JP5596100B2 - X-ray tomography equipment - Google Patents

Description

  The present invention relates to an X-ray tomography technique, and more particularly to an X-ray tomography apparatus related to dual energy imaging.

  In dual energy imaging, an image in which a specific substance of a subject is emphasized can be acquired based on X-ray projection data of a subject acquired by X-rays having two different energy spectra. In other words, a dual energy image that displays bones and calcified lesions in an easy-to-understand manner by performing addition and subtraction processing between an image obtained with high-energy X-rays and an image obtained with low-energy X-rays, or soft tissue is easy to understand. The displayed dual energy image can be obtained.

To perform dual energy imaging, the X-ray tube voltage irradiated by the X-ray imaging device is alternately switched between a high voltage and a low voltage for each scan, or the X-ray filter is replaced to change the X-ray energy. Thus, projection data obtained with high energy X-rays and projection data obtained with low energy X-rays are obtained. For example, Patent Document 1 discloses an invention that displays a bone image or a soft tissue image based on an image obtained with high energy X-rays and an image obtained with low energy X-rays. At this time, in order to obtain an image of bone or an image of soft tissue, a predetermined weighting coefficient is used according to atoms (calcium) such as bone.
JP2003-244542

  However, the weighting coefficient used in the weighted subtraction process for obtaining the bone image or the soft tissue image is not necessarily constant due to the difference in the size of the subject and the difference in the X-ray absorption coefficient due to the individual difference in the subject. Absent. Using a constant weighting factor and diagnosing with a dual energy image without considering the influence of the difference in the size of the subject leads to overestimation or underestimation of illness or injury.

  SUMMARY OF THE INVENTION An object of the present invention is to provide an X-ray tomography apparatus that can set an appropriate weighting coefficient for each subject and each region of the subject. Another object of the present invention is to provide an X-ray tomography apparatus capable of displaying an image that is quantitatively and visually easy to understand using an appropriate weighting coefficient.

The X-ray tomography apparatus according to the first aspect includes first energy projection data or first energy tomographic image by X-ray of first energy and second energy projection data by X-ray of second energy different from the first energy or In order to obtain a dual energy image by performing weighted subtraction processing for subtracting one or both of the weighting coefficients based on a specific material included in the subject and multiplying one or both of the second energy tomographic image. X-ray tomography apparatus. And in order to achieve the said objective, the image comparison information calculation part which calculates the image comparison information of 1st energy projection data or a 1st energy tomogram, and a 2nd energy projection data or a 2nd energy tomogram, A region of interest A region-of-interest specifying unit for specifying the weight, a weighting factor determining unit for determining a weighting factor that makes image comparison information in the region of interest substantially erasable, and a weighting factor determined by the weighting factor determining unit Then, by performing a load subtraction process on the first energy projection data or the first energy tomographic image and the second energy projection data or the second energy tomographic image used in the image comparison information calculation unit, the dual energy image is re-imaged. A dual energy image reconstruction unit configured.
The weighting coefficient used to obtain the bone image or the soft tissue image varies depending on the size of the subject. FIG. 10 shows the relationship between the pixel value ratios of fat, calcium and iodine tomograms when the tube voltage is 140 kV on the horizontal axis and the tube voltage is 80 kV on the vertical axis. It is. It can be seen that the ratio of pixel values of each substance differs between the phantom having a cross-sectional area of 700 cm 2 and the phantom having a cross-sectional area of 300 cm 2 due to the difference in cross-sectional area. With a phantom, you can predict how much the ratio of pixel values will be. However, in the subject, the ratio of pixel values varies depending not only on the cross-sectional area but also on the cross-sectional shape and other differences in X-ray absorption coefficients due to individual differences. Therefore, if the pixel value ratio cannot be obtained accurately, it leads to overestimation or underestimation such as illness or injury.
The weighting coefficient determination unit of the X-ray tomography apparatus according to the first aspect determines a weighting coefficient that makes it possible to substantially erase the image comparison information of the region of interest specified by the region of interest specifying unit. Since the dual energy image reconstruction unit reconstructs the dual energy image with the weighting coefficient, it is possible to display an image that is quantitatively and visually easy to understand.

The image comparison information calculation unit of the X-ray tomography apparatus according to the second aspect displays a comparison image by subtracting the first energy projection data or the first energy tomogram from the second energy projection data or the second energy tomogram. Reconstructing and calculating the image feature amount of the comparison image as image comparison information.
With this configuration, since the image feature amount of the comparison image can be obtained as image comparison information, the image feature amount and weighting coefficient of the comparison image can be easily determined.

In the second aspect, the X-ray tomography apparatus according to the third aspect further includes an image display unit that displays a comparison image, and the region-of-interest specifying unit determines the region of interest based on the comparison image displayed on the image display unit. It can be specified.
This configuration is convenient because the operator can specify the region of interest based on the comparison image by displaying the comparison image that the operator wants to see on the image display unit.

In a fourth aspect, in the second and third aspects, the X-ray tomography apparatus further includes an image feature amount display unit that displays an image feature amount that changes in conjunction with a change in the weighting factor, and the weighting factor determination unit includes The weighting coefficient can be manually changed while viewing the change in the displayed image feature amount.
With this configuration, not only the comparison image but also the operator can manually adjust the weighting coefficient by the weighting coefficient adjustment unit while visually checking the change of the image feature amount displayed on the image feature amount display unit. Specifically, the weighting coefficient can be adjusted with a slider bar or the like.

