JP2006312030A - X-ray ct apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an X-ray CT apparatus capable of displaying the objectively quantified fat content of the region of interest from CT values which are measured based on image information acquired by using the X-ray CT apparatus. <P>SOLUTION: The X-ray CT apparatus comprises an HD 44 which stores therein a first table where fat contents are respectively associated with the values of the ratios of CT values, a CT value measurement unit 62 which irradiates an object with X-rays under a plurality of different irradiation conditions, and which obtains actually-measured CT values for the respective irradiation conditions, and a fat content extraction unit 65 which calculates the ratio of the actually-measured CT values for the respective irradiation conditions, and which extracts the fat content corresponding to the ratio of the actually-measured CT values, by referring to the first table. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a technique for generating an image inside a subject based on projection data obtained by exposing the subject to X-rays, and X-ray CT for quantifying the fat content in a predetermined region from the image. It relates to the device.

  Recent progress in X-ray CT (Computed Tomography) apparatus is remarkable. In response to the strong demand from the medical field to capture images with higher definition (higher resolution) and a wider range, multi-slice X-ray CT apparatuses have been developed and have become quite popular. The multi-slice X-ray CT apparatus has a structure in which an X-ray source that radiates cone beam X-rays that spread in the slicing direction (longitudinal direction of the couch top) and a plurality of detection element rows are arranged in the slicing direction. And a two-dimensional detector, which is configured to perform a helical scan. Thereby, compared with a single slice X-ray CT apparatus, volume data over a wide range inside the subject can be obtained with high accuracy and in a short time.

Such an X-ray CT apparatus is disclosed, for example, in Patent Document 1 below.
JP 2004-305527 A

  In such a conventional X-ray CT apparatus, for example, when a liver portion of a subject is imaged, the examiner's visual impression on the obtained image, or a CT value based on a region of interest (ROI: Region Of Interest) The degree of progression of fatty liver may be judged from measurements. However, the degree of progression of fatty liver largely depends on the subjectivity of the examiner.

  In addition, the measured CT value also tends to be dependent on size due to the difference in the physique of the subject. Therefore, judging the degree of progression of fatty liver based on the CT value measured without taking into account the physique of the subject was not always an appropriate diagnosis.

  The present invention has been made in consideration of the above-mentioned circumstances, and objectively quantifies the fat content in a predetermined region from CT values measured based on image information obtained using an X-ray CT apparatus. An object is to provide an X-ray CT apparatus capable of displaying.

  In order to solve the above-described problem, an X-ray CT apparatus according to the present invention stores a first table that associates a fat content with each of a plurality of different CT value ratio values, A X-ray is exposed to the subject under the plurality of different irradiation conditions, and a CT value measurement unit that measures the actual CT value for each irradiation condition; and a ratio of the actual CT values between the irradiation conditions; A fat content extraction unit that extracts the fat content corresponding to the ratio of the measured CT values with reference to the first table;

  The X-ray CT apparatus according to the present invention is obtained by exposing X-rays to a desired water phantom containing a predetermined amount of fat under a plurality of different irradiation conditions in order to solve the above-described problems. In addition, a first storage device that stores in advance a first table that correlates the ratio of the sample CT value between the irradiation conditions of the water phantom and the fat content, and the water equivalent thickness of each of the water phantoms of different sizes A second storage device that stores in advance a second table in which sample CT values are stored for each of the plurality of different irradiation conditions; and X-rays are irradiated to the subject under the plurality of different irradiation conditions. Referring to the second table, the CT value measuring unit that measures the actual CT value for each time, the subject size measuring unit that measures the water equivalent thickness of the subject, and the desired water phantom size and the Subject size measurement A size-dependent correction unit that calculates a size-dependent correction coefficient based on the size of the subject measured by the unit, and multiplies the actual CT value by a size-dependent correction coefficient under the same irradiation condition to correct the actual CT value; A fat coefficient calculation unit that calculates a ratio of measured CT values corrected by the size-dependent correction unit as a fat coefficient, and contains the fat content corresponding to the fat coefficient with reference to the first table And a fat percentage extraction unit.

  In order to solve the above-described problem, an X-ray CT apparatus according to the present invention stores a first table in which a fat content is associated with each of a plurality of different CT value differences, A X-ray is exposed to the subject under the plurality of different irradiation conditions, and a CT value measurement unit that measures an actual CT value for each irradiation condition; and a difference between the actual CT values between the irradiation conditions; A fat content extraction unit that extracts the fat content corresponding to the difference between the measured CT values with reference to the first table;

  The X-ray CT apparatus according to the present invention is obtained by exposing X-rays to a desired water phantom containing a predetermined amount of fat under a plurality of different irradiation conditions in order to solve the above-described problems. In addition, a first storage device that stores in advance a first table that correlates the difference in sample CT value between the irradiation conditions of the water phantom and the fat content, and the water equivalent thickness of each of the water phantoms of different sizes A second storage device that stores in advance a second table in which sample CT values are stored for each of the plurality of different irradiation conditions; and X-rays are irradiated to the subject under the plurality of different irradiation conditions. Referring to the second table, the CT value measuring unit that measures the actual CT value for each time, the subject size measuring unit that measures the water equivalent thickness of the subject, and the desired water phantom size and the Subject size measurement A size-dependent correction unit that calculates a size-dependent correction coefficient based on the size of the subject measured by the unit, and multiplies the actual CT value by a size-dependent correction coefficient under the same irradiation condition to correct the actual CT value; A fat coefficient calculation unit that calculates a difference between measured CT values corrected by the size dependent correction unit as a fat coefficient, and a fat content corresponding to the fat coefficient is extracted with reference to the first table And a fat percentage extraction unit.

