JP2000051197A - Medical image processing system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To get a clear tomogram with helical scanning by compensating the motions of an examinee's heart and a bed. SOLUTION: A system controller 5 adds an examinee's electrocardiogram detected by an electrocardiogram transmitter 10, the rotation phase of the rotary part 3 of a frame, and the position (sliced position) of a bed, to projection data gotten by helical scanning using an X-ray detector 2 for multi-slicing, and stores the data into a data storage 13. The projection data gotten when an electrocardiogram phase matches with a rotation phase so that the prescribed slicing position intervenes therebetween, are selected, helically interpolated, and then reconstructed to form a tomogram. This can compensate the motion of the examinee's heart and the motion of the bed and interpolate helically at a dense interpolating interval using projection data gotten by the X-ray detector 2 for multi-slicing, so that a clear tomogram can be gotten.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a medical image processing apparatus for forming a tomographic image or a three-dimensional image based on projection data from an X-ray CT apparatus for imaging a desired part of a subject by helical scan.

[0002]

2. Description of the Related Art Today, a bed on which a subject is placed is gradually moved along the body axis direction of the subject.
By rotating the X-ray tube and the X-ray detector around the subject by 360 degrees and applying X-rays at predetermined angles (or continuously), a desired part of the subject is spirally formed. A helical scan type X-ray CT apparatus for performing scanning is known. Further, medical image processing for performing image reconstruction processing based on 360-degree (minimum 180-degree) projection data obtained from the helical scan type X-ray CT apparatus to form a three-dimensional image of a desired site Devices are also known.

[0003] When imaging is performed by such a helical scan method, for example, when a stationary part such as the head is imaged, a clear three-dimensional image can be formed by the medical image processing apparatus. Although it is possible, when capturing a moving part such as the heart, the movement is reflected in the tomographic image obtained by the helical scan, and a clear three-dimensional image is formed in the medical image processing apparatus. It becomes difficult. In order to solve such a problem, a three-dimensional image diagnostic apparatus disclosed in Japanese Patent Application Laid-Open No. Hei 5-3867 has been proposed.
Japanese Patent Publication No. 36 discloses an image generation method, an image display method, and an X-ray CT apparatus.

A three-dimensional diagnostic imaging apparatus disclosed in Japanese Patent Laid-Open Publication No. Hei 5-3867 performs a helical scan, detects an electrocardiographic waveform, and outputs projection data of the electrocardiographic waveform having the same phase timing. The image reconstruction processing is performed by using this.

The image generation method, the image display method, and the X-ray CT apparatus disclosed in Japanese Patent Application Laid-Open No. 9-75336 disclose a large number of helical scans of a scan target such as a heart at a fine pitch. After forming the reconstructed image, a plurality of reconstructed images having the same cardiac potential phase are selected, and a tomographic image at a desired slice position is formed (resampling) based on these images.

[0006] According to each of these disclosed techniques, even in a region that moves, such as the heart, each tomographic image can be formed using only projection data of the diastolic timing of the heart, for example. Therefore, it is possible to form a three-dimensional image in which the motion of the scanning target such as the heart is corrected based on each tomographic image.

[0007]

However, in each of the disclosed techniques described above, it is good to form a tomographic image in which the motion of the scan target such as the heart is corrected. However, there is a problem that the image quality is deteriorated due to the movement of the bed on each tomographic image and the three-dimensional image.

In the image generation method, the image display method, and the X-ray CT apparatus disclosed in Japanese Patent Application Laid-Open No. 9-75336, after the image reconstruction processing is performed, the Since only the projection data at a predetermined timing is selected from the data and a tomographic image at a desired slice position is formed based on the selected data, the width of the selection, that is, the Z direction in the body axis direction (slice direction) is selected. There has been a problem that the interpolation interval becomes large and the image quality also deteriorates.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems, and corrects the movement of a scan target such as a heart and the movement of a bed by a helical scan, and also prevents the inconvenience of increasing the interpolation interval in the Z direction. It is another object of the present invention to provide a medical image processing apparatus capable of forming a clear tomographic image and a three-dimensional image.

