JP2006334046A - Radiographic equipment and radiographing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To find the amount of bone mineral based on the mean pixel value of a bone profile of a part to be measured and the relation between the thickness of an aluminum plate and the amount of the pixel value corresponding to radiographic conditions. <P>SOLUTION: This radiographic equipment inputs the digital image of the whole face of an input effective area of an X-ray detector in S01. This radiographic equipment executes corrections on the input digital image of the effective area whole face such as a correction of dispersion between photoelectric transducers, a correction of the time course of the photoelectric transducers, and a correction of shading in S02 and calculates the mean pixel value of the bone profile of the measurement area prescribed by and operator in S103. This equipment calculates an aluminum thickness equivalent corresponding to the calculated means pixel value from database and finds the amount of bone mineral in S04; and provides the aluminum thickness equivalent calculated in S04 and the relation between the thickness of an aluminum step and the pixel value corresponding to the thickness of the radiographing conditions, associated with the image in S05. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an X-ray imaging apparatus and an imaging method for acquiring an X-ray image of a subject and calculating a bone mineral content of a measurement site from the X-ray image.

  Since the number of fractures of the femur due to osteoporosis has increased over the past few years, the number of municipalities conducting osteoporosis screening for the purpose of early detection and prevention of osteoporosis has increased. To screen those who are at high risk of fractures.

  As a bone measurement method at this time, as shown in Patent Document 1 and Non-Patent Documents 1 to 3, based on an X-ray photograph obtained by irradiating a bone to be examined with an X-ray, MD method for measuring bone density by measuring density with a microdensitometer, photon and absorptiometry for measuring bone quantity by irradiating a test bone with gamma rays and measuring the amount of transmitted gamma rays with a detector Are known.

  The MD method can be performed relatively easily using a widely used X-ray imaging apparatus as an apparatus for fracture diagnosis or organ or organ diagnosis. Moreover, it is easy to employ | adopt by the point which uses a X-ray photographic film, and has spread gradually. As for photon and absorptiometry, it is difficult to say that an apparatus for generating gamma rays to be used is generally widely used as compared with an X-ray imaging apparatus.

  The bone measurement by the conventional MD method is performed as follows. First, an X-ray photographic film F as shown in FIG. 8 is obtained by irradiating an aluminum step made of aluminum, which is a stepped standard material, together with a bone to be examined. In order to perform bone measurement using the film F, first, in the bone image on the film F, an intermediate point of the second metacarpal bone indicated by line AB is selected.

  Since the purpose of screening is to prevent fracture of the femur, it is desirable that the site to be measured is the femur, but there is a problem that imaging is difficult. Therefore, the ratio of cancellous bone and cortical bone is close to that of the femur, and measurement is often performed at the midpoint of the second metacarpal of the hand, which is easy to photograph.

  In the microdensitometer, in the X-ray photographic film F, the intensity of transmitted light obtained by irradiating light along the AB line crossing the second metacarpal is measured, and the transmission corresponding to the scanned region is measured. A diagram of light intensity or absorbance is described on a predetermined chart paper. Further, a chart of the intensity or absorbance of the transmitted light obtained by scanning a microdensitometer on the vertical line of the image in the film F of the aluminum step AS photographed on the left side of the X-ray photographic film F is also charted. Write on paper.

  A diagram of the absorbance for the test bone and the absorbance for the aluminum step AS obtained in this way is input to a computer using a digitizer, and the absorbance of the test bone at each point is determined by the thickness of the aluminum step. Convert.

  FIG. 9 shows a chart created in this manner. The thickness equivalent (mmAl) of the aluminum plate, which is an index of the amount of bone mineral (m-BMD), is the average thickness of the aluminum plate from A to B. It is obtained by calculating the value.

  As described above, the conventional bone mineral content measurement by the MD method is performed by scanning the measurement range and the aluminum chart with a microdensitometer for the bone to be examined on the X-ray photographic film F, and importing it into a computer. Calculated.

