JP2008142343A - Digital mammographic instrument and program - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve the decision precision of imaging conditions in a digital mammographic instrument. <P>SOLUTION: The digital mammographic instrument is equipped with an X-ray tube 2 generating X rays, a compression mechanism 11 compressing a subject's breast, a plane detector 5 detecting X rays transmitting the compressed breast, a thickness sensor 13 measuring the thickness of the compressed breast, a pressure sensor 12 measuring pressure applied to the breast by the compression mechanism, a recording section 14 repeatedly recording the pressure and thickness measured during the period from the start of compression to the end of compression by the compression mechanism, and photographing conditions deciding sections 16 and 17 deciding on photographing conditions on the basis of the thickness of the breast at the time when pressurization ends and pressure applied to the breast at the time when compression ends, thickness at the time when compression ends or the rate of change of compression with respect to time. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a digital mammography apparatus that takes an image with an X-ray tube and a flat panel detector by compressing a breast in a slab shape with a compression plate.

  As a conventional technique for imaging a breast, there is a breast radiography that expands a mammary gland by compressing the breast and collects a two-dimensional image from one direction. The mammary gland in the breast has a three-dimensional structure consisting of small bunches such as grapes. For this reason, the breasts are compressed and stretched thinly, thereby reducing the overlap of the mammary glands and enabling X-ray imaging with a lower dose.

  In a mammography device using a conventional film, an AEC detector (automatic exposure control X-ray) that determines the quality of radiography based on the thickness of the breast when compression is completed (called compression thickness) and places the detector on the back of the cassette The dose is controlled during imaging with the detector. As is well known, the radiation quality is determined by a combination of the tube voltage and the radiation filter, and the dose is determined by the tube current and the X-ray exposure time.

  A digital mammography apparatus using a flat panel detector (flat panel detector; also referred to as FPD) cannot use AEC because FPD hardly transmits X-rays. Therefore, in general, pre-imaging (referred to as test imaging) is performed before the main imaging for determining both the radiation quality and the dose before imaging. The radiation quality and dose for test imaging are determined from the compression thickness. A method is used in which the quality and dose are finally determined from image information obtained by test imaging, and actual imaging is performed under the conditions.

  Even with breasts compressed to the same thickness, the X-ray absorption coefficient differs by a maximum of about 6 times due to factors such as differences in mammary gland density. Therefore, as described above, when the test imaging condition is determined only from the compression thickness, the incident dose of the FPD has a maximum error of 6 times. Since the image data collected by the test imaging is used only for determining the conditions of the actual imaging, if the dose is too high, unnecessary exposure is given. On the other hand, if the amount is too small, the image data becomes close to the noise level, so that the error of the analysis result becomes large, and the error of the photographing condition determined in this way becomes large.

  An object of the present invention is to improve the determination accuracy of photographing conditions in a digital mammography apparatus.

In the first aspect of the present invention, a digital mammography apparatus includes an X-ray tube that generates X-rays, a compression mechanism that compresses a breast of a subject, and a flat panel detector that detects X-rays transmitted through the compressed breast. A thickness sensor that measures the thickness of the compressed breast, a pressure sensor that measures the pressure applied to the breast by the compression mechanism, and the measurement over a period from the start of compression by the compression mechanism to the completion of compression. A recording section that repeatedly records the pressure and thickness, the thickness of the breast at the time of completion of compression, the pressure applied to the breast at the time of completion of compression, and the pressure relative to the thickness or time at the time of completion of compression. An imaging condition determining unit that determines the imaging condition based on the change ratio;
In a second aspect of the present invention, a digital mammography apparatus includes an X-ray tube that generates X-rays, a compression mechanism that compresses a breast of a subject, and a flat panel detector that detects X-rays transmitted through the compressed breast. A thickness sensor that measures the thickness of the compressed breast, a pressure sensor that measures the pressure applied to the breast by the compression mechanism, and the measurement over a period from the start of compression by the compression mechanism to the completion of compression. A recording section that repeatedly records the pressure and thickness, the thickness of the breast when the compression is completed, the pressure applied to the breast when the compression is completed, and the change of the pressure with respect to the thickness or time when the compression is completed A photographing condition determining unit for determining a photographing condition based on one of the ratios.
In a third aspect of the present invention, a digital mammography apparatus includes an X-ray tube that generates X-rays, a compression mechanism that compresses a breast of a subject, and a flat panel detector that detects X-rays transmitted through the compressed breast. A thickness sensor that measures the thickness of the compressed breast, a pressure sensor that measures the pressure applied to the breast by the compression mechanism, and the measurement over a period from the start of compression by the compression mechanism to the completion of compression. A recording unit that repeatedly records the pressure and thickness, and an imaging condition determination unit that determines imaging conditions based on the measured breast thickness and the measured pressure applied to the breast.
According to a fourth aspect of the present invention, there is provided a program for determining imaging conditions of a digital mammography apparatus for imaging a breast of a subject compressed by a compression mechanism with an X-ray tube and a flat panel detector, the compression of the breast Correction based on means for determining imaging conditions based on thickness at the time of completion, pressure applied to the breast at the time of completion of compression, and rate of change of the pressure with respect to the thickness or time at the time of completion of compression A program for causing a computer to realize means for determining a coefficient and means for correcting the determined photographing condition with the determined correction coefficient.