[0010]

According to the medical image processing apparatus of the present invention, as a means for solving the above-mentioned problem, an object phase for detecting an object phase corresponding to a movement of a scanning object of the object is provided. A detecting means, a couch position detecting means for detecting each couch position at the time of the helical scan of the couch on which the subject is placed, and a rotational phase detecting means for detecting a rotational phase of the gantry rotating unit at the time of the helical scan. Further, in addition to these units, among the projection data obtained by the helical scan, projection data near the designated slice position is detected based on the detection output from the couch position detection unit, and the designated From the projection data in the vicinity of the slice position, the projection data obtained at the timing when the object phase is within a predetermined phase range and the rotation phase matches, is output from the object phase detection unit and the rotation phase detection unit. An interpolation unit that forms projection data corresponding to the specified slice position by interpolation processing based on the selected projection data, and projection data formed by the interpolation unit. Image reconstruction means for performing image reconstruction processing using the image data to form a tomographic image at the designated slice position.

In such a medical image processing apparatus, after selecting projection data whose rotation phase and object phase are the same (or within a predetermined range) and performing interpolation processing in the body axis direction (Z direction),
An image reconstruction process is performed. Thereby, it is possible to obtain interpolation data in which the movement of the bed by the helical scan is corrected together with the movement of the scan target such as the heart. Therefore, the image quality of the tomographic image and the three-dimensional image reconstructed based on the interpolation data can be improved.

Further, the medical image processing apparatus according to the present invention comprises:
As the projection data, X having a plurality of X-ray detector rows
The projection data detected by the line detector is used, or the projection data obtained by moving the bed at a pitch smaller than the pitch of the X-ray detector row of the X-ray detector is used.

[0013] As a result, since projection data obtained by helical scanning with a fine pitch is used, dense interpolation processing can be performed in the body axis direction (Z direction), and reconstruction is performed based on the interpolation data. The image quality of the tomographic image and the three-dimensional image to be obtained can be further improved.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the medical image processing apparatus according to the present invention will be described below in detail with reference to the drawings. The medical image processing device according to the present invention,
The present invention can be applied to a three-dimensional image diagnostic apparatus that captures a tomographic image of a subject using an X-ray CT apparatus capable of helical scan as shown in FIG. 1 and forms a three-dimensional image based on each tomographic image.

Referring to FIG. 1, a three-dimensional diagnostic imaging apparatus according to an embodiment of the present invention includes an X-ray tube 1 and an X-ray detector 2 which rotate while maintaining a positional relationship therebetween, and an inner peripheral portion. A x-ray tube 1 and an x-ray detector 2 rotatably provided on a gantry rotating unit 3, a bed 4 on which a subject is placed, and a system control unit for controlling the whole of the three-dimensional image diagnostic apparatus 5, a bed controller 6 for controlling the movement of the couch 4 in the body axis direction of the subject, and an X-ray tube drive controller for driving the X-ray tube 1 with a tube voltage, a tube current and an exposure timing supported by an operator. 7 and a data collection unit 9 for collecting projection data formed by the X-ray detector 2 capturing an X-ray image.

The three-dimensional diagnostic imaging apparatus is mounted on a subject, detects an electrocardiographic waveform of the subject, and transmits electrocardiographic data, and an electrocardiographic waveform transmitter. Antenna 11 for receiving electrocardiographic data transmitted from 10
And an electrocardiographic waveform input unit 12 for supplying electrocardiographic data received by the antenna 11 to the system control unit 5, and data storage for storing projection data collected by the data collecting unit 9, reconstructed tomographic images, and the like. And a part 13.

Further, the three-dimensional image diagnostic apparatus detects projection data at the same bed position and at a timing when the cardiac potential phase and the rotation phase match, and based on the projection data, a tomographic image at a target slice position is detected. It has an image reconstruction unit 15 for reconstructing an image, and an image display unit 16 for displaying a tomographic image formed by the image reconstruction unit 15.

