JPH0991466A - Pseudo three-dimensional image configuration method and projection image display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To display a 3-dimensional image as if the inside were looked in from a small hole by setting in advance a prescribed area including a sight direction and differentiating the extract condition depending on the inside or outside of the area among picture elements of projection object in the case of projection so as to make a shadow to the extracted picture element. SOLUTION: Coordinates X, Y on a projected face are set in advance as a prescribed area including a sight direction (S20), a Y-coordinate of a tomographic closest to the sight is decided (S21), cross points z, x between the tomographic image and a projection line tying the coordinates X, Y and the sight are obtained to obtain a distance L from the sight to the cross points (S22). When the cross point is discriminated on a side face of a cylinder model area (S23), whether the relation of L>(d/COSγ) or L>(γ/sinγ) is in existence is discriminated (S24, S25), a picture element (S26, S27) in matching with the extract condition 1 is extracted and a vein picture element from the sight to the cross point is extracted respectively by an extract condition 2 (S28). Shadow processing is updated to the picture element extracted (S29, 30) and the processing is finished by a maximum value (S31-35).

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pseudo three-dimensional image constructing method and a display device suitable for displaying a pseudo three-dimensional image for observing the inside with an endoscope or a laparoscope.

[0002]

2. Description of the Related Art There is a technique of stacking X-ray CT images to obtain a three-dimensional image and projecting the three-dimensional image on a projection surface to obtain a pseudo three-dimensional image. It is a technique used to support surgery and to create treatment plans. The projection method includes a parallel projection method and a central projection method.

[0003]

The parallel projection method is suitable for observing the outer shape and the cut shape, but the central projection method is used for obtaining a projection image simulating an endoscopic movement. Suitable. For example, with an endoscope or a laparoscope, when it is advanced, the field of view changes rapidly. However, the tip of the endoscope is small, and it is required to observe the changing visual field from this small output. To obtain a simulated pseudo three-dimensional image as if you were observing with such an endoscope,
Central projection is optimal.

[0004] The applicant filed an application for Japanese Patent Application No. 6-3492 for obtaining a projected pseudo three-dimensional image obtained by such observation, particularly endoscopic observation. Here, the pseudo three-dimensional image is an image obtained by projecting a stacked three-dimensional image on the projection surface, but when projecting, a far object is small, and a near object is large. It is an image obtained by performing a concealment process in which only the nearest pixel is displayed without displaying the far one at the position. The shading algorithm includes depth method, surface method, volume rendering method, and the like. The depth method is based on the distance R between the pixel position on the stacked three-dimensional image and the projection point on the projection surface from the pixel position.
With reference to (the distance R in the central projection method is the distance between the viewpoint and the tomographic plane projection target point), the larger the distance R, the smaller the pixel value at the projection point, and the distance R is The smaller the value, the larger the pixel value at the projection point. In the surface method, instead of the distance R, the pixel value of the projection point is given by the magnitude of the pixel value around the pixels of the stacked three-dimensional image (that is, the magnitude of the inclination). The volume rendering method takes the transparency of each tomographic plane viewed in the depth direction, and takes the pixel value that can be assumed to be reflected by using the reflection and transmission based on the transparency as the pixel value of the projection point. .

When projecting onto the projection surface, coordinate conversion between the pixel position of the stacked three-dimensional image and the projection point on the projection surface is indispensable. This coordinate transformation follows the central projection method. The projection plane is a projection memory coordinated (addressed) in the coordinate system XY.

FIG. 8 is an explanatory diagram of the central projection method. The tomographic image 30 is an X-ray CT image, and shows one example of the stacked tomographic images. Stacked fault planes are parallel to each other. The coordinate system of the stacked 3D image is x, y,
z, the y axis indicates the stacking position, the xz plane is the tomographic plane of the X-ray CT image, and the coordinate position on this plane can be defined by (x, z). Therefore, the coordinate value y
Indicates the stacking position of CT images (actually equivalent to CT image number), and the pixel position of the CT image is indicated by (x, z).

