X-ray ct apparatus

The present invention relates to an X-ray CT (Computed Tomography) apparatus, and more particularly to dual energy imaging.

A dual energy imaging method using an X-ray CT apparatus is known. One of them is to irradiate the subject with X-rays while repeatedly switching the tube voltage of the X-ray tube between a high tube voltage and a low tube voltage in units of several views, and the transmitted X of the subject in multiple views. There is a method of detecting a line with a detector and generating a so-called dual energy image by using the projection of the above-mentioned multiple views based on the detection signal intensity of transmitted X-rays (see, for example, Patent Document 1, FIG. 4 and the like). ..<patcit num="1"><text>Japanese Unexamined Patent Publication No. 2008-279153</text></patcit>

<p> By the way, in dual energy photography, in order to improve the image quality of the generated image, the photon noise in the detected signal intensity of transmitted X-rays is set to a predetermined level or less at high tube voltage and low tube voltage, and further at the same level. It is desirable to. Therefore, it is ideal to set the tube current larger when the tube voltage is lower than when the tube voltage is high so that the dose of X-rays applied to the subject becomes constant even if the tube voltage changes.</p><p> On the other hand, the tube current of an X-ray tube is difficult to switch at high speed unlike the tube voltage, and when a single X-ray tube is used, the tube current cannot be significantly changed between a high tube voltage and a low tube voltage. In some cases. Further, in this case, if the tube current is set to match the low tube voltage, there is a problem that the dose of X-rays irradiated to the subject becomes excessive when the tube voltage is high, and the exposure to the subject increases. is there.</p><p> Therefore, in dual energy radiography, if there is a situation where the tube current cannot be changed significantly as described above, the current value that is lower than ideal when the tube voltage is low is set, and the tube voltage side is low. In some cases, the X-ray dose to be applied to the subject is insufficient, and an artifact may occur in the generated image.</p><p> Various projection correction methods for suppressing artifacts in generated images due to insufficient dose have been proposed (see, for example, Patent Documents, Japanese Patent Application Laid-Open No. 2001-112749, Japanese Patent Application Laid-Open No. 2004-208713, etc.). The method is intended for imaging with a single tube voltage, and it is difficult to obtain an accurate and high-quality image even if it is applied as it is to dual energy imaging.</p><p> In view of the above circumstances, it is an object of the present invention to provide an X-ray CT apparatus capable of obtaining an image with high accuracy and high image quality even in dual energy imaging in which the difference in tube current between a high tube voltage and a low tube voltage is small. And.</p>

