KR101433032B1 - Method and apparatus of producing functional flow images using plain wave - Google Patents

Abstract

The present invention relates to an apparatus for generating a functional blood flow image using a plane wave, the apparatus comprising: a transducer for transmitting a plane wave to a target object and receiving an ultrasound signal reflected from the target object; A reception beam focusing unit for beam focusing the ultrasound signal by applying a reception time delay; An orthogonal demodulator for generating an in-phase component and an ideal component from the beam-focused signal; A velocity calculation unit for calculating a blood flow velocity at an image point on a two-dimensional cross-section from the in-phase component and the ideal component; A mapping unit for mapping the blood flow velocity to an image point; And a display unit for displaying a blood flow velocity mapped to an image point. In order to improve the accuracy of blood flow information analysis, a large number of samples are secured and blood flow characteristics index You can show color images.

Description

TECHNICAL FIELD The present invention relates to a method and apparatus for generating a functional blood flow image using a plane wave,

The present invention relates to a functional blood flow image generating apparatus, and more particularly, to a functional blood flow image generating apparatus capable of obtaining a large number of samples in order to improve the accuracy of blood flow information analysis and to provide functional blood flow images using a plane wave showing a color image on a two- And more particularly, to a method and apparatus for generating an image.

An ultrasound medical imaging system is a device that transmits and receives ultrasound signals in the human body and then uses the information contained in the reflected signals to image the structure and characteristics of the human body noninvasively. Ultrasound medical imaging devices provide various types of clinical information. Of these, Doppler imaging techniques used for real-time blood flow information in the human body are becoming increasingly important.

Quantitative information on velocity and changes in blood flow within the human body, distribution of one- or two-dimensional blood flow, cross-sectional and cubic morphology of blood vessels and the heart are very important in diagnosing cardiovascular diseases. Therefore, techniques for extracting information on blood flow in various ways have been actively studied.

However, most of the methods have a problem that blood flow information at a specific position inside the human body can not be separately observed. The ultrasonic Doppler system has been widely used as an indispensable device for diagnosing diseases of the circulatory system because it has made rapid technological progress in recent years and can solve such problems and provide dynamic information according to the time of blood flow.

Over the past decades, existing ultrasonic diagnostic devices have been limited to the role of anatomical structures in the human body based on B-mode, color flow, and Doppler mode, and function tests have to be performed based on anatomical information to diagnose diseases. Recently, many functional flow image techniques have been studied. Functional blood flow imaging is not only imaging anatomical signals, but also analyzing the characteristics of blood flow signals, quantifying them, and displaying them as indicators. Functional blood flow imaging differs from conventional anatomical imaging in that it imaged functional aspects of what is happening in the body.

In order to properly analyze the characteristics of a bio-signal, accurate information about the bio-signal must be provided. The provided bio-signal is blood flow information calculated from the Doppler frequency. In order to obtain the Doppler frequency, it is necessary to transmit and receive as many times as the number of ensembles, so that the frame rate of the color Doppler image is limited.

At this time, the frame rate of the color Doppler image is the sampling frequency of the blood flow information. There must be sufficient blood flow information for high accuracy of blood flow information analysis. That is, the sampling rate must be high. In order to overcome these limitations, many studies have been made, and in commercialized devices through interleave techniques, color Doppler images of 10 ~ 20Hz in average are provided in real time. However, there are limitations in analyzing the characteristics of blood flow velocity in a cardiac cycle with samples of about 10 to 20 per second. Therefore, currently commercialized equipment provides a function to analyze blood flow characteristics only in spectral Doppler mode. However, the spectral Doppler mode can be analyzed only in one range gate on one dimension. Thus, the range of use is limited and it takes a lot of time to obtain information on a two-dimensional cross-section in clinical practice.

Therefore, in order to improve the accuracy of the blood flow information analysis, it is necessary to acquire a large number of samples and to display the blood flow characteristics on a two-dimensional sectional image in a colorimetric manner while taking a small amount of time using flow indices.

Therefore, the first problem to be solved by the present invention is to obtain a large number of samples in order to improve the accuracy of the blood flow information analysis, to obtain a functional blood flow which can display color images on a two- And an image generating device.

The second problem to be solved by the present invention is to estimate the cardiac cycle using only the signals imaged without the electrocardiogram signal and to provide the two-dimensional images, so that the whole tendency can be grasped at a glance, And to provide a functional blood flow image generating method capable of improving the accuracy of water channel diagnosis.

It is another object of the present invention to provide a computer-readable recording medium storing a program for causing a computer to execute the above-described method.

In order to achieve the first object, the present invention provides a transducer for transmitting a plane wave to a target object and receiving an ultrasound signal reflected from the target object; A reception beam focusing unit for beam-focusing the ultrasonic signal by applying a reception time delay; An orthogonal demodulator for generating an in-phase component and an ideal component from the beam converged signal; A velocity calculation unit for calculating a velocity of blood flow at an image point on a two-dimensional section from the in-phase component and the abnormal component; A mapping unit for mapping the blood flow velocity to the image point; And a display unit for displaying a blood flow velocity mapped to the image point.

According to an embodiment of the present invention, the apparatus further includes a blood flow index generator for generating a blood flow index from the blood flow velocity calculated at the image point, wherein the mapping unit maps the blood flow index to the image point, It is possible to display the blood flow index mapped to the point.

Further, the image processing apparatus may further include a variance calculation section for calculating a variance of the power spectrum from the in-phase component and the abnormal component, the mapping section maps the variance to the image point, and the display section displays the variance mapped to the image point .

