JP2003299644A - Computer tomographic equipment - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a computer tomographic equipment capable of reducing the generation of artifacts caused by shortage of the sampling number by sacrificing the time resolution, reducing the noise, and improving space resolution. <P>SOLUTION: A sampling adjusting means 17 is mounted to differentiate a circumferential sampling position of a preceding radiation source and a circumferential sampling position of a trailing radiation source from each other in the circumferential direction, and the sampling density is increased by determining the sampling position of the second rotation at an intermediate position of the sampling positions in the first rotation upon acquiring one sectional image by two rotation, by determining the sampling number per one rotation to be (integer + 1/n) upon acquiring one sectional image by n-rotations. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a computer tomograph capable of taking a tomographic image of a subject.

[0002]

2. Description of the Related Art A third-row single-row detector type X-ray computed tomography apparatus using a single-row detector (hereinafter, referred to as
In SDCT), the slice thickness of a tomographic image is determined by limiting the radiation irradiation area to an arbitrary width by a collimator before irradiating a subject with radiation such as X-rays. Multi-row detector type X-ray computed tomography apparatus (hereinafter referred to as MD
In CT), the slice thickness is determined by the element width of the detector in the body axis direction. 1 for improving the axial resolution and spatial resolution generated in this MDCT
One method is to reduce the element size in the body axis direction and the channel direction of the detector. However, in order to reduce the element size, appropriate processing accuracy is required, and the limit is about 1 mm. Further, in order to reduce the element size, a separator for dividing the element is required, but this separator lowers the incident dose, increases noise due to insufficient dose, and reduces the use efficiency of irradiation radiation.

Up to now, in order to improve the spatial resolution of a tomographic image generated in MDCT, the detector is shifted by 1/4 channel in the channel direction to shift the beam path to the opposite data, and the sampling density is set to 2 Techniques such as doubling the quarter offset have been generalized.

[0004]

However, in the conventional computer tomography apparatus, a higher resolution image can be obtained by using this quarter offset, but a microstructure such as an ossicle is diagnosed. In some cases, it is insufficient, and further improvement in spatial resolution is desired. In addition, when the radiation source is rotated with respect to the subject on the bed, the image quality improves as the number of samplings per rotation in the rotation direction increases, and when the number of samplings decreases, a fine straight line appears on the reconstructed image. It is generally known to produce artifacts. On the other hand, in the current X-ray CT system,
The scan speed, which is the time required for one rotation of the radiation source, is less than 1 sec / rot and is about to reach 0.5 sec / rot. From now on, this scan speed will be 0.
It is considered that the distance becomes higher at 3 sec / rot and 0.1 sec / rot. It is considered that the amount of data that can be obtained per unit time will be dramatically improved as the scanning speed is improved. At 0.1 sec / rot, 1 sec / rot will be 10
The amount of data is doubled, and it is considered that a problem of data transfer rate will occur. Therefore, there is a possibility that the number of samplings per one rotation of the radiation source cannot be sufficiently obtained at 0.1 sec / rot.

Moreover, the noise amount in the reconstructed image depends on the effective radiation irradiation dose of the projection data used for one image, and the noise amount decreases as the radiation irradiation amount increases. Here, when the scanning speed is improved, it is considered that noise is increased because the radiation dose irradiated per unit time is decreased. To suppress the increase in noise amount, the radiation source capacity is increased and the unit It is necessary to increase the radiation dose applied per hour. However, increasing the capacity of the radiation source leads to increased costs,
It also leads to an increase in the size of the radiation source and the radiation cooling device.

Further, an image originally obtained on a two-dimensional plane is now three-dimensionalized, and in the future, a four-dimensional image will be acquired by adding a time axis to the image. In this four-dimensional image, a change in the time direction can be diagnosed by photographing the same region a plurality of times. This is possible because the X-ray CT apparatus has improved the time resolution due to the improved scanning speed and the increased amount of data obtained at one time due to the multi-row detector. At present, there is a technique called fluoroscopy for observing changes with time in the same site. When acquiring the fluoroscopy and the four-dimensional image, when the same region is photographed multiple times, sampling is performed at the same position in the phase direction in the first rotation and the second rotation, and despite the multiple photographing, No improvement in image quality other than noise can be expected. Further, in a CT apparatus using a flat panel detector or CCD, the scanning speed cannot be improved because the number of samplings obtained per unit time is low due to the detector characteristics.

It is an object of the present invention to provide a computer tomography apparatus that reduces the amount of noise and reduces the amount of noise by reducing the number of samplings by sacrificing the temporal resolution.

