JPH0719452Y2 - X-ray CT system - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION A. Field of Industrial Application This invention relates to an X-ray CT apparatus for reconstructing a CT image from transmitted X-rays.

B. Prior Art Reconstruction of a CT image by a conventional X-ray CT apparatus is generally performed as follows.

First, the X-rays emitted from multiple directions toward the subject are detected by the X-ray detector, and the detection signals are logarithmically converted and integrated by the data collector, and then converted into digital signals. The multi-directional projection data sent from the data collecting unit is subjected to processing such as back projection calculation in the image reconstructing unit, then added, and displayed on a display such as a CRT as a reconstructed image.

At this time, if the subject can only take a horizontal posture for convenience, the reconstructed CT image is also displayed on the CRT in a horizontal state. This makes it difficult for the operator to read the image, so the image reconstruction unit stores angle data in 90 ° units in advance, and when the subject is instructed to be in the sideways posture, the back projection calculation is performed. After the angle correction of 90 ° is performed on the angle term of the expression, the arithmetic processing is performed. As a result, the CT image in a fixed posture (for example, on the back) is displayed on the CRT screen.

C. Problems to be Solved by the Invention However, the above-described conventional device has the following problems.

Since the angle can only be corrected in 90 ° increments, if the tilt of the subject is a very small angle, the tilt angle cannot be corrected and the display screen tilts. There is a problem that the image becomes difficult to see.

In this case, the subject may be forced to incline in 90 ° units, but this may cause pain to the subject.

The present invention has been made in view of such circumstances, and provides an X-ray CT apparatus capable of always displaying a CT image in a constant posture even when the subject maintains an arbitrary tilt posture. Is intended.

D. Means for Solving the Problems This invention has the following configurations in order to achieve the above object.

That is, the X-ray CT apparatus according to the present invention calculates the tilt angle around the body axis of the subject from the detection means for detecting the tilt around the body axis of the subject lying on the top and the detection signal. Angle calculating means, corrected image deriving means for obtaining a CT image in which the tilt is corrected based on the calculated angle data, and the obtained
It is characterized by including a display unit for displaying a CT image.

E. Action According to this invention, the detecting means detects the inclination of the subject lying on the top about the body axis and sends the detection signal to the angle calculating means. The angle calculation means calculates an angle from a fixed posture (for example, a supine posture) of the subject to a tilted posture on the basis of the given detection signal, and sends the angle data to the corrected image deriving means. The corrected image deriving means performs correction based on the angle data so that the CT image of the subject becomes an image in a fixed posture, and displays the corrected CT image on the display means.

F. Embodiment An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a perspective view showing the appearance of the X-ray CT apparatus of the present invention, and FIG. 2 is a perspective view showing the rotating mechanism of the projector 6.

The side surface of the gantry 1 is provided with an opening 3 for inserting a top plate 2 on which a subject is placed, and the top plate 2 is a base 4
Supported by. A circular guide groove 5 is provided around the vicinity of the opening 3, and a support body 7 that supports the projector 6 is slidably mounted in the guide groove 5. The light projector 6 corresponds to the detecting means of the present invention, and detects the tilted posture of the subject by irradiating the subject with a linear light beam.

A gear 10 is rotatably supported on the support body 7.
10 is driven by the motor 9. Also, the motor 9
The rotation amount of is detected by the rotary encoder 8. The gear 10 is meshed with a link gear 11 provided concentrically with the guide groove 5. The motor 9
A motor drive unit 12 that receives a command signal from the operation unit 13 and drives the motor 9 is connected to the.

The rotation of the motor 9 causes the gear 10 to be a link gear.
11 Rolling while rolling on, by this rolling action,
The support 7 slides in the guide groove 5, and the light projector 6 is configured to rotate around the opening 3 provided in the gantry 1.

FIG. 3 is a block diagram showing a schematic configuration of the device.

In the figure, reference numeral 15 is an X-ray tube that irradiates the subject M with X-rays, reference numeral 16 is an arc-shaped X-ray detector consisting of several hundred detection element groups, and reference numeral 17 is an X-ray detection element. It is a data collection unit that converts the detection signal into a digital signal and sends the collected data to the image reconstruction unit 18. The image reconstructing unit 18 includes a preprocessing unit 19 for performing processing such as normalization on the collected data, a projection data storage unit 20 for storing preprocessed projection data, and a back projection process for the projection data. ,
A background for reconstructing an image by obtaining the distribution of X-ray absorption coefficients.
A projection processing unit 21 is provided, and a CRT 26 as a display unit for displaying a reconstructed image is connected to the projection processing unit 21.

The X-ray tube 15 and the X-ray detector 16 are configured so as to rotate around the subject M for each predetermined minute angle θ.

Further, this X-ray CT apparatus is provided with a tilt correction system 22 that detects the tilt posture of the subject M and corrects the supine posture, and its constituent blocks will be described below.

The tilt correction system 22 uses the rotary encoder 8 that detects the amount of rotation of the motor 9 described above, and the angle as the angle calculation unit that calculates the angle of the light projector 6, that is, the tilt angle of the subject M from the detection signal of the rotary encoder 8. Calculation unit 14, an angle correction unit 24 that corrects the angle parameter used in the back projection calculation based on the calculated angle data,
The angle storage unit 25 stores the corrected angle data. The angle correction unit 24, the angle storage unit 25, and the back projection processing unit 21 described above correspond to the corrected image deriving means of the present invention.

