JP2013111214A - X-ray photographing equipment - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide X-ray photographing equipment capable of correcting the fluctuation of a pixel value caused by the error of X-ray quantity in a case that photographing is repeatedly executed.SOLUTION: This X-ray photographing equipment is constituted so that the pixel value of an X-ray image measured in measurement on and after the second time is multiplied by the ratio of the integrated value of X rays operated in the first measuring process and the integrated value of X rays operated in the measuring process on and after the second time. Therefore, even in a case that the measurement of bone density is repeatedly executed, the fluctuation of a pixel value caused by the error of X-ray quantity can be corrected.

Description

  The present invention relates to an X-ray imaging apparatus including an X-ray tube and an X-ray detector that detects X-rays irradiated from the X-ray tube and passed through a subject.

  FIG. 7 is a schematic diagram of such a conventional X-ray imaging apparatus.

  This X-ray imaging apparatus includes a table 2 on which a subject 1 is placed, an X-ray irradiation unit 3 having an X-ray tube 31 and a collimator 33, a flat panel detector 4 as an X-ray detector, A scattered radiation removal grid 42 and a phototimer 41 are provided between the examiner 1 and the flat panel detector 4. In this X-ray imaging apparatus, the subject 1 is irradiated with X-rays that are irradiated from the X-ray tube 31 and whose X-ray irradiation field is limited by the collimator 33. The scattered radiation is removed from the X-rays that have passed through the subject 1 by the scattered radiation removal grid 42, and is detected as an X-ray image by the flat panel detector 4.

  Further, when the phototimer 41 is irradiated with X-rays that have passed through the subject 1, the X-rays are converted into light by the fluorescent screen in the phototimer 41 and detected by a photosensor. Then, the fluorescence amount at this time is compared with a preset reference value, and when the fluorescence amount reaches the reference value, the X-ray irradiation is automatically stopped.

  Such a phototimer is described in Patent Document 1, for example.

Published Japanese Patent Application Laid-Open No. 2002-257939

  Since the X-ray imaging apparatus using the above-described phototimer 41 stops the X-ray irradiation when the X-ray dose that has passed through the subject 1 reaches a certain value, the imaging is always performed with a constant X-ray dose. can do. However, the tube current of the X-ray tube may be indirectly controlled by heating of the filament of the X-ray tube. It cannot be said that a line is taken.

  For example, in an X-ray imaging apparatus that performs X-ray imaging for follow-up observation such as bone density measurement, imaging is performed with high reproducibility, no matter how many times the same subject is imaged under fixed imaging conditions. Therefore, a system with a low fluctuation rate and high accuracy is required. In addition, for example, in an X-ray imaging apparatus that joins a plurality of detection images captured every predetermined time while moving the X-ray tube and the X-ray detector in the body axis direction of the subject, It is necessary to maintain a constant detection condition for pixel values of a plurality of images to be taken.

  The present invention has been made to solve the above-described problem, and an object of the present invention is to provide an X-ray imaging apparatus capable of correcting pixel value fluctuations due to an X-ray dose error when performing repeated imaging. To do.

  The invention according to claim 1 is an X-ray tube, an X-ray detector that detects X-rays emitted from the X-ray tube and passed through the subject, and is emitted from the X-ray tube and reaches the subject. An X-ray sensor for measuring the intensity of X-rays before the correction, and a correction means for correcting the detection value of the X-ray detector based on an integrated value of the X-ray dose measured by the X-ray sensor. .

  According to a second aspect of the present invention, in the first aspect of the present invention, the correction means is configured to obtain a reference X-ray dose integrated value and an imaging with respect to the pixel value of the X-ray image detected by the X-ray detector. Sometimes, the pixel value of the corrected X-ray image is created by multiplying the ratio with the integrated value of the X-ray dose measured by the X-ray sensor.

  According to a third aspect of the present invention, in the first or second aspect of the present invention, when the integrated value of the X-ray dose emitted from the X-ray tube and passed through the subject becomes a constant value, The X-ray sensor measures the X-ray intensity between the start of X-ray irradiation and the stop of X-ray irradiation due to the action of the phototimer. To do.

  According to a fourth aspect of the present invention, in the invention according to any one of the first to third aspects, bone density measurement is performed by observing the same site.

  According to a fifth aspect of the present invention, in the invention according to any one of the first to third aspects, the moving mechanism that moves the X-ray tube and the X-ray detector in the body axis direction of the subject. The images detected by the X-ray detector taken at regular intervals are connected together.

