JP3450937B2 - Ultrasound image processing device - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ultrasonic image processing apparatus, and more particularly to an ultrasonic image processing apparatus capable of automatically optimizing a mutual positional relationship between a plurality of ultrasonic two-dimensional images forming a three-dimensional ultrasonic image. .

[0002]

2. Description of the Related Art A two-dimensional scanning plane can be formed by electronically or mechanically scanning an ultrasonic beam formed by an ultrasonic probe, and the two-dimensional ultrasonic image (tomographic image) Image, Doppler image) can be formed. further,
If such a two-dimensional scanning plane is mechanically or manually moved in a direction orthogonal to it, a large number of two-dimensional ultrasonic images (z0 to zn) parallel to each other can be captured, as shown in FIG. That is, ultrasonic diagnosis can be performed on a three-dimensional region in the living body. Then, a three-dimensional ultrasonic image can be constructed by stereoscopically expressing the three-dimensional region in gray scale.

Conventionally, when an ultrasonic probe for insertion into a body cavity is inserted into a living body to perform ultrasonic diagnosis around the ultrasonic probe, the ultrasonic probe is formed by the ultrasonic probe. The operator pulls out the ultrasonic probe at a constant speed while electronically or mechanically performing radial scanning with the ultrasonic beam. That is, a plurality of two-dimensional ultrasonic images corresponding to the scanning surface formed by radial scanning are taken in along the probe axis direction, and a three-dimensional ultrasonic image is constructed based on the plurality of ultrasonic images. is there.

[0004]

However, as shown in FIG.
As shown in (A), when the ultrasonic probe is pulled out in the z direction, if there is a displacement in the x direction or the y direction between adjacent ultrasonic images, an accurate three-dimensional ultrasonic image is formed. I can't. For example, there is a case where camera shake occurs during the extraction, or the insertion tube of the ultrasonic probe may rotate around its central axis as a rotation center during the extraction. The continuity cannot be maintained, and a distorted three-dimensional ultrasonic image results, which causes a problem that it is difficult to accurately recognize the affected area.

Needless to say, the same problem may occur when the ultrasonic probe that is in contact with the body surface is artificially moved, which may cause camera shake of the operator, respiration and pulsation of the patient. This causes a problem of shift between ultrasonic images.

The present invention has been made in view of the above-mentioned conventional problems, and an object thereof is an ultrasonic image processing apparatus capable of correcting a positional deviation between ultrasonic images to form an accurate three-dimensional ultrasonic image. To provide.

Another object of the present invention is to correct the positional deviation of the ultrasonic image in the vertical and horizontal directions or to correct the rotational deviation of the ultrasonic image.

[0008]

In order to achieve the above object, the present invention provides a plurality of ultrasonic probes which are scanned by scanning an ultrasonic probe in the xy plane in the z direction. In an ultrasonic image processing apparatus that forms a three-dimensional ultrasonic image based on the two-dimensional ultrasonic image, the correlation value is calculated while sequentially shifting the rear image as a whole with respect to the front image in the adjacent two-dimensional ultrasonic image. A correlation value calculating means for obtaining a correlation value function, a determining means for determining a displacement amount of the rear image with respect to the front image from a position of the rear image where the correlation value function is maximum, and A correction unit that corrects the deviation of the rear image.

Further, in the present invention, the correlation value calculating means is
The rear image is shifted in the x direction and the y direction as a whole, the determining unit determines the shift amount of the rear image in the x direction and the y direction, and the correcting unit determines the x direction and the y direction of the rear image. It is characterized in that the deviation of is corrected.

Further, according to the present invention, the correlation value calculating means is
The rear image as a whole is rotationally changed in the θ direction, the determination unit determines the amount of deviation of the rear image in the θ direction, and the correction unit corrects the displacement of the rear image in the θ direction. And

Further, the present invention is characterized in that the two-dimensional ultrasonic image is an ultrasonic tomographic image or an ultrasonic Doppler image.

[0012]

According to the above structure, the correlation value calculating means calculates the correlation value while sequentially shifting the rear image as a whole with respect to the front image in the adjacent two-dimensional ultrasonic image, thereby obtaining the correlation value function. That is, the correlation value calculation means calculates the correlation value while shifting the relative positions of the front image and the rear image. The determining means determines the amount of deviation of the rear image from the front image from the positional relationship between the two images having the maximum correlation value function, that is, from the position of the rear image having the maximum correlation value function. That is, when the correlation value is obtained by sequentially superimposing the rear image on the front image while shifting the rear image, the position at which the correlation value is maximum seems to indicate a state in which the positional relationship between the two images is optimum. Therefore, the amount of positional deviation is specified from that state. Therefore, the correction means corrects the deviation of the subsequent image based on the deviation amount thus obtained.