JP-A-5-95940 Radiation utilization technology database: Data No. 030092 Mass screening in osteoporosis screening “Bone Metabolism” Vol. 13, pp. 187-195 (1980) "Bone metabolism" Vol. 14, pp. 91-104 (1981)

  In the conventional bone mineral content measurement by the MD method, since an aluminum step must be simultaneously photographed together with a bone to be examined at the time of photographing, in consideration of work efficiency, one photographing step is always required for the photographing apparatus. With the introduction of the device, it is necessary to purchase a new aluminum step, troublesome installation of the aluminum step in the vicinity of the bone to be examined during imaging, or the target bone is small, but the aluminum step The irradiation field area must be widened so that the whole can be seen, and an additional reduction given to the subject is desired.

  An object of the present invention is to provide an X-ray imaging apparatus and an imaging method capable of automatically obtaining a bone mineral content.

  In order to achieve the above object, the technical features of the X-ray imaging apparatus according to the present invention include means for acquiring a value of a predetermined pixel in a target area in image data, preset imaging conditions, and bones. It is provided with the means which calculates | requires the amount of bone salt based on the information which shows a relationship with a salt amount, and the value of the said predetermined pixel.

  The technical feature of the X-ray imaging method according to the present invention is that the value of a predetermined pixel in a target region in image data is acquired, and then a relationship between a preset imaging condition and bone mineral content is obtained. The bone mineral content is calculated based on the information to be shown and the value of the predetermined pixel.

  According to the X-ray imaging apparatus according to the present invention, it is not necessary to image a staircase standard material simultaneously with a bone to be examined, and it is not always necessary to prepare a new staircase standard material with the introduction of the apparatus, which is useless. The cost is reduced, and the trouble of installing the staircase standard material in the vicinity of the bone to be examined is eliminated. In addition, the work efficiency can be improved and the operator can concentrate on the original imaging work, and it is not necessary to expand the irradiation field area so that the entire staircase standard material can enter, so that the subject can be exposed more than necessary. This reduces the load on the subject.

The present invention will be described in detail based on the embodiment shown in FIGS.
FIG. 1 is a schematic diagram of an X-ray imaging system when X-ray imaging of a subject O is performed. An X-ray irradiation field stop 1 and X-rays are generated in front of the subject O so as not to emit unnecessary X-rays. X-ray tubes 2 to be arranged are arranged. Further, an X-ray detection device 3 that detects X-rays that have passed through the subject O is disposed behind the subject O. An X-ray control device 4 for controlling the X-ray tube 2 is connected to the X-ray tube 2, and the X-ray detection device 3 and the X-ray control device 4 are connected to an image photographing control device 5 such as a computer. ing. The image capturing control device 5 is connected to a simple image display device 6 using a liquid crystal panel having an operation console composed of touch sensors, and is connected to a PACS 8 which is an image diagnosis system via a network 7.

  Here, the X-ray detection device 3 detects an X-ray irradiated from the X-ray tube 2 by a fixed image sensor and obtains a digital image signal, a grid for removing scattered radiation, and an X-ray detection. It comprises an A / D converter for outputting the output of the device as a digital image signal.

  FIG. 2 shows a screen of the simple image display device 6. The simple image display device 6 displays the captured image, and at the same time, operates the image capturing control device 5, changes the setting of the output image size, displays the message and the sequence state. be able to. The simple image display device 6 may also serve as a display on the console of the image capturing control device 5.

  The screen of the simple image display device 6 is provided with a plurality of display units and buttons for preparing for imaging, and includes a patient information display unit 11, an imaging condition display unit 12, an imaging method selection button 13, a parameter change button 14, and a message. A display unit 15, a setting window calling button 16, and a patient information calling button 17 are displayed.

  The patient information display unit 11 is an area for displaying patient information such as a patient's name, ID, gender, date of birth, etc., and the imaging condition display unit 12 is an imaging site name, tube current, tube voltage, irradiation time, patient-tube This is an area for displaying shooting conditions such as the distance between balls. The patient information is input by clicking the patient information call button 17 and using a patient information input window (not shown).

