Method for real-time control of exposure at x-ray dose

Abstract

The invention relates to a method of real-time controlling an exposure at an X-ray dose emitted by a generator tube for generating an X-ray beam and received by a detector comprising a flat panel detector comprising a set of pixels organized in a matrix along rows and columns and configured to generate a signal based on an X-ray dose impinging on the detector, the generator tube comprising a control unit for controlling the generator tube configured to control the emitted X-ray dose; the method is characterized in that it comprises the steps of: exposing the flat panel detector at an X-ray dose emitted by a generator tube for generating an X-ray beam; repeatedly reading out at least one row of pixels while the flat panel detector is exposed at the X-ray dose; determining a payload signal and a stray signal based on the readout signals from the at least one row; transmitting the payload signal to the control unit for controlling the generator tube.

Description

Technical Field

[0001] This invention relates to the field of radiographic technology with digital flat panel detectors, and more particularly to a device for real-time control of exposure levels. Background Technology

[0002] Exposure parameters (voltage, current, source / patient / detector distance) must be adjusted to minimize the dose received by the patient while still ensuring optimal image quality for the radiologist. Optimal exposure parameters depend on the patient's body size, the type of examination required, and the sensitivity characteristics of the X-ray imager (silver film, PSP plate, digital flat panel detector, etc.). These parameters are typically determined using system software based on instructions provided by the radio operator regarding the examination context (patient body size, type of image required). If these parameters are not defined correctly (whether due to incorrect or inaccurate instructions or incorrect system calibration), there is a significant risk of overexposure or underexposure. These risks involve direct overexposure of the patient to X-rays or overexposure due to the need for re-image capture.

[0003] Figure 1 A conventional radiology assembly 50 is schematically illustrated. The radiology assembly 50 consists of two elements: a generator tube 20 for generating an X-ray beam 22 and a flat panel detector 11 for radiographic imaging. This assembly is primarily used to take radiographic images of patients in a hospital setting. A patient whose region of interest 40 is to be photographed is positioned between the generator tube 20 for generating the X-ray beam 22 and the flat panel detector 11. Therefore, these two elements must be correctly positioned relative to each other so that all X-rays emitted by the generator tube 20 for generating the X-ray beam are captured by the flat panel detector 11. Alignment between the two elements then needs to be corrected. Alignment should be performed before the generator tube 20 for generating the X-ray beam emits the X-rays. The aim is to avoid over-exposing the patient to X-rays that reach outside the detector. Several methods for aligning the two elements are known.

[0004] In addition to properly aligning the X-ray beam with the flat panel detector, it is important to control the exposure parameters to ensure that a sufficient dose of X-rays has been delivered in order to guarantee good images without over-exposing the patient.

[0005] To date, one or more of the following solutions have been used in practice to address the problem of quantifying exposure dosage:

[0006] - External AEC (Automatic Exposure Control) equipment, such as an "ionization chamber" or "solid-state detector." This is a functional unit for automatic dose control (e.g., an ionization chamber) based on an "X-ray detector + current amplifier" hardware unit, which is separate from the imager and connected to a control unit for controlling the X-ray generator. The detector is placed upstream of the imager and absorbs a very small fraction of the X-rays to avoid interfering with the image. The detector is divided into multiple regions of interest (typically 3 or 5 regions) and is able to provide current to the amplifier for each region. One side of the amplifier is connected to the detector, and the other side is connected to the control unit for controlling the X-ray generator. The amplifier's function is to provide the generator with a signal that corresponds to the updated total exposure level without delay. This signal allows the control unit for controlling the generator to interrupt the emission of X-rays (the stop level is calibrated during system installation).

[0007] - Internal AEC (Automatic Exposure Control) devices typically involve using signals received on a portion of an image. There are two main types of solutions. In the first type of solution, the pixel matrix is ​​physically modified such that the electrical signal specifically designed for measurement is first routed to a charge-to-voltage converter and then to an analog-to-digital converter. In the second type of solution (e.g., disclosed in document JP5481053), the matrix is ​​not modified a priori, but the problem of stray signals from all illuminated pixels not within the defined area of ​​interest for adjusting exposure is not addressed.

[0008] - A "preshot" device, also known as a "pre-image" device, takes an initial exposure with a very low dose. Just before the "actual image" is taken, a "pre-image" of the patient is captured with a very low dose. Instead of providing a real-time signal to the system, the system automatically determines and implements the final parameters using a pre-image analysis algorithm.

