JPH1128201A - X-ray ct - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an X-ray CT which can inhibit unnecessary exposure to X-rays of a specific tissue that is highly sensitive to X-rays, during continuous or successive radiography. SOLUTION: In an X-ray CT device which displays tomograms of a subject B on a display whenever necessary by rotating an X-ray source 200 continuously, measuring data about the projection of the subject B plural times in succession by use of detectors 250, and reconfiguring the tomograms on the basis of the data about the projection, an area A of interest in the subject B, such as a specific tissue that is highly sensitive to X-rays, can be set as the range where as little X-ray as possible is applied to the internal part. Application of X-rays to a region within the set area A of interest is reduced to once in several tens of times by a channel collimator 210 to reduce the exposure to X-rays of a specific tissue highly sensitive to X-rays, such as the eyeball, and an image processing device performs correction whereby padding with data and the like acquired in advance is effected, thereby keeping the quality of the picture of the inside of the area A of interest almost as good as those of normal pictures.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an X-ray CT apparatus for continuously (or intermittently) obtaining real-time tomographic images of a body such as a patient using X-rays in real time.

[0002]

2. Description of the Related Art X-ray CT apparatuses have already been widely used in medical treatment and the like, and various usages have been made by users. For example, recently, when performing histological examination or treatment of a lesion percutaneously, an X-ray CT
It has been practiced to use the device as a puncture guide.
As described above, by performing the tissue examination and treatment of the lesion under the guide of the X-ray CT apparatus, the operation time is reduced, and the accuracy is considered to be improved.

[0003] By the way, as a guide method using such an X-ray CT apparatus, puncturing and CT imaging are alternately and intermittently repeated so as to confirm the position of the tip of a puncture needle, or CT imaging. Is performed continuously,
There is a method of sequentially displaying images so that the position of the puncture needle can be immediately confirmed. Among them, the latter method has an advantage that the operation time can be further shortened since a tomographic image can be obtained in real time.

[0004]

However, in the above-described method in which CT imaging is performed intermittently or continuously, the X-ray exposure due to the intermittent or continuous CT imaging is required for a patient or an operator. Is a problem. On the other hand, in order to reduce the dose, the X-ray tube current may be lowered to lower the irradiation dose. However, the decrease in the irradiation dose (mAs = mA × sec) is caused by the X-ray fluctuation noise. This means that the image quality of the tomographic image is significantly deteriorated.

[0005] When CT imaging is performed intermittently or continuously, in addition to the problem of the increase in the above-mentioned exposure dose, there is also a problem of meaningless X-ray irradiation to normal tissues. This is because, for example, the eyeball is more sensitive to X-rays than other tissues, but the current head examination determines that there is no eyeball disease, and even if an image of the eyeball is not required, the eyeball is not sensitive to other tissues. Similarly, X-rays are irradiated. Therefore, in extreme cases, in this head examination, meaningless X to the normal eyeball
Irradiation may cause diseases such as cataracts in some cases.

In view of the problems in the prior art, the present invention can be obtained even when the X-ray imaging is performed continuously or intermittently at the time of puncturing by the guide of the X-ray CT apparatus. An object of the present invention is to provide an X-ray CT apparatus capable of reducing the amount of unnecessary exposure of a patient or an operator without causing a decrease in image quality of tomographic images.

[0007]

According to the present invention, in order to achieve the above object, the X-ray source is continuously rotated to continuously measure the projection data of the subject a plurality of times. In an X-ray CT apparatus that reconstructs a tomographic image of a subject based on data and sequentially displays the tomographic images on a display device, a region of interest for setting an irradiation range of the X-ray from the X-ray source within the subject X-rays comprising setting means, and a channel collimator or attenuator for suppressing irradiation of X-rays in a region set by the region of interest setting means when measuring projection data by rotating the X-ray source. A CT device is provided.

[0008]

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings. First, FIG. 2 shows an overall configuration of an X-ray CT apparatus according to an embodiment of the present invention. As is clear from the figure, this X-ray C
The T device is equipped with a display device 100, a host computer 101 controlling the whole device, an X-ray generation system, an X-ray detection system, etc., a scanner system 102 capable of continuous scanning by a slip ring, and a pre-processing of images. Processing apparatus 103 including a preamplifier (indicated by reference numeral 106 in FIG. 3) which is responsible for image reconstruction processing or various analysis processing
And a high voltage generator 104 for supplying a high voltage to the X-ray generation system, and a patient table 105 on which a subject is placed
Etc. Although not shown, the host computer 101 includes a keyboard,
A mouse, tracking ball, etc. are provided.