  The shooting condition is automatically set by clicking the shooting method selection button 13. The shooting method selection button 13 is a state maintaining button. When the button is clicked, the shooting method selection button 13 remains in a depressed state so that the selected shooting method can be seen. In FIG. Is selected. The imaging method selection button 13 is preset with imaging conditions of a region to be imaged, AEC area setting, image processing parameter setting and correction processing setting, and generator settings such as an aperture and a focus size.

  The parameter change button 14 is used to call a window for changing the parameter of the selected photographing method selection button 13. A message display unit 15 displays messages and system status, and a setting window call button 16 is used to call various setting windows.

  FIG. 3 is a block diagram of the image capturing control device 5. The output of the image input unit 21 is connected to the image output unit 25 via the correction processing unit 22, the average pixel value calculation unit 23, and the aluminum thickness equivalent calculation unit 24, and the average pixel value calculation unit 23 includes the measurement range input unit 26. The output is connected. The aluminum thickness equivalent calculation unit 24 is connected to the output of the database 29 having a relationship between the aluminum thickness and the pixel value based on the output of the imaging condition input unit 27 and the aluminum step imaging unit 28. Further, the output of the measurement range input unit 26 is connected to the imaging condition input unit 27, and the output of the database 29 is connected to the image output unit 25.

  The image input unit 21 acquires all digital data of the effective pixel area of the X-ray detection apparatus 3 after the X-rays are exposed. Alternatively, the digital image data of the effective pixel area already acquired from the X-ray detection apparatus 3 may be acquired from a storage medium such as a hard disk. The next correction processing unit 22 performs correction processing such as correction of variations among photoelectric conversion elements constituting the sensor, correction of changes over time of the sensor elements, and shading.

  Next, the reference position of the bone to be examined is designated by the measurement range input unit 26 as shown in the AB cross section of FIG. The measurement range input unit 26 can obtain the same effect by a method of manually specifying a reference position from the simple image display device 6 or a method of automatically obtaining a reference position by performing image processing from a captured image.

  As a method for automatically obtaining the reference position, for example, it is obtained by image processing such as extracting an edge with a twice differential value of density, or statistical data classified in advance by sex, age, height or the like is used. In the latter case, a mechanism for fixing the test site on the sensor is necessary so that the specific position of the test bone is always the same position in the image. In the method of automatically extracting the bone to be examined, since the irradiation field can be narrowed down to the bone to be examined in the present invention, the target site can be easily extracted with high accuracy.

  Subsequently, the average pixel value calculation unit 23 of the reference point calculates the average pixel value P = S / n, where n is the number of pixel values in the AB cross section and S is the sum of the pixel values along the AB cross section. To do.

The imaging condition input unit 27 inputs imaging conditions such as tube current, tube voltage, irradiation time, tube-patient distance, and the reference point aluminum thickness equivalent calculation unit 24 calculates the average pixel value of the reference point. The aluminum thickness equivalent to the average pixel value obtained in step 23 is obtained from the pixel value and aluminum thickness database 29 corresponding to each photographing condition. A database 29 of pixel values and aluminum thickness corresponding to each photographing condition holds a database of a relationship represented by Expression (1), where aluminum thickness equivalent Y (mmAl). The aluminum equivalent Y is calculated by substituting the photographing condition and the average pixel value into the expression (1).
Y = f (tube voltage, tube current, irradiation time, tube-patient distance, pixel value) (1)

  The image output unit 25 transfers the aluminum equivalent Y (mmAl) together with the image and the aluminum step and pixel value data corresponding to the photographing conditions as shown in Table 1 to the PACS 8.