[0009] External AEC solutions have three main drawbacks. First, they typically include an X-ray-absorbing detector upstream of the imager, which can increase the patient's dose by several percentage points. Second, in some cases, the external detector may be located downstream of the imager, distorting the beam quality information seen by the imager and thus requiring complex calibration. Third, the AEC solution is only suitable for stationary systems due to its bulk: the detector needs to be mounted on the imager, and cables are required to route the signal to the amplifier. Therefore, it is unsuitable for mobile radiographic systems or for capturing images on portable detectors outside their dedicated housings. Finally, integrated systems are economically expensive: a typical room with a worktable and support arm requires two AEC units, each costing at least €500.

[0010] Internal AEC solutions have the following drawbacks: They require modification of the pixel matrix, making implementation impossible on existing products. Although proposed in the literature, they are difficult to implement due to technical issues related to capacitive coupling between the illumination pixels and the AEC signal readout columns.

[0011] The so-called pre-image solution also has two main drawbacks. It requires perfect system calibration, that is, establishing a correlation between the parameters of the low-dose (pre-image) and the parameters of the normal-dose (image). This correlation must also take into account the context of the examination (patient body size, type of image required). It also assumes a time delay between the pre-image and the image, which can worsen application flow (waiting time, the impact of patient movement, etc.). Summary of the Invention

[0012] This invention aims to overcome all or some of the aforementioned problems by proposing a method for real-time control of exposure under X-ray dose. This method enables real-time indication to the system of the grayscale level for a predetermined region of interest in the image currently being formed by the imager (digital flat panel detector, hereinafter referred to as the detector), ensuring correct exposure for the patient. This method is based on real-time analysis of the signal level in the region of interest of the image using the detector's plate directly without any modification. Furthermore, the method according to the invention proposes an algorithmic approach to address the significant problem of coupling between the signal of interest (also known as the payload signal) and stray signals primarily originating from the uncollimated illumination region. Finally, the method according to the invention can be implemented without wired connections, thus allowing its implementation on mobile radiographic systems or in a portable cassette mode within a radiographic room.

[0013] Therefore, one aspect of the present invention is a method for real-time control of exposure at an X-ray dose emitted by a generator tube for generating an X-ray beam and received by a detector including a flat panel detector. The generator tube includes a control unit configured to control the X-ray dose emitted by the generator tube. The flat panel detector includes:

[0014] a. A set of pixels, which are organized into a matrix along rows and columns and configured to generate a signal based on the dose of X-rays irradiating the detector;

[0015] b. A circuit configured to determine a payload signal based on signals from at least one row;

[0016] c. A transmission module for transmitting payload signals to a control unit for controlling the generator tube;

[0017] The control method is characterized in that it includes the following steps:

[0018] - Expose the flat panel detector to an X-ray dose emitted by a generator tube used to generate an X-ray beam;

[0019] -While the flat panel detector is exposed to X-ray dose, at least one row of pixels is read out repeatedly;

[0020] - The payload signal and spurious signal are determined based on the signals read from the at least one row;

[0021] - Transmit the payload signal to the control unit used to control the generator tube.

[0022] Advantageously, the exposure control method according to the invention further includes the step of adjusting the X-ray dose emitted by the generator tube based on a payload signal transmitted to a control unit for controlling the generator tube.

[0023] Advantageously, the step of repeatedly reading at least one row of pixels includes the following steps: for each row of the at least one row,

[0024] - Read the column without activating row Li to obtain the first signal A. n ;

[0025] - Read the column while activating row Li to obtain the second signal B. n .

[0026] Advantageously, the steps for determining the payload signal and spurious signals include the following:

[0027] - Estimate the multiplication factor (FM') between the payload signal and the spurious signal;

[0028] - Estimate the payload signal based on the multiplication factor using the following relationship:

[0029] DS' n =(A n +B n ) / (FM'+1), and S' n =Cumul(A+B) n / (FM'+1).

[0030] Advantageously, the step of estimating the multiplication factor (FM') between the payload signal and the spurious signal includes the following steps:

[0031] -Based on 3 consecutive samples (A) of the first signal n-1 A n A n+1 ) = (VA) n To estimate the second signal B nThe measured value A' of the stray signal at time. n (For example, interpolation can be performed using the following spline filter: A') n =1 / 16.(-110 7).t(VA)n)

[0032] - For 3 consecutive points {(x i y i Linear regression is performed on {i = 1 to 3} to obtain the proportionality coefficient FP, where:

[0033] ο{x i} = [Cumul(A+B)] n-2 Cumul(A+B) n-1 Cumul(A+B) n ]

[0034] ο{y i} = [Cumul(B-A') n-2 Cumul(B-A') n-1 Cumul(B-A') n ]

[0035] οCumul(A) n It equals A0 + A1 + ... + A n

[0036] -Use the relation FM' = (FP) -1 -1 is used to calculate the multiplication factor.