[0008]

In order to achieve the above object, the present invention provides a radiation source capable of irradiating radiation, and the radiation from the radiation source when the radiation source is rotated. Limiting means for limiting and irradiating the subject on the bed, a radiation detector for detecting the radiation transmitted through the subject, and the subject from the projection data detected by the radiation detector at the circumferential sampling position of the radiation source. In a computer tomography apparatus including a calculation device for creating a tomographic image of the radiation source, the sampling in which the sampling position in the circumferential direction of the preceding radiation source and the subsequent sampling position in the circumferential direction of the radiation source are shifted in the circumferential direction. It is characterized by having an adjusting means.

According to the computer tomography apparatus of the present invention as described above, when one cross-section image is acquired by a plurality of rotations,
Since the sampling adjustment means for shifting the sampling positions of the first rotation and the second rotation in the circumferential direction is provided, the sampling position of the second rotation is different from the sampling position of the first rotation, the sampling density is increased, and the scan speed is increased. Even if the sampling rate is improved and a sufficient number of samplings cannot be obtained, artifacts that occur can be reduced, and images with high temporal resolution can be acquired in one shot, and at the same time, high-quality images can be obtained at the expense of temporal resolution. It is also possible to create.

In order to achieve the above-mentioned object, the present invention described in claim 2 is the sampling adjustment means according to claim 1, wherein the number of samplings per revolution of the radiation source is one cross section per n revolutions. When acquiring a tomographic image of
Per rotation of the radiation source in the circumferential direction (integer + 1 /
n) is set.

According to the computer tomography apparatus of the present invention as described above, when one cross-sectional image is acquired by n rotations, 1
By setting the number of samplings per rotation to (integer tenths / n), 2 is obtained when acquiring one cross-sectional image in two rotations.
The sampling position of the second rotation is an intermediate position of the sampling position of the first rotation, and it is possible to obtain approximately twice the sampling density, and the same purpose can be achieved.

In order to achieve the above object, the present invention described in claim 3 is the same as the sampling adjusting means according to claim 1, in which the rotational speed adjusting means capable of changing the rotational speed of the radiation source in the circumferential direction. It is characterized in that it is configured with.

According to such a computer tomography apparatus of the present invention, the circumferential sampling position of the preceding radiation source and the succeeding circumferential sampling position of the radiation source are simply changed by changing the rotational speed of the radiation source. The sampling position can be shifted in the circumferential direction, and the object can be achieved in the same manner.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. FIG. 2 is an external view of a computer tomography apparatus according to an embodiment of the present invention. A scanner 1 used for imaging, a bed 2 on which a subject is placed and moved, and a bed 2 including a mouse and a keyboard.
Input device 3 for inputting measurement reconstruction parameters such as moving speed information and reconstruction position, arithmetic unit 5 for processing data obtained from multi-row radiation detectors 4, and reconstructed image are displayed. The display device 6 is provided.

FIG. 1 is a block diagram of the computer tomography apparatus described above. Here, the scanning method of the computer tomography apparatus is a rotate-rotate method (third generation), and is mainly composed of the scanner 1 and the operation unit 7. The scanner 1 includes an X-ray generator 8, a high voltage switching unit 9, and a high voltage generator 1.
0, an X-ray controller 11 and the like, a bed 2 on which a subject is mounted, a radiation detector 4 facing the radiation source with the subject in between, and a collimator arranged between the radiation source and the subject. 12 is controlled by a collimator control device 13, a limiting device configured to control the collimator control device 13, a driving device 14 and a scanner control device 15 that rotate the scanner 1 located on the outer circumference of the subject in the circumferential direction, and radiation detected by the radiation detector 4. By a preamplifier 16 for converting the current into a current and amplifying it and inputting it to the arithmetic unit 5 as a projection data signal; A circumferential shift of the circumferential sampling position of the preceding radiation source that is constructed and that follows. And pulling the adjustment means 17 is constituted by a central control unit 18 for controlling these.

When the imaging conditions, that is, the bed moving speed, the tube current, the tube voltage, the slice position, the number of views, the number of imaging rotations, and the reconstruction conditions (reconstruction algorithm) are input from the input device 3 of the operation unit 7, the instruction is given. A control signal necessary for photographing is transmitted from the central controller 18 to the X-ray controller 11, the bed controller 19, and the scanner controller 1 based on
Then, the image pickup is started in response to the image pickup start signal. When imaging is started, a control signal is sent from the X-ray controller 11 to the high voltage generator 10, and a high voltage is applied to the X-ray generator 8 via the high voltage switching unit 9,
The X-ray generator 8 irradiates the subject with radiation such as X-rays. At the same time, a control signal is sent from the scanner control device 15 to the drive device 14, and the X-ray generation device 8, the radiation detector 4, the preamplifier 16 and the like rotate around the outer circumference of the subject.

