JP2009082498A - Radiographic equipment, radiographic system, information processing device, and incident dose derivation measure for mamma - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide radiographic equipment, a radiographic system, and an information processing device enabling to easily measure the average mammary gland dose. <P>SOLUTION: Radiographic equipment 100 takes an image by X-ray irradiation of a phantom 20 having a plurality of constant transmissivity domains 22A to 22D, each of which has different specified transmissivity to the X rays; a medical image reading device 200 obtains image data showing the concerned phantom; a medical image processor 300 estimates a half-value layer of the X rays irradiation based on the image data obtained as well as calculates a correlation value which correlates to the amount of noise contained in a pixel value of a prespecified domain among domains corresponding to a plurality of the constant transmissivity domains of an image shown by the image data, estimates an incident dose based on the correlation value, and derives the average mammary gland dose from the estimated half-value layer and incident dose and displays it. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a radiation imaging apparatus, a radiation imaging system, an information processing apparatus, and an incident dose derivation method.

  Conventionally, imaging methods using radiation (X-rays, α-rays, β-rays, γ-rays, electron beams, ultraviolet rays, etc.) have been used in various fields, and especially in the medical field, it is the most important for diagnosis. It is one of the means. Since the first X-ray photography was realized, the X-ray photography method has been improved many times, and at present, a method combining a fluorescent screen and an X-ray film has become mainstream.

  On the other hand, in recent years, various digitized apparatuses such as X-ray CT, ultrasound, and MRI have been put into practical use, and the construction of diagnostic information processing systems and the like in hospitals is being promoted. Many studies for digitizing X-ray images have also been made, and a radiographic method using a stimulable phosphor has been established and has attracted attention as a replacement for conventional X-ray photography.

  A photostimulable phosphor (accumulative phosphor) accumulates a portion of its radiation energy when irradiated with radiation, and then accumulates when irradiated with excitation light such as visible light. It is a substance that emits photostimulative light according to its energy, and its existence has been conventionally known. The radiography method using this is as follows. That is, first, a radiographic image of a subject such as a human body is photographed and recorded on a sheet-like recording sheet coated with a stimulable phosphor using an image photographing device. Next, the recording sheet is scanned with an excitation light such as a laser beam using an image reading device, and the excited emission light generated thereby is photoelectrically generated by a photomultiplier (photoelectron amplifier tube) of the image reading device. read. Digital image data is obtained based on the analog image signal thus obtained. Furthermore, after this image data is appropriately processed using a medical image processing apparatus, it is output to a display such as a CRT or printed on a film by a laser printer or the like. Thereby, a radiation image in which the energy level of radiation transmitted through the subject is visualized by shading can be obtained.

  By the way, when using such a radiographic image for medical diagnosis or the like, it is necessary that the radiography system is highly reliable and, therefore, the performance of the radiography system must be measured and verified as needed. I must. If any of the radiographic system including the photostimulable phosphor of the sheet or the image reader deteriorates or becomes abnormal, a normal radiographic image cannot be obtained, and the reliability when analyzing the image is impaired. Because it is. In addition, since irradiation with a high level of radiation energy adversely affects the human body, verification of the performance of the radiation imaging system is also important in terms of safety.

  In particular, in breast radiography systems (mammography), the average mammary gland dose is measured and evaluated in consideration of the effect of radiation energy applied to the human body. As a method for measuring the average mammary gland dose, for example, Non-Patent Document 1 discloses a method for measuring the average mammary gland dose using a dosimeter and an aluminum plate by changing the tube voltage and changing the quality of X-rays to be irradiated. Is described.

  On the other hand, in a radiography system, image quality evaluation items such as, for example, linearity, dynamic range, sharpness, contrast, S / N ratio, and reduction ratio are evaluated using images obtained by photographing a physical phantom or a body imitation phantom. Yes.

For example, Patent Document 1 discloses a technique for measuring the quality of a radiation image detector by evaluating a desired image quality evaluation item using a radiation image obtained by photographing a phantom.
Japan Radiological Technology Society Radiation Medical Technology Series (14-3) Mammography Accuracy Control Manual (Revised) P85- JP 2004-298617 A

  However, in the conventional radiography system for breasts, there is a problem that evaluation of the average mammary gland dose and measurement of image quality using fonts must be performed separately, which is complicated.

  The present invention has been made to solve the above problems, and an object thereof is to provide a radiation imaging apparatus, a radiation imaging system, and an information processing apparatus that can easily measure an average mammary gland dose.

  In order to achieve the above object, the breast radiography apparatus according to the first aspect of the present invention provides a phantom provided with a plurality of constant transmittance regions each having a predetermined transmittance different from each other with respect to X-rays. And obtaining an image data indicating the phantom by irradiating with X-rays, and estimating a half-value layer of the irradiated X-ray based on the image data obtained by the obtaining means, Of the areas corresponding to the plurality of constant transmittance areas of the image indicated by the image data, a correlation value that correlates with a noise amount included in a pixel value of a predetermined area is obtained, and incident is performed based on the correlation value Deriving means for estimating a dose and deriving an average mammary gland dose from the estimated half-value layer and incident dose; and a display means for displaying the average mammary gland dose derived by the deriving means.