[0037] In one implementation, the step of transmitting the payload signal to the control unit for controlling the generator tube is performed via wired transmission.

[0038] In another embodiment, the step of transmitting the payload signal to the control unit for controlling the generator tube is performed wirelessly, preferably via RF transmission.

[0039] The present invention also relates to a radiological assembly comprising:

[0040] a. A generator tube for generating an X-ray beam, the generator tube including a control unit for controlling the generator tube, the control unit being configured to control the dose of X-rays emitted by the generator tube;

[0041] b. A detector, the detector comprising a flat panel detector, the flat panel detector comprising:

[0042] i. A set of pixels (P(i,j)) is organized into a matrix along rows (Li) and columns (Cj) and configured to generate a signal based on the X-ray dose irradiated onto the detector;

[0043] ii. A circuit configured to determine the payload signal based on signals from some rows (Li);

[0044] iii. A transmission module for transmitting payload signals to a control unit for controlling the generator tube.

[0045] In one embodiment, the transmission module for transmitting the payload signal to the control unit for controlling the generator tube is a wired transmission module.

[0046] In another embodiment, the transmission module for transmitting the payload signal to the control unit for controlling the generator tube is a wireless transmission module, preferably an RF transmission module. Attached Figure Description

[0047] The invention will be better understood by reading the detailed description of the embodiments provided by way of example, and other advantages will become apparent, as illustrated in the accompanying drawings, in which:

[0048] Figure 1 A schematic diagram of a conventional radiological assembly;

[0049] Figure 2 A traditional image detector is shown;

[0050] Figure 3 A schematic diagram illustrating the steps of a method for real-time control of exposure under X-ray dose according to the present invention is shown;

[0051] Figure 4 A radiographic assembly according to the invention is schematically illustrated;

[0052] Figure 5 The principle of locating rows in the detector matrix dedicated to readout and repeated readout according to the present invention is illustrated;

[0053] Figure 6 The results of exposure simulations with rapid increases in an implementation of the method according to the invention are shown;

[0054] Figure 7 The results of exposure simulation with a slow increase are shown in the implementation of the method according to the invention.

[0055] For clarity, these figures are not all to the same scale. Furthermore, the same elements will have the same reference numerals in different figures. Detailed Implementation

[0056] Generally, this invention refers to a conventional image detector, which typically includes a flat panel detector comprising a set of pixels organized along a matrix of rows and columns, row addressing units, column readout units, row conductors connecting a row of pixels to the row addressing units, and column conductors connecting a column of pixels to the column readout units. It should be noted that, in the context of this patent application, the concepts of column and row are relative only; a row of pixels and a column of pixels simply refer to multiple rows of pixels arranged, for example (but not limited to), perpendicular to each other. A row conductor or column conductor is defined as parallel to a row of pixels or oriented along a row of pixels.

[0057] Figure 1 A conventional radiological component 50, as presented in the background art, is schematically shown.

[0058] Figure 2 A conventional image detector 10 is illustrated. The image detector 10 includes a detector 11 formed on a first monolithic substrate 12. The first monolithic substrate 12 includes a set of pixels P(i,j) organized into a matrix 13 along rows Li and columns Cj. The matrix 13 can contain any number of rows and columns to form pixels P(i,j). The matrix 13 forms a geographic region on the first substrate 12. Pixels are represented in the general form P(i,j), where i and j are natural integers representing the rank of a row and the rank of a column in the matrix 13, respectively. A set of pixels P(i,j) is configured to generate a signal based on radiation illuminating the detector 10. The detector 11 includes column conductors Yj, each connected to a pixel in a given column Cj. The column conductors Yj are used to transmit the signal generated by the pixels P(i,j). Similarly, the detector 11 includes row conductors Xi, each connected to a pixel in a given row Li. The matrix 13 of pixel P(i,j) contains columns Cj of even rank and columns Cj of odd rank. Similarly, the matrix 13 of pixel P(i,j) contains rows Li of even rank and rows Li of odd rank. Detector 10 includes contact pads 14 located at the edge of the first substrate 12 and outside the matrix 13 of pixel P(i,j). Contact pads 14 are connected to column conductors Yj. Image detector 10 includes row addressing units 15 located near the first substrate 12 and connected to row conductors Xi. Row addressing unit 15 is a name given to any component containing at least one row addressing unit. Unit 15 can be integrated into the first substrate 12, such as... Figure 1 As shown, they can be integrated into different substrates. The row addressing unit 15 can address each row of Li pixels individually. The image detector 10 includes a column readout unit 16 formed on a second substrate 17 different from the first substrate 12. The column readout unit 16 includes a connection point 18 connecting the column readout unit 16 to the contact pad 14. The column readout unit 16 can read the signals generated by the pixels in the row selected by the row addressing unit.