  In order to solve the above-described problem, an X-ray CT apparatus according to the present invention stores a conversion formula calculated based on a fat content for a difference value between a plurality of different CT values, and a subject. And calculating a difference between the CT value measuring unit for measuring the measured CT value for each irradiation condition and the measured CT value for each irradiation condition, With reference to the content fat percentage conversion unit for converting the difference between the measured CT values into the content fat percentage.

  In order to solve the above-described problem, an X-ray CT apparatus according to the present invention stores a first table that associates a fat content with respect to a comparison value of a plurality of different CT values, and a subject. A CT value measuring unit that emits X-rays under the plurality of different irradiation conditions and measures an actual CT value for each irradiation condition, and calculates a comparison value of the actual CT values for each of the irradiation conditions, A fat content extraction unit that extracts a fat content corresponding to the comparison value of the measured CT values with reference to the table;

  The X-ray CT apparatus according to the present invention can objectively quantify and display the fat content in a predetermined region from CT values measured based on image information obtained using the X-ray CT apparatus. .

  An embodiment of an X-ray CT apparatus according to the present invention will be described with reference to the accompanying drawings.

  FIG. 1 is a block diagram showing a hardware configuration of the X-ray CT apparatus.

  FIG. 1 shows an X-ray CT apparatus 1, in which a gantry apparatus 2 configured to collect data on a subject (human body) P and a subject P are moved. The couch device 3 for operating the X-ray CT apparatus 1 and an operation console 4 for performing input and image display are provided.

  The gantry device 2 of the X-ray CT apparatus 1 includes an X-ray tube 12, an X-ray detector 13, an aperture 14, a data acquisition device 15, a high voltage generator 16, an aperture drive device 17, a rotation drive device 18, and a main controller 19. And IF (InterFace) 20a and 20b.

  In addition, the X-ray tube 12, the X-ray detector 13, the diaphragm 14, and the data collection device 15 are installed in the rotating unit 21 of the gantry device 2. The rotating unit 21 is configured to rotate the X-ray tube 12 and the X-ray detector 13 around the subject P in a state where the X-ray tube 12 and the X-ray detector 13 face each other.

  The X-ray tube 12 generates X-rays according to the tube voltage supplied from the high voltage generator 16.

  The X-ray detector 13 is a two-dimensional array detector (also referred to as a multi-slice detector). The X-ray detection element has a square detection surface of 0.5 mm × 0.5 mm, for example. In the X-ray detector 13, for example, 916 X-ray detection elements are arranged in the channel direction, and for example, 64 or more rows are arranged in parallel along the slice direction (column direction of the detector).

  The diaphragm 14 adjusts the exposure range in the slice direction of the X-rays exposed to the subject P under the control of the diaphragm driving device 17. That is, the X-ray exposure range in the slice direction can be changed by adjusting the opening of the diaphragm 14 by the diaphragm driving device 17.

  The data acquisition device 15 is generally called DAS (Data Acquisition System), amplifies the signal output from the X-ray detector 13 for each channel, and further converts it into a digital signal. The converted data (raw data) is supplied to the external operation console 4 via the IF 20b of the gantry device 2.

  The main controller 19 controls the high voltage generation device 16, the aperture drive device 17, the rotation drive device 18, the data collection device 15 and the like based on the control signal input from the operation console 4 via the IF 20a.

  The couch device 3 of the X-ray CT apparatus 1 is provided with a couchtop 31 on which the subject P is placed and a couchtop drive device 32 that moves the couchtop 31 along the slice direction. The central portion of the rotating unit 21 has an opening, and the subject P placed on the top 31 of the opening is inserted. A direction parallel to the rotation center axis of the rotating unit 21 is defined as a Z-axis direction (slice direction), and planes orthogonal to the Z-axis direction are defined as an X-axis direction and a Y-axis direction.

  The operation console 4 of the X-ray CT apparatus 1 is a so-called workstation configured based on a computer, and is capable of mutual communication with a network N such as a hospital backbone LAN (Local Area Network). The operation console 4 is mainly composed of basic hardware such as a CPU (Central Processing Unit) 41, a memory 42, an HD (Hard Disc) 44, IFs 45a, 45b, 45c, an input device 46, and a display device 47. . The CPU 41 is interconnected to each hardware component constituting the operation console 4 via a bus as a common signal transmission path. Note that the operation console 4 may include a recording medium drive 48.

  The CPU 41 executes a program stored in the memory 42 when a command is input by operating the input device 46 by an examiner such as a doctor. Alternatively, the CPU 41 is read from a program stored in the HD 44, a program transferred from the network N, received by the IF 45c and installed in the HD 44, or read from a recording medium attached to the recording medium drive 48 and installed in the HD 44. The loaded program is loaded into the memory 42 and executed.

  The memory 42 has elements such as a ROM (Read Only Memory) and a RAM (Random Access Memory), and stores an IPL (Initial Program Loading), a BIOS (Basic Input / Output System), a memory of the CPU 41, and a data memory. This is a storage device used for temporary storage of data.