FIG. 3 is a detailed explanatory view of the scanner system 102. According to the X-ray CT apparatus of the present invention, an X-ray tube for generating X-rays by a high voltage supplied from a high voltage generator 104 A channel collimator 210 is provided close to the sample 200 and between the sample B and the subject. The movement of the channel collimator 210 in the X-axis direction in the figure is controlled by the controller 211. That is, the channel collimator 210 can limit the X-ray irradiation range in the channel direction to the region of interest A that can be set in advance. Reference numeral 250 in the drawing indicates a detector of the scanner system 102.

Next, the structure of the channel collimator 210, which is a feature of the present invention, is schematically shown in FIGS. As shown in FIG. 4A, the channel collimator 210 has a trapezoidal outer collimator case 212.
A compensating filter 213 is provided, and a lead shielding plate 214 is provided at a bottom portion thereof. FIG. 4B shows the structure of the lower surface of the channel collimator 210. A pair of guides 2 are provided on both sides of the lead shielding plate 214.
15 and 215 are provided, and the expansion and contraction of the lead shielding plate 214 is controlled by the operation of the motor 216 having an encoder and the like and the timing belt 217. FIGS. 5A and 5B show a state where the lead shielding plate 214 is contracted and a state where the lead shielding plate 214 is extended, respectively.

As shown in the above-mentioned figure, a collimator case 212 further includes a system controller 2 which performs overall control of the entire channel collimator 210.
11 and a motor driver 2 for driving the motor 216
18 are provided. Note that the system controller 211 and the motor driver 218 may be attached to other than the collimator case 212.

The system controller 211
Performs overall control of the entire channel collimator 210 as described above. For example, when setting the region of interest A of the present invention, several types of tables are stored in the controller as the first stage. Further, the motor driver 218 drives the motor 216 to rotate, and the rotation of the motor is transmitted to the timing belt 217, whereby the timing belt 217 is connected to the curtain-shaped lead shielding plate 2.
14 is expanded or contracted, thereby enabling a region of interest scan during scanning.

Next, the flow of imaging in the X-ray CT apparatus described above will be described. The X-ray CT apparatus according to the present invention can be used, for example, in a case where a site where X-rays are not desired to be irradiated as much as possible, such as a tissue highly sensitive to X-rays such as an eyeball, is known in advance. The photographing procedure will be described with reference to FIG. That is,
A region where the amount of X-ray irradiation is desired to be reduced as much as possible, such as a tissue having a high X-ray sensitivity, is set as a region of interest, and the set amount of X-ray exposure to the region of interest is reduced as much as possible.
It is intended to reduce the exposure of the apparatus.

As for the flow of shooting, when shooting is started,
First, a scanogram is displayed (step S11), and then a precise shooting range is determined (step S12). In this precise imaging range determination, after the patient has been set on the table 105, the above scanogram is first obtained to determine the imaging position of the tomographic image. The setting of the number of shots is performed on the displayed scanogram. The shooting range includes items related to the start of shooting, the shooting interval, the number of shots, and the like. For example, in the case of spiral scanning, a shooting start position, a table moving speed, the number of scans, and the like are also set.

After that, a precise photographing is performed (step S13). In this precise photographing, the host computer sets, for example, a tube voltage or a tube current in the high-voltage generator 104 according to the conditions set above. Further, in the patient table 105, the moving speed and the like in the spiral scan are set. At the time of this precise imaging, the channel collimator 210 is at a normal position, and X-rays are incident on all channels. Therefore, in the subsequent reconstruction of the precise image (step S14), a sufficiently diagnosable image is obtained.

