JP2009240420A - Radiographic image processing apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress a residual image overlapping on an image by high-dose irradiation. <P>SOLUTION: In order to carry out imaging for energy subtraction processing, high frame rate imaging is necessary to suppress effects of body motion of a subject (a motion artifact) during imaging. Because of such a situation, a residual image of a first image may overlap on a second image. Generation of such a problem is avoided by high-dose irradiation during the first imaging. In an embodiment of the invention, a radiographic image processing apparatus controls the quality of radiation generated by a radiation generating section 12 in such a way that high-dose irradiation is carried out during the first imaging and low-dose irradiation is carried out during the second imaging. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a radiation image processing apparatus.

  In radiographic image capturing, the same part of the subject is imaged with different tube voltages, and the image obtained by imaging with each tube voltage is weighted and the difference is calculated to calculate the bones in the image. There is known a technique for obtaining an image (hereinafter referred to as “energy subtraction image”) in which one of the image portion corresponding to the hard tissue and the image portion corresponding to the soft tissue is emphasized and the other is removed. For example, when an energy subtraction image corresponding to the soft tissue of the chest is used, it is possible to see a lesion hidden by the ribs, and the diagnostic performance can be improved.

  As a method for generating an energy subtraction image, a stimulable illuminant is used for the X-ray detector, and a filter such as a copper plate is inserted between the two detectors to substantially change the tube voltage by one imaging. A technique of obtaining two images and generating an energy subtraction image from these images (hereinafter referred to as “energy subtraction process”) has been conventionally known.

  On the other hand, an X-ray imaging system using a semiconductor detector has come to be used, and X-ray continuous shooting is possible in a short time, using images continuously taken twice while changing the radiation dose and the tube voltage. Energy subtraction processing has been performed.

  In general, as disclosed in Patent Document 1, in imaging for performing energy subtraction processing, a first image is acquired by irradiation with a low dose of radiation, and a large dose of radiation is acquired. In many cases, an energy subtraction image is generated by acquiring a second image by irradiation.

  Of the two images, an image taken by irradiation with a large dose of radiation is directly used as a diagnostic image.

However, since the imaging performed for energy subtraction processing requires imaging at a high frame rate from the viewpoint of suppressing the influence of motion of the subject during the imaging (motion artifact), the second image There is a possibility that an afterimage of the first image is superimposed on.
JP 2002-243860 A

  The present invention has been made in consideration of the above facts, and an object thereof is to obtain a radiation image processing apparatus that suppresses an afterimage superimposed on an image obtained by irradiation with a large dose of radiation.

  In order to achieve the above object, the radiation image processing apparatus according to the present invention irradiates a large dose of radiation with a predetermined dose and a predetermined energy, and after irradiation with the large dose of radiation, the dose is smaller than the predetermined dose, And a radiation irradiating means for irradiating a low-dose radiation having an energy different from the predetermined energy, and a plurality of charge generating layers for generating a charge corresponding to the received radiation dose. The detection means for detecting radiation, and the time from the start of reading after the large dose of radiation is applied to the time from the start of reading after the low dose radiation is applied are different from the detection means. A first reading process for reading a detection result, a reading time when the high-dose radiation is irradiated, and a reading time when the low-dose radiation is irradiated are different from each other. Second detection processing for reading detection results from the detection means, and detection from the detection means with different image resolutions for reading at the time of irradiation with the large dose radiation and image resolutions for reading at the time of irradiation with the low dose radiation Reading means capable of executing each reading process of the third reading process for reading the result, the amplification factor of the low-dose image signal read by the reading means when the low-dose radiation is irradiated, and the large-dose radiation An amplification unit capable of executing an amplification process with different amplification factors of the large-dose image signal read by the reading unit during irradiation, and an extraction unit for extracting a low frequency component from the amplified image signal. The characteristic amount of the low frequency component in the extraction of the low frequency component of the large dose image signal and the low amount in the extraction of the low frequency component of the low dose image signal. Extraction means capable of executing extraction processing with different characteristic quantities of wave number components, sampling frequency in analog-digital conversion of the large-dose image signal, and sampling in analog-digital conversion of the low-dose image signal Analog-to-digital conversion means capable of executing analog-to-digital conversion processing with different number of times, the first reading processing, the second reading processing, the third reading processing, the amplification processing, and the extraction Control means for controlling at least one of the reading means, the amplifying means, the extracting means, and the analog-to-digital conversion means so that at least one of processing and at least one of the analog-digital conversion processing is executed; Image processing means for performing image processing using the large-dose image data and the low-dose image data.

