JP2001054519A - Method and device for deciding scanning timing, and radiation tomograph - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize a method and device for deciding a scanning timing for properly executing contrast radiography and a radiation tomograph provided with such a scanning timing deciding device. SOLUTION: Two slices 802a, 802b extending across a blood stream at the upstream of an image-pickup site are simultaneously scanned by radiation to intermittently pickup a tomographic image to calculate the flowing speed of the contrast medium from a time difference at a time when the signal intensities of blood stream images ROIa, ROIb in the tomographic image are shifted across a common threshold and the scanning starting time of the image pickup site is decided in accordance with the flowing speed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a method and apparatus for determining scan timing and a radiation tomographic imaging apparatus, and more particularly, to a tomographic image by radiation in accordance with a time when a contrast agent in a blood stream reaches an imaging site. The present invention relates to a scan timing determining method and apparatus for starting a scan for imaging, and a radiation tomographic imaging apparatus including such a scan timing determining apparatus.

[0002]

2. Description of the Related Art A radiation tomography apparatus using X-rays, that is, an X-ray CT (computerized tomography).
In an aphy) apparatus, an X-ray irradiator irradiates an X-ray beam (beam) having a width (width) encompassing an imaging range and having a thickness in a direction perpendicular thereto. The thickness of the X-ray beam can be changed by adjusting the opening of an X-ray passing aperture (aperture) of a collimator, thereby adjusting the thickness of a slice for imaging.

An X-ray detection apparatus is a multi-channel array in which a large number (for example, about 1000) of X-ray detection elements are arranged in an array in the direction of the width of an X-ray beam.
e) X-ray detector, whereby X-rays are detected.

An X-ray irradiating / detecting device is rotated (scanned) around an imaging target to obtain X-ray projections of the imaging target in a plurality of directions around the imaging target. , A tomographic image is generated (reconstructed) by a computer.

When performing tomographic imaging with angiography, a contrast agent is injected into a blood vessel by, for example, intravenous injection or the like, and scanning is started at the time when the contrast agent reaches an imaging site. As the waiting time from the injection of the contrast agent to the start of the scan, a standard waiting time corresponding to the imaging site is used.

[0006] Alternatively, a slice that crosses the blood flow is set upstream of the imaging region, and a tomographic image is continuously taken, and when the CT value (CT number) of the cross section of the blood vessel reaches a predetermined value, the image is transferred to the imaging region. In some cases, the arrival of a contrast agent is determined, and a main scan of an imaging site is started.

[0007]

When the scan is started as described above, the arrival time of the contrast agent varies depending on the individual difference of the imaging target. Therefore, the scan cannot always be performed at an appropriate timing with a uniform scan start time. There was no problem.

In order to automate the start of a scan based on the CT value of a blood vessel image, the scan should be started at an appropriate timing due to a delay in switching from the monitoring scan to the main scan, especially when the blood flow is superior to the arterial phase. There was a problem that was difficult.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-described problems, and has as its object to provide a scan timing determining method and apparatus for appropriately performing contrast imaging, and a radiation having such a scan timing determining apparatus. The object is to realize a tomographic imaging apparatus.

[0010]

Means for Solving the Problems (1) The invention according to a first aspect for solving the above-mentioned problems is directed to imaging of a tomographic image by radiation in synchronization with the time when a contrast agent in a blood flow reaches an imaging site. At the beginning of the scan for scanning, at least two slices traversing the bloodstream upstream of the imaging site are simultaneously scanned with radiation to continuously capture their tomographic images, and the tomographic images of the at least two slices are taken. Calculating the flow rate of the contrast agent from the time difference at the time when the signal intensity of the blood vessel image in the image first crosses a common threshold value, and determining a scan start time of the imaging region according to the calculated flow rate. This is a scan timing determination method.