<p> From the first aspect, the present invention comprises an X-ray tube that irradiates a subject with X-rays by a first tube voltage and a second tube voltage that is smaller than the first tube voltage, and a transmission X of the subject. An X-ray CT apparatus including an X-ray detector that detects a line and an image generation means that generates an image using projection data (data) of a plurality of views based on the detection signal intensity of transmitted X-rays by the X-ray detector. The data in which the image generation means constitutes the projection data PL by the second tube voltage and the detection signal intensity of the transmitted transmitted X-ray based on the second tube voltage is equal to or lower than a predetermined level. It constitutes the specific means to be specified and the projected data PH by the first tube voltage, and passes through the same path as the transmitted X-ray on which the specified data is based and / or a path close to the path. X including a correction means for correcting the specified data based on the data obtained by transmitted X-rays and a creation means for creating an image using the projection data PH and the projection data PL including the corrected data. A line CT device is provided.</p><p> Here, "1 or several views" is about 1 to 10 views.</p><p> "View" is a concept defined by the view angle position of an X-ray tube and the time when the X-ray tube is located at that view angle position.</p><p> An "X-ray detector" has one or a plurality of detector rows composed of a plurality of X-ray detection elements arranged in a fan-shaped spreading direction of an X-ray beam generated from an X-ray tube.</p><p> The "detection signal strength" is also called a count number (value) after AD (analog-digital) conversion.</p><p> The "projection data" is, for example, so-called projection (data). The projection is composed of the data of each channel (channel) obtained by logarithmic conversion of the detection signal intensity of transmitted X-rays in each X-ray detection element of the X-ray detector, and the data of each channel is the data of the data. The smaller the detection signal intensity of the underlying transmitted X-ray, the larger the value.</p><p> From the second aspect, in the present invention, the X-ray tube repeatedly switches the tube voltage between the first tube voltage and the second tube voltage in units of one or several views while X-raying the subject. Provided is an X-ray CT apparatus of the above-mentioned first aspect of irradiating.</p><p> From a third aspect, the invention presents that the correction means is close to the corresponding data and / or the corresponding data whose view is close to the identified data and whose channel is identical to the identified data. Provided is an X-ray CT apparatus according to the second aspect, which corrects the specified data based on the data.</p><p> From the fourth aspect, in the present invention, the projection data PH by the first tube voltage and the projection data PL by the second tube voltage are based on the projection data by the first tube voltage and the second tube voltage. Correspondence in which projection data is obtained for each of the same plurality of views by performing interpolation processing in the view direction on at least one of the projection data, and the correction means has the same view and channel as the specified data. Provided is an X-ray CT apparatus of the second aspect, which corrects the identified data based on the data and / or data in close proximity to the corresponding data.</p><p> From a fifth aspect, the present invention is based on the ratio of the correction means to a representative value of a predetermined number of data close to the corresponding data and a representative value of a predetermined number of data close to the identified data. Provided is an X-ray CT apparatus according to the third aspect or the fourth aspect, which corrects the specified data.</p><p> From the sixth aspect, the present invention provides the X-ray CT apparatus according to the fifth aspect, wherein the representative value is any of an average value, an intermediate value, a maximum value, and a minimum value.</p><p> In a seventh aspect, the present invention presents the fifth or sixth aspect in which the correction means replaces the identified data with data obtained by multiplying the corresponding data by a coefficient based on the ratio. X-ray CT equipment is provided.</p><p> In an eighth aspect, the present invention comprises the fifth aspect or the fifth aspect in which the correction means replaces the identified data with data obtained by multiplying the ratio-based coefficient by data close to the corresponding data. The X-ray CT apparatus of the sixth aspect is provided.</p><p> From the ninth aspect, the present invention has the first aspect in which the predetermined level changes based on the detection signal intensity of the projected data PL or the transmitted X-rays on which the data constituting the projected data PL is based. An X-ray CT apparatus from any one of the eighth viewpoints is provided.</p><p> From the tenth aspect, the first aspect of the present invention is that the creating means creates an image representing the ratio or difference between the image based on the projected data PH and the image based on the projected data PL including the corrected data. From the viewpoint, an X-ray CT apparatus from any one of the ninth viewpoints is provided.</p><p> An "image representing a ratio or difference" is an image created in which the ratio or difference of pixel values between corresponding pixels is used as the pixel value of a pixel at the same position as that pixel. This includes the case where at least one pixel value of the two target images is subjected to shift conversion or linear conversion before taking the ratio or difference.</p><p> From the eleventh aspect, in the present invention, the creating means reconstructs the first image based on the projected data PH and creates the second image based on the projected data PL including the corrected data. Provided is an X-ray CT apparatus of the tenth aspect, which is reconstructed and creates an image representing the ratio or difference using the first and second images.</p><p> From the twelfth aspect, in the present invention, the creating means creates predetermined projection data using the projection data PH and the projection data PL including the corrected data, and is based on the predetermined projection data. Provided is an X-ray CT apparatus according to the tenth aspect, which reconstructs an image representing the ratio or difference.</p>

<p> According to the present invention, according to the above configuration, the correction target data having a small detection signal intensity of the transmitted transmitted X-ray which is the basis in the projection data with a low tube voltage is the corresponding data of the correction target data in the projection data with a high tube voltage. Since the correction is made based on the data in or near the data, it is highly reliable because the detected signal intensity of the transmitted X-ray is large, and it is originally obtained because the path of the transmitted X-ray that is the basis is almost the same as the data to be corrected. The data to be corrected can be corrected using the data that has a strong correlation with the data to be corrected, and the image can be obtained with high accuracy and high image quality even in dual energy photography in which the difference in tube current between high tube voltage and low tube voltage is small. be able to.</p>

Hereinafter, the present invention will be described in more detail with reference to the embodiments shown in the figure. It should be noted that this does not limit the present invention.

FIG. 1 is a configuration diagram showing an X-ray CT apparatus 100 according to the present embodiment.

The X-ray CT apparatus 100 includes an operation console (console) 1, a sleeper apparatus 10, and a scanning gantry (gantry) 20.

The operation console 1 includes an input device 2 that accepts user input, a central processing device 3 that performs various controls for performing dual energy photography, various data processing for generating images, and a scanning gantry. It is equipped with a data collection buffer 5 for collecting the data acquired in No. 20, a monitor 6 for displaying an image, and a storage device 7 for storing a program, data, and the like.