  The extraction means emphasizes reducing noise by increasing the characteristic amount of the low frequency component in the large dose image, while reducing the characteristic amount of the low frequency component in the low dose image to reduce the reading speed. Emphasis should be placed on speed.

  When a radiation irradiation means performs irradiation of a low dose and high energy radiation after performing irradiation of a large dose and low energy radiation when an image taken by irradiation of low energy radiation is used as a diagnostic image, Good.

  As described above, the present invention has an excellent effect that an afterimage superimposed on an image obtained by irradiation with a large dose of radiation can be suppressed.

  Furthermore, it has the outstanding effect that the delay of the switching of the energy of a radiation can be avoided by irradiating a high energy radiation after irradiating a low energy radiation.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 shows a radiographic image capturing system 10 according to the present embodiment. The radiographic imaging system 10 includes a radiation generation unit 12 that generates radiation (for example, X-rays (X-rays) and the like), a radiation detection panel 14 that is spaced from the radiation generation unit 12, and images from the radiation detection panel 14. A control device 16 including a microcomputer that acquires information and performs various processes and various electric circuits is provided. An imaging position where the subject 18 is located at the time of imaging is formed between the radiation generation unit 12 and the radiation detection panel 14, and an image is transmitted by passing through the subject 18 irradiated from the radiation generation unit 12 and positioned at the imaging position. The radiation carrying information is applied to the radiation detection panel 14.

  The control device 16 includes a radiation generation control unit 20, a signal detection correction unit 22, a control unit 24, a display 26 capable of displaying an image and the like, and an operation panel 28 including an input device such as a keyboard and a pointing device such as a mouse. Yes. The radiation generation control unit 20 is connected to the radiation generation unit 12 and the control unit 24, and in response to an instruction from the control unit 24, a tube voltage, a tube current, and a radiation generation time when the radiation generation unit 12 generates radiation. By controlling the above, the radiation quality of the radiation generated by the radiation generator 12 is controlled.

  By the way, of the two images obtained by the two photographings performed for the energy subtraction process, an image photographed by irradiation with a large dose of radiation is used as the diagnostic image.

  However, the imaging performed for the energy subtraction process requires imaging at a high frame rate from the viewpoint of suppressing the influence of the body motion of the subject during the imaging (motion artifact). For this reason, there is a possibility that an afterimage of the first image is superimposed on the second image. The occurrence of this problem can be avoided by irradiating a large dose of radiation at the time of photographing the first image. For the above reasons, in the present embodiment, the radiation dose so that the radiation dose irradiated at the previous imaging out of the two imagings becomes a large dose and the radiation dose irradiated at the subsequent imaging becomes a low dose. In some cases, the quality of radiation generated by the generator 12 is controlled.

  Also, in radiography for energy subtraction processing, if radiation of a low voltage tube voltage is applied after radiation of a high voltage tube voltage, the high voltage tube voltage cannot be lowered to a low pressure in a short time. Therefore, from the viewpoint of motion artifacts, it is desirable to irradiate radiation having a high tube voltage following irradiation with radiation having a low tube voltage. In particular, when photographing the lumbar vertebrae and limb bones, an image photographed with low-voltage tube voltage radiation is used as a diagnostic image. Therefore, in the first photographing, a low-voltage tube voltage and a large dose of radiation are irradiated. In this imaging, high voltage tube voltage and low dose radiation should be irradiated.

  In addition, every time the subject 18 is photographed, the signal detection unit 22 reads out an image signal from the radiation detection panel 14 and converts it into digital image data, and performs offset correction on the image data obtained by the conversion, and Correction processing such as gain correction is performed.

  The control unit 24 controls the photographing of the subject 18 in accordance with an instruction input via the operation panel 28, or performs image processing such as generation of an energy subtraction image using image data input from the signal detection correction unit 22. Or processing for providing a predetermined user I / F via the display 26 and the operation panel 28. The control unit 24 includes a non-volatile storage unit 24A composed of an HDD, a flash memory, or the like, and an imaging condition information DB (database) is stored in the storage unit 24A. The storage unit 24A also stores a program for the control unit 24 to perform energy subtraction processing.

