JP2012245142A - X-ray imaging method, method for creating data for subtraction imaging, x-ray imaging apparatus, and recording medium which records data for subtraction imaging - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an X-ray imaging method and the like capable of obtaining a clearer subtraction image in consideration of a continuous spectrum in X-rays.
An X-ray imaging apparatus includes a table 2 on which a subject 1 is placed, an X-ray tube 3, a flat panel detector 4, a control unit 5, an X-ray tube control unit 6, and a display unit 7. With. Further, the control unit 5 includes a high voltage image memory 11, a LOG conversion unit 12 and a weighting unit 13 used during high voltage imaging, and a low voltage image memory 14, a LOG conversion unit 15 and weights used during low voltage imaging. A subtraction unit 17 that executes a subtraction process, a reference table 18, and an image processing unit 19. The reference table 18 records data indicating the relationship between the detected value of the flat panel detector 4 and the soft tissue and bone thickness when a high voltage and a low voltage are applied to the X-ray tube 3.
[Selection] Figure 1

Description

  The present invention relates to an X-ray imaging method, a data creation method for subtraction imaging, an X-ray imaging apparatus, and a storage medium storing data for subtraction imaging, and more particularly, an X-ray imaging method using dual energy subtraction and data generation for subtraction imaging. The present invention relates to a method, an X-ray imaging apparatus, and a storage medium storing subtraction imaging data.

  In such an X-ray imaging apparatus for performing dual energy subtraction imaging, an X-ray measurement value when a high voltage value is applied to the X-ray tube and a low voltage value when the X-ray tube is applied. By performing a subtraction process on the X-ray measurement values, tissues having different X-ray absorption coefficients are extracted (see Patent Document 1).

JP 2009-160100 A

  In such a conventional X-ray imaging apparatus, it is assumed that monochromatic X-rays having a very narrow spectrum width are used as X-rays. However, since actual X-rays have a continuous spectrum, there is a case where a higher-precision X-ray image cannot be obtained without considering them. For example, when an image of the subject's chest is taken, there may be a problem that the image of the spine becomes unclear even if the rib image is obtained with high accuracy.

  The present invention has been made to solve the above-described problems, and an object thereof is to provide an X-ray imaging method and the like that can obtain a clearer subtraction image in consideration of a continuous spectrum in X-rays.

  According to a first aspect of the present invention, there is provided an X-ray imaging method for capturing an X-ray image by detecting X-rays irradiated from an X-ray tube and passing through a subject with an X-ray detector. X-ray detection when a high voltage and a low voltage are applied to an X-ray tube based on the distribution of X-ray energy when a voltage and a low voltage are applied and the mass attenuation coefficient corresponding to the X-ray energy The detection value of the vessel is calculated multiple times by changing the thickness of the soft tissue and bone, and high voltage and low voltage are applied to the X-ray tube based on the calculation result in the calculation process Storing the data indicating the relationship between the detected value of the X-ray detector and the thickness of the soft tissue and bone as a table, and passing through the subject when a high voltage is applied to the X-ray tube A high voltage imaging step of detecting the X-rays performed by the X-ray detector; A low-voltage imaging step of detecting, by the X-ray detector, X-rays that have passed through the subject when a low voltage is applied to the tube, and a high voltage and a low voltage stored in the X-ray tube stored in the storage step Data indicating the relationship between the detected value of the X-ray detector and the thickness of the soft tissue and bone, the detected value of the X-ray detected in the high-voltage imaging process, and detected in the low-voltage imaging process An image processing step for creating an image of soft tissue and bone from the detected X-ray value, and a display step for displaying an image of the soft tissue and bone created in the image processing step. Features.

The invention described in claim 2 is based on the X-ray detector according to the invention described in claim 1 when a high voltage is applied to the X-ray tube and X-rays are directly irradiated from the X-ray tube to the X-ray detector. The detection value of X-rays is I _OH , and the detection value of X-rays by the X-ray detector when the X-ray tube is directly irradiated with X-rays by applying a low voltage to the X-ray tube is I _OL , When the high voltage is applied to the X-ray tube and the soft tissue is passed through the thickness L _S and the bone is passed through the thickness L _B , the detected value of the X-ray by the X-ray detector is I _H , and the low voltage is applied to the X-ray tube When the soft tissue passes through the soft tissue by the thickness L _S and the bone portion passes by the thickness L _B , the X-ray detection value by the X-ray detector is I _L , and the X-ray irradiated from the X-ray tube is the soft tissue The mass attenuation coefficient when passing through the tube is μ _S , the mass attenuation coefficient when X-rays irradiated from the X-ray tube pass through the bone part is μ _B , and the X-ray energy is E. In the calculation step, the calculation is performed based on the following equation.

