KR102115446B1 - Side lobe suppression method using centroid weighting for medical ultrasonic imaging - Google Patents

Abstract

The present invention relates to a side lobe suppression method using centroid weighting for a medical ultrasonic image. With the present invention, it is possible to effectively suppress a side lobe region without significant main lobe region deformation by using centroid weighting during reception and focusing of a channel signal received through an array transducer. The method includes: (a) a step in which an ultrasonic signal reflected at an image point is received at a receiving element of the array transducer and output as channel signals; (b) a step in which the channel signals are respectively focus-delayed and temporally aligned; (c) a step in which the centroid position with respect to the entire reception channel is calculated by means of each of the channel signals; and (d) a step in which the ultrasonic image is processed by means of a weight corresponding to the centroid position. According to the present invention, the image is processed by means of weighting corresponding to the centroid position, and thus the side lobe region can be effectively suppressed without main lobe region deformation. In the case of high-power ultrasound transmission, the present invention can be especially useful in detecting an ultrasonic signal generated in bubbles resulting from cavitation in the human body.

Description

A method for suppressing the side lobe using weight calculation of the center of mass position in medical ultrasound images {SIDE LOBE SUPPRESSION METHOD USING CENTROID WEIGHTING FOR MEDICAL ULTRASONIC IMAGING}

In the present invention, the side lobe is not significantly deformed in the region of the main lobe by using the weight calculation of the center of mass position in the process of receiving and focusing the channel signal received through the array transducer. The present invention relates to a method of suppressing side lobes by using a weighting calculation of a center of mass position in a medical ultrasound image capable of effectively suppressing an appearing area.

In general, an ultrasound imaging apparatus is a device for diagnosing lesions using ultrasound. When an ultrasound signal transmitted to a transducer is reflected inside the human body, the reflected signal is received and focused, and the magnitude of the ultrasound signal is adjusted to a predetermined brightness. It is converted into an image and imaged.

Ultrasound images have low resolution when compared with other medical images, despite the advantages of safety and real-time imaging. In order to increase the resolution of the ultrasound image, a method of focusing and transmitting ultrasound with a short pulse length using an array transducer is applied.

For example, by transmitting ultrasonic waves having a short pulse length in the axial direction and focusing in the lateral direction, the lateral width of the ultrasonic sound field is reduced. The size of the space occupied by the transmitting ultrasound at any point inside the human body becomes the spatial resolution of the ultrasound image. In the ultrasound imaging system, the ultrasound spatial resolution region has a finite size, and human tissue can be modeled as having many point reflectors non-uniformly distributed in the spatial resolution region.

Looking at the sound field in the ultrasonic focusing system, the main lobe is formed based on the scan line of the array transducer, and the side lobe due to leakage of the ultrasonic signal is formed on both sides. In this way, when the side lobe is formed, the signal from the reflector in that direction is also received, which causes noise in the image, thereby degrading the resolution of the image.

Various attempts to reduce side lobes in ultrasound images are disclosed in Patent Documents 1 and 2 below. However, since the following patent documents are a method of applying a weight to each received channel data, there is a problem that excessive calculation must be performed in order to reduce side lobe, and this problem increases as the number of channels increases.

On the other hand, the ultrasonic signal is reflected to have a different phase according to the position of the reflector in the human body, returns to the array transducer and overlaps in the focusing process. When the signals reflected from each reflector overlap, the signal amplitude increases when the constructive interference is performed, and the signal amplitude decreases when the cancelation interference is performed. This irregular signal appears as an inherent noise image called a speckle in the ultrasound image. When observing an ultrasound image, when the speckle noise is covered with an ultrasound image made of a signal returning from an organ inside the human body, it causes difficulties in diagnosis of detailed lesions. Therefore, as described in Patent Document 3 below, methods for removing speckle noise are being studied to improve the image quality of the ultrasound image.

However, in a speckle image in which many reflectors such as the human body are present, signals are randomly received in all receiving channels, and thus, when radiating ultrasonic waves in the human body, ultrasonic waves in bubbles generated by cavitation are detected. There is a difficult problem to do.

Patent Publication No. 10-2009-0042152 Registered Patent Publication No. 10-0971433 Registered Patent Publication No. 10-0778823

In the present invention, in the process of receiving and converging the channel signal received through the array transducer, the position of the centroid of the entire receiving channel is calculated, and the image is processed using a weight corresponding to the position of the center of mass, An object of the present invention is to provide a method of suppressing a side lobe using a weight calculation of a center of mass position in a medical ultrasound image that can effectively suppress a region where a side lobe appears without deforming the region of the main lobe.