Table 1 Relationship between aluminum step and pixel value
(68kV, 50mA, 20msec, 60cm)
Aluminum equivalent Y (mmAl) 1 2 3 4 5 ... 20
Pixel value 2000 1948 1892 1840 1788 ... 1012

  The pixel value and aluminum thickness database 29 corresponding to each photographing condition is constructed by executing the aluminum step photographing unit 28. That is, the aluminum step is photographed under photographing conditions used for photographing, and correction processing such as correction of variation among photoelectric conversion elements constituting the sensor, correction of changes in sensor elements over time, and shading are performed. A pixel value corresponding to the thickness of each aluminum is obtained from the image after the correction processing. The aluminum step is a stepped standard material made of aluminum. For example, when measuring bone mineral content in the second metacarpal bone, the thickness is from 1 (mm) to 20 (mm) in increments of 1 (mm). Things are used.

(How to create a database)
Before the radiographer or doctor who is an operator performs imaging, the relationship between the aluminum thickness and the pixel value under imaging conditions similar to those at the time of imaging is stored as a database. For this reason, the operator photographs the aluminum step under the same conditions as when photographing. Here, for example, under the imaging conditions of the metacarpal bone as shown in Table 2, the aluminum step is irradiated with X-rays to perform imaging.

Table 2
Imaging conditions Set value Tube-patient distance 600 (mm)
Irradiation field area 40 (mm) x 30 (mm)
Tube voltage 68 (kV)
Tube current 50 (mA)
Irradiation time 20 (mS)

  At this time, the operator inputs imaging conditions for preparing the imaging of the aluminum step, confirms that the imaging conditions are being met, and then replaces the aluminum step with the X-ray detection device 3 instead of the subject O. The irradiation field stop 1 is adjusted so that the entire surface of the aluminum step is irradiated at the previous predetermined position.

  When the preparation for imaging is completed in this way, the X-ray detection device 3 applies a voltage to the solid-state imaging device using the solid-state imaging device drive control signal from the imaging control device 5, so that image input to the solid-state imaging device is performed. Be prepared to be in any state at any time. The set imaging conditions are transferred to the X-ray detection device 3, the X-ray control device 4, and the image imaging control device 5, and stand by in a state where imaging can be performed with the designated parameters.

  Here, when the operator presses an X-ray exposure button installed in the vicinity of the simple image display device 6, the exposure button generates an exposure signal that serves as a trigger for generating X-rays in the X-ray tube 2. To do. The exposure signal is generated when a second switch of the exposure button is pressed, and the X-ray control device 4 transmits the exposure signal to the X-ray tube 2, whereby the X-ray tube 2 A line is generated. The generated exposure signal is temporarily supplied to the image capturing control device 5, and the image capturing control device 5 that has received the exposure signal is ready to be imaged when the solid-state imaging device receives the X-rays from the X-ray tube 2. If the X-ray detector 3 is ready, an exposure signal is sent to the X-ray controller 4 and X-rays are emitted from the X-ray tube 2.

  X-rays from the X-ray tube 2 are focused by the irradiation field stop 1 and sequentially transmitted through the aluminum step, the grid, and the scintillator, and are formed on the X-ray detection device 3 as a transmission image of the aluminum step. In the X-ray detection apparatus 3, an X-ray image is generated by an electric signal corresponding to the intensity of light by a solid-state imaging device, and a digital X-ray image is obtained by passing through an A / D converter.

  This image signal is captured by the image capturing control device 5, and the captured image is corrected for variations among photoelectric conversion elements constituting the sensor, correction for changes in sensor elements over time, scattered ray correction, grid correction, and radial irradiation. After performing various correction processes such as shading correction, which is correction of the X-ray position, density conversion is performed with reference to an LUT held in an LUT table holding unit (not shown). The average pixel value of each aluminum step is obtained from the image of the aluminum step, and the aluminum thickness and pixel value as shown in Table 1 are entered by inputting the thickness of each aluminum step on the aluminum step concentration measurement screen (not shown). The relationship is obtained.

