JP3678382B2 - X-ray CT system - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an X-ray CT (Computed Tomography) apparatus that performs a pre-scan for confirming, for example, the presence or absence of a contrast medium before a main scan, and particularly, for example, a CT value, a projection data level, and an injection obtained at the time of a pre-scan. A plurality of threshold values are set for the data such as the injection amount of the contrast medium, and the pre-scan interval is controlled based on each threshold value, thereby reducing the exposure during pre-scanning and the main scan at the appropriate timing. The present invention relates to an X-ray CT apparatus that can be started.
[0002]
[Prior art]
In an X-ray CT apparatus that takes a tomographic image of a subject by exposing the subject to X-rays, the contrast agent injected into the subject is used for imaging before obtaining a diagnostic image. In some cases, a pre-scan is performed to determine whether or not the region has reached the region (blood vessel or the like).
[0003]
As this prescan, a continuous scan method shown in FIG. 8A and a discrete scan method shown in FIG. 8B are known.
[0004]
In the continuous scanning method shown in FIG. 8A, the subject is continuously exposed to X-rays, and the presence or absence of the contrast agent is confirmed based on the tomographic image obtained thereby, A CT value (data obtained by quantifying the X-ray absorption rate of the substance) of a blood vessel for confirming the presence or absence of a contrast agent is detected. Then, the CT value of the blood vessel that rises in accordance with the amount of contrast medium flowing in the blood vessel shifts to the main scan at a timing when it exceeds a predetermined threshold indicated by a dashed line in FIG. .
[0005]
In such a continuous scanning method, since the subject is continuously exposed to X-rays, it can be detected with almost no error that the CT value has reached the threshold level.
[0006]
That is, the CT value is detected based on projection data formed by the X-ray detector by the exposure. Further, in the continuous scanning method, there is actually a slight interval between the exposure and the next exposure. For this reason, when the CT value becomes a value near the threshold value as shown in FIG. 8A, the CT value exceeds the threshold value if the exposure and the next exposure are performed across the threshold value. This is detected for the first time by X-ray exposure immediately after the threshold value is exceeded.
[0007]
Therefore, a deviation (error) occurs from the timing when the CT value actually exceeds the threshold value until it is detected. As described above, the exposure between the continuous scanning method and the next exposure is performed. Since the interval is a short time, it can be detected with a small error that the CT value exceeds the threshold value, and the main scan can be started at a substantially optimal timing when the contrast medium reaches the target blood vessel. .
[0008]
On the other hand, in the discrete scan method shown in FIG. 8B, the subject is intermittently exposed to X-rays, and the presence or absence of the contrast agent is confirmed based on the tomographic image obtained thereby. The CT value of the blood vessel for confirming the presence or absence of the contrast agent (data obtained by quantifying the X-ray absorption rate of the substance) is detected. Then, the CT value of the blood vessel that rises according to the amount of contrast medium flowing in the blood vessel shifts to the main scan at a timing when it exceeds a predetermined threshold value indicated by a one-dot chain line in FIG. .
[0009]
In such a discrete scan method, the subject is exposed to X-rays intermittently, so that the amount of exposure of the subject can be reduced more than the continuous scan method.
[0010]
[Problems to be solved by the invention]
However, since the above-described continuous scanning method continuously exposes X-rays, the main scan can be started at a substantially optimal timing. There was a problem that the amount increased.
[0011]
On the other hand, since the above-described discrete scanning method intermittently exposes X-rays, the amount of exposure on the subject can be reduced. On the other hand, FIG. As shown in the figure, there is a gap between the exposure and the next exposure, so there is a large time error from when the CT value actually exceeds the threshold until it is detected. There was a problem that caused a shift.
[0012]
The present invention has been made in view of the above-described problems, and provides an X-ray CT apparatus capable of reducing exposure during pre-scanning and starting main scanning at an appropriate timing. Objective.
[0013]
[Means for Solving the Problems]
The X-ray CT apparatus according to the present invention performs X-ray pre-scanning to determine whether or not the inspection site can be inspected before performing the main scan for capturing a tomographic image of the inspection site by the imaging means. In order to solve the above-mentioned problems, the CT apparatus has the following characteristic means.
[0014]
That is, the X-ray CT apparatus according to the present invention includes a threshold setting unit that sets a plurality of thresholds for data for determining whether or not the examination site obtained at the time of pre-scanning can be examined, Until the level of data obtained at the time of scanning exceeds a predetermined threshold set by the threshold value setting means, the imaging means is controlled so that the pre-scan interval is coarse, and the level of data obtained at the time of pre-scanning However, it has control means for controlling the imaging means so that the pre-scan interval is close until the predetermined threshold is exceeded and the level for performing the main scan is reached.
