JP2863153B2 - X-ray CT system - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [0001] BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention performs a spiral scan.
The present invention relates to an X-ray CT apparatus. [0002] 2. Description of the Related Art A helical scan of an X-ray CT apparatus
A conventional example is “Application of digital image processing to medical equipment and
Problems ”(a seminar hosted by the Giken Center
Digital signal processing technology and its problems for clinical application "
Table paper. October 26, 1981. Written by Isao Horiba. II42
-II page 44) (referred to as Conventional Example A), and
-1111738 (referred to as Conventional Example B). Conventional example A
Is a document showing the principle of a spiral scan CT apparatus.
Rotating the source around the subject, along with this rotation
It has the two features of moving the subject in the body axis direction
The principle of the spiral scan is disclosed. Further, Conventional Example A is
Disclosure of reconstructing data collected by spiral scan
I do. Thus, the origin of the spiral scan X-ray CT system
The reason is described. [0003] Conventional example B is the same as conventional example A
An X-ray CT apparatus is disclosed. Further, in Conventional Example B, the spiral
Reconstruction methods and artifacts from data collected in the
Various disclosure methods are disclosed. [0004] The above-mentioned conventional example is an
Helical scanning by moving the patient bed and rotating the X-ray scanner
Although there is a statement to perform a scan, an actual spiral scan is performed.
There is no description of the procedure for this. In particular, perform a spiral scan
When scanning, a slice plane to obtain a tomographic image or scanning
If the range can be specified freely, waste of X-rays to other parts
Irradiation can be avoided and shooting time can be shortened.
And An object of the present invention is to provide reconstruction by spiral scanning.
Spiral scan meter, giving a swivel scan range if necessary
The present invention provides an X-ray CT apparatus that enables measurement. [0006] According to the present invention, a subject is mounted.
The bed to be moved in the body axis direction of the subject, and
An X-ray source that rotates around the subject
Perform a spiral scan, and obtain the
X-ray CT system for reconstructing tomographic images based on acquired data
Obtaining a tomographic image of the subject in the body axis direction.
Means for setting the reconstruction range to be reconstructed, and setting by the setting means.
Based on the determined start position of the reconstruction range side edge,
To reconstruct the tomographic image at the starting position of the side edge of the composition range
Extra measurement sections required and the reconstruction of the patient bed
The acceleration value up to the start point of the range and the position just before it is
Move the patient bed to the position added to the start of the
Patient bed control means for moving
An X-ray CT apparatus is disclosed. According to the present invention, a reconstruction range is set and
Move the patient bed to accommodate this area
Thus, CT measurement is performed. The present invention further provides a bed on which a subject is mounted.
While moving in the body axis direction of the subject,
Helical to the subject by an X-ray source rotating
Perform a scan, and save the data obtained by the scan.
X-ray CT apparatus that performs tomographic image reconstruction based on
Reconstruction range for obtaining a tomographic image of the subject in the body axis direction
Means for setting the frame, and the reconfiguration set by the setting means.
Based on the composition range, at both end positions of the reconstruction range,
Extra measurement sections required to reconstruct each tomographic image
And the starting point of the reconstruction area of the patient bed and the
Acceleration and deceleration to the position were added to the reconstruction range
Patient bed system for moving the patient bed over a range
Control section and the reconstruction area,
Data collection means for collecting data for the range
An X-ray CT apparatus having the following features is disclosed. According to the present invention, the reconstruction range is set and
Patient bed movement and data including extra measurement sections
CT measurement is performed by collecting data. [0010] FIG. 2 is an external view of an RR type CT apparatus.
FIG. An X-ray CT device is an X-ray tube device (X-ray generation device).
1), X-ray detector 2, X-ray tube high voltage generator (illustration
No), consisting of a patient bed 3. X-ray tube device 1 and X-ray inspection
The dispenser 2 was opposed to each other with the subject on the bed 3 interposed therebetween.
In a positional relationship. Under this opposing positional relationship, X-ray
The tube device 1 and the X-ray detector 2 are continuously rotated. Consecutive times
High voltage from the high voltage device to the X-ray tube device 1
Was powered via a slip ring. This rotation speed
At a constant speed as can be seen from the sinusoidal locus of FIG.
is there. The X-ray tube device 1 and the X-ray detector 2 are composed of a frame.
