, <NUM> configured to display images captured by the DR detector <NUM>, according to one embodiment. The DR detector <NUM> may include a two dimensional array <NUM> of detector cells <NUM> (photosensors), arranged in electronically addressable rows and columns. The DR detector <NUM> may be positioned to receive x-rays <NUM> passing through a subject <NUM> during a radiographic energy exposure, or radiographic energy pulse, emitted by the x-ray source <NUM>. As shown in <FIG>, the radiographic imaging system <NUM> may use an x-ray source <NUM> that emits collimated x-rays <NUM>, e.g. an x-ray beam, selectively aimed at and passing through a preselected region <NUM> of the subject <NUM>. The x-ray beam <NUM> may be attenuated by varying degrees along its plurality of rays according to the internal structure of the subject <NUM>, which attenuated rays are detected by the array <NUM> of photosensitive detector cells <NUM>. The curved or planar DR detector <NUM> is positioned, as much as possible, in a perpendicular relation to a substantially central ray <NUM> of the plurality of rays <NUM> emitted by the x-ray source <NUM>. In a curved array embodiment, the source <NUM> may be centrally positioned such that a larger percentage, or all, of the photosensitive detector cells are positioned perpendicular to incoming x-rays from the centrally positioned source <NUM>. The array <NUM> of individual photosensitive cells (pixels) <NUM> may be electronically addressed (scanned) by their position according to column and row. As used herein, the terms "column" and "row" refer to the vertical and horizontal arrangement of the photosensor cells <NUM> and, for clarity of description, it will be assumed that the rows extend horizontally and the columns extend vertically. However, the orientation of the columns and rows is arbitrary and does not limit the scope of any embodiments disclosed herein. Furthermore, the term "subject" may be illustrated as a human subject in the description of <FIG>, however, a subject of a DR imaging system, as the term is used herein, may be a human, an animal, an inanimate object, or a portion thereof.

In one exemplary embodiment, the rows of photosensitive cells <NUM> may be scanned one or more at a time by electronic scanning circuit <NUM> so that the exposure data from the array <NUM> may be transmitted to electronic read-out circuit <NUM>. Each photosensitive cell <NUM> 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 a pixel of a radiographic image <NUM>, e.g. a brightness level or an amount of energy absorbed by the pixel, that may be digitally decoded by image processing system <NUM> and transmitted to be displayed by the digital monitor <NUM> for viewing by a user. An electronic bias circuit <NUM> is electrically connected to the two-dimensional detector array <NUM> to provide a bias voltage to each of the photosensitive cells <NUM>.

Each of the bias circuit <NUM>, the scanning circuit <NUM>, and the read-out circuit <NUM>, may communicate with an acquisition control and image processing system <NUM> over a connected cable <NUM> (wired), or the DR detector <NUM> and the acquisition control and image processing system <NUM> may be equipped with a wireless transmitter and receiver to transmit radiographic image data wirelessly <NUM> to the acquisition control and image processing system <NUM>. The acquisition control and image processing system <NUM> may include a processor and electronic memory (not shown) to control operations of the DR detector <NUM> as described herein, including control of circuits <NUM>, <NUM>, and <NUM>, for example, by use of programmed instructions, and to store and process image data. The acquisition control and image processing system <NUM> may also be used to control activation of the x-ray source <NUM> during a radiographic exposure, controlling an x-ray tube electric current magnitude, and thus the fluence of x-rays in x-ray beam <NUM>, and/or the x-ray tube voltage, and thus the energy level of the x-rays in x-ray beam <NUM>. A portion or all of the acquisition control and image processing system <NUM> functions may reside in the detector <NUM> in an on-board processing system <NUM> which may include a processor and electronic memory to control operations of the DR detector <NUM> as described herein, including control of circuits <NUM>, <NUM>. and <NUM>, by use of programmed instructions, and to store and process image data similar to the functions of standalone acquisition control and image processing system <NUM>. The image processing system may perform image acquisition and image disposition functions as described herein. The image processing system <NUM> may control image transmission and image processing and image correction on board the detector <NUM> based on instructions or other commands transmitted from the acquisition control and image processing system <NUM>, and transmit corrected digital image data therefrom. Alternatively, acquisition control and image processing system <NUM> may receive raw image data from the detector <NUM> and process the image data and store it, or it may store raw unprocessed image data in local memory, or in remotely accessible memory. A user input <NUM> may include input devices such as a keyboard, a mouse, a touchscreen, or other input devices configured to allow an operator to set or request specific parameters to be used by either of the processing systems <NUM>, <NUM>, for controlling operations, such as exposure levels, AEC trigger levels and duration, of the digital radiographic (DR) imaging system <NUM>.

