JP2000229081A - Ultrasonograph - Google Patents

Abstract

PROBLEM TO BE SOLVED: To perform a processing with addition of small-scale hardware without having the influence of noise by sliding a probe in the long axial direction to provide time series ultrasonic images, searching proper positions for image connection, and connecting a plurality of them. SOLUTION: A probe 1 is driven by an ultrasonic transmitter-receiver part 2 to transmit ultrasonic waves into a subject, and the reflection signal thereof is received. At this time, the probe 1 is slid in the long axial direction to form time series ultrasonic waves, which are stored in a cine memory 3 as a plurality of frames of time series. A characteristic point extraction part 6 removes low-frequency component and high-frequency component by a filter to remove the obstruction factor of characteristic point estimation. Further, power calculation, weighting, clustering, and correlation preprocessing are performed to determine the distribution peak position. An image connection part 7 deforms and adheres the images of the cine memory 3 so that the present image characteristic point group is conformed to the previous connected image characteristic point group. According to this, the influence of noise can be reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a device capable of transmitting and receiving ultrasonic waves to and from an object and displaying an ultrasonic tomographic image or a blood flow image of a diagnostic site of the object. The present invention relates to a method of joining time-series ultrasonic images acquired by sliding to enlarge an apparent angle of view, and particularly to an ultrasonic diagnostic apparatus capable of performing high-accuracy image joining by extracting feature points of an image. .

[0002]

2. Description of the Related Art As a technique for expanding an apparent visual field by joining time-series ultrasonic moving images, for example, US Pat. No. 5,575,28
It is described in 6. This involves dividing each time-series image into a plurality of small processing regions, determining the inter-image correlation for each small region, determining the motion vector of the small region group, and determining the motion vector group and the motion vector of the image estimated in the past. Is used to estimate the motion of the entire image, and translate and rotate the image according to the estimated motion vector of the image to join the images.

[0003]

In the prior art, since uniform processing is performed on the entire image or a part of the image, acoustic noise and artifacts peculiar to the ultrasonic apparatus are used for estimating the movement of the cross section. This affects the quality of the joined image. Further, according to the method described in US Pat. And the number of calculation steps is enormous. Further, many steps are further required for an optical flow-like calculation for estimating a movement vector of a small area, and as a result, a huge amount of dedicated hardware is required to perform processing in real time.

Accordingly, the present invention addresses such a problem, and provides an ultrasonic diagnostic apparatus capable of minimizing the influence of noise and artifacts and performing processing by adding a relatively small-scale hardware. That is.

[0005]

In order to achieve the above object, a low-frequency component and a high-frequency component of an image are removed to remove a factor that hinders estimation of a feature point of the image. Power is obtained to remove localized fine fluctuations while simplifying the handling of the positive and negative values of, and the distribution position of feature points is set to the center in the probe movement direction (usually the horizontal direction of the screen) as much as possible. In the ultrasonic beam direction (usually the vertical direction of the screen), the power was weighted in order to deviate to a position distant, and the weighting was performed in order to select a feature point to be processed thereafter. Clustering is performed on the power, and the distribution function is applied to the representative feature points selected by clustering in order to make the subsequent image correlation result more effective and simplify the subsequent calculations. The cross-correlation between the bandpass of the spatial frequency component of the spliced image synthesized with the previous image and the bandpass of the current image to estimate the correspondence between the feature points is calculated on the immediately preceding spliced image. In order to find the corresponding feature point of the plurality of distribution peak positions from the correlation result, the feature point group of the current image and the feature point group of the immediately preceding joined image are matched to obtain the latest joined image. The present invention is characterized in that the current image is deformed and adhered to the immediately preceding joined image.

[0006]

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings. FIG. 1 is a block diagram showing an embodiment of the ultrasonic diagnostic apparatus according to the present invention. This ultrasonic diagnostic apparatus transmits / receives ultrasonic waves to / from a subject and displays an ultrasonic tomographic image or a blood flow image for a diagnostic site of the subject. As shown in FIG. It has a sound wave transmitting / receiving unit 2, a cine memory 3, a frame memory 4, and an image display unit 5, and further includes a feature point extracting unit 6 and an image joining unit 7.

The probe 1 transmits and receives ultrasonic waves to and from the subject by mechanically or electronically operating a beam. Although not shown, the probe 1 is a source of ultrasonic waves and a source for generating ultrasonic waves. It has one or more transducers for receiving reflected echoes from the body.