The apparatus may further include a Doppler frequency estimator for estimating an average frequency of the power spectrum generated from the in-phase component and the abnormal component, and the velocity calculator may calculate the blood flow velocity from the estimated average frequency. The Doppler frequency estimator may estimate the average frequency of the power spectrum using an autocorrelation method or a cross-correlation method that can calculate the average frequency of the power spectrum on a time axis.

Another aspect of the present invention is a transducer for transmitting a plane wave to a target object and receiving an ultrasound signal reflected from the target object. A reception beam focusing unit for beam-focusing the ultrasonic signal by applying a reception time delay; An orthogonal demodulator for generating an in-phase component and an ideal component from the beam converged signal; A velocity calculation unit for calculating a velocity of blood flow at an image point on a two-dimensional section from the in-phase component and the abnormal component; A blood flow index generator for generating a blood flow index from the blood flow velocity calculated at the image point; A mapping unit for mapping the blood flow index to the image point; And a display unit for displaying a blood flow index mapped to the image point.

According to another embodiment of the present invention, the blood-flow indicator generating unit includes an envelope detector that detects an envelope from a blood flow velocity stored corresponding to the image point; A heart cycle detector for detecting at least two maximum values of the envelope by passing the envelope through a threshold filter to detect one cardiac cycle signal; A maximum / minimum value detector for detecting a maximum value, a minimum value, or an average value from the detected cardiac cycle signal; And an indicator generating unit for generating a blood flow indicator using at least one of the maximum value, the minimum value, and the average value, and the indicator generator may transmit the generated blood indicator to the mapping unit. At this time, the blood flow index is representative of a resistance index and a pulse index, and various other blood flow indexes can be used.

According to another aspect of the present invention, there is provided a method of transmitting ultrasonic waves, comprising the steps of: transmitting a plane wave to a target object and receiving an ultrasound signal reflected from the target object; A beam focusing step of applying the ultrasonic signal with a reception time delay; Generating an in-phase component and an ideal component from the beam focused signal; Calculating a blood flow velocity at an image point on a two-dimensional cross-section from the in-phase component and the abnormal component; Mapping the blood flow velocity to the image point; And displaying a blood flow velocity mapped to the image point.

According to another aspect of the present invention, there is provided an ultrasonic diagnostic apparatus comprising: a receiving unit that receives a reflected ultrasound signal from a target object; A beam focusing step of applying the ultrasonic signal with a reception time delay; Generating an in-phase component and an ideal component from the beam focused signal; Calculating a blood flow velocity at an image point on a two-dimensional cross-section from the in-phase component and the abnormal component; Generating a blood flow index from the blood flow velocity calculated at the image point; Mapping the blood flow index to the image point; And displaying a blood flow index mapped to the image point.

According to another aspect of the present invention, there is provided a computer-readable recording medium storing a program for causing a computer to execute the above-described method for generating a functional blood flow image.

According to the present invention, a sufficient number of samples can be secured to improve the accuracy of blood flow information analysis, and a color image can be displayed on a two-dimensional cross section while taking a short time using the blood flow characteristic index. Further, according to the present invention, since the heart cycle is estimated by only the signal imaged without the electrocardiogram signal and is also provided as the two-dimensional image, the whole tendency can be grasped at a glance, Can be improved.

1 is a view showing a concept of acquiring a functional blood flow index image.
FIG. 2 is a block diagram of a functional blood flow image generating apparatus according to a preferred embodiment of the present invention.
3 shows a general transmission beam focusing method and a plane wave transmission method according to the present invention.
4 is a flowchart of a functional blood flow index generation method according to an embodiment of the present invention.
5 is a flowchart of a blood flow velocity and variance calculation method according to an embodiment of the present invention.
6 is a flowchart of a blood flow index generation method according to an embodiment of the present invention.
FIG. 7 shows signals in respective steps of the blood flow index generation method according to the embodiment of the present invention.
FIG. 8 shows a configuration of a two-dimensional color flow image.
FIG. 9 shows a method of mapping a blood flow velocity of a two-dimensional color flow image.
FIG. 10 is a diagram illustrating a transmitting and receiving process of the functional blood flow image generating apparatus according to the present invention.

Prior to the description of the concrete contents of the present invention, for the sake of understanding, the outline of the solution of the problem to be solved by the present invention or the core of the technical idea is first given.

According to an embodiment of the present invention, there is provided an apparatus for generating a functional blood flow image, including: a transducer for transmitting a plane wave to a target object and receiving an ultrasound signal reflected from the target object; A reception beam focusing unit for beam-focusing the ultrasonic signal by applying a reception time delay; An orthogonal demodulator for generating an in-phase component and an ideal component from the beam converged signal; A velocity calculation unit for calculating a velocity of blood flow at an image point on a two-dimensional section from the in-phase component and the abnormal component; A mapping unit for mapping the blood flow velocity to the image point; And a display unit for displaying a blood flow velocity mapped to the image point.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. It will be apparent to those skilled in the art, however, that these examples are provided to further illustrate the present invention, and the scope of the present invention is not limited thereto.

BRIEF DESCRIPTION OF THE DRAWINGS The above and other objects, features and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings, in which: It is to be noted that components are denoted by the same reference numerals even though they are shown in different drawings, and components of different drawings can be cited when necessary in describing the drawings. In the following detailed description of the principles of operation of the preferred embodiments of the present invention, it is to be understood that the present invention is not limited to the details of the known functions and configurations, and other matters may be unnecessarily obscured, A detailed description thereof will be omitted.