  According to the first aspect of the present invention, imaging is performed by irradiating a phantom provided with a plurality of constant transmittance regions each having a predetermined transmittance different from each other with respect to the X-ray by the obtaining unit. Image data indicating the phantom is acquired, and the derivation means estimates a half-value layer of the irradiated X-ray based on the image data acquired by the acquisition means, and a plurality of images indicated by the image data A correlation value that correlates with the amount of noise included in a pixel value of a predetermined area among areas corresponding to the constant transmittance area is obtained, the incident dose is estimated based on the correlation value, and the estimated half price The average mammary gland dose is derived from the layer and the incident dose, and the display unit displays the average mammary gland dose derived by the deriving unit. The display by the display means includes visible display by a display device, permanent visible display by a printer, audible display by a speaker, and the like.

  As described above, according to the first aspect of the present invention, X-rays are irradiated to the phantom in which a plurality of constant transmittance regions each having a predetermined transmittance different from each other with respect to the X-rays are provided. Since the average mammary gland dose is derived and displayed based on the image data indicating the phantom obtained by performing the measurement, the average mammary gland dose can be easily measured.

  On the other hand, in order to achieve the above object, the radiation imaging apparatus for breast according to claim 2 is provided with a phantom provided with a plurality of constant transmittance regions each having a predetermined transmittance different from each other with respect to X-rays. An acquisition means for acquiring image data indicating the phantom by reading a recording medium on which an image indicating the phantom is recorded by irradiating X-rays to the image and an image acquired by the acquisition means Based on the data, the half-value layer of the irradiated X-ray is estimated and included in the pixel value of a predetermined region among the regions corresponding to the plurality of constant transmittance regions of the image indicated by the image data A derivation means for obtaining a correlation value correlated with the amount of noise generated, estimating an incident dose based on the correlation value, and deriving an average mammary dose from the estimated half-value layer and the incident dose; And a display means for displaying the average glandular dose derived by serial deriving means.

  According to the second aspect of the present invention, the acquisition unit performs imaging by irradiating the phantom provided with a plurality of constant transmittance regions each having a predetermined transmittance different from each other with respect to the X-rays. The image data indicating the phantom is acquired by reading the recording medium on which the image indicating the phantom is recorded, and the half value layer of the irradiated X-ray is obtained based on the image data acquired by the acquiring means by the deriving means And a correlation value that correlates with the amount of noise included in the pixel value of a predetermined area among areas corresponding to a plurality of constant transmittance areas of the image indicated by the image data is obtained, and the correlation The incident dose is estimated based on the value, the average mammary gland dose is derived from the estimated half-value layer and the incident dose, and the average derived by the deriving means by the display means Glandular dose is displayed.

  Therefore, since the invention described in claim 2 operates in the same manner as the invention described in claim 1, the average mammary gland dose can be easily measured as in the invention described in claim 1.

  In the invention according to claim 1 or 2, as in the invention according to claim 3, the plurality of constant transmissions of the image indicated by the image data acquired by the acquiring means by the derivation means. A predetermined index value may be obtained from an average pixel value between two or more predetermined areas among the areas corresponding to the rate area, and the half-value layer may be estimated based on the index value.

  Further, the invention according to claim 3 is the correspondence between the index value obtained from the average pixel value between the two or more predetermined regions and the half-value layer, as in the invention according to claim 4. First storage means for storing half-value layer information indicating a relationship in advance is further provided, and the derivation means uses the half-value information stored in the first storage means to calculate the half value from the calculated index value. The layer may be estimated.

  Further, in the invention described in claims 1 to 4, as in the invention described in claim 5, the correspondence between the correlation value of the predetermined region and the incident dose is classified for each half-value layer. Second storage means for preliminarily storing incident dose information to be displayed, and the derivation means estimates the incident dose from the obtained correlation value based on the incident dose information stored in the second storage means. Also good.

  Further, in the inventions described in claims 1 to 5, when the display means has an average mammary gland dose derived by the derivation means larger than a predetermined allowable amount as in the invention described in claim 6. A warning may be displayed.

  Further, according to the first to sixth aspects of the present invention, as in the seventh aspect of the present invention, the phantom may be used for evaluating the image quality of a photographed image.

  On the other hand, in order to achieve the above object, the radiation imaging system for breast according to claim 8 is a phantom provided with a plurality of constant transmittance regions each having a predetermined transmittance different from each other with respect to X-rays. A reader that acquires image data indicating the phantom by reading a recording medium on which an image indicating the phantom is recorded by irradiating X-rays to the image, and an image acquired by the reader Based on the data, the half-value layer of the irradiated X-ray is estimated and included in the pixel value of a predetermined region among the regions corresponding to the plurality of constant transmittance regions of the image indicated by the image data A derivation process that calculates a correlation value that correlates with the amount of noise generated, estimates the incident dose based on the correlation value, and derives the average mammary dose from the estimated half-value layer and incident dose It includes an information processing apparatus which performs, and a display device for displaying the average glandular dose derived by the information processing apparatus.

