JPH09270029A - Method for updating and correcting viewpoint position and method for displaying viewpoint position - Google Patents

Abstract

PROBLEM TO BE SOLVED: To smoothly update the viewpoint position in a blood vessel through easy operation by inputting a vertical and/or a horizontal viewpoint coordinate movement quantity for a projection surface exclusively by an input device, and updating the viewpoint position. SOLUTION: When the viewpoint position (P) to be updated is specified, the distances dX and dY from the center of an image to the point P are found (step 300) and the coordinates of a point S on a tomographic image corresponding to the point P is found (step 301). The viewpoint position is moved in parallel to the projection plane 20, the new viewpoint position is denoted as e1 (step 302), and its (y) coordinate y1 is regarded as an object to be corrected (step 303). Further, the CT value of the coordinate point y1 is compared with a threshold value (step 304); when the viewpoint position e1 is outside the blood vessel, a fixed value is added to the coordinate point y1 and the result is compared again with the threshold value (step 305). Then the viewpoint position e1 is changed to a viewpoint position e2 which is moved by y-jump (step 307) unless the conditions of the threshold value are met.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for constructing a three-dimensional image obtained by projecting and shading pixel points included in a plurality of tomographic images on a two-dimensional plane, and particularly updating the viewpoint position. Regarding the method.

[0002]

2. Description of the Related Art One of three-dimensional image construction methods,
A method using the central projection method is shown in FIG. FIG. 7 is a diagram for explaining coordinate conversion by central projection when the viewpoint, tomographic image, and projection plane have a complicated positional relationship. By designating the viewpoint position e, each pixel point of the tomographic image 23 is projected on the projection surface 20. That is, the projection result of the S point (x0, y0, z0) on the tomographic image 23 becomes the P point (x, y, z) on the projection plane. By using such a projection method, it becomes possible to construct a three-dimensional image of the inner surface of the blood vessel. As a result, for example, FIG.
A three-dimensional image of the inside of the blood vessel as shown in (b) is constructed. If a viewpoint is set inside the blood vessel and a three-dimensional image is constructed while updating the viewpoint position, a continuous image as if moving inside the blood vessel can be obtained. Such a processing method is disclosed in JP-A-8-16813.
No. 7-231496.

[0003]

However, when the viewpoint position is updated, the operation is complicated where the blood vessel or the like is complicatedly winding or thinning. An object of the present invention is to provide a method capable of smoothly updating the viewpoint position inside a blood vessel by a simple operation.

[0004]

In order to solve the above problems, the present invention provides a viewpoint coordinate movement amount in a vertical direction with respect to a projection plane and / or a viewpoint coordinate movement amount in a horizontal direction with respect to the projection plane, The input position is exclusively input to update the viewpoint position.

Further, according to the present invention, the viewpoint coordinate movement amount in the vertical direction displays a distance selection table having a maximum value as a distance to a display pixel point on the tomographic image corresponding to the viewpoint position, and displays only the selected distance. The viewpoint is changed in the direction perpendicular to the projection plane to update the viewpoint position.

Further, according to the present invention, it is determined whether the viewpoint position updated to a desired position is valid or invalid. If the changed viewpoint position is invalid, the viewpoint position is moved to a valid position and the viewpoint position is changed. To correct.

Further, according to the present invention, the viewpoint position is updated by inputting the vertical or horizontal viewpoint coordinate movement amount from the input device, and the image data at the updated viewpoint position is compared with a preset threshold value. If the image data is included in the threshold condition, the viewpoint position is moved vertically or horizontally until the viewpoint position is out of the threshold condition, and the viewpoint position is updated and corrected.

Further, according to the present invention, the viewpoint position obtained by the above update is displayed on the orthogonal coordinate system.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION First, a method of constructing a three-dimensional image using the central projection method will be described.

In FIG. 7, the projection plane 20 by central projection is shown.
Conversion of pixel coordinates of the tomographic image 23 into xyz coordinates projected on the projection plane 20 in projecting the tomographic image 23 onto the image is performed as follows.

A is the intersection of the x-axis and the projection plane 20, b is the intersection of the y-axis and the projection plane 20, and c is the intersection of the z-axis and the projection plane 20. Further, α is an angle formed by a line obtained by projecting a perpendicular line drawn from the origin onto the projection plane 20 onto the zx plane with the x axis, and β is the perpendicular line x-
The angle with the z plane, e (x1, y1, z1) is the viewpoint position, P (x, y,
z) is the projection point on the projection plane (corresponding to the screen) 20, S (x0, y
0, z0) is the viewpoint position e (x1, y1, z1) and the projection point P (x, y,
z) and a pixel point at which the tomographic image 23 intersects, the following equation holds.