The sleeper device 10 includes a table 12 on which the image pickup target H is placed and placed in and out of the opening B of the scanning gantry 20. The table 12 is moved up and down and horizontally linearly moved by a motor built in the sleeper device 10. Here, the linear movement direction of the table 12 is the z direction, the vertical direction is the y direction, and the horizontal direction perpendicular to the z direction and the y direction is the x direction.

The scanning gantry 20 has a rotating portion 15 and a main body portion 20a that rotatably supports the rotating portion 15. The rotating unit 15 includes an X-ray tube 21, an X-ray controller 22 that controls the X-ray tube 21, and a collimator that shapes the cone beam X-rays generated from the X-ray tube 21. 23, X-ray detector 24 in which a plurality of detector rows in which a plurality of X-ray detectors are arranged in the channel direction are arranged in the z direction, and the output of the X-ray detector 24 is converted into projection data and collected. A DAS (Data Acquisition System) 25 and a rotating part controller 26 that controls an X-ray controller 22, a collimator 23, and a DAS 25 are installed. The main body 20a includes a control controller 29 that exchanges control signals and the like with the operation console 1 and the sleeper device 10. The rotating portion 15 and the main body portion 20a are electrically connected via a slip ring 30.

The scanning gantry is an example of an embodiment of the X-ray irradiation / detection means in the present invention. Further, the central processing unit 3 is an example of an embodiment of an image generation means having a specific means, a correction means, and a creation means in the present invention, and these means are realized by the function of the central processing unit 3.

Hereinafter, the image generation process by dual energy photographing in the present embodiment will be described.

FIG. 2 is a flow diagram showing an example of image generation processing by dual energy imaging in the present embodiment.

In step S1, make a scan plan. Here, based on the information input by the user via the input device 2, various scan conditions required for dual energy photography are set. Scan conditions include, for example, slice thickness, scan range, switching tube voltage, tube current, one rotation time (rotation speed) of the rotating portion 15, table speed, and the like. For the switching tube voltage, for example, the high tube voltage (first tube voltage) HV is set to 140 kV, and the low tube voltage (second tube voltage) LV is set to 80 kV. One rotation time is set to, for example, 1 second. The tube current is set to, for example, 120 mA.

In step S2, dual energy imaging is performed by performing a scan according to the set scan conditions. First, the rotating portion 15 is rotated. Next, as shown in FIG. 3, for example, while alternately switching the tube voltage between the high tube voltage HV and the low tube voltage LV in 1-view units, the X-ray Xb from the focal point F of the X-ray tube 21 is transferred to the subject H. Irradiates the imaging field SFOV where is placed. The X-ray detector 24 outputs a detection signal of transmitted X-rays of the subject H in each channel. The DAS25 collects the detection signals of each channel in view units, performs AD conversion, and sends raw data having a count value according to the detection signal strength to the data collection buffer 5. The data collection buffer 5 stores the raw data in the storage device 7. The number of views to be scanned is, for example, about 2000 views. That is, data is collected for about 1000 views with a high tube voltage HV and about 1000 views with a low tube voltage LV.

In step S3, pretreatment is performed for each tube voltage. First, the central processing unit 3 reads raw data for a predetermined view angle corresponding to a designated predetermined slice position from the storage device 7. Then, the read raw data is divided into raw data due to a high tube voltage HV and raw data due to a low tube voltage LV, and predetermined preprocessing is performed for each. Pretreatment includes, for example, logarithmic transformation, beam hardening correction, reference channel (reference). There is normalization of raw data (reference correction) using channel). Here, the data obtained by logarithmically converting the count value of raw data is called projection (projection data). In addition, the data obtained by logarithmic conversion of raw data with high tube voltage HV is called projection by high tube voltage HV, and the data obtained by logarithmic conversion of raw data with low tube voltage LV is called projection with low tube voltage LV. To.

In step S4, the projection is corrected by the low tube voltage. The content of this correction will be described in detail later.

In step S5, image reconstruction processing is performed for each tube voltage. That is, the projection for a predetermined view angle by the high tube voltage HV is image-reconstructed to obtain the tomographic image GH by the high tube voltage HV. Further, the projection for a predetermined view angle with the low tube voltage LV is image-reconstructed to obtain the tomographic image GL with the low tube voltage LV. For the image reconstruction process, for example, filtered back projection is used.