A method of suppressing side lobes using weight calculation of a center of mass position in a medical ultrasound image according to an embodiment of the present invention includes: (a) receiving an ultrasound signal reflected from an image point at a receiving element of an array transducer and channel signal Outputting as; (b) arranging temporally by delaying focusing of the channel signals, respectively; (c) calculating a position of a centroid for all received channels using each of the channel signals; And (d) processing the ultrasound image using a weight corresponding to the location of the center of mass.

In a method for suppressing a side lobe using a weight calculation of a position of a center of mass in a medical ultrasound image according to another embodiment of the present invention, the step (c) uses the following (Equation 1) to determine the position of the center of mass. To calculate.

(Equation 1)

Here, Centroid is the center of mass position for all receive channels, r (ch) is the value of the signal received at the ch th receive channel, and Nch is the number of all receive channels.

In another embodiment of the present invention, a method of suppressing a side lobe using a weight calculation of a position of a center of mass in a medical ultrasound image, the step (c) is a position of the center of mass using (Equation 2) below. Computes

(Equation 2)

Here, Centroid is the center of mass position for all receive channels, r (ch) is the value of the signal received at the ch th receive channel, and Nch is the number of all receive channels.

In the method of suppressing the side lobe using the weight calculation of the center of mass position in the medical ultrasound image according to another embodiment of the present invention, the step (d) processes the ultrasound image using (Equation 3) below do.

(Equation 3)

PX _weighting = α ㆍ PX

Here, PX is an input video value, α is a weight, and PX _weighting is a video value after processing.

In a method of suppressing side lobes using weight calculation of a center of mass position in a medical ultrasound image according to another embodiment of the present invention, a triangular weight is applied to the weight.

In a method of suppressing side lobes using weight calculation of a center of mass position in a medical ultrasound image according to another embodiment of the present invention, the weight is applied to a fourth power of a Hamming window.

According to another embodiment of the present invention, in a method for suppressing side lobe using a weight calculation of a center of mass position in a medical ultrasound image, the step (d) is an area in which the weight of the input image value has a value greater than or equal to a predetermined value. The image value after the process is derived by multiplying the image value of.

According to another embodiment of the present invention, a method of suppressing side lobe using a weight calculation of a center of mass position in a medical ultrasound image, the predetermined value is 0.95.

According to a method of suppressing side lobes using a weight calculation of a center of mass position in a medical ultrasound image of the present invention, by processing an image using a weight calculation corresponding to a position of the center of mass (centroid), the main lobe The area where side lobes appear can be effectively suppressed without deforming the area, and ultrasonic signals generated by bubbles generated by cavitation in the human body can be effectively suppressed, especially when transmitting high-power ultrasound. There is an effect that can be usefully used to detect.

1 is a block diagram showing an example of an ultrasound imaging apparatus for implementing the present invention.
2 is a view illustrating the shape of the signal and the position of the center of mass of the ultrasonic signal (a) returned from the on-axis and the ultrasonic signal (b) returned from the off-axis. to be.
3 is a flowchart illustrating a method of suppressing side lobes by using a weighting operation of a center of mass position in an ultrasound image according to the present invention.
4 is a view showing an example of the weight used in the present invention, the solid line is a triangle weight, the dotted line is a diagram showing the fourth weight of the Hamming window (Hamming window).
FIG. 5 is a diagram illustrating the results of image processing by computer simulation of the results of the present invention, (a) is a point spread function (PSF), and (b) is apodization using a Hamming window. ), (C) is the image of the center of mass triangle weighting operation, (d) is the image of the center of mass hamming weighting operation, and the image of the region having an α value of 0.95 or more, (e) is ( The result image multiplied by a) and (c), and (f) is the result image multiplied by (a) and (d).
Figure 6 is a view comparing the lateral sound field characteristics in the results of Figure 5, the solid line is the PSF of Figure 5 (a), the disadvantage line is the image of Hamming apodization of Figure 5 (b), the advantage line is Figure 5 (f) ) Is multiplied by the PSF by an α value of 0.95 or more, respectively.

Hereinafter, specific embodiments of the present invention will be described with reference to the accompanying drawings. However, this is not intended to limit the present invention to specific embodiments, and should be understood to include all modifications, equivalents, and substitutes included in the spirit and scope of the present invention.

The same reference numerals are used for parts having similar configurations and operations throughout the specification. And the drawings attached to the present invention are for convenience of description, the shape and relative scale may be exaggerated or omitted.