Therefore, according to the present invention, even if a shift occurs between two adjacent ultrasonic images due to camera shake or the like as shown in FIG. Can be aligned with the previous image, so that an accurate three-dimensional ultrasonic image can be constructed.

The deviation correction is performed in the x direction and the y direction, or in the θ direction. One of these deviation corrections may be performed alone, or two kinds of deviation corrections may be combined.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT A preferred embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 shows the overall configuration of an ultrasonic image processing apparatus according to the present invention. The apparatus shown in FIG. 1 is substantially an ultrasonic diagnostic apparatus.

In FIG. 1, a probe 10, which is an ultrasonic probe, is an ultrasonic probe inserted in the body cavity, which is inserted into the esophagus in this embodiment. The probe 10 is composed of an insertion tube to be inserted into the esophagus and a tip portion including an ultrasonic transducer provided at the tip of the insertion tube, and ultrasonic waves are transmitted and received by the ultrasonic transducer. In this embodiment, as the ultrasonic transducer, an array transducer arranged in a ring shape or a single transducer is used, and when the latter single transducer is used, the transducers in the tip portion are used. Are mechanically rotationally scanned. In any case, the radial scan is performed by electronic scanning or mechanical scanning. Of course,
Various methods can be adopted as long as the two-dimensional ultrasonic wave capturing region is formed in the direction orthogonal to the axial direction of the probe, and the three-dimensional ultrasonic image can be formed by pulling out the probe 10.

Although the ultrasonic probe of the body cavity insertion type is used in this embodiment, the present invention is also applicable to the case of using the ultrasonic probe which contacts the body surface.

The transmitting / receiving circuit 12 supplies a transmission signal to the probe 10 and amplifies the reception signal output from the probe 10. The received signal output from the transmission / reception circuit 12 is the A / D converter 14
After being converted into a digital signal by, it is stored in the three-dimensional echo data memory 16. That is, as shown in FIGS. 6 and 7A, a plurality of two-dimensional ultrasonic images are stored in the three-dimensional echo data memory 16 as the probe 10 is pulled out. The 2D ultrasound image is
For example, it is an ultrasonic tomographic image or an ultrasonic Doppler image. The present invention can be applied to any image. Therefore, the three-dimensional echo data memory 16 stores the echo data captured in the three-dimensional region in the living body, and specifically, as described above, a large number of ultrasonic images parallel to each other ( Ultrasonic image information) is stored.

However, as shown in FIG. 7A, if there is a deviation between the ultrasonic images, the three-dimensional ultrasonic image cannot be accurately constructed. Therefore, in this embodiment, the deviation correction unit 18 is provided.

The deviation correction unit 18 performs deviation correction in the xy direction or deviation correction in the θ direction, and the specific processing contents thereof will be described in detail later. Deviation correction unit 1
According to FIG. 8, finally, as shown in FIG. 7B, the positional deviation between the ultrasonic images is corrected, and the image information aligned in the z direction can be obtained.

The three-dimensional image forming section 20 forms a three-dimensional ultrasonic image by a known method on the basis of each ultrasonic image whose displacement has been corrected as described above, and its image information is D / After being converted into an analog signal by the A converter 22, it is displayed on the display 24.

Next, the specific processing contents of the deviation correction unit 18 will be described.

FIGS. 2 and 3 show a first embodiment of deviation correction. The first embodiment corrects the deviation in the x direction and the y direction. In the deviation correction of the first embodiment, as shown in FIG. 2 (A), the correlation value is shifted while sequentially shifting the image b (rear image) with respect to the image a (front image) in the x direction and the y direction. The shift position at which the correlation value function obtained by the calculation is maximum is specified as the shift amount. For later description, the shift amount in the x direction of the rear image with respect to the front image is defined as δ, and the shift amount in the y direction is defined as ε.

In FIG. 3, in S101, 0 is substituted as an initial value for z, which is the serial number of the ultrasonic image, and finally 0 is substituted for the coefficient CMAX which indicates the maximum correlation value. In S102, ZMAX is set as the number of ultrasonic images, and it is determined whether the number z of the ultrasonic images is larger than ZMAX-1. If the result of S102 is YES, this routine ends.

In S103, the shift amount in the x direction, δ
-MASK / 2 is substituted as an initial value into. And
In S104, it is determined whether δ is larger than MASK / 2. That is, in S103 and S104, the shift of the subsequent image in the x direction is changed from -MASK / 2 to + MASK.
It is provided in order to perform up to 1/2. In S105, as in S103, the initial value of ε is -MASK /
2 is substituted, and in S106, it is determined whether or not ε is larger than MASK / 2. This S105 and S1
06 means that the shift amount of the subsequent image in the y direction is from −MASK / 2 to + MASK / 2.