The projection plane 20 of FIG. 8 has an arbitrary inclination as compared with the X-ray CT image 30. A typical example is X-ray CT image 3
It is parallel to 0 and is generally not parallel. The inclination is determined by what kind of projected image is desired and what the purpose of observation is. In the figure, the projection plane 20 is defined by angles α and β. The angle α is defined by the z perpendicular to the projection plane 20 from the origin.
An angle formed by the line projected on the −x plane with the x axis, and an angle β is an angle formed by the perpendicular line with the xz plane.

In FIG. 8, the viewpoint e is the viewpoint in the central projection method, and the coordinates are e (x ₁ , y ₁ , z ₁ ). Viewpoint e
From the projection plane 20 to the orthogonal plane c
₁ (x _c1 , y _c1 , z _c1 ), the projection point on the projection surface 20 at any one-point pixel position S (x ₀ , y ₀ , z ₀ ) of the tomographic image 30 is P (x, y, z ). The pixel position S facing the projection point P is called a projection target point. Furthermore, the coordinate system of the projection plane 20 is shown by X and Y. The projection plane 20 intersects the x, y, and z axes, and the distances to the intersections for the x, y, and z axes are a, b, and c.

The pixel position S based on the above coordinate relationship
The relationship between the projection target point S and the projection point P for projecting (x ₀ , y ₀ , z ₀ ) onto the projection point P (x, y, z), and P (x,
A conversion formula for converting y, z) into coordinates P (X, Y) of the coordinate system on the projection plane will be described below. First, when the projection plane 20 is defined by the x, y, z coordinate system,

[Equation 1] It is represented by In addition, point e (x ₁ , y ₁ , z ₁ ) and point P (x,
A straight line 22 passing through (y, z) is in the x, y, z coordinate system,

[Equation 2] Given in. The projection plane 20 has a C ₁ point (x _c1 , y _c1 ,
Since z _c1 ) is orthogonal to the viewpoint,

(Equation 3) The relation between x, y, z of P (x, y, z) and X, Y when the coordinates of this point P in the projection plane X, Y coordinate system are P (X, Y) Becomes

[Equation 4] Here, at the point C ₁ (x _c1 , y _c1 , z _c1 ), for example, a point where the perpendicular line drawn from the viewpoint e (x ₁ , y ₁ , z ₁ ) to the projection surface 20 and the projection surface 20 intersect ( The distance between this point and the viewpoint e is h),

(Equation 5) May be used.

The relationship between the projection surface and the display screen is as follows. The projection plane is a projection memory defined by the coordinate system XY, and the whole or a part of this projection memory is sent to the display memory and displayed on the display screen.

When an image projected on the projection surface 20 is displayed on a display screen (not shown) of a display device with 512 vertical pixels × 512 horizontal pixels, X and Y take values from −256 to +256. . For each of X and Y, x, y, and z are determined by (Equation 4). Since x _1, y _1, z ₁ point e is optionally provide, by (number 6), y ₀ = d coordinate x ₀ of the pixel point S on the tomographic images of _0, z ₀ is determined.

(Equation 6) Since they are piled up, a tomographic image 3 is formed between the points P and e.
Since there are a plurality of _0s and a plurality of d _0s accordingly, a plurality of points x ₀ and z ₀ to be projected on one set of X and Y.
Is decided. If the plurality of projection target points are directly projected onto the projection point and projected, they will be displayed in an overlapping manner, and if the concealment processing is performed, only the pixel value after the shadowing of the projection target point closest to the front will be projected. .

It should be noted that L in FIG. 8 indicates the distance from the viewpoint e to the S point, and this L is a parameter (distance R on the depth method) for obtaining the pixel value (luminance) at the P point. Becomes
The pixel value at point P is a shaded pixel value. For example, in the depth method described above, the pixel value at point P is proportional to the value obtained by subtracting L from the maximum value Lmax of the set pixel value (luminance). The coordinate conversion as described above is performed for all points on the projection surface 20 corresponding to the display screen. In addition, it is performed for all tomographic images 30. According to this method, the projection plane 2
The pseudo three-dimensional image projected and displayed on 0 becomes an image as if the inside of the object is viewed with an endoscope.

However, the above method is based on the assumption that the viewpoint e is placed in a space that is originally inside the object, such as the esophagus, trachea, and intestine. ) Pseudo three-dimensional image, which looks like
In particular, as shown in FIG. 9, it is not possible to construct a pseudo three-dimensional image that can be seen while inserting it into the subject 61 while observing it with the laparoscope 60, and it is desired to obtain such an image. Could not meet the demand.

