JP2011135935A - X-ray computed tomography apparatus and control program - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an X-ray computed tomography apparatus and a control program improving the accuracy in calculating the concentration of a contrast medium within an ROI (a region of interest). <P>SOLUTION: A scanning mechanism 10 executes a pre-scan of a subject P into which the contrast medium is injected with X rays and collects projection data on the subject P. An image generating part 34 generates CT image data on the subject P based on the projection data. An ROI setting part 36 sets the ROI on a CT image. A concentration index calculating part 38 calculates the index to vary according to the concentration of the contrast medium in the ROI based on the CT value of pixels included in a specific CT value range of CT values of pixels included in the ROI. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an X-ray computed tomography apparatus and a control program for monitoring a contrast agent concentration in an ROI.

  As one of the applications of scanning by X-ray computed tomography using a contrast agent, a function has been developed that monitors the contrast agent concentration in the ROI on the CT image and starts the main scan according to the contrast agent concentration. (For example, refer to Patent Document 1). The ROI for monitoring is set in the blood vessel region on the CT image. The position and size of the ROI on the CT image are fixed. Therefore, when there is a body movement or an organ movement of the subject, there is a possibility that the ROI is out of the blood vessel region. When the ROI deviates from the blood vessel region, the contrast medium monitoring accuracy deteriorates. Along with this, the main scan may be started at an incorrect timing.

JP 2008-499 A

  An object of the present invention is to provide an X-ray computed tomography apparatus and a control program that can improve the monitoring accuracy of contrast agent concentration.

  An X-ray computed tomography apparatus according to a first aspect of the present invention includes a scan unit that performs a first scan with X-rays on a subject into which a contrast agent has been injected, and collects projection data related to the subject; A generating unit that generates CT image data related to the subject based on the collected projection data, a setting unit that sets an ROI on the generated CT image, and a CT of pixels included in the set ROI And a calculation unit that calculates an index that changes in accordance with the concentration of the contrast agent in the ROI, based on the CT values of pixels belonging to a specific CT value range among the values.

  A control program according to a second aspect of the present invention is a control program for an X-ray computed tomography apparatus equipped with a scanning mechanism for scanning a subject into which a contrast medium has been injected with X-rays, the X-ray computer A function of causing a computer built in the tomography apparatus to set an ROI on a CT image related to the subject, and CT of pixels belonging to a specific CT value range among the CT values of pixels included in the set ROI And a function of calculating an index that changes in accordance with the concentration of the contrast agent in the ROI based on the value.

  ADVANTAGE OF THE INVENTION According to this invention, provision of the X-ray computed tomography apparatus and control program which can improve the monitoring precision of contrast agent density | concentration is realizable.

The figure which shows the structure of the X-ray computed tomography apparatus which concerns on embodiment of this invention. The figure which shows the typical flow of monitoring of the contrast agent density | concentration performed according to control by the system control part of FIG. The figure which shows an example of the time density curve of the average CT value in ROI in this embodiment and the conventional method. The schematic diagram of CT image in the time t1 of FIG. The schematic diagram of CT image in the time t2 of FIG. The schematic diagram of CT image in the time t3 of FIG. The figure which shows the histogram of CT value regarding all the pixels in ROI in the time t2 and the time t3 of FIG. The figure which shows the CT value range of the calculation object of an average CT value on the histogram of FIG. The figure which shows CT image and ROI regarding a neck. The figure which shows the histogram regarding ROI of FIG. 9, and CT value range of calculation object.

  Hereinafter, an X-ray computed tomography apparatus and a control program according to an embodiment of the present invention will be described with reference to the drawings.

  In the X-ray computed tomography apparatus, an X-ray tube and an X-ray detector are combined into one body, and a ROTATE / ROTATE type in which the periphery of the subject is rotated, and a large number of detection elements are arranged in a ring shape. Although there are various types such as a STATIONARY / ROTATE type in which only the X-ray tube rotates around the subject, this embodiment is applicable to any type. Here, the ROTATE / ROTATE type will be described.