[0059] Pixel P(i,j) includes a photodiode DP(i,j) associated with an electronic switch T(i,j). Of course, the photodiode DP(i,j) can be replaced by any photosensitive element capable of generating an electrical signal when exposed to photon radiation. Figure 2 The pixel structure shown is intentionally simplified, and more complex structures can be implemented within the scope of this invention.

[0060] A switch T(i,j) formed by a transistor is connected to the row conductor Xi of row i via its gate Gi, to the column conductor Yj via its drain Dj, and to the cathode of a photodiode DP(i,j) via its source Sij. The anodes of all photodiodes DP(i,j) are connected to a common potential (e.g., ground). Row addressing unit 15 includes elements for generating a signal to be injected onto row conductor Xi to drive the transistor T(i,j) to turn on and off. Column readout unit 16 may include elements for processing the signal received on column conductor Yj. In particular, these may be amplifiers and / or analog-to-digital converters.

[0061] Traditionally, the image detector 11 operates as follows. During the image capture phase, exposure of the photodiode DP(i,j) to radiation generates charge at source Sij. The amount of charge at each source Sij depends on the radiation intensity received by the pixel P(i,j) under consideration. Following the image capture phase is a row-by-row readout phase. Signals injected into each row conductor Xi are sequentially moved to the active state, such that the potential of each column conductor Yj sequentially represents the amount of charge accumulated in each pixel P(i,j) of column j.

[0062] As mentioned above, quantizing exposure dose in the prior art requires modification of the pixel matrix. Furthermore, even without modifying the matrix, the prior art does not offer any solution for eliminating unavoidable stray signals.

[0063] Figure 3 A schematic diagram illustrating the steps of a method for real-time control of exposure under X-ray dose according to the present invention is shown. For a better understanding of these elements, please refer to... Figure 2 However, the proposed solution does not require modification of the pixel matrix.

[0064] This invention relates to a method for real-time control of exposure at an X-ray dose 22, the X-ray dose 22 being emitted by a generator tube 20 for generating an X-ray beam and received by a detector 10. The detector 10 includes a flat panel detector 11, and the generator tube 20 includes a control unit 21 for controlling the generator tube 20, the control unit 21 being configured to control the X-ray dose emitted by the generator tube 20. The flat panel detector 11 includes:

[0065] - A set of pixels P(i,j), which are organized into a matrix 13 along rows Li and columns Cj and configured to generate a signal based on the X-ray dose 22 irradiated on the detector 10;

[0066] -Circuit 30, which is configured to determine a payload signal based on signals from at least one row of Li;

[0067] - Transmission module 31, which is used to transmit the payload signal to the control unit for controlling the generator tube 20.

[0068] Circuit 30 is preferably an integrated circuit. However, other equivalent variations may be used. In other words, any device used to determine the payload signal based on a signal from a row Li is suitable.

[0069] According to the present invention, the control method includes the following steps:

[0070] - Expose the flat panel detector 11 to an X-ray dose 22 emitted by the generator tube 20 used to generate the X-ray beam (step 100);

[0071] -While the flat panel detector 11 is exposed to X-ray dose 22, at least one row Li in pixel P(i,j) is repeatedly read out (step 101);

[0072] - Determine (step 102) the payload signal and spurious signal based on the readout signals from at least one row of Li;

[0073] - Transmit the payload signal (step 103) to the control unit 21 for controlling the generator tube 20.

[0074] During exposure step 100, step 101 occurs where at least one row Li of pixels P(i,j) in matrix 13 is repeatedly read out. In other words, this readout step occurs when rows Li cannot be read out in the prior art. Specifically, in the normal mode, detector 10 is not operational during the exposure phase.