  ADVANTAGE OF THE INVENTION According to this invention, the determination precision of imaging conditions can be improved in a digital mammography apparatus.

  Hereinafter, embodiments of a digital mammography apparatus according to the present invention will be described with reference to the drawings. Note that the present invention can be provided as a program for causing a computer to determine photographing conditions incorporated in a digital mammography apparatus, and as a computer-readable storage medium storing the program.

  FIG. 1 shows the configuration of a digital mammography apparatus according to this embodiment. The digital mammography apparatus has an X-ray imaging table 1. As shown in FIG. 2, the support mechanism 4 is provided with the X-ray tube 2 at one end of the U-shaped arm 20. The X-ray tube 2 receives a high voltage (tube voltage) from the high voltage generator 3 and receives a filament current to generate X-rays. A radiation quality adjusting filter 21 is detachably provided on the front surface of the X-ray tube 2 together with an irradiation field limiting mask. The X-ray quality is determined by the combination of the quality control filter 21 and the tube voltage. The tube current (mA) is controlled by the filament current, and the dose is determined by the time product (mAs) of the tube current.

  An imaging table 23 is attached to the other end of the U-shaped arm 20 so as to face the X-ray tube 2. A flat detector (flat panel detector; FPD) 5 is installed inside the imaging table 23. A grid for removing scattered radiation and improving image contrast is disposed on the front surface of the flat detector 5. The flat detector 5 is a direct conversion type that directly converts incident X-rays into an electrical signal, or an indirect conversion type semiconductor that converts incident X-rays into light with a phosphor and converts the light into electrical signals. It has an element. The plurality of semiconductor detection elements are arranged in a two-dimensional lattice pattern. Signal charges generated by X-ray incidence by a plurality of semiconductor detection elements are output as digital signals via the data acquisition unit 6. In the data collecting unit 6, the signal charge is amplified and converted into a voltage by an amplifier, and converted into a digital signal by an analog / digital converter.

  A compression mechanism 11 is mounted on the column portion of the U-shaped arm 20. The compression mechanism 11 includes a compression plate 22, a movement mechanism thereof, and a movement drive unit. The compression plate 22 moves in a direction approaching / separating from the imaging table 23 while maintaining a state parallel to the imaging table 23. The movement of the compression plate 22 is typically performed by foot operation of the foot pedal 24. The breast of the subject is compressed in a slab shape between the imaging table 23 and the compression plate 22. The thickness of the breast compressed by the compression plate 22 is measured by the thickness sensor 13. The thickness of the breast (referred to as breast thickness) is equivalent to the distance between the compression plate 22 and the imaging table 23. Since the imaging stand 23 is fixed, a position sensor such as a rotary encoder that measures the position of the compression plate 22 is actually applied to the thickness sensor 13. The pressure applied to the breast by the compression plate 22 (referred to as compression force) is measured by the pressure sensor 12 attached to at least one of the compression plate 22 and the imaging table 23. Breast thickness data and compression force data are recorded in the compression force / breast thickness recording unit 14 together with the time code. In particular, during the period from the start of compression to the completion of compression, breast thickness and compression force data are repeatedly recorded in the compression force / breast thickness recording unit 14 at a constant cycle.