Subsequently, a photographing slice (step S15)
Is determined (step S16). That is, when the above-described precision imaging is completed, in the imaging slice,
The surgeon observes the photographed image and, for example, in the case of a reexamination, selects a slice suitable for the part to be observed most. In addition, in the case of CT fluoroscopy, information on the periphery of the target such as the position of the target tissue (tumor) and whether there is an important tissue on the puncture route to the target is obtained, and a puncture slice for CT fluoroscopy is determined. . Further, in the region of interest determination, a region where X-rays are not irradiated on the slice determined above, that is, a region of interest A is set. In addition, for example, as shown in FIG. 7, for example, a circular region or an elliptical region is set on the display screen of the display device 100 by using a pointing device PD such as a mouse or a trackball as an input device. It is set by drawing, so that X-rays are not irradiated as much as possible inside the set region of interest. Further, the table moving slice direction is set (step S17).

Next, a reference scan (step S)
18) In response to an instruction from the host computer 101,
The patient table 105 moves the tabletop to the selected slice position. Here, imaging (reference scan) is performed at a normal position of the channel collimator 210 with an X-ray dose suitable for the purpose of CT fluoroscopy, such as for reexamination or puncturing, and further, slice position And setting of the region of interest is confirmed (step S19).

Subsequently, setting of a normal scanning interval and setting of a region of interest enlarged photographing are performed (step S20). In the setting of the normal scan interval, the number of times the channel collimator 210 performs shooting at a normal position during continuous shooting is set before shifting to continuous shooting or the like described below. Note that the finer the setting here, the less the time lag of the image outside the region of interest is required, and the more precise the image can be obtained, but the dose of exposure is not reduced much.
The photographing interval can also be set automatically as a set. In this case, the setting stored in the host computer 101 in advance, for example, “l every 10 slices”
A setting such as "perform normal scan" may be used as it is, or a setting such as "once every 30 slices" may be manually set instead of the automatic setting. In addition, the setting may be made such that “normal scanning is not performed during continuous-speed scanning”. In this case, data outside the region of interest is executed in step S18 or data of reference scanning is embedded and image reconstruction is performed. Processing will be performed.

In the setting of the region of interest enlargement photographing, if the reduction and enlargement setting is selected here, the region of interest A and the region of the normal scan gradually approach between the region of interest photographing and the normal scan. In other words, From the normal scan range or the set range to the region of interest A, a scan in which the measurement range is gradually reduced can be performed. That is, in the case of the above enlargement, from the region of interest A to the normal scan region,
The measurement range gradually expands. Also, in the reduction, if the region of interest A is circular, the circle of the normal scan range or the set range gradually decreases, and finally the measurement range reaches the region of interest A (in the case of enlargement, the reverse is true). Measurement).
The data captured outside the region of interest A while being reduced (or enlarged) is used for correction of image reconstruction described below, thereby improving the image quality of the range image inside the region of interest A. Can be.

Finally, if a desired image is obtained by the above-described reference scan (step S18), the flow shifts to continuous shooting (step S21) and image reconstruction (step S22). In the continuous imaging, the continuous-speed imaging or the puncture imaging set as described above is performed, and the imaging data thus captured is sequentially reconstructed, thereby forming a temporally continuous tomographic image.

Here, the control of the channel collimator 210 whose detailed configuration has been described with reference to FIG. 4 will be described below with reference to FIG.

First, as shown in FIG. 8, a line connecting the focal position (Xs, Ys) of the X-ray tube, which is the source of X-rays, and the center of rotation intersects the y-axis at right angles to the y-axis. Let the line be the x-axis. Here, the collimator 210 (corresponding to the lead shielding plate 214 of the channel collimator 210) is movable in the x-direction as described above, and is a mechanism capable of arbitrarily limiting the X-ray irradiation range. .

Now, assuming that the region of interest is defined by a circle having a radius r centered on the center coordinates (Xc, Yc) in FIG. 8, the set X-ray irradiation range is as follows. , ΘL to θR. Where X
The calculation of the focal point of the line is assumed to be a point focal point as described above, and the coordinates thereof are defined as (Xs, Ys). On the other hand, the spread positions of the X-ray on the collimator are defined as XL0 and XR0. In other words, the position of the collimator 210 on the x-axis is defined by a right end (XR0- △ XR) and a left end (XL0- △ X).
L).

The amount of movement of the collimator 210 △ X
As means for obtaining L, △ XR, which can be obtained by the following calculation formula, these are obtained in advance. Further, it is also possible to approximate with a periodic function such as a trigonometric function without using the following calculation formula.

That is, △ XL and △ XR are obtained as follows.