[0075] It can also be noted that the readout step 101 is performed on one or more rows Li of the pixel matrix. These rows exist and contribute to the proper functioning of the detector. In other words, the pixel matrix does not need to be modified to achieve the specific steps of reading out the rows during X-ray exposure.

[0076] To achieve the fastest possible readout step 101, all rows provided in step 101 can be opened simultaneously, which has the negative effect of combining all regions of interest into a single information item. Alternatively, only one or more rows corresponding to predefined regions of interest can be activated.

[0077] In exposure step 100, exposing a pixel results in the creation of a charge outside pixel P(i,j) in column Cj because capacitive coupling connects the columns of the matrix, and all pixels (transistors and photodiodes) are attached to this column. Therefore, the reading of the currently exposed pixel (step 100) cannot represent the level in the image in the same way as the reading would be after exposure step 100: there is an additional stray signal from the charge created by coupling in the column. This stray signal can be significant because, for each column, the coupling originates from all the illuminated pixels in that column. Since the pixel of interest is typically located below the patient, the value of the stray signal could be up to 100 times the payload signal if a large number of other pixels are illuminated without attenuating the direct flux (low collimation). Therefore, this stray signal must be considered in step 102, which determines the (payload and stray) signal.

[0078] To determine the payload signal and spurious signal, step 101 of repeatedly reading at least one row Li in the pixels includes the following steps: for each row Li in the at least one row Li,

[0079] - Read column Cj without activating row Li to obtain the first signal A. n ;

[0080] - Read column Cj (step 111) with row Li active to obtain the second signal B. n .

[0081] Therefore, a double readout is performed for each row dedicated to the readout in step 101: first, the column (step 110) is read out without activating that row to obtain the sample A of the nth double readout. n And then, with the row active, read the column again (step 111) to obtain sample B of the nth double reading. n This double reading can subtract stray effects. Repeat this double reading until the end of the window XRW (XRW is an abbreviation for the term X-ray window, i.e., the duration during which the detector is able to receive X-ray photons and convert them into electrical charges before the readout phase). Based on the double reading A... n and B n The information obtained can be used to infer the true signal level in the image.

[0082] Simple subtraction from dual readings (B n -A n The effective payload signal DS cannot be clearly obtained. n The increase is due to the fact that the dose flux is not constant throughout the exposure (step 100). In the initial phase of the dose flux increase, the first non-zero reading A in the column... n0 Having a ratio in reading Bn0 The date is read from a lower level column. In other words, the reading is B. n0 Includes more than A n0 More spurious signals. Therefore, subtract B. n0 -A n0 It contains some spurious signals and overestimates the additional payload signal DS. n0 In contrast, with reduced flux, for example, after exposure has reached its maximum (“overshoot”), signal A... n1 Greater than B n1 The spurious signals contained therein, and therefore subtract B. n1 -A n1 The effective payload signal DS was underestimated. n1 The changes in the data even yielded negative results.

[0083] To address this issue, the solution proposed in this invention makes the following assumptions: the minimum exposure time is slightly less than a short duration, for example, on the order of 1 ms (e.g., 0.8 ms); and imposes the constraint that the electrical stop signal must arrive at the control unit for controlling the generator only after a short period of time (e.g., less than 0.1 ms), within which the effective realization of a specific signal level in the imager can be removed (CP constraint). This means that a buffer delay of 0.8 ms is provided for analysis at the start of exposure, and after this delay, the constraint (CP) will be complied with again. In terms of hazard analysis, this means that the responsibility for preventing patient overexposure still rests with the radiographic system, primarily based on selecting non-abnormal parameters during this initial 0.8 ms delay.

[0084] In the following text, it is assumed that the master hypothesis (HP) is valid, according to which the algorithm has a delay of 0.8 ms from the start of exposure until the constraint (CP) must be explicitly complied with.

[0085] This delay time (HP) is then used to robustly estimate the multiplication factor FM' between the payload signal and stray signal in the current exposure. Specifically, this factor remains constant throughout the exposure, regardless of the temporal distribution of the dose flux, because (for each column) it is determined entirely by the relative exposure configuration between the pixel of interest in that column and the remaining pixels in that column. If multiple columns are combined to improve the signal quality of each readout, the multiplication factor applied to this set of columns will also remain constant.

[0086] Therefore, step 102 of determining the payload signal and spurious signals includes the following steps:

[0087] - Estimate (step 120) the multiplication factor (FM') between the payload signal and the spurious signal;

[0088] - The payload signal is estimated based on the multiplication factor using the following relationship (step 121):

[0089] DS' n =(A n +B n ) / (FM'+1), and S' n =Cumul(A+B) n / (FM'+1).

