JP2002204797A - X-ray ct apparatus and image forming method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a CT image free from the ineffective exposure of a subject and reduced in image strain. SOLUTION: At first, an electrocardiographic synchronous gate pulse generation circuit forms an electrocardiographic synchronous gate pulse (b) on the basis of an electrocardiographic waveform (a). A measuring angle range flag (c) obtained by previous rotation is recorded on an X-ray control pulse generation circuit to take AND of the electrocardiographic synchronous gate pulse (b) and the measuring angle range flag (c) to form an X-ray output pulse (d). An X-ray control circuit forms measuring data (e) on the basis of the waveform of the formed X-ray output pulse (d) and a measuring angle range flag (f) making the angle range of the measuring data (e) zero by the rotations of the previous time and this time is formed. A measuring angle range flag circuit renews the measuring angle range flag (f) to record the same.

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 and an image forming method, and more particularly to an X-ray apparatus for irradiating an object with X-rays and displaying an image based on projection data indicating transmitted X-rays of the object. The present invention relates to a CT apparatus and an image creation method.

[0002]

2. Description of the Related Art At present, an X-ray CT apparatus repeats X-ray irradiation (one scan) for one tomographic image of a subject while changing the relative position of a rotating disk with respect to the subject, thereby obtaining a desired imaging region. , A plurality of tomographic image data can be obtained. As a scanning method for obtaining tomographic image data, a full scan in which one scan is completed by rotating the X-ray tube around the subject by 360 degrees, and a scan in which 210 to 2
There is a half scan in which the scan is completed by moving the X-ray tube by about 40 degrees. In the case of a full scan, an image is usually taken in a scan time of 0.5 seconds to several seconds. There is also an X-ray CT apparatus in which an image reconstruction unit is provided with a three-dimensional image forming unit for extracting three-dimensional information from tomographic image data and displaying a three-dimensional image. In this case, a plurality of tomographic image data collected by a plurality of scans is reconstructed as three-dimensional image data to display an MPR cross-sectional image other than a cross-sectional image, extract components, and display the three-dimensional surface thereof. Display.

[0003]

By the way, when performing a heart image diagnosis, the current X-ray CT apparatus causes image distortion due to the pulsation of the heart in a tomographic image. In particular, since the pulsation phases are not uniform in a plurality of images, there is a problem that image distortion increases in a three-dimensional image or an MPR reconstructed image.

On the other hand, in order to avoid this inconvenience, ECG G is a method of collecting only data measured at a fixed phase of electrocardiogram from measurement data of a plurality of scans and performing an image operation.
Atted tomographic image reconstruction methods have been proposed. However, since this method uses only specific data among a large number of measurement data, the image noise increases due to a shortage of data amount, or the number of scans increases to increase the S / N. There was an inconvenience that invalid exposure increased.

[0005] The present invention has been made in view of such circumstances, and there is no invalid exposure of a subject and CT images with little image distortion.
An object of the present invention is to provide an X-ray CT apparatus and an image creation method capable of obtaining an image.

[0006]

Means for Solving the Problems To achieve the above object, according to the first aspect of the present invention, an X-ray tube is continuously rotated around a subject, and X-rays are emitted from the X-ray tube.
In an X-ray CT apparatus that captures projection data indicating transmitted X-rays of a subject by an X-ray detector disposed opposite to the X-ray tube with the subject interposed therebetween and displays an image based on the projection data, An electrocardiogram synchronization generating means for generating an electrocardiogram synchronization gate pulse indicating a stationary period of the subject in synchronization with an electrocardiogram waveform from the meter, and the electrocardiogram synchronization for each rotation of the X-ray tube and X-ray detector. 0 ° to 360 ° based on the gate pulse
X-ray control means for irradiating X-rays from the X-ray tube only in an angle range in which projection data has not yet been captured within the angle range of °, and the X-ray for each rotation of the X-ray tube and X-ray detector Image constructing means for fetching projection data in an angle range necessary for image construction from the detector and constructing an image based on the projection data.