  Image reconstruction methods used by the X-ray computed tomography apparatus include a full scan method and a half scan method. In the full scan method, in order to reconstruct CT image data of one slice, projection data for one round around the subject, that is, about 2π [rad] is required. In the half scan method, projection data for π + α [rad] (α: fan angle) is necessary to reconstruct image data of one slice. In this embodiment, any of the full scan method and the half scan method can be applied. However, in the following description, it is assumed that the present embodiment employs the full scan method for specific description.

  FIG. 1 is a diagram showing a configuration of an X-ray computed tomography apparatus 1 according to the present embodiment. As shown in FIG. 1, a scanning mechanism (gantry) 10 and a computer 30 are mounted.

  The scanning mechanism 10 has various mechanisms for scanning the subject P with X-rays. Specifically, the scanning mechanism 10 rotatably supports an annular or disk-shaped rotating frame 12. On the inner peripheral side of the rotating frame 12, an imaging region into which the subject P placed on the top 14 is inserted is formed. In the present embodiment, a contrast agent for visually confirming a blood vessel on a CT image is injected into the subject P. The top plate 14 is supported by a bed (not shown) so as to be slidable along the longitudinal direction and the vertical direction.

  The rotating frame 12 includes an X-ray tube 16 and an X-ray detector 18 so as to face each other with the subject P placed on the top plate 14 interposed therebetween. The rotating frame 12 receives the supply of the driving signal from the rotation driving unit 20 and continuously rotates the X-ray tube 16 and the X-ray detector 18.

  The X-ray tube 16 generates X-rays in response to application of a high voltage and supply of a filament current from the high voltage generator 22. The high voltage generator 22 applies a high voltage to the X-ray tube 16 according to control by the scan controller 42 in the computer 30 and supplies a filament current.

  The X-ray detector 18 detects X-rays generated from the X-ray tube 16 and transmitted through the subject P, and generates a current signal corresponding to the detected X-ray intensity. A data acquisition circuit (DAS) 24 is connected to the X-ray detector 18.

  The data acquisition circuit 24 reads a current signal from the X-ray detector 18 according to control by the scan control unit 42. The data acquisition circuit 24 amplifies the read current signal and digitally converts the amplified current signal to generate projection data that is a digital signal. The generated projection data is supplied to the computer 30 via the non-contact data transmission unit 26.

  The computer 30 includes a preprocessing unit 32, an image generation unit 34, an ROI setting unit 36, a density index calculation unit 38, a determination unit 40, a scan control unit 42, a display unit 44, an operation unit 46, a storage unit 48, and a system control unit. 50.

  The preprocessing unit 32 performs preprocessing such as logarithmic conversion and sensitivity correction on the projection data supplied from the data collection circuit 24. Projection data used for image reconstruction is generated by preprocessing.

  The image generation unit 34 generates CT image data based on the preprocessed projection data. Specifically, the image generation unit 34 reconstructs CT image data related to the subject P by performing reconstruction processing on the projection data.

  The ROI setting unit 36 sets an ROI (region of interest) for monitoring the contrast agent concentration on the reconstructed CT image. The ROI is set in a region where a contrast medium flows, such as a blood vessel region. The ROI may be automatically set by image processing, or may be set manually via the operation unit 46.

  The density index calculation unit 38 calculates an index (hereinafter referred to as a density index) that changes according to the contrast agent concentration in the set ROI. As the density index, for example, an average CT value or an addition value of CT values of pixels included in the ROI is adopted. At this time, the density index calculation unit 38 calculates the density index based on the CT values of the pixels belonging to a specific CT value range among the CT values of the pixels included in the ROI. That is, the pixel for which the density index is calculated is limited to pixels belonging to a specific CT value range among all the pixels included in the ROI. For example, the specific CT value range is set in consideration of CT values that can be taken by the contrast agent region corresponding to the contrast agent injected into the subject.

  The determination unit 40 compares the magnitude relationship between the calculated concentration index and a preset threshold value. Then, the determination unit 40 determines whether or not the calculated concentration index has reached a threshold value. When it is determined that the density index has not reached the threshold value, a non-reaching signal to that effect is supplied to the scan control unit 42. On the other hand, when it is determined that the density index has reached the threshold value, an arrival signal to that effect is supplied to the scan control unit 42.