  Therefore, since the invention described in claim 8 operates in the same manner as the invention described in claim 2, the average mammary gland dose can be easily measured as in the invention described in claim 1.

  On the other hand, in order to achieve the above object, an information processing apparatus according to claim 9 provides an X-ray for a phantom provided with a plurality of constant transmittance regions each having a predetermined transmittance different from each other for X-rays. The half-value layer of the irradiated X-ray is estimated based on the image data indicating the phantom acquired by performing imaging by irradiating and the plurality of constant transmittance regions of the image indicated by the image data The correlation value correlating with the amount of noise included in the pixel value of the predetermined region is calculated, the incident dose is estimated based on the correlation value, and the estimated half-value layer and the incident dose are calculated. Deriving means for performing a deriving process for deriving an average mammary gland dose is provided.

  Therefore, since the invention described in claim 9 operates in the same manner as the invention described in claim 1 or 2, the average mammary gland dose can be easily measured as in the invention described in claim 1. .

  On the other hand, in the incident dose derivation method according to claim 10, the phantom is obtained by performing imaging by irradiating X-rays to a phantom provided with a constant transmittance region having a predetermined transmittance for X-rays. And obtaining a correlation value that correlates with the amount of noise included in the pixel value of the region corresponding to the constant transmittance region of the image indicated by the acquired image data, and based on the correlation value Deriving the incident dose.

  Therefore, the invention according to claim 10 can easily derive the incident dose.

  Thus, according to the present invention, there is an excellent effect that the average mammary gland dose can be easily measured.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. Hereinafter, a case where the present invention is applied to a mammography system will be described. FIG. 1 shows a schematic configuration of a mammography system 5 according to the present embodiment.

  As shown in the figure, the radiation imaging system 5 includes a radiation imaging apparatus 100 that records radiation image information on a recording sheet 10 by performing radiation imaging, and reads the radiation image information recorded on the recording sheet 10 to obtain an image. A medical image reading apparatus 200 that acquires data and a medical image processing apparatus 300 that performs predetermined processing on image data input from the medical image reading apparatus 200 are included. These radiation imaging apparatus 100, medical image reading apparatus 200, and medical image processing apparatus 300 are connected to each other via a network N1.

  The network N1 is used to manage a radiation information management system (radiology information system, hereinafter referred to as “RIS”) 500 used for managing various operations related to radiographic imaging and the entire hospital. A hospital information management system (hereinafter referred to as “HIS”) 510 and a communication control unit 540 for communicating with the maintenance center 530 via the Internet 520 are also connected. Furthermore, an external device 550 such as a hospital database server, an ID card reader, or a terminal device is connected to the network N1 as necessary.

  The radiation imaging apparatus 100 is an apparatus that records radiation that has passed through a subject on the recording sheet 10 as radiation image information about the subject by irradiating the recording sheet 10 with radiation through the subject. The recording sheet 10 is a sheet coated with a stimulable phosphor material that accumulates energy of irradiated radiation (stimulable phosphor sheet), and is used as a recording medium for recording radiation image information.

  The radiation imaging apparatus 100 includes an imaging position elevating mechanism 101 that adjusts the imaging position of the subject by moving the position of the recording sheet 10 up and down, an imaging table 102 that determines the position of the subject's feet, and the subject. A radiation generation unit 103 that generates radiation applied to the imaging unit, an imaging control unit 104 that controls the radiation generation unit 103 and the like according to a given imaging condition, and an input unit 105 that is used to input various commands and imaging conditions. Including. The shooting control unit 104 is connected to the network N1, and can set shooting conditions via the network N1.

  In the radiation imaging system 5, when performing an examination, the phantom 20 is disposed in the radiation imaging apparatus 100 as a subject. Then, radiation image information of the phantom 20 is recorded on the recording sheet 10 by performing radiation imaging under predetermined imaging conditions. After photographing, the recording sheet 10 is set at a predetermined position of the medical image reading apparatus 200. The phantom 20 will be described in detail later.

  The medical image reading apparatus 200 photoelectrically reads the radiation image information recorded on the recording sheet 10 and converts the energy level of the radiation irradiated on the recording sheet 10 into data, thereby converting image data indicating the phantom 20 into data. get. Reading of radiation image information is performed as follows. That is, the surface of the recording sheet 10 is scanned by the light beam emitted from the laser light source 201 and passed through the light scanning unit 202. As a result, an amount of stimulated emission light corresponding to the accumulated radiation energy is generated from the region of the recording sheet 10 irradiated with the light beam. This stimulated emission light is guided by a light guide, photoelectrically detected by a photomultiplier (photomultiplier tube) 203, and output as an analog signal representing radiation image information. Further, this analog signal is amplified by an amplifier 204 and digitized by an A / D converter 205. The image data acquired in this way is output to the medical image processing apparatus 300 via the network N1.

  Note that another method as described below may be used as the method of the medical image reading apparatus. That is, a line light source in which LEDs or the like are arranged in the main scanning direction is used as a light source for exciting the stimulated emission light, and a CCD line or the like arranged in the main scanning direction as a detector for detecting the stimulated emission light. A read head having a sensor is used. Then, while relatively moving the reading head and the recording sheet 10 in the sub-scanning direction orthogonal to the main scanning direction, the excitation light emitted from the line light source is incident on the recording sheet 10, and the brightness generated from the recording sheet 10 is detected. The exhaust light is read by the line sensor.

