JP2009268801A - Radiographic apparatus and dosage index value display - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a radiographic apparatus can fixedly evaluate an X-ray dosage regardless of existence of preliminary knowledge of an examiner, and to provide a dosage index value display. <P>SOLUTION: A dosage index value is calculated on the basis of the pixel value of an image obtained by the radiographic apparatus and the detector sensitivity value of the radiographic apparatus (S5). The dosage index value is displayed by calculating a deviation index value being a relative value when a standard dosage index value indicating the standard dosage in the same order is defined as reference (S7). <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an X-ray imaging apparatus and a dose index value display apparatus, and more particularly to a technique for evaluating an X-ray dose used in X-ray imaging.

Patent Document 1 discloses a technique regarding an apparatus capable of providing a value serving as an index of a dose used for imaging in an X-ray imaging image.
JP 2001-149359 A

  However, the above technique requires prior knowledge in order to determine whether or not imaging has been performed with an appropriate dose based on the provided dose index. For this reason, there is a problem that no one can perform an equivalent evaluation depending on the presence or absence of this prior knowledge.

  The present invention has been made in view of such circumstances, and an object of the present invention is to provide an X-ray imaging apparatus and a dose index value display apparatus capable of evaluating image quality regardless of the prior knowledge of the examiner. .

  In order to achieve the above object, the X-ray imaging apparatus and the dose index value display apparatus according to the present invention use the standard determined in accordance with the order used for the X-ray dose used at the time of the imaging. A deviation index value expressed as a relative value with reference to a typical dose index value is calculated and displayed.

More specifically, an X-ray imaging apparatus according to the present invention includes an X-ray source that generates X-rays, an X-ray detector that is disposed opposite to the X-ray source, detects the X-rays, and outputs image data; , A dose index value for calculating a dose index value that is an index of the X-ray dose when the image data is captured based on a representative pixel value representative of the pixel value of the image data and a sensitivity value of the X-ray detector Deviation index expressed as a relative value when the calculation means and the dose index value are based on a standard dose index value indicating an index of X-ray dose that is used as a standard in the order applied to the imaging of the image data A deviation index value calculating means for calculating a value; and a display means for displaying the deviation index value. The “order” as used herein refers to part information and imaging of a subject to be subjected to X-ray imaging. Information that defines various setting values required for Cormorant.

  In addition, the dose index display device according to the present invention includes: image data obtained by an X-ray imaging apparatus; an order applied to the imaging; and a sensitivity value of the X-ray detector used for the imaging. Based on the acquisition means for acquiring, the representative pixel value representing the pixel value of the image data, and the sensitivity value of the X-ray detector, a dose index value serving as an index of the X-ray dose used for imaging the image data A dose index value calculating means for calculating a deviation index value expressed as a relative value when the dose index value is based on a standard dose index value indicating an X-ray dose index that is normally used in the order; A deviation index value calculating means for calculating and a display means for displaying the deviation index value are provided.

  According to the present invention, it is possible to provide an X-ray imaging apparatus and a dose index value display apparatus capable of evaluating a constant X-ray dose regardless of the prior knowledge of the examiner.

  Hereinafter, preferred embodiments of an X-ray imaging apparatus and a dose index value display apparatus according to the present invention will be described in detail with reference to the accompanying drawings.

  FIG. 1 is a hardware configuration diagram of an X-ray imaging apparatus according to the present invention.

The X-ray imaging apparatus 1 of the present invention includes an X-ray tube 11, a support 12 that supports the X-ray tube 11, a tube voltage, a tube current, and an exposure time set in the X-ray tube 11. An X-ray generator 13 that pressurizes a high voltage, a diaphragm device 14 that limits the irradiation field of X-rays exposed from the X-ray tube 11, and an X-ray tube 11 and a subject 30 that are opposed to each other. An X-ray flat panel detector that detects 30 transmitted X-rays and outputs image data, and is an FPD (Flat Panel Detector) 15 formed by arranging X-ray detection elements made of semiconductors in a two-dimensional direction. And an ion chamber 16 that is provided on the X-ray incident surface of the FPD 15 and detects an X-ray dose incident on the FPD, and an X-ray image transmitted from the FPD 15 is subjected to gradation conversion for display and converted into a display image. The processing device 17 and an operation panel for operating the image processing device 17 A display 18, an image display device 19 for displaying a gradation-converted image, and an exposure hand switch 20.

