JPH05277111A - Ultrasonic blood flow imaging device - Google Patents

Abstract

(57) [Summary] [Object] An object of the present invention is to improve the ability to discriminate between a blood flow signal and a noise signal, to display the blood flow signal to the maximum and to display the noise signal to the minimum. An object is to provide an ultrasonic blood flow imaging device that can obtain a flow image. [Structure] An ultrasonic blood flow imaging apparatus of the present invention transmits and receives an ultrasonic beam while scanning an ultrasonic beam in a subject to obtain a reflected wave signal, and detects the Doppler signal using the reflected wave signal,
A means for performing multipoint frequency analysis processing and predetermined blood flow information calculation processing on the Doppler signal, and predetermined inter-frame processing for information for a plurality of frames continuously output from this blood flow information calculation means, Means for obtaining blank information representing points in the multipoints that should not be displayed by comparing the processing result with a predetermined threshold value, and blanking the output of the blood flow information computing means based on the blank information. And displaying the result as a blood flow distribution image.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ultrasonic blood flow imaging apparatus for obtaining blood flow distribution information in a subject by utilizing the Doppler effect of ultrasonic waves and displaying it for diagnosis.

[0002]

2. Description of the Related Art An ultrasonic blood flow imaging apparatus of this type is an apparatus capable of performing an ultrasonic Doppler method and a pulse reflection method, and such an apparatus has a single ultrasonic probe. It is possible to obtain blood flow information and tomographic image (B-mode image) information, and moreover, in recent years, MTI (Moving Marg) used in radar technology.
By adopting the "et Indication" process, it has become possible to obtain two-dimensional image information having a two-dimensional spread in real time. The principle of measuring the average velocity, which is one of the blood flow information, will be described below.

When an ultrasonic pulse (beam) is transmitted from the ultrasonic probe to the blood flow flowing in the subject, the center frequency fo in the transmission of this ultrasonic beam is scattered by the flowing blood cells. .. Therefore, the scattered center frequency fo undergoes the Doppler shift to generate the frequency fd.
Only changes. Therefore, at this time, the center frequency f in the reception of the ultrasonic echo received by the ultrasonic probe is f
= Fo + fd. In this case, the center frequency fo and the Doppler shift frequency fd in the transmitted wave are expressed by the following equations. fd = (2v cos θ) × fo / c where v is the average velocity, θ is the angle at which the ultrasonic beam and the blood vessel intersect, and c is the speed of sound. Therefore, the average velocity v can be measured by detecting the Doppler shift frequency fd.

The average velocity v thus obtained is 2
Displaying as a three-dimensional image is performed as follows. As shown in FIG. 9, ultrasonic pulses are sequentially transmitted from the ultrasonic probe 1 to the subject P in the directions a, b, c, ... (Sector scan). Of course, the scanning is not limited to sector scanning, and other scanning methods such as linear scanning may be used.

When the ultrasonic pulse is first transmitted several times in the a direction, the ultrasonic pulse is reflected by a moving reflector in the subject P, that is, mainly by blood cells, and the Doppler shift is caused by the movement. Receive. Then, the ultrasonic echo is received by the same ultrasonic probe 1, converted into an electric signal, and sent to the receiving circuit 2. The output of the reception circuit 2 is given to the phase detection circuit 3 where the Doppler shift signal is detected. In the device shown in FIG. 9, the transmission system is not shown.

The Doppler shift signal thus detected is arranged at, for example, 256 sample points SP which are predetermined in the ultrasonic wave transmitting / receiving direction of the ultrasonic pulse. The Doppler shift signal captured at each sample point is passed through an MTI filter, where some of the slow moving clutter signal is removed. The Doppler shift signal from which some crack signals have been removed is frequency analyzed by the frequency analyzer 4. A blood flow signal at multiple points is obtained by the analysis, and the blood flow information is sent to the digital scan converter DSC5 where it is scan converted and then sent to the monitor 6.

On the monitor 6, the blood flow image in the a direction is displayed in real time as a two-dimensional image. Hereinafter, the same operation is repeated for each of the directions b, c, ... And the blood flow distribution image corresponding to each scanning direction is displayed.