First, the projection plane 20 is represented by (x / a) + (y / b) + (z / c) = 1 ... (1). Also, the viewpoint position e (x1, y1, z1) and the projection point P
The straight line 22 passing through (x, y, z) is (x0-x) / (x1-x) = (y0-y) / (y1-y) = (z0-z) / (z1-z)… ( Given in 2). Projection plane 2 from viewpoint position e (x1, y1, z1)
The intersection C1 (xc1, yc1, z of the perpendicular line drawn to 0 and the projection plane 20)
c1), z = [X ・ k1-Y ・ k2-yc1 ・ k3- {ci ・ k3 ・ zc1 / bi} + {ai ・ k3 ・ X / (bi ・ cosα)}-ai ・ k3 ・xc1 / bi] / [1-ci ・ k3 / bi + (ai ・ k3 ・ sinα) / (bi ・ cosα)]… (3) x = (Xz ・ sinα) / cosα… (4) y = [yc1 + {- ci ・ (z-zc1) -ai ・ (x-xc1)}] / bi… (5) However, k1 = sinα k2 = cosα / sinβ k3 = cosα ・ cosβ / sinβ ai = 1 / a bi = 1 / b ci = 1 / c (X, Y) is the coordinate on the projection plane 20 (display image) where , Zc1 = z1 ± [h / sqrt {1+ (c ・ c) / (a ・ a) + (c ・ c) /, where h is the distance between the intersection C (xc1, yc1, zc1) and the viewpoint position e. (b ・ b)}] (-of z1 ± is when z0 <zc1) xc1 = x1 + c ・ (z1-zc1) / a yc1 = y1 + c ・ (z1-zc1) / b may be used .

When the projected image is displayed on the display screen corresponding to the projection plane 20 with 512 pixels in the vertical direction and 512 pixels in the horizontal direction, the coordinates (X, Y) on the projection plane are values from -256 to 256, respectively. (X = 0, Y = 0 at the center of the image) For each X and Y, x, y and z are determined by the equations (3), (4) and (5). Viewpoint position e
Since x1, y1, and z1 are given arbitrarily, y0 is given by equations (6) and (7).
The coordinates x0 and z0 of the pixel point S are determined on the tomographic image of = d0. x0 = {(d0-y) / (y1-y)} ・ (x1-x) + x… (6) z0 = {(d0-y) / (y1-y)} ・ (z1-z) + z … (7)

The above is the case of one tomographic image, but in reality there are a plurality of tomographic images and there are also a plurality of d0, so the coordinates x0 of a plurality of pixel points with respect to one set of projection planes X and Y, z0 is determined.

However, when constructing a three-dimensional image, the coordinates x0 and z0 of all pixel points are not projected, and only the pixel point closest to the viewpoint is projected (threshold processing).
A plurality of pixel points with a large reflectance are mainly projected (volume rendering processing). For example, in the case of threshold processing, among the plurality of pixel points on the projection line connecting the viewpoint and (X, Y) of the projection plane (screen), the point actually projected is the threshold condition. Is satisfied (for example, whether or not the CT value of the tomographic image falls between two certain constant values), the pixel point is closest to the viewpoint. That is, the pixel points of a plurality of tomographic images are sequentially compared with the threshold value from the viewpoint position e, and the tomographic image of the pixel points that first satisfy the condition is projected. The coordinates x0, z0 of the pixel point closest to this viewpoint and the distance D from the viewpoint position e to the pixel point S
Is stored in memory as the following array.

When the image size is 512 × 512, xaddr [256 + Y] [256 + X] = x0 zaddr [256 + Y] [256 + X] = z0 yaddr [256 + Y] [256 + X] = D dist [256 + Y] [256 + X] = It is the distance between the viewpoint and the pixel point, and the coordinate of the pixel point on the tomographic image 23 projected on the screen (X, Y) is x = xaddr [256 + Y] [256 + X] ...
(8) z = zaddr [256 + Y] [256 + X]… (9) y = yaddr [256 + Y] [256 + X]… (10) Distance = dist [256 + Y] [256 + X] It can be referred to as (11).

The distance D serves as a parameter for obtaining the pixel value (luminance) of the projection point P. The pixel value of the projection point P is proportional to the difference between the set maximum distance Dmax and the distance D. The three-dimensional image shaded at this distance D is the depth image.

Next, updating and correction of the viewpoint position will be described with reference to FIGS. Projection plane for ease of explanation
It is assumed that 20 and the CT image 23 are set in parallel. Further, the image is displayed such that the center of the screen is the viewpoint position e.