  According to the sixth aspect of the present invention, the X-ray detector detects X-rays emitted from the X-ray tube and passed through the subject, thereby measuring the pixel value of the X-ray image and emitting from the X-ray tube. A first imaging step of measuring the intensity of the X-ray before reaching the subject and calculating the integrated value, and detecting the X-ray emitted from the X-ray tube and passing through the subject by the X-ray detector Measuring the pixel value of the X-ray image by measuring the intensity of the X-ray emitted from the X-ray tube before reaching the subject, and calculating the integrated value; A correction step of multiplying a ratio between the integrated value calculated in the first imaging step and the integrated value calculated in the second imaging step by the pixel value of the X-ray image measured in the second imaging step. Features.

  According to the first, second, and sixth aspects of the invention, the detection value of the X-ray detector is corrected by the integrated value of the X-ray dose measured by the X-ray sensor, so that repeated imaging is performed. It is possible to correct the fluctuation of the pixel value due to the X-ray intensity error.

  According to the third aspect of the present invention, it is possible to correct the fluctuation of the pixel value due to the error of the X-ray intensity at that time while maintaining the X-ray integrated value constant by the phototimer.

  According to the fourth aspect of the present invention, when bone density measurement for observing the same site is performed, it is possible to perform imaging with a low variation rate and high accuracy.

  According to the fifth aspect of the present invention, it is possible to maintain a constant detection condition for the pixel values of a plurality of images when stitching together the detected images obtained by the X-ray detector taken every certain time. .

1 is a schematic diagram of an X-ray imaging apparatus according to a first embodiment of the present invention. It is a block diagram which shows the main control systems in the X-ray imaging apparatus which concerns on 1st Embodiment of this invention. It is a graph which shows the intensity | strength of X-ray when using X-ray imaging apparatus and performing X-ray irradiation 5 times trial on the same X-ray conditions. It is a schematic diagram of the X-ray imaging apparatus which concerns on 2nd Embodiment of this invention. It is a block diagram which shows the main control systems in the X-ray imaging apparatus which concerns on 2nd Embodiment of this invention. It is explanatory drawing which shows typically the joining process of an image. It is a schematic diagram of the conventional X-ray imaging apparatus.

  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 first embodiment of the present invention.

  This X-ray imaging apparatus performs bone density measurement by observing the bone part of the same site at regular intervals. The X-ray imaging apparatus includes a table 2 on which a subject 1 is placed, an X-ray irradiation unit 3 including an X-ray tube 31, an X-ray sensor 32, and a collimator 33, and a flat panel as an X-ray detector. The detector 4 includes a scattered radiation removal grid 42 and a phototimer 41 disposed between the subject 1 and the flat panel detector 4. In this X-ray imaging apparatus, the subject 1 is irradiated with X-rays that are irradiated from the X-ray tube 31 and whose X-ray irradiation field is limited by the collimator 33. The scattered radiation is removed from the X-rays that have passed through the subject 1 by the scattered radiation removal grid 42, and is detected as an X-ray image by the flat panel detector 4.

  When the X-ray emitted from the X-ray tube 31 and passing through the subject 1 is irradiated to the phototimer 41, the X-ray is converted into light by the fluorescent plate in the phototimer 41 and detected by the photosensor. . Then, the fluorescence amount at this time is compared with a preset reference value, and when the fluorescence amount reaches the reference value, the X-ray irradiation is automatically stopped.

  Further, in this X-ray imaging apparatus, the X-ray dose of X-rays emitted from the X-ray tube 31 and reaching the subject 1 using the X-ray sensor 32 disposed in the X-ray irradiation unit 3. The integrated value is measured. As the X-ray sensor 32, a sensor that measures the intensity of X-rays such as a phototimer, a fluorescent light meter, or an X-ray dosimeter can be used.

  FIG. 2 is a block diagram showing a main control system in the X-ray imaging apparatus according to the first embodiment of the present invention.

  This X-ray imaging apparatus includes a control unit 60 that controls the entire apparatus. The control unit 60 includes an integrated value calculation unit 61, a coefficient calculation unit 62, a coefficient multiplication unit 63, and a storage unit 64, which will be described later. The control unit 60 is connected to the above-described X-ray tube 31, flat panel detector 4, X-ray sensor 32, and phototimer 41 via an interface 66. The control unit 60 is also connected to a display unit 5 including a liquid crystal display panel, a CRT, and the like for displaying an X-ray image through an interface 66.

  FIG. 3 is a graph showing the X-ray intensity when this X-ray imaging apparatus is used and X-ray irradiation is performed five times on the same X-ray condition.