(2) According to a second aspect of the present invention for solving the above-described problem, a scan for imaging a tomographic image by radiation is started at a time when a contrast agent in a blood stream reaches an imaging site. Scan timing determining device for
Preceding imaging means for simultaneously scanning at least two slices traversing the blood flow upstream of the imaging region with radiation and continuously capturing tomographic images thereof, and a blood vessel image in the tomographic images of the captured at least two slices Flow velocity calculation means for calculating the flow velocity of the contrast agent from the time difference at the time when the signal strength of each crosses a common threshold for the first time,
A scan start time determining means for determining a scan start time of the imaging region in accordance with the calculated flow velocity.

(3) According to a third aspect of the invention for solving the above-mentioned problem, a scan for imaging a tomographic image by radiation is started at a time when a contrast agent in a blood stream reaches an imaging site. A radiation tomographic imaging apparatus, wherein at least two slices traversing the bloodstream upstream of the imaging region are simultaneously scanned with radiation to continuously capture tomographic images thereof;
Flow velocity calculating means for calculating the flow velocity of the contrast agent from the time difference when the signal intensity of the blood vessel image in the tomographic image of one slice crosses the common threshold value for the first time, and the scan start timing of the imaging region according to the calculated flow velocity And a scan start time determining means for determining the scan start time.

(4) The invention according to a fourth aspect for solving the above-mentioned problem is the radiation tomographic imaging apparatus according to (3), wherein X-rays are used as the radiation. (5) According to another aspect of the invention for solving the above-described problem, the present invention provides a method for starting a scan at a time when a contrast agent in a blood stream reaches an imaging site and performing tomographic imaging with radiation. At least two slices traversing the bloodstream upstream of the region are simultaneously scanned with radiation to continuously capture their tomographic images, and the signal intensity of the blood vessel image in the tomographic images of the at least two slices is common. A radiation tomographic imaging method characterized in that a flow velocity of the contrast agent is calculated from a time difference at a time when each threshold value is first crossed, and a scan start timing of the imaging region is determined according to the calculated flow velocity.

(6) Another aspect of the invention for solving the above-mentioned problem is the radiation tomography method according to (5), wherein X-rays are used as the radiation. (Function) In the present invention, at least two slices crossing the blood flow at the upstream of the imaging site are simultaneously scanned with radiation to continuously capture their tomographic images, and the signal intensity of the blood vessel image in these tomographic images is common. Is calculated from the time difference at the time of first crossing each of the threshold values, the time at which the contrast agent reaches the imaging region is predicted, and the scan start time of the imaging region is determined according to the predicted time.

[0015]

Embodiments of the present invention will be described below in detail with reference to the drawings. Note that the present invention is not limited to the embodiment. FIG. 1 shows a block diagram of the X-ray CT apparatus. This device is an example of an embodiment of the present invention. The configuration of the present apparatus shows an example of an embodiment relating to the apparatus of the present invention. An example of an embodiment of the method of the present invention is shown by the operation of the present apparatus.

As shown in FIG. 1, this apparatus comprises a scanning gantry 2 and an imaging table 4.
And an operation console (console) 6. The scanning gantry 2 has an X-ray tube 20. X-ray tube 20
X-rays (not shown) emitted from the collimator 22 are, for example, fan-shaped X-ray beams, that is, fan beams (fa).
n beam) and the detector array 2
4 is irradiated. The detector array 24 has a plurality of X-ray detection elements arranged in an array in the direction of the width of the fan-shaped X-ray beam. The configuration of the detector array 24 will be described later.

The X-ray tube 20, collimator 22 and detector array 24 constitute an X-ray irradiation / detection device. The X-ray irradiation / detection device will be described later. A data collection unit 26 is connected to the detector array 24. The data collection unit 26 collects detection data of the individual X-ray detection elements of the detector array 24.

The irradiation of X-rays from the X-ray tube 20 is controlled by an X-ray controller (controller) 28. The illustration of the connection relationship between the X-ray tube 20 and the X-ray controller 28 is omitted. The collimator 22
It is controlled by the collimator controller 30. The illustration of the connection relationship between the collimator 22 and the collimator controller 30 is omitted.

