X-ray imaging apparatus

Abstract

Provided is an X-ray imaging apparatus which utilizes characteristic values of a field emission type X-ray generator and an X-ray detector so as to perform X-ray imaging through the high-speed pulse driving of X-rays, thereby providing an image of the same quality at a relatively low dose, or providing an image of relatively high quality at an equal or lower dose. The X-ray imaging apparatus according to the present invention comprises: an imaging unit including an X-ray generator, which irradiates a subject with X-rays, and an X-ray detector, which receives the X-rays that passed through the subject, so as to generate frame-by-frame projection data; an input unit into which imaging information including at least one from among tube voltage, tube current and an irradiation time is input; a storage unit for storing generator irradiation information including a rising time and / or a falling time of the X-ray generator, detector detection information including a frame rate and / or a readout time of the detector, and dose-pulse-image quality relationship information about the relationship between the X-ray dose, number of X-ray pulses and image quality of an X-ray image; and a control unit for calculating, according to the imaging information, the number of X-ray pulses for X-ray imaging of the subject by using the generator irradiation information, the detector detection information and the dose-pulse-image quality relationship information.

Description

X-ray imaging device

[0001] The present invention relates to an X-ray imaging device, and more particularly, to an X-ray imaging device that drives an X-ray generator with on / off pulses.

[0002] In the medical field and other industrial fields, an X-ray imaging device is a device that detects X-rays that have passed through an object to be photographed after being emitted from an X-ray generator using an X-ray detector, and constructs an X-ray image based on the detected electrical signal. X-rays are attenuated at different attenuation rates depending on the material along their path and are transmitted, and when they reach the X-ray detector, they are converted into an electrical signal by the photoelectric effect. In this way, an X-ray imaging device provides information about the inside of the object to be photographed in the form of an X-ray image by using an electrical signal that reflects the accumulated attenuation amount according to the X-ray propagation path.

[0003] Recently, research and development of field emission X-ray sources using nanostructures such as carbon nanotubes (CNTs) are being conducted. X-ray generators using carbon nanotubes have a different electron emission mechanism from conventional thermionic emission X-ray generators using tungsten filaments. Field emission X-ray generators can emit electrons by applying voltage, allowing for faster electron emission and control compared to thermionic emission. Therefore, it is relatively easy to emit X-rays in the form of on / off pulses, which allows for various applications such as X-ray video shooting, and offers the possibility of relatively low-dose X-ray photography.

[0004] Currently, X-ray imaging in medical settings is determined by imaging conditions such as tube voltage, tube current, focusing distance (FFD), dose, and imaging time. However, these imaging conditions are presented based on conventional X-ray imaging devices that use thermionic X-ray tubes, i.e., thermionic emission type X-ray generators. Therefore, when the above imaging conditions are followed, there is a problem in that the advantages of field emission type X-ray generators that enable low dose and high image quality through pulse operation cannot be fully utilized.

[0005] The present invention is intended to solve the above-mentioned problem, and the purpose of the present invention is to provide an X-ray imaging device having an X-ray generator of a field emission type advantageous for pulse driving, which can provide an image of the same image quality at a relatively low dose, or a relatively high-quality image at a lower dose, compared to a thermionic X-ray generator, by utilizing the characteristic values ​​of the X-ray generator and the X-ray detector.

[0006] In order to solve the above-described problem, an X-ray imaging device according to the present invention includes a photographing unit including an X-ray generator that irradiates an X-ray to a subject and an X-ray detector that receives the X-rays transmitted through the subject and generates projection data in units of frames; an input unit for inputting photographing information including at least one of a tube voltage, a tube current, and an irradiation time; a storage unit for storing generator irradiation information including at least one of a rising time and a falling time of the X-ray generator, detector detection information including at least one of a frame rate and a readout time of the detector, and dose-pulse-quality relationship information regarding the relationship between an X-ray dose, an X-ray pulse number, and an X-ray image quality; and a control unit for calculating an X-ray pulse number for X-ray photographing of the subject by using the generator irradiation information, the detector detection information, and the dose-pulse-quality relationship information according to the photographing information.

[0007] The control unit calculates an X-ray pulse rate of the X-ray source according to the X-ray pulse number, adjusts a frame rate of the X-ray detector according to the X-ray pulse rate, and controls the X-ray generator and the X-ray detector to take an X-ray photograph of the subject at the X-ray pulse rate and the adjusted frame rate during the irradiation time.

[0008] The X-ray dose according to the above pulse number may be less than or equal to the X-ray dose according to the above shooting information.

[0009] The above shooting information may further include mode information for selecting a low-dose mode and a high-definition mode.

[0010] The pulse number of the X-ray generator in the low-dose mode may be configured to be smaller than the pulse number of the X-ray generator in the high-definition mode.