By the way, the output of the phase detection circuit 3 is
All of them may be noise rather than signals related to blood flow. It is known that the noise signal has a smaller power (square of amplitude) than the blood flow signal. Therefore,
With this in mind, a certain threshold is set for the power output of the frequency analyzer 4, the blood flow signal and the noise signal are discriminated from each other, and the noise signal is eliminated, that is, the blank process is performed. Attempts have been made not to display the signal.

[0009]

FIG. 10 is a diagram showing a general frequency distribution regarding the power information output from the power calculation unit of the frequency analyzer 4. As shown in FIG. 10 (a), the stability of the output signal of the phase detection circuit 3 is insufficient, and therefore, there are overlapping portions in each band of the blood flow signal and the noise signal. The reliability of discrimination ability is low. For example, as shown in FIG. 10 (b), the threshold serving as a discrimination reference is set to the maximum value (BL1
When set to around 0), the blood flow signal in the power range shown by the diagonal lines is removed together with the noise signal, resulting in the loss of useful diagnostic information. on the other hand,
As shown in FIG. 10C, when the discrimination threshold is set near the minimum value (BL20) of the power band of the blood flow signal, the noise signal in the power range indicated by the diagonal line is displayed together with the blood flow signal. There has been a problem that noise pixels are included in the three-dimensional blood flow image, which makes the information very difficult to see.

Therefore, an object of the present invention is to obtain a two-dimensional blood flow image in which the blood flow signal and the noise signal are discriminated from each other and the blood flow signal is displayed at the maximum and the noise signal is displayed at the minimum. The object is to provide an ultrasonic blood flow imaging device capable of performing the above.

[0011]

An ultrasonic blood flow imaging apparatus according to the present invention transmits and receives an ultrasonic beam while scanning an ultrasonic beam in a subject to obtain a reflected wave signal, and the reflected wave signal is used to obtain a Doppler signal. And means for performing multipoint frequency analysis processing and predetermined blood flow information calculation processing on the Doppler signal,

A predetermined inter-frame process is performed on a plurality of frames of information continuously output from the blood flow information calculation means, and the result of the process is compared with a predetermined threshold to display among the multiple points. A means for obtaining blank information indicating points that should not be performed, and means for blanking the output of the blood flow information computing means based on the blank information, and displaying the result as a blood flow distribution image. Characterize.

[0013]

According to the apparatus of the present invention, a reflected wave signal is obtained by transmitting and receiving an ultrasonic beam while scanning an ultrasonic beam in a subject, and the Doppler signal is detected using the reflected wave signal, and the Doppler signal is detected. Frequency analysis processing of points and predetermined blood flow information calculation processing are performed, and predetermined inter-frame processing is performed on information of a plurality of frames continuously output from the blood flow information calculation means, and the processing result and a predetermined threshold value. By obtaining a blank information representing a point which should not be displayed among the above-mentioned multiple points by performing a blank process on the output of the blood flow information calculating means based on this blank information, no noise signal is mixed. A blood flow distribution image can be displayed.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of the present invention will be described with reference to the drawings. Prior to the description of this embodiment, the principle of this embodiment will be described.

FIG. 4 is a diagram for explaining this principle. FIG. 4 (a) is a frequency distribution diagram showing the power value distribution of the blood flow signal and the power value distribution of the noise signal in the conventional case, and FIG. 4 (b) performs the averaging process on the signals at the same sample points SP. FIG. 6 is a frequency distribution diagram showing the power value distribution of the blood flow signal and the power value distribution of the noise signal in the case of As shown in FIGS. 4 (a) and 4 (b), the bandwidth of the power value distribution of the normal blood flow signal and the bandwidth of the power value distribution of the noise signal after performing the averaging process are at the center of each. Level (average level of each signal) will be concentrated on PLC and PLN, and the distribution state will be differentiated into these bipolar PLC and PLN, and as a result, as shown in FIG. 4 (b), blood flow signal distribution and noise signal The range in which the distribution and superimpose each other is reduced. Therefore, the ability to discriminate between the blood flow signal and the noise signal can be improved by setting the blank level BL1 according to the state of differentiation.