As the X-ray detector 2, for example, as shown in FIG. 2, an X-ray detector row 2a formed by arranging a plurality of X-ray detecting elements in parallel in the channel direction is sliced perpendicular to the channel direction. An X-ray detector for multi-slice, which is formed in four rows in the thickness direction (rotation center axis of the gantry rotating unit 3: body axis direction, Z axis), is provided.

Next, the operation of the three-dimensional image diagnostic apparatus according to the present embodiment having such a configuration will be described.

First, when a helical scan of a desired part of the subject is designated by the operator, the system control unit 5 moves the bed 4 on which the subject is placed by a predetermined amount in the body axis direction of the subject. The movement of the bed 4 is controlled via the bed control unit 6 as described above. Specifically, in the case of this example, the X-ray detector 2 has four X-ray detector rows. 1
Assuming that the pitch is a moving distance of the width at the rotation center of the X-ray beam corresponding to the width of one X-ray detector row 2,
The system control unit 5 controls the movement of the bed 4 so that the bed 4 is gradually moved by four pitches or less, for example, by 2.5 pitches.

Also, the system control unit 5
The X-ray tube 1 and the X-ray detector 2 in the gantry rotating unit 3 are controlled to rotate, and X-rays are emitted from the X-ray tube 1 to the subject at predetermined rotation angles. The X-ray tube 1 is driven for irradiation through the tube drive control unit 7. As a result, the X-ray tube 1 rotating around the subject on the couch 4 irradiates the subject with X-rays in a spiral manner, and so-called helical scanning is performed. In addition,
In this helical scan, as described above, the bed 4 is controlled so as to gradually move by 2.5 pitches. Therefore, the helical scan (overlap) is performed in a state where the latter 1.5 pitches are overlapped. Scan). The data collection unit 9 forms projection data by capturing an X-ray image formed by such an overlap scan, and supplies the projection data to the system control unit 5.

On the other hand, the electrocardiogram waveform transmitter 10 detects an electrocardiogram waveform of the subject as shown in FIG. 4A during the imaging, and transmits the electrocardiogram data. The transmitted electrocardiogram data is received by the antenna 11 and supplied to the electrocardiogram waveform input unit 12. The electrocardiogram waveform input section 12 captures the electrocardiogram data and supplies it to the system control section 5. The system control unit 5 detects a cardiac potential phase as shown in FIG. 4B based on the electrocardiographic data. Then, as shown by hatching in FIG. 4B, a cardiac potential phase θh (t) that periodically appears, for example, between phases θ1 and θ2 corresponding to the diastolic phase of the heart is detected in the cardiac potential phase. I do.

Since the system control unit 5 controls the movement of the couch 4, the couch position (slice position) corresponding to the currently supplied projection data can be detected.
Further, since the rotation of the X-ray tube 1 and the X-ray detector 2 of the gantry rotating unit 3 is controlled, the rotational phase of these can also be detected. For this reason, when each projection data is supplied from the data collection unit 9, the system control unit 5 adds the couch position data indicating the couch position, the rotation phase data indicating the rotation phase, and the cardiac potential phase to each projection data. Is added, and this is temporarily stored in the data storage unit 13.

FIG. 4 (c) shows projection data for every 360 degrees (2π) obtained for each bed position by helical scan. In FIG. 4 (c), the projection data shown by the solid line is the actual data. Also, the projection data indicated by the dotted line indicates the opposite data of the same X-ray path, and FIG.
(C) during the cardiac potential phase θh (t) shown in FIG.
The actual data indicated by the dashed line can be obtained. That is, the actual data indicated by the chain line is the actual data in which the scan positions are adjacent and the cardiac potential phase and the rotational phase are the same. Similarly, in the case of facing data, there is also facing data obtained at the same timing of the cardiac potential phase θh (t) and the rotation phase. Looking at the actual data and the opposing data obtained at the timing of the cardiac potential phase θh (t), 36
It can be seen that the projection data for 0 degrees is complete.