It was installed in one. Slip on the frame (scanner)
Attach a pulling mechanism to supply high voltage. The patient bed 3 is perpendicular to the plane of rotation of the scanner.
Can move at a constant speed in various directions (arrows). Patient bed 3
Movement and X-ray irradiation by the X-ray tube device 1 and the X-ray tube device 1
Are synchronized with each other. Here, synchronization means
As shown in the example of FIG.₁And R_TwoIn the section with
The rotation speed of the scanner and the moving speed of the patient bed are determined respectively.
At a constant speed, and during this time X-rays are
Means being fired. Synchronization of these three parties
Scanning by spiral scan and spiral scan
Measurement becomes possible. Furthermore, constant speed rotation of the X-ray scanner,
In order to achieve constant movement of the patient bed and the patient bed,
Control based on such a predetermined speed pattern is performed. The patient bed and the X-ray tube apparatus 1 are respectively
By moving and rotating at a fixed speed,
There is an advantage that the management of the collected data at the can is easy.
If the movement of the patient bed and the rotation of the X-ray tube device 1
If they are not constant, the coefficients a and b in the interpolation processing described later
Setting is not easy, and two data with the same projection angle can be extracted.
Not easy. Now, the scanner has a fixed rotating surface.
Rotate continuously and at high speed. At this time, the patient bed
3 into the gantry opening 4 at a constant speed as shown in FIG.
The area including the desired tomographic plane F is inserted (ie, as shown in FIG. 3).
Scan range W₀Scan). Here, the scanning range W₀Is for reconstruction
This is a required measurement section (synonymous with the imaging section) and
The plane F is a slice plane obtained from the scanning range.
Yes, various slice planes are set within the width of this tomographic plane F
Is done. Here, the slice plane is a slice plane S (X_n)
Arbitrarily selected surface such as
The image will be calculated. In the figure, the scanning range W₀Is B and
B ′ and the desired tomographic plane F is C and
C ′. B is the scanning range W₀Scan open
The start point indicating the start position, B 'is the end point indicating the scan end point position
End point, C is the start point of desired tomographic plane F, C 'is its end point
It is. Further, the section connecting A and A 'is the scanning range W₀Yo
The bed movement section is set wider than
A 'is the movement start point of the bed, and A' is the movement stop point of the patient bed.
You. In the section connecting A and B, the patient bed starts moving.
It is necessary and sufficient time to move at a constant speed.
The section connecting A 'is from constant speed movement to deceleration to stop.
It's time. Thus, the scanning range W₀Now, patient bed
The constant speed of the scan is secured, and the X-ray scan does not rotate at a constant speed.
And this section W₀And, by irradiating X-ray, CT spiral
Perform scan measurement. Scanning range W₀From the starting point B to the desired fault plane
Section to start point C of F and end point of desired tomographic plane F
Scan range W from C '₀The section up to the end point B '
This is a data measurement section used for Such interpolation
By measuring extra data for the desired tomographic plane F
CT tomographic image can be obtained. Prior to such scanning, a position for scanning is set.
Make a placement. For positioning, naturally the desired slice
Define the surface F and scan range W₀It is necessary to determine
Desired tomographic plane F and scanning range W₀Are uniquely determined from each other
It is clear that in practice,
You just need to decide which way you want. Scan range W₀A, B,
The positions of C, A ', B', and C 'are obtained. So, A
Is the bed movement start point, and the scanning range B is the constant speed movement.
W₀And C is the starting point of the desired tomographic plane F,
Let C 'be the end point of the desired tomographic plane F and B' be the scanning range W
₀And A 'is the stop point of the patient bed.
Is positioned. After this, the patient bed is moved from position A.
Start moving. As described above, a desired tomographic plane is used for positioning.
F or the corresponding scanning range W₀Give the desired fault
A distance a from the start point C (position 6) of the plane F
C and A are given so that the position A comes to the separated position. A
And the section between B, that is, the section of the distance (ab) is
This is the interval until the patient and the patient bed reach a constant speed. Further, B
The section between C and C performs interpolation in the direction in which the patient bed moves.