With regard to a direct detection embodiment of DR detector <NUM>, the photosensitive cells <NUM> 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 <NUM>, photosensitive cells <NUM> 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 <NUM> (or DR detector <NUM> in <FIG> or DR detector <NUM> in <FIG>) may include an indirect or direct type of DR detector.

Examples of sensing elements used in sensing array <NUM> include various types of photoelectric conversion devices (e.g., photosensors) such as photodiodes (P-N or PIN diodes), photo-capacitors (MIS), photo-transistors or photoconductons. 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. An automatic exposure control (AEC) device <NUM> may be positioned between the subject <NUM> and the DR detector <NUM> in the path of the x-ray beam <NUM>. An anti-scatter grid <NUM> may be positioned between the subject <NUM> and the AEC device <NUM> in the path of the x-ray beam <NUM>. The AEC device <NUM> and the anti-scatter grid <NUM> are represented in <FIG> in a miniaturized form for clarity of illustration. A full size AEC device <NUM> and anti-scatter grid <NUM> may be positioned in the planes occupied by the AEC device <NUM> and the anti-scatter grid <NUM> represented in <FIG>. The full size AEC device <NUM> and anti-scatter grid <NUM> may be formed having a size approximately equivalent in area to the DR detector <NUM>, and are described in more detail herein in relation to <FIG>. The AEC device <NUM> may be communicatively connected to the processing systems <NUM>, <NUM>, in a similar fashion as the detector <NUM>, as described herein, for transmitting an x-ray source termination signal to, and for receiving an instruction to set a variable AEC trigger level from. the processing system <NUM>, <NUM>.

<FIG> is a schematic diagram <NUM> of a portion of a two-dimensional array <NUM> for a DR detector <NUM>. The array of photosensor cells <NUM>, whose operation may be consistent with the photosensor array <NUM> described above, may include a number of hydrogenated amorphous silicon (a-Si:H) n-i-p photodiodes <NUM> and thin film transistors (TFTs) <NUM> formed as field effect transistors (FETs) each having gate (G), source (S), and drain (D) terminals. In embodiments of DR detector <NUM> disclosed herein, such as a multilayer DR detector (<NUM> of <FIG>), the two-dimensional array of photosensor cells <NUM> may be formed in a device layer that abuts adjacent layers of the DR detector structure, which adjacent layers may include a rigid glass layer or a flexible polyimide layer or a layer including carbon fiber without any adjacent rigid layers. A plurality of gate driver circuits <NUM> may be electrically connected to a plurality of gate lines <NUM> which control a voltage applied to the gates of TFTs <NUM>, a plurality of readout circuits <NUM> may be electrically connected to data lines <NUM>, and a plurality of bias lines <NUM> may be electrically connected to a bias line bus or a variable bias reference voltage line <NUM> which controls a voltage applied to the photodiodes <NUM>. Charge amplifiers <NUM> may be electrically connected to the data lines <NUM> to receive signals therefrom. Outputs from the charge amplifiers <NUM> may be electrically connected to a multiplexer <NUM>, such as an analog multiplexer, then to an analog-to-digital converter (ADC) <NUM>, or they may be directly connected to the ADC, to stream out the digital radiographic image data at desired rates. In one embodiment, the schematic diagram of <FIG> may represent a portion of a DR detector <NUM> such as an a-Si:H based indirect flat panel, curved panel, or flexible panel imager.