  The medical image processing apparatus 300 is configured using, for example, a personal computer. The medical image processing apparatus 300 includes an input unit 310 such as a keyboard and a mouse, a display unit 320 such as a CRT monitor that displays radiographic images, and the like, which are used for inputting various commands and examination results. And a printer 330 that prints a diagnostic image on a film or the like.

  The medical image processing apparatus 300 generates a radiation image by performing image processing on the image data acquired by the medical image reading apparatus 200. Further, the medical image processing apparatus 300 performs an image process on the acquired image data and measures a predetermined image quality evaluation item, thereby inspecting the performance of the radiation imaging system 5 and the invariance of parameters.

  FIG. 2 shows a configuration of a medical image processing apparatus 300 according to the present embodiment.

  As shown in the figure, the medical image processing apparatus 300 includes a CPU (central processing unit) 400 that controls the operation of the entire medical image processing apparatus 300, a memory 402 that is used as a work area when executing various programs, and the CPU 400. Various programs such as a basic program that is executed and controls the operation of the entire apparatus, an inspection processing program used to inspect the radiation imaging system 5, half-value layer information, incident dose information, etc. A hard disk 404 in which various types of information are stored in advance, an operation input unit 410 to which various types of information are input via the input unit 310 such as a mouse or a keyboard, and a display control unit 412 that controls display of various types of information on the display unit 320 Send and receive data to and from an external device connected to network N1 via connector 414A A network interface unit (network I / F unit) 414 for performing, an external interface unit (external I / F unit) 416 for transmitting image data to be printed to the printer 330 via an external interface such as a USB, It has.

  The CPU 400, the memory 402, the hard disk 404, the operation input unit 410, the display control unit 412, the network interface unit 414, and the external interface unit 416 are connected to each other via the system bus BUS. Therefore, the CPU 400 accesses the memory 402 and the hard disk 404, grasps the contents of instructions by the user's operation on the input unit 310, displays various information on the display unit 320 via the display control unit 412, and the network interface unit Transmission / reception of data to / from an external device connected to the network N1 via the network 414 and a request for printing to the printer 330 connected via the external interface unit 416 can be performed.

  Next, the phantom 20 according to the present embodiment will be described.

  3 and 4 show an example of the configuration of the phantom 20 according to the present embodiment.

  As shown in FIG. 3, the phantom 20 according to the present embodiment includes a step-like transmission region portion 24 provided with a plurality of constant transmittance regions 22 each having a predetermined transmittance different from each other with respect to X-rays. And a uniform exposure unit 26 for inspecting whether the exposure state is the same.

  In the phantom 20 according to the present embodiment, four constant transmittance regions 22 </ b> A to 22 </ b> D are provided in the step-like transmission region portion 24. As shown in FIG. 4, the constant transmittance regions 22 </ b> A to 22 </ b> D are each made to have a constant transmittance by changing the thickness of a member 23 such as a copper plate, for example. FIG. 4 shows only the constant transmittance regions 22A and 22B, and shows the difference in thickness larger than the actual thickness so that the thickness of the member 23 can be easily discriminated. The transmittances of the constant transmittance regions 22A to 22D are T_A to T_D.

  The constant transmittance regions 22A to 22D may have different transmittances by changing the material and thickness of the member.

  Next, a method for deriving the average mammary gland dose AGD according to the present embodiment will be described.

  The average mammary gland dose AGD is defined as the following equation (1).

AGD = K × g (HVL) × c (HVL) × s (T / F) (1)
here,
K: incident dose,
g, c, s: Calculation coefficient according to the half-value layer HVL: Half-value layer T / F: Constant determined by the target filter In the radiographic system 5 according to the present embodiment, the half-value layer HVL is estimated as the first step. Then, the incident dose K is estimated as the second step, and the values of the respective calculation coefficients g, c, and s are determined as the third step, and then the average mammary dose AGD is derived from the above equation (1).

  Hereinafter, each step will be described separately.

  In the first step, using the average pixel value PV of each region corresponding to each constant transmittance region 22A to 22D of the image obtained by photographing the phantom 20 as shown in FIG. The half-value layer HVL, which is an index representing the quality of the radiation, is measured. Here, the average pixel value PV and the half-value layer HVL will be supplemented.

  PV stands for Pixel Value and is a digital value representing the density of the X-ray image. This PV is an index representing the incident dose reaching the recording sheet 10, and the value changes in proportion to the incident dose or the logarithm of the incident dose. The phosphor material as in this embodiment is applied. In the system using the recorded sheet 10 (CR system), it changes in proportion to the logarithm of the incident dose.

  HVL stands for Half Value Layer and is an index representing the quality of X-rays. This radiation quality refers to the spectral distribution of X-rays, and is defined by the thickness of the aluminum filter that reduces the X-ray dose by half when transmitted through the aluminum filter. For example, when an aluminum filter having a thickness of 3 mm is inserted and the dose is halved, HVL = 3 mm Al. As the X-ray spectrum changes, the thickness of the aluminum filter, which reduces the dose by half, also changes.

