JP2933107B2 - CT device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a CT apparatus for reconstructing a tomographic image of a subject from data obtained by irradiating the subject with radiation such as X-rays, and more particularly to scanning the subject in a circumferential direction. The present invention relates to a CT apparatus that performs a so-called helical scan that moves the subject in the body axis direction.

[0002]

2. Description of the Related Art In recent years, various CT apparatuses have been proposed.
For example, an imaging system including an X-ray tube and a detector as a radiation source is rotated around the subject around the subject, and the subject is moved in a body axis direction (a direction perpendicular to a circle formed by the imaging system). ) That performs a so-called helical scan that moves the image to a position.

In this case, as shown in the perspective view of FIG. 15, the relative trajectory of the X-ray tube with respect to the subject is a "spiral".
Draw a shape. Therefore, when reconstructing an image, it is necessary to obtain data at a required position by interpolation.

For example, in FIG. 16, in order to obtain a tomographic image Img on a plane including a point D _1C and a point D _mC , first, data at the points D _1A and D _1B on the spiral locus are obtained, and then the point Distance between D _1A and point D _1C , point D _1C and point D _1B
The data value at the point D _1C is interpolated from the data at the point D _{1A and} the data at the point D _1B in accordance with the ratio of the distance between Similarly, the points D _1C , D _2C ,..., D _mC ,
By sequentially interpolating the data at D _{(m + 1) C} ,..., Data equivalent to one rotation of the tomographic plane is obtained, and the image is reconstructed. Obtain a tomographic image. Such a helical scan has an advantage that three-dimensional information of a subject can be obtained in a short time.

[0005] In addition, if imaging is performed by moving only the subject P in the body axis direction without rotating the imaging system including the X-ray tube and the detector, a fluoroscopic image (scanogram) of the subject can be obtained. .

[0006]

However, in an actual inspection, a portion requiring a detailed inspection (FIG.
In addition to the tomographic image of the region of interest (ROI), a tomographic image of a portion surrounding the part for the detailed inspection is required for so-called screening inspection. Therefore, first, Figure 1
As shown in FIG. 5 (a), after performing a helical scan while moving the couch at a predetermined constant speed for a screening test, once returning the couch to a portion where a detailed inspection is required, FIG. As shown in (b), the helical scan pitch is set to “dense” while moving the bed at a constant speed lower than the predetermined speed.

Therefore, after performing the scan for the screening test, the bed is once returned to the portion where the precision test is required, and after the positioning, the scan for the precision test must be performed at a reduced bed speed. In addition, the inspection required time and effort. Further, X-ray irradiation is performed twice in a partial ROI requiring a precise inspection, which is not preferable.

The present invention has been made in view of the above problems, and provides a CT apparatus capable of quickly scanning a wide area and designating a part requiring a fine tomographic image. With the goal.

[0009]

In order to achieve the above object, according to the first aspect of the present invention, a spiral scan is performed on a subject by a radiation source rotating around the subject, and the spiral scan is performed. In a CT apparatus for reconstructing a tomographic image based on data obtained by scanning, a display means for displaying a fluoroscopic image of a predetermined range of the subject, and a plurality of desired plural images based on the fluoroscopic images in the display means Designating means for designating a photographing range; pitch setting means for setting a pitch of each of the spiral scans in each of the photographing ranges designated by the designating means;
A control device for controlling the pitch of the helical scan in accordance with the value set by the setting means, and reconstructing means for reconstructing each tomographic image for each photographing range of the respective
The gist is to have. To achieve the above purpose
Therefore, the invention of claim 2 of the present application provides a
A spiral scan is performed on the subject with a radiation source.
Based on the data obtained by this spiral scan
A CT apparatus for reconstructing a tomographic image by using
Of each spiral scan in multiple imaging ranges
Pitch setting means for setting the pitch, and the pitch
The spiral scanning according to the value set by the setting means.
A control device for controlling the pitch of the scan,
Reconstruction means for reconstructing a tomographic image for each shadow range,
The gist is to have. And achieve the above objectives
Therefore, the invention of claim 3 of the present application rotates around the subject.
A spiral scan of the subject with the radiation source
And based on the data obtained by this spiral scan
CT apparatus for reconstructing a tomographic image by performing
Spiral scans of multiple areas of the body
Pitch setting means for setting the pitch of the
Display means for displaying the value set by the switch setting means.
And the screw according to the value set by the pitch setting means.
Control device for controlling pitch of spiral scan, and said control device
Reconstruction to reconstruct tomographic images for each imaging range
And means. Achieve the above objectives
To achieve this, the invention of claim 4 of the present application circulates around the subject.
Helical scanning of the subject by the rotating radiation source
Scan, and the data obtained by this spiral scan
CT apparatus that reconstructs a tomographic image based on
Means for designating a number of photographing ranges, and
Set the moving speed of the subject for each specified imaging range
Speed setting means, and the subject is set to the speed setting means.
Moving means for controlling to move at a set speed
And reconstruct a tomographic image for each of the imaging ranges.
And reconstructing means for performing the above.