Incident x-rays, or x-ray photons, <NUM> 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 <NUM>. In one embodiment, an exemplary detector cell <NUM>, which may be equivalently referred to herein as a pixel, may include a photodiode <NUM> having its anode electrically connected to a bias line <NUM> and its cathode electrically connected to the drain (D) of TFT <NUM>. The bias reference voltage line <NUM> can control a bias voltage of the photodiodes <NUM> at each of the detector cells <NUM>. The charge capacity of each of the photodiodes <NUM> 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 <NUM> to create an electric field (and hence a depletion region) across the pn junction of each of the photodiodes <NUM> to enhance its collection efficiency for the charges generated by incident light rays. The image signal represented by the array of photosensor cells <NUM> may be integrated by the photodiodes while their associated TFTs <NUM> are held in a non-conducting (off) state, for example, by maintaining the gate lines <NUM> at a negative voltage via the gate driver circuits <NUM>. The photosensor cell array <NUM> may be read out by sequentially switching rows of the TFTs <NUM> to a conducting (on) state by means of the gate driver circuits <NUM>. When a row of the pixels <NUM> is switched to a conducting state, for example by applying a positive voltage to the corresponding gate line <NUM>, collected charge from the photodiode in those pixels may be transferred along data lines <NUM> and integrated by the external charge amplifier circuits <NUM>. 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 <NUM> has been read out. The integrated signal outputs are transferred from the external charge amplifiers <NUM> to an analog-to-digital converter (ADC) <NUM> using a parallel-to-serial converter, such as multiplexer <NUM>, which together comprise read-out circuit <NUM>.

This digital image information may be subsequently processed by image processing system <NUM> to yield a digital image which may then be digitally stored and immediately displayed on monitor <NUM>, or it may be displayed at a later time by accessing the digital electronic memory containing the stored image. The flat panel DR detector <NUM> having an imaging array as described with reference to <FIG> is capable of both single-shot (e.g., static, radiographic) and continuous (e.g., fluoroscopic) image acquisition.

<FIG> shows a perspective view of an exemplary prior art generally rectangular, planar, portable wireless DR detector <NUM> according to an embodiment of DR detector <NUM> disclosed herein. The DR detector <NUM> may include a flexible substrate to allow the DR detector to capture radiographic images in a curved orientation. The flexible substrate may be fabricated in a permanent curved orientation, or it may remain flexible throughout its life to provide an adjustable curvature in two or three dimensions, as desired. The DR detector <NUM> may include a similarly flexible housing portion <NUM> that surrounds a multilayer structure comprising a flexible photosensor array portion <NUM> of the DR detector <NUM>. The housing portion <NUM> of the DR detector <NUM> may include a continuous, rigid or flexible, x-ray opaque material or, as used synonymously herein a radio-opaque material, surrounding an interior volume of the DR detector <NUM>. The housing portion <NUM> may include four flexible edges <NUM>. extending between the top side <NUM> and the bottom side <NUM>, and arranged substantially orthogonally in relation to the top and bottom sides <NUM>. The bottom side <NUM> may be continuous with the four edges and disposed opposite the top side <NUM> of the DR detector <NUM>. The top side <NUM> comprises a top cover <NUM> attached to the housing portion <NUM> which, together with the housing portion <NUM>, substantially encloses the multilayer structure in the interior volume of the DR detector <NUM>. The top cover <NUM> may be attached to the housing <NUM> to form a seal therebetween, and be made of a material that passes x-rays <NUM> without significant attenuation thereof. i.e., an x-ray transmissive material or, as used synonymously herein, a radiolucent material, such as a carbon fiber plastic, polymeric, or other plastic based material.

With reference to <FIG>. there is illustrated in schematic form an exemplary cross-section view along section <NUM>-<NUM> of the exemplary embodiment of the DR detector <NUM> (<FIG>). For spatial reference purposes, one major surface of the DR detector <NUM> may be referred to as the top side <NUM> and a second major surface may be referred to as the bottom side <NUM>, as used herein. The multilayer structure may be disposed within the interior volume <NUM> enclosed by the housing <NUM> and top cover <NUM> and may include a flexible curved or planar scintillator layer <NUM> over a curved or planar the two-dimensional imaging sensor array <NUM> shown schematically as the device layer <NUM>. The scintillator layer <NUM> may be directly under (e.g., directly connected to) the substantially planar top cover <NUM>, and the imaging array <NUM> may be directly under the scintillator <NUM>. Alternatively, a flexible layer <NUM> may be positioned between the scintillator layer <NUM> and the top cover <NUM> as part of the multilayer structure to allow adjustable curvature of the multilayer structure and/or to provide shock absorption. The flexible layer <NUM> may be selected to provide an amount of flexible support for both the top cover <NUM> and the scintillator <NUM>, and may comprise a foam rubber type of material. The layers just described comprising the multilayer structure each may generally be formed in a rectangular shape and defined by edges arranged orthogonally and disposed in parallel with an interior side of the edges <NUM> of the housing <NUM>, as described in reference to <FIG>.