  The invention according to claim 3 is the detection value of the X-ray detector when a high voltage and a low voltage are applied to the X-ray tube calculated in the calculation step in the invention according to claim 1 or claim 2. And the thickness of the soft tissue and bone when the high voltage and the low voltage are applied to the X-ray tube by complementing the relationship between the thickness of the soft tissue and the bone. And a normalizing step of normalizing data indicating the relationship between the two.

  According to a fourth aspect of the present invention, there is provided an X-ray imaging method for capturing an X-ray image by detecting an X-ray irradiated from an X-ray tube and passing through a subject with an X-ray detector. A high-voltage imaging process in which the X-ray detector detects X-rays that have passed through the subject when a high voltage is applied, and X-rays that have passed through the subject when a low voltage is applied to the X-ray tube A low-voltage imaging step of detecting the X-ray detector by the X-ray detector, and the relationship between the detected value of the X-ray detector and the thickness of the soft tissue and bone when the high voltage and the low voltage are applied to the X-ray tube. An image processing step for creating an image of a soft tissue and a bone part from a table shown, an X-ray detection value detected in the high-voltage imaging step, and an X-ray detection value detected in the low-voltage imaging step; Display images of soft tissue and bone created in the image processing step Characterized by comprising a shows steps.

  The invention according to claim 5 is the invention according to claim 4, wherein the detected value of the X-ray detector and the thickness of the soft tissue and bone when the high voltage and the low voltage are applied to the X-ray tube. The table showing the relationship between the X-ray tube and the X-ray tube is based on the distribution of X-ray energy when a high voltage and a low voltage are applied to the X-ray tube and the mass attenuation coefficient corresponding to the X-ray energy. Based on the calculation result in the calculation step of calculating the detection value of the X-ray detector when the voltage and the low voltage are applied, by changing the thickness of the soft tissue and the bone portion a plurality of times, It is created by a storing step of storing data indicating the relationship between the detection value of the X-ray detector when the high voltage and the low voltage are applied to the X-ray tube and the thickness of the soft tissue and the bone as a table.

The invention described in claim 6 is based on the X-ray detector according to the invention described in claim 5 when a high voltage is applied to the X-ray tube and X-rays are directly irradiated from the X-ray tube to the X-ray detector. The detection value of X-rays is I _OH , and the detection value of X-rays by the X-ray detector when the X-ray tube is directly irradiated with X-rays by applying a low voltage to the X-ray tube is I _OL , When the high voltage is applied to the X-ray tube and the soft tissue is passed through the thickness L _S and the bone is passed through the thickness L _B , the detected value of the X-ray by the X-ray detector is I _H , and the low voltage is applied to the X-ray tube the imparted soft tissue thickness L _S, X-rays soft tissue to be irradiated with the detected value of the X-rays by the X-ray detector when it passes through only the thickness L _B of the bone portion I _L, the X-ray tube The mass attenuation coefficient when passing through the tube is μ _S , the mass attenuation coefficient when X-rays irradiated from the X-ray tube pass through the bone part is μ _B , and the X-ray energy is E. In the calculation step, the calculation is performed based on the following equation.

  According to a seventh aspect of the invention, in the invention of the fifth or sixth aspect, the detected value of the X-ray detector when a high voltage and a low voltage are applied to the X-ray tube calculated in the calculation step. And the thickness of the soft tissue and bone when the high voltage and the low voltage are applied to the X-ray tube by complementing the relationship between the thickness of the soft tissue and the bone. And a normalizing step of normalizing data indicating the relationship between the two.

  According to the eighth aspect of the invention, the X-ray detector detects X-rays that have been irradiated from the X-ray tube and passed through the subject when a high voltage and a low voltage are applied to the X-ray tube. In a subtraction imaging data creation method used for an X-ray imaging method for imaging an X-ray image, the distribution of X-ray energy when a high voltage and a low voltage are applied to the X-ray tube, and the X-ray energy corresponding to the distribution Based on the mass attenuation coefficient, the detection value of the X-ray detector when a high voltage and a low voltage are applied to the X-ray tube is calculated multiple times by changing the thickness of the soft tissue and bone. Data indicating the relationship between the detected value of the X-ray detector and the thickness of the soft tissue and the bone when the high voltage and the low voltage are applied to the X-ray tube based on the calculation result in the process and the calculation process Storage process for storing the data as a table Characterized in that was.