In describing the embodiments in detail, overlapping descriptions or descriptions of technologies that are apparent in the art have been omitted. Also, in the following description, when a part “includes” another component, it means that the component may be further included in addition to the described component, unless otherwise stated.

In addition, terms such as “~ unit”, “~ group”, and “~ module” described in the specification mean a unit that processes at least one function or operation, which may be implemented by hardware or software or a combination of hardware and software. Can be. In addition, when it is said that a part is electrically connected to another part, this includes not only a case in which it is directly connected, but also a case in which another component is interposed therebetween.

Terms including ordinal numbers such as first and second may be used to describe various components, but the components are not limited by the terms. The terms are used only for the purpose of distinguishing one component from other components. For example, the second component may be referred to as the first component without departing from the scope of the present invention, and similarly, the first component may also be referred to as the second component.

1 is a block diagram showing an example of an ultrasound imaging apparatus for implementing the present invention.

Referring to FIG. 1, the ultrasound imaging apparatus includes an array transducer 100, a receiving focusing unit 200, an image processing unit 300, and a display means 400.

The array transducer 100 is a unit that linearly arranges a plurality of transducers (receiving elements) that transmit ultrasonic waves and receive reflected signals. The ultrasonic signal of each channel received by the array transducer 100 is divided into a specular signal reflected from the internal organs of the human body and a speckle signal reflecting characteristics of non-uniformly distributed reflectors. Can be.

The reception focusing unit 200 delays the signal returned from an organ inside the human body to focus the reception, align in time, and demodulate to form a scanning line. The specular signal has a shape of a highly correlated signal in all channels, and the speckle signal is added or canceled to the phase of the signal in the receiving channel according to the distribution of reflectors and the position of the array transducer.

Referring to FIG. 1, the reception focusing unit 200 includes a focusing delay unit 210, a channel selection unit 220, and a demodulation unit 230.

The focusing delay unit 210 adjusts focusing delay for each channel in order to temporally align a plurality of channel signals in which an arrival time difference occurs in a process in which the signal reflected by the reflector reaches the array transducer 100. do.

The channel selector 220 selects an arbitrary channel by applying a specific function to a plurality of channel signals that are temporally aligned due to focusing delay.

The multi-channel focused signals output from the channel selector 220 are added and then demodulated by the demodulator 230 to form one scan line.

The image processing unit 300 synthesizes a plurality of scanning lines to form a unit image frame, stores unit image frames corresponding to a selected channel, and averages the image to form an ultrasound image. The ultrasound image is displayed through the display means 400.

2 is a view illustrating the shape of the signal and the position of the center of mass of the ultrasonic signal (a) returned from the on-axis and the ultrasonic signal (b) returned from the off-axis. to be.

When a focusing delay time is applied to a receiving channel signal of the array transducer 100 arranged in a multi-channel, a signal returned from an image point is received in the same phase on-axis with respect to all receiving channels. However, the signal returned from the off-axis is received in a different phase to the receiving channel according to the incident direction of echo. The ultrasound imaging apparatus transmits an ultrasound pulse signal having a short time length for axial resolution. Therefore, the signal returning from the off axis arrives at an angle of incidence to the receiving array transducer, and thus does not arrive at the receiving channel at the same time, but is only partially received.

Figure 2 (a) is a signal shape of the receiving channel of the ultrasonic waves returned from the image point, and since all channels are received in the same phase, a signal having a uniform size appears across all channels. Here, the transmission pulse is assumed to be a sine wave of several cycle lengths.

2 (b) is an ultrasonic signal returned from the off-axis direction. Since the time length of the ultrasonic pulse signal is short, the signal appears only in part of the entire reception channel according to the incident angle.

The receiving focusing process compensates the focusing delay time and then adds all channel signals. The signal returned from the on axis becomes a large signal by adding all the received channel data, but all signals returned from the off axis must be removed. However, the signal remains even if all the channel signals are added during the focusing process, which appears as a clutter or side lobe and affects the image.

In the medical ultrasound image of the present invention, a method of suppressing side lobes using weight calculation of a center of mass position, calculates a position of a centroid for all receiving channels, and calculates a weight corresponding to the position of the center of mass Suggestions are made to suppress side lobes.

First, the process of calculating the position of the center of mass will be described with reference to FIG. 2.