Therefore, a three-dimensional image construction method disclosed in Japanese Patent Application No. 6-173972 was considered. This is a method of stacking a plurality of tomographic images including volume images to obtain a stacked 3D image, and shading the 2D image viewed from an arbitrary direction to construct a 3D image. When projecting each tomographic image onto a plane, the pixel coordinates of each tomographic image are converted to coordinates on the projection plane by using the central projection method, and the pixel value at each pixel coordinate on the projection plane according to the shading algorithm. In the coordinate image constructing method for constructing a three-dimensional image by giving the above, a certain area including the viewpoint is set in advance, and the image coordinates in the area are not subjected to the coordinate conversion and shading. The coordinate conversion and shading are performed only for pixel coordinates outside the area.

A certain spread area set including the viewpoint plays a role like a small peephole when the inside is looked through from the laparoscope, and the central projection method is used for pixel coordinate conversion of the tomographic image. Therefore, not only can the internal area corresponding to the size of the hole be displayed (no information), but since the field of view is enlarged by the central projection method, a size larger than the size of the hole can be seen. As a result, a three-dimensional image as if the inside (extended inside) is looked into from a small hole, especially when inserting it into the subject 61 while observing it with the laparoscope 60 as shown in FIG. A visible three-dimensional image will be obtained. However, according to this method, since the coordinate conversion and the shading are not performed in the area set including the viewpoint, there is no information and it is ignored. Thus, the information that this area should have is erased and not displayed.

It is an object of the present invention to provide a method of constructing a pseudo three-dimensional image and a display device which can be obtained when the subject is actually looking through with a laparoscope.

In particular, since a blood vessel appears around the laparoscope when it is inserted into a subject, the present invention provides a configuration method and a display device capable of displaying a specific object such as the blood vessel.

[0018]

SUMMARY OF THE INVENTION The present invention is a pseudo three-dimensional image construction method for projecting a stacked three-dimensional image from the viewpoint direction starting from the viewpoint on the projection surface by shading by the central projection method. In advance, a certain area including is set, and when the projection is performed, the extraction condition is made different inside or outside the area of the pixel to be projected, and thus the extracted pixel is shaded. A pseudo three-dimensional image construction method for performing and projecting is disclosed.

Further, according to the present invention, an image obtained when a stacked three-dimensional image is viewed through a laparoscopic image model from a viewpoint as a viewpoint, and a shadow is projected on a projection surface by a central projection method. In the pseudo-three-dimensional image construction method of projecting by converting, in the above projection, the extraction condition of the pixel to be projected is made different between the image area inside the laparoscopic image model and the other external area, and thus extracted A pseudo three-dimensional image construction method in which a pixel is shaded and projected is disclosed.

Further, according to the present invention, first means for storing the stacked three-dimensional images, second means for setting a constant area including the viewpoint direction starting from the viewpoint, and pixels inside and outside the constant area. Third means for making the extraction conditions of pixels to be projected different from each other, and only the pixels extracted according to the extraction conditions for the image of the first means are subjected to central projection and shading from the viewpoint direction to the projection surface. Disclosed is a projection image display device including fourth means for projecting and means for displaying a pseudo three-dimensional image obtained on this projection surface.

[0021]

BEST MODE FOR CARRYING OUT THE INVENTION The concept of an embodiment of the present invention will be described with reference to FIGS. 2 is a laparoscopic image model 2
FIG. 3 is a diagram showing a relationship among the image 1, the tomographic image 30, and the projection plane 20.
The laparoscopic image model 21 is used to obtain a projection image as if the subject was observed while the laparoscope was pressed and advanced.
It is a cylindrical model figure which has a cylindrical outline similar to a laparoscope. For simplicity, the tip surface 21A of the laparoscopic image model 21 is
It is assumed that it is parallel to the projection plane 20. The end surface 21B indicates a contact surface with the front tomographic image. The center line of the model 21 is the projection plane 2
It is orthogonal to the 0 point 20A. When looking forward from the viewpoint e,
This is a region that belongs to the front from this viewpoint and that the projection image from inside the model 21 and on the outer peripheral line of the model 21 can be observed from the model 21. In the figure, an arbitrary point of the projected image is (X, Y), the distance from the point 20A is R, and the angle from the center line Q to this one point (X, Y) is δ. FIG. 10 shows a perspective view of the model 21 and a plurality of tomographic images 30. 40 is a passage opening of the model 21.