In addition, in the entire specification, when a part is referred to as being 'connected' to another part, it may be referred to as 'indirectly connected' not only with 'directly connected' . In the present specification, the singular form includes plural forms unless otherwise specified in the specification. &Quot; comprises " or "comprising" when used herein should be interpreted as excluding the presence or addition of one or more other elements, steps, operations, or elements in addition to the stated element, step, I never do that.

Hereinafter, the functional blood flow image referred to in the present invention includes functional blood flow indicator images and color Doppler images.

Functional blood flow index images are generated by analyzing the blood flow characteristics of each image point from color Doppler images of various frames. At this time, one blood flow characteristic index is calculated based on the cardiac cycle.

1 is a view showing a concept of acquiring a functional blood flow index image.

Referring to FIG. 1, first, in order to acquire a functional blood flow indicator image, it is necessary to confirm whether or not a current cardiac cycle signal can be normally expressed without aliasing in a currently obtained color Doppler image. To verify this, we use Nyquist Sampling Theorm. The frame rate of the color Doppler image is based on the sampling frequency of the blood flow velocity signal, and the heartbeat per second can be assumed to be the dominant frequency of the signal.

In the color Doppler image, several times of transmission and reception are performed in order to use the Doppler effect. This limits the frame rate in the color Doppler image, which means that the sampling frequency is limited. If the sampling frequency is limited, the frequency of the recoverable signal is also limited, so you should consider whether aliasing occurs. If aliasing occurs, it is not possible to analyze blood flow characteristics using only blood flow information provided by color Doppler imaging, and blood flow velocity analysis should be performed after reconstructing signals without aliasing using external signals such as electrocardiogram.

The maximum heart rate of a person is 210-220 times per minute for newborn babies, and the heart rate decreases with age. The fastest heartbeat has a frequency of about 3.67Hz per minute for approximately 220 pulses per minute. If the bandwidth of the signal is called BW (Bandwidth) and it is applied to the Nyquist sampling theory to check whether aliasing is performed, it can be confirmed that aliasing does not occur when the sampling frequency is higher than 7.34 (+ BW) Hz. If aliasing occurs, the aliasing can be eliminated by raising the frame rate of the color Doppler image while limiting the view depth (View depth).

For a typical adult male, the heart rate is about 60 to 150, so it has a maximum frequency of 2.5 Hz. Since the frame rate in general color Doppler is 10 Hz to 20 Hz, it can be assumed that aliasing does not occur since the frame rate is 4 times or more the main frequency. Therefore, aliasing does not occur in the current color Doppler image, and blood flow characteristics can be extracted by modeling the blood flow normally. Therefore, aliasing does not occur at the frame rate of the currently commercialized color Doppler image.

However, this is an example in which there is no abnormality in the blood flow. In the case of having a vascular disorder, the blood flow signal locally may have a wider frequency band. Therefore, in order to acquire more accurate functional blood flow index information, it is desirable to have a higher frame rate (sampling frequency of functional blood flow indicator image) than the color Doppler image of existing commercialized equipment.

The functional blood flow image generating apparatus according to an embodiment of the present invention, which will be described below, obtains an accurate Doppler index by securing sufficient blood flow velocity information in one cardiac cycle at a constant data acquisition rate using a plane wave have. Further, by using a method of transmitting and receiving once to generate one frame, the frame rate of the Doppler image can be increased. Through this, it is possible to calculate a functional blood flow index in an accurate blood vessel by securing a larger number of samples.

FIG. 2 is a block diagram of a functional blood flow image generating apparatus according to a preferred embodiment of the present invention.

2, the functional blood flow image generating apparatus according to the present embodiment includes a pulsar 210, a transducer 220, a receiving beam focusing unit 230, a DC removing filter unit 240, a right angle demodulating unit 250, A Doppler unit 260, a blood flow index generating unit 270, a mapping unit 280, and a display unit 290.

The pulser 210 generates and transmits a plane wave to the transducer 220.

First, a general plane wave will be described as an example, and one frame can be generated through one transmission and reception. However, the SNR and the resolution of the image are lower than those of the conventional focus image technique. However, the plane wave transceiver can be implemented simply and can be used in a carotid artery requiring a low depth because it provides a high frame rate.

On the other hand, SNR is lower than that of the conventional focusing image technique because transmission focusing is not performed using a plane wave. Thus, coded excitation techniques can be used to image deep depths.

The coded excitation technique improves the SNR by increasing the transmission energy by 15 ~ 20dB without increasing the transmit peak voltage.

Chirp, Golay, Barker, etc. are used in the coding excitation technique. In order to improve the SNR, it is necessary to use a long code. For the Barker code, the longest length has a length of 13 bits.

When using the coded excitation technique, a filter is required to decode the long coded signal at the receiving end. This filter is called a decode filter or a compress filter, and can be configured as a matched filter or a mismatched filter. The decoding filter is preferably located between the DC rejection filter portion and the orthogonal demodulation portion.

Also, a compounding technique can be used for plane wave transmission. The compounding technique is to transmit and receive plane waves at various angles during transmission and synthesize them to produce a single image. Because the compounding technique requires transmission and reception of plane waves several times, the frame rate drops by the number of times it is synthesized. On the other hand, as the number of composites increases, the quality and reliability of the image increases, so a trade-off is required. Even when the compounding technique is used, a frame rate of several times to several tens of times is secured as compared with the conventional focusing image technique, and thus a sufficient frame rate can be secured.

The transducer 220 transmits the plane wave received from the pulser 210 to the object and receives the ultrasonic signal reflected from the object.