[0010]

According to the first to third aspects of the present invention configured as described above ,
According to the helical scan pitch for each of a plurality of shooting ranges,
Can be changed, and tomographic images
Can be reconstructed. And according to the invention of claim 1, displays a previously captured subject fluoroscopic image (scanogram image), to specify a desired plurality of shooting range tomographic image on the fluoroscopic image is this designated Further, the pitch of each spiral scan for each shooting range is set .
According to the third aspect of the present invention, the pitch setting means is provided.
Displays the scan pitch in multiple defined shooting ranges
Is done. According to the invention of claim 4, a plurality of subjects
Specify the imaging range and set the moving speed of the subject for each imaging range.
When set, the subject is moved according to this speed.
Is controlled.

[0011]

An embodiment according to the present invention will be described below with reference to the drawings.

FIG. 1 shows an X-ray CT according to an embodiment of the present invention.
It is a block diagram which shows the structure of a device schematically.

Referring to FIG. 1, a gantry 1 includes an X-ray tube 3, an X-ray detector 5, a data acquisition unit 7, a bed 9, a bed driving unit 11, a bed position detector 13, and the like.

The X-ray tube 3 serving as a radiation source is supplied with a high voltage from a high voltage generator 27 provided outside the gantry 1, generates X-rays, and irradiates the subject P with X-rays. The high voltage generator 27 generates a high voltage under the control of the X-ray controller 25. Further, the X-ray detector 5 as a radiation detecting means is arranged to face the X-ray tube 3 and is composed of a large number of X-ray detecting elements for outputting a signal corresponding to the irradiated X-ray dose.

Further, a data collection unit (so-called DAS) 7
Is a multiplexer that converts analog imaging data detected and output from a large number of X-ray detection elements of the X-ray detector 5 and the bed position detector 13 simultaneously and in parallel (parallel). After the data is read out sequentially and converted into digital data, the digital data is output to the outside of the gantry 1, for example, to the FRU 15 provided in an operator room.

The bed 9 is configured to be able to move the placed subject P in a direction perpendicular to the body axis direction and the opposite axis of the subject P. When the subject P is placed, the The bed surface is positioned low at a position away from the camera, and at the time of imaging, the range where imaging of the subject P is desired is adjusted so as to be located at the rotation center of the pair of the X-ray tube 3 and the X-ray detector 5. .

Further, during imaging, the X-ray tube 3 and the X-ray detector 5
Are rotated about the body axis of the subject P, and the couch 9 is moved by the couch driving unit 11 in the body axis direction of the subject P, so that the X-ray tube 3 and the X-ray detector 5 A so-called helical scan in which the trajectory relative to the sample P draws a spiral shape can be performed.

The position of the bed 9 relative to the pair of the X-ray tube 3 and the X-ray detector 5 when the bed 9 is moved in the body axis direction is detected by the bed position detector 13. FIG. 7 shows a case where a rotary encoder 13 a is used as an example of the bed position detector 13.

Referring to FIG. 7, the bed driving unit 11 includes a clutch brake 11a, a speed reducer 11b, a motor 11c, a drive sprocket 11d, a chain 11e, a connection fitting 11f, and a tension sprocket 11g. Further, the rotary encoder 13a is directly connected to the rotating shaft of the clutch brake 11a.
The driving force of c is reduced in rotation speed by a speed reducer 11b, is driven to rotate via a clutch brake 11a, and outputs a pulse every time the rotation shaft rotates by a predetermined rotation angle.

For example, one pulse corresponds to a moving distance of the bed 9 of 0.0.
1 mm, and when the pixel size of the image display unit 17a is 0.5 mm, when 5 pulses are output from the rotary encoder 13a, the bed 9 becomes 0.5 m.
It is determined that the cursor has moved by m, and the cursor displayed on the image display unit 17a and indicating the imaging position is moved by one pixel (however, at the same magnification).