The X-ray tomography apparatus according to the fifth aspect is the X-ray tomography apparatus according to the fourth aspect, wherein the image feature amount is an average value or a median value of the pixel values in the pixels of the region of interest in the comparison image. The weighting coefficient when it becomes zero or within a predetermined range near zero is determined as the weighting coefficient of the region of interest.
With this configuration, the weighting coefficient can be set to an appropriate value by using the average value or the median value of the comparison images in the region of interest as the image feature amount of the region of interest. Here, the median is a median when the comparison images in the region of interest are arranged in order from the lowest value to the higher value (or vice versa). Further, if the image feature amount is within a predetermined range of zero or near zero, the image becomes substantially erasable.

The image comparison information calculation unit of the X-ray tomography apparatus according to the sixth aspect uses a ratio of pixel values of the 1 energy projection data or the first energy tomogram and the second energy projection data or the second energy tomogram as image comparison information. The region-of-interest specifying unit calculates the region having the same pixel value ratio as the region of interest.
With this configuration, the weighting coefficient can be automatically changed from the distribution of the ratio of the pixel values of the first energy projection data or the first energy tomogram and the second energy projection data or the second energy tomogram. Actually, the weighting coefficient is automatically determined from the tomographic image obtained by imaging the subject with X-rays. That is, the weighting coefficient can be determined in consideration of the difference in X-ray absorption coefficient due to the cross-sectional area of the subject, the cross-sectional shape, and other individual differences. Since it is possible to diagnose with a dual energy image calculated with an accurate weighting coefficient, it is possible to accurately evaluate illness or injury.

In the sixth aspect, the weighting coefficient determination unit of the X-ray tomography apparatus according to the seventh aspect provides the first energy projection data or the first energy tomogram and the second energy projection data or the second energy tomogram in the region of interest. The weighting coefficient is determined based on the peak value of the distribution of the pixel value ratio.
With this configuration, by determining the weighting coefficient based on the peak value of the distribution of the ratio of actually captured pixel values, a dual energy image of an equivalent image of the peak value can be obtained. For example, the peak value can be obtained from the differential value of the histogram distribution.

The X-ray tomography apparatus according to the eighth aspect further includes a colored display unit that colors the region of interest and displays the region of interest on the first energy tomographic image or the second energy tomographic image.
With this configuration, since the region of interest is colored, the operator can make a diagnosis while recognizing the region of interest when diagnosing the dual energy image.

In the X-ray tomography apparatus of the ninth aspect, in the eighth aspect, the colored display unit can display a plurality of different regions of interest of the same subject with different colors.
With this configuration, two or more regions of interest can be identified with different colors, and the two or more regions of interest can be diagnosed and diagnosed simultaneously. For example, blue is displayed as water and yellow is displayed as calcium.

The X-ray tomography apparatus according to the tenth aspect changes color tone according to a ratio of pixel values of the first energy projection data or the first energy tomogram and the second energy projection data or the second energy tomogram. A coloring display unit for coloring is further provided.
With this configuration, the region of interest is colored according to the ratio of pixel values, and the operator can make a diagnosis while recognizing the region of interest when diagnosing the dual energy image.

  According to the present invention, when an operator examines and diagnoses a dual energy image, the operator can accurately grasp the weighting coefficient necessary for obtaining the dual energy image. Therefore, it is possible to accurately recognize and diagnose a specific substance (atom) to be diagnosed by taking a dual energy image, for example, a contrast agent, fat, or calcium in the subject.

1 is a block diagram showing a configuration of an X-ray CT apparatus 10 according to the present embodiment. 3 is an operation flowchart of the X-ray tomography apparatus 10. It is a conceptual diagram which calculates | requires the dual energy image DI by carrying out the weighted subtraction process of the tomogram HT of a high energy spectrum, or the tomogram LT of a low energy spectrum. (A) is the figure which represented the subject HB by the three-dimensional image, (b) is xz surface of (a). (A) is a block diagram of the image processing apparatus 20 for manually setting the weighting coefficient, and (b) is a state in which the dual energy image DI is displayed on the display 60, and the operator manually selects an appropriate weighting coefficient. It is an example of a display for setting. It is a flowchart for an operator to manually set an appropriate weighting coefficient. (A) is a block diagram of the image processing apparatus 20 for automatically setting a weighting coefficient, and (b) is a flowchart for automatically setting an appropriate weighting coefficient. It is a histogram in which the horizontal axis represents the ratio obtained by dividing the X-ray tomographic image LT having a low energy spectrum by the X-ray tomographic image HT having a high energy spectrum, and the vertical axis represents the number of pixels. It is a figure explaining coloring of the dual energy image DI. It is the figure which showed the relationship of the ratio of the pixel value of the tomogram of fat, calcium, and iodine by the X-ray of low energy and high energy.

<Configuration of X-ray tomography apparatus>
FIG. 1 is a block diagram showing a configuration of an X-ray tomography apparatus (X-ray CT apparatus) 10 according to the present embodiment. The X-ray tomography apparatus 10 is equipped with a gantry 100 and a bed 109 for inserting a subject HB into an imaging region of the gantry 100. The bed 109 moves in the Z direction, which is the body axis direction of the subject HB. The gantry 100 includes a rotating ring 102, and an X-ray tube 101 that irradiates the rotating ring 102 with cone-beam-shaped X-rays and a multi-row X-ray detector 103 disposed opposite to the X-ray tube 101. Have. The X-ray tube 101 is configured to irradiate X-rays having a high energy spectrum and X-rays having a low energy spectrum. The multi-row X-ray detector 103 detects X-rays that have passed through the subject HB.