FIG. 1 is a block diagram showing the configuration of the apparatus of this embodiment. The apparatus of this embodiment includes an electronic scanning ultrasonic probe (hereinafter referred to as “probe”) 11, an electronic scanning apparatus analog section 12, a 90 ° phase shifter 25, mixers 24a and 24b,
Low-pass filters 26a and 26b, MTI calculator 27,
Blank processing means 40, scan conversion means (digital scan converter; DSC) 34, 35, color information changing means 36, multiplexer (MPX) 37, D / A
(Digital / analog) conversion means 38, display means 39
Have.

The ultrasonic probe 11 comprises a plurality of piezoelectric vibrators arranged side by side, and these vibrators transmit and receive ultrasonic pulses to and from the subject P. The electronic scanning device analog section 12 includes a preamplifier 13, a pulser 14, an oscillator 15, a delay line 16, an adder 17, and a detector 18. The electronic scanning device analog section 12 transmits the ultrasonic probe 11 as described above. When driven, as shown in FIG. 3, a pulsed ultrasonic beam is transmitted into the subject P in the order of rasters a, b to z, and is reflected by blood cells flowing in the subject P to cause a Doppler shift. The received signal is received by the same transducer. The received signal obtained by transmitting and receiving this ultrasonic wave is
The preamplifier 13 amplifies the received signal to a predetermined level, and the amplified received signal is given a delay time for each transducer by the delay line 16 so as to restore it based on the delay time given at the time of transmission. The adder 17 adds and combines the outputs of the delay line 16.

The signal output from the adder 17 is the detector 1
The image data is supplied to the display unit 8 and is subjected to logarithmic amplification processing and envelope detection processing to be sent to the scanning conversion unit 34 to be formed as a B mode image, which is displayed on the display unit 39 via the multiplexer 37 and the D / A conversion unit 38.

On the other hand, the signal output from the adder 17 is also sent to the line 39 together with the detector 18. The line 39 is branched into two lines, and supplies the output signal from the adder 17 to each of the mixers 24a and 24b. One signal supplied to the mixer 24a is mixer processed and supplied to the low-pass filter 26a, and the other signal supplied to the mixer 24b is mixer processed and the reference signal fo from the oscillator 15 and the 90 ° shift signal are supplied. A 90 ° phase difference is added based on the 90 ° phase shift signal from the phase shifter 25,
It is supplied to the low-pass filter 26b, the high-frequency components are removed by the low-pass filters 26a and 26b, and output as a phase detection output signal having Doppler shift information. The phase detection output signals output from the low pass filters 26 a and 26 b are supplied to the MTI calculation unit 27.

The MTI calculator 27 is composed of an A / D converter 28a,
28b, MTI filters 29a and 29b, autocorrelator 3
0, an average speed calculator 31, a variance calculator 32, a power calculator 33, and a blank processor 40. Note that this MTI is a technology used in radar,
As mentioned above, it is an abbreviation for Moving-Target-Indicator,
This is a method of detecting only a moving target using the Doppler effect, and the moving target here is a blood cell. The MTI filters 29a and 29b detect the motion of blood flow by the phase change between the same sample points SP in the rate pulse repeatedly transmitted a predetermined number of times, and remove the clutter component.

The autocorrelator 30 is a kind of frequency analysis method, which receives the outputs from the MTI filters 29a and 29b and performs frequency analysis on a large number of sample points SP shown in FIG. Is much smaller than the number of operations in the FFT (Fast Fourier Transform) method, and therefore real-time processing is possible.

The average velocity calculation unit 31, the dispersion calculation unit 32, and the power calculation unit 33 receive the output of the autocorrelator 30 and execute predetermined calculations to obtain blood flow information for each sample point SP.
That is, average flow velocity information v, variance information σ2, power information p
Is output.

The blank processing means 40 is a characteristic part of the present embodiment, and is composed of an average speed calculating section 31 and a dispersion calculating section 3.
2. The output from the power calculator 33 is blanked to remove noise signals, which will be described in detail later.

The output of the blank processing means 40 is taken into the color information changing means 36 via the scanning conversion means 35, and the predetermined color processing is performed here. The scan conversion means 35 is also called a digital scan converter (DSC), and converts the output order so as to match the scanning method of the display means 39. The color information changing means 36 color-processes the output of the scan conversion means 35. The output of the color information changing means 36 is sent to the display means 39 through the MPX 37 and the D / A converting means 38 in order and displayed as a blood flow image. Next, the blank processing means 40, which is a characteristic part of this embodiment, will be described.