  The scan control unit 42 controls the scan mechanism 10 in order to scan the subject P into which the contrast agent has been injected with X-rays. Specifically, the scan control unit 42 performs pre-scanning and main scanning. A prescan is performed to monitor the contrast agent concentration. The main scan is executed when the density index reaches the threshold value. When it is determined that the concentration index has not reached the threshold value, that is, when a non-reaching signal is supplied, the scan control unit 42 (specifically, the rotation drive unit 20, the high voltage generation unit 22). And the data acquisition circuit 24) are controlled to continue the pre-scan. On the other hand, when it is determined that the density index has reached the threshold, that is, when the arrival signal is supplied, the scan control unit 42 (specifically, the rotation drive unit 20, the high voltage generation unit 22, And the data acquisition circuit 24) is controlled to execute the main scan.

  The display unit 44 displays the CT image and the density index on the display device. As the display device, for example, a CRT display, a liquid crystal display, an organic EL display, a plasma display, or the like can be used.

  The operation unit 46 receives various commands and information input from the operator. For example, the operation unit 46 inputs the ROI setting position via the input device by the user. As an input device, a keyboard, a mouse, a switch, or the like can be used.

  The storage unit 48 stores projection data, CT image data, and density index data. In addition, the storage unit 48 stores a control program for the X-ray computed tomography apparatus for executing the monitoring of the contrast agent concentration peculiar to the present embodiment. This control program has a function for calculating the contrast agent concentration and a function for controlling the start timing of the main scan in accordance with the calculated contrast agent concentration.

  The system control unit 50 functions as the center of the X-ray computed tomography apparatus 1. Specifically, the system control unit 50 reads out the control program stored in the storage unit 48 and expands it on the memory, and controls each unit according to the expanded control program.

  Hereinafter, a typical flow of contrast agent concentration monitoring executed according to control by the system control unit 50 will be described with reference to FIG.

  First, the system control unit 50 waits for an instruction to start monitoring via the operation unit 46. When the operator is ready to start monitoring, the operator inputs a monitoring start instruction via the operation unit 46. The contrast agent may be injected before or after the start instruction is input. However, in order to specifically describe the following, it is assumed that the contrast agent is injected into the subject before the start instruction is input.

  When a start instruction is given by the operator, the system control unit 50 causes the scan control unit 42 to perform a pre-scan (step S1). In step S1, the scan control unit 42 controls the scan mechanism 10 to execute a pre-scan for monitoring the contrast agent concentration. It is assumed that the scan area in the pre-scan is a slice related to an arbitrary position and direction set in advance. Since the pre-scan is performed for monitoring the contrast agent concentration, the scan conditions are set to be rougher than those of the main scan. For example, in the pre-scan, the scan is repeated not intermittently but intermittently (for example, every second). In the prescan, X-rays having a weaker dose than the main scan are irradiated. The scan control unit 42 controls the high voltage generation unit 22 to generate X-rays in the X-ray tube 16 in accordance with the scan conditions relating to such prescan. The X-ray detector 18 detects X-rays that have passed through the subject P and generates a current signal. The data collection unit 24 reads a current signal from the X-ray detector 18 according to the control by the scan control unit 42, and generates projection data based on the read current signal. Note that one prescan is synonymous with collecting projection data for a CT image of one slice (2π projection data in the case of the full scan method).

  When step S1 is performed, the system control unit 50 causes the image generation unit 34 to perform image generation processing (step S2). In step S2, the image generation unit 34 generates CT image data related to the slice to be scanned based on the projection data for one slice collected in step S1.

  When step S2 is performed, the system control unit 50 causes the ROI setting unit 36 to perform ROI setting processing (step S3). In step S3, the ROI setting unit 36 sets the ROI for monitoring the contrast agent concentration on the CT image. A specific setting example will be described below. When step S2 is performed, the display unit 44 displays the CT image generated in step S2. The operator observes the displayed CT image and designates the setting location and size of the ROI via the operation unit 46. The ROI setting unit 36 sets an ROI having a specified size at a specified location. For example, the ROI is set on a lumen region corresponding to the lumen of the left ventricle into which contrast agent is introduced.