  FIG. 4 is a graph in which the relationship between the pixel value and the aluminum thickness is calculated after the output of the aluminum step photographing unit 28 is executed to perform photographing and perform various correction processes. The relationship between the pixel value and the aluminum thickness is stored in the pixel value and aluminum thickness database 29 corresponding to each photographing condition.

  With the above operation, the relational database 29 between the pixel value and the aluminum thickness has been created, so that it is possible to obtain the bone mineral content by photographing only the target site of the subject alone without placing an aluminum step. Become.

(Measurement method of bone density)
When imaging the subject O, which is the subject, the operator determines patient information and an imaging method from the screen of the simplified image display device 6 shown in FIG. 2 in order to prepare for imaging. Patient information can be entered from the patient input screen that is called by clicking the patient button 17, or from a magnetic card or a bar code, or via the network 7 from the viewpoint of improving the efficiency of input work and preventing erroneous input. Input from the hospital information system (HIS) or radiation information system (RIS). The input patient information is displayed on the patient information display unit 11.

  In order to set an imaging region, a desired imaging method selection button 13 is clicked. In this embodiment, in order to photograph the second metacarpal, the imaging method selection button 13 labeled “metacarpal” is clicked. By selecting the shooting method selection button 13, preset values of shooting parameters, correction processing, and generator setting parameters are set, and some of the shooting parameters are displayed on the shooting condition display unit 12 in FIG. As shown in Table 1, the imaging conditions for the “metacarpal” are as follows: tube voltage 68 kV, tube current 50 mA, irradiation time 20 mS, and tube-patient distance 600 mm.

  By clicking the parameter change button 14, a parameter change window is called and the shooting parameters, correction processing, and generator setting parameters can be changed, but they are not changed here.

  As shown in FIG. 1, the subject O is positioned in front of the X-ray detection device 3 and positioned so as to be in an appropriate position with respect to the X-ray detection device 3. FIG. 5 is an explanatory diagram of the relationship between the effective region R of the X-ray detection device 3 and the irradiation field region T. In the X-ray detection device 3 of the present embodiment, the test site and the aluminum step are not exposed simultaneously. Therefore, the irradiation field region T can be narrowed down to a region where the second metacarpal bone that is the bone to be examined enters without matching the size of the aluminum step.

  When preparation for photographing is completed in this way, preparation is made so that the image input of the subject O can be performed at any time on the solid-state imaging device. Various parameters called by the imaging method selection button 13 and preset are transferred to the X-ray detection device 3, the X-ray control device 4, and the image imaging control device 5 and wait for the imaging with the designated parameters. To do.

  Here, as in the case of photographing the aluminum step, the operator presses an X-ray exposure button installed in the vicinity of the simple image display device 6 to irradiate the X-ray tube 2 with X-rays. X-rays from the X-ray tube 2 are focused by the irradiation field stop 1 and sequentially transmitted through the aluminum step, the grid, and the scintillator, and are formed on the X-ray detection device 3 as a transmission image of the aluminum step. In the X-ray detection apparatus 3, an X-ray image is generated by an electric signal corresponding to the intensity of light by a solid-state imaging device, and a digital X-ray image is obtained by passing through an A / D converter.

  This image signal is captured by the image capturing control device 5, and after the X-rays are emitted from the image input unit 21, all digital data in the effective pixel region of the X-ray detection device 3 is acquired. Alternatively, the digital image data of the effective pixel area already acquired by the X-ray detection apparatus 3 may be acquired from a storage medium such as a hard disk. The digital image data acquired by the image input unit 21 is output to the correction processing unit 22, and correction of variation among photoelectric conversion elements constituting the X-ray detection device 3, correction of temporal changes of the photoelectric conversion elements, shading, etc. The correction process is performed.