  The digital mammography apparatus according to the present embodiment includes a structure such as the support mechanism 4, a system control unit 7, an imaging control unit 8, an operation unit 9, an image configuration / storage unit (not shown), a compression force / breast thickness recording unit 14, An imaging condition table / correction table 15, an imaging condition determination unit 16, and an imaging condition correction unit 17 are provided. The imaging control unit 8 controls the high voltage generation unit 3, the support mechanism 4, and the data collection unit 6 according to the imaging conditions set in advance, thereby performing imaging for the breast of the subject pressed into a slab shape. Let it run. As described above, the compression force / breast thickness recording unit 14 records the breast thickness data measured by the thickness sensor 13 and the compression force data measured by the pressure sensor 12 together with the time code.

  The photographing condition table / correction table 15 stores a pre-configured photographing condition table 101 for test photographing illustrated in FIG. 3 and a pre-configured correction table 103 for correcting photographing conditions for test photographing shown in FIG. To do. These test condition shooting condition table 101 and test condition correction table 103 are used when a test mode for performing test shooting is selected in order to determine shooting conditions for actual shooting.

  In the imaging condition table 101 for test imaging, a plurality of imaging conditions applied for test imaging are associated with a range of a plurality of breast thicknesses (compression thickness) at the time of completion of compression. The imaging conditions include a tube voltage, a quality control filter 21, and a dose (mAs). In the photographing condition table 101 for test photographing, photographing conditions associated with the compression thickness are initially determined as photographing conditions at the time of test photographing.

  The correction table 103 for correcting the shooting conditions for the test shooting includes the shooting conditions for the test shooting initially determined using the shooting condition table 101 for the test shooting for a plurality of combinations of the correction coefficient and the compression thickness. A plurality of correction values for correction are associated with each other. The correction coefficient is calculated by the imaging condition correction unit 17 as (b / a) from the compression force (a) when the compression is completed and the inclination (b) of the compression force when the compression is completed. The slope (b) of the compression force at the time of completion of compression is given as the ratio of the change in compression force to the change in breast thickness at the time of completion of compression. The slope (b) of the compression force at the time of completion of compression may be given as a change amount of the compression force per unit time at the time of completion of compression. Further, the correction coefficient may be one of the compression force (a) at the time of completion of compression and the inclination (b) of the compression force at the time of completion of compression.

  In the present embodiment, the photographing condition to be corrected is a tube voltage, and other filters and mAs are not corrected.

  Similarly, the photographing condition table / correction table 15 includes a pre-configured photographing condition table 105 for main photographing illustrated in FIG. 5 and a pre-configured photographing condition correction for main photographing shown in FIG. The correction table 107 is stored. These photographing condition table 105 for main photographing and correction table 107 for correcting photographing conditions for main photographing do not perform test photographing in order to determine photographing conditions for main photographing, and use the compression information after the compression is completed. This is used when the direct mode for determining the shooting condition and immediately performing the main shooting is selected.

  In the imaging condition table 105 for main imaging, similarly to the table 101, a plurality of imaging conditions applied for main imaging are associated with ranges of a plurality of breast thicknesses (compression thicknesses) at the time of completion of compression. ing. In the photographing condition table 105 for the main photographing, the photographing condition associated with the compression thickness is initially determined as the photographing condition at the time of the main photographing.

  The correction table 107 for correcting the shooting conditions for the main shooting is based on the shooting conditions for the main shooting initially determined by using the shooting condition table 105 for the main shooting for a plurality of combinations of the correction coefficient and the compression thickness. A plurality of correction values for correction are associated with each other. The correction coefficient is equivalent to the correction coefficient used in the correction table 103 for correcting the shooting conditions for test shooting.