  The HD 44 is configured by a nonvolatile semiconductor memory or the like. The HD 44 is a storage device that stores programs installed in the operation console 4 (including application programs, OS (Operating System), and the like) and data. In addition, the OS can be provided with a GUI (Graphical User Interface) that can use the graphics for displaying information to the examiner and perform basic operations with the input device 46.

  The IFs 45a, 45b, and 45c perform communication control according to each standard. The IFs 45a and 45b communicate with the gantry device 2 and are connected to the IFs 20a and 20b of the gantry device 2, respectively. Further, the IF 45c has a function capable of being connected to the network N through a telephone line, whereby the operation console 4 can be connected to the network N network from the IF 45c.

  The input device 46 is a pointing device that can be operated by the examiner, and an input signal according to the operation is sent to the CPU 41.

  An example of the display device 47 is a monitor. An image is displayed on the display device 47 by expanding the image data or the like in a memory such as a VRAM (Video Random Access Memory (not shown)) that expands the image data to be displayed.

  The recording medium drive 48 is detachable from the recording medium, reads out data (including a program) recorded on the recording medium, outputs the data on the bus, and outputs data supplied through the bus. Write to a recording medium. Such a recording medium can be provided as so-called package software.

  FIG. 2 is a block diagram showing a first embodiment of an X-ray CT apparatus according to the present invention.

  In the hardware configuration shown in FIG. 1, when the CPU 41 of the operation console 4 of the X-ray CT apparatus 1 executes a program, the operation console 4 has a preprocessing unit 51, a scattered radiation correction unit 52, and a reconstruction processing unit 53. And functions as the image processing unit 54. In addition, although each part 51 thru | or 54 shall function by CPU41 running a program, it is not limited to that case. Each unit 51 to 54 may be provided in the operation console 4 as hardware.

  The preprocessing unit 51 generates projection data by performing logarithmic conversion processing and correction processing such as sensitivity correction on the raw data input from the device data collection device 15 of the gantry device 2 via the IF 45b shown in FIG. To do.

  The scattered radiation correction unit 52 performs scattered radiation removal processing on the projection data input from the preprocessing unit 51. The scattered radiation correction unit 52 removes scattered radiation based on the value of the projection data within the X-ray exposure range, and the magnitude of the projection data to be subjected to the scattered radiation correction or the value of the adjacent projection data. The scattered radiation estimated from the above is subtracted from the target projection data to perform the scattered radiation correction. The projection data after removal of the scattered X-rays is sent to the reconstruction processing unit 53.

  The image reconstruction processing unit 53 performs reconstruction methods such as fan beam reconstruction assuming that the X-ray paths in the slice direction are parallel, cone beam reconstruction considering the X-ray exposure angle (cone angle) in the slice direction, and the like. Is used to reconstruct an image of biological information inside the subject P.

  The image processing unit 54 performs various image processing on the image data stored in the storage device such as the HD 44 to generate a display image. The image processing unit 54 includes a subject size measurement unit 61, a CT value measurement unit 62, a size dependence correction unit 63, a fat coefficient calculation unit 64, and a contained fat percentage extraction unit 65 in order to generate a display image.

  Here, the first table and the second table are stored in advance in the storage device. The first table measures CT values under a plurality of different irradiation conditions with respect to the fat content as sample CT values, and shows the relationship between the fat content and the ratio of each sample CT value measured under each irradiation condition. Is. On the other hand, the second table is for correcting the measured CT value according to the size of the subject P. Note that the first table and the second table may be stored in separate storage devices.

  FIG. 3 is a diagram showing an outline for acquiring the first table.

  In order to obtain the first table in the preparatory stage before the inspection, first, samples of various fat contents are prepared. For example, samples containing 10%, 20%, 30%, 40%, 50% and 60% by weight of fat for a fixed amount of water phantom are prepared. FIG. 3 is images obtained by photographing the samples having various fat percentages using the X-ray CT apparatus 1 in the same manner as the normal subject P.

  FIG. 4 is a diagram illustrating an example of the first table.

The first table shown in FIG. 4 shows, as sample CT values, CT values measured under different irradiation conditions, such as tube voltage, for samples with various fat percentages. For example, a sample CT value measured by irradiating a sample with a fat content of 10% at a tube voltage of ¹²⁰ kV is ¹²⁰ C _10%, and a sample CT value measured by irradiating the sample at a tube voltage of 100 kV is ¹⁰⁰ C _10%. And a sample CT value measured by irradiating a sample with a fat content of 20% at a tube voltage of ¹²⁰ kV with ¹²⁰ C _20%, and a sample CT value measured by irradiating the sample with a tube voltage of 100 kV at ¹⁰⁰ C _20%. And a sample CT value measured by irradiating a sample having a fat content of 30% at a tube voltage of ¹²⁰ kV with ¹²⁰ C _30%, and a sample CT value measured by irradiating the sample with a tube voltage of 100 kV at ¹⁰⁰ C _30% When the sample CT value and ¹²⁰ C _40% as measured by irradiating the sample tube voltage 120kV of fat content is 40%, the tube collector of the same sample Samples CT value and ¹⁰⁰ C _40% as measured by irradiating at 100 kV, and the sample CT value ¹²⁰ C _50% of fat content was measured by irradiating 50% of the sample in the tube voltage 120 kV, a tube voltage of the same sample The sample CT value measured by irradiating at 100 kV is ¹⁰⁰ C _50% , the sample CT value measured by irradiating a sample with a fat content of 60% at a tube voltage of 120 kV is ¹²⁰ C _60% , and the sample is tube voltage The sample CT value measured by irradiation at 100 kV is defined as ¹⁰⁰ C _60% . Hereinafter, the case where the irradiation condition is a tube voltage will be described. However, the irradiation condition is not limited to the tube voltage, and may be, for example, a tube current (mA).