According to the present invention, when constructing an image based on projection data obtained by irradiating X-rays, the projection data is fetched only during a period when the projection data has not yet been fetched from the X-ray control means. . Thus, data measurement is performed without the subject being subjected to invalid exposure.

In order to achieve the above object, the invention according to claim 2 is to continuously rotate the X-ray tube around the subject, irradiate the subject with X-rays from the X-ray tube, and sandwich the subject with the X-ray tube interposed therebetween. In an image creation method for taking in projection data indicating transmitted X-rays of a subject by an X-ray detector arranged opposite to an X-ray tube and creating an image based on the projection data, an electrocardiographic waveform from an electrocardiograph is obtained. Synchronously generating an ECG gate pulse indicating a period of rest of the subject;
Irradiating X-rays from the X-ray tube during the first rotation of the X-ray detector during the output period of the ECG gate pulse to capture projection data, and performing two rotations of the X-ray tube and X-ray detector After the eye, 0 ° based on the ECG gate pulse
A step of irradiating the X-ray tube with X-rays and fetching projection data only in an angle range in which projection data has not yet been captured within an angle range of up to 360 °, wherein projection data in an angle range necessary for image formation is obtained. It is characterized by including a step of repeating the capture of the projection data until the capture, and a step of forming an image based on the projection data in the angle range necessary for the image configuration.

According to the present invention, when constructing an image based on projection data obtained by irradiating X-rays, the projection data is fetched only during a period in which the projection data has not yet been fetched from the X-ray control means. . Thus, an image with improved image distortion is configured.

According to a third aspect of the present invention, there is provided a three-dimensional projection system in which the X-ray tube and the X-ray detector and the subject are relatively moved in the body axis direction of the subject. It is characterized in that it takes in data and generates a three-dimensional image or a two-dimensional image on a plane parallel to the body axis direction of the subject.

According to the present invention, a plurality of images can be obtained for a desired imaging region by capturing projection data while changing the relative positions of the X-ray tube and X-ray detector and the subject.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the X-ray CT apparatus according to the present invention will be described below in detail with reference to the accompanying drawings.

As shown in the configuration example of the present invention in FIG. 1, this X-ray CT apparatus includes a scanner gantry section 10 for irradiating and detecting X-rays, and a measurement data detected by the scanner gantry section 10 as a CT image. An image reconstruction unit 20 that processes signals, a display 30 that outputs a CT image, an electrocardiograph 50, and an X-ray control pulse generation unit that generates an X-ray control pulse based on an electrocardiographic waveform from the electrocardiograph 50 60.

In the scanner gantry section 10 of the X-ray CT apparatus, the rotating disk 11 includes an X-ray tube 12, a collimator 13 for controlling the X-ray radiation direction, an opening 14, an X-ray detector 15, and a detector circuit. 16 is mounted, and is rotatable around a subject on a bed (not shown) installed in the opening 14. Further, the rotating disk 11 includes an X-ray control circuit 17 for controlling the rotation and the width of the X-ray flux.

While rotating the X-ray tube 12 by the rotating disk 11, the X-rays emitted by the X-ray tube 12
Thus, the transmitted X-ray is detected by the X-ray detector 15 through one cross section of the subject on the bed. The detected output signal is converted into a digital signal S1 by the detector circuit 16 for each scan, and transmitted to the image reconstruction unit 20.