In step S6, a dual energy image DG is created using the tomographic image GH with a high tube voltage HV and the tomographic image GL with a low tube voltage LV. Examples of the dual energy image DG include a ratio image showing the ratio between the tomographic image GH and the tomographic image GL, a difference image showing the difference between the tomographic image GH and the tomographic image GL, and the like. Both are known as images that are effective in identifying substances in tomographic images. A dual energy image can also be obtained by creating a predetermined projection using a projection with a high tube voltage and a projection with a low tube voltage, and performing image reconstruction processing on the predetermined projection. Therefore, the procedure for creating a dual energy image is not limited to this embodiment.

In step S7, the created dual energy image DG is displayed on the monitor 6.

Here, the content of the projection correction due to the low tube voltage in step S4 will be described in detail. Here, for the sake of simplicity, the data collected by a single detector sequence will be focused on. In addition, the view number is represented by v, the channel number is represented by i, the low data count value by low tube voltage LV is CL (i, v), the projection data by high tube voltage HV is PH (i, v), and the low tube is low. The projection data by voltage LV is represented by PL (i, v).

FIG. 4 shows the raw data count value CL obtained when X-ray Xb is irradiated from the focal point F of the X-ray tube 21 to the subject H in the view of the view number vc, which is the tube voltage LV with a low tube voltage. It is a figure which shows (i, vc) and projection PL (i, vc).

In the case of dual energy imaging in which the tube voltage is switched at high speed in view units, as described above, the dose of X-ray Xb generated when the tube voltage LV is low is small, so the low data count value CL due to the low tube voltage LV. (i, vc) is generally smaller than in the case of high tube voltage HV. The channel data with a very small count value in the raw data is greatly affected by noise called photon noise or shot noise, so it is unreliable and may cause artifacts in the reconstructed image. There are many. Therefore, among the individual data constituting the projection PL (i, vc) with the low tube voltage LV, that is, the data of each channel, the count value CL (i, vc) in the underlying raw data has a predetermined threshold. Correct the data PL (is, vc) to PL (ie, vc) that are less than or equal to the value (predetermined level) th.

However, the correction here does not improve the image quality only by the tomographic image GL due to the low tube voltage LV, but makes it possible to obtain the target image, the dual energy image DG, with high accuracy and high image quality. Therefore, the correction here does not simply apply the conventional correction method to the projection PL (i, v) with the low tube voltage LV.

FIG. 5 is a flow chart showing an example of projection correction processing with a low tube voltage.

In step S41, the attention view vc and the attention channel ic are set within the range in which the projection PL (i, v) due to the low tube voltage exists. When executing this step from the second time onward, set the views and channels that have already been set.

In step S42, it is determined whether or not the low data count value CL (ic, vc) due to the low tube voltage of the attention view vc and the attention channel ic is equal to or less than the threshold value th. If the determination condition is satisfied, the process proceeds to step S43, and if the determination condition is not satisfied, the process proceeds to step S47.

In step S43, the same threshold value determination processing as in step S42 is performed on the continuous channels following the attention channel ic, and for example, the correction target data PL (is, vc) to PL (ie, vc) shown in FIG. 4 are specified. To do.

In step S44, at the projection PH (i, v) with a high tube voltage HV, the view is close to the view vc of the data to be corrected and the channel is the same as the channels is ~ ie of the data to be corrected, for example FIG. Specify the corresponding data PH (is, vr) to PH (ie, vr) shown in. Here, since the tube voltage is switched in 1-view units to collect data, the adjacent view vr is vc-1 or vc + 1.

In step S45, the correction data PL'(is, vc) to PL'(ie, vc) are calculated based on the corresponding data PH (is, vr) to PH (ie, vr).

The data to be corrected is usually data for which it is unknown how much error there is from the data that should be originally obtained. However, in projections with high tube voltages and projections with low tube voltages where the views are identical or close to each other, the data between channels that are identical or close to each other are approximately the same path. It is considered that it is due to the transmitted X-ray passing through. Therefore, it can be estimated that the ratio of the corresponding data to the correction target data takes a value close to the ratio of the data close to the corresponding data and the data close to the correction target data.

Therefore, for example, as shown in FIG. 7, the corresponding data PH (is, vr) to PH (ie, vr) include a representative value of a predetermined number of data close to the corresponding data and a predetermined number close to the correction target data. The correction data PL'(is, vc) to PL'(ie, vc) are calculated by multiplying by a predetermined coefficient K based on the ratio of the data to the representative value of the data. As the representative value, an average value, an intermediate value, a minimum value, a maximum value, and the like can be used, but the representative value is not particularly limited thereto.