Further, the bed 9 at the start and end of the scan
It is also possible to calculate the position on the couch 9 for each sampled data by calculating the moving distance of the couch 9 during scanning from the position, and equally dividing the moving distance by the number of samples. In this case, since the actual scan start position and the scan end position deviate from the scan start position and the scan end position specified by the operator, the position on the bed 9 with respect to the actual scan start position and the scan end position. Is measured in advance, and the moving distance L is equally divided by the number of samples to obtain the position of each sampling data on the bed 9.

FRU (First Reconstruction)
ct Unit) 15 is a pre-processing unit, the image reconstruction device 1
5a and the like, and this image reconstructing device 15a
Is a processing unit that reconstructs a tomographic image of a specific cross section of the subject P, and provides convolution (Comvolution) for giving basic characteristics such as blur and resolution to the imaging data.
n) Convolution processing for integration and back projection processing for image reconstruction are performed, respectively, to reconstruct a tomographic image for a specific cross section.

The operation unit 17 includes an image display unit 17a and an operation console 17b.
Displays a tomographic image of a desired specific cross section reconstructed by the connected image reconstructing device 15a and various data such as an operation state, and a CRT display or the like is used. The operation console 17b has a keyboard for instructing the computer 19 to input programs and data and various operations, and a slide volume as a moving speed adjusting means for the bed 9 as shown in FIG. Can be easily changed with one finger. In addition to the slide volume, a sliderac accelerator (for example, a foot-operated pedal), a trackball, a joyful stick, and the like are used as the moving speed adjusting means.

The computer 19 is connected to each of the FRU 15, the operation unit 17, the image storage device 21, the mechanism control device 23, and the X-ray control device 25, and controls the entire CT device. The storage device built in the computer 19 is for storing programs and the like for performing various controls in the computer 19, and in this embodiment, also stores data relating to an inspection procedure described later.

The image storage device 21 mainly stores a tomographic image reconstructed by the image reconstruction device 15a.

The mechanism control unit 23 includes a gantry control unit 23a and a bed control unit 23b. Under the control of the computer 19, the gantry control unit 23a mainly
The bed control unit 23b mainly controls the bed driving unit 11 and controls the bed when the subject P is placed on the bed 9 by controlling the rotation of the pair of the tube 3 and the X-ray detector 5. The bed surface is positioned low at a position away from the position 1 and adjusted so that a range where imaging of the subject P is desired at the time of imaging is positioned at the rotation center of the pair of the X-ray tube 3 and the X-ray detector 5. When performing the helical scan, the bed 9 is moved in the body axis direction of the subject P in synchronization with the rotation of the pair of the X-ray tube 3 and the X-ray detector 5.

The X-ray controller 25 applies high-voltage power supplied from the high-voltage generator 27 to the X-ray generator 1 under the control of the computer 19. The high-voltage generator 27 has a high-voltage transformer or the like, generates high-voltage power, and supplies it to the X-ray generator 1.

Next, the operation and operation of the present embodiment based on the above configuration will be described with reference to FIGS.

In this X-ray CT apparatus, during imaging, the X-ray tube 3 and the X-ray detector 5 installed in the gantry 1 rotate continuously around the subject P, and the subject P is mounted. The couch 9 is moved by the couch drive circuit 5 in the body axis direction of the subject P (in a direction substantially perpendicular to the circle drawn by the X-ray tube 3 and the X-ray detector 5) at a fast speed and then slowly. At the specified speed, and at a higher speed. That is,
As shown in FIG. 2, the helical scan in which the relative trajectory of the X-ray tube 3 and the X-ray detector 5 with respect to the subject P draws a spiral shape is performed at a coarse pitch first, and subsequently to the coarse helical scan. Scan at a finer pitch and at a coarser pitch. At this time, the X-ray tube 3 is supplied with high-voltage power by the high-voltage generator 27 to irradiate the subject P with X-rays,
The X-ray detector 5 detects the X-ray transmitted through the subject P.

Data relating to the X-ray absorption coefficient of the subject P detected by the X-ray detector 5 is sent to the data collection unit 7 as an electric signal, where the data is subjected to A / D conversion and the like.
Sent to RU15. The FRU 15 sends projection data obtained by performing a process such as logarithmic conversion on the basis of this data to the magnetic disk of the image storage device 21, and all the data obtained by the helical scan are stored on the magnetic disk.

The image reconstructing device 15a is an image storage device 21
The projection data is read out from these, and arithmetic processing is performed on these data to reconstruct an image. The reconstructed image is stored in the image storage device 21 and is displayed as a tomographic image of the subject P on the screen of the display monitor of the image display unit 17a.