  The multi-row X-ray detector 103 is composed of a scintillator and a photodiode. The multi-row X-ray detectors 103 are arranged in a plurality of rows along the Z direction substantially parallel to the rotation axis of the rotating ring 102 so that projection data for a plurality of slices (a plurality of rows) can be detected simultaneously. The multi-row X-ray detector 103 has a multi-channel shape formed in an arc shape with the focal point of the X-ray tube 101 as the center. The Z direction parallel to the rotation axis is referred to as “slice direction”, and the arc direction of the X-ray detection element array is referred to as “channel direction”. The multi-row X-ray detector 103 is connected to a data acquisition circuit 104 generally called a DAS (data acquisition system). The data acquisition circuit 104 includes an IV converter that converts a current signal of each channel of the multi-row X-ray detector 103 into a voltage, and the voltage signal periodically in synchronization with an X-ray exposure cycle. An integrator for integrating, an amplifier for amplifying the output signal of the integrator, and an analog / digital converter for converting the output signal of the preamplifier into a digital signal are provided for each channel. A digital signal from the data acquisition circuit 104 is sent to the image processing device 20 via the data transfer device 105.

  On the operation console side, a high voltage / low voltage generator 51 for supplying a voltage to the X-ray tube is provided. The high voltage / low voltage generator 51 periodically generates a high voltage and a low voltage, and supplies the high voltage and the low voltage to the X-ray tube 101 via the slip ring 113.

  The scan controller 53 on the operation console side executes a plurality of scan patterns such as an axial scan, a helical scan, and a variable pitch helical scan. The axial scan is a scanning method in which projection data is acquired by rotating the X-ray tube 101 and the X-ray detection unit 103 by the rotation mechanism 111 every time the bed 109 is moved by a predetermined pitch in the Z-axis direction. The helical scan is a scanning method for acquiring projection data by moving the bed 109 at a predetermined speed while the X-ray tube 101 and the X-ray detection unit 103 are rotating. The variable pitch helical scan is a scanning method for acquiring projection data by changing the speed of the bed 109 while rotating the X-ray tube 101 and the X-ray detection unit 103 by the rotation mechanism 111 as in the helical scan. The scan controller 53 controls the control related to scanning such as driving the rotation mechanism 111 in synchronization with the high voltage / low voltage generator 51 and periodically collecting projection data by the data collection circuit 104.

The image processing apparatus 20 includes an image reconstruction unit 21 and a dual energy image reconstruction unit 22.
The image reconstruction unit 21 receives low energy projection data LD or high energy projection data HD, and reconstructs an image based on the low energy projection data LD or high energy projection data HD. The low energy projection data LD or the high energy projection data HD is subjected to a fast Fourier transform (FFT) to be converted into the frequency domain, and is subjected to an inverse Fourier transform by applying a reconstruction function thereto. Then, a three-dimensional backprojection process is performed on the projection data subjected to the reconstruction function superimposition process, and a tomographic image (xy plane) is obtained for each body axis direction (Z direction) of the subject HB. This tomographic image is stored in the storage device 59 and displayed on the display 60. In this embodiment, since the X-ray tube 101 irradiates the subject HB with X-rays having a low energy spectrum and X-rays having a high energy spectrum, the image reconstruction unit 21 uses X-rays with a high energy spectrum. An image is reconstructed from a high-energy tomographic image HT and a low-energy tomographic image LT by X-rays having a low-energy spectrum.

  The dual energy image reconstruction unit 22 multiplies the weighting coefficient from one or both of the projection data HD of the high energy spectrum and the projection data LD of the low energy spectrum, subtracts both projection data, and calculates the weighted subtraction. A dual energy image DI is obtained by reconstructing the projection data. Further, the dual energy image reconstruction unit 22 multiplies the weighting coefficient from one or both of the high energy spectrum tomographic image HT and the low energy spectrum tomographic image LT, and subtracts both images to thereby obtain the dual energy image. It is also possible to reconstruct DI images. The dual energy image DI will be described later with reference to FIG.

The input device 55 is configured by a keyboard or a mouse that receives an input from the operator.
The storage device 59 stores programs, X-ray detector data, projection data, and X-ray tomographic images. A dual energy image DI is also stored.
The display 60 sets imaging conditions for the subject and displays an X-ray tomographic image. In the present embodiment, a dual energy image DI in which a specific substance of the subject is emphasized by color is displayed.

<Operation of X-ray tomography apparatus>
FIG. 2 is an operation flowchart of the X-ray tomography apparatus 10. An operation procedure of the X-ray tomography apparatus 10 according to the present embodiment will be described.

  In step S11, the subject is placed on the bed 109 and aligned. The subject placed on the bed 109 aligns the slice center position of the gantry 100 with the reference point of each part. Then, a scout image (also called a scanogram or an X-ray fluoroscopic image) is collected. Scout images can capture two types of scout images for adults or children depending on the size of the body of the subject, and can usually be captured at 0 and 90 degrees. Depending on the part, for example, the head may be a 90-degree scout image only. In scout imaging, the X-ray tube 101 and the multi-row X-ray detector 103 are fixed, and the data collection operation is performed while moving the bed 109 linearly.