[0015]
Specifically, the data for determining whether or not the examination site can be examined is data obtained by quantifying the X-ray absorption rate of the substance obtained from the imaging means, so-called CT value, This is projection data obtained from the imaging means or data indicating the amount of contrast medium injected from the contrast medium injection means for injecting the contrast medium into the subject.
[0016]
In the present invention, when the first and second threshold values are set by the threshold setting unit, for example, the control unit first determines the CT value, projection data, or contrast agent injection amount. The imaging means is controlled to perform pre-scanning with a rough pre-scan interval until the indicated data exceeds the first threshold. In addition, after the CT value, projection data, or data indicating the contrast medium injection amount exceeds the first threshold, the prescan interval is increased until the data exceeds the second threshold. The imaging means is controlled to perform scanning. Then, the main scan is started when the data exceeds the second threshold.
[0017]
Thereby, in the first half until the contrast agent reaches the target blood vessel, the pre-scan with a rough pre-scan interval can detect the level of the data while reducing the amount of exposure to the subject. In the second half when the level rises, the data level is detected at a fine timing by pre-scanning with a narrow pre-scan interval, and the transition timing to the main scan can be measured. Therefore, it is possible to reduce the exposure during pre-scanning and to start the main scanning at an appropriate timing.
[0018]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, preferred embodiments of an X-ray CT apparatus according to the present invention will be described in detail with reference to the drawings.
[0019]
First, as shown in FIG. 1, the X-ray CT apparatus according to the first embodiment of the present invention exposes a subject to X-rays, and thereby detects X-rays transmitted through the subject. An imaging unit 1 which detects projection data to form projection data, a reconstruction unit 2 which forms reconstructed image data for monitor display based on projection data from the imaging unit 1, and a display on the reconstructed image data A display control unit 3 that performs control, and a monitor device that displays an image corresponding to the reconstructed image data that is display-controlled by the display control unit 3;
[0020]
In addition, the X-ray CT apparatus stores a reference image of a site to be observed and a recording / reproducing unit 5 that stores and reproduces a plurality of CT values as threshold values used during pre-scanning, and inputs a plurality of CT values as the threshold values. An input unit 6 to perform the CT value of the prescan image supplied from the reconstructing unit 2 and a plurality of CT values as threshold values reproduced by the recording / reproducing unit 5, or an input unit And a system control unit 7 that controls a pre-scan interval at the time of pre-scanning of the imaging unit 1 based on a plurality of CT values as threshold values input from 6.
[0021]
As shown in FIG. 4, the imaging unit 1 is, for example, a so-called third generation (Rotate-) in which an X-ray tube 1a and an X-ray detector 1b are rotatably provided at opposing positions on the inner diameter of a ring-shaped gantry. Rotate method) X-ray CT apparatus, and when imaging a tomographic image of the subject, the subject on the bed is positioned on the central axis of the gantry and the X-ray tube 1a The X-ray detector 1b is rotated along the inner diameter of the gantry, and the X-ray tube 1a is driven at a predetermined interval during the one rotation to perform X-ray exposure a plurality of times. The X-ray passing through the subject is detected by the X-ray detector 1b for each X-ray exposure, and based on a plurality of projection data from the X-ray detector 1b obtained during the one rotation. The reconstruction unit 2 reconstructs one tomographic image. The display controller 3 controls the monitor device 4 to display the reconstructed tomographic image.
[0022]
Further, by repeatedly performing such imaging while gradually moving the subject on the bed along the central axis of the gantry, it is possible to obtain a plurality of tomographic images of the subject according to the movement interval. (Helical scan), detailed observation of a lesioned part, etc. can be made possible.
[0023]
Here, for example, in order to examine the quality of the blood flow in the affected area, a contrast medium is injected into the subject, and imaging is performed at the timing when the contrast medium reaches the affected area. Can be obtained. For this reason, the X-ray CT apparatus is provided with a pre-scan function that makes it possible to determine whether or not the contrast agent injected into the subject has spread to the target blood vessel to be imaged.
[0024]
When performing this pre-scan, the operator first operates the input unit 6 to pick up an image of a site where the target blood vessel is located, and displays this as a reference image on the monitor device 4, or the target blood vessel is located. When a part is imaged in advance and stored in the recording / reproducing unit 5, the input unit 6 is operated to read it and display it on the monitor device 4.