The reception beam focusing unit 230 focuses the ultrasound signals reflected by the object and applying the reception time delay to the beams. That is, the electric signal generated by the pulsar 210 is converted into an ultrasonic signal through a transducer and is transmitted and received into the object. The received signal is applied to the reception beam focusing unit 220 through an appropriate reception time delay Thereby focusing the beam.

The DC elimination filter unit 240 removes a DC component generated by an analog to digital converter (ADC).

The orthogonal demodulator 250 generates an inphase component and a quadrature component of the baseband. The envelope detection and the Doppler component of the received signal can be detected using the generated in-phase component and the ideal component.

The Doppler unit 260 calculates the blood flow velocity and the dispersion using the baseband in-phase and the abnormal component signals.

The Doppler unit 260 acquires blood flow information at every image point on a two-dimensional cross-section to be examined using a burst pulse pulse of a limited cycle. Then, the mapping unit 280 maps the obtained blood flow information into a color, and displays the color mapped by the display unit 290 and displays it on the screen in real time. At this time, the velocity information of the blood flow can be obtained by using the Doppler phenomenon between the ultrasonic waves and the moving red blood cells in the bloodstream.

The Doppler unit 260 includes a clutter filtering unit 261, a Doppler frequency estimating unit 262, a velocity calculating unit 263, and a dispersion calculating unit 264.

The clutter filtering unit 261 removes a clutter that is reflected from a blood vessel wall or a body tissue, rather than a signal reflected from a blood stream (red blood cells) to be measured using a clutter filter. The clutter signal is a signal that exists in a very low band in the frequency spectrum. At this time, a clutter filter can be designed using an infinite impulse response filter (IIR filter). The clutter filter is needed to remove the clutter components and reduce the error of Doppler frequency estimation of the blood flow.

The Doppler frequency estimator 262 estimates an average frequency by an autocorrelation method or a cross-correlation method capable of calculating an average frequency of received ultrasonic signals on an ensemble basis in a time axis.

A method of estimating the average frequency by the Doppler frequency estimator 262 will be described in detail with reference to an autocorrelation method as follows.

Assuming that the input of the Doppler frequency estimator 262 is z (k) = i (k) + jq (k), obtaining the average frequency of the Doppler signal is equivalent to obtaining the average frequency of the power spectrum of z (k).

The process of estimating the average frequency using the autocorrelation method that can calculate the average frequency of the power spectrum on the time axis is as follows.

Let us suppose that the continuous time function corresponding to z (k) is z (t) = i (t) + jq (t). If the power spectrum of z (t) is denoted by S (f), the mean frequency to be obtained is as follows.

S (f) is the Fourier transform of the autocorrelation function R (τ) of z (t), and the relationship between these functions is

From Equation (2), the following relationships can be derived.

Therefore, Equation (1) can be expressed as Equation (6) and Equation (7) as follows.

Now, if R (τ) is expressed as follows,

The following relation holds from the equation (5).

In other words, A (τ) and Φ (τ) have the following symmetry.

Now, using Equation (9) and Equation (11), Equation (8) can be rewritten as follows.

The Doppler frequency estimator 262 can not calculate Equation 12 because z (k) is used as an input and R (?) Is also an autocorrelation function defined by? = NT (T is 1 / PRF) , Instead use the approximate value as follows.

Now, since R (T) is defined as follows,

Equation (14) can be rewritten as

를 구하는 식을 나타내고 있다.Referring to Equation (15), an autocorrelation value having a time delay of one sample of the i (k) signal and the q (k) signal, which are the in-phase and the abnormal input signals, is obtained, To match the frequency

Is obtained.

는 다음과 같은 영역을 가짐을 알 수 있다.In Equation 15, tan ^-1 () is a phase value, and thus has a value of -π to + π. Therefore,

Can be found to have the following areas.

Area of measurable Doppler frequency from the equation (16) it can be seen that _{-PRF / 2 <f d <PRF} / 2.

The velocity calculator 263 estimates the velocity of blood flow from the estimated Doppler frequency.

The ultrasonic wave is incident at an angle θ with respect to the direction of blood flow in the blood vessel, the moving velocity of the blood cell is V [m / sec], and the incident frequency f ₀ and the reflection frequency f _r And the speed of the ultrasonic wave is C [m / sec], the Doppler shift f _D is approximated as follows.

When the negative incidence of θ ^o cos90 is the 90 ^o in this case is not measured is the Doppler frequency bias so zero. Here, the moving velocity of the blood cells is V [m / sec], which generally ranges from 0.2 cm / sec to 2 m / sec. In the ultrasonic Doppler system, the velocity of the blood flow can be measured by estimating the Doppler shift frequency f _D from the received signal.

On the other hand, when the estimated Doppler frequency f _d is PRF / 2 + ㅿ, the average frequency estimated by the equation (15) will be -PRF / 2 +.. That is, if the velocity of the blood flow in the forward direction corresponds to a Doppler frequency equal to or greater than 1/2 of the PRF (Pulse Repetition Frequency), this blood flow will be estimated to flow in the reverse direction. This phenomenon is called velocity aliasing. The reason for this phenomenon is explained by the Nyquist sampling theorem.

The variance calculation unit 264 calculates the variance of the power spectrum to estimate the degree of turbulence of the blood flow.

The degree of turbulence in this blood stream is proportional to the variance of the power spectrum. The variance σ ² of the power spectrum is given by

The variance can be approximated as shown in Equation 19 by a similar method to that of Equation (12) using A (τ) to the quadratic power series expansion followed by the approximation equation.