  When step S3 is performed, the system control unit 50 causes the concentration index calculation unit 38 to perform calculation processing (step S4). In step S4, the concentration index calculation unit 38 calculates a concentration index related to the ROI set in step S3. Hereinafter, a method for calculating the concentration index will be described. In the following description, the concentration index is an average CT value.

  First, the density index calculation unit 38 specifies a plurality of pixels belonging to a specific CT value range from a plurality of pixels included in the ROI. It is assumed that the specific CT value range is preset by the operator via the operation unit 46. Typically, the specific CT value range is set to include the CT value of the contrast agent region corresponding to the contrast agent injected into the subject. The specific CT value range is set so as not to include the CT value of a region (for example, a myocardial region or a calcified region) that is a factor that deteriorates the monitoring accuracy. A specific example of the specific CT value range will be described later. The density index calculation unit 38 calculates the average CT value by averaging the CT values assigned to the plurality of specified pixels. In this way, by limiting the CT value range for calculating the average CT value, even if a region other than the contrast agent region is mixed into the ROI, the mixed region can be excluded from the target for calculating the average CT value. That is, the variation in the average CT value due to the mixed area can be reduced.

  When step S4 is performed, the system control unit 50 causes the determination unit 40 to perform determination processing (step S5). In step S5, the determination unit 40 determines whether or not the average CT value calculated in step S4 has reached a threshold value. The threshold can be arbitrarily set via the operation unit 46 by an operator or the like.

  When it is determined that the average CT value has not reached the threshold value (step S5: NO), the system control unit 50 supplies a non-reaching signal to the scan control unit 42. When the non-reaching signal is supplied, the scan control unit 42 continues the pre-scan according to the scan condition related to the pre-scan. Then, Step S1 to Step S5 are repeated again. In this way, steps S1 to S5 are repeated until the average CT value reaches the threshold value.

  When it is determined in step S5 that the average CT value has reached the threshold value (step S5: YES), the system control unit 50 supplies an arrival signal to the scan control unit 42. When the arrival signal is supplied, the scan control unit 42 controls the scan mechanism 10 to stop the pre-scan, and controls the scan mechanism 10 to start the main scan.

  When the main scan is started, the system control unit 50 ends the monitoring of the contrast agent concentration.

  Next, the calculation method of the density | concentration parameter | index which concerns on this embodiment, and its effect are demonstrated, comparing with the conventional method. In the conventional method, the average CT value is calculated based on the CT values of all the pixels included in the ROI. Also, the ROI setting method between the present embodiment and the conventional method is the same. The ROI setting location can be applied to any part of the subject. However, in order to specifically describe the following, it is assumed that the ROI is set in the lumen of the left ventricle.

  FIG. 3 is a diagram showing an example of a time concentration curve of an average CT value in the ROI in this embodiment and the conventional method. FIG. 4 is a schematic diagram of a CT image at time t1 in FIG. FIG. 5 is a schematic diagram of a CT image at time t2 in FIG. FIG. 6 is a schematic diagram of a CT image at time t3 in FIG.

  At time t1 in FIG. 3, pre-scanning is started, and CT image data shown in FIG. 4 is generated. In FIG. 4, the position of the ROI is assumed to be set in a part of the lumen region corresponding to the lumen of the left ventricle. A myocardial region is distributed around the lumen region. The CT value range of the myocardial region is smaller than the CT value range of the contrast agent region. The position and size of the ROI do not vary with time and are fixed at the same coordinate position on the CT image.

  As shown in FIG. 3, at time t1, the contrast agent is not flowing into the left ventricle, and the average CT value in the ROI is low. Since the contrast agent flows into the left ventricle after time t1, the average CT value in the ROI rises with time.