Here, we propose some methods for calculating correction data, including a method for calculating the coefficient K.

The following formula is a formula showing the first correction data calculation method.<maths num="1"><img file="JP2010142478A_D0001.tif" /></maths> In the first correction data calculation method, the correction target data PL (is, vc) is used for the average value avePH in the data for each Δi channel before and after the corresponding data PH (is, vr) to PH (ie, vr). The ratio of the average value avePL in the data for each Δi channel before and after close to ~ PL (ie, vc) is defined as the coefficient K, and this coefficient K is multiplied by the corresponding data to correct the data PL'(i, v), i. Calculate = is, ..., ie. However, if Δi is too large, it cannot be seen that the transparent X-ray path corresponding to each channel of these proximity data and the transparent X-ray path corresponding to the channel of the data to be corrected are almost the same. Therefore, set it from 1 to 10. The data used in the calculation, that is, the corresponding data and the data close to the correction target data do not have to be the same number before and after, and may be only the data for the front Δi channel or only the data for the rear Δi channel. ..

The following formula is a formula showing the second correction data calculation method.<maths num="2"><img file="JP2010142478A_D0002.tif" /></maths> In the second correction data calculation method, the correction target data PL (is, vc) is used for the average value avePHs in the data for the front Δi channel close to the corresponding data PH (is, vr) to PH (ie, vr). The ratio of the average value avePLs in the data for the front Δi channel close to ~ PL (ie, vc) and the data for the rear Δi channel close to the corresponding data PH (is, vr) ~ PH (ie, vr) The coefficient K is obtained by weighting and adding the ratio of the average value avePLe in the data for the rearward Δi channel close to the correction target data PL (is, vc) to PL (ie, vc) to the average value avePHe in. The correction data PL'(i, v), i = is, ..., ie is calculated by multiplying the corresponding data by the coefficient K. The weighting coefficients α and β may be constant at all times or may be changed according to various conditions.

The following formula is a formula showing the third correction data calculation method. This calculation method is a calculation method in the case where the weighting coefficients α and β are changed according to the position of the channel in the second correction data calculation method.<maths num="3"><img file="JP2010142478A_D0003.tif" /></maths> As a simpler method, data obtained by multiplying data close to the corresponding data by a predetermined coefficient can be calculated as correction data. Further, the correction data for one channel may be used as the correction data for each channel of the correction target data.

In step S46, the correction target data PL (is, vc) to PL (ie, vc) are replaced with the correction data PL'(is, vc) to PL'(ie, vc) for correction.

In step S47, it is determined whether or not the processing for identifying the correction target of steps S42 and S43 has been performed for all the planned views and channels. If the determination condition is satisfied, this correction process is terminated. If the determination condition is not satisfied, the process proceeds to step S41, a new attention channel or attention view is set, and the correction process is continued.

In the image generation process by dual energy imaging, as shown in FIG. 8, before correcting the projection by the low tube voltage LV in step S4, the projection process for each tube voltage is interpolated in the view direction (step S8). ) May be performed. In other words, for the missing view for which data could not be collected for each tube voltage, the raw data or projections of the views before and after that are weighted and added, so that the projection by the high tube voltage HV and the projection by the low tube voltage LV can be obtained. Try to get for the same multiple views.

In this case, since there is a projection by a high tube voltage HV and a projection by a low tube voltage LV for the same view, the view vr of the corresponding data specified in step S44 is a view close to the view vc of the data to be corrected. It is better to make it the view vc itself instead.

As described above, according to the above embodiment, the correction target data having a small detection signal intensity of the transmitted transmitted X-ray which is the basis in the projection with a low tube voltage is the corresponding data of the correction target data in the projection with a high tube voltage. Since the correction is made based on the data in or near the data, the detection signal intensity (count value) of the transmitted X-ray is high, so the reliability is high, and the path of the transmitted transmitted X-ray that is the basis is almost the same as the data to be corrected. The data to be corrected can be corrected using the data that has a strong correlation with the data that should be originally obtained from, and the image can be accurately corrected even in dual energy photography where the difference in tube current between high tube voltage and low tube voltage is small. High image quality can be obtained.