  The average pixel value PV of each area corresponding to each of the constant transmittance areas 22A to 22D of the image obtained by photographing the phantom 20 varies depending on the X-ray dose, but also varies depending on the X-ray quality. To do. For this reason, when the average pixel value PV changes, it cannot be distinguished whether it is due to a change in X-ray dose or a change in X-ray quality. In the present invention, X-ray quality is estimated from PV having such characteristics.

  Here, when X [mR] X-rays are irradiated to the constant transmittance region of the phantom 20, assuming that the pixel values of the regions corresponding to the constant transmittance regions 22A to 22D are PV_A to PV_D, respectively, PV_A to PV_D Is defined as the following equations (2) to (5).

PV_A = C1 × Log (X × T_A) + C2 (2)
PV_B = C1 × Log (X × T_B) + C2 (3)
PV_C = C1 × Log (X × T_C) + C2 (4)
PV_D = C1 × Log (X × T_D) + C2 (5)
here,
C1, C2: Coefficient A difference value ΔPV of pixel values between two predetermined areas among the areas corresponding to the constant transmittance areas 22A to 22D is obtained, and a half value is obtained based on the obtained difference value ΔPV. Estimate the value layer HVL. For example, the difference ΔPV between the pixel value PV_A of the constant transmittance region 22A and the pixel value PV_B of the constant transmittance region 22B is obtained as in the following equation (6).

ΔPV = PV_A−PV_B (6)
Substituting the above equations (2) and (3) into this equation (6) yields the following equation (7). The value does not depend on X.

ΔPV = PV1-PV2
= C1 * Log (X * T_A) -C1 * Log (X * T_B)
= C1 × Log {(X × T_A) / (X × T_B)}
= C1 × Log (T_A / T_B) (7)
As shown in equation (7), ΔPV is a value that does not depend on X. These T_A and T_B are the transmittances of the constant transmittance regions 22A and 22B, and generally depend on only the radiation quality not depending on the dose.

  FIG. 5 shows a graph showing an example of the relationship between the half-value layer HVL and ΔPV in the radiation imaging system 5 according to the present embodiment.

  As shown in the figure, the half-value layer HVL is uniquely determined with respect to ΔPV.

  In the radiographic system 5 according to the present embodiment, the relationship between the half-value layer HVL and ΔPV of the phantom 20 in this system is obtained in advance, and the half-value layer information indicating the correspondence between the half-value layer HVL and ΔPV is obtained. The hard disk 404 is stored in advance as a table, and the half-value layer HVL is estimated based on the table of the half-value layer information.

  Next, in the second step, the average pixel value PV3 and the standard deviation σ of the area corresponding to the uniform exposure unit 26 of the image are obtained, and the square of SNR (Signal to Noise ratio) is calculated as a correlation value correlated with the amount of noise. calculate.

  By the way, in the CR system, the pixel value of the image to be calculated is an image system that changes linearly with respect to the logarithm of the incident dose K (hereinafter referred to as a log image system). On the other hand, the SNR is defined by an image system (hereinafter referred to as a linear image system) that is linearly related to the dose. Therefore, in the case of the log image system image, the SNR is calculated after the image is converted into a linear image system image that is linear with respect to the incident dose K.

  First, a procedure for converting the log image system image into a linear image system image will be described.

When the pixel value in the log image system image is PV _log , the relationship with the incident dose K is defined as follows.
PV _log = C1 × Log (K) + C2 (8)
here,
C1 and C2: Coefficients C1 and C2 are obtained by performing uniform exposure photographing in advance without a subject under a plurality of dose conditions to obtain the relationship between the PV _log and the incident dose K, and the relationship between the obtained PV _log and the dose. Is determined by fitting using equation (8).

In the radiation imaging system 5 according to the present embodiment, the conversion information indicating the correspondence between the PV _log and the incident dose K in this system is stored in advance in the hard disk 404 as a table from the equation (8), Using this stored conversion information table, a log image system image to be subjected to SNR calculation is converted into a linear image system image.

In the radiation imaging system 5 according to the present embodiment, the average pixel value PVlin and the standard deviation σlin of the region corresponding to the uniform exposure unit 26 of the converted linear image system image are obtained, and the following equation (9) is used. SNR ² is calculated.

SNR ² = (PVlin / σlin) (9)
The incident dose K of X-rays is uniquely determined according to the sent SNR ² and the half-value layer HVL estimated in the first step.

In an image system in which the pixel value of the image changes linearly with respect to the incident dose K (hereinafter referred to as a linear image system), ΔPV = PV1 / PV2. Further, when obtaining SNR ² , conversion to a linear image system according to equation (8) is not necessary.

FIG. 6 shows a relationship between the incident dose K with respect to the SNR ^{2 in} three X-rays having different quality at the half-value layer HVL.

As shown in the drawing, incident dose K is uniquely determined in accordance with Senshitsu HVL and SNR ^2.