Referring to FIG. 2 (b), the signal returned from the off-axis has a different distribution of signals appearing on the receiving channel depending on the direction in which the signal returns, so the center of mass is a parameter indicating the distribution in which the received signal exists in all receiving channels ( centroid). The position of the center of mass using all channel signals received at a specific time can be calculated by (Equation 1) below.

(Equation 1)

Here, Centroid is the center of mass position for all receive channels, r (ch) is the value of the signal received at the ch th receive channel, and Nch is the number of all receive channels.

As a result of the calculation of Equation (1), the position of the center of mass of the size of the entire received channel signal can be obtained as a value corresponding to the position of the channel. In the case of FIG. 2 (a), since the signal size is the same in all channels, when the position of the center of mass is obtained, it appears in the center position of the reception channel. However, in the case of FIG. 2 (b), the center of mass is located at a position away from the center of the aperture.

That is, the closer the position of the center of mass is to the position of the center channel, the more likely it is the signal returned from the on-axis. Therefore, in the case of an on-axis signal, the image value is multiplied by a large weight value. On the other hand, the closer the position of the center of mass is to the position of the edge channel, the more likely it is the signal from the off-axis. Therefore, the signal returned from the off-axis can suppress the off-axis signal by multiplying the small weight.

Even if (Equation 1) is transformed into the following (Equation 2), good results can still be obtained.

(Equation 2)

Here, Centroid is the center of mass position for all receive channels, r (ch) is the value of the signal received at the ch th receive channel, and Nch is the number of all receive channels.

3 is a flowchart illustrating a method of suppressing side lobes by using a weighting operation of a center of mass position in an ultrasound image according to the present invention.

Referring to Figure 3 to describe the method of inhibiting the side lobe according to the present invention.

First, in the block diagram illustrated in FIG. 1, the ultrasonic signal reflected from the image point is received by the receiving element of the array transducer 100 and output as a channel signal (ST310).

Then, the reception focusing unit 200 arranges the output channel signals in time by delaying focusing respectively (ST320).

Next, as described with reference to FIG. 2, the position of the centroid of the entire receiving channel is calculated using each of the channel signals (ST330). For example, the position of the center of mass can be calculated by (Equation 1) or (Equation 2).

Finally, the ultrasound image is processed using a weight corresponding to the location of the center of mass (ST340). The ultrasound image processing process using the weight will be described with reference to FIG. 4.

FIG. 4 is a diagram showing an example of weights used in the present invention. The solid line is a triangle weight, and the dotted line is a fourth square weight of a Hamming window.

Referring to FIG. 4, when the position of the centroid is located in the center channel, the weight is 1, and when it is located at both ends of the channel, the weight is normalized to 0 and calculated. That is, the weight has a value of 0 or more and 1 or less.

A value having a weight close to 1 means that the received channel signal is returned from the on-axis, and as it is smaller than 1, it means that the signal from the off-axis is included more. In FIG. 4, the weight using the fourth power of the Hamming window compared to the triangle weight depicted as a solid line may determine a larger weight for the signal returned from the on-axis.

The ultrasound image processing using the weight of step ST340 may be calculated through (Equation 3) below.

(Equation 3)

PX _weighting = α ㆍ PX

Here, PX is an input video value, α is a weight, and PX _weighting is a video value after processing.

FIG. 5 is a diagram illustrating the results of image processing by computer simulation of the results of the present invention, (a) is a point spread function (PSF), and (b) is apodization using a Hamming window. ), (C) is the image of the center of mass triangle weighting operation, (d) is the image of the center of mass hamming weighting operation, and the image of the region having an α value of 0.95 or more, (e) is ( The resulting image multiplied by a) and (c), and (f) represents the result image multiplied by (a) and (d).

The computer simulation of FIG. 5 is a point spread function (PSE) obtained by placing a point target at 50 mm. As a simulation condition, a 5 MHz linear array was used, and the width of each element constituting the array was set to 0.3 mm corresponding to one wavelength. Also, a 64-channel transmission / reception system is assumed, the transmission focusing depth is 30 mm, and dynamic reception focusing is performed. The image was log compressed to 60 dB to distinguish side lobes.

FIG. 5 (a) is a PSF, and FIG. 5 (b) is an image obtained by apodizing a reception channel using a Hamming window. 5 (c) is an image performed by performing a weighting operation (centroid weighting) corresponding to the center of mass calculated at all image points by applying the triangle weight illustrated in FIG. 4. When comparing FIGS. 5 (a) and 5 (c), it can be seen that a tendency to have a small value of α in the region where the side lobe appears.

