JPH05212022A - X-ray ct system - Google Patents

Abstract

PURPOSE:To facilitate the position management of helical data and the specification of helical data for obtaining CT images by separately synchronously storing position data together with helical data when speed is fluctuated or variable speed control is executed in helical scan. CONSTITUTION:This X-ray CT system executes helical scan by continuously moving a bed 3 forward or backward and continuously rotating an X-ray source 1 and an X-ray detector 2 and obtains CT images from the obtained helical data. In this case, a two-dimensional buffer 11 is provided to store X-ray source position data beta and bed position data X detected by a scanner position detector 5 and a bed position detector 6 according to an address (i, j) decided by a measuring cycle number (j) and a projective number (projective angle number) (i). On the other hand, the helical data are specified by providing a two-dimensional buffer 12 to store X-ray detecting signals (helical data) obtained by a data collection circuit 2A similarly according to the address (i, j).

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a helical scanning type X-ray CT apparatus having an X-ray source and bed position control function.

[0002]

2. Description of the Related Art Conventional examples of CT devices for helical scanning include Japanese Patent Laid-Open Nos. 59-111738 and 62-87137. Japanese Patent Laid-Open No. 59-111738 discloses an example in which a CT image is obtained by spiral scanning. JP-A-62-87137
The publication discloses an example of interpolation according to distance distribution in order to obtain projection data for CT image calculation by helical scanning.

[0003]

[Problems to be Solved by the Invention] Japanese Patent Application Laid-Open No. 59-1117
No. 38 discloses various techniques for obtaining a CT image by helical scanning, but does not describe the concept of position management of the X-ray source and the bed. Japanese Patent Laid-Open No. 62-87137 is practical in that it describes an example of interpolation on a vertical tomographic plane (slice plane), but does not describe the concept of position control of the X-ray source and bed.

Especially, in the helical scan, if the rotational speed of the X-ray source and the moving speed of the bed are both constant, it is easy to manage their positions. However, there are cases where it is necessary to make the speed variable and there is a case where the speed fluctuates. The former is
Typically, the velocity is made variable depending on the slice position, and the region of interest is moved slowly and the other regions are moved roughly. In the latter case, there is a case where the speed control of the X-ray source or the bed is not sufficient and the constant speed cannot be executed, or the bed moving speed varies depending on the weight difference.

When there is such a speed fluctuation, it is necessary to properly manage the position of the X-ray source and the position of the bed.

An object of the present invention is to provide an X-ray CT apparatus which manages the position of the X-ray source and the bed position in the spiral scan and facilitates the specification of the spiral data for obtaining the CT image. It is in.

[0007]

According to the X-ray CT apparatus of the present invention, an X-ray detector detects an object according to an address (i, j) defined by a helical scanning measurement cycle number j and an X-ray source projection angle number i. Then, the first buffer memory for storing the rotation data and the actual X-ray source position and bed position at the time of obtaining the rotation data are fetched as data, and the same address (i, j)) for storing a second buffer memory (claim 1).

Further, the X-ray CT apparatus of the present invention stores the rotation data when it is detected by the X-ray detector according to the address (i, j) determined by the spiral scanning measurement cycle number j and the X-ray source projection angle number i. The first buffer memory and the actual X-ray source position and bed position at the time of obtaining the spiral data are fetched as data, and the same address (i,
j)) a second buffer memory for storing, and an X-ray source position and bed position data in the second buffer memory.
An address for an arbitrary slice position according to the data, and means for creating projection data at the slice position from the rotation data when read out from the first buffer memory according to this address; And a means for creating an image at an arbitrary slice position (claim 2).

Further, in the CT apparatus of the present invention, the address for the arbitrary slice position is used for the interpolation when the projection data for the arbitrary projection angle at the slice position is created by interpolation. It is used as an address for rotation data (claim 3).

[0010]

According to the present invention, in addition to the first buffer memory for storing the spiral data, the second buffer memory for storing the position data (X-ray source position, bed position) having the same address is stored. Since the buffer memory is provided, the position management of the spiral data can be realized by the contents of the second buffer memory (claim 1).

Further, according to the present invention, the helical data for interpolation can be extracted according to the speed fluctuation by the position data of the second buffer memory (claims 2 and 3).