In the radiation imaging system 5 according to the present embodiment, the relationship between the SNR ² and the incident dose K with a plurality of (three in the present embodiment) X-rays with different half-value layers HVL in this system in advance. Thus, incident dose information indicating the correspondence between SNR ² and incident dose K is created in advance as a table and stored in the hard disk 404 for each radiation quality HVL. Then, the incident dose K is estimated from the SNR ² sent based on the stored table of incident dose information and the half-value layer HVL estimated in the first step.

That is, for example, when the SNR ² calculated as shown in FIG. 6 is N, the incident doses K in the X-rays of the three radiation qualities are obtained as K1, K2, and K3.

  Then, as shown in FIG. 7, K1, K2, and K3 are plotted according to the X-ray quality half-value layer HVL, and a straight line that approximates each plotted point is obtained. The incident dose K of the half-value layer HVL estimated in the step is obtained.

  Next, in the third step, g, c, and s AGD calculation coefficients are determined from the estimated HVL.

  Here, the relationship between the AGD calculation coefficients g (g-factor) and c (c-factor) and the half-value layer HVL is obtained by Dance et al. As shown in FIGS. . Details of this are described in D.R. Dance et al., Additional factors for the estimation of mean glandular dose using the UK mammography protocol, Phys. Med. Biol., 2000, Vol. 45, 3225-3240.

  Further, the relationship between the AGD calculation coefficient s (s-factor) and the target filter (T / F) is obtained by Dance et al. As shown in FIG.

  In the radiation imaging system 5 according to the present embodiment, a conversion formula that approximates the relationship between HVL and g, c-factor at each PMMA thickness in the system with a first-order curve or more in advance is created in advance. Are stored in the hard disk 404, and g and c of AGD calculation coefficients are obtained from the half-value layer HVL estimated in the first step based on the conversion information.

  In the radiation imaging system 5 according to the present embodiment, filter information indicating the relationship between the target filter and the s-factor is created in advance and stored in the hard disk 404. For example, the user uses the system in this system. By inputting information of the target filter to be input, s of the AGD calculation coefficient is obtained from the input information based on the filter information.

  Next, a method for verifying the performance of the radiation imaging system 5 according to the present embodiment will be described. When performing performance verification, it is preferable to perform shading correction for correcting X-ray non-uniformity caused by the radiation apparatus in advance. Since this shading correction method is described in, for example, Japanese Patent Application No. 2006-318391, description thereof is omitted here.

  In the radiation imaging system 5 according to the present embodiment, when performing performance verification, the phantom 20 is arranged in the radiation imaging apparatus 100 and radiation imaging is performed under predetermined imaging conditions. Thereby, the radiation image information of the phantom 20 is recorded on the recording sheet 10. The recording sheet 10 on which the radiation image information of the phantom 20 is recorded is set at a predetermined position of the medical image reading apparatus 200, and the radiation image information recorded on the recording sheet 10 is read. Image data indicating the phantom 20 obtained by reading by the medical image processing apparatus 300 is input to the medical image processing apparatus 300 via the network N1 and stored in the hard disk 404.

  In the medical image processing apparatus 300, when a predetermined operation for instructing the input unit 310 to start performance verification is performed by the user, the CPU 400 executes an inspection processing program.

  FIG. 11 shows the flow of processing of the inspection processing program according to the present embodiment. This inspection processing program is stored in advance in a predetermined area of the hard disk 404.

  In step S <b> 10, the average pixel values of the areas corresponding to the constant transmittance areas 22 </ b> A to 22 </ b> D of the image indicated by the image data indicating the phantom 20 stored in the hard disk 404 are calculated.

  In the next step S12, as described in the first step, the difference value ΔPV of the average pixel value PV between two predetermined areas (in the present embodiment, constant transmittance areas 22A and 22B). And the half-value layer HVL is estimated from the difference value ΔPV based on the half-value layer information table stored in the hard disk 404.

In the next step S 14, as described in the second step above, the average pixel value PV 3 and the standard deviation σ of the uniform exposure unit 26 of the image are obtained, SNR ² is calculated, and the incident stored in the hard disk 404 is calculated. The incident dose K is estimated from the SNR ² based on the dose information table.

  In the next step S16, as described in the third step, the AGD calculation coefficients of g, c, and s are determined from the half-value layer HVL and the incident dose K estimated in the steps S12 and S14.

  In step S18, the average mammary dose AGD is calculated from the values obtained in steps S12, S14, and S16 using (1) above.

  In the next step S20, it is determined whether or not the average mammary gland dose AGD calculated in step S18 is larger than a predetermined allowable amount. If the determination is affirmative, the process proceeds to step S22 while the determination is negative. In this case, the process proceeds to step S24. In addition, the standard of the average mammary gland dose AGD in the Japanese Society for Medical Radiology is 3 mGy. For this reason, what is necessary is just to make the said allowance 3mGy in order to satisfy | fill the standard of the Japan Radiological Society. Further, in order to further reduce the patient's exposure amount, the allowable amount may be a value smaller than 3 mGy.

  In step S22, since the average mammary gland dose AGD exceeds an allowable level, a warning message indicating that there is a problem in performance is displayed on the display unit 320, and the present inspection processing program is terminated.