(Equation 1) Here, d is a distance between two points of the focal point and the center coordinate of the region of interest. And, if θL and θR are expressed using this d,
It looks like this:

(Equation 2)

(Equation 3) Here, d ₀ is the distance from the X-ray focal point to the rotation center of the scanner. Then, if △ XL and △ XR are expressed using these θL and θR, the following is obtained.

(Equation 4)

(Equation 5)

That is, by controlling the position of the collimator 210 of the channel collimator at each projection angle in accordance with 求 め XL and △ XR obtained as described above, as shown in FIG. 3, X-rays are emitted only to the region of interest of the subject. Will be irradiated. In the above example, the region of interest has been described as a circle. However, the shape of the region of interest is not limited to a circle, and may be set to, for example, an ellipse. In this case, a parameter is added to the following procedure for obtaining $ XL and $ XR.

Next, image reconstruction using projection data obtained by irradiating only the region of interest with X-rays limited thereto will be described.

As described above, the projection data obtained by irradiating only the region of interest with the X-rays limited is, as shown by the thick solid line in FIG. 9, the data in the region shielded by the above-described collimator. It becomes almost zero after offset correction. Therefore, very high frequency components are generated in the channels ia ′ and ib ′ in FIG.
If the obtained projection data is used for image reconstruction processing as it is, an artifact will occur on the image. To solve this, as already proposed by the present applicant (Japanese Patent Application No. 9-112302), the data of the area shielded by the collimator is
A process for embedding the projection data measured in advance is performed.

This is realized, for example, by the image processing apparatus 103 shown in FIG. That is, in the figure, the image processing apparatus 103 includes a reconstruction operation unit 11 and a weighted image adder 12, and outputs the result to the display device 100.
Then, the reconstruction arithmetic unit 11 includes the projection data memory 20,
It comprises a pre-processing calculator 21, a fan beam-parallel beam converter 22, a filter correction calculator 23, and a back projection calculator 24. On the other hand, the weighted image adder 12 includes seven image memories 10 (# 1 to # 7) and seven weight coefficient multipliers 13
(W1 to W7 are weighting coefficients) and an adder 25.

In this example, the image processing device 103
Can be reconstructed in less than one second per image, for example. This is to sequentially and sequentially obtain the divided reproduction constituent images at a 30 ° width, and further, in one reconstruction screen, add the latest newly obtained 30 ° width divided reconstructed image to the previous one. It is because of what can be achieved. For example, when the angle is updated at a width of 30 °, a reconstructed image of 12 sheets / second can be obtained.

The reconstruction arithmetic unit 11 includes a pre-processing unit 21, a parallel beam conversion by a fan beam-parallel beam conversion unit 22, a filter correction process by an arithmetic unit 23, and a back projection arithmetic unit 24. To obtain a reconstructed image. This reconstruction operation is 3
This is not a collective reconstruction for 60 °, but an addition operation for the divided reconstructed images obtained from the parallel beam data with a partial angular width (for example, 30 ° width).

Then, the weighted image adder 12 sequentially assigns the divided reconstructed images obtained by the reconstruction operation unit 11 to the memories # 1 to # 7 of the image memory 10 in order. For example, the divided reconstructed image g1 is assigned to # 1, the divided reconstructed image g2 is assigned to # 2,..., And the divided reconstructed image g7 is assigned to # 7 and stored. .., Etc. The subsequent divided and reconstructed images g8, g9,... Are allocated and stored in such a way that g8 replaces g1 with # 1, g2 replaces g2 with # 2, and so on.

The multiplier 13 weights each of the divided images by multiplying the images of the memories # 1 to # 7 in association with the weighting factors W1 to W7. The adder 25 performs total addition to obtain one reconstructed image.

The concept of the reconstructed image processing by the image processing apparatus 103 described above will be described again with reference to FIG. That is, the effective data range obtained by the pre-scan or the normal scan is shown by a thick solid line in FIG. 9A, whereas the region of interest A of the present invention is irradiated with the X-rays being restricted. The projection data obtained by performing the continuous scan or the continuous scan such as the fluoroscopic imaging is, as shown in FIG. 9B, the image data in the region of interest A is discontinuous in time. And high image quality cannot be obtained.