The concept of the embodiment of the present invention will be described with reference to FIG. The model 21 has a cylindrical shape (or a cylindrical shape).
The same shall apply hereinafter), its radius is r, and the distance from the viewpoint e to the tip of the cylinder (region 21) is d.

FIG. 1A shows an example of setting extraction conditions 1 and 2. The outside of the model 21 is the extraction condition 1 (threshold condition 1), and the inside of the model 21 (including the outer peripheral line of the model 21).
Is an example of setting extraction condition 2 (threshold condition 2). The extraction conditions 1 and 2 are that the angle γ of the projection line from the viewpoint is the model 21
Of angle γ greater than or less than ₁ to the left end contour point C _1, and the magnitude of the sine value or the cosine value of the CT fault point of the projected line is to choose on whether larger or smaller than r or d .

This will be described with reference to FIGS. FIG. 1B shows the states of the projection points P, P ₁ , P ₂ when the angle γ of the projection line is γ> γ ₁ . P ₁ is the CT closest to the viewpoint
One point of the fault plane 30 (# 1), P is the second fault plane 30
One point (# 2) and P ₂ are one point of the third tomographic plane 30 (# 3). All of these three tomographic planes 30 (# 1 to # 3) intersect the model 21. On the other hand, the fourth tomographic plane 30 (# 4) does not intersect with the model 21.

Then, the distance between the viewpoint e and each of the points P ₁ , P, P ₂ is L, and the sine value L sin γ from each point is obtained. The magnitude of the sine value Lsinγ and the magnitude r of the radius of the model 21 is compared.

(1) If Lsinγ> r, the projection point exists outside the model 21 as P ₂ . (2) If Lsinγ <r, the projection point exists inside the model 21 as P ₁ . (3) If Lsinγ = r, the projection point becomes the contour point of the model 21 as P. Therefore, Lsinγ in (1)
If> r, extraction condition 1 is applied, and L in (2) and (3) is applied.
If sinγ ≦ r, extraction condition 2 is applied.

FIG. 1C shows an example in which γ <γ ₁ . P ₃
Is the projection point on the tomographic plane 30 (# 4), and P ₄ is the tomographic plane 30
The projection point on (# 3) is shown. Therefore, in this case, the cosine value Lcosγ from each point is obtained, and the magnitude of the cosine value Lcosγ and the distance d between the viewpoint e and the left end face of the model 21 are compared. (1) If Lcosγ> d, the projection point exists outside the model 21 as P ₃ . (2) If Lcosγ <d, the projection point exists inside the model 21 as P ₄ . (3) If Lcosγ = d, the projection point is model 2
1 on the left end face. Therefore, Lcosγ of (1)
If> d, extraction condition 1 is applied, and L in (2) and (3) is applied.
If cosγ ≦ d, extraction condition 2 is applied.

FIG. 1A shows the conclusion of FIGS. 1B and 1C. The extraction condition 2 for the area E ₃ inside the model 21 (including the outer peripheral line of the model 21) in front of the viewpoint e
And the external regions E ₁ and E _{2 of} the model 21 (however, E ₁
The-described embodiment the projection point P ₂ in FIG. 1 (b), E ₂ for 1 such example of a projection point P ₃ (iii)) applies the extraction condition 1.

When the position of the viewpoint e is determined and the tomographic plane 30 is determined, each projection point P (concept including P ₁ and P ₂ ) is each point on the tomographic plane 30. Therefore, each projection point P And the distance L between the viewpoint e and the viewpoint e are also uniquely determined. Therefore, in the calculation, for the distance L to the viewpoint e at each projection point P, sin γ and cos γ are shifted to the right side, and the magnitude of the distance L and (r / sin γ) and (d / cos γ) is compared. Just take the steps. The above is summarized as follows (1), (2), and (3).

(1) If the projection point p is in the area E ₁ outside the cylindrical model 21, that is, if 90 °>γ> γ ₁ , then if L> (r / sinγ), that is, Lsinγ> r, then extract. If condition 1 is specified, coordinate conversion and shading are performed, and if not, jump to (3).