First, the operator exclusively inputs the amount of coordinate movement in the direction perpendicular to the projection plane 20 and the amount of coordinate movement in the direction parallel to the projection plane 20 with the input device. For example, pressing the mouse button 203 to update the viewpoint position e1 from the first viewpoint position e1 in the vertical direction with respect to the projection plane 20 (change to the viewpoint y coordinate direction), and then use the mouse button 201 to change the point P on the screen. Click to update the viewpoint position from the viewpoint position e2 to the viewpoint position e3 in the direction parallel to the projection plane 20 (fix the y coordinate direction and change to the x and z coordinate directions). Further, the mouse button 203 is pressed again to update the viewpoint position e3 to the viewpoint position e4. By performing such processing, the viewpoint position is updated.

The viewpoint position e in the direction perpendicular to the projection plane 20
As a method for moving, the maximum moving distance eC1 (= dist [0] [0]) is calculated from the equation (11) using the above threshold processing,
For example, as shown in FIG. 4, there is a method in which several divided and set distances within the range of the maximum movement distance eC1 are displayed on the screen and the operator selects from the distance display on the screen. In FIG. 4, the maximum movement distance is 5.8 mm, and the distance between them is appropriately divided and the distance selection table 200 is displayed. This maximum movement distance can be applied to both forward and backward movements. When moving forward, the threshold value processing is advanced from the viewpoint position to the point where it hits the wall of a blood vessel (conditions are met). When the vehicle moves backward in the reverse direction, the threshold value processing is performed backward from the viewpoint position, and the distance to the point where the wall of the blood vessel or the like is abutted (a condition is satisfied) is defined as the maximum backward movement distance.

Next, when the point P on the screen of FIG. 2 (b) is clicked with the mouse button 201, it is updated in the direction parallel to the projection plane 20, but the transfer position e2 → viewpoint position e3 in FIG. An image at a new viewpoint position can be obtained with respect to updating inside the blood vessel such as, but with updating such as viewpoint position e2 → viewpoint position e5, the viewpoint position deviates from the blood vessel and enters the wall. That is, when trying to obtain the above-described maximum movement distance from the viewpoint position e5, the condition is satisfied at the first pixel point from the viewpoint position, and an image cannot be obtained.

Therefore, in the present invention, as shown in FIG. 2 (a), from the viewpoint position e (x1, y1, z1) inside the blood vessel, the parallel direction (d
If the viewpoint position e1 is updated to (x) and the viewpoint position e1 moves outside the interior of the blood vessel and enters the wall, the distance y_ju in the projection plane direction.
mp, move to a new viewpoint position e2, and automatically correct the viewpoint position. The correction of the viewpoint position will be described with reference to a flowchart.

The viewpoint position (point P) to be updated is designated with the mouse, and the distances dX and dY from the center of the image to point P are obtained (step 300). By referring to the equation (11), the distance eS (= dist [256 + dY] [256 + dX]) to the S point on the tomographic image corresponding to the P point is calculated,
The coordinates (x0, y0, z0) of the S point are calculated by the equations (8), (9) and (10) (step 301). The viewpoint position is translated with respect to the projection plane 20, and the new viewpoint position is set to e1 (x, y1, z) (step
302). When the viewpoint position e1 is updated, the point (y1) at the y coordinate which is the direction perpendicular to the projection plane 20 is set as the correction target (step 303). The CT value at coordinate point y1 is compared with a preset threshold value (step 304). Step 3
If the condition is satisfied in 04 (viewpoint position e1 is out of the blood vessel), a fixed value is added to coordinate point y1 (viewpoint position e1
The distance you want to shift in the direction of the projection plane 20 from), return to step 304 again, and compare with the threshold value (step 30).
Five). The coordinate point y1 is updated until the CT value of the coordinate point y1 does not satisfy the threshold condition (until the viewpoint position e1 moves inside the blood vessel), and when the threshold condition is not satisfied,
(Y1) After the update −y1 (before the update), the moving distance y_jump is obtained (step 306). The viewpoint position e1 is changed to the viewpoint position e2 which is moved by y_jump (step 307).

In this way, if the first viewpoint position e is translated to the point P, an image cannot be obtained at the translated viewpoint position e1, so that the viewpoint position e2 is automatically moved to
Construct and display a three-dimensional image.

Here, the correction movement can be similarly performed when the viewpoint position is moved backward. In the present embodiment, the correction movement is moved toward the projection plane 20 direction, but in the case of backward movement, it may be moved away from the projection plane 20 direction.

As described above, in the present embodiment, even when the viewpoint position is translated and the new viewpoint position is the wall of the blood vessel, the viewpoint position can be automatically corrected and moved to the inside of the blood vessel. The viewpoint can be smoothly moved inside the blood vessel with a simple operation.