  The invention according to claim 9 is irradiated from the X-ray tube, an X-ray tube that irradiates the subject with X-rays, an X-ray tube controller that controls a tube voltage applied to the X-ray tube, and the X-ray tube. An X-ray detector for detecting X-rays that have passed through the subject, a distribution of X-ray energy when a high voltage and a low voltage are applied to the X-ray tube, and a mass attenuation coefficient corresponding to the X-ray energy, Based on the above, the detected value of the X-ray detector when a high voltage and a low voltage are applied to the X-ray tube is calculated a plurality of times by changing the thickness of the soft tissue and the bone part, and thereby calculating the X-ray tube. A storage unit for storing a table in which data indicating a relationship between a detection value of an X-ray detector and a thickness of a soft tissue and a bone when a high voltage and a low voltage are applied to the X-ray tube; and the X-ray tube X-ray measured by the X-ray detector when a high voltage value is applied to the X-ray tube, and a low voltage value is attached to the X-ray tube. Measured values of the X-rays when the X-ray detector is applied, and detected values of the X-ray detector and soft tissue when a high voltage and a low voltage are applied to the X-ray tube stored in the storage unit; An image processing unit that creates an image of a soft tissue and a bone part from data indicating a thickness relationship of the bone part, and a display unit that displays an image of the soft tissue and the bone part created by the image processing unit It is characterized by having.

  The invention according to claim 10 is irradiated from the X-ray tube, an X-ray tube that irradiates the subject with X-rays, an X-ray tube controller that controls a tube voltage applied to the X-ray tube, and the X-ray tube. Relationship between the X-ray detector for detecting X-rays passing through the subject, the detected value of the X-ray detector when a high voltage and a low voltage are applied to the X-ray tube, and the thickness of the soft tissue and bone A storage unit that stores data indicating X, a measurement value of X-rays by the X-ray detector when a high voltage value is applied to the X-ray tube, and a low voltage value is applied to the X-ray tube The X-ray measurement value of the X-ray detector and the detection value of the X-ray detector when a high voltage and a low voltage are applied to the X-ray tube stored in the storage unit and the soft tissue and bone part An image processing unit that creates images of soft tissues and bones from data indicating the thickness relationship, and the image processing unit Characterized by comprising a display unit for displaying the soft tissue and bone image was.

  According to an eleventh aspect of the present invention, in the invention according to the tenth aspect, the detected value of the X-ray detector and the thickness of the soft tissue and bone when the high voltage and the low voltage are applied to the X-ray tube. The data indicating the relationship between the X-ray tube and the X-ray tube is based on the distribution of X-ray energy when a high voltage and a low voltage are applied to the X-ray tube and the mass attenuation coefficient corresponding to the X-ray energy. It consists of a table created by calculating the detection value of the X-ray detector when a voltage and a low voltage are applied by changing the thickness of the soft tissue and the bone part a plurality of times.

  According to the twelfth aspect of the present invention, when a high voltage and a low voltage are applied to the X-ray tube, X-rays irradiated from the X-ray tube and passed through the subject are detected by the X-ray detector. A storage medium storing data for subtraction imaging used in an X-ray imaging method for imaging an X-ray image, the distribution of X-ray energy when a high voltage and a low voltage are applied to the X-ray tube, and the X-ray energy distribution Based on the mass attenuation coefficient corresponding to the line energy, the detection value of the X-ray detector when applying high voltage and low voltage to the X-ray tube, and changing the thickness of the soft tissue and bone Calculated a plurality of times, and based on the calculation result, data indicating the relationship between the detected value of the X-ray detector and the thickness of the soft tissue and bone when the high voltage and low voltage are applied to the X-ray tube It is memorized as a table.

  According to the first to twelfth aspects of the present invention, even when X-rays have a continuous spectrum, it is possible to obtain a clearer subtraction image in consideration thereof.

  According to invention of Claim 3 and Claim 7, when the high voltage and the low voltage are provided to the X-ray tube, the relationship between the detection value of the X-ray detector and the thickness of the soft tissue and the bone part Even when the data is small, it is possible to obtain normalized data corresponding to the assumed tube voltage.

1 is a schematic diagram of an X-ray imaging apparatus according to the present invention. It is explanatory drawing which shows typically the state which irradiated the high voltage | pressure X-ray and the low voltage X-ray with respect to the soft tissue and the bone part. 3 is a flowchart of an X-ray imaging method according to the present invention. It is a graph which shows the relationship between the X-ray energy and the relative photon number when a tube voltage of 120 kV is applied to the X-ray tube 3 and when a tube voltage of 60 kV is applied. It is a graph which shows the relationship between the mass attenuation coefficient and the photon energy of water corresponding to a soft tissue and cortical bone corresponding to a bone. Relationship between I _H and _{L S} and _{L B,} and is a graph showing the relationship between _{I L} and _{L S} and _{L B.}

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a schematic diagram of an X-ray imaging apparatus according to the present invention.