[0011] The above generator investigation information may further include an interval time between X-ray pulses.

[0012] The above interval time may be greater than or equal to the readout time of the detector.

[0013] The image quality of the above X-ray image may include a SNR value.

[0014] According to the configuration of the present invention, in an X-ray imaging device equipped with an X-ray generator of a field emission type advantageous for pulse driving, there is an effect of providing an image of the same image quality at a relatively low dose, or an image of relatively high quality at a dose lower than that, by X-ray photography using high-speed pulse driving of X-rays by utilizing the characteristic values ​​of the applied X-ray generator and X-ray detector.

[0015] Figure 1 is a graph showing the theoretical relationship between the number of X-ray pulses and image quality under the same X-ray dose conditions.

[0016] Figure 2 shows the results of improved image quality as the number of X-ray pulses increases under the same X-ray dose conditions in an actual device.

[0017] FIG. 3 shows a waveform of X-ray dose according to pulse driving in an X-ray imaging device according to one embodiment of the present invention.

[0018] FIG. 4 is a block diagram showing the configuration of an X-ray imaging device according to one embodiment of the present invention.

[0019] FIG. 5 is a flowchart showing an X-ray photographing method of an X-ray imaging device according to one embodiment of the present invention.

[0020] Hereinafter, various embodiments of the present invention will be described with reference to the drawings. The technical concepts of the present invention will be more clearly understood through these embodiments. However, the present invention is not limited to the embodiments described below.

[0021] Figure 1 is a graph showing the theoretical relationship between the number of X-ray pulses and image quality under the same X-ray dose conditions.

[0022] The horizontal axis of the graph represents the number of X-ray pulses that are evenly divided when the total number of photons is 100, and the vertical axis of the graph represents the signal-to-noise ratio (SNR), which is an indicator of image quality. X-rays have a Poisson distribution in probability. Considering this, the SNR value, which is an indicator of the quality of an X-ray image, is theoretically proportional to the square root of the number of photons.

[0023] That is, when defining X-ray dose = number of photons = N, if 100 photons are continuously irradiated, the SNR is root(100) = 10, and if 100 photons are divided into two pulses of 50 each, root(50) = 7.07, and since 2 x 7.07 = 14.1, the theoretical result is that the SNR value is improved by about 40% when the same photons are used in two pulses compared to when 100 photons are used at once. Based on this principle, it can be seen that the image quality of the X-ray image can be improved in the same trend as this graph as the number of pulses used to divide and irradiate it increases under the condition that the total number of photons of the X-ray is constant.

[0024] Figure 2 shows the results of improved image quality as the number of X-ray pulses increases under the same X-ray dose conditions in an actual device.

[0025] The increase in the image quality index SNR value according to the increase in the number of X-ray pulses under the same X-ray dose conditions in an actual X-ray imaging device does not exactly match the theoretical increase trend mentioned above due to various factors. However, when comparing the SNR value of an image exposed once at 30 FPS (Frame Per Second) using the applicant's actual product (EOX) of the X-ray imaging device with the SNR value of an image exposed twice at 60 FPS to meet the same dose conditions, it was confirmed that the SNR improved by approximately 19%.

[0026] FIG. 3 shows a waveform of X-ray dose according to pulse driving in an X-ray imaging device according to one embodiment of the present invention.

[0027] When driving a field emission type X-ray generator using a square wave signal in an X-ray imaging device according to the present embodiment, the irradiated X-ray dose reaches a target value with a predetermined rising time from the time the driving signal is turned on, as shown in this graph, and decreases with a predetermined falling time from the time the driving signal is turned off. The rising time and falling time may vary depending on the characteristics of the X-ray generator. In the case of a field emission type X-ray generator, the rising time and falling time are considerably shorter than in a thermionic emission type X-ray generator, but they also vary slightly depending on the individual characteristics of field emission type X-ray generators.

[0028] The existence of rising time and falling time in actual X-ray imaging devices is one of the reasons why the improvement in SNR value according to the increase in pulse number under the same X-ray dose condition is somewhat different from the theoretically estimated value. Another reason is that, as shown in this figure, only a higher dose than the minimum dose standard, which is a figure related to the efficiency of the imaging device, can contribute to the generation of X-ray images. Due to these various factors, the increase in SNR value according to the pulse number under the same X-ray dose condition does not match the theoretical estimate. However, as has been confirmed through actual products, the improvement in SNR value according to the increase in pulse number is the same as that confirmed previously.

[0029] In this drawing, the interval time represents a pause between pulse driving of the X-ray generator. The interval time may be inserted between X-ray pulses as shown in this drawing, or may be inserted periodically between segments consisting of multiple pulses. The interval time may be inserted to be equal to or longer than the readout time of the X-ray detector. In addition, the interval time may be inserted to match the pulse driving frequency of the X-ray generator to the frame rate of the X-ray detector, i.e., the number of acquisition frames per second.