  The imaging condition input unit 27 outputs imaging conditions such as tube current, tube voltage, irradiation time, and tube-patient distance to the aluminum thickness equivalent calculating unit 24 at the reference point. The aluminum thickness equivalent to the average pixel value obtained by the average pixel value calculation unit 23 is calculated from the pixel value and aluminum thickness database 29 corresponding to each photographing condition. The pixel value and aluminum thickness database 29 corresponding to each photographing condition holds a relational database represented by the formula (1) for obtaining the above-described aluminum thickness equivalent Y (mmAl). In Expression (1), the aluminum equivalent Y is calculated by substituting the photographing condition and the average pixel value.

  Subsequently, in the image output unit 25, the aluminum equivalent Y (mmAl) together with the image and the aluminum step and pixel value data corresponding to the photographing conditions (68 kV, 50 mA, 20 mS, 600 mm) as shown in Table 2 above are stored in the PACS 8. Forward.

  FIG. 6 is a flowchart of the processing procedure. First, in step S01, the input digital image of the subject O on the entire effective area of the X-ray detection apparatus 3 is input. Next, in step S02, for the digital image of the entire effective area of the X-ray detection apparatus 3 input in step S01, correction of variation between photoelectric conversion elements, correction of change over time of the photoelectric conversion elements, shading, etc. In step S03, the average pixel value of the bone profile in the measurement range designated by the operator is calculated.

  Subsequently, in step S04, an aluminum thickness equivalent corresponding to the average pixel value calculated in step S03 is calculated from the database 29. In step S05, the relationship between the aluminum thickness equivalent calculated in step S04 and the thickness of the aluminum step corresponding to the photographing condition and the pixel value is output to the PACS 8 in association with the image.

  This processing procedure will be described in detail. The reference range of the bone to be examined is designated by the measurement range input unit 26 as shown in FIG. 8 and is output to the average pixel value calculation unit 23 of the reference point. The input from the measurement range input unit 26 can be obtained by a method of manually specifying a reference position from the simple image display device 6 or a method of performing image processing from a captured image and automatically obtaining the reference position.

  In the method of automatically obtaining the reference position, for example, the reference position is determined based on statistical data classified in advance by gender, age, height, etc., or by image processing such as extracting an edge with a twice differential value of density. . In the latter case, a mechanism for fixing the test site on the X-ray detection apparatus 3 is necessary so that the specific position of the test bone is always the same position in the image. In the method of automatically extracting the bone to be examined, in this embodiment, X-rays can be narrowed down to the bone to be examined by the X-ray irradiation field stop 1, so that the target portion can be easily and accurately extracted.

  Further, in order to display the photographed image on the simplified image display device 6, the image is subjected to density conversion using a LUT that is a density conversion curve serving as a reference for density conversion processing, and is stored in another frame memory. The image data that has undergone density conversion is displayed on the simplified image display device 6 as shown in FIG. At this time, the aluminum step AS is displayed near the image of the bone to be examined. The relation of the aluminum thickness and the pixel value corresponding to the current photographing condition is obtained from the database 29, and the display density is obtained by converting the pixel value by the LUT. Each step width is obtained by dividing a predetermined length by the number of steps, and a step thickness number is written on the left side of each step, thereby enabling display as shown in FIG.

  The operator designates points A and B, which are reference points for bone mineral measurement, on this image. Line segment AB is a straight line perpendicular to the axis of the second metacarpal bone. At this time, as an aid for specifying the points A and B, a profile of the cross section AB (pixel value distribution diagram of the cross section AB) may be displayed, or the points A and B are automatically measured. Also good.

  In this way, the designated measurement point is input by the measurement range input unit 26, and the average pixel value in the measurement range is calculated by the average pixel value calculation unit 23 of the reference point. The average pixel value P is calculated as P = S / n, where n is the number of pixel values in the A-B cross section and S is the sum of the pixel values along the A-B cross section. As the image data at this time, the data before the LUT conversion is used, the average pixel value P is LUT converted, and an arrow is attached to a corresponding portion of the aluminum step AS shown in FIG. You will be able to visually understand where to deal with.