  This X-ray imaging apparatus is for displaying, for example, an X-ray image of a soft tissue or a bone part by extracting tissues having different X-ray absorption coefficients using a dual energy subtraction process. A table 2 on which the subject 1 is placed, an X-ray tube 3, a flat panel detector 4 as an X-ray detector, a control unit 5, and a tube voltage applied to the X-ray tube 3 are controlled. An X-ray tube control unit 6 and a display unit 7 such as a CRT are provided.

  Further, the control unit 5 includes a high voltage image memory 11, a LOG conversion unit 12 and a weighting unit 13 used during high voltage imaging, and a low voltage image memory 14, a LOG conversion unit 15 and weights used during low voltage imaging. A subtraction unit 17 that executes a subtraction process, a reference table 18 that will be described later, and an image processing unit 19. In this X-ray imaging apparatus, the subtraction unit 17 is used when general dual energy subtraction imaging similar to the conventional one is executed. The reference table 18 is used when performing dual energy subtraction imaging according to the present invention.

  First, an operation when performing general dual energy subtraction imaging will be described. In this X-ray imaging apparatus, when a high voltage value is applied to the X-ray tube 3, a high voltage image measured by the flat panel detector 4 is stored in the high voltage image memory 11. The high voltage image stored in the high voltage image memory 11 is logarithmically processed by the LOG conversion unit 12 and converted into an image signal, and then the weighting unit 13 multiplies the weighting coefficient according to body thickness information and the like. The Similarly, when a low voltage value is given to the X-ray tube 3, a low voltage image measured by the flat panel detector 4 is stored in the low voltage image memory 14. The low voltage image stored in the low voltage image memory 14 is subjected to logarithmic processing in the LOG conversion unit 15, and then multiplied in the weighting unit 16 by a weighting factor corresponding to body thickness information and the like.

  A subtraction process, which is a subtraction process, is performed in the subtraction unit 17 on the high voltage image and the low voltage image that have been logarithmically processed and weighted. The subtraction image subjected to the subtraction process is subjected to image processing in the image processing unit 19, and a soft tissue or bone subtraction image is displayed on the display unit 7.

  FIG. 2 is an explanatory view schematically showing a state in which high voltage X-rays and low voltage X-rays are irradiated to the soft tissue and bone.

Here, the detected value of the X-rays by the flat panel detector 4 when irradiated with direct X-ray from the I _OH is the X-ray tube 3 by applying a high voltage to the X-ray tube 3 in the flat panel detector 4, I _OL is the detected value of the X-rays by the X-ray tube 3 by applying a low voltage from the X-ray tube 3 in the flat panel detector 4 when irradiated with direct X-ray flat panel detector 4, I _H is high in the X-ray tube 3 by applying a voltage soft tissue thickness L _S, the detection value of the X-rays by the flat panel detector 4 when it passes through only the thickness L _B of the bone portion, I _L is the low voltage applied to the X-ray tube 3 The detected value of X-rays by the flat panel detector 4 when the soft tissue passes through the thickness L _S and the bone part through the thickness L _B , and μ _SH shows the X-rays when a high voltage is applied to the X-ray tube 3. Mass when X-rays irradiated from tube 3 pass through soft tissue Μ _SL is an attenuation coefficient, μ _SL is a mass attenuation coefficient when X-rays irradiated from the X-ray tube 3 pass through the soft tissue when a low voltage is applied to the X-ray tube 3, and μ _BH is an X-ray tube 3 The mass attenuation coefficient when X-rays radiated from the X-ray tube 3 pass through the bone part when a high voltage is applied, and μ _BL indicates from the X-ray tube 3 when a low voltage is applied to the X-ray tube 3. The mass attenuation coefficient when the irradiated X-ray passes through the bone part is shown.

The high voltage memory 11 stores a high voltage image obtained based on the pixel value I _H calculated by the following formula 1, and the low voltage memory 14 stores the pixel value I calculated by the following formula 2. A high voltage image obtained based on _L is stored.

  By taking LOG for these equations in the LOG conversion units 12 and 15, the following equations 3 and 4 are derived.

The weighting unit 13 multiplies the above equation 3 by [μ _SL / μ _SH ], and the subtraction unit 17 subtracts the equation 4 from the multiplication result, thereby eliminating the mass attenuation coefficient portion of the soft tissue and the bone image. Can be obtained. Similarly, the weighting unit 16 multiplies the above equation by [μ _BL / μ _BH ], and the subtraction unit 17 subtracts Equation 4 from the multiplication result, thereby eliminating the mass attenuation coefficient portion of the bone portion, and soft tissue. Images can be obtained. Then, these subtraction results are transmitted to the display unit 7 via the image processing unit 19, and a soft tissue or bone subtraction image is displayed on the display unit 7. The image data at that time is stored in a storage unit (not shown) as necessary.