  In this figure, the horizontal axis indicates time, and the vertical axis indicates the output current value of the X-ray sensor 32, that is, the intensity of X-rays. As shown in this figure, even when X-ray irradiation is performed under the same X-ray conditions, the change in X-ray intensity differs for each irradiation. In addition, in this figure, the area of the area | region enclosed by each graph and a horizontal axis represents the integrated value of X-ray dose.

  Table 1 below shows the area (integrated value of X-ray dose) of the area surrounded by each graph and the horizontal axis when five X-ray irradiations were performed on a trial basis, as described above, and at that time It is a table | surface which shows the relationship with the pixel value etc. which were detected by the flat panel detector 4. FIG.

  The “pixel value” detected by the flat panel detector 4 in Table 1 represents, for example, an average value of pixel values in a 3 cm × 3 cm region near the center of the flat panel detector 4. In addition, “dispersion” in this table indicates a dispersion value when five trial X-ray irradiations are performed. The “variation rate” indicates a value (%) calculated by [(variance / average) × 100]. The “coefficient” indicates a ratio between the value of “area” at the first X-ray irradiation and the value of “area” at the second and subsequent X-ray irradiations. Further, “after correction” indicates a value obtained by multiplying “pixel value” by “coefficient”.

  As is apparent from this table, when five X-ray irradiations were performed on the same X-ray condition on a trial basis, the pixel values detected by the flat panel detector 4 were also shown in the graph and the horizontal axis in FIG. There is a relatively large variation in the integrated value of the X-ray dose expressed by the area of the region surrounded by. However, the variation rate of the pixel value after correction obtained by multiplying the pixel value by the ratio of the integrated value of the first X-ray dose as a reference and the measured value of the integrated value of the X-ray dose after the second time is extremely high. It is small. For this reason, in the X-ray imaging apparatus according to the present invention, with respect to the pixel value of the X-ray image detected by the flat panel detector 4, the X-ray integrated value of the reference X-ray dose and the X-ray measured by the X-ray sensor 32 at the time of imaging. The pixel value of the X-ray image is corrected by multiplying the ratio of the integrated value of the dose with the measured value.

  When bone density measurement is performed by the X-ray imaging apparatus according to the first embodiment, imaging is performed as usual during the first imaging. That is, X-rays are emitted from the X-ray tube 31, and the X-rays that have passed through the subject 1 and the scattered radiation removal grid 42 are detected by the flat panel detector 4. Then, when the integrated value of the X-ray dose detected by the phototimer 41 reaches the reference value, the X-ray irradiation is automatically stopped. Then, the X-ray image is displayed on the display unit 5 based on the pixel value of the X-ray image obtained by detecting the X-ray with the flat panel detector 4 at that time. The X-ray dose emitted from the X-ray tube 31 at this time is measured by the X-ray sensor 32, and the integrated value is calculated by the integrated value calculating unit 61 in the control unit 60. The integrated value of the X-ray dose is stored in the storage unit 64.

  Even during the second and subsequent imaging for bone density measurement, X-rays are emitted from the X-ray tube 31 and X-rays that have passed through the subject 1 and the scattered radiation removal grid 42 are detected by the flat panel detector 4. Then, when the integrated value of the X-ray dose detected by the phototimer 41 reaches the reference value, the X-ray irradiation is automatically stopped. Also in this case, the X-ray dose emitted from the X-ray tube 31 is measured by the X-ray sensor 32, and the integrated value is calculated by the integrated value calculating unit 61 in the control unit 60.

  At the time of the second and subsequent imaging, the coefficient calculation unit 62 in the control unit 60 performs the integrated value of the X-ray dose emitted from the X-ray tube 31 at the time of the first measurement and the X value at the time of the second measurement. The coefficient is calculated based on the ratio with the integrated value of the X-ray dose emitted from the tube 31. In addition, the coefficient multiplication unit 63 corrects the pixel value by multiplying the pixel value of the X-ray image obtained by detecting the X-rays by the flat panel detector 4 by this coefficient. An X-ray image is displayed on the display unit 5 based on the pixel value multiplied by the coefficient.

  As described above, when the bone density is measured by the X-ray imaging apparatus according to the present invention, the integrated value of the X-rays calculated in the first measurement process and the X-rays calculated in the second and subsequent measurement processes. Since the pixel value of the X-ray image measured at the second and subsequent measurements is multiplied by the ratio with the integrated value, the pixel value due to the X-ray dose error can be obtained even when repeatedly measuring bone density. Variations can be corrected.

  Next, another embodiment of the present invention will be described. FIG. 4 is a schematic diagram of an X-ray imaging apparatus according to the second embodiment of the present invention. FIG. 5 is a block diagram showing a main control system in the X-ray imaging apparatus according to the second embodiment of the present invention. In addition, about the member same as 1st Embodiment mentioned above, the same code | symbol is attached | subjected and detailed description is abbreviate | omitted.