Another embodiment of the velocity calculation and dispersion calculation method using the autocorrelation method described above will be described.

(1-lag auto correlation) with a time delay of one sample of the i (k) signal and the q (k) signal, The denominator and numerator values of Equation 15 can be obtained.

Then, the power of the signal can be obtained through an operation (0-lag auto correlation) of an autocorrelation value having no time delay of the inphase signal and the abnormal input signal. This is the power Doppler output that expresses the power of the blood flow by the brightness of the screen and the value required for the calculation of Equation 19, and the variance calculation unit 264 is used to obtain the variance value. The numerator, denominator, and power value are expressed as N, D, and P, respectively.

The N, D, and P values obtained through the Doppler frequency estimator 262 are used to calculate the velocity and variance value of the blood flow in the velocity calculator 263 and the equation 24 in the variance calculator 264, .

The blood-flow index generator 270 generates a blood-flow index using the velocity of the blood flow. And uses the velocity of the blood flow estimated by the velocity calculator 263 for detecting the cardiac cycle. The velocity value of the blood flow is suitable for expressing the relaxation-contraction of the movement of the heart.

The blood flow index generation unit 270 includes a data buffer unit 271, an envelope detection unit 272, a low pass filter 273, a cardiac cycle detection unit 274, a maximum / minimum value detection unit 275, and an index calculation unit 276 .

The data buffer unit 271 stores the velocity of the blood flow obtained at each point in the Doppler unit 260 through the data buffer.

The envelope detector 272 detects the envelope of the received signal using envelope detection from the stored velocity of the blood stream.

The low-pass filter 273 passes the detected envelope signal to the low-pass filter to remove the high-frequency noise signal.

The cardiac cycle detector 274 finds the maximum value of the cardiac cycle signal that has passed through the low-pass filter using a threshold filter, and finds a cardiac cycle of one of several cardiac cycles.

The maximum / minimum value detector 275 detects a maximum value, a minimum value, and an average value in one cardiac cycle.

The index calculator 276 calculates a resistance index, a pulse index, and an arbitrary blood flow index designated by the user, which are functional blood flow indexes. The average velocity, maximum value, and minimum value within a cardiac cycle are required to obtain a pulsatility index (PI) and a resistance index (representative index of functional blood flow). On the other hand, in order to calculate the characteristic index of the blood flow, the blood flow characteristic index can be calculated by synthesizing the signals of the cardiac cycles of several samples.

Pulse index (PI) is a quantitative representation of the pulsatility of the blood flow velocity waveform, which means that the total vibration energy of the blood flow velocity waveform is divided by the mean velocity energy value. The pulse index (PI) is defined as:

M is the mean velocity in the cardiac cycle, and a _n is the magnitude of the nth harmonic component. However, due to the computational difficulties, we simply redefine it as follows.

S is the maximum velocity of the blood flow velocity waveform, D is the minimum value, and M is the mean velocity within one cardiac cycle. The above equations do not have exactly the same value, but have correlation with each other.

The resistance index is used as an index of resistance to blood circulation on the carotid artery and is defined as follows.

S is the maximum velocity of the blood flow velocity waveform, and D _end is the height of the final value of the cardiac diastole (diastole). In this case, the RI value has a value of 0 to 1. Depending on the examiner, D _end may be defined as the minimum value of the waveform as in the pulse index. In this case, when there is cloudy backflow in the bloodstream, D _end has a negative value, and therefore, it has a value greater than 1. In addition, there are various blood flow characteristics such as S / D ratio, D / S ratio, and constant flow ratio. These indexes of blood flow characteristics are widely used for diagnosis of diseases. For example, in the presence of stenosis, the pulse rate increases with the increase of the blood flow velocity, and when the intracranial pressure (ICP) increases, the velocity of the blood flow decreases and the pulse index increases . In addition, blood flow characteristics index is widely used as a standard of disease diagnosis in clinical practice.

The mapping unit 280 can selectively map velocity, variance, and blood flow index of blood flow obtained at each image point to each image point. At this time, if the velocity of the blood flow is positive, the sign of the phase has a positive value, and if the velocity of the blood flow is a negative direction, it has a negative value. Therefore, when color mapping of blood flow velocity is positive, it is determined to be red if the sign of the phase is positive, and blue if it is negative. The size of the phase is mapped to the size of each corresponding color. Since each color is 6 to 8 bits, it can be obtained simply by bit shifting. The phase of the blood flow can be calculated by obtaining the phase of the ensemble signal, the velocity can be estimated from the calculated ensemble signal, and the blood flow index can be calculated from the estimated velocity. The variance value can be simply implemented by bit shifting the same expression for mapping to green.

The display unit 290 maps the pulse index and resistance index values, which are functional blood flow indexes calculated for each image point, to a color, and maps the color Doppler velocity (or phase) and variance value obtained at each image point to color Lt; / RTI &gt;

In the present invention, a plane wave B-mode image having about 7 to 8 kHz is used to make an ensemble while skipping samples so that a frame rate is 2 to 3 kHz in a color Doppler image. On the other hand, in the two-dimensional color flow system, since blood flow information at all image points constituting a frame must be obtained, only a limited number of data should be used for 8 to 16 pixels for an image point. In an ensemble, It is called length.

3 shows a general transmission beam focusing method and a plane wave transmission method according to the present invention.