In the image reconstruction unit 20, a digital signal S1 for each scan is sent from the detector circuit 16 to the measurement data collection circuit 21. In the measurement data collection circuit 21, calculations such as an arrangement process, a filtering process, and a back projection process are performed in order to store the measurement data and remove the offset added by the detector circuit 16. Further, the measurement data collection circuit 21 performs correction to remove an offset included in the measurement data, log correction to correct a logarithmically attenuated signal to linear characteristics, and reference correction to correct fine fluctuations in X-ray tube intensity. Processing such as calibration correction and ring correction for correcting the reference point of the CT value is also performed as preprocessing. The data obtained in the preprocessing is transmitted to the image operation circuit 22 for tomographic image reconstruction,
Arrangement processing for converting projection data by radially irradiated X-rays into projection data of parallel irradiation, filtering processing, and back projection processing for reproducing the original object by projection images from various directions are performed, and image information is added. You. The two-dimensional data (cross-sectional data) to which image information for each scan is added by the image arithmetic circuit 22 is composed of a series 300 of several sets of 301 to 310 scans and sent to the three-dimensional image forming unit 23. The three-dimensional image forming unit 23 extracts three-dimensional information from this series and performs image processing for three-dimensional display, new cross-sectional image display, or synthesis. The data on which the three-dimensional image information is formed by the three-dimensional image forming unit 23 is gain-adjusted by the display circuit 24,
It is sent to the display 30 and displayed.

It is possible to scan a predetermined portion of the subject while moving the scanner gantry unit 10 along the body axis of the subject simultaneously with one rotation of the rotating disk 11.

Further, the X-ray CT apparatus receives an electrocardiographic waveform from an electrocardiograph 50, generates an X-ray output pulse based on the electrocardiographic waveform, and generates an X-ray control pulse based on the pulse. An X-ray control circuit 17 for controlling X-ray output is provided.

As shown in FIG. 2, the X-ray control pulse generator 60 comprises an ECG gate pulse generator 61, a measurement angle range flag circuit 62, and an X-ray control pulse generator 63.

In such a configuration, the ECG gate pulse generating circuit 61 receives an electrocardiographic waveform (FIG. 3A) of the subject and corresponds to a peak (for example, an R wave) of the electrocardiographic waveform (a). Repetitive ECG-gated pulse (Fig. 3 (b))
Is output. The measurement angle range flag circuit 62 is a measurement angle range flag corresponding to an angle range that has not yet been measured in synchronization with the electrocardiogram waveform (a) among data of one rotation of the scanner required for image reconstruction (FIG. 3 (c)) is output. Further, the X-ray control pulse generation circuit 63 performs an AND operation on the ECG gate pulse (b) and the measurement angle range flag (c), and outputs an X-ray output pulse (FIG. 3D). The outputted X-ray output pulse (d) is controlled by the X-ray control circuit 17, and creates a measurement angle range flag for each rotation of the scanner. Further, the X-ray control circuit 17 controls the X-ray CT so as not to output X-rays in the angle range where data has already been measured.
Control the X-ray output of the device.

Next, as shown in FIG. 4, after the NOT (f) of the X-ray output pulse (e) is taken, the AND with the measurement angle range flag (g) is taken, and a new measurement angle range flag (h) is taken. ) To create. Measurement angle range flag circuit 62
Updates and records this measurement angle range flag (h).

Data Measurement According to the Present Invention FIGS.
The details will be described with reference to FIG. The first rotation is shown in FIG. First, the ECG gate pulse generating circuit 61 creates an ECG gate pulse (b) based on the ECG waveform (a). Since the reconstruction data has not yet been measured in the first rotation scan, the measurement angle range flag (c) is 1 over the entire measurement angle range. Subsequently, the X-ray control pulse generation circuit 63 generates an X-ray output pulse (d) by ANDing the ECG gate pulse (b) and the measurement angle range flag (c). Measurement angle range flag (c)
Is 1 over the entire measurement angle range, the X-ray output pulse (d) has the same waveform as the electrocardiographic gate pulse (b) as shown in FIG. Based on the waveform of the X-ray output pulse (d), the X-ray control circuit 17 intermittently turns ON / OFF the X-ray output to create the measurement data (e). In addition,
The angle range of the measurement data (e) created in the first rotation is indicated by oblique lines. Thereafter, the X-ray control circuit 17 creates a measurement angle range flag (f) that sets the angle range of the measurement data (e) to 0 for each rotation of the scanner, and the measurement angle range flag circuit 62 generates this measurement angle range flag. (F) is updated and recorded.