  When the test mode for performing test imaging is selected to determine the imaging conditions for the main imaging, the imaging condition determining unit 16 uses the imaging condition table 101 for test imaging to determine the compression thickness of the breast when compression is completed. The associated shooting conditions for test shooting are determined as initial shooting conditions for test shooting. The imaging condition determination unit 16 also has a function of analyzing the image obtained by the test imaging and determining the imaging conditions for the main imaging based on the analysis result and the corrected test imaging conditions, as in the conventional case. I have.

  Further, when the direct mode for directly determining the shooting conditions for the main shooting from the compression result without selecting the test shooting is selected, the shooting condition determining unit 16 uses the shooting condition table 105 for the main shooting to determine when the compression is completed. The imaging conditions for the main imaging associated with the compression thickness of the breast are determined as the initial imaging conditions for the main imaging.

  When the test mode is selected, the imaging condition correction unit 17 calculates the compression force gradient (b) when the compression is completed, and the compression force gradient (b) when the compression is completed and the compression force ( a), the correction coefficient (b / a) is calculated, and the correction value of the test imaging condition associated with the correction coefficient (b / a) and the compression thickness (c) of the breast at the time of completion of compression, The shooting condition for test shooting, which is initially determined using the shooting condition table 101 for test shooting, is corrected using the correction value specified by the correction table 103 for shooting condition correction for test shooting.

  Further, when the direct mode is selected, the imaging condition correction unit 17 calculates the compression force gradient (b) at the time of completion of compression, and the compression force gradient (b) at the time of completion of compression and the compression at the time of completion of compression. The correction coefficient (b / a) is calculated from the force (a), and the correction value of the imaging condition associated with the correction coefficient (b / a) and the compression thickness (c) of the breast at the time of compression completion Is determined from the correction table 107 for correcting shooting conditions for main shooting, and the shooting conditions for main shooting initially determined using the shooting condition table 105 for main shooting are corrected based on the specified correction value.

  Next, a procedure for determining shooting conditions according to the present embodiment will be described. As described above, the digital mammography apparatus according to the present embodiment is equipped with the test mode and the direct mode, and the imaging condition is determined under any mode selected from the operation unit 9. First, the test mode will be described, and then the direct mode will be described.

  FIG. 7 schematically shows a photographing condition determination procedure in the test mode. The radiographer operates the foot pedal 24 to move the compression plate 22 and compresses the subject's breast. When the compression force reaches a predetermined threshold, the movement of the compression plate 22 is stopped and the compression is completed. During the period from the start of compression to the completion of compression, breast thickness data measured by the thickness sensor 13 and compression force data measured by the pressure sensor 12 are respectively measured under the control of the system control unit 7. It is recorded in the compression force / breast thickness recording unit 14 repeatedly at a constant cycle together with the time code.

  Upon completion of the compression, the imaging condition determination unit 16 uses the imaging condition table 101 for test imaging, and the imaging condition for test imaging associated with the compression thickness of the breast at the time of completion of compression is the initial value for test imaging. Is determined as an appropriate shooting condition.

  Further, the imaging condition correction unit 17 calculates the inclination (b) of the compression force at the time of completion of compression, and corrects it from the inclination (b) of the compression force at the time of completion of compression and the compression force (a) at the time of completion of compression. A coefficient (b / a) is calculated. Further, the imaging condition correction unit 17 calculates the correction value for the test imaging condition from the correction coefficient (b / a) and the compression thickness (c) of the breast when the compression is completed, and the correction table 103 for correcting the imaging condition for the test imaging. Identify from. Then, the shooting conditions for test shooting, which are initially determined using the shooting condition table 101 for test shooting, are corrected by the specified correction value.

  Specifically, the correction target is a tube voltage, and the correction value is given as an increase / decrease value with respect to the tube voltage. This correction value is added to the initially determined tube voltage for test photography. Thereby, the corrected tube voltage for test photographing is determined. In mammography, the difference in the X-ray absorption coefficient of the breast is generally adjusted by the radiation quality. Therefore, the tube voltage is to be corrected. However, the imaging condition correction target is not limited to the tube voltage, and the quality filter and mAs may be corrected as the correction target.