[0030] FIG. 4 is a block diagram showing the configuration of an X-ray imaging device according to one embodiment of the present invention.

[0031] An X-ray imaging device according to the present invention comprises a photographing unit (40) including an X-ray generator (hereinafter referred to as a generator) and an X-ray detector (hereinafter referred to as a detector), a control unit (20) for controlling the generator and the detector to control X-ray imaging, an input unit (30) for receiving an input for selecting photographing conditions and a photographing mode from a photographer, and a storage unit (30) for storing various types of information (31, 32, 33, 34) necessary for generating a control signal of the control unit (20). The generator may be, for example, a field emission type X-ray generator equipped with a carbon nanotube (CNT) emitter.

[0032] As one of the various pieces of information mentioned above, the storage unit (30) stores shooting information (31) for each type of imaging medical examination. The shooting information (31) may include shooting conditions such as tube voltage, tube current, irradiation time, X-ray dose (mAs: tube current × time), and shooting distance for each type of imaging medical examination that can be performed using the X-ray imaging device according to the present embodiment.

[0033] As one of the various pieces of information, generator irradiation information (32) is stored in the storage unit (30). The generator irradiation information (32) may include at least one of the rising time, falling time, and interval time of the generator mounted on the corresponding X-ray imaging device. For example, the generator irradiation information (32) may include the aforementioned rising time and falling time as characteristic values ​​of the generator confirmed during the initial setting process of the X-ray imaging device. When there are two or more generators mounted on the X-ray imaging device, the storage unit (30) stores the generator irradiation information (33) for each generator.

[0034] In the above storage unit (30), detector detection information (33) is stored as one of the various types of information. The detector detection information (33) may include at least one of a frame rate and a read-out time of a detector mounted on an X-ray imaging device. The frame rate refers to the speed at which the detector can acquire image data, i.e., the number of image frames per second, and the read-out time refers to the time taken to transmit one frame of image data to the control unit (20). When there are two or more detectors mounted on the X-ray imaging device, the detector detection information (33) for each detector is stored in the storage unit (30).

[0035] In addition, the storage unit (30) may store dose-pulse-image quality relationship information (34) as one of the various pieces of information. When the X-ray dose values ​​included in the photographing information (31) are divided into a plurality of pulses having predetermined tube voltage and tube current values ​​and irradiated, information regarding the relationship between the image quality index (e.g., SNR) values ​​of the image acquired from the detector may be included in the dose-pulse-image quality relationship information (34). The predetermined tube voltage and tube current may have multiple values. The dose-pulse-image quality relationship information (34) may be provided and utilized as a type of look-up table. The dose-pulse-image quality relationship information (34) may be written in a manner that indicates the X-ray dose and image quality according to the number of pulses when the X-ray pulse is irradiated at a predetermined pulse rate (number of pulses per second). The above-described pulse rate may be in multiple stages and may be equal to or higher than the frame rate of the detector included in the detector detection information (33). In other words, one or more pulses may be configured to correspond to each frame of the detector.

[0036] FIG. 5 is a flowchart showing an X-ray photographing method of an X-ray imaging device according to one embodiment of the present invention.

[0037] Here, with reference to the above-described FIG. 4 and this drawing together, we will examine how the control unit (20) is configured to use the information stored in the storage unit (30) to control the X-ray imaging device according to the present embodiment.

[0038] When starting to capture an X-ray image, the shooting conditions are first input (s1) through the input unit (10) depending on which X-ray image is to be captured. For example, when capturing an X-ray image corresponding to any one of the standardized imaging medical examinations, the photographer can replace the input of shooting conditions by selecting which part is to be captured. At this time, the control unit (20) can load the shooting conditions corresponding to the shooting from among the shooting information (31) in the storage unit (30), and the photographer can also adjust some of the loaded shooting conditions through additional input.

[0039] In addition, the above shooting condition input step (s1) may be configured so that the photographer can selectively input any one of a plurality of shooting modes, such as a low-dose mode and a high-definition mode, through the input unit (10). The control unit (20) may use the previously input shooting conditions and the generator irradiation information (32), the detector detection information (33), and the dose-pulse-image quality relationship information (34) pre-stored in the storage unit (30) according to the mode selection of the photographer to calculate (s41, s51) shooting unit control information (35) for controlling the shooting unit (40) when taking an X-ray image. Here, the calculation includes not only direct calculation but also finding an appropriate value in a lookup table.

