JPH0626545B2 - CT scanner - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a tomography apparatus using radiation such as X-rays, a so-called CT scanner, and particularly in a fourth-generation CT scanner, an X-ray source having a 360 ° angle. Full rotation, high resolution,
The present invention relates to a CT scanner that enables high-quality image reconstruction.

(Prior Art) A stationary rotation type CT scanner called a fourth generation (explaining the case of X-ray) has a detector arranged on the circumference of the entire circumference, and the detector is fixed while the X-ray is fixed. It is an apparatus of a system in which a radiation source is rotated around a reconstruction area accommodating a subject. The gantry section of this device is shown in FIG. In the figure, reference numeral 1 denotes an image reconstruction area for accommodating a subject therein and for reconstructing a tomographic image of the subject present therein, and 2 is fixedly arranged on the circumference to irradiate the reconstruction area 1. It is a detector for detecting the generated X-rays. X-ray source 3
In the case of the pulse method, a fan-shaped X-ray beam covering the reconstruction area 1 is generated in a pulsed manner and continuously rotates in a circle around the reconstruction area 1. During the rotational scanning of the X-ray source 3, data is sampled by each detector 2 in synchronization with the generation of X-rays at constant angles. The merit of this method is that the image can be taken simply by rotating the X-ray source, so the mechanical reliability is high,
Since the imaging speed can be increased and each detector 2 can obtain the projection information of the reconstruction area 1 uniformly,
It is useful for reducing false images such as ring artifacts.

FIG. 9 shows the scanning of the X-ray CT scanner and the spatial arrangement of the data acquisition part thereof. In the figure, the same parts as those in FIG. 8 are designated by the same reference numerals. In the figure, O is the reconstruction area 1
, L _A is the circumference around which the detector 2 is arranged, and the detectors 2 are arranged at equal intervals and at equal angular intervals. The X-ray source 3 rotates on the circumference L _B , and in the case of the pulse system, the X-ray source 3 has points Xi (i = −n ... O ... n) and Yi (i = i) on the circumference L _B.
-N ... O ... n) is irradiated with X-rays, and transmission data (view data) of the subject with respect to the fan-shaped X-rays is collected for each direction. The range of data to be collected is the angular range that covers the minimum reconstruction area 1.

By the way, a so-called offset detection method is adopted in order to improve the resolving power (spatial resolution) of the reconstructed image, particularly in order to improve the resolving power in the radial direction. This because the offset detection method considered X-ray generating point X _0, with respect to a straight line connecting the reconstruction center O and the X-ray generating point X _0, the center and the X detector D ₀ located at the center of this case ₀
Consciously shift the straight line connecting the lines, in other words, detect such a geometrical position to generate an X-ray, and at least reconstruct it with respect to the collected data at the X-ray generation point Y ₀ shifted by 180 °. This is an attempt to increase the effective sample data by interpolating the transmission X-ray paths in the vicinity of the center O of the region 1 without matching each other.

(Problems to be solved by the invention) However, it is very difficult to further improve the resolution, and it is necessary to arrange a larger number of detector groups densely for scanning or to use a detector group with a narrow aperture width. There is a method such as changing the offset amount for each rotation and performing multi-rotation scanning,
The scan time is long, the radiation dose is significantly increased, and an expensive device is required.

The present invention has been made in view of the above points, and an object thereof is to perform rotation of an X-ray source that performs high-speed scanning over 360 °, so that the scan time is short and therefore an effective dose is small. High sample rate, high resolution,
It is to realize a CT scanner that enables high-quality image reconstruction.