[0012]

1 is a diagram showing an embodiment of an X-ray CT apparatus according to the present invention. The scanner body 100 includes a rotating X-ray source 1,
A multi-channel type X-ray detector 2 which rotates in opposition to the X-ray source, a gantry opening 4 having a measurement space, a bed 3 for loading and unloading the subject 32 into and out of the gantry opening 4.
It comprises a scanner position detector 5 and a bed position detector 6.
In addition to this, a rotation mechanism and various control mechanisms are provided, but they are omitted.

In this embodiment, the X-ray source 1 and the X-ray detector 2 continuously rotate, while the bed 3 continuously moves forward or continuously moves backward. This realizes the spiral scanning. Further, it is assumed that the X-ray source 1 generates X-rays continuously or discontinuously (in pulse form). The X-ray source 1 is assumed to generate a fan-shaped X-ray beam, and its slice width (width of the X-ray beam in the direction orthogonal to the spreading direction of the fan-shaped X-ray beam) is a negligibly small value. There are two examples, that is, a certain finite predetermined value set for body movement correction. In this embodiment, both can be targets.

The scanner position detector 5 detects the rotational position β of the X-ray source, and the rotational position β is the angle at which the X-ray source exists (the angle viewed from the center point). There are the following two detection timings. (1), the method of detecting at a constant time period, (2), the method of detecting at every constant rotation distance, and the method of (1) have an advantage that the timing of angle detection is easily set, and the rotation is detected when the speed changes. It is characterized in that the position changes according to its speed. The method (2) is characterized in that the position can be detected without being affected by the speed.

The bed position detector 6 detects the position X of the bed irradiated with the fan beam from the X-ray source. The detection timing is the same as the scanner position detector 5 in two ways. is there.

The scanner position detector 5 and the bed position detector 6 may actually exist, but if the scanner rotation control unit and the bed movement control unit respectively perform position management, they can be detected from the inside. It is also possible to replace the detector with the above data.

In FIG. 1, the data processing unit 200 includes a data collection circuit 2A, two-dimensional buffers 11 and 12, a projection data forming circuit 13, a filter correction circuit 14, and a back projection calculation circuit 1.
5 and the CT image display unit 16.

The two-dimensional buffer 11 addresses the X-ray source position data β and the bed position X detected by the detectors 5 and 6 determined by the measurement cycle number j and the projection number (projection angle number) i ( Store according to i, j). Here, the measurement cycle number j
Is the number of the period during which the X-ray source 1 rotates once.
The projection number i refers to the X-ray exposure position of the X-ray source or the X-ray source position corresponding to the measurement position of the X-ray detector. When the X-ray intermittent exposure method is adopted (pulse control), the X-ray exposure position of the X-ray source coincides with the X-ray source position corresponding to the measurement position of the X-ray detector. When the X-ray continuous exposure method is adopted, the projection number i is not the X-ray exposure position but the X-ray source position corresponding to the measurement position of the X-ray detector.

When the movement amount of the bed during one rotation (360 °) of the X-ray source is d, the total movement amount up to the measurement cycle number j is d × j.

The two-dimensional buffer 12 is a data collection circuit 2
This is a memory for storing the X-ray detection signal (data-converted) obtained in A according to the address (i, j) determined by the measurement cycle number j and the projection number i like the buffer 11. Here, the X-ray detection signal (data) means the data obtained by the helical scan, and this is displayed as the helical data SR. The spiral data SR has one address (i, j).
It goes without saying that there are as many channels as there are.

The projection data forming circuit 13 produces CT calculation projection data from the rotation data SR when it is stored in the two-dimensional buffer 12. To reconstruct one CT image,
Basically, data for 360 ° is required for one slice plane. Since the spiral data SR cannot be essentially the data of one slice plane, the spiral data SR is processed in some way to be processed into the data on one slice plane. Things are needed. The projection data forming circuit 13 is provided to achieve this purpose. However, the address (i, j) itself of the buffer 12 is not directly suitable for forming projection data on the slice plane, and the buffer 11
It is necessary to obtain the data for slicing by utilizing the position data inside. Therefore, the buffer 11 of FIG.
A route to 3 is needed. The buffer 11 is used to determine the read address for the two-dimensional buffer 12 and to determine the interpolation coefficient (described later).