In the section to be measured extra to obtain projection data using
That was mentioned earlier. The patient's bed is in the final section C '(position
When the device 7) reaches the plane B ', which is a distance b away, the X-ray exposure
The firing is stopped and the patient bed decelerates and stops at plane A '.
Thus, the scanning range W while scanning the patient bed₀At constant speed
Motion, the scanning range is
W₀During the section of 走, run spirally as shown in FIG.
Will be examined. At this time, the X-ray tube apparatus is unidirectional with respect to the subject.
FIG. 5 shows the trajectory of the scan. The above-described setting of the scanning range and the A,
Setting of B, C, A ', B', C ', and subsequent positions
Control of patient bed using positioning, control of X-ray exposure
Is performed in FIG. 11 described later. The projection data obtained by helical scanning (hereinafter referred to as projection data)
Later, the data will be referred to as spiral data), as shown in FIG.
Is obtained when the scanner is rotated around the subject and scanned.
Is equivalent to the projection data obtained. The spiral data SR has a projection angle β,
It is determined by the position X in the body axis direction. Here at the start of scanning
Position X₀The bed (and the test object) while the scanner makes one revolution
Let D be the distance that the body moves. Subject position X_nIn
Rice surface (fault surface) S (X_n) To reconstruct the tomographic image
Is the projection data R (β, X_n) (However, β = 0 ゜ 36
0 °) is required. Then, from the spiral data SR,
Layer surface S (X_n) Projection data R (β, X_n) By interpolation
And reconstruct an image from the projection data. To obtain a tomographic image, the
Projection data R (β, X_n) (However, β = 0 ゜ 360
I) can be obtained. When the spiral data is represented by the general formula,
Becomes ## EQU1 ## SR = (β_i, X_j) Where the projection angle β_iIs 0 ゜ ≦ β_i≤ 360 °
Position X_jIs X₀≤X_j≤X_eAt any one point to satisfy
is there. X₀Is the scan start position, X_eIs a scanning end position.
Projection angle β_iCorresponds to the X-ray tube height on the vertical axis in FIG. Therefore, in one-way scanning, X_j
= X_nPosition X_nSlice plane S (X_n), Projection
Angle β_iProjection data at ## EQU2 ## R (β_i, X_n) Is X_n1 rotation (± D) before and after (ie, X_n-D
<X_n<X_n+ D section), and
Same projection angle β_iFrom the spiral data, the projection angle R (β_i, X_n)
Is obtained by interpolation. This supplement
The interval is a two-point linear interpolation, for example, a projection angle β shown in FIG.
₁The projection angle β₁Matches X_nBefore and after
X_g, X_mAnd the projection data at that time is SR (β₁,
X_g), SR (β₁, X_m) And X_gAnd X_nDistance with
Separation b is b = X_n-X_g, X_mAnd X_nIs a = X_m−
X_nTherefore, the interpolation equation is (Equation 3). ## EQU3 ## R (β₁, X_n) = ｛SR (β₁, X_g) × a +
SR (β₁, X_m) × b｝ / (a + b) This process is called X_nIs fixed and 0 ゜ ≦ β_i≤360 ゜
360 ° in all directions (all projection angles), the position X
_nIs obtained. An embodiment of an X-ray CT apparatus for one-way scanning
Is shown in FIG. The X-ray CT apparatus is an X-ray generator 1, an X-ray
Detector 2, data collection circuit 2A, buffer memory 12,
Interpolation circuit 13, filter correction circuit 14, back projection operation circuit
15, CRT16. X-ray generator 1 generates a fan-shaped X-ray beam. X-ray detector 2: Multiple detector for detecting transmitted fan-shaped X-ray beam
It consists of a channel detection element. Data collection circuit 2A: detection values of multi-channel detector 2
And perform processing such as preamplifier and A / D conversion.
Obtain projection data SR. Two-dimensional buffer having an address of i × j
It is a buffer. The helical projection data SR is stored. Immediately
The buffer 12 has a projection number i and a scanner rotation number.