Further, the first table shown in FIG. 4 associates the fat content with the comparison values of the sample CT values measured at a plurality of different tube voltages. For example, the fat content is associated with the value of the ratio of sample CT values measured at a plurality of different tube voltages. Specifically, the fat content 10% of the sample values of the ratio α of the sample CT value calculated from ^{_{(120 C 10% / 100 C}} 10%), the fat content of 20% of the sample ⁽¹²⁰ C _20% / ^100C _20% ) of the sample CT value ratio β, the sample of the ratio of the sample CT value calculated from ( ^120C _30% / ^100C _30% ) of the sample of 30% fat content The value γ is a sample CT value ratio δ calculated from ( ¹²⁰ C _40% / ¹⁰⁰ C _40% ) for a sample with a fat content of 40%, and ( ¹²⁰ C _{50 for} a sample with a fat content of 50%. _% / ¹⁰⁰ C _50% ), the sample CT value ratio value ε calculated from ( ¹²⁰ C _60% / ¹⁰⁰ C _60% ) is the sample CT value ratio value ζ. Each Associates. In this embodiment, as a representative example, different tube voltages are set to 120 kV and 100 kV (tube currents are respectively constant).

  As shown in FIG. 4, in this embodiment, the ratio of the sample CT value for each sample of each fat content is defined as “fat coefficient”. That is, in the present embodiment, since the tube voltage is varied between 120 kV and 100 kV as different irradiation conditions, the ratio between the sample CT value when the tube voltage is 120 kV and the sample CT value when the tube voltage is 100 kV. Is calculated, and the fat content is made to correspond to this result.

  FIG. 5 is a diagram illustrating an example of the second table.

  As shown in FIG. 5, the second table exposes X-rays to a normal water phantom, and samples corresponding to different water equivalent thicknesses as a predetermined FOV (Field Of View; effective field of view, eg, 400 mm). It is the table which acquired CT value for every different irradiation conditions (for example, different tube voltage 120kV and 100kV). This is a table for correcting the CT value error caused by the size of the subject P even under the same irradiation condition and in the same FOV.

For example, as shown in FIG. 5, when the water equivalent thickness of the water phantom is 180 mm, 240 mm, 320 mm, and 400 mm under FOV = 400 mm, the sample CT values are obtained when the tube voltage is 120 kV and 100 kV. taking measurement. Here, the sample CT value with a tube voltage of ¹²⁰ kV and a water equivalent thickness of 180 mm is ¹²⁰ C ₁₈₀ , the sample CT value with the tube voltage and a water equivalent thickness of 240 mm is ¹²⁰ C _240, and the water equivalent thickness with the tube voltage is ¹²⁰ C _240. The sample CT value of 320 mm is ¹²⁰ C ₃₂₀ , the sample CT value of the same tube voltage and water equivalent thickness of 400 mm is ¹²⁰ C ₄₀₀ , the sample CT value of the tube voltage 100 kV and water equivalent thickness of 180 mm is ¹⁰⁰ C _180, and the same. Sample CT value with tube voltage and water equivalent thickness of 240 mm is ¹⁰⁰ C ₂₄₀ , sample CT value with tube voltage and water equivalent thickness of 320 mm is ¹⁰⁰ C ₃₂₀ , sample CT value with tube voltage and water equivalent thickness of 400 mm Are defined as ¹⁰⁰ C ₄₀₀ , respectively.

  In addition, the subject size measuring unit 61 shown in FIG. 2 exposes the subject P to the subject P based on the scan data of the subject P stored in the storage device after the subject P is exposed to X-rays at the examination stage. The size of the specimen P is measured.

  The CT value measuring unit 62 reads a plurality of CT images for each irradiation condition on the subject P from the storage device after the subject P is irradiated with X-rays. The CT value measuring unit 62 averages the CT values of the CT images read from the storage device based on the region of interest input by the examiner using the input device 46 with respect to the scan data of the subject P. The measured CT value is measured for each irradiation condition.

  The size-dependent correction unit 63 corrects the CT value error caused by the size of the subject P with reference to the second table for each actually measured CT value measured by the CT value measuring unit 62.

For example, the water equivalent thickness of the water phantom when creating the first table is 240 mm under FOV = 400 mm, and the water equivalent thickness of the subject P measured by the subject size measuring unit 61 for the region of interest is Consider the case of 320 mm under FOV = 400 mm. Size dependent correction unit 63, the measured CT value of the object P measured by CT value measuring section 62 under conditions of a tube voltage 120 kV, the second water-equivalent thickness obtained from the table of the ratio of ⁽¹²⁰ _C ^240/120 _{C 320} ) to obtain the “corrected measured CT value at a tube voltage of 120 kV”. On the other hand, the size-dependent correction unit 63 adds the ratio of the water equivalent thickness obtained from the second table to the actual CT value of the subject P measured by the CT value measurement unit 62 under the condition of the tube voltage of 100 kV ( ¹⁰⁰ C ₂₄₀ / ¹⁰⁰ C ₃₂₀ ) is multiplied to obtain the “corrected actual CT value at a tube voltage of 100 kV”.