  In step S <b> 12, the operator uses the keyboard of the input device 55 or the like to set the position / range of the tomographic image to be taken on the scout image displayed on the display 60. At this time, settings such as an axial scan, a helical scan, a cine scan, a variable pitch helical scan, or a helical shuttle scan are also performed. The variable pitch helical scan is an imaging method that collects X-ray projection data while moving the bed 109 while rotating the X-ray tube 101 and the multi-row X-ray detector 103 in the same manner as the helical scan. This is a variable method. The helical shuttle scan is an X-ray projection in which the bed 109 is accelerated and decelerated while rotating the X-ray tube 101 and the multi-row X-ray detector 103 and reciprocated in the positive direction of the z-axis or the negative direction of the z-axis. It is a scanning method that collects data.

  In step S13, tomographic image capturing conditions or dual energy image DI capturing conditions are set. In order for the X-ray tube 101 to irradiate the subject HB with X-rays having a high energy spectrum and X-rays having a low energy spectrum, for example, the high voltage and the low voltage are set to 140 kV and 80 kV, respectively. In addition, a setting is made so that high-voltage X-rays and low-voltage X-rays are alternately irradiated according to the rotation of the rotation mechanism 111 so as not to cause positional displacement as much as possible. For example, the X-ray tube 101 has a setting in which a high voltage and a low voltage are alternately repeated every rotation of the X-ray tube 101, or a setting in which a high voltage and a low voltage are alternately repeated for each short-term pulse. Do.

  In step S13, a specific substance (atom) to be diagnosed by taking a dual energy image DI is set. For example, a contrast medium, fat, or calcium in the subject is set. Also, set the filter function, kernel function, etc. for image reconstruction. These set conditions are recorded in the storage device 59. In this embodiment, the high energy spectrum and the low energy spectrum are generated by the voltage, but the energy spectrum may be changed by inserting a filter in the X-ray cone beam.

In step S14 to step S20, tomographic imaging is performed.
In step S14, X-ray projection data LD having a low energy spectrum and X-ray projection data HD having a high energy spectrum are collected. When data is collected by conventional scanning, the X-ray tube 101 and the multi-row X-ray detector 103 are rotated around the subject while the bed 109 is fixed, and the X-ray detector data Performs data collection operations. Then, the X-ray detector data D0 (view, j, i) (j = 1 to ROW, i = 1 to CH) represented by the view angle view, the detector row number j, and the channel number i is z direction. Coordinate position Ztable (view) is added.

In step S15, pre-processing is performed on the low energy projection data LD0 (view, j, i) and the high energy projection data HD0 (view, j, i). Specifically, offset correction is performed, logarithmic conversion is performed, X-ray dose correction is performed, and sensitivity correction is performed.
In step S16, beam hardening correction is performed on the preprocessed low energy projection data LD (view, j, i) and high energy projection data HD (view, j, i).
In step S17, the image reconstruction unit 21 performs z filter convolution processing. Here, a z filter convolution process for applying a filter in the z direction (column direction) to the projection data subjected to beam hardening correction is performed. That is, after pre-processing in each view angle and each X-ray data acquisition system, the column direction filter is applied in the column direction to the projection data D of the multi-row X-ray detector subjected to beam hardening correction.

In step S18, the image reconstruction unit 21 performs reconstruction function superimposition processing. That is, the Fourier transform (Fourier Transform) that transforms the X-ray projection data D into the frequency domain is performed, the reconstruction function is multiplied, and the inverse Fourier transform is performed. In the reconstruction function superimposing process, the reconstruction function Kernel (j) is superimposed. In step S19, the image reconstruction unit 21 performs a three-dimensional backprojection process. Here, three-dimensional backprojection processing is performed on the projection data D subjected to reconstruction function superimposition processing to obtain backprojection data. The image to be reconstructed is a three-dimensional image reconstructed with respect to the xy plane that is a plane perpendicular to the z axis. The following reconstruction area P is assumed to be parallel to the xy plane.
In step S20, the image reconstruction unit 21 performs post-processing. Post-processing such as image filter superimposition and CT value conversion is performed on the backprojection data to obtain a high energy spectrum tomogram HT and a low energy spectrum tomogram LT.

In step S21, the reconstructed tomographic image HT having a high energy spectrum and the tomographic image LT having a low energy spectrum are displayed on the display 60.
In step S22, the tomographic image HT and the tomographic image LT are stored in the storage device 59.
In step S <b> 23, the dual energy image reconstruction unit 22 displays the dual energy image DI on the display 60.
In step S24, the coloring display unit 28, which will be described later, colors the tomographic image HT and the tomographic image LT for each specific substance such as the same atomic substance, fat, water, calcium, or iodine contrast agent.

<Image reconstruction of dual energy image DI>
FIG. 3 is a conceptual diagram for obtaining a dual energy image DI by performing weighted subtraction processing on a tomographic image HT having a high energy spectrum or a tomographic image LT having a low energy spectrum.
In the dual energy imaging, a desired substance is quantitatively determined by weighting and subtracting a tomographic image LT having a low X-ray tube voltage, for example, 80 kV, and a tomographic image HT having a high X-ray tube voltage, for example, 140 kV, at a certain z-direction coordinate position. A tomographic image DI of a proper distribution image is obtained.