The number (the number of rotation) j is determined. Scanner 1
The number of projections in rotation is pp, the total number of rotations of the scanner (what
JC is the parameter of spiral data SR.
The meter uses the two-dimensional array arguments i and j to calculate
Is required. ## EQU4 ## Projection angle β_i= Β₀+ (I−1) × Δθ Position X_ij= X₀+ (J−1) × D + (i−1) × ΔD However, ## EQU5 ## Δθ = 360 ° / pp ΔD = D / pp Becomes Interpolation circuit 13: Position X_nIs specified,
X_nProjection data R (β_i, X_n) By interpolation
create. That is, the spiral projection data SR is converted to the projection data R.
Convert. Filter correction circuit 14 performs blur correction.
The filter function is determined by the details of the blur correction. Back projection operation circuit 15: Filter of filter correction circuit 14
Backproject the output after ringing. This gives us a tomographic image
You. CRT16 ... Displays a tomographic image. The operation will be described. X-ray generator 1 and X-ray detection
The dispenser 2 is continuously rotating on a predetermined plane.
You. In this state, the bed 3 on which the subject is placed is moved forward at a constant speed.
Proceed. In the process of moving forward, the X-ray
The line is exposed. This exposure is made by a spiral scan.
It will be. The transmitted X-ray obtained by helical scanning is
Various data are detected by the X-ray detector 2 and various data are detected by the data collection circuit 2A.
Preprocessing and AD conversion are performed. Thus, spiral data SR
Get. In this spiral data SR, the arguments i and j are
Stored in the two-dimensional buffer 12. Subject measurement range
Similarly, spiral data SR is obtained over the entire area,
The data is stored in the buffer 12. Spiral data is filled in the two-dimensional buffer 12.
After that, the interpolation circuit 13 calculates the desired tomographic plane from the spiral data SR.
Is obtained. That is, the position X_nSpecify desired
The fault plane is specified and the position X_nProjection data R at
(I, X_n) To create. Specifically, (Equation 4), (Equation 4)
As is apparent from 5), the body of the subject in the spiral data SR
The horizontal axis represents the sample position in the axial direction, and the vertical axis represents the projection number i.
Then, the relationship shown in FIG. 6 is obtained. Therefore, the projection data R (i,
X_n) Can be obtained by the following equation. R (i, X_n) = ｛SR (i, m) × a + SR
(I, m + 1) × b｝ / (a + b) Next, the obtained projection data R (i, X_n)
Undergoes blur correction processing in the filter correction circuit 14. Bob
The projection data after the correction processing is back-projected by the back-projection arithmetic circuit 15.
Shadow processing, position X_nObtain a tomographic image at. CRT1
6 displays a tomographic image. Both reciprocating in place of the above unidirectional scanning
Scan, and obtain a reconstructed image by interpolation.
An embodiment of the present invention to be performed will be described. Patient bed on one hand
It moves not only in the direction but also in the opposite direction.
Scan until At this time, the track of the forward movement (forward direction)
The trace 9 and the trajectory 8 of the backward movement (reverse direction) intersect
When scanning is performed, the subject is scanned as shown in FIG.
You. FIGS. 7A and 7B show a case where only one tomographic image is obtained.
A more detailed description will be given. FIG. 7A shows the scanner rotation speed 16 and the patient.
Time relationship between bed moving speed 17 and X-ray pulse 18
-This is shown in the chart. 7 (b), one sheet
180 ° (or less) to obtain a tomographic image of
Scan 9 above is performed in the forward direction, and the scanner
Move patient bed and X-ray exposure until it rotates 180 °
After resting and 180 ° out of phase (
Therefore, the trajectory in the forward direction and the trajectory in the reverse direction intersect),
Perform a scan 8 of 180 ° (or more) in the direction
And the trajectory 9 of the X-ray tube apparatus with respect to the subject is shown in FIG.
As shown. However, the broken line indicates the movement of the patient bed.
Stops exposure and indicates that only the scanner is rotating.