[0090] More precisely, step 120, which estimates the multiplication factor FM' between the payload signal and the spurious signal, includes the following steps:

[0091] -Based on 3 consecutive samples (A) of the first signal n -1, A n A n +1)=(VA) n To estimate (step 122) the second signal B n The measured value A' of the stray signal at time. n ;

[0092] - For 3 consecutive points {(x i y i Linear regression (steps 123) is performed on i = 1 to 3 to obtain the proportionality coefficient FP, where:

[0093] ο{x i} = [Cumul(A+B)] n-2 Cumul(A+B) n-1 Cumul(A+B) n ]

[0094] ο{y i} = [Cumul(B-A') n-2 Cumul(B-A') n-1 Cumul(B-A') n ]

[0095] οCumul(A) n It equals A0 + A1 + ... + A n

[0096] -Use the relation FM' = (FP) -1 –1 is used to calculate the multiplication factor (step 124).

[0097] For example, step 122 can be performed by interpolation using the following spline filter: A' n = 1 / 16.(-1107). t (VA) n ).

[0098] As is generally accepted, a good estimate is achieved if the shape of the pulse can be well approximated by a polynomial between the three measurement points. Other filters were tested, such as the arithmetic mean (0 0.5 0.5). t (A)

[0099] Estimated value A' n Corresponding to B n Measurement of stray signal at any given time.

[0100] The following facts demonstrate that steps 1, 2, and 3 of the linear regression are reasonable: Quantity Cumul(A+B) n In principle with B n The signal level accumulated over time is proportional to the multiplication factor, which is equal to FM'+1, corresponding to the spurious signal (FM'*DS). n ) and payload signal (1*DS n The accumulation of ) added to B. n The spurious signal at time A' is only caused by A' n It is estimated that, under conditions of rapid pulse changes, this could lead to a shift in the reproduced signal relative to the true signal.

[0101] The idea of ​​regressing at three points can compensate for this bias, provided that the "bumpy" period of the pulse is small and lasts for several double readings (without flux, which would otherwise have to be kept constant).

[0102] Therefore, the proportional coefficient FP given by the above linear regression can be used to give the estimated value of the multiplication factor FM': FM'+1=(FP) -1 That is, FM' = (FP) -1 -1.

[0103] If the correlation coefficient CC of the regression is considered to be sufficiently close to 1 (e.g., |1-CC|<10), then... -5 If ), then FM can be considered to be a robust estimate of FM'.

[0104] If the correlation coefficient CC is not close enough to 1, repeat steps 122 and 123 by changing n to n+1, while verifying that the delay time given by the master hypothesis (HP) has not exceeded.

[0105] Once the multiplication factor has been estimated with sufficient confidence, the following formula can be used to give the multiplication factor for each B. n The payload signal DS added at each moment n The estimated level DS' n DS' n =(A n +B n) / (FM'+1).

[0106] Therefore, this also gives: S' n =Cumul(A+B) n / (FM'+1).

[0107] The payload signal is transmitted to the control unit used to control the generator tube.

[0108] Finally, the exposure control method according to the invention advantageously includes step 104: adjusting the X-ray dose 22 emitted by the generator tube 20 according to a payload signal transmitted to the control unit 21 for controlling the generator tube 20. Therefore, this ensures that the patient receives the correct X-ray dose in order to obtain high-quality images without unnecessary overexposure.

[0109] This invention provides an algorithm-based solution for correcting capacitive coupling between pixels and columns.

[0110] These steps showed good results in the simulation. Figure 2 and Figure 3 This situation is more favorable for short pulses because of the high dose throughput and good signal-to-noise ratio per sample. This is good news because from the customer's perspective, critical situations often involve short pulses.

[0111] On the other hand, for long pulses (tens of milliseconds), the dose flux may be low, and the signal-to-noise ratio deteriorates with each readout. To overcome this problem, in addition to summing multiple columns (averaging effect), it is recommended to use the X-ray window (XRW) duration information passed to the detector in the frame request to define a longer readout time increment, while maintaining the target of less than 10% estimated signal error.

[0112] Step 103, which transmits the payload signal to the control unit for controlling the generator tube, can be performed via wired transmission or wireless transmission, preferably via radio frequency transmission. Generally, fast transmission with minimal and well-controlled latency is required. Therefore, Wi-Fi and Bluetooth links are not ideal, although they are suitable in the context of this invention.