A substrate layer <NUM> may be disposed under the imaging array <NUM>, such as a rigid glass layer, in one embodiment, or flexible substrate comprising polyimide or carbon fiber upon which the array of photosensors <NUM> may be formed to allow adjustable curvature of the array, and may comprise another layer of the multilayer structure. Under the substrate layer <NUM> a radio-opaque shield layer <NUM> may be used as an x-ray blocking layer to help prevent scattering of x-rays passing through the substrate layer <NUM> as well as to block x-rays reflected from other surfaces in the interior volume <NUM>. Readout electronics, including the scanning circuit <NUM>, the read-out circuit <NUM>, the bias circuit <NUM>, and processing system <NUM> (all of <FIG>) may be formed adjacent the imaging array <NUM> or, as shown, may be disposed below frame support member <NUM> in the form of integrated circuits (ICs) electrically connected to printed circuit boards <NUM>, <NUM>. The imaging array <NUM> may be electrically connected to the readout electronics <NUM> (ICs) over a flexible connector <NUM> which may comprise a plurality of flexible, sealed conductors known as chip-on-film (COF) connectors.

X-ray flux may pass through the radiolucent top panel cover <NUM>, in the direction represented by an exemplary x-ray beam <NUM>, and impinge upon scintillator <NUM> where stimulation by the high-energy x-rays <NUM>, or photons, causes the scintillator <NUM> to emit lower energy photons as visible light rays which are then received in the photosensors of imaging array <NUM>. The frame support member <NUM> may connect the multilayer structure to the housing <NUM> and may further operate as a shock absorber by disposing elastic pads (not shown) between the frame support beams <NUM> and the housing <NUM>. Fasteners <NUM> may be used to attach the top cover <NUM> to the housing <NUM> and create a seal therebetween in the region <NUM> where they come into contact. In one embodiment, an external bumper <NUM> may be attached along the edges <NUM> of the DR detector <NUM> to provide additional shock-absorption.

<FIG> is a schematic diagram of a radiographic imaging system <NUM> having an x-ray source <NUM>, a DR detector <NUM>, an AEC device <NUM> having x-ray energy sensor elements <NUM>, and an anti-scatter grid <NUM> wherein channels <NUM> extend through the anti-scatter grid <NUM> each having a central linear axis that altogether converge toward a focal point shown as x-ray source <NUM>. The position of a subject <NUM> relative to the x-ray system <NUM> is also shown in <FIG>. As described in <CIT>, the AEC device <NUM> measures an amount of x-ray energy accumulating in the x-ray energy sensor elements <NUM> as emitted by x-ray source <NUM>. which x-ray energy travels through the subject <NUM> and impacts the x-ray energy sensor elements <NUM>. The AEC device <NUM> may include a variable programmable threshold configured so that it transmits a shut-off. or termination, signal to turn-off the x-ray source <NUM> when the amount of x-ray energy accumulating in the x-ray energy sensor elements <NUM> reaches the variable programmable threshold.

The channels <NUM> that extend through the anti-scatter grid <NUM> may be formed to have a different focal length than the one illustrated, i.e., they may converge toward a point further or closer than the x-ray source <NUM> as illustrated. The channels <NUM> are separated by thin strips of lead having sufficient thickness to absorb scattered x-rays <NUM>. A grid ratio for anti-scatter grid <NUM> may be defined as a height, or thickness, h of the anti-scatter grid <NUM> divided by a distance separating the lead strips. The channels <NUM> may be filled with aluminum or an aluminum alloy to maintain their shape and alignment toward a desired focal point. The x-rays <NUM> of x-ray beam <NUM> emitted by the x-ray source <NUM> may be said to substantially coincide with the central linear axes of channels <NUM> such that they pass through the channels <NUM> of the anti-scatter grid <NUM> to the DR detector <NUM> along a linear trajectory. These x-rays <NUM> may be referred to a primary x-rays because they pass directly through the subject <NUM>, through the channels <NUM>, and then are captured by the DR detector <NUM> after travelling in a substantially linear path from the x-ray source <NUM>. The x-rays <NUM> may also pass through AEC device <NUM> and its x-ray energy sensor elements <NUM> depending on where the AEC device <NUM> is positioned. The primary x-rays <NUM> may be defined in relation to scattered x-rays <NUM> that impact a portion of the subject <NUM> and are deflected from their original linear trajectories in directions that are not substantially aligned with a central axis of a channel <NUM> and so are absorbed by the lead strips which form the sidewalls of the channels <NUM>. While not shown in <FIG> for clarity of illustration, the radiographic imaging system <NUM> may be configured to include the image processing systems <NUM> and/or <NUM> as illustrated in the digital radiographic (DR) imaging system <NUM> of <FIG>, including wired and/or wireless communication between the processing systems <NUM>, <NUM>, the x-ray source <NUM>, the detector <NUM> and the AEC device <NUM>.