  Next, an operation when performing dual energy subtraction imaging according to the present invention will be described. FIG. 3 is a flowchart of the X-ray imaging method according to the present invention.

FIG. 4 is a graph showing the relationship between the X-ray energy and the relative photon number when a tube voltage of 120 kV (kilovolt) is applied to the X-ray tube 3 and when a tube voltage of 60 kV is applied. Here, the horizontal axis in FIG. 4 indicates the X-ray energy, and the unit is keV (kiloelectron volts). Moreover, the vertical axis | shaft in FIG. 4 shows the number of relative photons, and the unit is a unitless. Further, FIG. 5 is a graph showing the relationship between the mass attenuation coefficient and the photon energy of water corresponding to the soft tissue and cortical bone corresponding to the bone. Here, the horizontal axis in FIG. 5 indicates photon energy, and its unit is keV. Moreover, the vertical axis | shaft in FIG. 5 shows a mass attenuation coefficient, and the unit is [cm < ² > / g].

When a monochromatic X-ray having an extremely narrow spectrum width is used, the high-pressure X-ray and the low-pressure X-ray before passing through the subject 1 and the subject 1 after passing through the subject 1 are shown. The relationship between the high-pressure X-ray and the low-pressure X-ray, that is, the relationship between I _H and I _L and I _OH and I _OL can be calculated by Equation 1 and Equation 2 described above. However, as shown in FIG. 4, even when a constant tube voltage is applied to the X-ray tube 3, the X-ray energy is distributed over a wide range as a continuous spectrum. And the attenuation coefficient of a soft tissue or a bone part also depends on photon energy corresponding to X-ray energy, as shown in FIG. For this reason, in the X-ray imaging method according to the present invention, instead of the above-described Equation 1 and Equation 2, the following Equation 5 and Equation 6 corresponding to the integral values for Equation 1 and Equation 2 described above are used. .

Here, μ _S in Expression 5 and Expression 6 below represents a mass attenuation coefficient when X-rays irradiated from the X-ray tube pass through the soft tissue, and μ _B represents X irradiated from the X-ray tube. The mass attenuation coefficient when a line passes a bone part is shown. E represents the X-ray energy described above.

Therefore, I _OH (E) is a detected value of X-rays by the flat panel detector 4 when a high voltage is applied to the X-ray tube 3 and X-rays are directly irradiated from the X-ray tube 3 to the flat panel detector 4. for I _OH, show the integrated value by the energy X-rays which form a continuous spectrum, and more specifically, shows a value taking the integrated value for each energy to X-rays which form a continuous spectrum. Similarly, I _OL (E) is a detected value of X-rays by the flat panel detector 4 when a low voltage is applied to the X-ray tube 3 and X-rays are directly irradiated from the X-ray tube 3 to the flat panel detector 4. For a certain _IOL , a value obtained by integrating X-rays forming a continuous spectrum with energy is shown, and more specifically, a value obtained by taking an integrated value for each energy with respect to X-rays forming a continuous spectrum is shown.

Μ _S (E) represents a value obtained by integrating X-rays forming a continuous spectrum by energy with respect to μ _S which is a mass attenuation coefficient when X-rays irradiated from the X-ray tube pass through the soft tissue. More specifically, a value obtained by taking an integrated value for each energy with respect to X-rays forming a continuous spectrum is shown. Similarly, μ _B (E) indicates a value obtained by integrating X-rays forming a continuous spectrum by energy with respect to μ _B which is a mass attenuation coefficient when X-rays irradiated from the X-ray tube pass through the bone. More specifically, a value obtained by taking an integrated value for each energy with respect to X-rays forming a continuous spectrum is shown.

That is, in the X-ray imaging method according to the present invention, first, in the equation 5 and equation 6, by varying the thickness of the soft tissue (distance) L _S and the thickness of the bone portion (distance) L _B A large number of operations are performed by changing the combination of the thicknesses L _S and L _B many times with respect to the relationship between the pixel values I _H and I _L to be detected when a high voltage and a low voltage are applied to the X-ray tube 3. (Step S1). Then, when the required number of data is obtained (step S2), the high voltage and the pixel value I _H and I _L and soft tissue is a detected value of the flat panel detector 4 when the grant and low voltage to the X-ray tube 3 The data indicating the relationship between the bone thickness L _S and L _B is stored as the reference table 18 shown in FIG. 1 (step S3).