FIG. 2 is a schematic part showing the structure of the blank processing means 40. The memory 41 stores the power information p for a plurality of consecutive frames output from the power calculator 33. The calculation unit 42 inputs the power information p for a plurality of frames stored in the memory 41, performs inter-frame processing of the power information p, that is, averaging processing for each sample point SP, and calculates each average value (hereinafter, “ The average power information P ”) is output via the memory 41. Threshold processing unit 43
As described in the above description of the principle, a predetermined blank level BL1 is set, the blank level BL1 is compared with the average power information P for each sample point SP, and the average power information of which sample point SP is Blank information BD indicating whether P is equal to or lower than the blank level BL1 or a noise signal is output to the blank processing unit 44.

The blank processing section 44 includes an average speed calculation section 3
1, the average flow velocity information v, the variance information σ 2, and the power information p are input from the variance calculation unit 32 and the power calculation unit 33, respectively,
According to the blank information BD supplied from the threshold processing unit 43, the average flow velocity information v, the variance information σ2, and the power information p corresponding to the sample points SP having the blank level BL1 or less.
Is output to the scan conversion means 35. In this way, by discriminating the blood flow signal and the noise signal from each other based on the average value of the average power information P, the discrimination ability can be improved. Next, the operation of the apparatus of this embodiment configured as above will be described.

FIG. 5 is a conceptual diagram for explaining the operation of the blank processing means 40. In this case, 5 consecutive
Blank information BD using the power information p for frames
Shall be obtained. The power information p for five frames is stored in the memory 41 (power information p for each one frame is input in the order of F
When p1, Fp2 ... Fp5 are stored, the averaging process is performed by the calculation unit 42 for each sample point SP, and the average power information P (Fhp1) for one frame is obtained. For example,
For the sample point SPa, five pieces of power information Pa1 to Pa5 over five frames, and for the sample point SPb, five pieces of power information Pb1 to Pb5 over five frames.
Is averaged to obtain average power information Pa and Pb. Such an averaging process is performed for all sample points SP, and the average power information P for one frame (Fhp
1) Obtained.

The average power information Fhp1 for one frame thus obtained is supplied to the threshold processing unit 43, and the blank level BL for each average power information P of each sample point SP.
The average power information P equal to or lower than the blank level BL1, for example, blank information BD1 indicating the sample point SPb corresponding to Pb is obtained by comparison with 1. The blank information BD1 is supplied to the blank processing unit 44.

Then, in the blank processing unit 44, based on this blank information BD1, the average velocity information v of each sample point SP outputted from the average velocity computing unit 31, the variance computing unit 32, and the power computing unit 33, and the variance. A blank process, for example, zero value is set for the information σ 2 and the power information p.

As described above, the average flow velocity information v, the dispersion information σ 2, and the power information p passed through the blank processing means 40 are output by the scan conversion means 35 in accordance with the display scanning method of the display means 39, and the color information conversion means 36. Two-dimensional color blood flow is converted into blue or red density information according to the positive / negative and level, superimposed on a B-mode image, for example, by a multiplexer 37, passed through a D / A converter 38, and displayed on a display means 39 with no noise signal. Displayed as a statue.

Then, the power information Fp6 for the next one frame
Is input, the power information Fp6 for one frame is stored in place of the power information Fp1 for one frame that was input first, and this time, power information Fp2 to Fp for five new frames is stored.
As described above, the blank information BD2 is obtained by subjecting p6 to the processing, and the blank information BD2 is obtained based on the blank information BD2, and the blank information BD, the variance information σ2, and the power information p are blank-processed. A two-dimensional color blood flow image is displayed. Such an operation is performed every time the power information for one frame is supplied from the power calculator 33, and a two-dimensional color blood flow image without a noise signal is displayed.

By thus performing threshold processing on the average power information P and obtaining blank information, the ability to discriminate between blood flow signals and noise signals can be improved, and two-dimensional color blood flow in which noise signals do not coexist. You can get a statue. In the above embodiment, the target of the blank processing is the average flow velocity information v, the variance information σ2, and the power information p from the various blood flow information calculation units, but it is assumed that the calculation unit 42 performs these information for a plurality of frames. The blanking process may be performed on the same average process.