Next, the operation of the above-mentioned device will be described.

First, the inclination around the body axis of the subject M lying on the top 2 is detected. This is because before the subject M is inserted into the gantry 1, it is positioned under the rotation orbit of the light projector 6 so that the light beam from the light projector 6 is placed on the body axis center line (for example, the nose position) in front of the subject M. The motor 9 is driven so as to hit, and the projector 6 is set.

The rotary encoder 8 detects the rotation data of the motor 9 at this time and sends it to the angle calculator 14. Angle calculator 14
Calculates the rotation angle of the projector 6 from this rotation data. That is, the light projector 6 is set to A- as shown in FIG.
When set on the A ′ axis, the set position of the light projector 6 when the subject M is in a fixed posture (in this example, the supine posture) is based on the OO ′ axis (see FIG. 4A). As the position, the tilt angle α between the AA ′ axis and the OO ′ axis is calculated.

At this time, if the projector 6 rotates clockwise, the rotation angle is given a positive sign, and if it is rotated counterclockwise, a negative sign is given.

The data of the calculated angle α is sent to the angle correction unit 24. The angle correction unit 24 stores a minute rotation angle θ of the X-ray tube 15 and the X-ray detector 16 in advance, and adds the calculated tilt angle α of the subject M for each rotation angle θ. The angle is corrected by. For example, when the X-ray tube 15 and the X-ray detector 16 rotate every 1 °, α is added for each rotation angle as shown by the following equation.

θ ₁ (= 1 °) + α, θ ₂ (= 2 °) + α, ..., θ
_n (= 360 °) + α Each corrected angle data calculated by the above equation is stored in the angle storage unit 25.

Next, from the X-ray tube 15 to the X-ray tube for each rotation angle θ with respect to the subject M
Expose the line. The X-ray detector 16 converts this into an electric signal. The data collection unit 17 converts the detection signal into a digital signal, collects data for each rotation angle θ, and the image reconstruction unit 18
It is sent to the pre-processing unit 19 therein.

The pre-processing unit 19 performs processing such as normalization on the collected projection data for each rotation angle θ, and then stores the processed projection data in the projection data storage unit 20.

The back-projection processing unit 21 performs a back-projection operation on the projection data stored in the projection-data storage unit 20 and adds it for each θ to obtain a reconstructed image. As shown in FIG. 5 (a), the back projection arithmetic expression for the point (x, y) is represented by the following expression.

F (x, y) = ΣP (xcosθ−ysinθ, θ) (1) In the above equation, there is a relation of xcosθ−ysinθ = X, and P (X, θ) is the projection data of the point (x, y). Is.

If the subject M is tilted and the arithmetic processing is performed as it is,
The obtained reconstructed image is in a tilted state, so (1)
After replacing the angle parameter of the equation with the corrected angle data stored in the angle storage unit 25, the calculation process is performed. The corrected back projection calculation formula is expressed by the following formula.

F (x, y) = ΣP [(xcos (θ + α) −ysin (θ + α), θ + α] In this equation, θ is stored in the angle storage unit 25.
By adding from ₁ to θ _n , a reconstructed image in which the tilt is corrected is obtained.

This is the reference axis x-, as shown in FIG.
The y-coordinate axis is replaced with an x'-y 'coordinate axis shifted by an angle α, and the tilt angle θ + α between the x'-axis and the X-axis is made to act as an angle parameter of the back projection calculation, whereby the angle-corrected reconstructed image is obtained. Is what you get.

The present invention can be modified as follows.

In the above-described embodiment, the tilt-corrected reconstructed image is obtained. However, this is the case where the reconstructed image with reference to the xy coordinate axes is used only by the angle α calculated by the angle calculation unit 23. Alternatively, the rotation may be reversed. Such a modified example can be configured with an image processing unit that performs image rotation processing as the corrected image deriving unit.

G. Effect of the Invention As is clear from the above description, the X-ray CT according to the invention
The device calculates the tilt posture angle of the subject lying on the top,
Since the CT image is corrected and displayed based on the angle data so that the CT image always has a constant posture, the CT image is easier to read as compared with the conventional example.

Moreover, since the subject is not forced to have an unreasonable posture,
There is no pain in the subject.

[Brief description of drawings]

1 to 5 relate to an embodiment of the present invention. FIG. 1 is an external perspective view of an X-ray CT apparatus, FIG. 2 is a perspective view showing a rotating mechanism of a projector, and FIG. 3 is an apparatus. 4 is a block diagram showing the schematic configuration of FIG. 4, FIGS. 4 (a) and 4 (b) are diagrams illustrating detection of the tilt of the subject, and FIG. 5 (a) is a diagram illustrating schematic reconstruction by the back projection method. FIG. 6B is a diagram for explaining image reconstruction after tilt correction. 6 ... Projector 21 ... Back projection processor 23 ... Angle calculator 24 ... Angle corrector 26 ... CRT

Claims (1)

[Scope of utility model registration request] 1. A detection means for detecting a tilt of a subject lying on a tabletop about a body axis, and an angle calculating means for calculating a tilt angle of the subject about the body axis from the detection signal. An X-ray CT apparatus comprising: a corrected image deriving unit that obtains a CT image whose inclination is corrected based on the angle data, and a display unit that displays the obtained CT image.