(Means for Solving Problems) According to the present invention for solving the above problems, a radiation source that irradiates a fan-shaped radiation, and an arrangement that opposes the radiation source via an image reconstruction area that houses a subject. And a detector group having a plurality of detected detectors, the radiation source rotates around the image reconstruction area while irradiating the radiation, and the detector group detects the radiation radiated in each direction of space. In a CT scanner comprising view data acquisition means for acquiring view data by means of this, and image reconstruction means for performing image reconstruction based on said view data, wherein said radiation source rotates around said image reconstruction area. Form a spatially continuous all view, the all views having no overlapping of views and spatially continuous two or more views, and an opposing view corresponding to each view. The view data acquisition means is configured such that the view data acquisition unit has two or more views at adjacent or near positions in each group and a radiation path of an opposite view corresponding to each view in the image reconstruction area. Of the view data are interpolated at equal intervals in at least the central portion of the. Here, the radiation transmission path means a geometrical center line when the radiation has a spread.

(Function) By controlling the spatial position of radiation generation and irradiating the radiation, the view data at an arbitrary position and the view data in the vicinity, and the view data at the opposite position and the view data in the vicinity of the view data are at the center of the reconstruction area. In the vicinity, the respective radiation transmission paths are interpolated with each other without overlapping, and are collected as different data.

(Example) Hereinafter, the present invention will be described in detail with reference to the drawings.

First, the principle of the present invention will be described. FIG. 1 is a diagram showing a geometrical arrangement of a scan system for explaining the principle of the present invention. In the figure, the same parts as those in FIGS. 8 and 9 are designated by the same reference numerals. In the figure, the detector 2 is composed of Di (i = -n ... O ... n) centered on the arbitrary detector D _0, it is fixedly arranged on the circumference L _A equidistant, at equal angular intervals ing. The X-ray generation source 3 rotates on the circumference L _B , and in the case of the pulse system, irradiates a fan-shaped X-ray at each point on L _B. Now, at the intersection of the circle L _{B of the} straight line connecting the center C _{0 of the} arbitrary detector D ₀ and O, the point on the opposite side of D ₀ with respect to O is X _0.
And the angle that OX ₀ makes with the positive x-axis direction is θ ₀ . C
Among the intersections of the line segment C ₀ X ₀ with ₀ as the starting point and the circumference L _{B of the} straight line forming the angles δ ′, −δ ″, the points on the opposite side of ₀ with respect to ₀ are X ₀ ′ and X ₀ ″, respectively. And these X ₀ ′,
Angles formed by line segments OX ₀ ′ and OX ₀ ″ connecting X ₀ ″ and O with the positive direction of the x-axis are θ ₀ ′ and θ ₀ ″, and line segments OX ₀ ′ and O, respectively.
The angles formed by X ₀ ″ with the line segment C ₀ X ₀ are β ′ and β ″.

When the X-ray source 3 rotates on the circumference L _B to irradiate the reconstruction area 1 from the X-ray source 3 and the transmitted radiation enters the detector Di, an arbitrary position of the X-ray source 3 and its adjacent position X-ray source 3 and each irradiation X-ray transmission path from X-ray source 3 and its adjacent X-ray source 3 when rotated by 180 ° from each other interpolate with each other in the vicinity of the center O of reconstruction area 1. Each irradiation position of the X-ray source 3 is obtained.

(1) Scan at the following points. However, it is assumed that the number of positions irradiated by the X-ray source 3 is 2N and the X-ray source 3 moves in the counterclockwise direction. The position of the view by the X-ray source 3 is the next point shown in FIG.

The first view is θ ₀ −β ″, the second view is θ ₀ + β ′, the third view is θ ₀ + Δθ−β ″, and the fourth view is θ ₀ + Δθ + β ′ ...・ ・ ・ ・ ・ The N + 1st view is θ ₀ + 180 ° −β ″ (first opposing view) The N + 2nd view is θ ₀ + 180 ° + β ′ ..... The 2N-1st view is θ ₀ + 360 ° −Δθ−β ″ The 2Nth view is θ ₀ + 360 ° −Δθ + β ′ This means that the scan is performed at the following point.