  The X-ray imaging apparatus according to the second embodiment includes an X-ray tube 31, an X-ray sensor 32, a collimator 33, a flat panel detector 4, a scattered radiation removal grid 42, and a phototimer 41. A moving mechanism 6 that moves in synchronization with the axial direction is provided, and a detection image obtained by the flat panel detector 4 that is captured at regular intervals is joined by a joining unit 65 in the control unit 60.

  FIG. 6 is an explanatory diagram schematically showing image joining processing.

  When images detected by the flat panel detector 4 are captured at regular intervals while moving the X-ray tube 31 in the body axis direction of the subject 1, for example, images P1 to P6 shown in FIG. 6 can be obtained. it can. In FIG. 6, only six images are shown for convenience of explanation, but in practice, a large number of images covering the entire imaging region are obtained. Then, the stitching unit 65 performs a stitching process on these images, so that a captured image P shown in FIG. 6 is formed.

  In such an X-ray imaging apparatus, when the X-ray tube 31 is not always lit but X-rays are emitted every time imaging is performed, as shown in FIG. However, the X-ray intensity is different. For this reason, also in the X-ray imaging apparatus according to this embodiment, when the second and subsequent images are captured, the coefficient calculation unit 62 in the control unit 60 removes from the X-ray tube 31 during the first image capture. A coefficient is calculated by a ratio between the integrated value of the emitted X-ray dose and the integrated value of the X-ray dose emitted from the X-ray tube 31 at the time of the second image capture. In addition, the coefficient multiplication unit 63 corrects the pixel value by multiplying the pixel value of the X-ray image obtained by detecting the X-rays by the flat panel detector 4 by this coefficient. Then, the stitching unit 65 stitches the images based on the pixel value multiplied by the coefficient, and then the stitched X-ray image is displayed on the display unit 5.

DESCRIPTION OF SYMBOLS 1 Subject 2 Table 3 X-ray irradiation part 4 Flat panel detector 5 Display part 6 Movement mechanism 31 X-ray tube 32 X-ray sensor 33 Collimator 41 Phototimer 42 Scatter removal grid 60 Control part 61 Integrated value calculating part 62 Coefficient calculating part 63 Coefficient multiplying unit 64 Storage unit 65 Joining unit

Claims (6)

An X-ray tube;
An X-ray detector for detecting X-rays emitted from the X-ray tube and passing through the subject;
An X-ray sensor that measures the intensity of X-rays emitted from the X-ray tube and reaching the subject;
Correction means for correcting the detection value of the X-ray detector by the integrated value of the X-ray dose measured by the X-ray sensor;
An X-ray imaging apparatus comprising: The X-ray imaging apparatus according to claim 1,
The correction means multiplies the pixel value of the X-ray image detected by the X-ray detector by the ratio of the reference X-ray integrated value and the X-ray integrated value measured by the X-ray sensor during imaging. An X-ray imaging apparatus that creates pixel values of the corrected X-ray image. The X-ray imaging apparatus according to claim 1 or 2,
A photo timer for stopping X-ray irradiation when the integrated value of the X-ray dose emitted from the X-ray tube and passed through the subject becomes a constant value;
The X-ray sensor is an X-ray imaging apparatus that measures X-ray intensity between the start of X-ray irradiation and the stop of X-ray irradiation by the action of the phototimer. The X-ray imaging apparatus according to any one of claims 1 to 3,
An X-ray imaging apparatus that performs bone density measurement to observe the same site. The X-ray imaging apparatus according to any one of claims 1 to 3,
An X-ray imaging apparatus comprising a moving mechanism for moving the X-ray tube and the X-ray detector in the body axis direction of the subject, and connecting detection images obtained by the X-ray detector taken at regular intervals. A pixel value of an X-ray image is measured by detecting an X-ray emitted from the X-ray tube and passing through the subject by an X-ray detector, and before being emitted from the X-ray tube and reaching the subject. A first imaging step of measuring the X-ray intensity and calculating the integrated value;
A pixel value of an X-ray image is measured by detecting an X-ray emitted from the X-ray tube and passing through the subject by an X-ray detector, and before being emitted from the X-ray tube and reaching the subject. A second imaging step of measuring the X-ray intensity and calculating the integrated value;
A correction step of multiplying a pixel value of the X-ray image measured in the second imaging step by a ratio between the integrated value calculated in the first imaging step and the integrated value calculated in the second imaging step;
An X-ray imaging method comprising:

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