FIG. 6 is a graph showing the relationship between I _H and L _S and L _B, and the relationship between I _L and L _S and L _B. Here, Z-axis in FIG. 6 (a) and _{I H,} the X-axis _{L S,} Y axis represents the _{L B.} Further, Z-axis in FIG. 6 (b) to _{I L,} the X-axis _{L S,} Y axis represents the _{L B.} In this figure, the range of 160mm to _{L S} from 0 mm, also shows a state in which was changed in the range of 10mm to _{L B} from 0 mm. In addition, I _H and I _L in this figure are expressed as a ratio to I _OH and I _OL . This graph, as described above, in the above Equation 5 and Equation 6, by varying the thickness of the soft tissue (distance) L _S and the thickness of the bone portion (distance) L _B, high X-ray tube 3 Obtained by a calculation process for calculating a large number of combinations of the thicknesses L _S and L _B many times with respect to the relationship between the pixel values I _H and I _L to be detected when a voltage and a low voltage are applied. It is. When creating this graph, the detected values I _H and I _L of the flat panel detector 4 when the high voltage and the low voltage are applied to the X-ray tube 3 calculated in the calculation process, the soft tissue, and the bone by complementing the relationship between the thickness L _S and L _B, the detection value of the X-ray detector I _H and I _L and soft tissue and bone when applying a high voltage and low voltage to the X-ray tube 3 Data indicating the relationship between the thickness L _S and L _B with the part is normalized. The normalized data is stored as the reference table 18 described above.

Next, the X-ray that has passed through the subject 1 when the high voltage is applied to the X-ray tube 3 is detected by the flat panel detector 4 (step S4), and the low voltage is applied to the X-ray tube 3 X-rays that have passed through the subject 1 are detected by the flat panel detector 4 (step S5). Then, each tube voltage values at these steps, based on a combination of pixel values I _H and I _L is the detected value of the flat panel detector 4, by referring to the reference table 18, the soft tissue thickness L _S and it can be certified by calling the thickness L _B of the bone portion (step S6).

In this case, in the graph shown in FIG. 6, based on the combination of the pixel values I _H and I _L that are the detection values of the flat panel detector 4, the common soft tissue thickness for the pixel values I _H and I _L Find a set of length L _S and bone thickness L _B. More specifically, for example, when I _H = 0.3 and I _L = 0.5, a plane parallel to the XY plane showing I _H = 0.3 in FIG. A combination of L _S and L _B indicated by the position of a perpendicular line drawn from the intersection of the curved line indicating the relationship between I _H and L _S and L _B to the XY plane, and I _L = 0.5 in FIG. Among the combinations of L _S and L _B indicated by the positions of the perpendiculars drawn from the intersections of the plane parallel to the XY plane and the curved surface indicating the relationship between I _H , L _S and L _B to the XY plane, they coincide with each other A combination of L _S and L _B is found and identified as soft tissue thickness L _S and bone thickness L _B.

Next, the image processing unit 19 executes the image processing based on the thickness L _B of the certified soft tissue thickness L _S and the bone part (step S7), and the display unit 7 of the soft tissue or bone A subtraction image is displayed (step S8).

As described above, according to the X-ray imaging method and X-ray imaging apparatus according to the present invention, the flat panel detector 4 stored in the reference table 18 can be stored in the reference table 18 without actually executing the subtraction process using the subtraction unit 17. The soft tissue thickness L _S and the bone thickness L _B are specified based on the combination of the detected pixel values I _H and I _L , and a subtraction image can be obtained based on this. At this time, since a continuous spectrum in X-rays is considered, a clearer subtraction image can be obtained.

DESCRIPTION OF SYMBOLS 1 Subject 2 Table 3 X-ray tube 4 Flat panel detector 5 Control part 6 X-ray tube control part 7 Display part 11 High voltage memory 12 LOG conversion part 13 Weighting part 14 High voltage memory 15 LOG conversion part 16 Weighting part 17 Subtraction unit 18 Reference table 19 Image processing unit

Claims (12)