X ₀ ″, X ₀ ′, X ₁ ″, X ₁ ′, X ₂ ″, X ₂ ′, ... Here, the setting of β ′ and β ″ will be described with reference to FIG. It should be noted that the detector, the X-ray generation point, etc. are enlarged in FIG. 3 for easy understanding. In the figure,
The same parts as those in FIG. 1 are designated by the same reference numerals. D in the figure
₀ and D ₁ are adjacent detectors, and C ₀ and C ₁ are their centers. The angle between the line segment C ₀ X ₀ and the line segment C ₁ X ₀ is Δ
γ, the angle between the line segment C ₀ X ₀ and the line segment C ₀ X ₀ ″ is δ ″, the angle between the line segment OX ₀ ″ and the line segment C ₀ X ₀ ″ is α ″, and the line segment C ₀ X _{0 0} the length L, a and a length of a line OX _0. takes a line segment _C 1 _X AX ₀ of ₀ on the line segment OX ₀ equal length of Let B be the intersection of and ▲ ▼.

In ΔC ₀ OX0 ″, β ″ is an external angle and β ″ = δ ″ + α ″ (1) Since Δγ and δ ″ are extremely small, the following equation is established.

When OB = (1/8) ▲ ▼ is selected, at ΔOC ₀ B (L−) δ ″ ≈ ▲ ▼ = (1/8) ▲ ▼ ...
(3) From the expressions (2) and (3), δ ″ ≈ · Δγ / {8 (L−)} (4) Also, from O to the base Let ▲ ▼ be the perpendicular line that is given to and let h be its length. To sin α ″ = h / ∴α ″ = sin ⁻¹ [{(L −) /} · sin δ ″] ...
(5) From equations (1), (4), and (5), β ″ = sin ⁻¹ [{(L −) /} · sin δ ″] + ・
Δγ / {8 (L −)} ... (6) β ′ is the same as the other adjacent detector D- ₁ of the detector D _0.
Segment OX ₀ to the line segment _{C-1 X 0} bear center _C-1 and _{X 0} of
Takes FX ₀ of length equal to
Let G be the intersection with ₀ X ₀ ′.

When ▲ ▼ = (3/8) ▲ ▼ is selected, the following equation is obtained.

δ ′ = 3 ·· Δγ / {8 (L −)} ... (7) α ′ = sin ⁻¹ [{(L −) /} · sin δ ′] ...
(8) β ′ = sin ⁻¹ [{(L −) /} · sin δ ′] + 3
· Δγ / {8 (L - )} ... (9) above the beta ', "Selecting the transmission path of the X-ray central beam in the vicinity of the reconstruction area center, X _0" beta -1 from / 8, X ₀ ′ passes through a point deviated from the center O by 3/8, and is rotated 180 ° on the opposite side Then, on the contrary, a deviation of 1/8 or -3/8 occurs, so that the distance just comes in between. However, the sign of the offset is from O to X
_With respect to the direction toward ₀ , the left side is + and the right side is −. The situation is shown in FIG. In the figure, the same symbols are used for the same parts as in FIG.

Is the position of the X-ray source 3 which is symmetrical with respect to the center O of X ₀ ′, X ₀ ″. As is apparent from the figure, the transmission path of the central beam in the first view X ₀ ″ is the reconstruction area 1 Center O to O
It is at a position shifted by ⅛ of A, and the transmission path of the central beam at X ₀ ′ is also displaced by 3/8 from the center O.

Is 180 ° rotated from X ₀ ″, The transmission path of the central beam at is at a position shifted from the center O on the opposite side of X ₀ ″ by 1/8, Is 180 ° rotated from X ₀ ′, The transmission path of the central beam at is located on the opposite side of the center O from X ₀ ′ by ⅜, and eventually the adjacent two views and the opposing two views overlap each other by 2/8. There is an interpolating relationship without.

FIG. 5 is a diagram showing a situation of interpolation. In the vicinity of the center O, X-ray paths from are interpolated with each other.

In the above description, the positions of X ₀ , X ₀ ′ and X ₀ ″ and their symmetrical positions have been described, but any X-ray source 3 on the circumference L _B is described.
It is natural to obtain the same result at the position of.