  Next, a control example of the X-ray imaging apparatus 1 will be described. First, when an examiner designates an order including site information on the operation panel 18, a dose condition that matches the order is transmitted from the operation panel 18 to the X-ray generator 13. The X-ray generator 13 sets the received tube voltage, tube current, and exposure time, and the irradiation field is adjusted by the diaphragm 14. Subsequently, when the examiner presses the exposure hand switch 20, X-rays are emitted from the X-ray tube 11. X-rays transmitted through the subject 30 are collected by the FPD 15, the X-ray dose incident on the ion chamber 16 is measured, and the exposure is stopped based on the measured value. The collected X-ray image information is subjected to gradation conversion for display by the image processing device 17. The converted X-ray image is transmitted to the image display device 19, and an image is displayed.

  The image processing device 17 includes a storage unit 21 for storing data or is externally attached. The storage unit 21 includes a parameter table 60 used in step S4 described later, and a standard used in steps S6 and S8. A dose index value table 61 and a dose index value table 62 used in step S8 are stored.

  8A shows a parameter table 60, FIG. 8B shows a standard dose index value table, and FIG. 8C shows a dose index value table 62.

  The parameter table 60 is a table that stores parameters used in calculating representative pixel values from image data in association with orders.

  The standard dose index value table 61 includes an order, a standard dose index value, and a standard dose index cumulative sample number (hereinafter referred to as “cumulative sample number”) indicating the number of times of imaging that is a basis for calculating the standard dose index value. , Are stored in association with each other.

  The dose index value table 62 is a table that stores an imaging sequence number (which may be a time stamp) indicating the number of times the X-ray imaging apparatus has taken an image, an order, and a dose index value obtained for each imaging in association with each other. .

  Next, a dose index value display program installed in the image processing apparatus 17 will be described with reference to FIG. FIG. 2 is a block diagram showing a dose index value display program.

  The dose index value display program represents an image reading unit 17a for reading an X-ray image, an ROI setting unit 17b for setting a region of interest (hereinafter referred to as “ROI”) in the read X-ray image, and a pixel value of the ROI. A representative pixel value calculation unit 17c that calculates a representative pixel value to be performed, a dose index value calculation unit 17d that calculates a dose index value of the read X-ray image, and the dose index value indicates a standard X-ray dose in the order A deviation index value calculation unit 17e that calculates a deviation index value expressed as a relative value when the standard dose index value is used as a reference, and a standard dose index value is calculated based on a pixel value of an X-ray image captured in the past. And a standard dose index value calculation unit 17f for updating the standard dose index value using the dose index value of the X-ray image obtained by the current imaging.

  These programs are loaded into a main memory (not shown) provided in the image processing apparatus, and perform their functions by being executed by a CPU (not shown).

  Next, the operation of the embodiment will be described with reference to FIG.

(Step S1)
The image reading unit 17a acquires an X-ray image composed of 14-bit data from the FPD 15 (S1). Further, the image reading unit 17a acquires order information indicating an order applied when an X-ray image is captured, and sensitivity value information of the FPD 15.

(Step S2)
The ROI setting unit 17b sets the ROI for the X-ray image acquired in step S1 (S2). The ROI is set by a method using the region of the ion chamber 16 or a method of extracting an edge by edge processing and setting the inside of the edge as an ROI. There is also a method of extracting a region where the subject is imaged (hereinafter referred to as “subject region”) using the aperture position and direct X-ray region recognition, and setting the subject region as an ROI.

  When the ion chamber 16 is used at the time of taking an X-ray image, a region where the ion chamber 16 installed on the incident surface of the FPD 15 is located in the X-ray image may be set to ROI.

  FIG. 4 is a diagram in which the ROI is set based on the region of the ion chamber 16. FIG. 4A is an example in which the ROI 50 is set on the image 40 obtained by photographing the cervical side surface, and FIG. The example which set ROI51 on the image 41 which image | photographed the waist | hip | lumbar part side surface is shown. Since the ion chamber 16 is used for dose measurement at the time of imaging, the dose index value reflecting the incident dose can be expected more accurately by using the pixel value of that region.

  Alternatively, the ROI setting unit 17b may extract the subject region using edge extraction processing, that is, processing for extracting an edge by differentiating the profile of the pixel value, and set this region as the ROI.