The components from the X-ray tube 20 to the collimator controller 30 are mounted on the rotating unit 34 of the scanning gantry 2. The rotation of the rotation unit 34 is controlled by a rotation controller 36. The illustration of the connection relationship between the rotation unit 34 and the rotation controller 36 is omitted.

The imaging table 4 carries in and out an imaging object (not shown) into and out of the X-ray irradiation space of the scanning gantry 2. The relationship between the imaging target and the X-ray irradiation space will be described later.

The operation console 6 has a central processing unit 60. The central processing unit 60 is, for example, a computer (co.
mputer) and the like. Central processing unit 6
0 is the control interface (interface) 6
2 are connected. The scanning gantry 2 and the imaging table 4 are connected to the control interface 62. The central processing unit 60 controls the scanning gantry 2 and the imaging table 4 through the control interface 62.

The data collection unit 26, X in the scanning gantry 2
The line controller 28, collimator controller 30, and rotation controller 36 are controlled through a control interface 62. It should be noted that illustration of individual connections between these units and the control interface 62 is omitted.

A data acquisition buffer 64 is also connected to the central processing unit 60. Data collection buffer 6
4 is connected to the data collection unit 26 of the scanning gantry 2. The data collected by the data collection unit 26 is input to the central processing unit 60 through the data collection buffer 64.

The central processing unit 60 performs image reconstruction using the projection data of a plurality of views collected through the data collection buffer 64. Image reconstruction includes, for example, filtered back projection (filter
For example, a red back projection method is used.

The central processing unit 60 also has a storage device 6
6 are connected. The storage device 66 stores various data, reconstructed images, programs, and the like. The display device 68 and the operation device 70 are also connected to the central processing unit 60. Display device 68
Displays the reconstructed image and other information output from the central processing unit 60. The operation device 70 is operated by an operator, and inputs various instructions and information to the central processing unit 60.

FIG. 2 shows a schematic configuration of the detector array 24. As shown in the figure, the detector array 24 is a multi-channel X-ray detector in which a number of X-ray detection elements 24 (ik) are arranged in two rows. Many X-ray detection elements 2
4 (ik) forms an X-ray incident surface curved as a cylindrical concave surface as a whole. i is a channel number, for example, i
= 1 to 1000. k is a column number, for example, k =
1, 2. The X-ray detection element 24 (ik) has a column number k
Constitute a detection element row with the same elements. Note that the detector array 24 is not limited to two rows, and may be a multi-row of three or more rows.

The X-ray detecting element 24 (ik) is composed of, for example, a combination of a scintillator and a photodiode. The present invention is not limited to this, and may be, for example, a semiconductor X-ray detection element using cadmium tellurium (CdTe) or the like, or an ionization box type X-ray detection element using xenon (Xe) gas.

FIG. 3 shows the relationship among the X-ray tube 20, collimator 22, and detector array 24 in the X-ray irradiation / detection device. FIG. 3A is a diagram illustrating a state of the scanning gantry 2 viewed from the front, and FIG. 3B is a diagram illustrating a state of the scanning gantry 2 viewed from the side. As shown in the figure, the X-ray radiated from the X-ray tube 20 is converted into a fan-shaped X-ray beam 40 by a collimator 22.
It is shaped so as to be zero, and is irradiated on the detector array 24.

FIG. 3A shows a fan-shaped X-ray beam 40.
0 indicates the spread, that is, the width of the X-ray beam 400. The width direction of the X-ray beam 400 matches the arrangement direction of the channels in the detector array 24. (B) shows the thickness of the X-ray beam 400. The thickness direction of the X-ray beam 400 is
This corresponds to the direction in which the columns in the detector array 24 are arranged.