A sixth embodiment of the CT scanner using such a principle
Shown in the figure. In the figure, reference numeral 11 is a table on which the subject 12 is placed, and the subject 12 is accommodated by moving the subject 12 in a horizontal direction with respect to a hole in the central portion of the gantry 13. Gantry 13
Has a cross section formed as indicated by 13 '.
That is, the X-ray tube X of the X-ray source 3 rotates and moves on the circumference L _B centered on the center O of the reconstruction area 1. Detector 2 is further fixedly arranged on the circumference L _A of the outside. Reference numeral 14 is a table and a gantry controller for controlling the rotation of the X-ray tube X, while controlling the table 11 so that the subject 12 is appropriately arranged in the reconstruction area, and 15 is a high voltage for the X-ray tube X. A high-pressure X-ray tube control unit for supplying X-ray generation control device 1
Controlled by 6. Reference numeral 17 denotes an operation photographing control device for controlling the operation timing and the photographing time of the table / gantry control device 14 and the X-ray generation control device 16.

Reference numeral 18 denotes a data collecting device for collecting the transmitted X-ray intensity signal detected by the detector 2, and this data is sent to the data processing device 19. Reference numeral 20 is a mass storage device that stores data from the data processing device 19, reference numeral 21 is an image display device that displays an image reconstructed by the data processing device 19, and reference numeral 22 is a photographic device that captures the image.

Next, the operation of the apparatus of the embodiment thus configured will be described. In response to a control signal from the operation / imaging controller 17, the table / gantry controller 14 stores the table 11 on which the subject 12 is placed in the gantry 13, and rotates the X-ray source 3.
At the same time, the X-ray generation controller 16 is controlled. The X-ray generation control device 16 gives a high voltage to the X-ray tube X while controlling the irradiation timing of the X-ray tube X by a signal given to the high-voltage X-ray control unit 15 as described in the principle explanatory diagram. The detector 2 detects the X-ray intensity transmitted through the reconstruction area 1, and the data is acquired by the data acquisition device 18. Appropriate processing such as logarithmic conversion and X-ray intensity correction is performed on the obtained data in the data processing device 19 and stored in the mass storage device 20. In this way, when the data of 2N views are gathered, the data processing device 19 performs a normal image reconstruction process, the obtained image is displayed on the image display device 21, and if necessary, the photography control device 22. Photographed.

As described above, since the view data is completely interpolated in the vicinity of the center of the reconstruction area 1 at each of the adjacent and opposing irradiation positions, (1) as compared with an assumed high resolution CT scanner, CT with short scan time and hence high speed scan and low dose
A scanner can be realized.

(2) A device with high resolution and high image quality can be realized for the same rotation angle and exposure dose.

(3) If the aperture width of the detector is made sufficiently small, a very high spatial resolution can be obtained for the same imaging system (X-ray generation source (including focus size), number of detectors, geometrical arrangement). You can

(4) By using similar multiple view groups in the vicinity and their opposing view groups, C with higher resolution and less artifacts
A T-scanner is obtained.

The present invention is not limited to the above embodiment. For example, the following may be done.

(1) Various scanning methods can be applied.

For example, the following method shown in FIG. 7 may be used (the number of views N).

The first view is θ ₀ −β ″, the second view is θ ₀ + Δθ + β ′, the third view is θ ₀ + 2Δθ−β ″, and the fourth view is θ ₀ + 3Δθ + β ′ ... ... View is θ ₀ + 180 ° -β ″ The view _{θ 0 + 180 ° + Δθ +} β '············ the first N-1 th view _{θ 0 + 360 ° -2Δθ-β} " N-th view θ ₀ + 360 ° -Δθ -Β 'This means that the scan was made at the next point.

(2) The next scanning method does not matter.

The first view is θ ₀ + β ′ The second view is θ ₀ + Δθ−β ″ The third view is θ ₀ + 2Δθ + β ′ The fourth view is θ ₀ + 3Δθ−β ″ This is the next point It was scanned in.

X ₀ ′, X ₁ ″, X ₂ ′, X ₃ ″ (3) Of course, scanning in the CW direction is also possible.

(4) The method of giving Δθ may be different for each view.