  On the other hand, in step S24, since the average mammary gland dose AGD is within an allowable level, a message indicating that the average mammary dose AGD is normal is displayed on the display unit 320, and the present inspection processing program is terminated.

  When the display unit 320 displays a warning message on the display unit 320, the user can maintain the performance of the radiation imaging system 5 in a good state by requesting maintenance of the radiation imaging system 5.

  As described above, according to the present embodiment, in the radiation imaging apparatus 100, X is applied to the phantom 20 provided with the plurality of constant transmittance regions 22A to 22D having predetermined transmittances different from each other with respect to X-rays. The medical image reading apparatus 200 acquires image data indicating the phantom, and the medical image processing apparatus 300 derives and displays an average mammary gland dose based on the acquired image data. Therefore, the average mammary gland dose can be easily measured.

  In the present embodiment, the case where image data is acquired by photoelectrically reading radiation image information recorded on the recording sheet 10 has been described. However, the present invention is not limited to the above-described embodiment. In addition, various changes in design can be made without departing from the spirit of the invention described in the claims of the present invention. For example, the image data may be acquired using a flat panel device that converts the transmitted radiation level into an electrical signal.

In the present embodiment, the case where the incident dose K of X-rays is estimated using SNR ² and the half-value layer HVL estimated in the first step has been described. For example, the uniform exposure unit 26 is an image of a log image system. The average pixel value PV _log of the region corresponding to ## EQU3 ## is obtained, and the incident dose K may be obtained using the equation (8) or conversion information indicating the correspondence between the PV _log and the incident dose K.

However, there is an advantage of obtaining the incident dose K from the SNR ² as in the present embodiment.

That is, it is known that the sensitivity of the photomultiplier 203 used in the medical image reading apparatus 200 varies with temperature and changes with time. For this reason, when the sensitivity change rate is α, the true value is K, and when there is a sensitivity change, K is K ′ when calculated using the equation (8) or conversion information,
K ′ = α × K (10)
Therefore, accurate K cannot be obtained.

On the other hand, the SNR is not affected by this sensitivity variation α. When PVlin and σlin when there is a sensitivity fluctuation are PV′lin and σ′lin, they are expressed as follows.
PV'lin = α × PVlin (11)
σ'lin = α × σlin (12)
Therefore, SNR ′, which is the SNR when the sensitivity fluctuates, is SNR ′ = αPVlin / ασlin = PVlin / σlin = SNR (13)
And the influence of α is cancelled.

  On the other hand, in the case of a method of acquiring image data using a flat panel device, it is affected by sensitivity change, but SNR is not affected. Therefore, K can be accurately obtained even using equation (8) or conversion information. Can do.

  In the present embodiment, the case where the average pixel value PV3 and the standard deviation σ of the area corresponding to the uniform exposure unit 26 are obtained and the square of the SNR is calculated has been described, but the present invention is not limited to this. Instead, for example, the average pixel value PV3 and the standard deviation σ of any constant transmittance region 22 may be obtained to calculate the square of the SNR.

  In the present embodiment, the case where the warning message is displayed on the display unit 320 when the average mammary gland dose AGD exceeds an allowable level has been described. However, the present invention is not limited to this, for example, The average breast dose AGD and warning information may be printed by the printer 330, or warning may be issued by voice or the like, and maintenance is performed via the network N1 via the RIS 500, the network N1, and the Internet 520. The warning information may be transmitted to the center 530.

  In the present embodiment, the case where the average mammary gland dose AGD is derived by the phantom 20 provided with the step-like transmission region portion 24 and the uniform exposure portion 26 has been described. However, the present invention is not limited to this. Instead, for example, evaluation regarding image quality may be performed. That is, for example, an image quality evaluation region as described in Patent Document 1 may be provided in the phantom 20 to evaluate the image quality while deriving the average mammary gland dose AGD.

  In the present embodiment, the case where the present invention is applied to the radiation imaging system 5 has been described. However, the present invention is not limited to this, and for example, a radiographic image is formed on the recording sheet 10 by performing radiation imaging. You may apply to the radiography apparatus with which the imaging | photography part which records information, and the reading part which reads the radiographic image information recorded on the recording sheet 10 were united.

  In addition, the configuration of the radiation imaging system 5 (see FIG. 1) described in each of the above embodiments is merely an example, and it is needless to say that the configuration can be appropriately changed without departing from the gist of the present invention.

It is a block diagram which shows the whole structure of the radiography system which concerns on embodiment. It is a block diagram which shows the detailed structure of the medical image processing apparatus which concerns on embodiment. It is a block diagram which shows the structure of the phantom which concerns on embodiment. It is sectional drawing which showed roughly the cross section of the constant transmittance | permeability area | region of the phantom which concerns on embodiment. It is a graph which shows an example of the relationship between the half value layer HVL and (DELTA) PV which concerns on embodiment. It is a graph showing an example of the relationship between SNR ² and incident dose K in the X-ray three radiation quality that HVL HVL differ according to the embodiment. FIG. 7 is a graph showing an example of a result obtained by plotting K1, K2, and K3 shown in FIG. 6 according to the embodiment according to a half-value layer HVL and approximating each point to obtain a straight line passing therethrough. It is a figure which shows the relationship between g (g-factor) which concerns on embodiment, and a half value layer HVL. It is a figure which shows the relationship between c (c-factor) which concerns on embodiment, and the half value layer HVL. It is a figure which shows the relationship of the relationship between the target filter which concerns on embodiment, and s (s-factor). It is a flowchart which shows the flow of a process of the test | inspection processing program which concerns on embodiment.