The ultrasonic transmission / reception unit 2 drives the probe 1 to generate ultrasonic waves and processes the received reflected echo signal. The ultrasonic transmission / reception unit 2 transmits the ultrasonic waves transmitted from the probe 1 into the subject. A known transmitting pulsar and a transmitting delay circuit for forming a beam, a receiving amplifier for amplifying a reflected echo signal received by each transducer of the probe 1, and adding the amplified received signals in phase. And a delay-and-sum circuit.

The cine memory 3 stores a plurality of frames of the signal from the ultrasonic transmission / reception unit 2 in time series, and has a memory for storing frame information.

The frame memory 4 writes the frame information from the cine memory 3 for each scanning line of the ultrasonic beam to form image data. The affine conversion circuit, the image data storage memory, and the color information are superimposed on the display unit. 5 has an overlay circuit.

The display unit 5 displays a signal from the frame memory 4 as an image, and includes, for example, a television monitor for inputting and displaying a television signal of a B-mode tomographic image.

The feature point extracting section 6 searches for the corresponding feature points from the time series data recorded in the cine memory and the joined image created by the image joining section 7.

The image joining section 7 transforms the information in the cine memory so that the feature points found by the feature point extracting section 6 coincide with each other, and adheres the information to the joined image created immediately before itself. The distance between two feature points obtained by the feature point extraction unit 6 from the image and the feature point extraction unit from the image joining unit 7
The width and height of the image from the cine memory are expanded or contracted by the ratio of the distance between the two feature points obtained in step 6. Next, the joining boundary is defined as a straight line passing over the two feature points. Further, a tapering process is performed on the above-mentioned boundary, and bonding is performed with a smooth luminance change.

FIG. 2 shows the feature point extracting unit 6 in more detail.
An embodiment will be described. The feature point extraction unit 6 includes a first filter unit 8, a power calculation unit 9, a weighting unit 10, a clustering unit 11, a correlation preprocessing unit 12, a cross-correlation unit 13, a corresponding point calculation unit 14, , A second filter unit 15.

The first filter section 8 selectively passes the spatial frequency of the image from the cine memory 3. In the present invention, the first filter section 8 has a pass band on a concentric circle centered on the spatial frequency 0 as shown in FIG. Characteristics. FIG. 10 shows details of the passband. In the present invention, when the Nyquist frequency is π, a band-pass filter is used in which the cutoff frequency in the low band is around π / 16 and the cutoff frequency in the high band is π / 4 to π / 2.

The power calculation unit 9 calculates the power of the image from the first filter unit 8, and as shown in FIG. 3, all the points P (within the radius r from the point of interest O (x, y). The calculation of the sum of squares of (x, y) and the power value at point O is performed for all (x, y).

The weighting unit 10 applies a predetermined weight to the power distribution from the power calculation unit 9, and in the present invention, this weight is used in the probe moving direction (normally) as shown in FIG. Is a value such that the weight increases toward the center in the horizontal direction of the screen, and a value decreases such that the weight decreases toward the center in the ultrasonic beam direction (normally, the vertical direction of the screen).

The clustering unit 11 includes a weighting unit 10
In the present invention, the position (x1, y1) where the largest peak is located and the component value Q1 are numbered 1, as shown in FIG. Then, the position (x2, y2) having the next largest peak and its component value Q2 are found as the second. In order to separate and recognize a peak position from a two-dimensional distribution having a plurality of peaks, a known propagation process is implemented.

The correlation pre-processing unit 12 includes the clustering unit 1
A weighting function is applied to the two peak positions and the component values obtained in step 1. The weighting function is multiplied by the output of the first filter unit 8 to cut out a local region of the image and to be generated accordingly. Truncation errors can be reduced. FIG. 6 illustrates a state in which a weighting function is applied so as to form a 3σ Gaussian distribution having peak component values Q1 and Q2 centered at two peak positions (x1, y1) and (x2, y2). It is. FIG. 6 shows a Gaussian distribution, but other distribution functions such as Hamming, Hanning, and Blackman-Harris may be used.

The cross-correlation section 13 calculates a correlation between the weight distribution from the pre-correlation processing section 12 and the image from the second filter section 15.

The corresponding point calculation unit 14 finds two peak positions and component values of the peak positions from the correlation distribution from the cross-correlation unit 13 and performs the same calculation as that of the cluster link unit 11. FIG. 7 shows the result 2 of the operation.
This is a state in which two peak positions (x3, y3) and (x4, y4) and component values Q3 and Q4 of these peak positions are obtained.

The second filter section 15 selectively passes a spatial frequency to the joined image from the image joining section 7 and performs the same processing as the first filter section 8.