  Here, when the density of the mammary gland is high and the amount of fat is small, it is hard and elastic. On the other hand, when the density of the mammary gland is low and the fat is high, it is soft and has a low elasticity. Therefore, when the density of the mammary gland is high, the correction coefficient (b / a) as a ratio of the compression force (a) at the time of completion of compression and the inclination (b) of the compression force is high, and the correction coefficient (b / A) is lowered. Therefore, the correction coefficient (b / a) is used as an index representing the mammary gland density, and this is used to correct the test imaging conditions.

  Test shooting is performed under the control of the shooting control unit 8 according to the corrected test shooting conditions. After the test shooting, the shooting condition determination unit 16 analyzes the image obtained by the test shooting and determines the shooting conditions for the main shooting based on the analysis result and the corrected test shooting conditions. The

  This test mode improves the quality and dose accuracy of test imaging, so that imaging conditions for main imaging can be determined with high accuracy. As a result, high image quality of the main photographing can be ensured, unsuccessful photographing can be prevented, and other effects such as shortening of time, ensuring of diagnostic ability, and reduction of exposure can be expected.

  Next, the direct mode will be described. FIG. 8 schematically shows a shooting condition determination procedure in the direct mode. As in the test mode, the radiographer operates the foot pedal 24 to move the compression plate 22 and compresses the subject's breast. Upon completion of compression, the imaging condition determination unit 16 uses the imaging condition table 105 for actual imaging, and the imaging conditions for actual imaging associated with the compression thickness of the breast at the time of completion of compression are the initial conditions for actual imaging. Is determined as an appropriate shooting condition.

  The imaging condition correction unit 17 calculates a correction coefficient (b / a) in the same manner as in the test mode. From the correction coefficient (b / a) and the compression thickness (c) of the breast when compression is completed, The correction value for the main photographing condition is specified from the correction table 107 for correcting the photographing condition for the main photographing. Then, the shooting conditions for main shooting that are initially determined using the shooting condition table 105 for main shooting are corrected by the specified correction value.

  The main shooting is performed under the control of the shooting control unit 8 according to the corrected main shooting conditions.

  With this direct mode, it is possible to accurately determine the shooting conditions for the main shooting without test shooting. As a result, high image quality can be ensured in the actual photographing, and failure photographing can be prevented, and other effects such as time reduction, ensuring diagnostic ability, and reducing exposure can be expected.

  Note that the present invention is not limited to the above-described embodiment as it is, and can be embodied by modifying the constituent elements without departing from the scope of the invention in the implementation stage. In addition, various inventions can be formed by appropriately combining a plurality of constituent elements disclosed in the embodiment. For example, some components may be deleted from all the components shown in the embodiment. Furthermore, constituent elements over different embodiments may be appropriately combined.

The figure which shows the structure of the digital mammography apparatus which concerns on embodiment of this invention. The perspective view of the support mechanism of the digital mammography apparatus of FIG. The figure which shows the imaging condition table for test imaging | photography memorize | stored in the imaging condition table / correction table memory | storage part of FIG. FIG. 3 is a diagram showing a correction table for correcting shooting conditions for test shooting stored in the shooting condition table / correction table storage unit of FIG. 1. The figure which shows the imaging condition table for the main imaging | photography memorize | stored in the imaging condition table / correction table memory | storage part of FIG. FIG. 3 is a diagram illustrating a correction table for correcting shooting conditions for main shooting stored in a shooting condition table / correction table storage unit in FIG. 1. FIG. 5 is a diagram illustrating a first routine for determining shooting conditions for main shooting in the present embodiment. The figure which shows the 2nd routine for determining the imaging | photography condition of this imaging | photography in this embodiment.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 2 ... X-ray tube, 3 ... High voltage generator, 4 ... Support mechanism, 5 ... Planar detector, 6 ... Data collection part, 7 ... System control part, 8 ... Imaging | photography control part, 9 ... Operation part, 10 ... Image Storage unit 11: Compression mechanism 12 ... Pressure sensor 13 Position sensor 14 Compression force / breast thickness recording unit 15 Imaging condition table / correction table storage unit 16 Imaging condition determining unit 17 Imaging condition Correction unit.