Here, in the present embodiment, the viewpoint position is automatically corrected and moved (moved from the viewpoint position e5 to e6 in FIG. 1) in the direction of the projection plane 20 (y direction). Correction movement may be performed so as to return to the x direction) (movement from viewpoint position e5 in FIG. 1 to e ′), or correction movement may be performed by detecting the direction with the shortest correction movement distance. If the viewpoint position after parallel movement satisfies the threshold condition, a constant value is added to coordinate point y1 and the comparison with the threshold value is repeated. Since it is the same as moving the position little by little forward, the viewpoint position can be automatically corrected and moved to the vicinity of the wall of the blood vessel (moved from viewpoint position 5 to e'or e "in FIG. 1) and corrected. It is possible to obtain an image that does not cause a sense of discomfort even if the image of the moved viewpoint position is less displaced from the image of the desired viewpoint position.

The above method is implemented by hardware as shown in FIG. The image data is stored in the magnetic disk 602, read into the main memory 601 as necessary, and calculated by the central processing unit 600. The calculation result is transferred to the display memory 603 and displayed on the display device 604.
In addition, the viewpoint position by the operator is the mouse 606 or the keyboard 6
Input by 07.

Further, a series of viewpoint positions updated by the above method are plotted on an orthogonal coordinate system as shown in FIG. 6 and displayed on the display device 604 or the like. That is, the updated series of viewpoint positions e (x1, y1, z1) is stored in the magnetic disk 602 together with the image data, and the series of viewpoint positions is represented by orthogonal coordinates, which is displayed on the display device 604. At this time, a series of viewpoint positions may be displayed by connecting with a line. This allows
It becomes easy to grasp the outer shape of the blood vessel and the advanced trajectory.

In this embodiment, the case where the projection plane and the CT image are parallel has been described, but the present invention can be applied even if they are not parallel. Further, although the updating and correction of the viewpoint position inside the blood vessel have been described, the present invention is not limited to this. Further, although the CT value is used in the present embodiment, other tomographic images such as an image by nuclear magnetic resonance, an ultrasonic image, etc. may be used.

[0031]

According to the present invention, since the viewpoint position can be updated by inputting the viewpoint coordinate movement amount in the vertical and horizontal directions with respect to the projected image, the operation can be easily performed.
In addition, it is determined whether the moved viewpoint position can be an effective viewpoint position by updating, and if it is not an effective viewpoint position, it is automatically moved to an effective viewpoint position, so smooth viewpoint position update can be performed with a simple operation. . Further, since a series of update viewpoint positions are displayed on the orthogonal coordinate system, the update route can be easily grasped.

[Brief description of drawings]

FIG. 1 is a diagram illustrating updating of a viewpoint position.

FIG. 2 is a diagram illustrating correction of a viewpoint position.

FIG. 3 is a flowchart showing correction of a viewpoint position.

FIG. 4 is a diagram showing a screen for selecting vertical viewpoint update.

FIG. 5 is a block diagram showing a hardware configuration example of the present invention.

FIG. 6 is a diagram in which the locus of updating the viewpoint position is plotted on Cartesian coordinates.

FIG. 7 is a diagram showing a relationship between a projection plane, a tomographic image, and coordinate axes.

[Explanation of symbols]

 20 Projection plane 23 Tomographic image e Viewpoint position P Projection point S Pixel point

Claims (6)

[Claims] 1. A viewpoint position characterized in that an amount of viewpoint coordinate movement in a direction perpendicular to a projection plane and / or a amount of viewpoint coordinate movement in a direction horizontal to the projection plane is exclusively inputted by an input device. How to update. 2. The vertical direction coordinate movement amount displays a distance selection table having a maximum value as a distance to a display pixel point on the tomographic image corresponding to the viewpoint position, and displays the viewpoint by the selected distance. The method for updating the viewpoint position according to claim 1, wherein the position is changed in the vertical direction with respect to. 3. The viewpoint position updated to a desired position is judged to be valid or invalid, and when the changed viewpoint position is invalid, the viewpoint position is moved to a valid position. Correction method. 4. A vertical or horizontal viewpoint coordinate movement amount is input from an input device to update the viewpoint position, and the image data at the updated viewpoint position is compared with a preset threshold value to obtain the image data. Is included in the threshold condition, the viewpoint position is moved vertically or horizontally until the viewpoint position is out of the threshold condition. 5. The method of updating and correcting the viewpoint position according to claim 1, wherein the updating and correction of the viewpoint position is used for a three-dimensional image configuration. 6. A method of displaying a viewpoint position for displaying the viewpoint position obtained by the updating in a rectangular coordinate system.