  FIG. 5 is a diagram showing an example in which the subject region is extracted by the edge extraction process and the ROI is set. Edges displayed with black lines are extracted from the image 43 obtained by photographing the cervical side surface, and the inside of the edge is set as ROI 53. Set.

  Further, the ROI setting unit 17b may extract a subject area by removing pixel values corresponding to a diaphragm and a direct line calculated from position information of the irradiation field and imaging conditions. In FIG. 4A and FIG. 4B, a black region along the edge (a region hatched using an oblique line from the upper right to the lower left) is an incident surface region corresponding to the stop position, that is, a stop device. Indicates an area where X-rays are shielded. 4 (a) and 4 (b), the area displayed in white (the area hatched by using the diagonal lines from the upper left to the lower right) is the area corresponding to the direct line, that is, the X-rays indicate the subject. A region directly incident on the FPD 15 without passing through is shown. Only the subject region can be extracted from the image 40 and the image 41 by removing the incident surface region corresponding to the stop position and the region corresponding to the direct line.

  When setting the ROI by extracting the subject region, the ROI is set regardless of whether the ion chamber is mounted on the X-ray flat panel detector and whether the ion chamber is used for imaging. be able to.

(Step S3)
The representative pixel value calculation unit 17c generates a histogram indicating the distribution of pixel values of the pixels constituting the extracted ROI set in step S2 (S3). FIG. 6 shows a histogram generated in this step.

(Step S4)
The representative pixel value calculation unit 17c calculates the representative pixel value of the ROI by analyzing the histogram generated in step S3 (S4).

  The representative pixel value may be obtained from the median value, average value, mode value, and centroid value of the ROI.

  Further, the representative pixel value calculation unit 17c calculates a histogram cumulative value from the histogram of FIG. 6, and generates a histogram cumulative value graph shown in FIG. Then, the cumulative rate r determined for each order may be extracted from the parameter table 60 of FIG. 8A, and the pixel value corresponding to the cumulative rate r in the histogram cumulative value graph of FIG. 7 may be used as the representative pixel value. FIG. 7 is an example of a histogram cumulative value display of an image of the front of the head. When the cumulative value determined for each order is “front of head”, it is temporarily displayed as r.

(Step S5)
The dose index value calculation unit 17d calculates a value obtained by dividing the representative pixel value calculated in step S4 (for example, the median value of the histogram) by the sensitivity value unique to the FPD 15 as a dose index value (S5). For example, if the median value is 1100 as the representative pixel value and the FPD sensitivity value is 160, the dose index value is 6.875. This dose index value may be displayed.

(Step S6)
The deviation index value calculation unit 17e stores a standard dose index value indicating a standard dose used based on the order information acquired before imaging, and a standard dose index value stored in a storage unit included in the image processing apparatus 17. Extracted from the table 61 (S6).

(Step S7)
The deviation index value calculation unit 17e uses the dose index value obtained in step S5 and the standard dose index value extracted in step S6 to indicate the relative value when the dose index value is based on the standard dose index value. The calculated deviation index value is calculated and displayed (S7).

The deviation index value calculation part 17e calculates | requires a deviation index value by Formula (1) or Formula (2), and displays this.
[Equation 1]
Deviation index value = 10 x Log10 (dose index value / standard dose index value) (1)
[Equation 2]
Deviation index value = (dose index value / standard dose index value)] × 100 (2)
For example, in the case of the dose index value 500 and the standard dose index value 1000, according to the formula (1), 10 × Log10 (500/1000) = − 3, and the deviation index value is −3. In the same example, according to the equation (2), (500/1000) × 100 = 50 (%), and the deviation index value is 50%.

(Step S8)
The standard dose index value calculation unit 17f updates the standard dose index value for each exposure using the dose index value calculated in S5, the standard dose index value in the standard dose index value table 61, and the cumulative number of samples. (S8).

  Since the standard dose index value is calculated from the dose index value based on the image data output from the X-ray imaging apparatus 1, it becomes a standard value for each X-ray imaging apparatus 1.

  Two examples of the method for updating the standard dose index value are shown below.

(First method of updating standard dose index values)
The first method is a method of calculating / updating using the standard dose index value in the standard dose index value table 61 and the cumulative sample number (x). The standard dose index value calculation unit 17f multiplies the standard dose index value by the cumulative number of samples (x) of the X-ray image to obtain the sum of the standard dose index value for the number of samples, and this is obtained in S5. The dose index value by imaging is added, and this added value is divided by the value obtained by adding 1 to the cumulative number of samples. Formula (3) shows the said process.