Further, according to the above embodiment, the corresponding data is multiplied by a coefficient based on the ratio of the representative value of a predetermined number of data close to the corresponding data and the representative value of the predetermined number of data close to the correction target data. Since the correction data is obtained, the correction data closer to the originally obtained data can be obtained as compared with the case where the correction data is obtained by linear interpolation or the like using the data close to the correction target data. ..

In the above description regarding the correction of projection due to a low tube voltage, the data collected by a single detector row has been focused on, but the same applies even when considering that there are a plurality of detector rows. You can make corrections. That is, when specifying the correction target data and its corresponding data, it is possible to similarly correct the projection with a low tube voltage simply by adding the detector column number in addition to the view number and the channel number as parameters.

Further, in the above embodiment, the threshold value th in the threshold value determination when specifying the correction target data is fixed, but the projection by a low tube voltage or the transmitted X-ray that is the basis of the projection It may be changed based on the detection signal strength. For example, the threshold value is changed based on the data constituting the projection, the histogram of the detection signal intensity on which the projection is based, the shape in the channel direction, and the like. As a result, the data that needs to be corrected can be specified more accurately, so that highly accurate correction can be expected.

Further, in the above embodiment, the tube voltage is switched for each view, but of course, it may be switched for each view of 2 or more. The number of views due to the high tube voltage and the number of views due to the low tube voltage do not have to be equal. Further, the tube voltage may be switched between a high tube voltage and a low tube voltage every time the rotating portion 15 is rotated by π + fan angle or 2π.

Further, in the above embodiment, dual energy imaging is performed using a single X-ray tube, but dual energy imaging may be performed using a plurality of X-ray tubes having different X-ray irradiation directions. .. In this case, the first X-ray tube may be set to a high tube voltage, and the second X-ray tube may be set to a low tube voltage.

Further, in the above embodiment, among the projections with high tube voltage, the projections in which the correction target data and the view are the same or close to each other are configured, and the corresponding data or the proximity data thereof whose channel is the same as the correction target data is used. The data to be corrected is corrected. However, among the projections due to the high tube voltage, the projection of the opposite view of the view of the correction target data or the view close to the opposite view is configured, and the corresponding data whose channel is the same as the correction target data or the adjacent data thereof. Can be similarly corrected by using. In short, among the projections with high tube voltage, if the data is from the transmitted X-ray that passes through the same path as the transmitted X-ray path that is the basis of the corrected data or the adjacent path, the corrected data is based on it. Can be corrected.

Further, in the above embodiment, the correction data of the correction target data in the projection by the low tube voltage is estimated and obtained from the projection by the high tube voltage, but as a simpler method, for example, by the low tube voltage. On the projection side, apply a well-known correction method (linear interpolation method, etc.) that makes the value of the data that has increased due to the small detection signal intensity of the underlying transmitted X-ray smaller, and it is equivalent to the correction result. It is conceivable to apply the correction to obtain the result to the corresponding data on the projection side due to the high tube voltage. According to this method, the same data change is applied to both the projection with high tube voltage and the projection with low tube voltage, so the value between the corresponding data in the projection with high tube voltage and the projection with low tube voltage It is possible to create a dual energy image with suppressed artifacts without sacrificing accuracy while maintaining the ratio and difference of. Further, as a result, the spatial resolution and noise level in the projection are about the same between the high tube voltage and the low tube voltage, so that artifacts in the generated image can be suppressed.

<figref num="1">It is a block diagram which shows the X-ray CT apparatus which concerns on this embodiment.</figref><figref num="2">It is a flow chart which shows an example of the image generation processing by dual energy photography in this embodiment.</figref><figref num="3">It is a figure which shows the correspondence relationship between each view and a tube voltage.</figref><figref num="4">It is a figure which shows the count value and projection of raw data by a low tube voltage.</figref><figref num="5">It is a flow chart which shows an example of the correction processing of the projection by a low tube voltage.</figref><figref num="6">It is a figure which shows the count value and projection of raw data by a high tube voltage.</figref><figref num="7">It is a figure which shows an example of the calculation method of the correction data.</figref><figref num="8">It is a flow chart which shows another example of the image generation processing by dual energy photography in this embodiment.</figref>

Code description

100 X-ray CT equipment 1 Operation console 2 Input device 3 Central processing unit 5 Data collection buffer 6 monitor 7 Storage device 10 sleeper 12 tables 15 Rotating part 20 scanning gantry 20a body 21 X-ray tube 22 X-ray controller 23 Collimator 24 X-ray detector 25 DAS 26 Rotating part controller 29 Control controller 30 slip ring B opening H subject