  The radiographic image capturing system 10 includes an imaging region moving unit 30. The imaging part moving unit 30 includes a radiation generating unit 12 and an actuator that can move the radiation detection panel 14. The imaging target part of the subject 18 (imaging part: for example, chest, lumbar spine, limb bone, breast, etc.) Is notified from the control device 16, the radiation generating unit 12 and the radiation detection panel 14 are moved to a position for imaging the notified imaging part of the subject 18. Note that the positions of the radiation generating unit 12 and the radiation detection panel 14 for imaging a certain imaging region of the subject 18 are different depending on the physique of the subject 18 and the like. When the adjustment of the imaging position is instructed via the radio button, the positions of the radiation generator 12 and the radiation detection panel 14 are adjusted according to the instruction.

  Next, configurations of the radiation detection panel 14 and the signal detection correction unit 22 will be described. The radiation detection panel 14 is formed with a photoelectric conversion layer (charge generation layer) 42 that generates charges on the TFT active matrix substrate 34 shown in FIG. Further, a bias electrode (not shown) connected to a high voltage power source is formed on the upper side. The photoelectric conversion layer is made of amorphous a-Se (amorphous selenium) containing, for example, selenium as a main component (for example, a content rate of 50% or more), and when irradiated with radiation, the amount of charge corresponding to the amount of irradiated radiation. The generated radiation (electron-hole pair) is internally generated to convert the irradiated radiation into charges. Thereby, the image information carried by the irradiated radiation is converted into charge information.

  In addition, on the TFT active matrix substrate 34, a pixel unit 40 including a storage capacitor 36 for storing charges generated in the photoelectric conversion layer and a TFT 38 for reading out the charges stored in the storage capacitor 36 (note that FIG. 2, a plurality of bias electrodes and photoelectric conversion layers corresponding to the individual pixel portions 40 are schematically shown as photoelectric conversion portions 42), and are arranged in a matrix, and in the direction of arrow A in FIG. And a plurality of gate wirings 44 for turning on and off the TFTs 38 of the individual pixel portions 40 and the TFTs 38 extending and turned on along the arrow B direction perpendicular to the arrow A direction in FIG. A plurality of data wirings 46 for reading out stored charges from the storage capacitor 36 are also provided.

  On the other hand, the signal detection correction unit 22 includes a gate line driver 48 connected to each gate wiring 44 of the radiation detection panel 14. The gate line driver 48 is connected to the gate wiring 44 that has supplied the ON signal by supplying a high-level voltage signal (ON signal) to the specific gate wiring 44 when the signal charge is read from the radiation detection panel 14. The TFT 38 of each pixel unit 40 is changed from OFF to ON, and after a certain time, the supply of the ON signal to the gate wiring 44 is stopped, so that the gate wiring 44 that has supplied the ON signal is connected. A gate line driving process for changing the TFT 38 of each pixel unit 40 from on to off is sequentially performed on the individual gate wirings 44.

  Here, the readout of the signal charges from the radiation detection panel 14 is performed with respect to the time from when the radiation generator 12 emits a large dose of radiation (hereinafter referred to as “large dose radiation”) to the start of readout, The time from when the low-dose radiation (hereinafter referred to as “low-dose radiation”) is emitted from the generation unit 12 to when reading is started is different.

  Leakage charge generated due to TFT during irradiation with large dose radiation (to prevent TFT, it is a charge that leaks charge from back gate during irradiation with large dose radiation. Leakage current is exponential with time In order to prevent artifacts due to attenuation (for example, see JP-A-2000-75039) from being superimposed on an image, there is a case where a waiting time from the irradiation of a large dose of radiation to the start of reading may be provided.

  Further, the reading is performed so that the reading time when the large dose radiation is irradiated and the reading time when the low dose radiation is irradiated are different.

  Further, the reading is performed so that the image resolution of reading when a large dose of radiation is irradiated is different from the image resolution of reading when a low dose of radiation is irradiated.