In this ^embodiment, defines a respective size dependent correction coefficient the ratio of the water-equivalent thickness shown as _{^{(120 C 240/120 C 320}} ) and _{^{(100 C 240/120 C 320}} ). That is, in the above example, the size dependent correction coefficient ¹²⁰ k in the tube voltage 120kV a _{^{(120 C 240/120 C 320}} ), the size dependent correction coefficient ¹⁰⁰ k in the tube voltage _{^{100kV (100 C 240/100 C}} 320) It is.

  The fat coefficient calculation unit 64 shown in FIG. 2 calculates the ratio of the measured CT values under different irradiation conditions measured by the CT value measurement unit 62. The ratio is, for example, (actual CT value at a tube voltage of 120 kV) / (actual CT value at a tube voltage of 100 kV), but when the correction by the size-dependent correction unit 63 is performed, (at a tube voltage of 120 kV) Corrected actual CT value) / (corrected actual CT value at a tube voltage of 100 kV).

  The fat content extraction unit 65 refers to the first table stored in the storage device, and calculates the ratio of the measured CT values obtained by the fat coefficient calculating unit 64 or the corrected ratio of the measured CT values. The content fat percentage corresponding to the value, that is, the numerical value corresponding to the fat coefficient is extracted. The contained fat percentage extracted by the contained fat percentage extracting unit 65 is displayed by the display device 47, and is quantified and displayed as an objective contained fat percentage in a predetermined region in the scanogram.

  Next, the operation of the image processing unit 54 in the first embodiment of the X-ray CT apparatus according to the present invention will be described with reference to the flowchart shown in FIG.

  First, after the reconstruction processing is completed by the reconstruction processing unit 53 shown in FIG. 2, the image processing unit 54 acquires scan data from a storage device such as the HD 44 (step S1), and the display device 47 The scan data is displayed as a scan image.

  Next, the region of interest is set when the examiner designates a predetermined region for the scanogram displayed on the display device 47 (step S2).

  FIG. 7 is a diagram illustrating an example of a display screen including a scanogram when specifying a predetermined area.

  The designation of the predetermined area on the display screen shown in FIG. 7 is performed by processing the coordinates on the scan data specified by the input device 46 such as a pointing device.

  Next, the CT value measuring unit 62 shown in FIG. 2 measures the actual measured CT values averaged for different irradiation conditions for the region of interest set in step S2 (step S3), and displays the CT image on the display device 47. Let

  FIG. 8 is a diagram showing an example of a display screen including a CT image when the tube voltage is 120 kV. On the other hand, FIG. 9 is a diagram showing an example of a display screen including a CT image when the tube voltage is 100 kV.

  Next, the size dependent correction unit 63 shown in FIG. 2 calculates the water equivalent thickness in the region of interest set in step S2 for the scan data, and refers to the second table to calculate the size dependent correction coefficient. Calculate (step S4).

Thereafter, the size dependent correction unit 63 multiplies the actual CT value of the corresponding irradiation condition by the size dependent correction coefficient calculated for each irradiation condition to correct an error in the actual CT value caused by the size of the subject P (step). S5). For example, when the CT actual measurement value in the region of interest when the tube voltage is ₁₂₀ kV is C ₁₂₀ and the average CT actual measurement value in the region of interest when the tube voltage is 100 kV is C ₁₀₀ , “corrected at the tube voltage of ₁₂₀ kV” The “actual CT value” is obtained as C ₁₂₀ × ¹²⁰ k, and the “corrected actual CT value at a tube voltage of 100 kV” is obtained as C ₁₀₀ × ¹⁰⁰ k ₂₄₀ (see ¹²⁰ k and ¹⁰⁰ k, see above. .)

Next, the fat coefficient calculating unit 64 uses the “corrected measured CT value at the tube voltage of 120 kV” and the “corrected measured CT value at the tube voltage of 100 kV” obtained by the size-dependent correction unit 63, The ratio ((C ₁₂₀ × ¹²⁰ k) / (C ₁₀₀ × ¹⁰⁰ k)) is calculated as a fat coefficient (actual value) (step S6).

The fat content extraction unit 65 refers to the first table stored in the storage device with respect to the fat coefficient (measured value) obtained in this manner, and the fat coefficient (sample) indicating a numerical value that almost matches. The fat content rate associated with (value) is extracted (step S7). For example, when the fat coefficient (actual value) calculated by the fat coefficient calculation unit 64 ((C ₁₂₀ × ¹²⁰ k) / (C ₁₀₀ × ¹⁰⁰ k)) is close to the fat coefficient γ shown in the first table, The content fat percentage “30%” is extracted from the table 1. The fat coefficient γ is a numerical value calculated by ( ¹²⁰ C _30% / ¹⁰⁰ C _30% ) with reference to the first table.

  In addition, when there is no fat coefficient (α to ζ) as the sample values shown in FIG.