Next, the second rotation is shown in FIG. First, the ECG gate pulse generating circuit 61 creates an ECG gate pulse (b) based on the ECG waveform (a). The measurement angle range flag (c) obtained in the first rotation is recorded in the X-ray control pulse generation circuit 63 in advance. Subsequently, the X-ray control pulse generation circuit 63 generates an X-ray output pulse (d) by ANDing the ECG gate pulse (b) and the measurement angle range flag (c). Based on the waveform of the X-ray output pulse (d), the X-ray control circuit 17 intermittently changes the X-ray output to O.
N / OFF to create measurement data (e). In addition, 2
The angle range of the measurement data (e) created at the revolving eye is shown by wide oblique lines. Thereafter, the X-ray control circuit 17 creates a measurement angle range flag (f) that sets the angle range of the measurement data (e) to 0 at the first rotation and the second rotation, and the measurement angle range flag circuit 62 generates the measurement angle range flag (f). Update and record flag (f).

Next, the third rotation is shown in FIG. First, the ECG gate pulse generating circuit 61 creates an ECG gate pulse (b) based on the ECG waveform (a). The measurement angle range flag (c) obtained in the second rotation is recorded in the X-ray control pulse generation circuit 63 in advance. Subsequently, the X-ray control pulse generation circuit 63 generates an X-ray output pulse (d) by ANDing the ECG gate pulse (b) and the measurement angle range flag (c). Based on the waveform of the X-ray output pulse (d), the X-ray control circuit 17 intermittently turns ON / OFF the X-ray output to create the measurement data (e). In addition,
The angle range of the measurement data (e) created at the third rotation is indicated by wide oblique lines. Thereafter, the X-ray control circuit 17 creates a measurement angle range flag (f) in which the angle range of the measurement data (e) at the first, second, and third rotations is set to 0, and the measurement angle range flag circuit 62 Updates and records this measurement angle range flag (f).

In this way, the measurement angle range flag is updated while repeatedly measuring, and the scanner 1 necessary for reconstruction is updated.
When the data for the rotation is measured, the measurement ends.

There are various methods for three-dimensional image processing. For example, as shown in FIG. 8, when reconstructing a cross-sectional image other than a cross-sectional image, a large number of the above-mentioned cross-sectional data are transferred in the scanning direction. The stack is reconstructed as a tomographic image of another section, for example, a sagittal plane (sagittal section) 31 or a coronal plane 32. At this time, data between sections is interpolated as necessary. For example, in the case of a three-dimensional surface display for displaying the surface of a heart or the like, first, a region is extracted from each of the two-dimensional data by threshold processing, and an outline is drawn. If it is difficult to do so only by threshold processing, it is manually traced and input. Next, the contour lines between the cross sections are connected. For the connection between the cross sections, a known method such as a method of interpolating the data between the cross sections as necessary to obtain voxel data and a method of constructing a triangular surface element is employed. Next, necessary shading is performed to obtain a surface display image. Furthermore, it is also possible to combine the surface display image and the above-described cross-sectional image. Thus, the three-dimensional image forming unit 2
The image signal formed in 3 is gain-adjusted by the display circuit 24 and sent to the display 30, where a reconstructed cross-sectional image, surface display image, or a composite image thereof is displayed. In each of the above cases, since each of the cross-sectional data in FIG. 8 is data formed using signals imaged under the same conditions of the cardiac cycle, it is possible to minimize an increase in image distortion due to a mismatch in beat phases. Thus, a three-dimensional image or a sagittal (coronal) reconstructed image having a high diagnostic value can be obtained.

In the above embodiment, the case where the rotating disk makes one rotation (360 degrees) in one scan has been described. However, a so-called half scan in which scanning is performed by moving the X-ray tube at 210 to 240 degrees is also possible. Applicable. X-ray CT that rotates and scans an X-ray tube mounted on a rotating disk
Although the apparatus has been described, the image forming method of the present invention is also applicable to an electron beam type X-ray CT apparatus and a cone beam type X-ray CT apparatus having a two-dimensional sensor.