[0113] Advantageously, this information is transmitted in real time. The information about B obtained in step 102 should be... n Information about the signal level at a given time relative to B nThe information is transmitted to the control unit 21, which controls the generator tube 20, with a delay of less than 0.1ms. Since the algorithm for executing step 102 is implemented in an FPGA integrated circuit, its principle does not require extensive computation; therefore, this delay constraint is largely related to the transmission of information from the integrated circuit to the control unit in step 103. Wired links do not present any particular problems. RF wireless links present much more difficulties.

[0114] If the delay to the RF link is greater than 0.1ms, the step of extrapolating the information provided in step 102 can be considered, provided that the information is timestamped and the transmitter (transmission module) and receiver (control unit) components are pre-synchronized.

[0115] Figure 4 A radiographic assembly 51 according to the present invention is schematically shown. The radiographic assembly 51 includes:

[0116] - A generator tube 20 for generating an X-ray beam, the generator tube 20 including a control unit 21 for controlling the generator tube 20, the control unit 21 being configured to control the X-ray dose 22 emitted by the generator tube 20;

[0117] - Detector 10, which includes a flat panel detector 11, the flat panel detector 11 comprising:

[0118] A set of pixels P(i,j) is organized into a matrix 13 along row Li and column Cj (similar to...). Figure 2 The detector presented in the middle is configured to generate a signal based on the X-ray dose 22 irradiated on the detector 10;

[0119] circuit 30, which is configured to determine the payload signal based on signals from some rows of Li;

[0120] The transmission module 31 is used to transmit the payload signal to the control unit 21 for controlling the generator tube 20.

[0121] Circuit 30 can be an integrated circuit. An integrated circuit can be any circuit suitable for performing computation. By way of example and not limitation, it can be an FPGA (an abbreviation for "Field-Programmable Gate Array," meaning a programmable logic array). The integrated circuit performs the step of analyzing the data in the dedicated line to extract signal level information at a given time. This information is routed directly to a control unit for controlling the generator via a wired link or via a radio link (RF option).

[0122] The transmission module 31, used to transmit the payload signal to the control unit 21 for controlling the generator tube 20, can be a wired transmission module or a wireless transmission module, preferably an RF transmission module. It transmits signal information at a given time to the receiver module of the generator tube. The receiver module receives signal level information at a given time, converts the received signal level information into an electrical signal, and provides this electrical signal to the control unit for controlling the X-ray generator.

[0123] Figure 5 The principle of locating rows of a detector matrix dedicated to readout and rereading is illustrated according to the present invention. Only the rows involved in rereading step 101 are shown (upper part of the figure). These are existing rows that already exist in the detector matrix. Measurements are given in an indicative manner to illustrate possible exemplary implementations. In this figure, there are three rows for step 101. There may be only one, or two, or even more rows. These rows are read out sequentially as quickly as possible during X-ray window 60 (reference numeral 61 indicates the X-ray emission window). To determine representative values, it is mandatory to read out columns at least without activating rows (step 110) and with activating rows. This means that during the X-ray window, step 110 is performed alternately followed by step 111 (i.e., reading out columns with activated rows).

[0124] Figure 6 The results of exposure simulations with a rapid increase in intensity are shown in an implementation of the method according to the invention.

[0125] Figure 7 The results of exposure simulation with a slow increase are shown in the implementation of the method according to the invention.

[0126] For both graphs, the shape of the simulated pulse can be seen in the upper right corner. (Based on Cumul(A+B)) n Cumul(B-A') n The diagram is shown in the lower left. The verification of the operation based on the runtime estimate can be seen in the lower right: actual payload signal (represented by a solid line); using Cumul(A+B). n The estimated payload signal (represented by a triangle) is given by / (FM'+1), which is non-zero as long as CC is sufficiently close to 1; and Cumul(B-A') is estimated. n What will it be (indicated by dashed lines).

[0127] exist Figure 6 In the sample A n and B n The simulation was performed using a multiplication factor FM = 100. It can be seen that linear regression may be working as early as the triangle at the second point.

[0128] exist Figure 7 In the sample A n and B n It is simulated using a multiplication factor FM = 10.

[0129] These two figures demonstrate the effectiveness of the proposed solution to the capacitive coupling problem.