  The contained fat percentage extracted by the contained fat percentage extracting unit 65 is displayed on the display device 47 so that the examiner can visually recognize it (step S8). For example, a character string “The fat content of the corresponding region is ~%” is displayed by being superimposed on a display displaying a CT image.

  Note that this embodiment is an example of the present invention, and the present invention is not limited to the configuration and operation described in this embodiment. Various modifications can be made according to the design or the like as long as they do not depart from the technical idea of the present invention. For example, the fat coefficient shown in the first table may be a difference value between a sample CT value measured at a tube voltage of 120 kV and a sample CT value measured at a tube voltage of 100 kV. In that case, the size-dependent correction unit 63 multiplies the actual CT value of the subject P measured at the tube voltages of 120 kV and 100 kV by the value of the difference in water equivalent thickness obtained from the second table to obtain a predetermined tube voltage. The actual CT value corrected by the above is obtained.

  According to the image processing unit 54 of the X-ray CT apparatus 1 according to the present invention, the fat content of the region of interest is objectively determined from the CT value measured based on the image information obtained using the X-ray CT apparatus 1. Can be displayed.

  FIG. 10 is a block diagram showing a second embodiment of the X-ray CT apparatus according to the present invention.

  In the hardware configuration shown in FIG. 1, when the CPU 41 of the operation console 4 of the X-ray CT apparatus 1 executes a program, the operation console 4 has a preprocessing unit 51, a scattered radiation correction unit 52, and a reconstruction processing unit 53. And functions as the image processing unit 54A.

  The image processing unit 54A performs various image processing on the image data stored in the storage device such as the HD 44 to generate a display image. The image processing unit 54A includes a CT value measurement unit 62 and a contained fat percentage conversion unit 66 in order to generate a display image. In FIG. 10, the same members as those shown in FIG.

  Here, the fat content conversion formula is stored in advance in a storage device such as HD44. The fat content conversion formula measures the CT value under a plurality of different irradiation conditions with respect to the fat content as a sample CT value, and the relationship between the fat content and the difference between each sample CT value measured under different irradiation conditions Is shown.

  FIG. 11 is a diagram showing an outline for obtaining the contained fat percentage conversion formula, and an example of the relationship between sample CT values measured under different irradiation conditions and differences between the sample CT values measured under different irradiation conditions It is a figure which shows as a table.

In order to obtain the contained fat percentage conversion formula in the preparatory stage before the inspection, first, samples of various contained fat percentages are prepared. For example, samples containing 2%, 5%, 8%, 10%, 15% and 20% by weight of fat for a fixed amount of water phantom are prepared. The table shown in FIG. 11 shows, as sample CT values, CT values measured under different irradiation conditions, for example, tube voltage, for samples having various fat percentages. For example, a sample CT value measured by irradiating a sample with a fat content of 2% at a tube voltage of ¹²⁰ kV is ¹²⁰ C _2%, and a sample CT value measured by irradiating the sample at a tube voltage of 80 kV is ⁸⁰ C _2%. And a sample CT value measured by irradiating a sample having a fat content of 5% at a tube voltage of ¹²⁰ kV with ¹²⁰ C _5%, and a sample CT value measured by irradiating the sample with a tube voltage of 80 kV at ⁸⁰ C _5%. The sample CT value measured by irradiating a sample with a fat content of 8% at a tube voltage of ¹²⁰ kV was ¹²⁰ C _8%, and the sample CT value measured by irradiating the sample at a tube voltage of 80 kV was ⁸⁰ C _8% When the sample CT value and ¹²⁰ C _{of 10%} of fat content was measured by irradiating 10% of the sample in the tube voltage 120 kV, Sa was measured by irradiating the sample with a tube voltage 80kV And a pull CT value ⁸⁰ C _10%, and ¹²⁰ C _15% sample CT value fat content was measured by irradiating the 15% sample tube voltage 120 kV, as measured by irradiating the sample with a tube voltage 80kV The sample CT value was measured by irradiating a sample with ⁸⁰ C _15% and a fat content of 20% at a tube voltage of ¹²⁰ kV. The sample CT value was ¹²⁰ C _20% , and the sample was irradiated with a tube voltage of 80 kV. The sample CT value is defined as ⁸⁰ C _20% . Hereinafter, the case where the irradiation condition is a tube voltage will be described. However, the irradiation condition is not limited to the tube voltage, and may be, for example, a tube current (mA).

Further, the table shown in FIG. 11 correlates the fat content and the difference value between the sample CT values measured at different tube voltages. For example, a sample CT value difference value η calculated from ( ¹²⁰ C _2% ⁻⁸⁰ C _2% ) is calculated for a sample with a fat content of 2%, and ( ¹²⁰ C _5% − The difference value θ of the sample CT value calculated from ⁸⁰ C _5% ), and the difference value ι of the sample CT value calculated from ( ¹²⁰ C _8% ^-80 C _8% ) for the sample with a fat content of 8% For samples having a fat content of 10%, the difference value κ of the sample CT value calculated from ( ^120C _10% ^-80C _10% ) is used, and for samples having a fat content of 15% ( ^120C _15% ^-80 C _15% ) and the difference CT value of the sample CT value calculated from ( ^120C _20% ^-80C _20% ) are related to the sample CT value difference value λ calculated from the sample fat content 20%. ing. In the present embodiment, as a representative example, different tube voltages are set to 120 kV and 80 kV (tube currents are respectively constant).