[0025]
Next, the operator operates the input unit 6 to set a region of interest (ROI) so that a reference image displayed on the monitor device 4 includes a blood vessel for confirming the presence or absence of the contrast agent. 2, the first and second threshold values for the CT value of the blood vessel that increases as the amount of contrast medium flowing in the blood vessel increases as indicated by the one-dot chain line in FIG.
[0026]
This CT value (CT Number: CT Value) is a value representing the absorption rate of X-rays with moisture as a reference value (0), and has a unique value depending on the tissue. For example, “0” for water, “−100” for fat, “16” for blood, “800 to 1000” for bone, and the like.
[0027]
When such two types of thresholds are set, the system control unit 7 controls the imaging unit 1 so as to perform intermittent pre-scan every predetermined time. As a result, the tomographic image by this intermittent prescan is displayed on the monitor device 4. At this time, the reconstruction unit 2 determines the CT value of the tomographic image by this intermittent prescan to the system control unit 7. To supply.
[0028]
The system control unit 7 detects the CT value of the image in the region of interest (mainly blood vessels in this case) from the CT values of the tomographic image, and this CT value exceeds the first threshold shown in FIG. Until then, the imaging unit 1 is controlled to continue the intermittent pre-scan, and the imaging unit 1 is controlled to perform continuous pre-scan at the timing when the CT value exceeds the first threshold. Then, the imaging unit 1 is controlled so that the main scan is performed at the timing when the CT value exceeds the second threshold.
[0029]
Thereby, in the first half until the contrast agent reaches the target blood vessel, the CT value can be detected while reducing the amount of exposure to the subject by the discrete pre-scan, and the contrast agent is applied to the target blood vessel. In the second half when the level of the CT value gradually rises and the CT value level rises, the CT value is detected at a fine timing with few errors by the continuous pre-scan, and the transition timing to the main scan can be measured.
[0030]
Therefore, it is possible to reduce the exposure of the subject during the pre-scan, and to start the main scan at an appropriate timing when the contrast medium has sufficiently spread to the target blood vessel, which is useful for diagnosis without failure. Can be imaged.
[0031]
Next, an X-ray CT apparatus according to the second embodiment of the present invention will be described.
[0032]
The X-ray CT apparatus according to the first embodiment sets a plurality of thresholds for the CT value of the blood vessel. However, the X-ray CT apparatus according to the second embodiment includes the A plurality of threshold values are set for the projection data formed by the X-ray detector 1b of the imaging unit 1, and the above-described pre-scan control is performed.
[0033]
In the description of the X-ray CT apparatus according to the second embodiment, the same reference numerals are given to portions showing the same operations as those of the X-ray CT apparatus according to the first embodiment described above. Detailed description thereof will be omitted.
[0034]
That is, the X-ray CT apparatus according to the second embodiment includes projection data formed by the X-ray detector 1b having the first channel to the n-th channel of the imaging unit 1 as shown in FIG. The system control unit 17 compares a plurality of threshold values input via the unit 6 and controls the prescan interval based on the comparison result.
[0035]
In such an X-ray CT apparatus, when the first and second threshold values are set through the input unit 6 as described above, for example, the imaging unit first performs intermittent pre-scanning. 1 is controlled. The imaging unit 1 supplies projection data obtained by this intermittent prescan to the system control unit 17. When the projection data by the intermittent prescan is supplied, the system control unit 17 detects a difference between the projection data and the projection data of the reference image, and compares the difference value with each of the threshold values. .
[0036]
Specifically, as shown in FIG. 5, the projection data changes in the value of the projection data when the contrast agent reaches the blood vessel. This change gradually increases as the amount of contrast agent that reaches the blood vessel increases. Therefore, the main scan is performed by detecting the difference between the projection data of the reference image before the contrast agent injection and the projection data obtained by the pre-scan after the contrast agent injection, and comparing the difference with the respective threshold values. It is possible to measure the optimal timing to shift to.
[0037]
That is, the system control unit 17 controls the imaging unit 1 to perform intermittent prescan until the difference value exceeds the first threshold, and the timing at which the difference value exceeds the first threshold. The imaging unit 1 is controlled so as to perform continuous pre-scanning. Then, the imaging unit 1 is controlled so as to shift to the main scan when the difference value exceeds the second threshold.
[0038]
Thereby, the same effect as the X-ray CT apparatus which concerns on the above-mentioned 1st Embodiment can be acquired.