(2) If the projection point p is in the area E ₂ on the outer surface of the cylindrical model 21, that is, if γ <γ ₁ , if L> (d / cosγ), then the extraction condition 1 is specified and the coordinates are set. Convert and shade, otherwise jump to (3).

(3) In cases other than (1) and (2) above,
That is, in the area E ₃ inside the model 21 (including on the outer peripheral line), L ≦ (r / sin γ) or L ≦ (d / cos γ). Shading is done.

Where

(Equation 7) It is.

When the shape of the model 21 is cylindrical, the target pixel exists outside the model 21 and inside the model 21 only in the cases (1), (2), and (3). In this case, coordinate conversion and shading are performed only in this case. The method of projection, coordinate conversion, and shading are basically the same as those of FIG. 7 described later.

Here, the first threshold condition which is the first extraction condition is, for example, the extraction threshold for visceral extraction, and the second threshold condition which is the second extraction condition. If the above-mentioned internal organs are the target, it is the threshold value for extracting blood vessels formed in the internal organs. In addition, the first and second threshold conditions can be applied to all regions where the laparoscope is advanced.

The coordinate transformation is performed by the above-mentioned central projection method. For shading, a predetermined shading algorithm such as depth method or volume rendering method is used.
A pixel value is given to each pixel coordinate on the projection plane 20 according to the shading algorithm.

FIG. 3 is a flow chart showing an embodiment of the three-dimensional image constructing method according to the present invention. Step 20 The coordinates (X, Y) on the projection plane are X = -256, Y = -25
6 Step 21 The coordinate y is set as the position of the tomographic image 30 (# 1) closest to the viewpoint e. Step 22 The intersection point p (z, x) of the tomographic image 30 and the straight line connecting the coordinates (X, Y) and the viewpoint e (this is a projection line) is determined, and the distance L from the viewpoint e to the intersection point p is determined.

Step 23: It is judged whether the intersection point p is the side surface E ₁ or the front end surface E _{2 of the} cylindrical model area 21. If it is a side surface, jump to step 24, and if it is the front end surface E ₂ , jump to step 25. Step 24 If the intersection point p is the side surface E ₁ of the cylinder (region 21), L>
It is determined whether (d / cosγ). If this is satisfied, the process jumps to step 26, and if not satisfied, the process jumps to step 28.

Step 25 If the intersection point p is the side surface E ₁ of the cylindrical model 21, L>
It is determined whether or not (r / sinγ). If this is satisfied, the process jumps to step 27, and if not satisfied, the process jumps to step 28.

Steps 26 and 27 If there is a pixel which meets the extraction condition 1, the pixel is extracted according to it. Step 28 From the viewpoint e to the intersection point p, pixels that are blood vessels are extracted under extraction condition 2. Step 29 The above-mentioned coordinate conversion and shading processing are performed. Step 30: y is updated in order to process the next tomographic image 30. Step 31: It is judged whether or not the above processing is completed for all the tomographic images 30. If not finished, jump to step 22.

Step 32 The X position of the projection point is shifted by one pixel. Step 33: It is judged whether X is the maximum value (+256). If it is not the maximum value, the process returns to step 21, and the process is repeated until the maximum value is reached. Step 34 Set the projection point on the next line (1 is added to Y), and X =
-256. Step 35: It is judged whether Y is the maximum value (+256). If it is not the maximum value, the process returns to step 21, and the process is repeated until the maximum value is reached, and all the processes are finished at the maximum value.

As described above, the display of blood vessels running three-dimensionally in the region is constructed in a three-dimensional image as if the inside (extended inside) is looked into from a small hole.

FIG. 4 is an explanatory diagram of another embodiment.
Here, the second extraction condition is set only for the portion visible from only the upper and lower side surfaces of the model 21 (in this case, unlike the laparoscopic model unlike the first embodiment), the portion visible from the left end surface is the first extraction condition. This is the extraction condition. FIG. 4 is a diagram for explaining the relationship between the angle δ and the extraction condition.
Here, the extraction condition is a threshold. The contour point at the circumferential end of the front end surface 21A of the model 21 is P _1, and the contour point of the open circle when the tomographic image at the forefront is opened by the model 21 from the viewpoint direction is P ₂ . The contour point P ₂ is a change point of the threshold value on the side surface of the cylinder. The angle of the straight line connecting the viewpoint e and the point P ₁ with respect to the center line Q is δ ₁ . The angle of the straight line connecting the viewpoint e and P ₂ with respect to the center line Q is δ ₂ .