  In particular, if the first radiograph is irradiated with a low-voltage tube voltage and a large dose of radiation, and the second radiograph is irradiated with a high-voltage tube voltage and a low-dose radiation, the low-dose radiation is applied. The obtained image (hereinafter referred to as “low-dose image”) is a non-diagnostic image necessary only for separating the bone part and the soft part, and it is not necessary to increase the resolution of the image. Therefore, the low-dose image may be read by binning. As a result, the time required for imaging can be reduced, and a decrease in waiting time for engineers and patients can be expected. For example, when binning two rows, the readout time is halved.

  Further, the signal detection correction unit 22 includes the same number of operational amplifiers 50 as the number of data wirings 46 provided on the TFT active matrix substrate 34, and the individual data wirings 46 of the radiation detection panel 14 are inversions of mutually different operational amplifiers 50. Each is connected to the input terminal. Each operational amplifier 50 has a non-inverting input terminal connected to a GND wiring (ground wiring), one end of a capacitor 52 connected to the inverting input terminal, and the other end connected to an output terminal. . With the above configuration, each operational amplifier 50 and capacitor 52 functions as a charge amplifier that integrates a current (signal charge) flowing through the data wiring 46 connected to the inverting input terminal and outputs a signal having a level corresponding to the integration result. To do.

  An output terminal of each operational amplifier 50 (charge amplifier) is connected to an input terminal of a low-pass filter (LPF) 53 through an amplifier (not shown).

  The LPF 53 performs extraction processing of low frequency components from the signal. The LPF 53 in the present embodiment is characterized by the characteristic amount of the low frequency component in the extraction processing of the low frequency component of the signal obtained by the irradiation of the large dose radiation and the low frequency component of the signal obtained by the irradiation of the low dose radiation. The extraction process can be performed so that the characteristic amount of the low frequency component in the extraction process is different.

  That is, it is preferable to reduce the LPF time constant of the ASIC when reading out a low-dose image. If the LPF time constant is reduced, the readout time for one line can be reduced. Thereby, it is possible to reduce the time required for photographing.

  The output terminal of the LPF 53 is connected to one of a plurality of input terminals of a multiplexer (MUX) 54, and individual output signals are input to the MUX 54 in parallel.

  Here, the amplifier can amplify the signal so that the amplification factor of the signal output at the time of capturing the low-dose image is different from the amplification factor of the signal output at the time of capturing the large-dose image. Increasing the gain when reading out the low-dose image can relatively reduce the electrical noise in the low-dose image. Thereby, the noise of an energy subtraction image can be reduced as a result. In addition, since the radiation dose is low, saturation does not occur even when the gain is increased.

  The output terminal of the MUX 54 is connected to the input terminal of an analog-digital (A / D) converter 56. The A / D converter 56 performs A / D conversion so that the number of samplings in A / D conversion when a large dose of radiation is irradiated is different from the number of samplings in A / D conversion when a low dose of radiation is irradiated. Conversion can be performed.

  In particular, when reading an image obtained by irradiation with a large dose of radiation (hereinafter referred to as a “large dose image”), the number of A / D conversion samplings is increased to reduce noise, so-called oversampling is performed, When reading out a low-dose image, the number of A / D conversion samplings is reduced. As a result, the image reading time can be shortened, and the diagnostic image noise can be reduced and the time required for the energy subtraction process can be shortened.

  With the above processing, parallel-serial conversion and A / D conversion are sequentially performed on a plurality of signals (the same number as the number of data wirings 46) input in parallel to the MUX 54.

  The output end of the A / D converter 56 is connected to the input end of the image quality correction processing unit 58, and the output end of the image quality correction processing unit 58 is connected to the input end of the control unit 24 (see FIG. 1). The image quality correction processing unit 58 performs, for example, basic correction such as offset correction and gain correction as image quality correction processing for improving the image quality of an image.

  The control unit 24 performs energy subtraction processing using image data representing a large dose image and image data representing a low dose image, and obtains an energy subtraction image.

  Thus, by obtaining the large dose image before the low dose image, it is possible to suppress the afterimage superimposed on the large dose image obtained by the irradiation of the large dose radiation.

  In addition, by irradiating the high-voltage tube voltage radiation after irradiating the low-voltage tube voltage radiation, delay in switching the radiation tube voltage can be avoided.