[0040] According to the shooting mode selection (s2), when the photographer selects the high-definition mode, the shooting unit control information for driving the generator and detector to divide the X-ray dose into multiple pulses and acquire projection data under the condition that the same X-ray dose as the shooting conditions input by the photographer is irradiated can be calculated (s41). Even in this case, an upper limit can be set for the SNR value of the high-definition mode X-ray image, and the number of X-ray pulses irradiated can be limited so that the expected SNR value of the image within the range of the corresponding dose does not exceed the upper limit. The high-definition mode can be further subdivided into a general high-definition mode and an ultra-high-definition mode. In addition, in the process of forming an X-ray image simultaneously with shooting, projection data by multiple X-ray pulses can be accumulated, the degree of SNR improvement of the X-ray image can be checked, and the X-ray pulse irradiation can be stopped when the value reaches the target value of the high-definition mode.

[0041] According to the shooting mode selection (s2), when the photographer selects the low-dose mode, the shooting unit control information can be calculated (s51) to provide an X-ray image with the same image quality (SNR) as the shooting conditions input by the photographer at a dose lower than the X-ray dose of the corresponding shooting conditions. The control unit (20) calculates shooting unit control information (35) for controlling the shooting unit (40) when shooting an X-ray image by using the shooting conditions previously input and the generator irradiation information (32), the detector detection information (33), and the dose-pulse-image quality relationship information (34) pre-stored in the storage unit (30).

[0042] Compared to the above shooting conditions loaded from the above shooting information (31) being based on a conventional X-ray generator that irradiates continuous X-rays, in the case of the X-ray imaging device according to the present invention, by irradiating X-rays in a pulse waveform, the SNR of the image can be improved as described above. Therefore, even if the total sum (mAs) of the tube current or X-ray pulse irradiation time is reduced compared to the 'tube current × time' (mAs) according to the shooting conditions to lower the X-ray dose irradiated to the subject, the image quality level required for normal X-ray imaging can be satisfied. Accordingly, the shooting unit control information (35) according to the low-dose mode has a smaller value at least among the tube current and time included in the above shooting information (31). When controlling the generator and detector at the maximum frame rate and the pulse rate suitable therefor considering the generator investigation information (32) and the detector detection information (33), the photographing unit control information (35) in the low-dose mode can be calculated in a manner that calculates the minimum number of pulses that satisfies the image quality (SNR) condition required as an image for the corresponding imaging medical examination.

[0043] When the shooting unit control information is generated (s41, s51) as above, the control unit (20) stores the shooting unit control information (35) at least temporarily in the storage unit (30), and controls the shooting unit (40) using the shooting unit control information (35) to perform X-ray shooting (s42, s52) according to each shooting mode.

[0044] The present invention relates to an X-ray imaging device, and can be used in a medical X-ray imaging device and an X-ray imaging device for non-destructive testing for industrial purposes.

Claims

1. A photographing unit including an X-ray generator that irradiates an X-ray to a subject and an X-ray detector that receives the X-ray passing through the subject and generates projection data in frame units; An input unit into which shooting information including at least one of tube voltage, tube current, and irradiation time is input; A storage unit storing generator investigation information including at least one of a rising time and a falling time of the X-ray generator, detector detection information including at least one of a frame rate and a readout time of the detector, and dose-pulse-quality relationship information regarding the relationship between the X-ray dose, the number of X-ray pulses, and the quality of an X-ray image; An X-ray imaging device, comprising a control unit that calculates the number of X-ray pulses for X-ray imaging of the subject by using the generator investigation information, the detector detection information, and the dose-pulse-image quality relationship information according to the above-mentioned shooting information.

2. In paragraph 1, The above control unit, An X-ray imaging device that calculates an X-ray pulse rate of the X-ray source according to the X-ray pulse number, adjusts a frame rate of the X-ray detector according to the X-ray pulse rate, and controls the X-ray generator and the X-ray detector to take an X-ray image of the subject at the X-ray pulse rate and the adjusted frame rate during the irradiation time.

3. In paragraph 1, An X-ray imaging device, wherein the X-ray dose according to the above pulse number is less than or equal to the X-ray dose according to the above shooting information.

4. In paragraph 1, An X-ray imaging device, wherein the above shooting information further includes mode information for selecting a low-dose mode and a high-definition mode.

5. In paragraph 4, An X-ray imaging device, wherein the pulse number of the X-ray generator in the low-dose mode is smaller than the pulse number of the X-ray generator in the high-definition mode.

6. In paragraph 1, An X-ray imaging device, wherein the generator investigation information further includes an interval time between X-ray pulses.

7. In paragraph 6, An X-ray imaging device wherein the above interval time is greater than or equal to the readout time of the detector.

8. In paragraph 1, An X-ray imaging device, wherein the image quality of the above X-ray image includes an SNR value.

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