Therefore, the above continuous scan or
During continuous scanning such as fluoroscopic imaging, the channel collimator 210 performs scanning at a normal position (pre-scan or normal scanning). It is possible to realize reconstructed image processing that can be exposed to light and that can improve the image quality even in an area inside the region of interest A. In other words, this makes it possible to obtain images with a small temporal difference with low exposure in the region inside and outside the region of interest A, and obtain images that are easier to see.

Also, as described above, in step S20
By setting the region of interest enlarged photographing, the channel collimator 210 gradually reduces or enlarges the region of interest from the normal scan region to the region of interest A during scanning such as continuous scanning or fluoroscopic photographing. With this, data in an area that cannot be obtained by its own scan (that is, data in an occluded area)
By embedding a plurality of or a single piece of projection data before the normal scan and the time, high image quality can be obtained.

In a head examination or the like using an X-ray CT apparatus, there is a case where it is not desirable to irradiate an X-ray sensitive eyeball (indicated by a region of interest A in FIG. 1A) with X-rays. . In such a case, it is necessary to set a plurality of regions of interest A, and accordingly, as shown in FIG. 1B, a plurality of channel collimators 210 are required. However, such control of the plurality of channel collimators 210 and the like is basically the same as the control method of the single collimator described above, and can be handled by the control method of the single collimator described above. Here, the detailed description is omitted. If, for example, the eyeball is not to be irradiated with X-rays instead of the channel collimator 210, even if an attenuator having an X-ray absorption coefficient equivalent to the eyeball is arranged instead of the collimator, the same effect as the channel collimator can be obtained. Obtainable.

[0038]

As is apparent from the above detailed description,
According to the X-ray CT apparatus of the present invention, in a reexamination, CT fluoroscopy, or the like, a region not to be irradiated with X-rays is set in advance as a region of interest, and the region of interest is not irradiated with X-rays as much as possible. By controlling the collimator or the attenuator so as to perform a scan, meaningless exposure to a patient or specific tissue highly sensitive to X-rays can be suppressed, and low exposure can be achieved.

Further, the image data in the area within the region of interest shielded by the collimator or the attenuator can be reconstructed in the image processing apparatus by a process such as embedding data measured in advance in time, etc. It is possible to obtain few images. For this reason, it is possible to obtain an accurate high-quality image with low exposure and with a temporally suppressed image difference even for an image of an area in the area of interest.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram illustrating setting of a region of interest, which is a feature of an X-ray CT apparatus according to one embodiment of the present invention.

FIG. 2 is a diagram showing an entire configuration including a circuit configuration of the X-ray CT apparatus of the present invention.

FIG. 3 is a detailed explanatory view of a scanner system of the X-ray CT apparatus of the present invention.

FIG. 4 is a detailed explanatory view of a channel collimator of the X-ray CT apparatus of the present invention.

FIG. 5 is an explanatory diagram illustrating an operation of a lead shielding plate of the channel collimator.

FIG. 6 is a flowchart illustrating a flow of imaging in the X-ray CT apparatus of the present invention.

FIG. 7 is a diagram illustrating an example of a method of setting a region of interest in the flow of the above-described imaging.

FIG. 8 is a geometric explanatory view of the operation of the channel collimator in the X-ray CT apparatus of the present invention.

FIG. 9 is a diagram illustrating a method of correcting projection data and data in a region of interest in a scan obtained by the channel collimator.

FIG. 10 is a circuit block diagram illustrating an example of an image processing apparatus in the X-ray CT apparatus according to the present invention.

[Explanation of symbols]

 REFERENCE SIGNS LIST 100 Display device 101 Host computer 102 Scanner 103 Image processing device 104 High voltage generator 105 Patient table 200 X-ray source 210 Channel collimator 211 Controller 214 Lead shield 250 Detector A Region of interest B Subject C Irradiation field of view

Claims (1)

[Claims] An X-ray source is continuously rotated to continuously measure projection data of a subject a plurality of times, and a tomographic image of the subject is reconstructed on the basis of the projection data and displayed on a display device. In an X-ray CT apparatus for sequentially displaying, when a region of interest setting means for setting an irradiation range of the X-ray from the X-ray source in the subject, and measuring the projection data by rotating the X-ray source, An X-ray CT apparatus comprising: a channel collimator or an attenuator for suppressing irradiation of X-rays in a region set by the region of interest setting means.