  Note that, in the above, the time from when radiation is applied until the start of reading, the reading time, the image resolution of reading, the amplification factor at the time of amplification, the characteristic amount of the frequency component at the time of low frequency component extraction processing, and In the above description, the number of times of sampling at the time of A / D conversion is different for high-dose radiation irradiation and low-dose radiation irradiation. However, at least one of them may be different, and some combinations may be used. Good.

  Moreover, although the above demonstrated the case where the radiation detection panel 14 provided with the photoelectric converting layer which converts the irradiated radiation directly into an electric charge was used as an example of the image detection means concerning this invention, it is limited to this. The photoelectric conversion unit that converts the irradiated radiation into charges in the image detection means converts the irradiated radiation into electromagnetic waves (for example, visible light), and then converts the converted electromagnetic waves into charges. A configuration (indirect conversion method) may be used. In the above description, the configuration in which the photoelectric conversion layer is formed on the TFT active matrix substrate 34 has been described. However, the photoelectric conversion unit includes a substrate on which a plurality of pixel units each including a storage capacitor and a switching unit are arranged. It may be a separate body.

  In the above description, the radiation detection panel 14 having a configuration in which a large number of pixel portions 40 (TFTs 38 and storage capacitors 36) are arranged in a matrix (two-dimensionally) has been described as an example. However, the present invention is not limited to this. The radiation detection panel may have a configuration in which a plurality of pixel portions are arranged in a row (one-dimensionally).

  In the above description, X-rays have been described as an example of radiation generated by the radiation generating means according to the present invention. However, the present invention is not limited to this, and is converted into charges by the image detecting means and stored in the storage capacitor. Any other radiation such as an electron beam or an α-ray may be used as long as charges are accumulated.

  In the above description, the energy subtraction process using two images is described as an example of the image processing. However, the present invention is not limited to this, and for example, energy subtraction using three or more images. It may be a process.

It is a block diagram which shows schematic structure of the radiographic imaging system which concerns on this embodiment. It is a schematic block diagram of a radiation detection panel and a signal detection correction | amendment part.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Radiation imaging system 12 Radiation generation part 14 Radiation detection panel 16 Control apparatus 20 Radiation generation control part 22 Signal detection correction | amendment part 24A Storage part 24 Control part

Claims (2)

Radiation irradiating means for irradiating a large dose radiation with a predetermined dose and a predetermined energy, and for irradiating a low dose radiation with an energy different from the predetermined energy after the irradiation with the large dose radiation. When,
A detection unit that includes a large number of charge generation layers that generate charges according to the amount of radiation received;
First readout for reading out detection results from the detection means with different time from the start of reading after the irradiation with the large dose of radiation and the time from the start of reading out after the irradiation of the low dose of radiation. Processing, a second readout process for reading out the detection result from the detection means by making the readout time at the time of irradiation with the large dose radiation different from the readout time at the time of irradiation with the low dose radiation, and at the time of irradiation with the large dose radiation Reading means capable of executing each of the reading processes of the third reading process for reading out the detection result from the detecting means by differentiating the image resolution of reading and the image resolution of reading at the time of irradiation with the low-dose radiation;
The amplification factor of the low-dose image signal read out by the reading unit during irradiation with the low-dose radiation is different from the amplification factor of the large-dose image signal read out by the reading unit during the irradiation of the large-dose radiation. Amplifying means capable of performing amplifying processing;
Extraction means for extracting a low frequency component from the amplified image signal, the characteristic amount of the low frequency component in the extraction of the low frequency component of the large dose image signal, and the low frequency component of the low dose image signal Extraction means capable of performing extraction processing with different characteristic amounts of the low frequency components in the extraction of
An analog-to-digital conversion means capable of performing an analog-to-digital conversion process in which the number of sampling times in the analog-to-digital conversion of the large-dose image signal is different from the number of sampling times in the analog-to-digital conversion of the low-dose image signal;
The reading so that at least one of the first reading process, the second reading process, the third reading process, the amplification process, the extraction process, and the analog-digital conversion process is executed. Control means for controlling at least one of means, amplification means, extraction means, and analog-digital conversion means;
Image processing means for performing image processing using the large-dose image data and the low-dose image data;
A radiographic image processing apparatus comprising:   The radiation irradiating means irradiates a low-dose and high-energy radiation after irradiating a large-dose and low-energy radiation when an image taken by irradiating the low-energy radiation is used as a diagnostic image. The radiographic image processing apparatus according to claim 1.

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