  As shown in FIG. 3, at time t2, the average CT value between the conventional method and the present embodiment is not different. However, at time t3, the average CT value between the conventional method and this embodiment is very different. This is because the ROI at time t3 includes more myocardial regions than the ROI at time t2 due to the pulsation of the heart, as can be seen by comparing FIG. 5 and FIG.

  Hereinafter, the deviation of the average CT value will be described in detail. FIG. 7 is a diagram showing a histogram of CT values for all pixels in the ROI at time t2 and time t3 in FIG. As shown in FIG. 7, at time t2, since the myocardial region is not included in the ROI, the histogram shows a frequency distribution based on the CT value of the contrast agent. On the other hand, at time t3, the myocardial region is included in the ROI. Therefore, the histogram at time t3 is shifted to a lower CT value than the histogram at time t2 due to the CT value of the myocardial region. For this reason, in the conventional method of calculating the average CT value based on the CT values of all the pixels included in the ROI, the contrast agent concentration cannot be accurately monitored under the influence of the myocardial region.

  In order to reduce the deterioration of the calculation accuracy of the average CT value due to the myocardial region in the ROI, the concentration index calculation unit 38 further limits the pixels for which the average CT value is calculated from all the pixels in the ROI. More specifically, the density index calculation unit 38 limits the pixels for which the average CT value is calculated to pixels in the ROI that belong to a specific CT value range based on the CT value range of the contrast agent region. ing.

  FIG. 8 is a diagram showing the CT value range to be calculated for the average CT value on the histogram of FIG. As shown in FIG. 8, the concentration index calculation unit 38 sets a lower limit threshold Th1 and an upper limit threshold Th2, and calculates a CT value range between the set lower limit threshold Th1 and the upper limit threshold Th2 as a CT value range to be calculated. Set to. For example, the lower limit threshold Th1 is set between a minimum CT value that can be taken by the contrast agent region and a maximum CT value that can be taken by the myocardial region. The upper limit CT value Th2 is set, for example, between the lowest CT value that can be taken by the bone region or the calcified region and the highest CT value that can be taken by the contrast agent region. The bone region and the calcified region typically have a larger CT value than the contrast agent region. The lower limit threshold Th1 and the upper limit threshold Th2 can be arbitrarily set by the operator via the operation unit 46. For example, the CT value of the contrast agent region is 300 H.000. U. In this case, the lower threshold is 100H. U. The upper threshold is 400H. U. Set to Typically, there is no bone region or calcification region in the lumen region of the left ventricle. Therefore, when setting the ROI in the lumen region of the left ventricle, it is not always necessary to set the upper threshold.

  In this way, the myocardial region can be excluded from the calculation target of the average CT value by setting the lower limit threshold value of the CT value range of the calculation target of the average CT value. Therefore, the concentration index calculation unit 38 can prevent the average CT value in the ROI from decreasing due to the myocardial region.

  Next, a CT range to be calculated and its effect when the present embodiment is applied to the neck will be described. FIG. 9 is a diagram showing a CT image and an ROI related to the neck. FIG. 9A shows the entire CT image related to the neck, and FIG. 9B is an enlarged view of a part of the CT image. FIG. 10 is a diagram showing a histogram relating to the ROI in FIG. 9 and the CT value range to be calculated.

  As shown in FIG. 9, the ROI includes a calcified region. Typically, the CT value of the calcified region is higher than the CT value of the contrast agent region. Therefore, when the contrast agent concentration is monitored in the ROI in which the existence of the calcified region is suspected, the CT value range of the calcified region is preferably not included in the CT value range to be calculated for the average CT value. In this case, the lower limit threshold Th3 of the CT value range is set, for example, between the minimum CT value that can be taken by the contrast agent region and the maximum CT value that can be taken by the muscle region. The upper threshold value of the CT value range is set, for example, between the minimum CT value that can be taken by the calcified region and the maximum CT value that can be taken by the contrast agent region. CT value of the calcified region is 800H. U. For example, the lower threshold is 100H. U. The upper threshold is 700H. U. Set to degree.