The imaging condition input unit 27 inputs imaging conditions such as tube current, tube voltage, irradiation time, tube-patient distance, and the reference point aluminum thickness equivalent calculation unit 24 inputs the reference point average pixel value calculation unit 23. The aluminum thickness equivalent Y with respect to the average pixel value P obtained in the above is obtained from the database 29. Since the relationship of Table 2 is obtained from the database 29, Formula (2) in which a numerical value is substituted into Formula (1) by the least square method or the like is previously derived.
Y = f (68 kV, 50 mA, 20 m, 600 mm, pixel value) (2)

  When the average pixel value P obtained by the average pixel value calculation unit 23 of the reference point is input to the pixel value of the expression (2), the corresponding aluminum thickness equivalent Y is calculated.

  If Y = 9.5, the previously obtained arrow location is 9.5 (mmAl), and is displayed as shown in FIG.

  When the bone measurement is completed, the imaging is completed by pressing the examination end button, and the image is transferred to the PACS 8 by the image output unit 25. At this time, accompanying the image, an aluminum thickness equivalent that is the amount of bone mineral, and the relationship between the aluminum step and the pixel value as shown in Table 2 are output. Alternatively, the relationship between the aluminum step and the pixel value as shown in Table 2 may be printed on the image as a diagram of the aluminum step AS in FIG. Thus, by outputting the relationship between the aluminum step and the pixel value as shown in Table 2, the bone mineral content can be measured even on the PACS 8 side.

  The X-ray detector incorporated in the X-ray detector 3 is designed to withstand about 100,000 exposures, but its performance deteriorates as the number of exposures increases, or It is known that its performance deteriorates over time. Therefore, if the database 29 is not updated at an appropriate timing, the correct bone mineral amount cannot be calculated. Therefore, in the embodiment, when either the predetermined number of exposures has been reached or the predetermined time has elapsed since the aluminum step and pixel value data were taken, the “database 29 is updated. Please display "message on the simple image display device 6.

  In the above example, the aluminum thickness equivalent is obtained from the relationship between the aluminum thickness and the pixel value, but the aluminum thickness equivalent may be obtained from the relationship between the aluminum thickness and the concentration. In this case, the average density of the measurement range is obtained from the image converted by the LUT, and the aluminum thickness equivalent can be obtained from the relationship between the average density, the aluminum thickness, and the density.

  Further, the stepped standard material is usually aluminum as in the embodiment, but the same effect can be obtained with other materials. In that case, in addition to the relationship between the physical quantity of the test step and the pixel value of this material, it is necessary to store the relationship between the physical quantity of the test step and the bone mineral content in the database. In this embodiment, this database is combined into a database of the relationship between the bone mineral content and the pixel value with respect to the imaging conditions.

  In the embodiment, when the imaging method button 13 is clicked on the imaging preparation screen shown in FIG. 2, the imaging conditions are determined and input from the imaging condition input unit 27, but from the console of the X-ray control device 4. Shooting conditions may be input. In addition, when X-ray irradiation is monitored by an X-ray dose control mechanism called AEC, X-rays are cut off in a state where the set irradiation time is not reached. The shooting conditions may be input.

  In the above example, the imaging condition of the “metacarpal” has been described. However, the same operation and effect can be obtained even with other parts or other imaging conditions. In this case, the aluminum step AS is photographed in advance under the photographing conditions for photographing with the aluminum step photographing unit 28, and the relationship between the aluminum thickness and the pixel value is obtained, or the aluminum chart is photographed under a plurality of predetermined photographing conditions. The relationship between the aluminum thickness and the pixel value for the desired shooting condition can be calculated from these shooting conditions.

  Furthermore, when measuring the amount of bone mineral more accurately, as disclosed in Patent Document 2, the exposure area dose of the aluminum step is calculated from the dose measured with the exit dosimeter, the aluminum step area, and the irradiation area area. This value may be calculated and held in the database as one of the shooting conditions. Even during radiography, the dose received by the area equivalent to the aluminum step can be calculated from the dose measured by the exit dosimeter, the aluminum step area, and the irradiation area, and the relationship between the corresponding aluminum thickness and the pixel value can be obtained from the aforementioned database. It is done.