It is assumed that the following threshold values are given based on the points P ₁ and P ₂ , that is, δ ₁ and δ ₂ . (1) The projection line (a straight line connecting the viewpoint, the projection target point, and the projection point) is located at a position P _i1 inside the point P ₁ at the circumferential end.
When passing through (that is, when δ <δ ₁ ). For all projection lines that satisfy the angle δ position that satisfies δ <δ ₁ , pixel extraction for each projection target point on that projection line is performed by extracting pixel values that satisfy the first threshold condition. Shall be projected. (2) When the projection line passes through the position P _i2 between P ₂ and P ₁ (that is, when δ ₁ ≦ δ ≦ δ ₂ ). For all projection lines that satisfy the angle δ position that satisfies δ ₁ ≦ δ ≦ δ ₂ , pixel extraction for each projection target point on that projection line is performed by selecting pixel values that satisfy the second threshold condition. It shall be extracted and projected. (3) When passing through a position P _i3 outside the projection line P ₂ (that is, when δ ₂ <δ). For all projection lines that satisfy the angle δ position that satisfies δ ₂ <δ, pixel extraction for each projection target point on the projection line is performed by extracting pixel values that satisfy the third threshold condition. It shall be projected.

FIG. 5 shows the relationship between the tomographic image to be projected and the two angles δ = δ _i1 and δ = δ _i2 in (1), (2) and (3) above. For simplicity, it is assumed that the tomographic images 30A to 30D are stacked in the direction orthogonal to the center line Q, but in reality, the tomographic images 30A to 30D are formed at any angle other than the center line Q. In FIG. 5, three tomographic images 30A, 30B, 30
C exists between the viewpoint e and the projection plane 20, and the tomographic image 30D
Is in front of the viewpoint e. Therefore, the angle δ _i1
And δ _i2 , the tomographic image 30D is not projected because the tomographic image 30D is in front of the viewpoint e, and the tomographic images 30A, 30B, 3
0C is the image of the projection target. Furthermore, tomographic images 30A, 3
Not all the pixel positions of 0B and 30C are projected, but at the angle δ = δ _i1 , the pixels of the pixel positions a to g that match this angle δ _i1 are projected. At the angle δ = δ _i2 , the pixels at pixel positions a ′ to g ′ on the projection line of this angle δ _i2 are projected. However, a to g and a'to g'are a and a shown in FIG.
It is a point on the circumference (outline point) as indicated by a ', and actually, a plurality of pixel positions of three or more points are projection targets along the pixel section.

Further, when δ = δ _i1 , δ ₁ ≦ δ ≦ δ ₂ is satisfied (passing the P _i2 position in FIG. 4). Therefore, for the projection target point on the projection line, the second threshold condition is pixel The first threshold condition is selected because it is selected for extraction and satisfies δ <δ ₁ for δ = δ _i2 .

Here, the relationship between the threshold value and pixel extraction will be described. There are three projection target positions on one projection line, and their pixel values (CT values) are CT ₁ , CT ₂ , and CT.
_Suppose it is ₃ . Then, assume that the threshold value is CT ₀₁ . For example, when it is desired to extract a CT value larger than the threshold CT ₀₁ , a CT larger than CT ₀₁ among CT ₁ , CT ₂ and CT ₃ is extracted.
Extract the value. There is also an example in which a CT value smaller than CT ₀₁ is desired to be extracted. The pixel value thus extracted becomes the projection target pixel value of the true projection target point.

Although the angles δ ₁ , δ ₂ , and δ were used in the classification of (1), (2), and (3), these angles are the distance D between the viewpoint e and the intersection 20A, and the viewpoint. δ ₁ from e,
Since it can be expressed by the intersection r between the straight line of the angles of δ ₂ and δ and the projection plane and the distance r with the center line intersection 20, these D and r are used to (1), (2), (3) Can be classified.