The filter correction circuit 14 is a so-called spatial filter for removing image blur.
It is publicly known. The back projection calculation circuit 15 performs reconstruction calculation on the projection data that has been subjected to the blur removal processing to obtain CT image data. This is displayed as a CT image on the display unit 16 or is stored and stored in various memories. Figure 2
FIG. 6 is a diagram showing a locus of a spiral scan. It can be seen that the X-ray scanning according to the spiral scanning locus is performed on the subject 32 by the rotation of the X-ray source 1 and the advance of the bed 3. By this spiral scan, the spiral data SR is obtained when the object 32 is aligned in the axial direction.

FIG. 3 shows an example of the scanning range of the head of the subject 32, in which the subject 32 is advanced in the direction of the arrow to
An example of capturing an image of the section −B ′ is shown. In this case, A
The −B section is a shooting start-up section, and B′−A ′ is a fall section at the end of shooting, which is included in the scanning range (A′−A) but excluded from the shooting area. The reason for the exclusion is due to the unstable control region of speed rising and speed falling. FIG. 4 shows a sequence in the example of FIG. In the section BB ′, the speed is constant (both the scanner and the bed are constant speed), X-ray irradiation is performed in this section, and the sections AB,
It is shown that X-ray irradiation is not performed in B'-A because the velocity is not constant. Although FIGS. 3 and 4 show examples of the head, it goes without saying that the position of the imaging region and the size of the width of the chest and abdomen can be set freely. Furthermore,
Where is the slice plane obtained from this set shooting area,
It is possible to freely set how many cards are taken. In addition, a and b are the section distances of A'-B 'and B-A, B'-B, respectively.

FIG. 5 is a diagram showing a control mechanism of the CT apparatus of FIG. The high-voltage generator 110 generates a prescribed high-voltage under the instruction of the X-ray controller 101, and supplies the X-ray irradiation voltage from the X-ray source 1. The X-ray control unit 10 gives instructions on the timing of X-ray generation (including both continuous and intermittent) and the magnitude of the generated voltage. Rotation mechanism 111
Is a mechanism for rotating the X-ray source 1 and the X-ray detector 2 of the scanner, and is driven by an instruction from the rotation mechanism control unit 102.
If the rotation is constant speed, the constant speed is instructed. The bed moving mechanism 112 moves the bed 3 forward (or backward) and receives an instruction from the bed moving mechanism control unit 103. The moving direction and speed pattern are given as instructions. Bed position detector 113, rotation position detector 114
Is for managing the projection number i and the measurement cycle number j, and corresponds to the detectors 6 and 5 in FIG.

The system control unit 120 manages and controls the entire system, and has a function of synchronizing the entire system in this control. However, the synchronization means a function used for recognizing the timing of the entire system and managing them in an integrated manner.

A method of determining the address (i, j) used in the buffers 11 and 12 will be described with reference to FIGS. 6 and 7. FIG. 6A is a diagram showing an example of addresses and data arrangement of the two-dimensional buffer 12, and FIG. 6B is a diagram showing an example of addresses and data arrangement of the two-dimensional buffer 11. The data stored in the buffer 11 is the X-ray source position β (i, j) and the bed position X (i, j), and the data stored in the buffer 12 is the spiral data SR (i, j). is there. Where (i,
j) means the address (i, j) of the data to be stored. Data SR (i, j), β (i, j), X (i,
With (j), the same address (i, j) is given and writing is performed almost simultaneously (synchronously). Therefore, specifically, a single write address generating mechanism is provided, and this write address generating mechanism is (1, 1) → (2, 1) →
(3, 1) → ... (pp, 1) → (2, 1), (2, 2)
→ ... (pp, 2) → (3, 1) → ... Sequential address generation is performed, and for each address (i, j),
It is preferable to write SR, X, β obtained at that time to the address (i, j). Of course, buffer 1
It is the same if separate write address generating mechanisms are provided for 1 and 12, and the generated address is synchronized with both its content and timing. Incidentally, pp refers to the final projection angle number of each measurement cycle (360 °). Further, jc in FIG. 7 refers to the final measurement cycle number.