According to the general transmission beam focusing method shown in FIG. 3 (a), a two-dimensional color Doppler system takes a long time to transmit and receive a large number of times in order to obtain a Doppler frequency, thereby limiting a frame rate of a color Doppler image. Therefore, the time required to obtain one frame corresponds to the transmission / reception time of L (number of scanning lines) * N (ensemble length). Therefore, a high sampling rate, i.e., a frame rate of a color Doppler image, must be high for high accuracy of blood flow information analysis.

Commercialized equipment provides color Doppler images of 10 to 20 Hz in real time. However, it is not enough to analyze the characteristics of the blood flow velocity within a cardiac cycle with a sample of about 10 to 20 per second. Since the conventional 2D functional blood flow imaging technique is difficult to restore a more accurate cardiac cycle from a small number of samples, quantitative information is provided as a method of acquiring blood flow information of various cardiac cycles and synthesizing them.

However, this results in non-uniform data acquisition time, and its accuracy is limited by motion. As shown in FIG. 2 (a), when a general transmission / reception beam focusing is performed, since one scanning line (N) is obtained through one transmission and reception, it is necessary to repeat transmission and reception N times in order to obtain one frame.

However, by using the plane wave shown in FIG. 3 (b), one frame is obtained through one transmission and reception process. Compared with FIG. 3 (a), the frame rate by N times is improved. That is, by using a plane wave, a high frame rate of a color Doppler image, that is, a sampling rate, can be increased to secure sufficient blood flow velocity information in one cardiac cycle to obtain an accurate Doppler index. However, when using a simple plane wave, the reliability of the estimated result may be lowered because the signal-to-noise ratio is lowered. In order to compensate for this, it is desirable to supplement techniques such as code excitation and image synthesis techniques such as Barker code.

4 is a flowchart of a functional blood flow index generation method according to an embodiment of the present invention.

Referring to FIG. 4, the method for generating a functional blood flow index according to the present embodiment includes steps that are processed in a time-series manner by the blood flow index generation unit 270 shown in FIG. Therefore, the contents described above with respect to the blood-flow-index generating unit 270 shown in FIG. 2 are applied to the functional blood-flow-index generating method according to this embodiment, even if omitted below.

In step 400, the pulsar 210 generates a plane wave, the transducer 220 transmits the generated plane wave to the object, and receives the ultrasound signal reflected from the object.

In step 410, the receiving beam focusing unit 230 focuses the beam reflected by the object by applying a reception time delay to the beam.

In operation 420, the DC removal filter 240 removes DC components generated by the ADC, and the quadrature demodulator 250 generates inphase and quadrature components of the baseband.

In operation 430, the Doppler unit 260 calculates velocity and variance of blood flow from the in-phase component and the abnormal component using an autocorrelation method or a cross-correlation method.

From the Doppler mean frequency estimated by the Doppler frequency estimator 262 of the Doppler unit 260, the velocity can be calculated using Equation (17), and the Doppler phase can also be calculated.

Since the number of data used to detect the velocity information of the bloodstream at each image point is very small, the high efficiency of the technique for estimating the Doppler mean frequency of the bloodstream is very important. A method for obtaining the Doppler mean frequency from a limited number of sample data is a cross-correlation method using an auto-correlation method using phase shift and a time shift time shift method. The autocorrelation method is performed on the RF demodulated echo data, while the cross-correlation method is performed on the RF data, while the autocorrelation method is performed on the echo data on the RF demodulation, while the cross-correlation method has an advantage of overcoming the blood flow rate limitation and increasing the axial resolution compared to the autocorrelation method. It is necessary to quickly process the signals.

In step 440, the blood-flow indicator generator 270 generates a blood-flow indicator using the velocity of the blood flow.

In step 450, the mapping unit 280 maps velocity, variance value, and blood flow index of blood flow obtained at each image point to each image point.

In step 460, the display unit 290 displays a result obtained by mapping the pulse index and the resistance index, which are functional blood flow indexes calculated for each image point, to the color, and mapping the velocity and variance value obtained from each image point to color, do.

5 is a flowchart of a blood flow velocity and variance calculation method according to an embodiment of the present invention.

In step 500, the clutter filtering unit 261 uses a clutter filter to transmit a signal reflected from the blood vessel wall or the body tissue, rather than a signal reflected from the blood flow (red blood cells) to be measured, to the orthogonal demodulation unit 250 From the in-phase component and the quadrature component output from the in-phase component.

In step 510, the Doppler frequency estimator 262 estimates the average Doppler frequency using an autocorrelation method or a cross-correlation method capable of calculating an average frequency of the power spectrum on a time axis.

In step 520, the velocity calculator 263 calculates the velocity of blood flow from the estimated Doppler frequency. The calculated blood flow velocity is passed to steps 530 and 600.

In step 530, the variance calculator 264 calculates the variance of the power spectrum to estimate the degree of turbulence of the bloodstream. The calculated velocity and variance of the blood flow is transferred to step 450.

6 is a flowchart of a blood flow index generation method according to an embodiment of the present invention.

In step 600, the data buffer unit 271 stores the velocity of the blood flow obtained from each image point in the velocity calculator 263 through the data buffer.

In operation 610, the envelope detector 272 detects the envelope of the received signal using envelope detection from the velocity of the stored blood flow.

In operation 620, the low pass filter 273 low-pass filters the detected envelope.

In operation 630, the cardiac cycle detector 274 finds the maximum value of the cardiac cycle signal that has passed through the low-pass filter using the threshold filter to find a cardiac cycle of one of several cardiac cycles.

In step 640, the maximum / minimum value detector 275 detects the maximum speed, the minimum speed, and the average speed in one cardiac cycle.