According to the above embodiment, if δ <δ ₁ , the first threshold condition is satisfied, if δ ₁ ≦ δ ≦ δ ₂ , the second threshold condition is satisfied, and if δ <δ ₂ , the third threshold condition is satisfied. The threshold condition of is selected,
Pixels having pixel values that meet those selection conditions are extracted.
Then, the extracted pixels are subjected to shading processing and concealing processing, and a pseudo three-dimensional image based on the central projection method can be obtained. It should be noted that the first threshold condition and the third threshold condition may be the same, the threshold condition may be a threshold condition for extracting an internal wall image of the internal organs, and the second threshold condition may be a threshold condition for extracting a blood vessel. For example, the projection image obtained on the projection surface is an image as when the subject is pierced by making a hole like a laparoscope. Then, as the laparoscope moves forward, the current image is pushed backward, and new images appear one after another in a forward manner, so that a realistic image can be obtained. Here, the state of being pushed backward is the projected image with δ ₂ <δ, and the projected image with δ ₁ > δ is a new image appearing forward.

In FIG. 7, the third threshold condition of δ> δ ₂ is matched with the first threshold condition of δ <δ ₁ , and δ ₁ ≦ δ ≦
The processing flow when the second threshold value condition at δ ₂ is the threshold value for blood vessel detection is shown.

Step S ₁ The coordinates (X, Y) on the projection plane 20 are X = −256, Y = −
256. This coordinate (-256, -256) is the starting point. The projection plane is X = −256 to +256, Y = −2
It is divided into 56 to +256.

Step S ₂ The angle δ at the projection point (X, Y) is calculated. The projection target point (x, y) of all tomographic images on the projection line that becomes this projection point (X, Y) is obtained. In the example of FIG. 5, since there are three tomographic images with respect to one projection point and the viewpoint, the projection target points (x, y) are three points that intersect these three tomographic images.

Step S ₃ The magnitudes of the angles δ ₁ and δ ₂ set in advance and the angle δ obtained in step S ₂ are compared. This comparison is the projection point (X, Y)
This is because it is to determine which of the angles P _i1 , P _i2 , and P _{i3 in} FIG. 4 corresponds to.

If steps S ₄ and S ₆ δ <δ ₁ , the projection point (X, Y) is P in FIG.
It corresponds to a position such as _i1 and only when the pixel value of the pixel position of the projection target satisfies the first threshold value condition, the satisfying pixel value is extracted (step S ₄ ). . If δ ₂ <δ, the projection point (X, Y) is as shown in FIG.
Corresponding to a position such as P _i3 , and only when the pixel value at the pixel position of the projection target satisfies the first threshold condition, this satisfying pixel value is extracted (step S ₆ ).

Step S _{5 If} δ ₁ ≤δ≤δ ₂ , the projection point (X, Y) is P in FIG.
_This corresponds to a position such as _i2 , and only when the pixel value of the pixel position of the projection target satisfies the second threshold condition, this satisfying pixel value is extracted.

Step S _{7 The} pixel values extracted in steps S _{4 to} S ₆ are shaded and projected onto the projection point (X, Y). What is shading processing?
This is processing by the voxel method described above, and is performed by using, for example, FIG.
In the example, only the pixel values satisfying the above threshold condition among the intersections a, b, c of the three tomographic images 30A, 30B, 30C, those far from the pixel position of the pixel value are close to the small pixel value. Is a large pixel value and the projection point (X, Y)
This is a process of setting the pixel value of. However, in the figure, 3 of a, b, and c
Since the points overlap, the hidden pixel position is removed by the concealing process, and only the pixel position closest to the extracted pixel position is projected.

Steps S ₈ and S ₉ X is updated to X + 1 among the projected points (X, Y). The update is continued until the maximum value (X = + 256) is reached.

In steps S ₁₀ and S ₁₁ , X is updated to Y + 1 among the projected points (X, Y). The update is continued until the maximum value (Y = + 256) is reached.

Although FIG. 7 above shows one viewpoint e,
In the example where the viewpoint e is advanced, each viewpoint e
The process of FIG. 1 is performed for each. In FIG. 7, if the threshold value condition 2 is the threshold value for blood vessel extraction, only the blood vessel can be extracted in the process of step S ₅ . If the threshold value condition 1 is a threshold value for general pixel extraction of the internal organs, the image of the general internal organs is extracted by the processing in steps S ₄ and S ₆ .