(5) L _A may be inside L _B. That is, in order to increase the resolution, the detector group may be arranged inside the X-ray source 3 (the detector 2 may be retracted to avoid passage of X-rays).

The values shown in the equations (9) and (6) of (6) β ′ and β ″ may be interchanged. In this case, δ ″ in the equation (6) is replaced by δ ′.
Then, δ ′ in equation (9) is replaced with δ ″.

(7) The X-ray CT scanner may have various configurations other than the configuration shown in the embodiment. Also, various image reconstruction algorithms can be adopted.

(Effects of the Invention) As described in detail above, according to the present invention, it is possible to realize a high-resolution and high-quality apparatus with high exposure speed, short scan time, and low exposure dose. In addition to being able to reduce the pain and burden on the patient and also reduce the effects of body movements, the practical effects are extremely large.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of the principle of the present invention, FIG. 2 is an arrangement diagram of irradiation positions according to the present invention, FIG. 3 is an explanatory diagram of calculation of β ′ and β ″, and FIG. 4 is an enlarged explanatory diagram of interpolation conditions. 5, FIG. 5 is an irradiation view by a mounted X-ray source, FIG. 6 is a view showing a CT scanner of one embodiment of the present invention, FIG. 7 is a view of irradiation positions by another embodiment of the present invention, and FIG. Fig. 9 is a diagram of the gantry part, and Fig. 9 is a spatial layout diagram of the scan data acquisition part in the ordinary offset detection method: 1 ... Reconstruction area, 2 ... Detector 3 ... X-ray source, 11 ... ... Table 12 ... Subject, 13,13 '... Gantry 14 ... Table / Gantry control device 15 ... High-pressure X-ray tube control unit 16 ... X-ray generation control device 17 ... Operation imaging control device 18 ... data acquisition device 19 ...... data processing apparatus L A _...... detector arranged circumferentially L _B ...... X-ray source rotates circumferentially

Claims (2)

[Claims] 1. A radiation source which emits fan-shaped radiation,
A detector group having a plurality of detectors arranged to face the radiation source through an image reconstruction region that houses a subject, and the radiation source rotates around the image reconstruction region while irradiating with radiation. A CT including view data acquisition means for acquiring view data by detecting the radiation emitted in each direction of space by the detector group, and image reconstruction means for performing image reconstruction based on the view data. In the scanner, the radiation source is rotated around the image reconstruction area to form a spatially continuous full view, the full view having two or more spatially continuous non-overlapping views. The view data acquisition unit is composed of a plurality of groups of views and facing views corresponding to the respective views, and the view data acquisition unit is adjacent to or adjacent to each of the groups. A CT scanner, characterized in that two or more views at a position and a radiation path of a counter view corresponding to each view interpolate at equal intervals in at least a central portion of the image reconstruction area to obtain view data. 2. The detector group is arranged at an equal angle on a circumference centered on the image reconstruction area, and the view data acquisition means includes the following (a) or (b):
The CT scanner according to claim 1, wherein view data corresponding to all views formed according to the above is acquired. (I) (B) However, in equations (a) and (b), M is the view number that starts at 1 and increases by 1; 2N is the maximum view number when the radiation source is rotated 360 °; β ″ is ) And (d), β ′ is an angle represented by the following formulas (e) and (f), Δθ is a predetermined angle, θ ₀ is an angle at the start of scanning, β ″, β ′ and Δθ satisfy the condition that they are not the same view with different view numbers. (C) β ″ = sin ⁻¹ [{(L-) /} sin δ ″] + δ ″ (d) δ ″ = · Δγ / [8 (L-)] (e) β ′ = sin ⁻¹ [{( L-) /} sinδ ′] + δ ′ (f) δ ′ = 3 · Δγ / [8 (L-)] However, L in the formulas (c), (d), (e) and (f) is The distance from the radiation source to the detector that passes through the center of the image reconstruction area, is the distance from the radiation source to the center of the image reconstruction area, and Δγ is between the adjacent detectors in the center of the image reconstruction area as seen by the radiation source. Represents the angle formed by.