  In the upper part of FIG. 3, as described in step S14 of FIG. 2, first, X-ray projection data LD of a low energy spectrum and X-ray projection data HD of a high energy spectrum are obtained.

Next, the image reconstruction unit 21 performs the processing from step S15 to step S20 described with reference to FIG. 2 from the low energy projection data LD and the high energy projection data HD to obtain a low energy spectrum tomogram LT and a high energy spectrum. The tomographic image HT is reconstructed.
In the lower part of FIG. 3, the dual energy image reconstruction unit 22 multiplies the tomographic image LT with the low energy spectrum by the weighting coefficient 1 and multiplies the tomographic image HT with the high energy spectrum by the weighting coefficient α, together with the constant C1. Perform weighted subtraction. In this way, the dial energy image DI can be obtained. The weighting coefficient α and the constant C1 are determined by the atom to be extracted, the atom to be emphasized, the atom or part to be deleted on the display. If α is a reciprocal, the weighting coefficient α can be set to the tomographic image LT of the low energy spectrum, and the weighting coefficient of the tomographic image HT of the high energy spectrum can be set to 1. FIG. 3 shows extraction of fat information.

  In addition, instead of obtaining the dual energy image DI from the low energy spectrum tomogram LT and the high energy spectrum tomogram HT, the X-ray projection data LD collected at a low X-ray tube voltage and a high X-ray tube voltage are used. It is also possible to obtain a dual energy image DI by performing weighted subtraction processing on the collected X-ray projection data HD and reconstructing the X-ray projection data subjected to weighted subtraction processing.

FIG. 4A is a diagram showing the subject HB as a three-dimensional image, and FIG. 4B is an xz plane of FIG.
A dual energy image DI of a plurality of tomographic planes T (including a tomographic image LT having a low energy spectrum and a tomographic image HT having a high energy spectrum) is stored in the storage device 59, and the tomographic images T are combined, A volume rendering three-dimensional image 31 as shown in FIG. 4 (a) can be displayed. Similarly, a three-dimensional image can be displayed for the dual energy image DI.

  A coronal image 33 shown in FIG. 4B is an image cut by the coronal surface (xz surface) 33 of FIG. 4A, and thus a dual energy image DI of an arbitrary coronal surface can be obtained. Although not shown, a dual energy image DI of the sagittal plane (yz plane) 34 can be obtained, and a dual energy image DI can be obtained even in a cross section in an arbitrary direction including an oblique direction. The operator can properly use the dual energy images DI suitable for diagnosis.

<Weight setting method>
<< Manual weighting coefficient setting method >>
FIG. 5A is a block diagram of the image processing apparatus 20 for performing the manual weighting setting method described in FIG. 5, and FIG. 5B is a comparative image on the display 60, that is, a dual energy image DI. It is an example of a display for an operator to set an appropriate weighting factor manually in the state where it did. This is a method for manually optimizing differences in the size of the subject HB, differences in the X-ray absorption coefficient due to individual differences in the subject HB, and the like.

  When manually setting the weighting coefficient, as shown in FIG. 5A, the image processing apparatus 20 includes an image reconstruction unit 21, a dual energy image reconstruction unit 22, and a first region of interest specifying unit 23. -1, a first image comparison information calculation unit 24-1, a weighting coefficient adjustment unit 25-1, an image feature amount display unit 27, and a coloring display unit 28. Since the image reconstruction unit 21 and the dual energy image reconstruction unit 22 have already been described above, a description thereof will be omitted.

  The first region-of-interest specifying unit 23-1 is a region of interest that the operator wants to confirm a part of the comparison image displayed on the display 60 and obtained in the first image comparison information calculation unit 24-1 described later. It can be specified as ROI. With the mouse which is one of the input devices 55, the operator arbitrarily sets the region of interest ROI.

  The first image comparison information calculation unit 24-1 first performs a subtraction process between the low energy X-ray projection data LD or the low energy tomographic image LT and the high energy X-ray projection data HD or the high energy tomographic image HT. The comparative image obtained by the above is reconstructed. This comparison image may be obtained by multiplying one or both of the weighting factors determined in advance by atoms or materials and subtracting both, or may be a difference image without applying the weighting factors. . Note that the image reconstruction of the comparison image may be performed by the dual energy image reconstruction unit 22. Next, with respect to the comparison image, an image feature amount is calculated for the region of interest ROI specified by the first region of interest specifying unit 23-1. Note that the image feature quantity may be calculated for the entire comparison image, and then only the information on the region of interest ROI may be extracted or may be calculated only on the region of interest ROI. Further, the image feature amount includes an average value or a median value of pixels specified by the region of interest ROI. In addition, the median value of the pixel is a pixel value intermediate between the pixel values in the set region of interest ROI.

The weighting coefficient adjustment unit 25-1 is an adjustment unit that can adjust the weighting coefficient used when the operator obtains the dual energy image DI. The operator determines a weighting coefficient by which at least one or both of the high energy projection data HD or the high energy tomographic image HT and the low energy projection data LD or the low energy tomographic image LT are multiplied.
The image feature amount display unit 27 displays the image feature amount 165 calculated by the first image comparison information calculation unit 24-1.

  The coloring display unit 28 colors the same atomic material, that is, a material having the same X-ray absorption rate in the same color, and different atomic materials in different colors. Specifically, the pixels identified as fat, calcium, and iodine contrast agent are colored red, blue, green, etc., respectively, and displayed on the display 60.