  Further, in order to obtain the contained fat percentage conversion formula, the relationship between the contained fat percentage and the difference between the sample CT values obtained at different tube voltages is obtained based on the table shown in FIG.

  FIG. 12 is a graph illustrating an example of a conversion formula for the contained fat percentage.

  FIG. 12 plots the relationship between the fat content (x) and the difference (y) in the sample CT value for each combination of the water equivalent thickness of the subject P and the FOV, and shows a regression line based on the plot. ing. In addition, the relationship between the fat content and the difference between the sample CT values was obtained for each combination of the water equivalent thickness of the subject P, the FOV, and the display FOV in consideration of the enlargement ratio. It has been confirmed that it is not related to FOV.

  For example, the combination of the water equivalent thickness of the subject P and the FOV (water equivalent thickness of the subject P / FOV) is 240 mm / 400 mm, 240 mm / 320 mm, 320 mm / 400 mm, 320 mm / 320 mm, and the fat content and sample CT The relationship with the value difference is plotted, and the regression lines based on the plot are shown as graphs. Thus, in any combination, the fat content and the difference between the sample CT values have a positive correlation. In addition, the correlation coefficient of each regression line showed 0.99 or more.

  In addition, in consideration of measurement errors and the like, it cannot be said that there is a difference in inclination between the combinations, and the inclinations are almost the same regardless of the combination. Therefore, a straight line with a y-intercept “0” having an inclination of any one of the regression lines or an average of the inclinations of the regression lines is used as a contained fat percentage conversion formula. In addition, the straight line of y intercept "0" which makes the average (40.597) inclination of each regression line the inclination here is a fat content conversion formula, and the fat content conversion formula is shown on the scatter diagram.

  The fat content conversion unit 66 shown in FIG. 10 calculates the difference value between the measured CT values under different irradiation conditions based on the measured CT values for each irradiation condition measured by the CT value measuring unit 62. The difference is, for example, (actual CT value at tube voltage 120 kV) − (actual CT value at tube voltage 80 kV). Further, the contained fat percentage conversion unit 66 refers to the contained fat percentage conversion formula stored in the storage device and converts the difference value between the actually measured CT values into the contained fat percentage. The contained fat percentage converted by the contained fat percentage converting unit 66 is displayed by the display device 47, and is quantified and displayed as an objective contained fat percentage in a predetermined region in the scanogram.

  Next, the operation of the image processing unit 54A in the second embodiment of the X-ray CT apparatus according to the present invention will be described with reference to the flowchart shown in FIG.

  First, after the reconstruction processing is completed by the reconstruction processing unit 53 illustrated in FIG. 10, the image processing unit 54 </ b> A acquires scan data from the storage device (step S <b> 1) and scans the display device 47 with the scan data. Is displayed as a scanogram.

  Next, as described with reference to FIG. 7, the region of interest is set by the examiner designating a predetermined region with respect to the scanogram displayed on the display device 47 (step S2).

  Next, the CT value measuring unit 62 measures the actual CT value averaged for each different irradiation condition for the region of interest set in step S2 (step S3), and as shown in FIGS. 8 and 9, the CT image Is displayed on the display device 47.

  Next, the fat content conversion unit 66 refers to the fat content conversion formula stored in the storage device, and converts the actual CT value measured by the CT value measurement unit 62 into the fat content rate (step S10).

  The contained fat percentage converted by the contained fat percentage converting unit 66 is displayed on the display device 47 so that the examiner can visually recognize it (step S11). For example, a character string “The fat content of the corresponding region is ~%” is displayed by being superimposed on a display displaying a CT image.

  Although the X-ray CT apparatus 1 shown in FIG. 1 is shown as a single tube type apparatus using one X-ray tube 12, the X-ray CT apparatus 1 may be a multi-tube type apparatus. In that case, by setting each X-ray tube to different irradiation conditions, CT values (sample CT values) can be acquired under different irradiation conditions by one scan.

  Note that this embodiment is an example of the present invention, and the present invention is not limited to the configuration and operation described in this embodiment. Various modifications can be made according to the design or the like as long as they do not depart from the technical idea of the present invention.

  According to the image processing unit 54A of the X-ray CT apparatus 1 according to the present invention, the fat content of the region of interest is objectively determined from the CT value measured based on the image information obtained using the X-ray CT apparatus 1. Can be displayed.

The block diagram which shows the hardware constitutions of a X-ray CT apparatus. 1 is a block diagram showing a first embodiment of an X-ray CT apparatus according to the present invention. The figure which shows the outline for acquiring a 1st table. The figure which shows an example of a 1st table. The figure which shows an example of a 2nd table. 3 is a flowchart showing the operation of the image processing unit in the first embodiment of the X-ray CT apparatus according to the present invention. The figure which shows an example of the display screen containing a scanogram at the time of designating a predetermined area | region. The figure which shows an example of the display screen containing CT image when a tube voltage is 120 kV. The figure which shows an example of the display screen containing CT image when a tube voltage is 100 kV. The block diagram which shows 2nd Embodiment of the X-ray CT apparatus concerning this invention. The figure which shows the outline for acquiring a contained fat percentage conversion type | formula. The figure which shows an example of a contained fat percentage conversion formula as a graph. The flowchart which shows operation | movement of an image process part in 2nd Embodiment of the X-ray CT apparatus concerning this invention.