In S107, the correlation value C is calculated between the front image z and the rear image z + 1. The arithmetic expression is as the following first expression.

[0028]

[Equation 1] The first expression is obtained by multiplying the values of pixels of both images having the same coordinates in the state where the rear image is superimposed on the front image and adding the multiplication values over the entire image. Of course, such addition is performed in the area where the previous image and the subsequent image overlap. Note that the area of such an overlapping region varies with the shift of the subsequent image, but the correlation value C is standardized so that the variation does not appear in the correlation value function.

In S108, it is judged whether or not the correlation value C obtained in S107 is larger than the coefficient CMAX.
In the case of ES, S109 is executed. In S109, δ when the condition of S108 is satisfied is substituted into mx, and at the same time, ε is substituted into my. In other words, the values of δ and ε having the largest correlation values among the correlation values obtained so far are stored in mx and my when the correlation values are sequentially obtained while sequentially shifting the subsequent image. Will be done. In other words, S108 and S109
Has a function of specifying the maximum value of the correlation value C and the coordinates at that time.

After S109 is executed, S110 is executed, ε is incremented by 1, and the process from S107 is executed again. When the condition of S106 is satisfied, S
111 is executed, δ is incremented, and S1 is again executed.
Each step from 06 is executed.

On the other hand, when the condition of S104 is satisfied,
That is, when the series of steps of obtaining the correlation value C while shifting the rear image with respect to the front image in all of the x direction and the y direction is completed, S112 is executed, and the image z + 1 which is the rear image uses mx and my. Then, the positional deviation is corrected. Specifically, the subsequent image z + 1 is shifted by mx pixels in the x direction and by my pixels in the y direction. As a result, the positional shift between the front image and the rear image is eliminated, and the continuity of the organ image can be secured.

FIG. 2B shows the correlation value function. That is, this correlation value function is created after executing the routine shown in FIG. 3 for all combinations of δ and ε, and the maximum value MAX of the correlation value C is selected by S108 as described above, The shift amount (coordinate value) at that time is specified in S109.

Thus, two ultrasonic images z and z + 1
After the above-mentioned shift correction is performed between S, S113 is executed, z is incremented by 1, and the next adjacent 2
Misalignment correction is performed between two ultrasonic images. Then, the condition of S102 is finally satisfied, and the processing of this routine ends.

Therefore, according to this first embodiment, as shown in FIG.
As shown in (B), a two-dimensional correlation value function with δ and ε as parameters is obtained, the deviation amount in the x direction and the y direction is specified based on the correlation value function, and the deviation correction is performed. It can be carried out. Therefore, this first embodiment is effective when the probe moves up and down or left and right in the body or on the body surface due to breathing or pulsation.

Next, a second embodiment of deviation correction will be described with reference to FIGS. 4 and 5.

FIG. 4A shows the principle of this second embodiment. In this second embodiment, the image b (post image) is rotated with respect to the image a (previous image) at a constant rotation angle. The correlation value C is obtained while rotating by θ, and the rotation deviation amount is specified from the correlation value function obtained thereby.

FIG. 5 shows the specific process. In S201, 0 is substituted for z, which indicates the serial number of the ultrasonic image, and 0 is also substituted for the coefficient CMAX. In S202, the ultrasonic image number z is ZMA.
It is determined whether or not it is larger than X-1.

At step S203, -MA is added to θ indicating the rotation angle.
SK / 2 is substituted as the initial value, and in S204, it is determined whether or not θ is larger than MASK / 2. That is, S203 and S204 mean that the variable range of θ is from −MASK / 2 to + MASK / 2. In S205, the front image z and the rear image z + 1
The correlation value C is calculated between. The calculation formula is as shown in the second formula below.

[0039]

[Equation 2] In the above second equation, (Xθ, Yθ) is defined by the following third equation.

[0040]

[Equation 3] The second expression above is to rotate the rear image with respect to the front image, and at that time, multiply the values of each pixel at the same coordinates in the overlapping regions in both images by each other, and add the multiplication value in that region. It was done. As in the first embodiment, since the overlapping range of both images changes according to the rotation angle θ, the correlation value C needs to be standardized so as not to be affected by the area variation of such overlapping region.

In S206, the calculated correlation value C
Is determined to be greater than the coefficient CMAX, S206
If the result is YES, S207 is executed and θ at that time is substituted into β. After S207 is executed, S20
In step 8, θ is incremented by 1, and again S205
Is executed and the condition of S204 is satisfied, that is, the correlation value C is obtained for all θ as shown in FIG. 4B, and the maximum value M of the correlation value function is obtained.
When AX is obtained, the subsequent image z + is obtained in S209.
1 is corrected by β. That is, the rotation deviation is corrected by rotating the rear image by the angle β in the θ direction.