On the other hand, the bed 2 on which the subject is placed by the bed control device 19 is stationary during the circular orbit scan, and moves parallel to the circumferential axis of the X-ray generator 8 or the like during the spiral orbit scan. At this time, the moving speed of the couch 2 that moves in parallel is measured by the couch movement measuring device 20 and input to the computing device 5. The radiation irradiated from the X-ray generator 8 limits the irradiation area by the collimator 12, is absorbed or attenuated by each tissue in the subject, and is detected by the radiation detector 4. The radiation detected by the radiation detector 4 is converted into a current, amplified by the preamplifier 16 and input to the arithmetic unit 5 as a projection data signal. The projection data signal input to the arithmetic unit 5 is reconstructed by the reconstruction arithmetic unit 21 in the arithmetic unit 5 based on the number of views input by the input unit 3, and the reconstructed image processed by the image processing unit 22. Is stored in the storage device 23 and displayed as a tomographic image on the display device 6.

FIG. 3 is a plan view showing a sampling position in a state where the sampling adjusting means 17 of the above-described computer tomography apparatus is not operated. Here, the number of views per rotation in the circumferential direction of the radiation source is eight, but since the sampling positions S1 to S8 are integers, the sampling positions of the subsequent second rotation are exactly the same.

On the other hand, when the sampling adjusting means 17 operates, as shown in FIG. 4, when acquiring one cross-sectional image in n rotations, a view per rotation in the circumferential direction of the radiation source (integer + 1 / n), In the figure, since the view is 7.5 views, the sampling positions are S1 to S8 in the preceding rotation, whereas the sampling position is S9 in the subsequent rotation.
Up to S15, the two are not coincident with each other and are measured at the shifted positions. Therefore, by determining the number of views so that the sampling positions do not coincide with each other in the subsequent rotation of the radiation source in the circumferential direction, it is possible to increase the density of data sampling.

Here, it is desirable that the number of views per rotation of the radiation source is changed according to the number of rotations at which one section is imaged, for example, by giving a condition to the sampling adjusting means 17 from the input device 3. Further, the sampling adjusting means 17 may be used to shift the circumferential sampling position of the preceding radiation source and the succeeding circumferential sampling position of the radiation source in the circumferential direction. When creating a photographed image, it is desirable to make an integer view in two rotations. Specifically, the imaging data for one rotation creates a tomographic image with 1000 views, whereas when creating a tomographic image with data for two rotations, the total number of views for two rotations is an integer. Therefore, it is desirable to set a value such as 999.5 views per rotation. Similarly, when a tomographic image is created using imaging data for four rotations, it is desirable that an integer view is obtained by four rotations. Specifically, the imaging data for one rotation creates a tomographic image with 1000 views, whereas when creating a tomographic image with data for four rotations, the total number of views for four rotations is an integer. So, for example, 1
A value such as 999.25 views per revolution is desirable.

It is desirable that the number of views is automatically determined. However, the number of views may be manually input from the input device 3 and adjusted by the sampling adjusting means 17, or the sampling adjusting means 17 may be operated. It may be provided on the unit 7 side and changed according to the image reconstruction algorithm.

As described above, the sampling adjusting means 1 for shifting the circumferential sampling position of the preceding radiation source and the succeeding circumferential sampling position of the radiation source in the circumferential direction.
Since the computer tomography apparatus is provided with 7, more specifically, when acquiring one cross-sectional image in n rotations, the number of samplings per rotation is (integer tenths / n) In the case of acquiring the first cross-section image, the sampling position of the second rotation is the intermediate position of the sampling position of the first rotation. Therefore, conventionally, one rotation is 10
If you were shooting for 00 views, it will be 1 even if you shoot twice.
Although the sampling density is 000 views, the sampling density of 1999 views can be obtained when two rotations are taken by setting 999.5 views per rotation. Therefore, even when the scan speed is improved and a sufficient number of samplings cannot be obtained, it is possible to reduce the generated artifacts. In other words, when shooting in integer view as in the past, when shooting at a low scan speed, it is not possible to obtain a high resolution image instead of obtaining a sufficient number of samplings, and when the scan speed is improved. Although an image with high temporal resolution is obtained, artifacts occur, whereas with the above-described computer tomography apparatus, an image with high temporal resolution can be acquired in one shot when the scanning speed is improved, and at the same time, the temporal resolution It is also possible to create a high quality image at the expense of.