With the body axis intersecting the fan surface of the X-ray beam 400, for example, as shown in FIG. 4, the imaging target 8 placed on the imaging table 4 is carried into the X-ray irradiation space. The scanning gantry 2 has a cylindrical structure including an X-ray irradiation / detection device inside. A contrast agent is injected into the blood vessel of the imaging target 8 by, for example, intravenous injection or the like using a contrast agent injection device (not shown).

The X-ray irradiation space is formed inside the cylindrical structure of the scanning gantry 2. An image of the imaging target 8 sliced by the X-ray beam 400 is projected on the detector array 24. The detector array 24 detects X-rays transmitted through the imaging target 8. The thickness th of the X-ray beam 400 applied to the imaging target 8 is adjusted by the aperture of the aperture of the collimator 22.

FIG. 5 is a block diagram of the main part of the present apparatus from the viewpoint of scan timing determination. The apparatus shown in the figure is an example of an embodiment of the scan timing determining apparatus of the present invention. The configuration of the present apparatus shows an example of an embodiment relating to the apparatus of the present invention. An example of an embodiment of the method of the present invention is shown by the operation of the present apparatus.

The preceding image pickup section 500 shown in FIG. 1 includes a scanning gantry 2, an image pickup table 4, and an operation console 6. The preceding imaging section 500 is an example of an embodiment of the preceding imaging means of the present invention.

The preceding image capturing section 500 performs
For example, as shown in FIG. 6, two slices 802 a and 802 traversing the blood flow upstream of the site where contrast imaging is performed
b are simultaneously scanned, and two tomographic images 804a and 804b are generated based on the detection signals of the detection arrays 24a and 24b, respectively. The scan starts with the start of contrast injection.

For example, if contrast imaging is performed on the liver, a tomographic image of two slices crossing the blood flow of the abdominal aorta is captured. Thereby, tomographic images 804a and 804b
Includes cross-sectional images of the abdominal aorta.

The operator operates the operation device 70 to display a cross-sectional image of the abdominal aorta on the tomographic images 804a and 804b, with a region of interest (ROI) R.
These are designated as OIa and ROIb, respectively.

The tomographic images 804a and 804b are input to CT value determination units (units) 502a and 502b, respectively. The CT value determination units 502a and 502b
For example, it is realized by a computer program for the central processing unit 60 or the like. The same applies to other units described below.

CT value determination units 502a and 502b
Determines the magnitude relationship between the CT values of the regions of interest ROIa and ROIb and a predetermined threshold value CTt. The threshold value CTt is set as close as possible to a CT value of normal blood as much as possible so as to detect an increase in CT value due to contamination of a contrast agent at an early stage.

The increase in the CT value due to the start of the flow of the contrast agent is first detected in the region of interest ROIa in the tomographic image 802a of the upstream slice, as shown in FIG. 7, for example, and is determined by the CT value determination unit 502a. Indicated by the output signal. Next, the tomographic image 802 of the slice on the downstream side
b is detected in the region of interest ROIb and is displayed by the judgment output signal of the CT value judgment unit 502b.

The judgment output signals of the CT value judgment units 502a and 502b are input to the time difference detection unit 504. The time difference detection unit 504 detects a time difference Δt between a time t1 when the CT value determination unit 502a detects the inflow of the contrast agent and a time t2 when the CT value determination unit 502a detects the inflow of the contrast agent.

The time difference Δt is input to the flow velocity calculation unit 506. The flow velocity calculation unit 506 determines the input time difference Δt and slices 802a and 802b that are known in advance.
The flow velocity v of the contrast agent is calculated from the distance therebetween. The flow velocity v of the contrast agent is also substantially the velocity of the blood flow.

The above-described CT value determination units 502a, 502
02b, a portion including the time difference detection unit 504 and the flow velocity calculation unit 506 is an example of an embodiment of the flow velocity calculation means in the present invention.

The flow velocity v is determined by the scan start timing determination unit 5
08 is input. Scan start time determination unit 50
FIG. 8 shows an example of an embodiment of the scan start time determining means according to the present invention. Scan start time determination unit 5
08 predicts the time at which the contrast agent reaches the imaging site, for example, the liver, based on the flow velocity v, and determines the scan start time, that is, the scan delay time Td, corresponding thereto.