<FIG> is a schematic diagram of a radiographic imaging system <NUM> similar to that shown in <FIG> but without the anti-scatter grid <NUM>. Without the anti-scatter grid <NUM> both primary x-rays <NUM> and scattered x-rays <NUM> reach the DR detector <NUM>. The scattered x-rays <NUM> cause image noise and blurring in the radiographic images captured by the DR detector <NUM>. Because the x-ray energy sensor elements <NUM> of the AEC device <NUM> do not distinguish between primary x-rays <NUM> and scattered x-rays <NUM> impacting these sensor elements, the x-ray energy sensor elements <NUM> will accumulate x-ray energy at a faster rate when a subject <NUM> is radiographically imaged without use of an anti-scatter grid <NUM>. Thus, the AEC device <NUM> will transmit a shut-off signal after a shorter duration of an x-ray exposure that does not include the anti-scatter grid <NUM>. When an anti-scatter grid <NUM> is used during an x-ray exposure a higher proportion of primary x-rays will reach the DR detector <NUM> because a portion of scattered x-rays <NUM> will be absorbed by the anti-scatter grid <NUM>. Because a portion of the scattered-x-rays <NUM> will be blocked by the anti-scatter grid <NUM> the rate of accumulation of x-ray energy in the AEC device <NUM> will be lower, so the AEC device <NUM> will transmit a shut-off signal after a longer duration of the x-ray exposure as compared with the exposure that does not use an anti-scatter grid <NUM>. Thus, a radiographic image capture by the DR detector <NUM> is clearer and less blurry when an anti-scatter grid <NUM> is used because the proportion of captured primary x-ray energy relative to scattered x-ray energy is higher and so forms a radiographic image with less noise caused by scattered x-rays <NUM>. The proportion of captured scattered x-rays relative to captured primary x-rays in a radiographic image may be referred to as a scatter-to-primary ratio (SPR).

When an anti-scatter grid <NUM> is used to capture a radiographic image of a subject <NUM> in a radiographic imaging system <NUM> having an AEC device <NUM>. the presence of the anti-scatter grid <NUM> inherently increases the duration of an exposure to x-ray source <NUM>, because less of the x-ray energy emitted by x-ray source <NUM> reaches the AEC device <NUM>. This increases the amount, and proportion relative to scattered x-rays <NUM>, of primary x-rays <NUM> captured by the DR detector <NUM>, which provides a radiographic image of the subject <NUM> having higher diagnostic quality, such as better contrast, than a more blurry radiographic image of the subject <NUM> captured without use of the anti-scatter grid <NUM>.

With respect to using a scatter removal algorithm to process captured radiographic images of a subject <NUM>. a radiographic imaging system <NUM>, <NUM>, and a method of operating such a system is disclosed herein. To improve radiographic image quality provided by processing a radiographic image using a scatter removal algorithm, the proportion of primary x-rays <NUM> captured by a DR detector <NUM> in such a radiographic image may be increased by raising an AEC trigger threshold to approximate the amount of increased primary x-ray energy that is provided to DR detector <NUM> when using an anti-scatter grid <NUM>, as described herein. In one embodiment, a formula may be used to program a higher trigger level for the AEC device <NUM>. For example, if a known default AEC trigger level t is used for a particular radiographic examination, then a formula such as T = (SPR + <NUM>) • t can be used to reset (increase) the trigger level of the AEC device <NUM> wherein T is the increased trigger level and SPR is the known scatter-to-primary ratio of x-rays in a radiographic image captured without use of an anti-scatter grid <NUM>.