When the projection data is stored in the data storage unit 13 based on such a theory, the image reconstruction unit 15 converts the projection data sandwiching the slice position designated for image reconstruction into the couch position data. (Projection data before and after the slice position designated for image reconstruction is detected based on the couch position data), and among the detected projection data, the cardiac potential phase and the rotational phase are the same. Projection data (actual data and facing data) is detected based on the rotation phase data and the cardiac potential phase data.
Then, helical interpolation data is formed based on the detected projection data (the helical interpolation is, for example, an inverse ratio of the distance). The selection of the projection data and the helical interpolation may be extrapolated.

That is, the image reconstructing unit 15 performs helical interpolation using projection data having the same cardiac potential phase and rotation phase collected at the closest position across the designated slice position. As described above, the X-ray detector 2 is a multi-slice X-ray detector having four X-ray detector rows 2a. Therefore, as shown in FIG. 4D, when the X-ray tube 1 and the X-ray detector 2 make one rotation, projection data for four columns can be collected at a time. This means that helical interpolation can be performed using only projection data at one focal position. Therefore, assuming that Zc shown in FIG. 4D is a target slice position, helical interpolation processing is performed using projection data closest to the target slice position Zc as shown by a dotted line in FIG. 4D. be able to.
That is, there is no omission in the projection data, and a constant sampling interval can be secured in the Z direction (= body axis direction). Even if the projection data obtained by different rotations (actual data or opposing data) matches the timing of the cardiac potential phase and the rotation phase, dense sampling in the Z direction can be performed. be able to.

The image reconstructing unit 15 performs a fan beam image reconstructing process after such a helical interpolation process, forms a tomographic image at a designated slice position, and generates an image display unit 16.
Or a three-dimensional image is formed based on the plurality of tomographic images and supplied to the image display unit 16. As a result, a three-dimensional image including the tomographic image at the specified slice position or the tomographic image at the specified slice position is displayed on the image display unit 16.

As is apparent from the above description, the three-dimensional diagnostic imaging apparatus according to the present embodiment is configured to collect projection data having the same electrocardiographic phase and the same rotational phase collected at the closest position across the designated slice position. Is used to perform helical interpolation.
For this reason, since helical interpolation uses projection data with the same cardiac potential phase (because the cardiac potential phase is matched when performing helical interpolation), it is used for image reconstruction after image reconstruction. The helical interpolation processing in which the motion of the heart and the motion of the bed are corrected can be performed as compared with the case where the electrocardiographic phase is matched with the center of gravity of the projection data.

Further, since the X-ray detector 2 having the X-ray detector rows 2a for four rows for multi-slice can collect projection data for four rows at one focus position, the target slice position can be obtained. The helical interpolation process can be performed using the projection data closest to the above, and the helical interpolation process can be performed at a dense sampling interval in the Z direction (= body axis direction) without omission in the projection data. Therefore, a clear tomographic image and a three-dimensional image can be formed.

In the above description of the embodiment, the cardiac potential phase is detected. However, it is also possible to detect another phase such as a respiratory phase. Although the helical interpolation process is used using the actual data and the opposing data, the helical interpolation process may be performed using only the actual data or only the opposing data.

The image reconstruction unit 15 performs the helical interpolation process using “projection data having the same cardiac potential phase”. This is because “the projection data (cardiac potential phase difference is within a predetermined range). Alternatively, the helical interpolation process may be performed using the projection data included in a predetermined phase range). As a result, projection data used for the helical interpolation processing can have a certain width, and the calculation time of the helical interpolation processing can be reduced.

Further, the bed 4 is moved by 2.5 pitches of the multi-slice X-ray detector row 2a (although the helical pitch is set to 2.5 pitches). It may be four or more. in this case,
Although the sampling interval of the projection data used for the helical interpolation process is increased, the scan time can be shortened, and the exposure of the subject can be reduced. Even when the helical pitch is set to 4 or more, there is not much problem because the sampling interval between the X-ray detector rows 2a for four rows is secured.

Further, the multi-slice X-ray detector 2 having four X-ray detector rows 2a is provided.
This means that a dual slice X-ray detector having two X-ray detector rows or a single slice X-ray detector having one X-ray detector row as shown in FIG. For example, another X-ray detector may be provided.