The scan data obtained by the FRU 15 can be used to create a scanogram, which is a perspective image of the subject P, by a scanogram creating means. The created scanogram is stored in the image storage device 21 and displayed on the screen of the display monitor 12 (for example, FIGS. 8 and 9).
See).

The positional information of the couch 9 obtained by the couch position detector 13 is sent to the computer 19 via the data collection unit 7 and the FRU 15 and, as shown in FIG. Bed 9 at fault plane position
The interpolation processing is performed using the weight coefficient obtained from the distance from the upper position. Here, when the bed speed is constant (see FIG. 3A), the conventional interpolation processing is employed. When the bed speed is accelerating (see FIG. 3B), a scan data format described later is used. The interpolation process used is adopted.

Next, the scan data format and image reconstruction when the couch speed is accelerating will be described with reference to FIGS. That is, the bed speed is changed by using the couch position as a parameter for _obtaining the data D _nC of the tomographic plane to be obtained from the data D _nA and D _nB shown in FIG. 4 by the interpolation processing. However, data serving as a basis for reconstruction can be easily created from the scan data format shown in FIG.

FIG. 6 summarizes the operation of this embodiment. For example, when the moving speed of the bed 9 is constant, the obtained data is dense and the interpolation data is accurate, but a longer time is required for data collection. In addition, when the moving speed is high and the speed is constant, the obtained data is coarse and the interpolation data has a large error, but has the advantage that the data collection time is short and the exposure dose is small.

As described above, according to the present embodiment, a wide area can be quickly scanned when performing a screening test, and a scan for a part where a detailed test requiring a fine tomographic image is performed is simultaneously performed. Since it can be performed, the inspection time and the amount of exposure as a whole can be reduced.

Next, with reference to FIGS. 8 to 14, a description will be given of a case in which an imaging range and a screening inspection range and a precision inspection range are classified based on the scanogram.

First, in FIG. 8, the imaging range in the scanogram of the subject P is set by moving the linear cursor C. At this time, as shown in FIG. 9, using the scanogram on the side surface of the subject P, the imaging surfaces S ₁ , S ₃ , S ₅
May be sequentially set. The setting is performed by operating the slide volume of the operation console 17b as shown in FIG. Further, the computer 19 drives the couch driving unit 11 via the couch control unit 23b in accordance with the imaging surface S set on the operation console 17b, and the position of the couch 9 and the moving speed of the couch (hereinafter simply referred to as the couch speed). Say)
Control.

As shown in FIG. 11, increasing the bed speed makes the spiral pitch coarser, which is ideal for performing a quick screening test, and lowering the bed speed makes the spiral pitch denser. , It is ideal for performing detailed inspection.

The tomographic image obtained in this way, for example as shown in FIG. 12, a tomographic image corresponding to the imaging surface S ₉ shown on the scanogram along with showing a scanogram of the subject P on the main screen 17A Is displayed on the sub-screen 17B, it is possible to improve the efficiency of the inspection. At this time, the sub-screen 17B may display the couch speed or the couch position other than the tomographic image.

Further, imaging surface S ₁₁ to screen test on scanogram as shown in FIG. 13 and the imaging surface S ₁₃
Workup by indicating the imaging surface (area) S ₁₅ to perform, it can be more easily determine the positional relationship between the screening test range and precision inspection range on the scanogram between.

Further, as shown in FIG. 14, by providing cursors Cb which move in conjunction with the cursor Ca on the scanogram on the graph of FIG. 11, the bed speed can be easily set. It should be noted that the cursors Ca and Cb shown in FIG. 14 are blinking, thereby determining that the couch speed is being set.

As described above, according to the display method of the present embodiment, it is possible to display the speed information and the position information of the bed in the helical scan in an easily understandable manner. Can easily grasp these.

It is to be noted that a light projector may be provided on the gantry 1 so that the scanning position can be easily grasped.

In the above embodiment, the case where the present invention is applied to a so-called third generation X-ray CT apparatus has been described as an example.
The present invention is not limited to this, for example, a so-called fourth detector in which a detector is arranged in an annular shape and an arbitrary radiation source such as an X-ray tube emits radiation appropriately while rotating around the subject. The present invention can be applied to a generation of CT apparatuses, in which case the imaging time can be further reduced, and the effect of the present invention can be further enhanced.