  The first region-of-interest specifying unit 23-1 displays a screen for region-of-interest setting shown in FIG. The operator sets the region of interest ROI1 in a part of the comparison image displayed on the display 60 with the mouse of the input device 55 or the like. The size of the region of interest ROI1 can be arbitrarily specified, and is not limited to a predetermined size or a circular shape. In FIG. 5, the region of interest ROI1 is specified for the heart. When the region of interest ROI1 is specified, the first image comparison information calculation unit 24-1 calculates the image feature quantity 165 of the pixel of the region of interest ROI1. The image feature amount display unit 27 displays the calculated result as M7.1 around the dual energy image DI as shown in FIG. If the image feature quantity 165 is an average value of the region of interest ROI1 of the comparison image, M3.0 or the like is displayed, and if the median value of the region of interest ROI1 of the comparison image is C3.0, C3.0 is displayed. The operator can select whether to use the average value or the median value.

  Next, the operator moves the weighting coefficient adjusting unit 25-1, specifically the slider bar, to the left and right so that the value of the image feature quantity 165 falls within a predetermined range of zero or near zero. An index 163 is displayed below the slider bar. The index 163 indicates the weighting coefficient α. That is, the operator can arbitrarily adjust the weighting coefficient (hereinafter described using the above-described weighting coefficient α) using the slider bar. The index 163 displays weighting factors 0 to 3, but when displaying the dual energy image DI using the tube voltage 140 kV and the tube voltage 80 kV of the X-ray tube 101, 0.5 to 2 .5 is sufficient. The slider bar 161 shown in FIG. 5 indicates 0.9. The index 163 may be automatically changed by a combination of high energy X-rays and low energy X-rays. 5 shows the slider bar 161, the weighting coefficient α may be directly input using a keyboard which is one of the input devices 55.

  When the operator adjusts the weighting coefficient α using the slider bar, the first image comparison information calculation unit 24-1 recalculates the image feature amount 165 of the pixel of the region of interest ROI1 based on the weighting coefficient α accompanying the adjustment. Further, the dual energy image reconstruction unit 22 reconstructs the comparison image with the adjusted weighting coefficient α, and the dual energy image DI also changes simultaneously. The operator performs weighting using the slider bar while confirming the image feature amount displayed on the image feature amount display unit 27 as to whether the image feature amount 165 is within the predetermined range from zero or from zero, or confirming the comparison image. Adjust the coefficient α. When the weighting coefficient α is adjusted, the operator presses the set button 162 so that the manual setting of the weighting coefficient can be completed. When the set button 162 is pressed, the frame of the region of interest ROI1 (dotted line in FIG. 5B) disappears. Further, when the color button 164 is pressed, the coloring display unit 28 is overlapped with either the low-energy tomographic image LT or the high-energy spectrum tomographic image HT so that the coloring display unit 28 is within the predetermined range from zero or zero as in the region of interest ROI1. Color the pixels. For example, when the iodine contrast medium becomes zero in the region of interest ROI1, the heart, aorta, blood vessels, etc. containing the iodine contrast medium are colored red.

  The operator can set not only the region of interest ROI1 of the comparison image displayed on the display 60 but also another region of interest ROI2. The first region-of-interest specifying unit 23-1 specifies the spine portion in FIG. 5 as a frame of the region of interest ROI2 (a chain line in FIG. 5B). Then, as described above, the operator adjusts the slider bar 161 so that the image feature quantity 165 of the region of interest ROI2 falls within a predetermined range from zero or zero. The operator presses the return button 167 when all settings are completed and the screen is switched to another screen.

  FIG. 6 is a flowchart for the operator described in FIG. 5 to manually adjust an appropriate weighting coefficient. That is, it is a flowchart for the operator to manually adjust an appropriate weighting coefficient.

In step S41, as shown in FIG. 4, a comparative image of an arbitrary cross section to be diagnosed is displayed on the display 60.
In step S42, the operator specifies the region of interest ROI of the displayed comparison image by the first region of interest specifying unit 23-1.

  In step S43, the first image comparison information calculation unit 24-1 calculates the image feature quantity 165 of the pixels in the region of interest ROI. That is, the image feature quantity 165 is obtained by obtaining the average value of the pixel values of the comparison image, and the image feature quantity 165 is displayed on the image feature quantity display unit 27.

In step S44, the operator adjusts the weighting coefficient α using the weighting coefficient adjusting unit 25-1, for example, a slider bar, while viewing the image feature amount 165 displayed on the image feature amount display unit 27.
In step S45, the image feature quantity 165 is changed by the adjusted weighting coefficient α, and the entire comparative image including the region of interest ROI is changed. The operator finely adjusts the weighting coefficient α using the slider bar 161, and puts the image feature quantity 165 within zero or a predetermined range from zero.

In step S46, when the image feature quantity 165 falls within a predetermined range of zero or near zero, the operator presses the set button 162 to fix the weighting coefficient α of the region of interest ROI.
In step S47, it is determined whether the operator continues to set another region of interest ROI. If another region of interest ROI is to be set, the process returns to step S42, and after setting all the regions of interest ROI, the process proceeds to step S48.
In step S48, the dual energy image reconstruction unit 22 reconstructs a dual energy image DI in which the region of interest ROI is an equivalent image with the adjusted weighting coefficient α. In addition, the colored display part 28 is equivalent to the one image of the low energy tomographic image LT or the high energy spectrum tomographic image HT so that the operator can easily diagnose the image displayed on the display 60. Are displayed in layers.