Explanation of symbols

5 Radiography system 10 Recording sheet (recording medium)
20 Phantom 22 Each constant transmittance region 26 Uniform exposure unit 100 Radiography unit 103 Radiation generation unit 200 Medical image reading device (acquisition means)
203 Photomultiplier 300 Medical image processing apparatus 320 Display unit (display unit)
400 CPU (derivation means)
404 Hard disk (first storage means, second storage means)

Claims (10)

Acquisition means for irradiating X-rays to a phantom provided with a plurality of constant transmittance regions each having a predetermined transmittance different from each other for X-rays to acquire image data indicating the phantom;
Based on the image data acquired by the acquisition means, the half-value layer of the irradiated X-ray is estimated, and predetermined among the regions corresponding to the plurality of constant transmittance regions of the image indicated by the image data. A derivation unit that obtains a correlation value that correlates with the amount of noise included in the pixel value of the determined region, estimates an incident dose based on the correlation value, and derives an average mammary dose from the estimated half-value layer and the incident dose; ,
Display means for displaying an average mammary gland dose derived by the derivation means;
Radiation imaging apparatus for breasts equipped with. A recording medium on which an image showing a phantom is recorded by irradiating an X-ray to a phantom provided with a plurality of constant transmittance regions each having a predetermined transmittance different from that of the X-ray. Obtaining means for obtaining image data indicating the phantom by reading;
Based on the image data acquired by the acquisition means, the half-value layer of the irradiated X-ray is estimated, and predetermined among the regions corresponding to the plurality of constant transmittance regions of the image indicated by the image data. A derivation unit that obtains a correlation value that correlates with the amount of noise included in the pixel value of the determined region, estimates an incident dose based on the correlation value, and derives an average mammary dose from the estimated half-value layer and the incident dose; ,
Display means for displaying an average mammary gland dose derived by the derivation means;
Radiation imaging apparatus for breasts equipped with. The derivation means is predetermined from an average pixel value between two or more predetermined areas among areas corresponding to the plurality of constant transmittance areas of the image indicated by the image data acquired by the acquisition means. The breast radiographic apparatus according to claim 1, wherein the half-value layer is estimated based on the index value. A first storage means that stores in advance half-value layer information indicating a correspondence relationship between an index value obtained from an average pixel value between the two or more predetermined regions and the half-value layer;
The radiation imaging apparatus for breasts according to claim 3, wherein the deriving unit estimates the half-value layer from the obtained index value based on the half-value layer information stored in the first storage unit. For each half-value layer, further comprising a second storage means for storing incident dose information indicating the correlation between the correlation value of the predetermined region and the incident dose in advance,
The derivation means estimates the incident dose from the obtained correlation value based on the incident dose information stored in the second storage means. 5. The breast use according to any one of claims 1 to 4. Radiography equipment. The radiographic apparatus for breast according to any one of claims 1 to 5, wherein the display means displays a warning when the average mammary gland dose derived by the deriving means is larger than a predetermined allowable amount. The radiation imaging apparatus for breasts according to any one of claims 1 to 6, wherein the phantom is used for evaluating an image quality of a captured image. A recording medium on which an image showing a phantom is recorded by irradiating an X-ray to a phantom provided with a plurality of constant transmittance regions each having a predetermined transmittance different from that of the X-ray. A reading device for acquiring image data indicating the phantom by reading;
Based on the image data acquired by the reading device, the half-value layer of the irradiated X-ray is estimated, and a predetermined one of regions corresponding to the plurality of constant transmittance regions of the image indicated by the image data is determined. A derivation process for obtaining a correlation value correlating with the amount of noise included in the pixel value of the obtained region, estimating an incident dose based on the correlation value, and deriving an average mammary dose from the estimated half-value layer and the incident dose An information processing device to perform;
A display device for displaying an average mammary gland dose derived by the information processing device;
Breast radiography system with Based on image data indicating the phantom acquired by irradiating and photographing X-rays to a phantom provided with a plurality of constant transmittance regions each having a different predetermined transmittance for X-rays, In addition to estimating the half-value layer of the irradiated X-ray, the amount of noise included in the pixel value of a predetermined region among the regions corresponding to the plurality of constant transmittance regions of the image indicated by the image data A derivation means for performing a derivation process for obtaining a correlated correlation value, estimating an incident dose based on the correlation value, and deriving an average mammary dose from the estimated half-value layer and the incident dose;
An information processing apparatus comprising: Image data representing the phantom is obtained by performing imaging by irradiating the phantom provided with a constant transmittance region having a predetermined transmittance with respect to the X-ray with X-rays,
Obtaining a correlation value that correlates with a noise amount included in a pixel value of a region corresponding to the constant transmittance region of the image indicated by the acquired image data, and deriving the incident dose based on the correlation value;
Method for deriving incident dose.