[0039]
As the projection data, projection data obtained for each exposure may be used as a comparison target with the threshold value, but this is obtained by adding each projection data for a plurality of exposures (for example, one rotation). The average value may be compared with each of the threshold values. As a result, the projection data to be compared with each threshold value can be normalized, and adverse effects due to noise or the like can be reduced.
[0040]
Next, an X-ray CT apparatus according to the third embodiment of the present invention will be described.
[0041]
The X-ray CT apparatus according to each of the embodiments described above sets a plurality of threshold values for the CT value or projection data of the blood vessel. The X-ray CT apparatus according to the third embodiment, The above-described pre-scan control is performed by setting a plurality of threshold values for data indicating the amount of contrast medium injected from a contrast medium injector that injects a contrast medium into a subject.
[0042]
In the description of the X-ray CT apparatus according to the third embodiment, the same reference numerals are given to the portions showing the same operations as those of the X-ray CT apparatus according to the first embodiment described above. Detailed description thereof will be omitted.
[0043]
That is, the X-ray CT apparatus according to the third embodiment injects a contrast agent into the subject as shown in FIG. 6 and outputs data indicating the injection amount of the contrast agent (injection amount data). The contrast medium injector 26, the injection amount data from the contrast medium injector 26, and a plurality of threshold values input via the input unit 6 are compared, and the pre-scan interval is controlled based on the comparison result. And a system control unit 27.
[0044]
In such an X-ray CT apparatus, when the first and second types of threshold values are set through the input unit 6 as described above, for example, the system control unit 27 first performs intermittent prescanning. The imaging unit 1 is controlled so that the injection amount of the contrast agent injected into the subject is detected based on the injection amount data from the contrast agent injector 26.
[0045]
The amount of contrast medium injected into the subject is proportional to the time required for the target blood vessel to be filled with the contrast medium. For this reason, the system control unit 27 sequentially compares the injection amount data supplied from the contrast medium injector 26 with the plurality of threshold values, and continues intermittently until the injection amount exceeds the first threshold value. The imaging unit 1 is controlled to perform pre-scanning, and the imaging unit 1 is controlled to perform continuous pre-scanning when the injection amount exceeds the first threshold. Then, the imaging unit 1 is controlled so as to shift to the main scan when the injection amount exceeds the second threshold value.
[0046]
Thereby, the same effect as the X-ray CT apparatus which concerns on the above-mentioned 1st Embodiment can be acquired.
[0047]
Next, an X-ray CT apparatus according to the fourth embodiment of the present invention will be described.
[0048]
In the X-ray CT apparatus according to each of the embodiments, two types of thresholds are set as thresholds for each data. However, the X-ray CT apparatus according to the fourth embodiment has four types of thresholds. In addition to setting a threshold value, the system control unit controls the imaging unit so as to gradually narrow the pre-scan interval based on this threshold value.
[0049]
That is, as shown in FIG. 7, the case where four types of threshold values are set for the CT value as in the X-ray CT apparatus according to the first embodiment described above will be described as an example. First, the imaging unit 1 is controlled so as to perform pre-scanning at time T intervals, and CT values from the reconstruction unit 2 by this pre-scanning are detected and compared with the respective threshold values. Then, when it is detected that the CT value exceeds the first threshold, the imaging unit 1 is controlled to perform pre-scan at time T / 2 intervals at this timing.
[0050]
Next, when the system control unit 7 detects that the CT value obtained by the prescan at the time T / 2 interval exceeds the second threshold value, the system control unit 7 performs the prescan at the time T / 4 interval at this timing. The imaging unit 1 is controlled. When it is detected that the CT value obtained by the pre-scan at the time T / 4 interval exceeds the third threshold value, the imaging unit performs pre-scan (continuous scan) at the time T / 8 interval at this timing. 1 is controlled, and the imaging unit 1 is controlled to shift to the main scan at a timing when it is detected that the CT value exceeds the fourth threshold value.
[0051]
When a plurality of threshold values are set as described above, the imaging unit 1 is controlled so that the pre-scan is performed by gradually narrowing the pre-scan interval every time the CT value obtained by the pre-scan exceeds each threshold value. As described above, the amount of exposure on the subject can be reduced in the same manner as described above, and the pre-scan can be performed at intervals according to the increase in the CT value level, at a more optimal timing. Can be shifted to the main scan.
[0052]
In the description of the fourth embodiment, the CT value is used as a comparison target with the threshold value. This is the same as the projection data as in the X-ray CT apparatus according to the second or third embodiment described above. Alternatively, the same effect can be obtained by using an injection amount for the contrast medium.