<< Automatic weighting coefficient setting method >>
FIG. 7A is a block diagram of the image processing apparatus 20 for automatically performing the weight setting method, and FIG. 7B is a flowchart for automatically setting an appropriate weighting coefficient. A dual energy image DI having an arbitrary cross section to be diagnosed is displayed on the display 60. Then, automatic weighting setting is started.
FIG. 8 is a histogram distribution in which the ratio of pixel values obtained by dividing the X-ray tomographic image LT having a low energy spectrum by the X-ray tomographic image HT having a high energy spectrum is plotted on the horizontal axis and the number of pixels is plotted on the vertical axis. is there.

  When the weighting coefficient is automatically set, as shown in FIG. 7A, the image processing apparatus 20 includes an image reconstruction unit 21, a dual energy image reconstruction unit 22, and a second region of interest specifying unit 23. -2, a second image comparison information calculation unit 24-2, a weighting coefficient determination unit 25-2, and a coloring display unit 28. Since the image reconstruction unit 21 and the dual energy image reconstruction unit 22 have already been described above, a description thereof will be omitted.

  The second image comparison information calculation unit 24-2 divides each pixel (512 * 512) of the low energy tomographic image LT by each pixel of the high energy spectral tomographic image HT, or a high energy spectral tomographic image HT. A value obtained by dividing each pixel by each pixel of the low-energy tomographic image LT is calculated. By calculating the pixel value ratio, the second image comparison information calculating unit 24-2 measures the histogram distribution with the horizontal axis representing the pixel value ratio and the vertical axis representing the number of pixels.

The second region-of-interest specifying unit 23-2 extracts a region having an equivalent pixel ratio as a region of interest from the ratio of the measured pixel values of the histogram distribution. Specifically, the second region-of-interest specifying unit 23-2 uses a pixel having a ratio of equivalent pixel values around the peak value of the histogram distribution as the region of interest.
The weighting coefficient determination unit 25-2 determines the weighting coefficient based on the ratio of the pixel values of the peak values of the histogram distribution. Therefore, a weighting coefficient used when obtaining a dual energy image is associated with the extracted region of interest.

  The coloring display unit 28 colors the same region of interest to the same color and different regions of interest to different colors. Specifically, the pixels identified as fat, calcium, and iodine contrast agent are colored red, blue, green, etc., respectively, and displayed on the display 60.

In step S51, the X-ray tomographic image LT having a low energy spectrum and the X-ray tomographic image HT having a high energy spectrum of the arbitrary cross section are read from the storage device 59.
In step S52, the second image comparison information calculation unit 24-2 obtains the ratio of the low energy spectrum X-ray tomographic image LT and the high energy spectrum X-ray tomographic image HT of each pixel. Usually, if an X-ray tomographic image LT with a tube voltage of 80 kV and an X-ray tomographic image HT with a tube voltage of 140 kV are used, the ratio of substances in the body of the subject is distributed from 0.5 to 2.5. Yes.
In step S53, the second image comparison information calculation unit 24-2 measures a histogram distribution in which the horizontal axis represents the ratio of pixel values and the vertical axis represents the number of pixels. An example of this is shown in FIG. Such FIG. 8 may be displayed on the display 60, or the ratio of each pixel may be stored in the memory.

  In step S54, the second region-of-interest specifying unit 23-2 determines whether or not there is a distribution of the number of pixels exceeding the threshold value SH1, so that the interest is based on the distribution of the number of pixels exceeding the threshold value SH1. Identify the area. In FIG. 8, the threshold value SH1 is set at a predetermined position. In FIG. 8, the peak P1, the peak P2, the peak P3, and the peak P5 exceed the threshold value SH1. For this reason, there are four distributions of the number of pixels exceeding the threshold value SH1. The peak at the location exceeding the threshold can be identified by differentiating the histogram distribution. On the other hand, the peak P4 does not exceed the threshold value SH1. It is possible to eliminate the peak P4 caused by the influence of noise, artifacts, or misalignment. The second region-of-interest specifying unit 23-2 performs such processing, and extracts a region having the same pixel value ratio as the region of interest. If there is one or more peaks P exceeding the threshold value SH1, the process proceeds to step S55. If there is no peak P exceeding the threshold value SH1, the process proceeds to step S57.

In step S55, the weighting coefficient determining unit 25-2 performs the peak P1, the peak P2, the peak P3, and the peak P5 extracted by the second region-of-interest specifying unit 23-2, that is, the specific material having the same pixel value ratio. The weighting coefficient α of the specific substance is fixed.
In step S56, the dual energy image reconstruction unit 22 reconstructs and displays a dual energy image DI in which the range around the peak P is an equivalent image with the fixed weighting coefficient α. When there are a plurality of peaks P, respective equivalent images are calculated, and the equivalent images are displayed in an overlapping manner. In addition, the colored display part 28 is equivalent to the one image of the low energy tomographic image LT or the high energy spectrum tomographic image HT so that the operator can easily diagnose the image displayed on the display 60. Are displayed in layers.