In an X-ray imaging method for imaging an X-ray image by detecting an X-ray irradiated from an X-ray tube and passing through a subject with an X-ray detector,
Based on the distribution of X-ray energy when a high voltage and a low voltage are applied to the X-ray tube and the mass attenuation coefficient corresponding to the X-ray energy, a high voltage and a low voltage are applied to the X-ray tube. A calculation step of calculating the detected value of the X-ray detector at a plurality of times by changing the thickness of the soft tissue and the bone, and
Based on the calculation result in the calculation step, data indicating the relationship between the detection value of the X-ray detector and the thickness of the soft tissue and bone when the high voltage and low voltage are applied to the X-ray tube as a table A storage step for storing;
A high-voltage imaging step of detecting, by the X-ray detector, X-rays that have passed through the subject when a high voltage is applied to the X-ray tube;
A low voltage imaging step of detecting, by the X-ray detector, X-rays that have passed through a subject when a low voltage is applied to the X-ray tube;
Data indicating the relationship between the detection value of the X-ray detector and the thickness of the soft tissue and bone when the high voltage and the low voltage are applied to the X-ray tube stored in the storage process, and the high voltage imaging process An image processing step of creating an image of a soft tissue and a bone portion from the detected value of the X-ray detected in step S and the detected value of the X-ray detected in the low-voltage imaging step;
A display step for displaying images of soft tissue and bone created in the image processing step;
An X-ray imaging method comprising: The X-ray imaging method according to claim 1,
When a high voltage is applied to the X-ray tube and the X-ray detector directly irradiates the X-ray detector with the X-ray detector, the detected value of the X-ray by the X-ray detector is I _OH , and a low voltage is applied to the X-ray tube. When the X-ray tube directly irradiates the X-ray detector with the X-ray detector, the X-ray detector detects the X-ray detection value as I _OL , and applies a high voltage to the X-ray tube to reduce the soft tissue thickness L _S , When the bone portion passes only by the thickness L _B, the detected value of the X-ray by the X-ray detector is I _H , a low voltage is applied to the X-ray tube, the soft tissue thickness L _S , and the bone portion thickness L _B only passes X-ray detector I detected value of X-rays by _L when _is irradiated from the mass attenuation coefficient mu _S, the X-ray tube when the X-rays emitted from the X-ray tube to pass through the soft tissue When the mass attenuation coefficient when X-rays pass through the bone part is μ _B and the X-ray energy is E, in the calculation step, calculation is performed based on the following formula: X-ray imaging method to be executed.

The X-ray imaging method according to claim 1 or 2,
By complementing the relationship between the detected value of the X-ray detector and the thickness of the soft tissue and the bone when the high voltage and the low voltage are applied to the X-ray tube calculated in the calculation step, the X-ray An X-ray imaging method further comprising a normalizing step of normalizing data indicating a relationship between a detection value of an X-ray detector and a thickness of a soft tissue and a bone when a high voltage and a low voltage are applied to a tube. In an X-ray imaging method for imaging an X-ray image by detecting an X-ray irradiated from an X-ray tube and passing through a subject with an X-ray detector,
A high-voltage imaging step of detecting, by the X-ray detector, X-rays that have passed through the subject when a high voltage is applied to the X-ray tube;
A low voltage imaging step of detecting, by the X-ray detector, X-rays that have passed through a subject when a low voltage is applied to the X-ray tube;
A table showing the relationship between the detection value of the X-ray detector and the thickness of the soft tissue and bone when the high voltage and the low voltage are applied to the X-ray tube, and the X-ray detected in the high voltage imaging process An image processing step for creating images of soft tissue and bone from detection values and detection values of X-rays detected in the low-voltage imaging step;
A display step for displaying images of soft tissue and bone created in the image processing step;
An X-ray imaging method comprising: The X-ray imaging method according to claim 4,
A table showing the relationship between the detection value of the X-ray detector and the thickness of the soft tissue and bone when a high voltage and a low voltage are applied to the X-ray tube,
Based on the distribution of X-ray energy when a high voltage and a low voltage are applied to the X-ray tube and the mass attenuation coefficient corresponding to the X-ray energy, a high voltage and a low voltage are applied to the X-ray tube. A calculation step of calculating the detected value of the X-ray detector at a plurality of times by changing the thickness of the soft tissue and the bone, and
Based on the calculation result in the calculation step, data indicating the relationship between the detection value of the X-ray detector and the thickness of the soft tissue and bone when the high voltage and low voltage are applied to the X-ray tube as a table A storage step for storing;
X-ray imaging method created by The X-ray imaging method according to claim 5,
When a high voltage is applied to the X-ray tube and the X-ray detector directly irradiates the X-ray detector with the X-ray detector, the detected value of the X-ray by the X-ray detector is I _OH , and a low voltage is applied to the X-ray tube. When the X-ray tube directly irradiates the X-ray detector with the X-ray detector, the X-ray detector detects the X-ray detection value as I _OL , and applies a high voltage to the X-ray tube to reduce the soft tissue thickness L _S , When the bone portion passes only by the thickness L _B, the detected value of the X-ray by the X-ray detector is I _H , a low voltage is applied to the X-ray tube, the soft tissue thickness L _S , and the bone portion thickness L _B only passes X-ray detector I detected value of X-rays by _L when _is irradiated from the mass attenuation coefficient mu _S, the X-ray tube when the X-rays emitted from the X-ray tube to pass through the soft tissue When the mass attenuation coefficient when X-rays pass through the bone part is μ _B and the X-ray energy is E, in the calculation step, calculation is performed based on the following formula: X-ray imaging method to be executed.