Thereby, a new standard dose index value reflecting the dose index value obtained by the current imaging can be calculated.
The standard dose index value calculation unit 17f calculates a new standard dose index value according to the equation (3), and overwrites the corresponding record in the standard dose index value table 61.

(Second method to update the standard dose index value)
In the second method, a standard index value is calculated using a dose index value obtained each time based on the dose index value obtained every time imaging is performed and the number of times information indicating the number of times of imaging in the X-ray imaging apparatus 1. How to update.

The standard dose index value calculation unit 17f goes back from the latest imaging a predetermined number of times (for example, 1500 times), calculates the average of the dose index values, and calculates the standard dose index value. Equation (4) shows the second method.
A1 in equation (4) corresponds to the dose index value obtained in step S5.

  The standard dose index value calculation unit 17f replaces the dose index value obtained by the current imaging with the dose index value obtained at the oldest out of the predetermined number of times, and recalculates to obtain the current dose by the current imaging. A new standard dose index value reflecting the obtained dose index value can be calculated. The calculated new standard dose index value is overwritten in the standard dose index value table 61 by the standard dose index value calculation unit 17f, and the standard dose index value is updated.

  Since the standard dose index value of the present embodiment is calculated based on the X-ray image captured by the X-ray imaging apparatus 1, a standard value for each apparatus can be determined. Therefore, dose evaluation can be performed using different standard values for each hospital (more specifically, for each device).

  Furthermore, since the standard dose index value is updated according to each exposure, it is possible to evaluate based on the standard value reflecting the most recent data. For example, even when the image processing in the hospital is changed Then, it can be gradually corrected to the standard value according to the image processing.

  In this embodiment, the standard dose index value for each apparatus is calculated / updated. However, when there are a plurality of imaging apparatuses in a hospital, the standard dose index value is obtained by the same order in one imaging apparatus based on the apparatus identification information. The standard dose index value for each imaging apparatus can be calculated by extracting only the dose index values obtained.

  The standard dose index value is calculated from past image data. However, a set value may be stored in the standard dose index value table 61 based on a dose generally used in the order. The set value may be used for calculation of the deviation index value every time, or the standard dose index value can be customized by using the set value as an initial value and updating it for each exposure.

  FIG. 9 is a schematic diagram illustrating a screen display example of the present embodiment. The screen 70 in FIG. 9 may be used to determine whether or not re-imaging is necessary by using an X-ray image captured by the examiner as a preview screen. If re-photographing is not required, trimming processing is subsequently performed. The screen 70 may be used by the examiner for dose evaluation at the time of diagnosis.

  On the screen 70, an X-ray image 71, a dose index value 72 calculated based on the X-ray image 71, and a standard dose corresponding to the order of the X-ray image 71 (corresponding to “neck side surface” in FIG. 9). A radio button 74 for switching display / non-display of the index value 73, the dose index value 72, and the standard dose index value 73, a deviation index value% display 75, a deviation index value scale 76, and a deviation index value of the X-ray image 71 are shown. An arrow 77 is displayed. The display of the deviation index value is not limited to the above.

  According to the present embodiment, the dose index value of the X-ray image to be viewed can be displayed as the deviation index value when the standard dose index value for each apparatus is used as a reference. A certain evaluation can be provided regardless of the prior knowledge of the examiner.

  In this embodiment, the ROI is set, and the dose index value is obtained from the pixel value of the ROI. However, the representative that is the basis for calculating the dose index value from the pixel value of the entire X-ray image without setting the ROI. The pixel value may be obtained.

  In this embodiment, the standard dose index value is updated using the X-ray image read in step S1, but the contribution ratio of the dose index value of the X-ray image taken more recently to the standard dose index value is higher. You may weight so that it may become larger. Further, a threshold value may be set for the deviation index value, and dose index values exceeding and below the threshold value may not be updated. As a result, it is possible to prevent an X-ray image obtained by remarkably wrongly taking a dose from affecting the standard dose index value.