  At the same time, as disclosed in Patent Document 2, the X-ray detection device 3 is calculated from the amount of charge per unit area generated by the X-ray detection device 3 that has received X-rays so that the exit dosimeter is not required. The exposure area dose may be obtained using an area dose conversion coefficient k for converting into an area exposure amount per unit area of X-rays received by the patient. The area dose conversion coefficient k may be given by a non-linear function or a reference table.

  Although the above description is a preferred embodiment of the present invention, it is needless to say that the present invention is not limited to these embodiments, and various modifications and changes can be made within the scope of the gist thereof.

JP 2004-69441 A

1 is a schematic diagram of an X-ray imaging system. It is explanatory drawing of the screen which performs imaging | photography preparation. It is a block circuit block diagram of an image capturing control device. It is a graph of the relationship between aluminum thickness and pixel value. It is explanatory drawing of the relationship between a test bone and an irradiation field. It is an operation | movement flowchart figure. It is explanatory drawing of a picked-up image display. It is explanatory drawing of the X-ray photographic film by the conventional MD method. It is a chart figure of the relationship of the aluminum plate thickness with respect to the position of a test bone.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 X-ray irradiation field stop 2 X-ray tube 3 X-ray detection apparatus 5 Image pick-up control apparatus 6 Simple image display apparatus 7 Network 8 PACS
DESCRIPTION OF SYMBOLS 11 Patient information display part 12 Imaging condition display part 13 Imaging | photography method selection button 14 Parameter change button 15 Message display part 16 Setting window call button 17 Patient information call button 21 Image input part 22 Correction process part 23 Average pixel value calculation part 24 Aluminum thickness Equivalence calculation unit 25 Image output unit 26 Measurement range input unit 27 Imaging condition input unit 28 Aluminum step imaging unit 29 Database of aluminum thickness and pixel value

Claims (10)

  Means for acquiring a value of a predetermined pixel in a target region in image data, information indicating a relationship between a preset imaging condition and a bone mineral content, and a bone mineral content based on the value of the predetermined pixel An X-ray imaging apparatus comprising: a means for obtaining.   2. The X-ray imaging apparatus according to claim 1, further comprising means for holding information indicating a relationship between preset imaging conditions and bone mineral content as a database.   The X-ray imaging apparatus according to claim 2, further comprising means for updating the database for the imaging conditions when imaging is performed a predetermined number of times since the database for the imaging conditions is created.   The X-ray imaging apparatus according to claim 2, further comprising a unit that updates the database for the imaging conditions when a predetermined time has elapsed from the time when the database for the imaging conditions is created.   The X-ray imaging according to any one of claims 1 to 4, wherein the database for the imaging conditions is a database of a relationship between a thickness of a staircase standard material and a pixel value for the imaging conditions. apparatus.   The stepped standard material is an aluminum plate, and the concentration according to the thickness of the predetermined aluminum plate is determined from the database of the relationship between the average pixel value of the bone profile at the measurement location and the thickness and pixel value of the stepped standard material with respect to imaging conditions. An X-ray imaging apparatus according to claim 5, wherein an aluminum chart showing the correspondence between the two is created and arranged in the vicinity of the image.   7. The X-ray imaging apparatus according to claim 6, wherein the thickness is displayed numerically next to the created aluminum chart, and the position of the average pixel value of the calculated bone profile is marked on the aluminum chart. .   The X-ray imaging apparatus according to any one of claims 1 to 7, wherein a measurement range is automatically determined from an X-ray image of a target part.   A value of a predetermined pixel in a target region in image data is acquired, and thereafter, a bone mineral amount is determined based on information indicating a relationship between a preset imaging condition and a bone mineral amount and the value of the predetermined pixel. An X-ray imaging method characterized by calculating.   A program for executing the X-ray imaging method according to claim 9 by a computer.