You. When scanning is performed in this manner, the projection data
Projection data when the bed is moving in the forward direction,
By interpolation with the projection data when moving in the direction
Confuse. In one-way scanning, interpolation is performed on any slice plane.
Error due to the same conditions, but in the bidirectional scan
The plane that includes the intersection and is perpendicular to the bed moving direction is the most interpolated
Error due to Therefore, the scanning shown in FIG.
Is performed, the tomographic plane 19 is obtained. In FIG. 8, (a) is from above, (b)
Is the projection of the trajectory from the side. Fault in Fig. 7 (b)
Surface 19 corresponds to surface S in FIG. Obtain tomographic image of surface S
, The projection data on the plane S may be obtained. Therefore,
Consider projection data P1 and P2 having the same projection angle β. P
Reference numeral 1 denotes forward data, and P2 denotes projection data at the time of backward movement.
The projection data P on the surface S is obtained from P1 and P2.
If linear interpolation is used for the projection data P (i, j), P (i, j) = (P1 (i, j) + P2 (i, j
j)) / 2 i = 1, 2,... CN CN: total number of channels j = 1, 2,... NP NP: total number of views Is obtained. This processing is performed for 0 ≦ β ≦ 180 °
Then, the projection data of the first half scan is obtained. 1 obtained
One tomographic image is obtained from the projection data for 80 °, and this
If the data is blur-corrected and back-projected, the desired tomographic image can be obtained.
You. FIG. 9 shows the bidirectional scan of FIG.
The corresponding diagram is shown. Sampling of the spiral data in the body axis direction of the subject
The horizontal axis represents the image position and the vertical axis represents the projection number. FIG. 6 and
Compare. In FIG. 6, the slice position X_nAgainst both sides
Two trajectories L₁And L_TwoTo obtain a reconstructed image. In FIG.
Is the trajectory L on both sides_ThreeAnd L_FourTo obtain a reconstructed image. L
₁And L_TwoIs the position X_nCompletely separated on both sides of the
Is also large in the body axis direction. That is, to obtain a reconstructed image,
It is necessary to obtain from the position in the body axis direction with a large width by interpolation.
You. On the other hand, in FIG._ThreeAnd L4 is X_nCross in
Then L_ThreeAnd L_FourAnd the width in the body axis direction is also small. That is,
Position X_nCan be reconstructed with data closer to
You. As a result, the reliability of the reconstructed image increases. In the above embodiment, the obtained 180 °
One tomographic image was obtained from the shadow data.
To obtain 360 ° projection data and obtain a tomographic image
State. In FIG. 10, projection data for 360 ° is obtained.
In order to achieve this, it is necessary to scan 360 ° in both the forward and reverse directions.
Assuming that the range of the second embodiment is 0 ° to 180 °,
Requires scanning in the range of -90 ° to 280 °. first half
Is obtained in the same manner as in the first embodiment.
In the inspection, Q was similarly obtained from Q1 and Q2 shown in FIG.
And a single tomographic image is reconstructed from the obtained total projection data.
it can. However, in the second embodiment, the latter half scan is performed.
When calculating, the projection data used for interpolation is far
Compared to obtaining the first half of the scan,
It must be considered that the resulting error increases. Only
However, the error is small compared to the one-way scan. FIG. 11 shows a control system diagram of the present invention. X-ray
The control unit 101 controls the high voltage generator 110 to control the high voltage
Is performed. This is so-called X-ray irradiation control. Times
The inversion frame control unit 102 is an X-ray tube device (X-ray generator)
With just the control to continuously rotate the X-ray detector and
And control that takes into account the projection angle is also possible.
Can control. The bed movement control unit 103 controls the bed movement
Direction and speed. However, the speed is constant during scanning.
You. The synchronization device 100 in the system control unit
Position information from bed position detector 113 and projection angle detection
X-ray controller 10 using the projection angle information from
1, rotating frame controller 102, bed movement controller 10
Synchronize 3. More specifically, in each embodiment,
Slice position (Equation 8)_n= X_s+3 (D / 4) + n (D / 2) Here, scanning is performed so that n = 0, 1, 2, 3,...
Start position X_sTo determine. However, D is the bed moving speed.