Here, the overall operation will be described with reference to FIGS. First, the probe 1 is driven by the ultrasonic transmitting / receiving unit 2 to generate ultrasonic waves. The probe 1 performs a beam operation mechanically or electronically to transmit ultrasonic waves into the subject. The reception signal reflected from the subject and returned to the probe 1 is amplified by the ultrasonic transmission / reception unit 2, and the amplified reception signals are added in phase. In the present invention, a signal obtained by storing a plurality of frames in the cine memory 3 in a time series with the added signal is sent to the frame memory 4 and also sent to a feature point extracting unit 6 for selecting a feature point suitable for image joining.

As shown in FIG. 2, the feature point extracting section 6 first removes the low frequency component and the high frequency component of the spatial frequency of the image in order to remove a factor that hinders the estimation of the feature point of the image. The power is obtained by the power calculator 9 in order to simplify the handling of the positive / negative values of the filtered image and to remove the localized fine distribution fluctuations. Power is weighted to bias the probe in the center in the direction of probe movement (usually the horizontal direction of the screen) and away from the ultrasonic beam direction (normally in the vertical direction of the screen). This is performed by the weighting unit 10.

The clustering unit 11 performs clustering on the weighted powers for selecting the feature points to be processed thereafter, and makes the subsequent image correlation results more effective, thereby simplifying the subsequent calculations. The distribution pre-processing unit 12 applies a distribution function to a representative feature point group selected by clustering to obtain
The second filter unit 15 bandpasses the spatial frequency component of the spliced image synthesized with the image immediately before to estimate the correspondence between the feature points and the current image.
The cross-correlation with the band-passed one by the filter unit 8 is obtained by the cross-correlation unit 13.

Then, a plurality of distribution peak positions are obtained from the correlation result by the corresponding point calculation unit 14 to find the corresponding feature points on the immediately preceding joined image, and by the image joining unit 7 to obtain the latest joined image. The current image from the cine memory 3 is deformed so that the feature point group of the current image coincides with the feature point group of the immediately preceding joined image, and is adhered to the joined image immediately before joined by the image joining unit 7 itself. Here, the latest joint image is sent to the frame memory 4 and written for each scanning line of the ultrasonic beam to form image data. Finally, by sending an image signal from the frame memory 4 to the display unit 5, a joined image can be displayed.

[0027]

According to the present invention, since the movement of the human body cross section is estimated based on the characteristic portion of the image, it is possible to selectively process the image portion most suitable for joining, and thus the movement estimation error is reduced. As small as possible, robust estimation against image noise and artifacts can be performed, and images can be deformed so that feature points match each other, so that correct joint images can be obtained while correcting distortion of tomographic images Since the image joining part can be smoothly joined by tapering, a joined image without unnatural image quality change due to joining can be obtained, and the processing target can be limited to a characteristic part at an early stage. It is easy to increase the speed, and a high-quality joined image can be obtained.

[Brief description of the drawings]

FIG. 1 is an overall block diagram showing an embodiment of an ultrasonic diagnostic apparatus according to the present invention.

FIG. 2 is a block diagram showing details of a feature point extracting unit in FIG. 1;

FIG. 3 is an explanatory diagram showing details of a power calculator in FIG. 2;

FIG. 4 is an explanatory diagram showing details of a weighting unit in FIG. 2;

FIG. 5 is an explanatory diagram showing details of a clustering unit in FIG. 2;

FIG. 6 is an explanatory diagram showing details of a correlation pre-processing unit in FIG. 2;

FIG. 7 is an explanatory diagram showing details of a corresponding point calculation unit in FIG. 2;

FIG. 8 is a block diagram showing an embodiment of a conventional ultrasonic diagnostic apparatus.

FIG. 9 is an explanatory diagram showing details of a first filter unit in FIG. 2;

FIG. 10 is an explanatory diagram showing details of a spatial frequency characteristic in FIG. 9;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Probe 2 ... Ultrasonic transmission / reception part 3 ... Cine memory 4 ... Frame memory 5 ... Display part 6 ... Feature point extraction part 7 ... Image joining part 8 ... First filter part 9 ... Power calculation part 10 ... Weighting part 11 ... Clustering unit 12 ... Correlation preprocessing unit 13 ... Cross correlation unit 14 ... Corresponding point calculation unit 15 ... Second filter unit

Claims (1)

[Claims] 1. A method for automatically searching a time-series ultrasonic image acquired by sliding a probe in a longitudinal direction for the most suitable place having sufficient information for image joining from each ultrasonic image, An ultrasonic diagnostic apparatus characterized in that images are joined gradually with high precision using a plurality of points.