FIG. 7 is a diagram showing the timing of data transfer into the buffers 11 and 12. In the spiral scan, since the measurement is continuously performed, there is no break in the spiral data during the measurement period. Here, the measurement means an operation of taking the transmitted X-ray detected by the X-ray detector into the data collection circuit 2A (FIG. 1). However, in reality, the X-ray generation time point, the transmission X-ray detection time point by the X-ray detector, and the measurement time point are so small as to be negligible in terms of time, and therefore, they are often measured in a broad sense in combination. As the measurement timing, the measurement trigger signal T is sent to the X-ray data acquisition circuit 2A at a constant cycle in synchronization with the rotation of the scanner frame and the movement of the bed, and this signal causes each channel from the detector 2 to operate.
Minute signal is converted into digital signal sequentially and spiral data SR
Is stored in the two-dimensional buffer 12. In addition, the position information at the same time from the scanner and the bed can be used as position information 2
It is stored in the dimension buffer 11. Therefore, as described above, both data are managed by the same address.

Here, the measurement timing is also the generation timing of the address (i, j). As described above, the measurement timing is performed by the measurement trigger signal T which is generated in a constant cycle in synchronization with the rotation of the scanner frame and the movement of the bed, but this synchronization has the following modes.

(1) The case where only the measurement start point is synchronized with the scanner frame rotation and the bed movement. In this case, after the measurement start point, the measurement trigger signal T is generated at a constant cycle, and the rotation and the movement are not recognized at all.

(2) The movements of the scanner frame rotation and the bed movement are grasped in synchronization with the measurement start point, and the movements of the scanner frame and the bed movement are grasped in the subsequent measurement period, and the movements are synchronized with the grasp (that is, in terms of timing). Is a case where the measurement trigger signal T is generated (in synchronization). In this case, the measurement trigger signal T is generated one after another in synchronization with either the measurement timing in the narrow sense or the measurement timing in the broad sense.

(3) The measurement trigger signal T
Is convenient when the scanner frame rotation speed and the bed movement speed are constant speeds. In this case,
The buffer 11 is used to grasp the speed fluctuation amount under the constant speed. In the case of variable speed control, in a constant cycle, the unit rotation or the unit movement distance varies depending on the speed, so that it becomes impossible to measure at a constant pitch. Therefore, in the case of variable speed control, it is desirable to generate the measurement trigger signal T at every constant distance when it is desired to perform measurement in constant pitch units. However, when it is desired to scan the region of interest slowly, the region outside the region of interest undergoes rapid rotation and movement. In this case, the measurement trigger signal T may be generated at a constant cycle.

The common address (i, j) for the buffers 11 and 12 is generated in synchronization with the above measurement trigger signal T. In this embodiment, the measurement trigger signal generator 20 in FIG.
The measurement trigger signal T is generated according to the above timing. As shown in FIG. 7, a total of pp measurement trigger signals T of 1 to pp are generated in one measurement period (360 ° minutes). 1
~ Pp is a projection angle number, and therefore, it may be considered that the measurement trigger signal T is generated for each projection angle number.
In one measurement trigger signal T, as shown in the measurement trigger signal “1”, the spiral data SR for n channels, the bed position X, and the X-ray source position β are fetched, and the buffers 11, 1
Store in 2. Here, the bed position X has almost no position change in all n channels with respect to one measurement trigger signal T, and may be regarded as the same value in all channels. The X-ray source position β may be regarded as a value at the same rotation position in all n channels when viewed from the X-ray source position. From the viewpoint of the channel position of the X-ray detector, the value of the X-ray detector channel position is determined depending on the position of each channel.

Now, in FIG. 8, the measurement trigger signal T is sent to the address generator 21, and the write address (i,
j) is generated (updated). In this update, i is updated to j + 1 every time one measurement trigger signal T is input. Therefore, the address (i, j) is (1,1) → (2,1) →
(3, 1) → ... → (pp, 1) → (2, 1) → (2,
2) → ... → (pp, 2) → ... On the other hand, the measurement trigger signal T is sent to the data collection circuit 2A, and the detection value of the X-ray detector 2 at that time is sent to the data collection circuit 2A.
It is taken into A and the spiral data SR is obtained. The spiral data SR and β and X at that time are written to the address (i, j).

Thus, the buffer memories 11 and 12 successively store SR, β, and X obtained at the time of occurrence of the address (i, j) according to the common address (i, j).

On the other hand, the reading of the buffer memories 11 and 12 is performed according to the address designated by the address generator 22, and is sent to the projection data forming circuit 13 to project the projection data.
It is used for forming the data.