If it progresses to step S57, since the 2nd region-of-interest specific | specification part 23-2 could not extract a peak value, threshold value SH1 will be lowered | hung. Then, the process returns to step S54 to determine whether there is a distribution of the number of pixels exceeding the threshold value SH1.
In the present embodiment, the flowchart for searching for the peak P by lowering the threshold value SH1 is shown. However, when there are a plurality of peaks P and the operator wants to narrow down the substance more, the threshold value is set like the threshold value SH2. May be raised.

<Example of coloring of substance of dual energy image DI>
FIG. 9 is a diagram for explaining how the coloring display unit 28 colors an equivalent image.
FIG. 9A shows the ratio of pixel values between the X-ray tomographic image LT with a low energy spectrum and the X-ray tomographic image HT with a high energy spectrum on the horizontal axis, in other words, the weighting coefficient α, and the hue on the vertical axis. This is a color map 90 that takes (Hue: color type (red, blue, yellow, etc.)). The vertical axis is normalized from 0 to 1, but may be expressed as an angle from 0 degrees to 360 degrees.

  Since the horizontal axis of the color map 90 is the weighting coefficient α, fat (α = 0.8), water (α = 1.0), calcium (α = 1.45) are easily recognized by the operator. ) And iodine contrast agent (α = 1.9) are colored red, blue, yellow and green, respectively. For example, in the color map graph 91, the range of the weighting coefficient α of 0.95 to 1.40 is assigned to the same color. When the color display section 28 wants to change the color, the color map graph 91 displayed on the display 60 can be dragged with the mouse and moved up and down in the direction of the arrow 93 to move as shown by the dotted line. Can be changed. If the weighting coefficient α is in the range of 1.00 to 1.40 and is to be assigned to the same color, the graph 91 is dragged with a mask and moved to the left and right in the direction of the arrow 95 and moved as indicated by a dotted line. The same color range can be changed.

Further, the color change from water to calcium has a completely different hue as indicated by a portion 95 of the graph 91. However, as the color changes from calcium to iodine contrast agent, the hue gradually changes as indicated by the portion 97 of the graph 91. Although only a linear change is shown in FIG. 9, a non-linear hue change may be set.
The hue set in this way colors the specific substance, and the specific substance colored in one of the low-energy tomographic image LT or the high-energy spectrum tomographic image HT is displayed. FIG. 9B is an example.

  According to the present invention, the weighting coefficient α of a specific substance can be accurately set manually or automatically in the dual energy image DI. The specific substance can be easily colored and displayed on the display 60. Therefore, the operator can make a diagnosis by seeing an accurate dual energy image DI. In the embodiment, the description has been made by paying attention to fat, water, calcium, iodine contrast medium, and the like, but it goes without saying that other substances may be noted.

  The image reconstruction method in the present embodiment may be a three-dimensional image reconstruction method by a conventionally known Feldkamp method. In the present embodiment, the scan format is not particularly limited. That is, the same effect can be obtained even in the case of axial scan, helical scan, variable pitch helical scan, and helical shuttle scan. Further, the inclination of the scanning gantry is not limited. That is, the same effect can be obtained even in the case of so-called tilt scanning. The present embodiment can also be applied to heartbeat image reconstruction in which images are reconstructed in synchronization with biological signals, particularly heartbeat signals.

DESCRIPTION OF SYMBOLS 10 ... X-ray tomography apparatus 20 ... Image processing apparatus 21 ... Image reconstruction part 22 ... Dual energy image reconstruction part 23 ... Region of interest specific part, 23-1 ... First area of interest specific part, 23-2 ... Second Region-of-interest specifying unit 24 ... image comparison information calculation unit, 24-1 ... first image comparison information calculation unit, 24-2 ... second image comparison information calculation unit 25-1 ... weighting coefficient adjustment unit, 25-2 ... weighting coefficient Determination unit 27 ... Image feature amount display unit 28 ... Colored display unit 51 ... High voltage / low voltage generator 59 ... Storage device 60 ... Display 100 ... Gantry 101 ... X-ray tube 103 ... Multi-row X-ray detector 161 ... Slider bar 165 ... Image feature quantity DI ... Dual energy image HD ... High energy spectrum projection data LD ... Low energy spectrum projection data HT ... High energy -Spectral tomographic image LT ... Low-energy spectral tomographic image HB ... Subject

Claims (2)

First energy projection data or first energy tomographic image of subject with X-rays of first energy, and second energy projection data or second energy tomographic image of subject with X-rays of second energy. An image display unit that displays a dual energy image obtained by performing a weighted subtraction process of subtracting both after multiplying one or both of the weighting coefficients with respect to

A region of interest identifying unit that identifies and displays a region of interest for each specific substance on the dual energy image displayed on the image display unit on a display screen;

A weighting coefficient adjustment unit that allows the operator to adjust the weighting coefficient by operating the dual energy image displayed by the image display unit and the identified region of interest;

Weight coefficient setting means for setting the weight coefficient;
With
The display unit also changes and displays the dual energy image in accordance with the change of the weighting factor by the weighting factor adjustment unit, and the weighting factor is set by the weighting factor setting unit, thereby identifying the region of interest. Hide display of region of interest by means

X-ray tomography apparatus characterized by the above. The image display unit displays a pixel that is zero or in a predetermined range from zero in the dual energy image based on the set weighting coefficient, and is superimposed on the first energy tomographic image or the second energy tomographic image. The X-ray tomography apparatus according to claim 1, further comprising a screen.