The X-ray imaging method according to claim 5 or 6,
By complementing the relationship between the detected value of the X-ray detector and the thickness of the soft tissue and the bone when the high voltage and the low voltage are applied to the X-ray tube calculated in the calculation step, the X-ray An X-ray imaging method further comprising a normalizing step of normalizing data indicating a relationship between a detection value of an X-ray detector and a thickness of a soft tissue and a bone when a high voltage and a low voltage are applied to a tube. X-ray imaging that captures a subtraction X-ray image by detecting X-rays irradiated from the X-ray tube and passing through the subject when a high voltage and a low voltage are applied to the X-ray tube. In the subtraction shooting data creation method used in the method,
Based on the distribution of X-ray energy when a high voltage and a low voltage are applied to the X-ray tube and the mass attenuation coefficient corresponding to the X-ray energy, a high voltage and a low voltage are applied to the X-ray tube. A calculation step of calculating the detected value of the X-ray detector at a plurality of times by changing the thickness of the soft tissue and the bone, and
Based on the calculation result in the calculation step, data indicating the relationship between the detection value of the X-ray detector and the thickness of the soft tissue and bone when the high voltage and low voltage are applied to the X-ray tube as a table A storage step for storing;
A method for creating data for subtraction imaging, comprising: An X-ray tube that irradiates the subject with X-rays;
An X-ray tube control unit for controlling a tube voltage applied to the X-ray tube;
An X-ray detector for detecting X-rays irradiated from the X-ray tube and passing through the subject;
Based on the distribution of X-ray energy when a high voltage and a low voltage are applied to the X-ray tube and the mass attenuation coefficient corresponding to the X-ray energy, a high voltage and a low voltage are applied to the X-ray tube. X-rays when a high voltage and a low voltage are applied to the X-ray tube by calculating the detection value of the X-ray detector at a given time by changing the thickness of the soft tissue and the bone part a plurality of times A storage unit for storing a table in which data indicating the relationship between the detection value of the detector and the thickness of the soft tissue and the bone is recorded;
X-ray measurement values by the X-ray detector when a high voltage value is applied to the X-ray tube, and X-ray values by the X-ray detector when a low voltage value is applied to the X-ray tube From the measured value and the data indicating the relationship between the detected value of the X-ray detector and the thickness of the soft tissue and bone when the high voltage and low voltage are applied to the X-ray tube stored in the storage unit, An image processor that creates images of soft tissue and bone;
A display unit for displaying images of soft tissues and bones created by the image processing unit;
An X-ray imaging apparatus comprising: An X-ray tube that irradiates the subject with X-rays;
An X-ray tube control unit for controlling a tube voltage applied to the X-ray tube;
An X-ray detector for detecting X-rays irradiated from the X-ray tube and passing through the subject;
A storage unit for storing data indicating a relationship between a detection value of the X-ray detector and a soft tissue and a bone thickness when a high voltage and a low voltage are applied to the X-ray tube;
X-ray measurement values by the X-ray detector when a high voltage value is applied to the X-ray tube, and X-ray values by the X-ray detector when a low voltage value is applied to the X-ray tube From the measured value and the data indicating the relationship between the detected value of the X-ray detector and the thickness of the soft tissue and bone when the high voltage and low voltage are applied to the X-ray tube stored in the storage unit, An image processor that creates images of soft tissue and bone;
A display unit for displaying images of soft tissues and bones created by the image processing unit;
An X-ray imaging apparatus comprising: The X-ray imaging apparatus according to claim 10,
Data indicating the relationship between the detected value of the X-ray detector and the thickness of the soft tissue and bone when the high voltage and low voltage are applied to the X-ray tube,
Based on the distribution of X-ray energy when a high voltage and a low voltage are applied to the X-ray tube and the mass attenuation coefficient corresponding to the X-ray energy, a high voltage and a low voltage are applied to the X-ray tube. An X-ray imaging apparatus comprising a table created by calculating the detection value of the X-ray detector at a time by changing the thickness of the soft tissue and the bone part a plurality of times. X-ray imaging that captures a subtraction X-ray image by detecting X-rays irradiated from the X-ray tube and passing through the subject when a high voltage and a low voltage are applied to the X-ray tube. A storage medium storing subtraction shooting data used in the method,
Based on the distribution of X-ray energy when a high voltage and a low voltage are applied to the X-ray tube and the mass attenuation coefficient corresponding to the X-ray energy, a high voltage and a low voltage are applied to the X-ray tube. When the detected value of the X-ray detector is calculated multiple times by changing the thickness of the soft tissue and bone,
Based on this calculation result, data indicating the relationship between the detected value of the X-ray detector and the thickness of the soft tissue and bone when the high voltage and the low voltage are applied to the X-ray tube is stored as a table. A storage medium storing subtraction imaging data characterized by the above.

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