[0046]

As described in the foregoing, according to claim 1 wherein
According to the invention of the item 3, in the shooting range including the region of interest,
Simple screening without area of interest
The pitch can be increased in the range to be inspected.
According to the first aspect of the present invention, the tomographic image photographing part is described.
Can be easily determined. According to the third aspect of the present invention,
The operator can easily know the scan pitch for each shooting range
And operability is improved. Furthermore, according to the invention of claim 4, it is possible to arbitrarily change the pitch of the helix scanned by movement speed setting of the subject while maintaining the rotational speed of the radiation source at a constant, precise for photographing range including a region of interest In this way, it is possible to simultaneously collect the image data and reduce the exposure amount of the subject and shorten the imaging time .

[Brief description of the drawings]

FIG. 1 is a block diagram showing a schematic configuration of an embodiment according to the present invention.

FIG. 2 is a diagram schematically showing a change in bed speed in a helical scan.

FIG. 3 is a diagram for explaining an interpolation method when the bed speed is constant and when the bed speed is changing.

FIG. 4 is a diagram for explaining data interpolation at the time of reconstructing an image of a helical scan when the bed speed is accelerated.

FIG. 5 is a diagram showing a scan data format.

FIG. 6 is a diagram for explaining an operation accompanying a change in bed speed.

FIG. 7 is a view specifically showing a main part of a mechanical part of a bed driving unit and a bed position detector shown in FIG. 1;

FIG. 8 is a diagram illustrating a display example on an image display unit.

FIG. 9 is a diagram illustrating a display example on an image display unit.

FIG. 10 is a diagram showing a configuration of a bed speed adjusting device.

FIG. 11 is a diagram showing a relationship between bed speed and time.

FIG. 12 is a diagram illustrating a display example on an image display unit.

FIG. 13 is a diagram illustrating a display example on an image display unit.

FIG. 14 is a diagram illustrating a display example on an image display unit.

FIG. 15 is a diagram for explaining a conventional helical scan operation.

FIG. 16 is a diagram for explaining a state of data interpolation at the time of image reconstruction in a conventional helical scan.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 gantry 3 X-ray tube 5 X-ray detector 7 data collection unit 9 couch 11 couch drive unit 13 couch position detector 15 FRU 15 a image reconstruction device 17 operation unit 17 a image display unit 17 b operation console 19 computer 21 image storage device 23 Mechanism controller 23a gantry controller 23b couch controller 25 X-ray controller 27 high voltage generator

Continued on the front page (72) Inventor Narumi Igarashi 1385-1 Shimoishigami, Otawara City, Tochigi Prefecture Toshiba Medical Engineering Co., Ltd. (72) Inventor Ryo Hayashibara 1385-1 Shimoishigami, Otawara City, Tochigi Prefecture Toshiba Medical Engineering Corporation (56) References JP-A-3-103229 (JP, A) JP-A-5-7582 (JP, A)

Claims (4)

(57) [Claims] 1. A CT apparatus for performing a helical scan on a subject with a radiation source rotating around the subject and reconstructing a tomographic image based on data obtained by the helical scan. A display means for displaying a perspective image of a predetermined range of the subject; a designation means for designating a plurality of desired imaging ranges based on the perspective images on the display means; Pitch setting means for setting a pitch of each of the spiral scans in a range; a control device for controlling a pitch of the spiral scan in accordance with a value set by the pitch setting means; And a reconstruction means for reconstructing a tomographic image for each range. 2. A CT apparatus for performing a helical scan on a subject with a radiation source rotating around the subject and reconstructing a tomographic image based on data obtained by the helical scan. In the above, pitch setting means for setting a pitch of each spiral scan in a plurality of imaging ranges of the subject, and control for controlling a pitch of the spiral scan according to a value set by the pitch setting means A CT apparatus comprising: an apparatus; and reconstruction means for reconstructing a tomographic image for each of the imaging ranges. 3. A CT apparatus for performing a helical scan on a subject with a radiation source rotating around the subject and reconstructing a tomographic image based on data obtained by the helical scan. in the pitch setting means for setting the pitch of each helical scan in a plurality of imaging range of the object, and display means for performing display regarding the value set in this pitch setting means, by said pitch setting means A CT apparatus comprising: a control device that controls a pitch of the spiral scan according to a set value; and a reconstructing unit that reconstructs a tomographic image for each of the imaging ranges. 4. A CT apparatus for performing a helical scan on a subject with a radiation source rotating around the subject and reconstructing a tomographic image based on data obtained by the helical scan. in a specifying means for specifying a plurality of shooting ranges, and speed setting means for setting a moving speed of the subject for each range specified photographing by the designating means, set by the speed setting means the subject A CT apparatus comprising: moving means for controlling movement at a speed; and reconstruction means for reconstructing a tomographic image for each of the imaging ranges.