FIG. 11 shows a system diagram of the projection display device of the present invention. This projection display device includes a CPU 53, a main memory 51, a magnetic disk 52, a display memory 53, a CRT.
54, controller 55, mouse 56, and common bus 5
It consists of 7. The magnetic disk 52 stores each tomographic image, and the projection display software (see FIG.
Alternatively, the CPU 53 performs a predetermined process according to FIG. 7). In this processing, input / output processing and processing operations are performed using the mouse 56 and the keyboard attached to the controller 55. The stacked three-dimensional image is displayed on the CRT 54 via the display memory 53, and the processing of FIGS. 3 and 7 is performed using the operation of the operator, and an image that meets the first and second threshold conditions is displayed on the laparoscope or the like. Obtained according to the image model. or,
Images viewed endoscopically appear on the screen one after another as the image model such as a laparoscope moves, and various kinds of treatment plan information can be provided to the operator. Further, the display contents are stored in the magnetic disk 52 and used for re-display.

Although the extraction conditions are made different according to the threshold value, in the volume rendering method, the extraction condition may be made different depending on the transparency value.
Furthermore, the extraction conditions 1 and 2 inside and outside the model 21 in FIG. 3 and the extraction conditions 1 and 2 on the end face and the side face of the model 21 in FIG. 7 are shown as an example. Various settings such as the classification of extraction conditions for an arbitrary area and other areas can be set. The model 21 also has an example other than a cylinder. Although the tomographic image is the X-ray CT apparatus image, it can be applied to the MRI image.

[0062]

According to the present invention, a three-dimensional image as if the inside (extended inside) is looked into from a small hole, especially when inserting it into a subject while observing with a laparoscope. In a visible three-dimensional image, the extracted image can be three-dimensionally displayed in the area that should be erased, including the viewpoint.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of a first embodiment of the present invention.

FIG. 2 is a diagram showing a relationship between a tomographic image and a projection plane based on a laparoscopic image model.

FIG. 3 is a flowchart of the present invention.

FIG. 4 is a diagram showing an example of threshold processing in the laparoscopic image model of the present invention.

FIG. 5 is a diagram showing various projection target points in the laparoscopic image model of the present invention.

FIG. 6 is a diagram showing a relationship between an angle δ _{i1 of the} present invention and a tomographic image.

FIG. 7 is another flowchart of the present invention.

FIG. 8 is a diagram showing a relationship between a viewpoint, a tomographic image, and a projection surface.

FIG. 9 is a perspective view of a laparoscopic image model.

FIG. 10 is a diagram showing a laparoscopic image model and a cross-sectional view.

FIG. 11 is a diagram showing an example of a projection display device of the present invention.

[Explanation of symbols]

 20 Projection plane 21 Laparoscopic image model 30 Tomographic image (plane)

Claims (3)

[Claims] 1. In a pseudo three-dimensional image construction method for projecting a stacked three-dimensional image from a viewpoint direction starting from a viewpoint on a projection surface by a central projection method, a predetermined area including the viewpoint direction is preset. It should be noted that, in the above projection, the extraction condition is made different inside or outside the area of the pixel to be projected, and the pixel thus extracted is shaded and projected. 3D image construction method. 2. An image obtained by looking at a stacked three-dimensional image in a viewpoint direction from a viewpoint as a starting point and from this viewpoint through a laparoscopic image model is projected on a projection surface by shading by a central projection method. In the pseudo three-dimensional image constructing method, in the above projection, the extraction conditions of the pixels to be projected are different between the image area inside the laparoscopic image model and the outside area other than that, and the pixels thus extracted are Pseudo-three-dimensional image construction method in which projection is performed by shading. 3. A first means for storing a stacked three-dimensional image, a second means for setting a constant area including a viewpoint direction starting from a viewpoint, and a projection target of pixels inside and outside the constant area. A third means for making the extraction conditions of the pixels different from each other different, and a third means for projecting only the pixels extracted according to the extraction conditions from the image of the first means by performing central projection and shading on the projection surface from the viewpoint direction. 4. A projection image display device comprising: 4 means; and means for displaying a pseudo three-dimensional image obtained on this projection surface.