The projection data forming circuit 13 has various projection data forming methods. A typical one is the interpolation method disclosed in Japanese Patent Laid-Open No. 62-87137 described in the conventional example. An example of this is shown in FIG. The horizontal axis represents the subject position X, the vertical axis represents the X-ray source position β, and the loci represented by sine waves are the loci of the X-ray source at a constant speed for the bed and the X-ray source, respectively. Now any position X
when the _n and slice position, in order to obtain a CT image at the slice position X _n is the projection data of 360 ° min at this position X _n - data is required. However, as can be seen from FIG. 9, at the position X _n , there is only one intersection with the locus, and 3
There is no projection data for 60 °. Therefore, the position X _n
360 degree by interpolation method by catching the spiral data before and after
Minute projection data is created.

FIG. 9 shows an example of obtaining the projection data R _n at the projection angle β ₁ . Attention is paid to two points X _e and X _m at the same phase angle on the sine wave function at this projection angle β ₁ , and the helix data SR _e and SR _m at these two points are distributed from the slice position. The interpolated value R _n is obtained by This formula becomes the following formula.

R _n = (SR _l × a + SR m × b) / (a + b) (1) Here, a = X _m −X _n and b = X _n −X _l . Similarly, all the projection data for 360 ° is converted to spiral data S before and after the slice position on the same projection angle and at the same phase angle.
It is obtained by interpolation using R.

In this projection data forming method, it is necessary to recognize that they are on the same projection angle and at the same phase angle before and after the slice position. This recognition is in buffer 1
It becomes possible by the addresses 1 and 12 and the position data X and β of the buffer 11.

Assuming that the scanner rotation speed and the bed movement speed are fixed at constant speeds, the addresses and data X and β in this buffer are uniformly positioned by the number of projections in one scan and the bed movement amount in one scan. The relationship can be determined. Specifically, assuming that the number of projections in one rotation of the scanner is pp, the parameter projection angle of the spiral data SR and the bed position are obtained by the arguments i and j of this two-dimensional array as follows. Projection angle β (i, j) = βo + (i−1) × Δθ (2) Position X (i, j) = Xo + (j−1) × d + (i−1) × Δ ... (3) According to the following definitions. Δθ = 360 ° / pp (4) Δd = d / pp (5) Therefore, the bed position X (i, j) is given, and the helix data of the projection angle β (i, j) at the bed position is given. SR (i,
When j) is read out, i is obtained from the equation (2),
This j is obtained by introducing this i into the equation (3). Thus, if the buffer memory 12 is accessed using (i, j) obtained from the equations (2) and (3) as an address, the bed position X
(I, j), projection data β (i, j) spiral data SR
(I, j) can be read.

To create one projection data, (1)
As shown in the interpolation formula of the equation, two spiral data having the same projection angle and the same phase before and after the slice position are required. The two spiral data may be read out by indicating two bed positions (such as X _e and X _{m in} FIG. 9) having the same projection angle β (i, j) and the same phase angle. Based on this idea, projection data for 360 ° is formed. Then, if data reconstruction is performed using the projection data for 360 °, CT tomographic data can be obtained and a CT image can be obtained.

An example of projection data formation by the above interpolation is shown in FIG.
It shows in 0. In FIG. 10, two points M and N having the same projection angle and the same phase are interpolated in two sections of the cycle numbers j = j _m and j = j _n, and the projection angle of the slice position X _{n and} the projection of this phase are obtained. An example of arrangement as data D is shown. The interpolation formula is (1)
It is an expression. However, when the bed movement speed and the scanner rotation speed are varied, the actual bed position and scanner position and the address of the buffer memory 12 are (2) and (3).
There is no correspondence like expressions. Therefore, position information 2
The data X and β in the dimension buffer 11 are used to set the address of the buffer memory 11 according to the speed fluctuation. An example of this setting will be described with reference to FIGS.

FIG. 11 shows an example of the bed moving speed pattern. This velocity pattern linearly rises for a certain period from the start, reaches a certain velocity, enters a constant velocity (velocity V _c ), and finally linearly falls and ends. However, speed fluctuations V ₁ and V _{2 as} shown by the dotted line may appear. These variations appear due to the speed control system and the difference in body weight of the subject.

FIG. 12 shows the locus of the bed position (shown on the horizontal time axis) and the X-ray source height (projection angle) (vertical axis) with and without the velocity fluctuation as shown in FIG. An alternate long and short dash line is an example in which there is no speed fluctuation, and a dotted line is an example in which there is a speed fluctuation. At the starting point, the positions of both coincide with X ₁ = X ₁ ′, but the position after 360 ° becomes X ₂ ≠ X ₂ ′ due to the appearance of the speed fluctuation V ₁ , and they do not coincide. Inconsistency also appears in the next speed fluctuation V ₂ .

In order to obtain the projection data at the slice position X _n in FIG. 12 in such a speed variation, when the projection angle at this time is β ₀ (for example, 0 ° ≦ β ₀ ≦ 180 °),
If there is no speed fluctuation, the projection data of q point can be obtained from the two points of P ₁ and P ₃ by interpolation, but if there is a speed fluctuation, the p ₁ point becomes the p ₂ point, and the p ₂ point and the p ₃ point It is necessary to obtain projection data of q points from two points by interpolation.

The points p ₂ and p ₃ can be obtained from the two-dimensional buffer 11 by giving the slice position X _n and the projection angle β ₀ . Then, this two-dimensional buffer 11
Than p ₂ points equivalent i, j, p ₃ points equivalent i, j in the accesses to the buffer 12, obtains the p ₂ points corresponding Nora旋data and p ₃ points corresponding Nora旋data. Furthermore, the interpolation coefficient a,
b is a = (distance between point q and point p ₃ ), b = (point p ₂
From the point q), the bed positions at the points p ₂ and p ₃ can be obtained from the buffer 11 and the difference from X _n can be obtained. The projection data are a, b and p ₁ , p ₂
It is calculated by the formula (1) using the spiral data at the points.

The above is an example of 0 ° ≦ β ≦ 180 °,
Also for 180 ° ≦ β ≦ 360 °, it is possible to calculate the projection data based on the correct interpolation relationship using the buffer 11.

As described above, when the bed moving speed and the scanner rotating speed are varied, an error occurs between the true position and the address of the buffer memory 12, so that the position information 2
By referring to the position data of the dimension buffer 11, data interpolation is performed with the value of the spiral data SR at the position at the same projection angle in the scanner position data X and β, and the interpolation coefficients a and b are obtained by the bed position information at the same address. The projection data without any position error can be calculated by obtaining

Actually, it takes much time to refer to the position information in all projection data. Therefore, the number of measurements is reduced like the position information at a fixed position of a certain specific period, for example, the projection angle 0 °, and the position information at the time point synchronized with the measurement trigger in the example of FIG. Create projection data by minimizing the increase in time and reducing position error, for example, by assuming that the calculation is constant, or by referring to the position information data only at the part of the scan cycle where the speed change exceeds a certain threshold. It is possible to

In the above embodiment, the bed moving speed has a constant pattern, and the speed fluctuation is unavoidable. However, even if the speed pattern is intentionally set to a variable speed pattern, the true position and its helical data and projection data can be obtained.

Further, although the above embodiment is an example in which the bed speed is changed, it can also be applied to an example in which the X-ray source rotation speed is changed.

Further, the projection data is an example in which all 360 ° is obtained by interpolation, but 0 ° to 180 ° is 0 ° to
The present invention can also be applied to a method in which the rotation data is arranged as it is after being obtained at 180 ° and interpolation is performed for 180 ° to 360 °. Further, in order to prevent the occurrence of image artifacts due to the mismatch between the start point and the end point, there are various methods for forcibly matching the start point and the end point to maintain continuity as data. However, the present invention can also be applied to the calculation of projection data in the case where the speed changes by these various methods.

Further, although the data in the buffer 11 is used for position correction, instead of storing it in the buffer 11, if this position correction can be realized at high speed, the address itself of the buffer 12 is allocated with the address after position correction. Then, the spiral data may be stored at this address.

Finally, the present measurement method and arbitrary projection data creation method exhibit effects regardless of the image reconstruction algorithm or the generation of the CT apparatus. As the interpolation method, in addition to linear interpolation, 2
Higher-order interpolation such as third-order and third-order is also possible.