[0130] This invention proposes a real-time exposure control method that, with the advantage of being able to be implemented without any physical modification or specific adjustment to the photodiode matrix (existing dedicated rows of the readout board during exposure). The signal level in the region of interest of the image is analyzed in real time. Step 102 enables the resolution of the important problem of coupling between the signal of interest and stray signals mainly originating from areas without collimated illumination.

[0131] Finally, the method is compatible with transmissions without wired connections, extending its application possibilities to mobile radiography or portable cassette modes in radiography rooms.

[0132] The proposed solution provides signal levels in real time. It involves directly using the detector board without any modifications to analyze the signal level in the region of interest of the image in real time. Furthermore, the proposed solution describes an algorithmic approach to address the significant problem of coupling between the signal of interest and stray signals primarily originating from areas without collimated illumination. Finally, the proposed solution can be implemented without wired connections, thus allowing implementation on mobile radiographic systems or in portable cassette mode within a radiographic chamber.

Claims

1. A method for real-time control of exposure at an X-ray dose, the X-ray dose being emitted by a generator tube (20) for generating an X-ray beam and received by a detector (10) including a flat panel detector (11), the generator tube (20) including a control unit (21) for controlling the generator tube (20), the control unit (21) being configured to control the X-ray dose emitted by the generator tube (20), the flat panel detector (11) including: a. A set of pixels (P(i,j)) is organized into a matrix (13) along rows (Li) and columns (Cj) and configured to generate a signal based on the X-ray dose (22) irradiated onto the detector (10); b. Circuit (30), the circuit (30) being configured to determine a payload signal based on the signal from at least one row (Li); c. A transmission module (31) for transmitting the payload signal to the control unit for controlling the generator tube (20); The method includes the following steps: - Expose the flat panel detector (11) to an X-ray dose emitted by the generator tube (20) used to generate the X-ray beam (100). -While the flat panel detector (11) is exposed to the X-ray dose, at least one row (Li) of the (101) pixels (P(i,j)) is repeatedly read out. - The payload signal and spurious signal are determined based on the signals read from the at least one row (Li); - The payload signal is transmitted (103) to the control unit (21) for controlling the generator tube (20). The method is characterized in that the step (101) of repeatedly reading at least one row (Li) of the pixels includes the following steps: for each row (Li) of the at least one row (Li). - Read (110) the column (Cj) without activating the row (Li) to obtain the first signal A. n ; - Read (111) the column (Cj) while the row (Li) is activated to obtain the second signal B. n ; The step (102) of determining the payload signal and the spurious signal includes the following steps: - Estimate the multiplication factor FM' between the payload signal and the spurious signal (120); - Estimate the payload signal (121) based on the multiplication factor using the following relationship: DS' n =(A n +B n ) / (FM'+1), and S' n =Cumul(A+B) n / (FM'+1), where DS' n It is the level of the payload signal, S' n This is the payload signal, and Cumul(A+B) n It is B n The signal level accumulated over time, Furthermore, the step (120) of estimating the multiplication factor FM' between the payload signal and the spurious signal includes the following steps: -Based on 3 consecutive samples (A) of the first signal n-1 A n A n+1 )=(VA) n To estimate (122) in the second signal B n The measured value A' of the spurious signal at time [time]. n ; - For 3 consecutive points {(x i y i Linear regression (123) is performed on i=1 to 3} to obtain the proportionality coefficient FP, where: oh i }=[Cum(A+B) n-2 ,How much(A+B) n-1 ,How much(A+B) n ] oh i }=[Cum(B-A') n-2 ,Cum(B-A') n-1 ,Cum(B-A') n ] oCumul(A) n It equals A0 + A1 + ... + A n -Use the relation FM'=(FP) -1 -1 is used to calculate the multiplication factor described in (124).

2. The method for real-time control of exposure under X-ray dose according to claim 1, the method further comprising the following steps: Step (104) to adjust the dose of X-rays emitted by the generator tube (20) based on the payload signal transmitted to the control unit (21) for controlling the generator tube (20).

3. The method for real-time control of exposure under X-ray dose according to any one of claims 1 and 2, wherein, The step (103) of transmitting the payload signal to the control unit for controlling the generator tube is performed via wired transmission.

4. The method for real-time control of exposure under X-ray dose according to any one of claims 1 and 2, wherein, The step (103) of transmitting the payload signal to the control unit for controlling the generator tube is performed wirelessly.

5. The method for real-time control of exposure under X-ray dose according to claim 4, wherein, The step (103) of transmitting the payload signal to the control unit for controlling the generator tube is performed via RF transmission.

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