[0053]
In the description of each of the above embodiments, the CT value, projection data, or contrast agent injection amount is used as a comparison target with the threshold value. You may make it use.
[0054]
In addition, the X-ray CT apparatus according to the present invention is applied to a so-called third generation X-ray CT apparatus, but this may be applied to other generations such as a first generation, a second generation, a fourth generation, and a fifth generation. You may make it apply to an X-ray CT apparatus.
[0055]
In addition, although two or four types of threshold values are set, it is only necessary to set desired types of threshold values such as three types, five types, six types, and the like.
[0056]
For example, when three types of threshold values are set, the system control unit 7 pre-defines at intervals of time T until the CT value, projection data, or data indicating the contrast agent injection amount exceeds the first threshold value. The imaging unit 1 is controlled to perform scanning. In addition, after the data exceeds the first threshold, the imaging unit 1 is controlled to perform pre-scanning at intervals of time T / 2 until the data exceeds the second threshold. In addition, after the data exceeds the second threshold, the imaging unit 1 is controlled to perform pre-scanning with a narrow pre-scan interval until the data exceeds the third threshold. Then, the imaging unit 1 is controlled to start the main scan at a timing when the data exceeds the third threshold.
[0057]
As a result, the amount of exposure on the subject can be reduced in the same manner as described above, and as the data level increases, pre-scanning can be performed at intervals corresponding to this, and at a more optimal timing. Can be shifted to the main scan.
[0058]
Finally, each of the above-described embodiments is an example, and it is needless to say that various modifications can be made according to the design or the like as long as the technical idea of the present invention is not deviated.
[0059]
【The invention's effect】
The X-ray CT apparatus according to the present invention can reduce exposure during pre-scanning and can start the main scanning at an appropriate timing.
[Brief description of the drawings]
FIG. 1 is a block diagram of an X-ray CT apparatus according to a first embodiment of the present invention.
FIG. 2 is a diagram for explaining how a pre-scan interval is controlled by two threshold values in the X-ray CT apparatus according to the first embodiment.
FIG. 3 is a block diagram of an X-ray CT apparatus according to a second embodiment of the present invention.
FIG. 4 is a diagram illustrating a configuration of an imaging unit provided in the X-ray CT apparatus.
FIG. 5 is a diagram illustrating a state in which the value of projection data obtained from the imaging unit changes before and after the contrast medium is introduced.
FIG. 6 is a block diagram of an X-ray CT apparatus according to a third embodiment of the present invention.
FIG. 7 is a diagram for explaining how a pre-scan interval is controlled by four threshold values in an X-ray CT apparatus according to a fourth embodiment of the present invention.
FIG. 8 is a diagram for explaining a pre-scan operation of a conventional X-ray CT apparatus.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Imaging part, 2 ... Reconstruction part, 3 ... Display control part, 4 ... Monitor apparatus 5 ... Recording / reproducing part, 6 ... Input part, 7, 17, 27 ... System control part 26 ... Contrast medium injector

Claims (5)

In an X-ray CT apparatus that performs a pre-scan to determine whether or not the inspection site can be inspected before performing a main scan for capturing a tomographic image of the inspection site by an imaging unit,
Threshold setting means for setting a plurality of thresholds for data for determining whether or not the examination site obtained at the time of pre-scanning can be examined;
Data obtained at the time of the pre-scan is controlled by controlling the imaging means so that the pre-scan interval is coarse until the level of the data obtained at the time of the pre-scan exceeds a predetermined threshold set by the threshold setting means. Control means for controlling the imaging means so that the pre-scan interval is close until the level exceeds the predetermined threshold and reaches the level for performing the main scan. Line CT device. When a plurality of threshold values are set by the threshold setting unit until the pre-scan interval reaches a level at which a dense pre-scan is started, the control unit determines that the level of data obtained at the time of the pre-scan has each threshold value. The X-ray CT apparatus according to claim 1, wherein the imaging unit is controlled so as to perform pre-scanning with a narrow pre-scanning interval every time it exceeds. The data for determining whether or not the examination site is inspectable is a CT value obtained from the imaging means, which is data obtained by quantifying the X-ray absorption rate of a substance. The X-ray CT apparatus according to claim 1 or 2. The X-ray CT apparatus according to claim 1, wherein the data for determining whether or not the examination site is inspectable is projection data obtained from the imaging unit. 2. The data for determining whether or not the examination site can be examined is data indicating a contrast medium injection amount from a contrast medium injection means for injecting a contrast medium into a subject. Alternatively, the X-ray CT apparatus according to claim 2.

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