In step 650, the index calculation unit 276 calculates a resistance index and a pulse index, which are functional blood flow indexes. The calculated blood flow index is transmitted to step 450.

FIG. 7 shows signals in respective steps of the blood flow index generation method according to the embodiment of the present invention.

FIG. 7A shows the envelope signal detected in step 610 of FIG. The envelope signal detected from the blood flow velocity is a cardiac cycle signal.

7 (b) shows a signal obtained by low-pass-filtering the cardiac cycle signal of FIG. 7 (a), and shows a process of detecting a maximum value among values corresponding to a threshold value or more. The interval between the maximum value and the maximum value detected is the cardiac cycle.

Fig. 7 (c) shows detection of the minimum value and the average value between the detected maximum value and the maximum value.

FIG. 8 shows a configuration of a two-dimensional color flow image.

The functional blood flow image generating apparatus according to the present invention provides spatial color and temporal change of blood flow in a two-dimensional color Doppler image of 6 to 30 frames per second.

Referring to FIG. 8, a cross section of an image is composed of L scanlines, and each scan line is composed of M image points. In the case of this cross-sectional image, it is composed of a total of L × M image points. Each image point is converted into a color according to the magnitude and direction of the mean blood flow velocity at the corresponding position of the cross-sectional image and displayed on the screen. B-mode images in black and white are displayed at the image points determined to have no blood flow.

FIG. 9 shows a method of mapping a blood flow velocity of a two-dimensional color flow image.

Referring to FIG. 9, there is shown a method for converting average speed to color in the functional blood flow image generating apparatus according to the present invention. The velocity of the blood flow was divided by N and divided by brightness. The omnivore blood flow was red and the posterior blood flow was blue. In addition, green is used to indicate the degree of turbulence in the bloodstream, and this information is useful for diagnosing cardiovascular disease in the cardiovascular system.

FIG. 10 is a diagram illustrating a transmitting and receiving process of the functional blood flow image generating apparatus according to the present invention.

l _n denotes an n-th scan line. At this time, the transmission waveform uses a burst pulse like the spectral Doppler.

Where transmit burst number represents the transmit index for each scan line. As shown in FIG. 10, it can be seen that N transmission and reception processes are required for each scanning line. The time required to obtain one frame corresponds to the transmission and reception times of L (the number of scanning lines) × N (the length of the ensemble) since data of all image points on the same scanning line can be obtained at the time of one transmission and reception. Therefore, the frame rate F of the color flow image can be obtained as follows.

Here, PRF is calculated in consideration of the time during which the ultrasonic waves are reciprocated with respect to the maximum depth ( _Zmax ) of the image as the reciprocal of the transmission period of the burst pulse.

In order to obtain a high frame rate required in clinical practice, it is understood that the PRF must be increased or the number of scanning lines or the number of times of transmission / reception per one scanning line, that is, ensemble length should be reduced. However, when the PRF is increased, the maximum depth of the image that can be observed becomes shallow. When the number of scanning lines is decreased, the lateral width is limited. When the number of times of transmission and reception is decreased, the error of blood flow velocity estimation becomes large. Therefore, it is preferable that the number of times of transmission and reception per scanning line is 8 to 16 times and the frame rate is about 10 to 20 Hz in a two-dimensional color flow imaging apparatus.

In addition, the functional blood flow index imaging device has a much higher transmission / reception frequency than the conventional Doppler color flow. That is, it is preferable to perform the operation at several tens to several thousands times per second to have a frame rate of Doppler image of several tens to several thousands Hz. At this time, the frame rate of the real-time functional blood-flow indicator image is set to be similar to the cardiac cycle because the value comes out every cardiac cycle. In order to increase the readability of the image, it is also possible to represent it by filling in the intermediate value.

The functional blood flow image generating apparatus according to the present invention provides quantitative information on the two-dimensional plane by using the Doppler index (e.g., resistance index, pulse index, etc.) of the blood flow characteristics, thereby improving the efficiency of diagnosing diseases of the heart and circulatory system . The conventional color Doppler based two-dimensional functional blood flow imaging technique provides quantitative information by acquiring blood flow information of various cardiac cycles and synthesizing them, but this accuracy is limited due to unevenness of data acquisition time and movement.

However, the present invention discloses a method for acquiring sufficient blood flow velocity information in one cardiac cycle at a high data acquisition rate at a constant data acquisition rate by using a plane wave to image accurate blood flow characteristics using a Doppler index.

In addition, the functional blood flow indicator image generation method according to the present invention estimates the heart cycle using the velocity of the blood flow, and obtains one heart cycle in various estimated heart cycles. In addition, the Doppler index values for each image point on the two-dimensional image can be calculated, and the color can be mapped to perform two-dimensional imaging in real time.

Therefore, the present invention provides a Doppler index value for all image points in a two-dimensional plane, compared to a spectral Doppler in which blood flow index characteristics within a single range gate can be seen. This can greatly improve the efficiency of diagnosing diseases of the heart and circulatory system.

Embodiments of the present invention may be implemented in the form of program instructions that can be executed on various computer means and recorded on a computer readable medium. The computer-readable medium may include program instructions, data files, data structures, and the like, alone or in combination. The program instructions recorded on the medium may be those specially designed and constructed for the present invention or may be available to those skilled in the art of computer software. Examples of computer-readable media include magnetic media such as hard disks, floppy disks and magnetic tape; optical media such as CD-ROMs and DVDs; magnetic media such as floppy disks; Magneto-optical media, and hardware devices specifically configured to store and execute program instructions such as ROM, RAM, flash memory, and the like. Examples of program instructions include machine language code such as those produced by a compiler, as well as high-level language code that can be executed by a computer using an interpreter or the like. The hardware devices described above may be configured to operate as one or more software modules to perform the operations of the present invention, and vice versa.