Then, in step S210, z is incremented by 1, and the image shift between the next adjacent ultrasonic images is corrected. Then, the condition of step S202 is finally satisfied, and this routine ends.

Therefore, according to the second embodiment, for example, when the insertion tube of the ultrasonic probe inserted in the body cavity has a partial twist and the twist is restored when the probe is pulled out. It is possible to automatically correct the rotational deviation between the images that occurs at.

In the first embodiment described above, for example, 40 (40 pixels) is set as the coefficient MASK that determines the upper limit of movement, and 20 degrees is set as the MASK that determines the rotation condition value in the second embodiment. Is set.

The above-described first and second embodiments may be operated separately, but the devices may be configured by combining those embodiments. In that case, it is desirable to correct the rotational deviation after correcting the positional deviation in the vertical and horizontal directions by performing the first embodiment.

The present invention is particularly effective when the ultrasonic probe is artificially moved to acquire the three-dimensional echo data, and even if the ultrasonic probe is moved a little rough, the obtained three-dimensional ultrasonic image is uniform. Has the advantage of maintaining high precision.

If the positional deviation is large, the correction may be impossible or insufficient. In that case, it is determined that the maximum correlation value is below a certain threshold value. For example, a warning is displayed to the operator.

[0048]

As described above, according to the present invention,
An accurate three-dimensional ultrasonic image can be constructed by correcting the positional deviation between ultrasonic images. Therefore, even when the mutual positions of the ultrasonic images are displaced due to camera shake, breathing, pulsation, etc., it is possible to automatically correct them and construct an appropriate ultrasonic image.

[Brief description of drawings]

FIG. 1 is a block diagram showing an overall configuration of an ultrasonic image processing apparatus according to the present invention.

FIG. 2 is an explanatory diagram showing the principle of the first embodiment of the present invention.

FIG. 3 is a flowchart showing specific steps of the first embodiment of the present invention.

FIG. 4 is an explanatory diagram showing the principle of the second embodiment of the present invention.

FIG. 5 is a flowchart showing specific steps of the second embodiment of the present invention.

FIG. 6 is a diagram showing capturing of a plurality of two-dimensional tomographic images.

FIG. 7 is a diagram showing a sequence of ultrasonic images before displacement correction and a sequence of ultrasonic images after displacement correction.

[Explanation of symbols]

10 probes, 12 transmission / reception circuits, 16 three-dimensional echo data memory, 18 shift correction section, 20 three-dimensional image forming section.

Continuation of the front page (56) Reference JP 61-260235 (JP, A) JP 63-49885 (JP, A) JP 2-100583 (JP, A) JP 5-168626 (JP , A) JP 7-65146 (JP, A) JP 7-213521 (JP, A) JP 7-222744 (JP, A) WILLIAM K. PRATT, Correlation Techniques of Image Registration, IEEE TRANS ACTIONS ON AEROSPA CE AND ELECTRONIC SYSTEMS, May 1974, Vol. 10, no. 3, pp. 353-358 (58) Fields investigated (Int.Cl. ⁷ , DB name) A61B 8/00

Claims (4)

(57) [Claims] 1. A three-dimensional ultrasonic image is formed based on a plurality of two-dimensional ultrasonic images captured by scanning an ultrasonic probe that scans an ultrasonic beam in an xy plane in the z direction. In the ultrasonic image processing apparatus, the correlation value calculating means for calculating the correlation value while sequentially shifting the rear image as a whole with respect to the front image in the adjacent two-dimensional ultrasonic image, and the correlation value function, And a correction unit that corrects the deviation of the posterior image based on the deviation amount from the position of the posterior image that maximizes the deviation of the posterior image with respect to the preceding image. Sound wave image processing device. 2. The apparatus according to claim 1, wherein the correlation value calculation means shifts the rear image in the x direction and the y direction as a whole, and the determination means determines a shift amount of the rear image in the x direction and the y direction. An ultrasonic image processing apparatus, characterized in that the y-direction is determined, and the correction means corrects a shift of the post-image in the x-direction and the y-direction. 3. The apparatus according to claim 1, wherein the correlation value calculation means rotates and changes the rear image as a whole in the θ direction, and the determination means determines a deviation amount of the rear image in the θ direction. The ultrasonic image processing apparatus, wherein the correction means corrects the deviation of the post-image in the θ direction. 4. The ultrasonic image processing apparatus according to claim 1, wherein the two-dimensional ultrasonic image is an ultrasonic tomographic image or an ultrasonic Doppler image.