In the above-described embodiment, when one cross-sectional image is acquired by n rotations of the radiation source, the sampling adjustment unit 17 sets the number of samplings per rotation of the radiation source to (integer + 1 / n). Adjustment means 1
7 may be configured as a rotation speed adjusting unit that changes the rotation speed of the drive device 14 that rotationally drives the radiation source in the circumferential direction. When the sampling adjusting unit 17, which is the rotating speed adjusting unit, acquires one cross-sectional image by two rotations of the radiation source, the drive unit 14 is set so that the sampling positions in the first rotation of the radiation source are S1 to S8 in FIG. When the rotation speed of the radiation source is controlled by, and the rotation speed of the radiation source is controlled by the drive device 14 so that the sampling position in the second rotation is S9 to S15 in FIG. 4, almost the same as in the above-described embodiment. The effect of can be obtained. Further, the detector elements may be arranged asymmetrically with respect to the center of the detector in accordance with a preset offset amount so that the opposite data and the beam path are different, and the preset offset amount is an integer + 1 / It may be four channels (quarter offset), and may depend on the number of samplings (number of views) per rotation of the radiation source, the detector shape, and the number of rotations used to acquire one cross-sectional image.

Although the multi-row detector type three-dimensional tomography apparatus is used in the above-described embodiment, the present invention is not limited to this.
It is needless to say that it is also applicable to a single-row detector type tomography device. Further, although the X-ray CT apparatus has been described in the present embodiment, the present invention is also applicable to a tomography apparatus using gamma rays, neutron rays, positrons, electromagnetic energy, and light. In an Imatron CT system that uses a light beam instead of X-rays. , The time resolution is high, but sufficient dose cannot be obtained, and noise tends to increase. However, as mentioned above,
By shifting the sampling positions in the second rotation and the second rotation by the sampling adjusting means 17, it is possible to obtain a high-resolution and low-noise image when the same site is photographed a plurality of times. The scanning method is not limited to any one of the first generation, the second generation, the third generation, and the fourth generation, and a multi-tube CT apparatus or a donut-type tube CT apparatus equipped with a plurality of X-ray sources. Can also be used for.

[0025]

As described above, according to the computer tomography apparatus of the present invention, when the radiation source is rotated by a plurality of turns around the subject in order to create a one-section image, the sampling position is changed. By shifting, it is possible to increase the sampling density with a simple configuration and obtain a good image with a higher spatial resolution than in the conventional case.

[Brief description of drawings]

FIG. 1 is a block diagram of a computer tomography apparatus according to an embodiment of the present invention.

FIG. 2 is an external view of the computer tomography apparatus shown in FIG.

FIG. 3 is a plan view showing a sampling position in a state where the sampling adjusting means of the computer tomography apparatus shown in FIG. 1 is not operated.

4 is a plan view showing a sampling position in a state in which a sampling adjusting means of the computer tomography apparatus shown in FIG. 1 is operated.

[Explanation of symbols]

1 scanner 2 sleeper 4 Radiation detector 5 arithmetic unit 8 X-ray generator 14 Drive 16 preamplifier 17 Sampling adjustment means

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Hiroto Kokubun             1-chome 1-14-1 Kanda, Chiyoda-ku, Tokyo             Inside the Hitachi Medical Co. F-term (reference) 4C093 AA22 CA02 CA06 CA13 EB21                       FA34

Claims (3)

[Claims] 1. A radiation source capable of irradiating radiation, a limiting means for irradiating the subject on the bed with radiation from the radiation source when the radiation source is rotated, and radiation transmitted through the subject. In a computer tomography apparatus including a radiation detector for detecting a tomography image and a calculation device for creating a tomography image of a subject from projection data detected by the radiation detector at a circumferential sampling position of the radiation source, A computer tomography apparatus comprising: a sampling adjusting unit that shifts a circumferential sampling position of the radiation source and a subsequent sampling position of the radiation source in the circumferential direction. 2. The sampling adjusting means according to claim 1, wherein when the tomographic image of one cross section is acquired by n rotations of the number of samplings per revolution of the radiation source, the sampling adjustment means A computer tomography apparatus characterized in that the number of rotations per direction is (integer + 1 / n). 3. The computer tomography apparatus according to claim 1, wherein the sampling adjusting means is a rotation speed adjusting means capable of changing a rotation speed of the radiation source in a circumferential direction.