Explanation of symbols

1 X-ray CT device 2 Mounting device 3 Sleeper device 4 Operation console 44 HD
46 Input device 47 Display device 51 Preprocessing unit 52 Scattered ray correction unit 53 Reconstruction processing unit 54, 54A Image processing unit 61 Subject size measurement unit 62 CT value measurement unit 63 Size dependent correction unit 64 Fat coefficient calculation unit 65 Fat contained Rate extraction unit 66 Containing fat rate conversion unit

Claims (10)

A storage device for storing a first table in which a fat content is associated with each of a plurality of different CT value ratios;
A CT value measuring unit that irradiates a subject with X-rays under the plurality of different irradiation conditions, and measures an actual CT value for each irradiation condition;
A fat content extraction unit that calculates a ratio of measured CT values for each of the irradiation conditions and extracts a fat content corresponding to the ratio of the measured CT values with reference to the first table; X-ray CT apparatus that is characterized. A ratio of sample CT values between the irradiation conditions of the water phantom obtained by exposing X-rays to a desired water phantom containing a predetermined amount of fat under a plurality of different irradiation conditions and the fat content A first storage device that pre-stores a first table associated with
A second storage device that pre-stores a second table in which the sample CT values of the water equivalent thicknesses of the water phantoms of different sizes are stored for each of the plurality of different irradiation conditions;
A CT value measuring unit that irradiates a subject with X-rays under the plurality of different irradiation conditions, and measures an actual CT value for each irradiation condition;
A subject size measuring unit for measuring a water equivalent thickness of the subject;
Referring to the second table, a size-dependent correction coefficient based on the desired water phantom size and the subject size measured by the subject size measurement unit is calculated, and is the same as the actual CT value A size-dependent correction unit that corrects the measured CT value by multiplying the irradiation-dependent size-dependent correction coefficient;
A fat coefficient calculation unit that calculates a ratio of measured CT values corrected by the size dependent correction unit as a fat coefficient;
An X-ray CT apparatus comprising: a fat content extraction unit that extracts a fat content corresponding to the fat coefficient with reference to the first table. The X-ray CT apparatus according to claim 2, wherein the size-dependent correction coefficient is obtained by a ratio between a sample CT value and an actual CT value under the same irradiation condition. A storage device for storing a first table in which a fat content is associated with each of a plurality of different CT value differences;
A CT value measuring unit that irradiates a subject with X-rays under the plurality of different irradiation conditions, and measures an actual CT value for each irradiation condition;
A fat content extraction unit that calculates a difference in measured CT values between the irradiation conditions and extracts the fat content corresponding to the difference in the measured CT values with reference to the first table; X-ray CT apparatus that is characterized. A difference in sample CT value between the irradiation conditions of the water phantom obtained by exposing X-rays to a desired water phantom containing a predetermined amount of fat under a plurality of different irradiation conditions, and the fat content A first storage device that pre-stores a first table associated with
A second storage device that pre-stores a second table in which the sample CT values of the water equivalent thicknesses of the water phantoms of different sizes are stored for each of the plurality of different irradiation conditions;
A CT value measuring unit that irradiates a subject with X-rays under the plurality of different irradiation conditions, and measures an actual CT value for each irradiation condition;
A subject size measuring unit for measuring a water equivalent thickness of the subject;
Referring to the second table, a size-dependent correction coefficient based on the desired water phantom size and the subject size measured by the subject size measurement unit is calculated, and is the same as the actual CT value A size-dependent correction unit that corrects the measured CT value by multiplying the irradiation-dependent size-dependent correction coefficient;
A fat coefficient calculation unit that calculates a difference between measured CT values corrected by the size dependent correction unit as a fat coefficient;
An X-ray CT apparatus comprising: a fat content extraction unit that extracts a fat content corresponding to the fat coefficient with reference to the first table. The X-ray CT apparatus according to claim 5, wherein the size-dependent correction coefficient is obtained by a difference between a sample CT value and an actual CT value under the same irradiation condition. A storage device for storing a conversion formula calculated based on the fat content for a difference between a plurality of different CT values;
A CT value measuring unit that irradiates a subject with X-rays under the plurality of different irradiation conditions, and measures an actual CT value for each irradiation condition;
A fat content conversion unit that calculates a difference in measured CT value for each irradiation condition and converts the difference in the measured CT value into a fat content with reference to the conversion formula X Line CT device. The water obtained by exposing X-rays to a desired water phantom containing a predetermined amount of fat under a plurality of different irradiation conditions for each combination of water equivalent thickness and effective visual field of the subject. 8. The relationship between sample CT value differences between phantom irradiation conditions and fat content is plotted, and a regression line for each combination based on the plot is used as the conversion formula. X-ray CT system. A storage device that stores a first table that correlates the fat content for comparison values of a plurality of different CT values;
A CT value measuring unit that irradiates a subject with X-rays under the plurality of different irradiation conditions, and measures an actual CT value for each irradiation condition;
A fat content extraction unit that calculates a comparison value of the measured CT values for each of the irradiation conditions and extracts the fat content corresponding to the comparison value of the measured CT values with reference to the first table; An X-ray CT apparatus characterized by that. The X-ray CT apparatus according to any one of claims 1, 2, 4, 5, 7, and 9, wherein the irradiation condition is a tube voltage of an X-ray tube.

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