When a single-slice X-ray detector having one row of X-ray detectors is provided, the bed 4 is controlled to move at a helical pitch of 1 pitch or less, and the projection obtained by this is controlled. Helical interpolation processing is performed based on the data. As a result, helical interpolation processing at a fine sampling interval can be performed, and a clear tomographic image and a three-dimensional image can be formed. In this case, the bed 4 may be controlled to move at a helical pitch of 1 pitch or more. As a result, the scan time can be reduced, and the exposure of the subject can be reduced.

Finally, the above embodiments are only examples of the present invention, and the present invention is not limited to the above embodiments. For example, in the description of the above-described embodiment, projection data synchronized with the cardiac potential phase is selected. However, this may be synchronized with substantially periodic data such as breathing. It goes without saying that various changes can be made in accordance with the design and the like without departing from the technical concept of the present invention.

[0036]

The medical image processing apparatus according to the present invention can perform the helical interpolation process by correcting the movement of the bed by the helical scan together with the movement of the scan target such as the heart. Further, the interpolation interval in the Z direction (body axis direction) can be made closer. Therefore, a clear tomographic image and a three-dimensional image can be formed.

[Brief description of the drawings]

FIG. 1 is a block diagram of a three-dimensional image diagnostic apparatus according to an embodiment to which a medical image processing apparatus according to the present invention is applied.

FIG. 2 is a schematic diagram of a multi-slice X-ray detector provided in the three-dimensional diagnostic imaging apparatus of the embodiment.

FIG. 3 is a schematic diagram of a single-slice X-ray detector provided in the three-dimensional image diagnostic apparatus of the embodiment.

FIG. 4 is a timing chart for explaining a helical interpolation operation of the three-dimensional diagnostic imaging apparatus of the embodiment.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... X-ray tube, 2 ... X-ray detector, 3 ... gantry rotating part, 4 ... Bed, 5 ... System control part, 6 ... Bed control part, 7 ... X-ray tube drive control part, 9 ... Data collection part, DESCRIPTION OF SYMBOLS 10 ... Electrocardiogram waveform transmitter, 11 ... Antenna, 12 ... Electrocardiogram waveform input part, 13 ... Data storage part, 15 ... Image reconstruction part, 16 ... Image display part

Claims (5)

[Claims] 1. An object phase detecting means for detecting an object phase corresponding to a movement of a scanning object of a subject, and a couch position for detecting each couch position in a helical scan of a couch on which the subject is placed Detection means, rotation phase detection means for detecting the rotation phase of the gantry rotating part at the time of the helical scan, and projection data obtained by the helical scan,
Along with detecting projection data near the designated slice position based on the detection output from the couch position detection means,
From the projection data in the vicinity of the designated slice position, projection data obtained at a timing when the target object phase is within a predetermined phase range and when the rotation phase matches the target object phase is detected by the target object phase detection means and the rotation. An interpolation unit that selects based on each detection output from the phase detection unit and forms projection data corresponding to the specified slice position by interpolation processing based on the selected projection data, Image reconstruction means for performing an image reconstruction process using the projection data obtained and forming a tomographic image at the designated slice position. 2. The apparatus according to claim 1, wherein the interpolating unit is configured to output the detected object phase based on each detection output from the object phase detecting unit and the rotational phase detecting unit.
2. The interpolation process according to claim 1, wherein the interpolation process is performed by selecting only the projection data that is the real data, or by selecting the real data and the opposite data of the same X-ray path as the real data. Medical image processing apparatus. 3. The medical image processing apparatus according to claim 1, wherein the projection data is projection data detected by an X-ray detector having a plurality of X-ray detector rows. 4. The medical image processing apparatus according to claim 1, wherein the projection data is projection data detected by an X-ray detector having one row of X-ray detectors. 5. The projection data according to claim 1, wherein the projection data is projection data obtained by moving a bed at a pitch smaller than a pitch of an X-ray detector row of the X-ray detector. The medical image processing device according to claim 4.