<FIG> is a flowchart of a method for operating a radiographic imaging system <NUM>, <NUM>, and an AEC device <NUM> used therein. The method starts <NUM> with determining a default trigger level, at step <NUM>, for the AEC device <NUM>. This involves an operator identifying and inputting into the imaging system <NUM>, <NUM>. a size of a subject to be radiographically imaged, such as small, medium M, or large L. The radiographic imaging system <NUM>, <NUM>, is programmed to receive the operator input and automatically set a default trigger level t of the AEC device <NUM>, at step <NUM>, using known parameters of the radiographic imaging system <NUM>. <NUM>, when examining subjects having a particular size. A table, as shown in <FIG> for step <NUM>, may be stored in the processing system <NUM>, <NUM>, of the radiographic imaging system <NUM>, <NUM>, corresponding to the operator input patient size which identifies, and thereafter is used by, the processing system <NUM>, <NUM>, to set, at step <NUM>, a determined trigger level t in the AEC <NUM>. If the operator then inputs an instruction, or data, to the radiographic imaging system, at step <NUM>, that a scatter removal algorithm will not be used because, for example, the operator intends to use an anti-scatter grid <NUM>, the radiographic imaging system <NUM>, <NUM>, then initiates a standard procedure for beginning a radiographic examination at step <NUM>. If the operator inputs to the processing system <NUM>, <NUM>, of the radiographic imaging system <NUM>, <NUM>, at step <NUM>, that a scatter removal algorithm will be used to process a radiographic image captured by the radiographic imaging system <NUM>, <NUM>, because the operator does not intend to use an anti-scatter grid <NUM> or intends to use an anti-scatter grid having a very low grid ratio. the radiographic imaging system then executes a program for resetting the trigger level of the AEC device, at step <NUM>, using a formula corresponding to the operator entered size of the subject to be imaged. The radiographic imaging system may use the determined default trigger level t from step <NUM> and increase it to a trigger level T using the formula T = (SPR + <NUM>) • t as described herein. wherein the value SPR may be obtained from the table stored in the processing system <NUM>, <NUM>, corresponding to the operator input subject size. After resetting (increasing) the trigger level of the AEC device <NUM>. at step <NUM>, the radiographic imaging system <NUM>, <NUM>. then initiates a standard procedure for beginning a radiographic examination at step <NUM>.

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 hardware embodiment, an entirely software embodiment (including firmware, resident software, micro-code, etc.), or an embodiment combining software and hardware aspects that may all generally be referred to herein as a "service," "circuit," "circuitry," "module," and/or "system.

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.

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.

Claim 1:
A radiographic imaging system (<NUM>; <NUM>) configured to capture and process a radiographic image (<NUM>) of a subject (<NUM>), the radiographic imaging system (<NUM>, <NUM>) comprising:
an x-ray source (<NUM>);
an x-ray detector (<NUM>);
an automatic exposure control device, AEC, (<NUM>) coupled to the x-ray source (<NUM>) and configured to shutdown the x-ray source (<NUM>) when the AEC (<NUM>) receives an amount of x-ray energy from the x-ray source (<NUM>) that satisfies a preset threshold; and
a processing system (<NUM>; <NUM>) configured to:
control the x-ray source (<NUM>) and the x-ray detector (<NUM>), and process the radiographic image (<NUM>) of the subject (<NUM>) captured by the x-ray detector (<NUM>);
receive a size input from an operator indicating a size of the subject (<NUM>) to be radiographically imaged and set the preset threshold for the AEC (<NUM>) using known parameters of the radiographic imaging system (<NUM>; <NUM>) for the size input from the operator;
receive a request whether or not to execute a program for reducing x-ray scatter noise in the captured radiographic image (<NUM>);
(I) if the program will be used:
increase the preset threshold of the AEC (<NUM>) according to a formula that is based on the size input from the operator; and
initiate a standard procedure for beginning a radiographic examination using the increased threshold of the AEC (<NUM>); and
(II) if the program will not be used:
initiate the standard procedure for beginning the radiographic examination using the preset threshold of the AEC (<NUM>).