And the rotation speed of the rotating frame.
You. Also, the position X at the end of the forward scan_e, And the projection angle θ_e
And the start position of the reverse scan is X_e, Start throw
Shadow angle is θ_eControl the system to + 180 °
You. Here, looking at (Equation 8) with respect to reciprocation, FIG.
From the above, it is as follows. With forward sampling points
Intersections with the backward sampling points occur at (D / 2) intervals
You. X_nTo find the point data by interpolation, X_nBefore the point
Later, sample data between (D / 2) is required. X_n
-X_s= (D / 4), X_sTo X_nTo the area de
Data is insufficient (only half) and interpolation data is
Addition, image reconstruction cannot be performed. Therefore, X_n-X_s=
3 (D / 4) and later are valid. here,
X _n-X_s= (D / 4) is X when n = -1_n-X_s=
3 (D / 4) corresponds to n = 0. In the third generation (RR type) CT apparatus
Algorithm for reconstructing tomographic images from projection data
The back projection of the detected fan beam data
Direct method, and parallel beam data
Arrangement method of back projection after converting to data
However, the present invention depends on those algorithms and generations.
For example, if you use a cone beam, you can use
Various applications such as a scanning type can be applied, and the effect is exhibited. Further, as an interpolation method, in addition to linear interpolation, 2
Next-order, third-order, and other higher-order interpolation (for several slices) is also possible. [0042] According to the present invention, the scanning range can be set at any position.
Can be set freely, and in this set scanning range,
Positioning in a spiral scan can be performed, and
Spiral scan measurement can be realized. In addition,
The position of the rice can be set anywhere.
Can be freely generated at any position.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an embodiment of a CT apparatus according to the present invention. FIG. 2 is an external view of an RR type CT apparatus. FIG. 3 is an explanatory diagram of one-way scanning. FIG. 4 is an explanatory diagram of one-way scanning and two-way scanning. FIG. 5 is a diagram illustrating a relationship between a rotational position and spiral data. FIG. 6 is a relationship diagram between a position and a projection number. FIG. 7 is a diagram showing a time chart and a trajectory according to the embodiment of the present invention. FIG. 8 is a diagram showing a trajectory in the embodiment of the present invention. FIG. 9 is a diagram illustrating a relationship between a position and a projection number in bidirectional scanning according to the present invention. FIG. 10 is an explanatory diagram of another embodiment of the present invention. FIG. 11 is a system configuration diagram of the present invention. [Description of Signs] 1 X-ray tube device 2 X-ray detector

Claims (1)

(57) [Claims] A bed on which the subject is mounted is moved in the body axis direction of the subject, and a spiral scan is performed on the subject by an X-ray source rotating around the subject, and data obtained by the scan is obtained. An X-ray CT apparatus for reconstructing a tomographic image on the basis of a reconstructing range for obtaining a tomographic image in the body axis direction of the subject; and a reconstructing range set by the setting means. Based on the start position of the side edge, an extra measurement section necessary for reconstructing a tomographic image at the start position of the reconstruction range side edge and the start point of the reconstruction range of the patient bed and a position immediately before it. An X-ray CT apparatus comprising: a patient bed control unit configured to move the patient bed to a position obtained by adding the acceleration amount to the start position of the reconstruction range. 2. A bed on which the subject is mounted is moved in the body axis direction of the subject, and a spiral scan is performed on the subject by an X-ray source rotating around the subject, and data obtained by the scan is obtained. An X-ray CT apparatus for reconstructing a tomographic image on the basis of a reconstructing range for obtaining a tomographic image in the body axis direction of the subject; and a reconstructing range set by the setting means. Based on the above, extra measurement sections necessary for reconstructing tomographic images at both end positions of the reconstruction range and acceleration and deceleration of the patient bed to the start point of the reconstruction range and a position immediately before the start point of the reconstruction range, respectively. A patient bed control means for moving the patient bed over a range obtained by adding the extra measurement section to the reconstruction range, and data collection for collecting data in a range obtained by adding the extra measurement section to the reconstruction range. X-ray CT apparatus characterized by comprising: a stage, a.