As described above, the present invention has been described with reference to particular embodiments, such as specific elements, and specific embodiments and drawings. However, it should be understood that the present invention is not limited to the above- And various modifications and changes may be made thereto by those skilled in the art to which the present invention pertains. Accordingly, the spirit of the present invention should not be construed as being limited to the embodiments described, and all of the equivalents or equivalents of the claims, as well as the following claims, belong to the scope of the present invention .

210: Pulser 220: Transducer
230: reception beam focusing section 240: DC removal filter section
250: orthogonal demodulation unit 260: Doppler unit
261: Clutter filtering unit 262: Doppler frequency estimating unit
263: velocity calculation unit 264: dispersion calculation unit
270: blood flow index generator 271:
272: envelope detection unit 273: low-pass filter
274: cardiac cycle detection unit 275: maximum / minimum value detection unit
276: Index calculation unit 280: Mapping unit
290:

Claims (14)

A transducer for transmitting a plane wave to a target object and receiving an ultrasound signal reflected from the target object;
A reception beam focusing unit for beam-focusing the ultrasonic signal by applying a reception time delay;
An orthogonal demodulator for generating an in-phase component and an ideal component from the beam converged signal;
A Doppler frequency estimator for estimating an average frequency of a power spectrum generated from the in-phase component and the abnormal component;
A velocity calculation unit for calculating a blood flow velocity at an image point on a two-dimensional cross-section from the estimated average frequency;
A mapping unit for mapping the blood flow velocity to the image point; And
And a display unit for displaying a blood flow velocity mapped to the image point. The method according to claim 1,
And a blood flow index generator for generating a blood flow index from the blood flow velocity calculated at the image point,
Wherein the mapping unit maps the blood flow index to the image point,
Wherein the display unit displays a blood flow index mapped to the image point. The method according to claim 1,
Further comprising a dispersion calculation section for calculating a dispersion of the power spectrum from the in-phase component and the abnormal component,
Wherein the mapping unit maps the variance to the image point,
Wherein the display unit displays a distribution mapped to the image point. delete The method according to claim 1,
Wherein the Doppler frequency estimator estimates an average frequency of the power spectrum using an autocorrelation method or a cross-correlation method capable of calculating the average frequency of the power spectrum on a time axis. A transducer for transmitting a plane wave to a target object and receiving an ultrasound signal reflected from the target object;
A reception beam focusing unit for beam-focusing the ultrasonic signal by applying a reception time delay;
An orthogonal demodulator for generating an in-phase component and an ideal component from the beam converged signal;
A velocity calculation unit for calculating a velocity of blood flow at an image point on a two-dimensional section from the in-phase component and the abnormal component;
A blood flow index generator for generating a blood flow index from the blood flow velocity calculated at the image point;
A mapping unit for mapping the blood flow index to the image point; And
And a display unit for displaying a blood flow index mapped to the image point. The method according to claim 6,
The blood-
An envelope detector for detecting an envelope from a blood flow velocity corresponding to the image point;
A heart cycle detector for detecting at least two maximum values of the envelope by passing the envelope through a threshold filter to detect one cardiac cycle signal;
A maximum / minimum value detector for detecting a maximum value, a minimum value, or an average value from the detected cardiac cycle signal; And
And an index generator for generating a blood flow index using at least one of the maximum value, the minimum value, and the average value,
Wherein the index generating unit transmits the generated blood flow index to the mapping unit. The method according to claim 6,
Wherein the blood flow index is a resistance index and a pulse index. Transmitting a plane wave to a target object and receiving an ultrasound signal reflected from the target object;
A beam focusing step of applying the ultrasonic signal with a reception time delay;
Generating an in-phase component and an ideal component from the beam focused signal;
Estimating an average frequency of the power spectrum generated from the in-phase component and the abnormal component;
Calculating a blood flow velocity at an image point on a two-dimensional section from the estimated average frequency;
Mapping the blood flow velocity to the image point; And
And displaying the blood flow velocity mapped to the image point. 10. The method of claim 9,
Further comprising generating a blood flow index from the blood flow velocity calculated at the image point,
Wherein the step of mapping to the image point comprises:
And maps the blood flow index to the image point,
Wherein the displaying comprises:
And displaying a blood flow index mapped to the image point. delete Transmitting a plane wave to a target object and receiving an ultrasound signal reflected from the target object;
A beam focusing step of applying the ultrasonic signal with a reception time delay;
Generating an in-phase component and an ideal component from the beam focused signal;
Calculating a blood flow velocity at an image point on a two-dimensional cross-section from the in-phase component and the abnormal component;
Generating a blood flow index from the blood flow velocity calculated at the image point;
Mapping the blood flow index to the image point; And
And displaying a blood flow index mapped to the image point. 13. The method of claim 12,
Wherein the step of generating the blood flow index comprises:
Detecting an envelope from the blood flow velocity corresponding to the image point;
Passing said envelope through a threshold filter to detect at least two maximum values of said envelope and detecting one cardiac cycle signal;
Detecting a maximum value, a minimum value, or an average value from the detected cardiac cycle signal; And
And generating a blood flow index using at least one of the maximum value, the minimum value, and the average value. A computer-readable recording medium storing a program for causing a computer to execute the method according to any one of claims 9, 10, 12, and 13.

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