  In the present embodiment, the dose index value display program shown in FIG. 2 is installed in the image processing apparatus 17 connected to the FPD 15, but these programs are not connected to the X-ray imaging apparatus 1, for example, an inspection apparatus. It can also be installed on a personal computer installed on a person's desk and function as viewer software for images acquired via a network such as a hospital LAN (not shown).

1 is a hardware configuration diagram of an X-ray imaging apparatus according to the present invention. The block diagram of the dose index value display program which concerns on this invention. The flowchart which shows the process example of this invention. FIG. 4A is a schematic diagram illustrating an example in which the ROI is set using the ion chamber region, and FIG. 4A is a schematic diagram illustrating an example in which the ROI is set on an image obtained by photographing the cervical side surface. ) Is a schematic diagram showing an example in which an ROI is set on an image obtained by photographing the waist side surface. It is a schematic diagram which shows the example which set ROI using the subject extraction process, Comprising: The example which set ROI on the image which image | photographed the neck side surface is shown. The schematic diagram which shows the histogram in ROI. The schematic diagram which shows a histogram accumulation rate. FIG. 8A is a schematic diagram showing a table stored in the image processing apparatus 17, FIG. 8A is a parameter table that defines parameters for calculating representative pixel values, and FIG. 8B is a standard dose index value table 61. FIG. 8C is a schematic diagram showing a dose index value table storing dose index values. The schematic diagram which shows the example of a screen display concerning this embodiment.

Explanation of symbols

1: X-ray imaging device, 11: X-ray tube, 12: supporter, 13: X-ray generator, 14: aperture device, 15: FPD, 16: ion chamber, 17: image processing device, 18: operation panel, 19: Image display device, 20: Exposure hand switch

Claims (9)

An X-ray source for generating X-rays;
An X-ray detector disposed opposite to the X-ray source and detecting the X-ray and outputting image data;
Dose index value calculation that calculates a dose index value that is an index of X-ray dose when the image data is captured based on a representative pixel value that represents a pixel value of the image data and a sensitivity value of the X-ray detector Means,
A deviation index value expressed as a relative value when the dose index value is based on a standard dose index value indicating an X-ray dose index that is normally used in an order applied to imaging of the image data is calculated. Deviation index value calculating means;
Display means for displaying the deviation index value;
An X-ray imaging apparatus comprising: A standard dose index value calculating means for calculating the standard dose index value based on a dose index value calculated based on image data output in the past by the X-ray imaging apparatus;
The X-ray imaging apparatus according to claim 1. The standard dose index value calculation means adds the dose index value calculated based on the image data, and again updates the standard dose index value by calculating the standard dose index value.
The X-ray imaging apparatus according to claim 2. The standard dose index value calculating means updates the standard dose index value according to either of the following formula (1) or formula (2):
The X-ray imaging apparatus according to claim 3. The deviation index value calculating means calculates the deviation index value according to any of the following formula (3) or formula (4):
[Equation 3]
Deviation index value = 10 x Log10 (dose index value / standard dose index value) (3)
[Equation 4]
Deviation index value = (dose index value / standard dose index value) × 100 (4)
The X-ray imaging apparatus according to any one of claims 1 to 4, wherein The image data further includes a region of interest setting means for setting a desired region as a region of interest,
The dose index value calculating means calculates the representative pixel value based on a pixel value of the region of interest;
An X-ray imaging apparatus according to any one of claims 1 to 5, wherein: The dose index value calculating means creates a histogram showing a distribution of pixel values in the region of interest, and calculates the representative pixel value based on a cumulative rate of the histogram.
The X-ray imaging apparatus according to claim 6. Parameter storage means for storing a parameter used for calculating the representative pixel value in association with the order;
The dose index value calculation means extracts a parameter corresponding to the order applied to the imaging of the image data from the parameter storage means, and calculates the representative pixel value using the parameter.
The X-ray imaging apparatus according to claim 1, wherein Acquisition means for acquiring image data acquired by the X-ray imaging apparatus, an order applied to the imaging, and a sensitivity value of the X-ray detector used for the imaging;
A dose index value for calculating a dose index value as an index of the X-ray dose used for imaging of the image data based on a representative pixel value representing a pixel value of the image data and a sensitivity value of the X-ray detector A calculation means;
A deviation index value calculating means for calculating a deviation index value expressed as a relative value when the dose index value is based on a standard dose index value indicating an X-ray dose index that is normally used in the order;
Display means for displaying the deviation index value;
A dose index value display device comprising: