JPH0454456B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field to Which the Invention Pertains] The present invention relates to a computer tomography apparatus used primarily in the field of electronic medical equipment. especially,
The present invention relates to an improvement in a computer tomography apparatus configured to collect fluoroscopic image data using Fan beam radiation or electromagnetic waves and reconstruct a distribution image of the response of radiation or electromagnetic waves regarding a cross-sectional portion of a subject by a back projection method.

[Description of prior art]

Conventional devices have a disadvantage that the shape of the reconstruction area is square or rectangular, and high-speed processing cannot be performed with an arbitrary shape (for example, an ellipse used for the head).

Documents regarding conventional devices include U.S. Patent Publication
4135247 (January 16, 1979)
There is a back projection device for "Processing system".

Furthermore, conventional devices cannot perform high-speed processing unless the large-capacity storage device is replaced with an inexpensive low-speed memory by an expensive high-speed memory.

[Purpose of the invention]

The present invention eliminates the above-mentioned drawbacks and aims to provide an economical computer tomography apparatus that can be flexibly adapted to various applications and that enables high-speed continuous backprojection control.

A further object of the present invention is to provide a computer tomography apparatus that can set a reconstruction region of any shape including an ellipse.

[Key points of the invention]

The present invention generates radiation or electromagnetic waves in the form of a fan beam, transmits the radiation or electromagnetic waves to a cross-sectional area of a subject, and obtains view data as a response to the radiation or electromagnetic waves with respect to the cross-sectional area as a large number of sampling data. a first means for collecting data in a large number of angular directions, and a second method for reconstructing a distribution image of the response regarding the cross-sectional area by a back projection method from a large number of view data obtained by the first means. and a third means for displaying the distribution image obtained by the second means on a screen, wherein the second means moves the reconstruction region from the x-axis and the y-axis. Expressed in xy coordinates, this x axis,
When the reconstruction area is divided into a lattice shape by straight lines parallel to the y-axis, and each intersection of the lattice shape is defined as a pixel constituting the reconstructed image, the x
the total number of pixels on each straight line parallel to the y-axis, the total number of pixels on each straight line parallel to the y-axis, dividing the reconstruction area into two by the straight line parallel to the y-axis, and dividing the first part of the two halves, or the number of pixels on each straight line parallel to the x-axis of the second portion, the number of pixels on each straight line parallel to the x-axis of the second portion; the number of pixels on each straight line parallel to the x axis, the total number of straight lines parallel to the x axis, the total number of straight lines parallel to the y axis; The total number of straight lines parallel to the x-axis of each part, and the total number of straight lines parallel to the y-axis of each part divided into a plurality of parts by one or more straight lines parallel to the y-axis. means for storing part or all of the control parameters regarding the shape of the reconstruction region; means for storing backprojection control parameters at one or more specific points existing inside or outside the reconstruction region; and a calculation means. and
The calculation means is characterized in that it includes means for generating backprojection control parameters for each pixel by sequential calculation from the control parameters regarding the shape of the reconstruction area and the backprojection control parameters of the specific point.

The second method involves repeatedly performing multiplication (weighted data) for each view of each pixel and adding the results for a large number of views, and storing intermediate or final results in a large capacity memory for each pixel. The backprojection integration means is configured to add weighted data for each view for a plurality of views, add the result to the data of the corresponding pixel, and store the result. It may be configured to reduce the number of reads and writes to the memory, ie, accesses of each pixel memory, making the pixel memory a slow access memory.

Further, the back projection integration means includes a cascade-connected multiplier and an adder, and the input circuit of the adder is a buffer circuit that can read and write data to different addresses at the same timing. may be provided.

Note that as a first means, data may be collected by each magnetic resonance absorption phenomenon.

[Principle of the invention]

The principle of back projection related to the present invention will be explained based on FIG. In FIG. 1, X _k is the fan beam X-ray source, and the central area PA is the image reconstruction area. The central area PA is defined by straight lines y=y ₁ , y ₂ ,..., y _2o and x=x ₁ , parallel to the x and y axes.
The image is divided by x ₂ , ..., X _2n , and the image is reconstructed at the intersections of these straight lines, that is, pixel points.
This reconstruction includes back projection. y=y ₁ ,...,
The intervals between the line segments of y _2o are equally spaced Δy, and x
The intervals between the line segments = x ₁ , ..., x _2n are equally spaced Δx, and x _n+1 = 0.5·Δx, yn = 0.5·Δy (where Δx, Δy>0).

The foot of a perpendicular line drawn from an arbitrary point Q(x,y) in the central area PA to the straight line X _k O or its extension is defined as a point Q'. However, point O is the center of the central area PA and the rotation center of the fan beam X-ray source _Xk . Here, QQ′=p,X _k
Let Q' = h, X _k O = L, and let the _length of the straight line connecting point Q (x, y) and X _- ray focus (X-ray source)
Let w, which is the weighting coefficient in back projection, be w=1/
(L ₀ ² ), h=L−x・cosθ _k −y・sinθ _k …(1) p=x・sinθ _k −y・cosθ _k …(2) w=1/(h ² +p ² ) ...(3) α=tan ^-1 (p/h) ...(4) y=y On _j , if x changes by Δx, the changes in p and h are respectively Δp and Δh, then Δp=Δx・sinθ _k …(5) Δh=−Δx・cosθ _k …(6) Also, on x=x _i , if y changes by −Δy, the changes in p and h are Δp′ and Δh′, respectively. , Δp′=Δy・cosθ _k …(7) Δh′=Δy・sinθ _k …(8) Also, y _j =(n−j+0.5)・Δy …(9) However, j=1, 2,… , 2n Also, let l _j be the number of intersections on the left side of the y-axis on the straight line y = y _j , let the coordinates of point R _j be (x _n+1 , y _j ), and let the straight line y = y _j If the upper left end point is S _j , the coordinates of point S _j are ((0.5−l _j )・Δx, (n−j
+0.5)・Δy).

Here, if the values of h and p at point R _j are h ₀ (j) and p ₀ (j), respectively, then the values h ₁ (j) and p ₁ (j) of h and p at point S _j are p ₁ (j)＝p ₀ (j)−l _j・Δp …(10) h ₁ (j)＝h ₀ (j)−l _j・Δh …(11) p ₀ (j+1)＝p ₀ (j) +Δp′ …(12) h ₀ (j+1)=h ₀ (j)+Δh′ …(13) Also, the values of p and h of point Qi(j) on the straight line y=y _j are expressed as p _i (j) and h _i (j), and its right neighbor point Q _i+1 (j)
If the values of p and h are p _i+1 (j) and h _i+1 (j), then p _i+1 (j)=p _i (j)+Δp …(14) h _i+1 (j)= h _i (j) + Δh …(15) Here, p ₀ , h ₀ , ;p ₁ , h ₁ are functions of j and θ _k , and Δp, Δh; Δp′, Δh′ are functions of θ _k Since it is a function, it can be expressed as follows.

Δp≡Δp(k)=Δx・sinθ _k …(5′) Δh≡Δh(k)=−Δx・conθ _k …(6′) Δp′≡Δp(k)′=Δy・cosθ _k …(7′ ) Δh′≡Δh(k)′=Δy・sinθ _k …(8′) p ₁ (j, k)=p ₀ (j, k)−l _j・Δp(k)…(10′) h ₁ ( j, k)=h ₀ (j, k)−l _i・Δh(k)…(11′) p ₀ (j+1, k)=p ₀ (j, k)+Δp(k)′…(12′
) h ₀ (j+1,k)=h ₀ (j,k)+Δh(k)′…(13′
) p(i+1,j,k)=p(i,j,k)+Δp(k)
...(14') h(i+1,j,k)=h(i,j,k)+Δh(k)
…(15′) w(i, j, k) = {(p(i, j, k)) ² + (h(i, j, k)) ² } ^-1 …(3′) CH(i, j, k)=CCH(k)+a・α(i, j,
k) ...(4') Here, CH(i, j, k) indicates the storage address of the back projection data at the pixel point (i, j); θ=θ _k , and CCH(k) indicates the storage address of the back projection data at the pixel point (i, j); θ=θ α= at θ _k
Indicates the central data storage address corresponding to 0.

However, a is a proportionality constant.

Further, the back projection of the point (i, j) is expressed by the following equation.

μ(i,j)=b _Vn 〓 ^k=1 w(i,j,k)×D(CH(i,j,k)) …(16) Here, D(CH(i,j,k) ) is θ=θ _k , data storage address CH(i, j) at point (i, j)
j, k), and b is a proportionality constant.

In this way, p ₀ (1, k), h ₀ (1, k), Δp(k), Δh(k), Δp corresponding to one point R ₁ (m+1,1)
(k)′, Δh(k)′ or those corresponding to the two points R ₁ and R _o+1 , and l _j corresponding to the shape of the image reconstruction area, all points (i, j, k) The backprojection control parameters p(i, j, k) and h(i, j, k) can be obtained using recurrence formulas.

[Explanation based on examples]

Hereinafter, a back projection apparatus according to an embodiment of the present invention will be explained based on the drawings. FIG. 2 is a block configuration diagram showing the configuration of the apparatus of this embodiment.

First, the configuration of this embodiment device will be explained based on FIG. 2. This embodiment device has a first memory group 1
, a second memory group 2, a third memory group 3,
Arithmetic unit 4, first register memory group 5, second register memory group 6, and first table 7
, a second table 8 and a fast access memory 9
, a multiplier 10, a buffer register group 11,
a low-speed access memory 12, a selector 13,
It is composed of an adder 14 and a control device 15.

A first input of the first memory group 1, a first input of the second memory group 2 and a first input of the third memory group 3 are connected to a data line 20, The output of the memory group 1, the output of the second memory group 2, and the output of the third memory group 3 are respectively connected to the first input of the arithmetic device 4, the second input of the arithmetic device 4, and the arithmetic device. 4 and a third input, respectively.

The first output of the arithmetic unit 4 is the first output of the first memory group 1
The second output of the arithmetic unit 4 is connected to the first input of the first register memory group 5, and the third output of the arithmetic unit 4 is connected to the second register memory group 5. connected to the first input of the group 6, the output of the first register memory group 5 is connected to the first input of the first register memory group 5, the first input of the first table 7 and the second table 8 and the output of the second register memory 6 is
It is connected to a first input of the second register memory 6 , a second input of the first table 7 and a second input of the second table 8 .

The first input of the fast access memory 9 is connected to the data line 20, the output of the first table 7 is connected to the second input of the fast access memory 9, and the output of the second table 8 is connected to the data line 20. , multiplier 10
The output of the fast access memory 9 is connected to the first input of the multiplier 10, the output of the multiplier 10 is connected to the buffer register group 1.
The output of buffer register group 11 is connected to the second input of adder 14 .

The output of adder 14 is connected to slow access memory 1
2 and a first input of a selector 13, the output of the slow access memory 12 is connected to a data line 20 and a second input of the selector 13, and the output of the selector 13 is connected to a first input of the adder 13. 14 first inputs.

Control device 15 is connected to control line 25 . The control device 15 and each device 1, 2, 3,..., 1
4 are connected by lines, and control signals, data, etc. are exchanged.

Next, the operation of this embodiment device will be explained based on the drawings. In this explanation, FIGS. 3 and 4 are used in addition to FIG. 1. FIG. 3 is a flowchart showing the operation procedure of backprojection, and FIG. 4 is a timing chart showing the operation timing of this embodiment device. The pixel point ( _i ,
The details and interrelationships of the operations, processing, calculations, and input data and output data of each part in the vicinity of j) are shown. However, this figure shows the case of back projection of 8 views at once.

First, the operation of the block circuit constituting the apparatus of this embodiment will be explained based on FIG.

In the first memory group 1, p ₀ (1,k) and h ₀
The initial value of (1, k) (k = 1, 2, ..., Vm) and its updated value p ₀ (j, k)
and h ₀ (j, k) (where j=1, 2,..., 2n
shall be. ) is stored. In addition, the second memory group 2 stores the values of Δp(k) and Δh(k), Δp(k)' and Δh(k)', or values such as Δx and Δy, sinθ _k and cosθ _k , etc. be done. In addition, in the third memory group 3, the straight line y
= Number _of pixels to the left of the y-axis on y _j (where j =
Let 1, 2, ..., 2n. ), the number m _j of pixels on the straight line y=y _j , the total number N of straight lines y, the total number of views Vm, etc. are stored.

In the arithmetic unit 4, the outputs of the first memory group 1, the second memory group 2, and the third memory group 3 are input, and the above-mentioned equations (10'), (11'), (12') and ( 13
′)
The calculation results are output to the first register memory group 5, the second register memory group 6, and the first memory group 1.

The first register memory 5 and the second register memory 6 have built-in arithmetic units, and the first register memory 5 calculates h ₁ (j, k) and Δh, and
In the second register memory 6, p ₁ (j, k) and Δp are initialized by the arithmetic unit 4, and these set values are used in the first table 7 and the second table 8.
The back projection control parameters p(i+1,j,k), h(i+1,j,
The calculation k) is performed, and the stored contents are updated based on the result.

The first table 7 and the second table 8 have built-in arithmetic units, and in each table, calculations corresponding to the above-mentioned equations (4') and (3') are performed.

The high-speed access memory 9 performs continuous read operations in minimum cycles and write operations in units of initial setting or data blocks of an appropriate number of views. A group of back projection data is stored in the high speed access memory 9, and the back projection data corresponding thereto is read out using the output of the first table 7 as a storage address, and is output to the multiplier 10.

In the slow access memory 12, image data or its intermediate result μ(i,j) is stored.

Reading and writing to this memory is performed in units of an appropriate number of views. Furthermore, reading and writing in continuous backprojection operations can be performed by sequential access. Also, the arrangement of the image data is points (1, 1), (2, 1), on the straight line y ₁ ,
...(m ₁ , 1), point (1, 2) on straight line y ₂ , (2,
2),..., (m ₂ , 2)..., _point (1,
j), (2, j), . . . , (m _j , j), . . . can be selected in this order, making addressing easy.

The multiplier 10 receives the output of the high-speed access memory 9 and the output of the second table 8, performs a multiplication operation on these two inputs, and outputs the result to the buffer register group 11. .

In the selector 13, the low speed access memory 12
The output of the adder 14, the output of the adder 14, and the data of value O are selected.

The adder 14 receives the output of the buffer register group 11 and the output of the selector 13, performs an addition operation on these two inputs, and outputs the result to the low-speed access memory 12 and the selector 13. .

In the buffer register 11, the output of the multiplier 10 is temporarily stored, read out as necessary, and provided to the adder 14. Further, the buffer register 11 is configured so that data can be simultaneously read and written from addresses that are not necessarily the same, at the same timing. This group of buffer registers absorbs delays in non-uniform response times between devices, allowing the adder 14 to be used at maximum speed, that is, the present device to be used at maximum speed.

The control device 15 generates signals that uniformly control the operations of each device, mutual timing, data exchange with external devices, and the like.

Next, an explanation will be given of the back projection operation procedure related to this embodiment apparatus. This operating procedure is shown in FIG. 3, and the basics of this operating procedure will now be explained.

() Back projection of the K views is performed.

() Back projection starts from the leftmost pixel point of the straight line y=y ₁ and moves sequentially to the right neighbor.

() After the back projection of the straight line y=y _j is completed, the same back projection as in () is performed for the straight line y=y _j+1 .

() After the back projection of all straight lines, that is, all pixel points, is completed, the operating procedure of () to () is repeated for the next K view.

Next, the operation timing of each part of this embodiment device will be explained. This operation timing is shown in FIG. 4. Here, the basics of this operation timing will be explained as follows: () First register memory group 5, second register memory group 6, and buffer register group 11 etc., read and write operations are completed within one cycle of the basic clock.

() In the first table 7 and the second table 8, the fast access memory 9 and the slow access memory 12, and the multiplier 10 and adder 14, from the time an input is given until the output is obtained, or As shown in the figure, time delays τ _c and τ _w , τ _h and τ _nn , and τ _n and τ _a occur from the time the device is started until the operation is completed.
Control is performed in consideration of this time delay in processing and control.

() In the adder 14, pixel points (i-1, j) and (i+1, j) are processed simultaneously with the processing of pixel point (i, j). Similar parallel operations are performed between each device.

() Each device is controlled so that complete parallel processing is executed, except for overhead at the start and end points.

Although the embodiment apparatus has been described above, the present invention can also be implemented with the following configuration.

() First memory group 1 and second memory group 2
and the third memory group 3 are composed of one or more sets of memories; () the arithmetic unit 4 is composed of an adder, a multiplier, a register, etc.; () the first register memory group 5 is composed of one or more sets of memories; , consists of two sets of register groups for h and Δh, an adder, etc. () The second register memory group 6 is composed of two sets of registers for p and Δp, an adder, etc. () The first table 7 is composed of an arithmetic unit and a table group or a memory group, etc. () The second table 8 is composed of an arithmetic unit and a table group or a memory group, etc. () The selector 13 and addition () The buffer register group 11 is configured by a plurality of register groups. () The high-speed access memory 9 and the low-speed access memory 12 are divided into a plurality of pieces. () The control device 15 as a micro program.
(xi) data and control lines 20, consisting of memory, decoders, control devices, etc.;
(xii) Configure multiple devices by combining them or by separating one device into multiple devices.

In addition, the back projection operation procedure is performed from the right end to the left end along the straight line y = y _j , the operation procedure is performed from the upper end to the lower end along the straight line x = x _i , and the operation procedure is performed from the upper end to the lower end along the straight line x = x _i . The present invention can also be implemented in an operating procedure from the top to the top.

Further, the present invention can be implemented even if the number of batch-processed views is not always kept constant.

Furthermore, the present invention can be practiced even if the equation (16) is changed to the following equation (16').

μ (i, j) = _Vn 〓 〓 ^k=1 b _k・w (i, j, k) × D (CH (i, j, k))...
(16') [Effects of the Invention] As explained above, the present invention has the following effects.

(1) Faster and more efficient back projection for fan beams.

(2) Speed up backprojection for reconstruction regions of arbitrary shapes, including ellipses.

(3) By reducing the frequency of access to image data, large amounts of image data can be placed in cheap, low-speed memory, and the use of expensive, high-speed memory can be limited to backprojection data, making the device cheaper and more economical. It can be designed in a practical manner, and cost performance can be improved.

(4) Even if the scan data deviates from the expected viewing direction or varies, the back projection control data can be changed by dynamic calculation or selection to match the actual value of each θ _k . By doing this, you can maintain high image quality,
In addition, the back projection processing time is maintained at high speed.

(5) Because the control structure is based on a simple and highly versatile design concept, field-of-view (field-of-view)
The center of the reconstruction area is the rotation center (Iso Center) of the X-ray source, regardless of the type and shape of the
Even if they do not match (enlarged reconstruction, etc.), the back projection firmware can be made the same.

(6) Since the control data for backprojection is extremely small, the data transfer of the control data to the high-speed processor becomes extremely small, thus speeding up the overall backprojection processing and reconstruction processing and making it highly efficient. .

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram explaining the principle of back projection related to the present invention. FIG. 2 is a block diagram showing the configuration of an embodiment of a back projection apparatus according to the present invention. FIG. 3 is a flowchart showing the backprojection operation procedure of the embodiment of the backprojection apparatus according to the present invention. FIG. 4 is a timing chart showing the operation timing of the embodiment device. 1, 2, 3...Memory group, 4...Arithmetic unit,
5, 6... Register memory group, 7, 8... Table, 9... High speed access memory, 10... Multiplier, 11... Buffer register section, 12... Low speed access memory, 13... Selector , 14...
Adder, 15...control device, 20...data line, 25...control line.

Claims (1)

[Claims] 1. Radiation or electromagnetic waves are generated, the radiation or electromagnetic waves are transmitted through a cross section of a subject, and view data obtained as a plurality of sampling data, each of which is a response to the radiation or electromagnetic waves, for the cross section is obtained. a first means for scanning and collecting data in a large number of angular directions; and a second means for reconstructing a distribution image of the response regarding the cross-sectional area by a back projection method from a large number of view data obtained by the first means. and a third means for displaying the distribution image obtained by the second means on a screen, the second means comprising: When the reconstruction area is divided into a grid by straight lines parallel to the x-axis and y-axis, and each intersection of the grid is defined as a pixel constituting the reconstructed image, the x-axis The total number of pixels on each line parallel to ,
The total number of pixels on each straight line parallel to the y-axis, the reconstruction area divided into two by a straight line parallel to the y-axis, and the x of this bisected first part or second part
The number of pixels (l _j ) on each straight line parallel to the axis, bisect the reconstruction area by a straight line parallel to the x-axis, and the number of pixels parallel to the y-axis of the first or second bisected part. The number of pixels on each straight line (l _i ), the total number of straight lines parallel to the x-axis (2n), the total number of straight lines parallel to the y-axis (2m), the reconstruction area to one or more parallel to the x-axis The reconstruction area is divided into a plurality of parts by one or more straight lines parallel to the y-axis, and the total number of straight lines parallel to the x-axis of each part is divided into a plurality of parts, and the reconstruction area is divided into a plurality of parts by one or more straight lines parallel to the y-axis. means for storing part or all of the total number of parallel straight lines as a control parameter regarding the shape of the configuration region; and means for storing a back projection control parameter (p ₀ (1, k), h ₀ (1, k), Δp(k), Δh(k),
Δp(k)′, Δh(k)′ or Δx, sinθ _k , cosθ _k , L,
x, y); and a calculation device, the calculation device calculating a backprojection control parameter for each pixel from the control parameter regarding the shape of the reconstruction area and the backprojection control parameter of the specific point. (p(i, j, k), h(i, j,
A computer tomography apparatus characterized by comprising means for generating k)) by sequential calculation. 2 The second method involves repeatedly performing multiplication (weighted data) for each view and addition of the results for each pixel over a large number of views, and storing the intermediate or final results in a large capacity memory for each pixel. The back projection integrating means is configured to add and accumulate the result of adding weighted data for each view for a plurality of views to the data of the corresponding pixel. 2. The computer tomography apparatus according to claim 1, wherein the number of reads and writes to the pixel memory, that is, the number of accesses to each pixel memory is reduced, and the pixel memory is configured with a low-speed access memory. 3. The backprojection integration means includes a cascaded multiplier and an adder, and the input circuit of the adder includes:
The computer tomography apparatus according to claim 2, comprising a buffer circuit that can read and write data to different addresses at the same timing. 4. The computer tomography apparatus according to claim 1, which collects data by a nuclear magnetic resonance absorption phenomenon as a first means.