FIG. 5 (d) is an image of an area where α has a value of 0.95 or more in the weight of the Hamming window depicted with a dotted line in FIG. 4. 5 (e) shows an image multiplied by FIGS. 5 (a) and 5 (c), and FIG. 5 (f) shows an image multiplied by 5 (a) and 5 (d). In FIG. 5 (f), it can be seen that most of the areas where the side lobes appear are suppressed. When multiplied by the image value using an appropriate α value, the signal region caused by the main lobe is maintained and the side lobe region is It can be confirmed that it can be effectively suppressed.

6 is a view comparing the lateral sound field characteristics in the results of FIG. 5, the solid line is the PSF of FIG. 5 (a), the disadvantage line is the image of Hamming apodization of FIG. 5 (b), and the advantage line is FIG. 5 (f) ) Is multiplied by the PSF by an α value of 0.95 or more, respectively.

Referring to FIG. 6, as a result of performing weighting corresponding to the center of mass position (centroid weighting) as in the present invention, the side lobe appears without deforming the main lobe even in the lateral sound field characteristics. It can be seen that can be effectively reduced.

According to the method of suppressing the side lobe using weight calculation of the center of mass position in the medical ultrasound image of the present invention, the area of the region where the side lobe appears in the ultrasound image can be reduced by suppressing the side lobe using centroid weighting.

However, in a speckle image in which many reflectors such as the human body are present, since a random signal is received in all receiving channels, it is difficult to distinguish the side lobe signal only by using the location of the center of mass, and proper weight calculation is performed. By adding, it was confirmed that it is useful for imaging a signal source in the form of a point source. The method of suppressing side lobes of the present invention is particularly useful when detecting ultrasonic signals when bubbles are generated by cavitation when emitting ultrasound waves in the human body. For example, it is suitable for detecting ultrasonic signals reflected from bubbles generated by cavity formation by transmitting high power ultrasonic waves.

The invention disclosed above can be modified in various ways without deteriorating the basic idea. That is, all of the above embodiments should be interpreted by way of example, and not of limitation. Therefore, the protection scope of the present invention should be determined according to the appended claims rather than the above-described embodiments, and when the components defined in the appended claims are replaced with equivalents, it should be regarded as belonging to the protection scope of the present invention.

100: array transducer 200: receiving concentrator
210: focusing delay unit 220: channel selection unit
230: demodulation unit 300: image processing unit
400: display means

Claims (8)

(A) receiving the ultrasonic signal reflected from the image point at the receiving element of the array transducer and outputting it as a channel signal;
(b) arranging temporally by delaying focusing of the channel signals, respectively;
(c) calculating a position of a centroid for all received channels using each of the channel signals; And
(d) processing an ultrasound image using a weight corresponding to the location of the center of mass
Method for suppressing the side lobe using weight calculation of the position of the center of mass in the medical ultrasound image including a.
According to claim 1,
The step (c) is a method of suppressing the side lobe using weight calculation of the center of mass position in a medical ultrasound image for calculating the position of the center of mass using Equation 1 below.
(Equation 1)

Here, Centroid is the center of mass position for all receive channels, r (ch) is the value of the signal received at the ch th receive channel, and Nch is the number of all receive channels.
According to claim 1,
The step (c) is a method of suppressing the side lobe using weight calculation of the center of mass position in the medical ultrasound image for calculating the position of the center of mass using Equation 2 below.
(Equation 2)

Here, Centroid is the center of mass position for all receive channels, r (ch) is the value of the signal received at the ch th receive channel, and Nch is the number of all receive channels.
According to claim 1,
The step (d) is a method of suppressing the side lobe using a weighting operation of the center of mass position in the medical ultrasound image processing the ultrasound image using (Equation 3) below.
(Equation 3)
PX _weighting = α ㆍ PX
Here, PX is an input video value, α is a weight, and PX _weighting is a video value after processing.
The method of claim 4,
The weight is a method of suppressing the side lobe using a weight calculation of the center of mass position in a medical ultrasound image to which a triangle weight is applied.
The method of claim 4,
The weight is a method of suppressing the side lobe using a weighting operation of the center of mass position in a medical ultrasound image applying a fourth power of a Hamming window.
The method of claim 6,
The step (d) suppresses the side lobe by using a weighting operation of the center of mass position in the medical ultrasound image to derive the image value after the processing by multiplying the input image value by the image value of an area where the weight has a value greater than or equal to a predetermined value. How to.
The method of claim 7,
The predetermined value is 0.95 method of suppressing the side lobe using a weight calculation of the center of mass position in the medical ultrasound image.

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