According to the embodiment, the moving speed of the bed shown in FIG. 10 fluctuates as shown by the dotted curve, and this is included in the actual photographing area. As shown in FIG. Even if fluctuations occur, optimal interpolation processing can be performed based on the bed and scanner rotation position information, so that a good image with accurate positional relationship and no artifacts due to positional deviation can be obtained. Scanning can be continuously completed by changing the imaging conditions according to the imaging region, such as decreasing the bed moving speed in the chest to increase the resolution and increasing the bed moving amount in the abdomen.

Further, in the past, when the subject having a heavy weight or the bed moving speed was increased, the moving speed fluctuation became large, and the accuracy of the bed mechanism portion was improved, and the control method was complicated, but it is unnecessary by the present invention. Therefore, the cost of the system can be reduced. Moreover, since the bed moving speed can be increased by conversely, there is an advantage that the examination time of the patient can be further shortened.

[0057]

According to the present invention, under helical scanning,
When there is a speed change or variable speed control is performed, the spiral data SR is stored and the position data (bed position, X position) is stored.
Position of radiation source) Since the data are separately synchronized and stored, the position of the spiral data can be easily managed. (Claim 1).

Further, according to the present invention, when the projection data is obtained from the helix data when the speed fluctuation or the variable speed control is performed, the projection data can be calculated by the correct interpolation according to the actual position data. .. (Claims 2 and 3).

[Brief description of drawings]

FIG. 1 is a diagram showing an embodiment of an X-ray CT apparatus of the present invention.

FIG. 2 is a diagram showing a spiral scanning locus of the present invention.

FIG. 3 is a diagram showing a scanning range and a photographing region in the spiral scanning of the present invention.

FIG. 4 is a diagram showing the timing of the scanner, bed, and X-ray exposure of the present invention.

FIG. 5 is a diagram showing an example of control coefficients of the CT device of the present invention.

FIG. 6 is a diagram showing addresses and data of two-dimensional buffers 11 and 12 according to the present invention.

FIG. 7 is a diagram showing measurement timing according to the present invention.

FIG. 8 is an embodiment diagram for accessing the buffer memories 11 and 12 of the present invention.

FIG. 9 is an explanatory diagram when the projection data of the present invention is obtained by interpolation.

FIG. 10 is another explanatory diagram when the projection data of the present invention is obtained by interpolation.

FIG. 11 is a diagram showing an example of bed speed patterns and an example of speed fluctuations according to the present invention.

FIG. 12 is a diagram showing an example of calculating spiral data for speed fluctuations according to the present invention.

[Explanation of symbols]

 100 Scanner Main Unit 200 Data Processing Unit 5 Scanner Rotation Position (X-ray Source Position) Detector 6 Bed Position Detector 11 Position Information Two-dimensional Buffer 12 Rotation Data Two-dimensional Buffer 13 Projection Data Forming Circuit

Claims (3)

[Claims] 1. An X-ray source is rotated to move a bed on which a subject is mounted to perform a helical scan, and C is determined from the helical data.
In an X-ray CT apparatus for obtaining a T image, an address (i, i, which is determined by a helical scanning measurement cycle number j and an X-ray source projection angle number i)
According to j), the first buffer memory for storing the rotation data when detected by the X-ray detector and the actual X-ray source position and bed position at the time of obtaining the rotation data are fetched as data, An X-ray CT apparatus comprising: a second buffer memory for storing data at the same address (i, j) as that for storing spiral data. 2. The X-ray source is rotated while the bed on which the subject is mounted is moved to perform spiral scanning, and C is determined from the spiral data.
In an X-ray CT apparatus for obtaining a T image, an address (i, i, which is determined by a helical scanning measurement cycle number j and an X-ray source projection angle number i)
According to j), the first buffer memory for storing the rotation data when detected by the X-ray detector and the actual X-ray source position and bed position at the time of obtaining the rotation data are fetched as data, A second buffer memory for storing at the same address (i, j) as that for storing the spiral data, and an address for an arbitrary slice position according to the X-ray source position and bed position data in the second buffer memory are obtained. Means for creating projection data at the slice position from the rotation data when read from the first buffer memory according to this address, and means for creating an image at the arbitrary slice position from the projection data And an X-ray CT apparatus comprising the 3. The X-ray CT apparatus according to claim 2, wherein the address for the arbitrary slice position is the address when the projection data for the arbitrary projection angle at the slice position is created by interpolation. An X-ray CT device that uses an address for spiral data used for interpolation.