[0028]

As described above, according to the present invention, X
When constructing an image based on the projection data obtained by irradiating the lines, the projection data is taken in only during the period in which the projection data has not yet been taken from the X-ray control means. Thus, data measurement is performed without the subject being subjected to invalid exposure, and an image with reduced image distortion is configured.

Further, by changing the relative position between the X-ray tube and the X-ray detector and the subject, the projection data is taken in.
It is possible to form a three-dimensional image or an MPR reconstructed image in which a plurality of tomographic images in a desired imaging region have the same pulsation phase. In particular, it is possible to form a three-dimensional image that is effective for a cardiac image diagnosis.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration example of an X-ray CT apparatus according to the present invention.

FIG. 2 is a block diagram of an X-ray control pulse generator.

FIG. 3 is a waveform chart showing an X-ray output pulse.

FIG. 4 is a waveform chart showing an X-ray output pulse.

FIG. 5 is a waveform chart showing a process of generating an X-ray output pulse.

FIG. 6 is a waveform chart showing a process of generating an X-ray output pulse.

FIG. 7 is a waveform chart showing a process of generating an X-ray output pulse.

FIG. 8 is a diagram used for explaining three-dimensional image reconstruction.

[Explanation of symbols]

10: scanner gantry section, 11: rotating disk, 12: X
Tube, 13 ... collimator, 14 ... opening, 15 ... X-ray detector, 16 ... detector circuit, 17 ... X-ray control circuit, 20 ...
Image reconstructing unit, 21: measurement data collection circuit, 22: image calculation circuit, 23: three-dimensional image forming unit, 24: display circuit, 30: display, 50: electrocardiograph, 60: X
Line control pulse generation unit, 61: ECG gate pulse generation circuit, 62: Measurement angle range flag circuit, 63: X-ray control pulse generation circuit

Claims (3)

[Claims] An X-ray tube is rotated continuously around an object, irradiated with X-rays from the X-ray tube, and irradiated with an X-ray detector arranged opposite to the X-ray tube with the object interposed therebetween. An X-ray CT apparatus that captures projection data indicating transmitted X-rays of a subject and displays an image based on the projection data, wherein an ECG synchronization indicating a stationary period of the subject is synchronized with an electrocardiogram waveform from an electrocardiograph. An electrocardiographic synchronization generating means for generating a gate pulse; and for each rotation of the X-ray tube and the X-ray detector, the projection data within an angle range of 0 ° to 360 ° based on the electrocardiographic gate pulse. X-ray control means for irradiating X-rays from the X-ray tube only to an angle range that has not been captured, and an angle range necessary for image formation from the X-ray detector for each rotation of the X-ray tube and X-ray detector Fetches the projection data of X-ray CT apparatus characterized by comprising: the image construction means for constructing an image. 2. An X-ray tube is continuously rotated around an object, irradiated with X-rays from the X-ray tube, and irradiated by an X-ray detector arranged opposite to the X-ray tube with the object interposed therebetween. An image creation method for capturing projection data indicating transmitted X-rays of a subject and creating an image based on the projection data, comprising: an ECG gate indicating a stationary period of the subject in synchronization with an electrocardiogram waveform from an electrocardiograph. Generating a pulse; irradiating X-rays from the X-ray tube during the first rotation of the X-ray tube and X-ray detector during the output period of the ECG gate pulse to capture projection data; After the second rotation of the X-ray tube and the X-ray detector, based on the output of the ECG gate pulse, only the angle range within the angle range of 0 ° to 360 ° and in which the projection data has not been captured yet. X-rays are emitted from the X-ray tube to project A step of capturing the data, repeating the capture of the projection data until the projection data of the angle range required for the image configuration is captured, and a step of configuring an image based on the projection data of the angle range required for the image configuration, An image creation method including and. 3. An X-ray tube and an X-ray detector and a subject are relatively moved in a body axis direction of the subject to acquire three-dimensional projection data, and a three-dimensional image or a body axis direction of the subject is captured. 3. The method according to claim 2, wherein a two-dimensional image on a plane parallel to the image is generated.