Claims (11)

An X-ray tube that generates X-rays;
A compression mechanism that compresses the breast of the subject;
A flat panel detector for detecting X-rays transmitted through the compressed breast;
A thickness sensor for measuring the thickness of the compressed breast;
A pressure sensor for measuring the pressure applied to the breast by the compression mechanism;
A recording unit that repeatedly records the measured pressure and thickness over a period from the start of compression to the completion of compression by the compression mechanism;
Imaging that determines imaging conditions based on the thickness of the breast when the compression is completed, the pressure applied to the breast when the compression is completed, and the rate of change of the pressure with respect to the thickness or time when the compression is completed A digital mammography apparatus comprising a condition determination unit.   The digital mammography apparatus according to claim 1, wherein the photographing condition determination unit determines photographing conditions in test photographing performed before main photographing.   The digital mammography apparatus according to claim 1, wherein the photographing condition determination unit determines a photographing condition in actual photographing.   The imaging condition determination unit performs the imaging based on the thickness of the breast at the time of completion of compression, the pressure applied to the breast at the time of completion of compression, and the rate of change of the pressure with respect to the thickness or time at the time of completion of compression. The tube voltage and the radiation quality filter included in the conditions are determined, and the tube current and the X-ray exposure time included in the imaging conditions are determined based on the thickness of the breast at the time when the compression is completed. Item 9. A digital mammography apparatus according to Item 1.   The imaging condition determination unit is configured to determine an imaging condition corresponding to the thickness of the breast at the time of completion of compression, a pressure applied to the breast at the time of completion of compression, and a rate of change of the pressure with respect to the thickness at the time of completion of compression. The digital mammography apparatus according to claim 1, wherein the correction is performed by:   6. The correction coefficient determining unit according to claim 5, further comprising: a correction coefficient determining unit that determines a correction coefficient based on a pressure applied to the breast at the time when the compression is completed and a rate of change of the pressure with respect to the thickness at the time when the compression is completed. Digital mammography device.   A table that associates imaging conditions with the thickness of the breast at the time of completion of compression, and a combination of the pressure applied to the breast at the time of completion of compression and the rate of change of the pressure with respect to the thickness at the time of completion of compression. 6. The digital mammography apparatus according to claim 5, further comprising a storage unit that stores a table for associating correction coefficients.   A memory for storing a table associating imaging conditions with the combination of the thickness of the breast at the time of completion of compression, the pressure applied to the breast at the time of completion of compression, and the rate of change of the pressure with respect to the thickness at the time of completion of compression. The digital mammography apparatus according to claim 1, further comprising a unit. An X-ray tube that generates X-rays;
A compression mechanism that compresses the breast of the subject;
A flat panel detector for detecting X-rays transmitted through the compressed breast;
A thickness sensor for measuring the thickness of the compressed breast;
A pressure sensor for measuring the pressure applied to the breast by the compression mechanism;
A recording unit that repeatedly records the measured pressure and thickness over a period from the start of compression to the completion of compression by the compression mechanism;
An imaging condition is determined based on the thickness of the breast at the time of completion of compression, and one of the pressure applied to the breast at the time of completion of compression and the rate of change of the pressure with respect to the thickness or time at the time of completion of compression. A digital mammography apparatus, comprising: An X-ray tube that generates X-rays;
A compression mechanism that compresses the breast of the subject;
A flat panel detector for detecting X-rays transmitted through the compressed breast;
A thickness sensor for measuring the thickness of the compressed breast;
A pressure sensor for measuring the pressure applied to the breast by the compression mechanism;
A recording unit that repeatedly records the measured pressure and thickness over a period from the start of compression to the completion of compression by the compression mechanism;
A digital mammography apparatus comprising: an imaging condition determining unit that determines imaging conditions based on the measured breast thickness and the measured pressure applied to the breast. In a program for determining imaging conditions of a digital mammography apparatus for imaging a breast of a subject compressed by a compression mechanism with an X-ray tube and a flat detector,
Means for determining imaging conditions based on the thickness of the breast when compression is completed;
Means for determining a correction factor based on the pressure on the breast at the time of completion of compression and the rate of change of the pressure with respect to the thickness or time at the time of completion of compression;
A program for causing a computer to realize means for correcting the determined photographing condition by the determined correction coefficient.

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