  Thus, the calcified region can be excluded from the calculation target of the average CT value by setting the upper limit threshold value of the CT value range of the calculation target of the average CT value. Therefore, an increase in the average CT value in the ROI due to the calcified region can be prevented.

  As described above, in the present embodiment, the calculation target pixel of the concentration index in the ROI is limited to a pixel included in the ROI and belonging to a CT value range based on the CT value of the contrast agent region. That is, a blood vessel to be contrasted by a contrast agent injected into a subject can be selectively set as a monitoring target. Therefore, even when a region other than the contrast agent region such as the myocardial region is mixed in the ROI, the mixed region can be excluded from the calculation target of the concentration index. Therefore, the concentration index of the contrast agent region in the ROI can be calculated without being affected by the body movement or organ movement of the subject. Furthermore, the accuracy of the start timing of the main scan can be improved by improving the calculation accuracy of the density index. Further, since the mixed region can be excluded from the calculation target of the density index, it is not necessary to set the ROI strictly. Further, due to this, the ROI can be set larger than the conventional one.

  Thus, according to the present embodiment, it is possible to provide an X-ray computed tomography apparatus and a control program that can improve the monitoring accuracy of the contrast agent concentration.

  Note that the present invention is not limited to the above-described embodiment as it is, and can be embodied by modifying the constituent elements without departing from the scope of the invention in the implementation stage. For example, a control program that can cause a computer to execute the function is stored in a recording medium such as a magnetic disk (floppy (registered trademark) disk, hard disk, etc.), an optical disk (CD-ROM, DVD, etc.), or a semiconductor memory. It can also be distributed. In addition, various inventions can be formed by appropriately combining a plurality of components disclosed in the embodiment. For example, some components may be deleted from all the components shown in the embodiment. Furthermore, constituent elements over different embodiments may be appropriately combined.

  As described above, according to the present invention, it is possible to provide an X-ray computed tomography apparatus and a control program capable of improving the contrast agent concentration monitoring accuracy.

  DESCRIPTION OF SYMBOLS 1 ... X-ray computed tomography apparatus, 10 ... Scan mechanism (gantry), 12 ... Rotary frame, 14 ... Top plate, 16 ... X-ray tube, 18 ... X-ray detector, 20 ... Rotation drive part, 22 ... High voltage Generating unit, 24 ... Data collection circuit (DAS), 26 ... Non-contact data transmission unit, 30 ... Computer, 32 ... Pre-processing unit, 34 ... Image generating unit, 36 ... ROI setting unit, 38 ... Concentration index calculation unit, 40 ... determination unit, 42 ... scan control unit, 44 ... display unit, 46 ... operation unit, 48 ... storage unit, 50 ... system control unit

Claims (4)

A scan unit that performs a first scan with X-rays on a subject into which a contrast agent has been injected, and collects projection data relating to the subject;
A generator for generating CT image data relating to the subject based on the collected projection data;
A setting unit for setting an ROI on the generated CT image;
A calculation unit that calculates an index that changes according to the concentration of the contrast agent in the ROI based on the CT value of a pixel belonging to a specific CT value range among the CT values of the pixels included in the set ROI; ,
An X-ray computed tomography apparatus comprising: A determination unit for determining whether the index has reached a threshold;
When the determination unit determines that the index has reached the threshold value, the scan unit performs a second scan having a scan condition different from the first scan on the subject.
The X-ray computed tomography apparatus according to claim 1. A control program for an X-ray computed tomography apparatus equipped with a scanning mechanism for scanning a subject into which a contrast medium has been injected with X-rays,
In a computer built in the X-ray computed tomography apparatus,
A function of setting an ROI on a CT image related to the subject;
A function of calculating an index that changes according to the concentration of the contrast agent in the ROI based on the CT value of a pixel belonging to a specific CT value range among the CT values of the pixels included in the set ROI;
A control program that realizes In the computer,
A function for determining whether or not the indicator has reached a threshold;
When it is determined that the index has reached the threshold, a function of scanning the subject according to other scanning conditions via the scanning mechanism;
The control program according to claim 3, further realizing the above.

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