Since the distance from the preceding imaging region to the imaging region is determined according to the physique of the imaging region 8, if the flow rate is known, the time required for the contrast agent to reach the imaging region can be predicted. Time prediction is based on the liver, pancreas, kidney, etc.
This is performed using a prediction formula defined for each imaging target site. Or, a look-up table (look-up table) in which arrival times obtained in advance for various flow rates are tabulated.
Is used. The use of the lookup table is preferable in that the arrival time is easily predicted. It is preferable to consider factors such as race, gender, and age in predicting the arrival time from the viewpoint of improving accuracy.

The scan delay time Td is given to the scanning gantry 2 through the control interface 62. The scanning gantry 2 starts scanning the imaging region after the scan delay time Td. Since the scan delay time Td is determined in accordance with the predicted arrival time based on the measured value of the flow rate of the contrast agent, it is possible to start scanning the imaging region at an optimal timing.

Further, since the detection of the flow velocity of the contrast agent is performed at the initial stage of the inflow to the preceding slice position, the scan delay time Td can be set to a time which can be sufficiently handled by the present apparatus.

When the detector array 24 has, for example, a four-row configuration as shown in FIG. 8, the CT value determination by the CT value determination units 502a and 502b determines the CT values of the slices 802a and 802d at both ends. Perform on the image.
In this case, the distance between the two tomographic images is increased, so that the accuracy of the flow velocity calculation is improved, and the accuracy of the scan delay time determination can be improved.

The operation of the present apparatus will be described. FIG. 9 shows a flowchart of the operation of the present apparatus. As shown in the figure, in step 902, the operator sets an imaging region (for example, a liver or the like) through the operation device 70.

Next, at step 904, the reference position of the object 8 is scanned. The reference position depends on the imaging region,
A slice position that traverses the blood flow upstream of the slice is predetermined. When imaging the liver, such a reference position may be, for example, an axial slice (axi
al slice). This axial slice crosses the abdominal aorta. By the reference position scan, a tomographic image at the reference position is obtained. Since the detector array 24 has a two-row configuration, two tomographic images can be obtained.

Next, at step 906, the operator sets a flow velocity detection ROI on the tomographic image. That is, as shown in FIG. 6, the blood vessel images are designated as the regions of interest ROIa and ROIb on the two tomographic images 802a and 802b, respectively.

Next, in Step 908, injection of the contrast agent is started, and then, in Step 910, a flow velocity detection scan is performed. By the flow velocity detection scan, two slice scans at the reference position are continuously performed, and their tomographic images are sequentially reconstructed.

Step 912 is performed on such a tomographic image.
Then, the CT values of the regions of interest ROIa and ROIb are set to the threshold CTt.
Is determined based on The determination of the CT value is performed by the CT value determination units 502a and 502b. As long as the CT value does not exceed the threshold value CTt, the flow returns to step 910 to continue the flow velocity detection scan.

With the start of the flow of the contrast agent into the slice 802a, the CT value of the region of interest ROIa first exceeds the threshold value CTt. At this time, since the contrast agent has not yet reached the slice 802b, the CT value of the region of interest ROIb has the threshold value CTt.
Not exceed. Therefore, the flow returns to step 910 to continue the flow velocity detection scan. When the contrast agent flows into the slice 802b and the CT value of the region of interest ROIb exceeds the threshold value CTt, the process branches to step 914.

At step 914, the flow velocity is detected. The flow velocity detection is performed by the time difference detection unit 504 and the flow velocity calculation unit 506 as described above. Next, in step 916, a scan start time is determined. The scan start time, that is, the scan delay time Td is determined by the scan start time determination unit 508 as described above.

Thereafter, in step 918, a main scan is performed at a designated timing, that is, a scan of the imaging region set in step 902 is performed. In the main scan, the imaging part is positioned by moving the imaging table or the like. However, since there is a margin in the scan delay time Td, it can be dealt with without any problem.

Since the main scan is started at an optimum timing according to the actually measured value of the flow rate of the contrast agent, it is possible to appropriately perform the contrast imaging of the imaging portion and obtain a good contrast image.

In the above, an example in which X-rays are used as radiation has been described. However, the radiation is not limited to X-rays, and may be other types of radiation such as γ-rays. However, at present, X-rays are preferable because practical means regarding generation, detection, control, and the like are the most substantial.

[0058]

As described above in detail, according to the present invention, a scan timing determining method and apparatus for appropriately performing contrast imaging and a radiation tomographic imaging apparatus having such a scan timing determining apparatus are realized. can do.

[Brief description of the drawings]

FIG. 1 is a block diagram of a device according to an example of an embodiment of the present invention.

FIG. 2 is a schematic view of a detector array in the apparatus shown in FIG.

FIG. 3 is a schematic diagram of an X-ray irradiation / detection device in the device shown in FIG.

FIG. 4 is a schematic view of an X-ray irradiation / detection device in the device shown in FIG.

FIG. 5 is a block diagram of an apparatus according to an embodiment of the present invention from the viewpoint of scan timing determination.

FIG. 6 is a conceptual diagram of tomographic imaging at a reference position.

FIG. 7 is a graph showing an increase in a CT value of a region of interest due to inflow of a contrast agent.

FIG. 8 is a conceptual diagram of a 4-slice simultaneous scan.

FIG. 9 is a flowchart showing the operation of the apparatus shown in FIG. 1;

[Explanation of symbols]

 Reference Signs List 2 scanning gantry 4 imaging table 6 operation console 8 imaging target 20 X-ray tube 22 collimator 24 detector array 26 data collection unit 28 X-ray controller 30 collimator controller 34 rotation unit 36 rotation controller 60 central processing unit 62 control interface 64 data collection buffer 66 storage device 68 display device 70 operating device 500 preceding imaging units 502a, 502b CT value determination unit 504 time difference detection unit 506 flow velocity calculation unit 508 scan start timing determination unit

Claims (4)

[Claims] In starting a scan for tomographic imaging by radiation in synchronization with a time when a contrast agent in a blood flow reaches an imaging site, at least two slices traversing the blood flow upstream of the imaging site. The tomographic images are continuously captured by simultaneously scanning with radiation, and the flow rate of the contrast agent is determined from the time difference when the signal intensity of the blood vessel image in the tomographic images of the at least two slices crosses a common threshold for the first time. Calculating a scan start timing of the imaging region according to the calculated flow velocity. 2. A scan timing determining apparatus for starting a scan for imaging a tomographic image by radiation in accordance with a timing at which a contrast agent in a blood flow reaches an imaging site, comprising: Preceding imaging means for simultaneously scanning at least two slices traversing the radiation with radiation and continuously capturing their tomographic images; and a signal intensity of a blood vessel image in the tomographic images of the captured at least two slices has a common threshold value. Flow rate calculating means for calculating the flow rate of the contrast agent from the time difference at the time of first crossing each time, and scan start time determining means for determining a scan start time of the imaging region according to the calculated flow rate, Scan timing determining device. 3. A radiation tomographic imaging apparatus which starts a scan for tomographic image imaging by radiation at a time when a contrast agent in a blood flow reaches an imaging site, and traverses a blood flow upstream of the imaging site. First imaging means for simultaneously scanning at least two slices with radiation and continuously capturing their tomographic images; and for the first time, the signal intensity of the blood vessel image in the tomographic images of the at least two slices has a common threshold. Flow rate calculating means for calculating the flow rate of the contrast agent from the time difference at the time of crossing, and scan start time determining means for determining a scan start time of the imaging region according to the calculated flow rate. Radiation tomographic imaging device. 4. The radiation tomographic imaging apparatus according to claim 3, wherein X-rays are used as the radiation.