Next, a second embodiment will be described. In the present embodiment, the averaging process is performed on the power information p for a plurality of consecutive frames in the first embodiment, blank information is obtained based on the result, and the ability to discriminate between the blood flow signal and the noise signal is improved. However, the present embodiment obtains a similar effect by using the maximum value detection process instead of the averaging process.

FIG. 6 is a diagram for explaining the principle of this embodiment for improving the discrimination ability. By the way, the maximum value detection process uses the power information p for a plurality of consecutive frames,
This is a process of selecting the maximum power information P indicating the maximum value in the power information p between a plurality of consecutive frames regarding the same sample point SP. As a result, the maximum power information P tends to exist in the range indicated by the diagonal lines in FIG. 6, and according to this tendency, the blank level BL2 is set near the maximum value of the bandwidth of the power value distribution of the noise signal, The maximum power information P of each sample point SP is compared with this blank level BL2 to obtain blank information BD. The configuration for this can be easily implemented only by changing the calculation unit 42 shown in FIG. 1 to a maximum value detection processing unit. Also, instead of detecting the maximum value, the power information p for a plurality of consecutive frames
It is also possible to control the blanking process by a majority decision based on the result of the judgment. Thus, according to the present embodiment as well, the first
Similar to the case of the averaging process of the embodiment, the ability to discriminate between the blood flow signal and the noise signal can be improved.

Next, a third embodiment will be described. Here, it is generally known that the level change rate (change rate) of the noise signal on the time axis is different from the level change rate of the blood flow signal on the time axis. The present embodiment utilizes this fact to improve the discrimination ability. For example, as shown in FIG. 7, the average flow velocity information v regarding the blood flow signal shown in FIG. 7A has a property of changing more gently than the average flow velocity information v regarding the noise signal shown in FIG. 7B.

In order to utilize this property, this embodiment modifies the arithmetic unit 42 of the blank processing unit 40 of the above embodiment as follows. That is, the calculation unit of the present embodiment is a change speed calculation processing unit for calculating the change speed by inputting the average flow speed information v from the average flow speed calculation unit 31 for a plurality of frames via the memory 41. In the calculation of the changing speed, the changing speed may be calculated based on the change of the frequency, or the changing speed may be calculated based on the change of the amplitude value. When calculating the rate of change based on the change in frequency, for example, the Fourier transform method, the zero-cross method, or the autocorrelation method is adopted. In the blank processing unit 43, blank information is obtained by comparing this changing speed with a predetermined threshold value,
Blank processing is performed on the average flow velocity information v, the dispersion information σ 2, and the power information p according to the blank information. The configuration for this can be easily implemented only by changing the calculation unit 42 shown in FIG. 1 to a change speed calculation processing unit for calculating the change speed.

As described above, according to this embodiment, the ability to discriminate between the blood flow signal and the noise signal can be improved as in the case of the above embodiment. In this embodiment, the average flow velocity information v
The rate of change of the variance information σ 2 or the power information p may be obtained.

As described above, since the ultrasonic blood flow imaging apparatus according to this embodiment adopts the interframe processing, it is possible to discriminate the blood flow signal and the noise signal with high reliability, It is possible to provide an ultrasonic blood flow imaging apparatus that maximizes the display of blood flow signals and minimizes the display of noise signals.

The present invention is not limited to the above embodiment, but can be implemented in various modifications. As shown in FIG. 8, the blank processing means 40 may be arranged between the autocorrelator 30 and the various calculation units 31, 32, 33. In this case, the output of the autocorrelator 30, that is, the autocorrelation function. Is blanked. In addition, the autocorrelator may be replaced with a Fourier transformer. Further, in the above embodiment, the averaging process or the like is performed for each sample point SP of a plurality of consecutive frames, but the averaging process or the like may be performed for each of a plurality of spatially adjacent sample points SP.

[0040]

As described above, according to the present invention, a reflected wave signal is obtained by transmitting and receiving an ultrasonic beam while scanning an ultrasonic beam in a subject, and a Doppler signal is detected using the reflected wave signal. Multipoint frequency analysis processing and predetermined blood flow information calculation processing are performed on the Doppler signal, and predetermined inter-frame processing is performed on a plurality of frames of information continuously output from the blood flow information calculation means, and the processing is performed. By obtaining a blank information representing a point that should not be displayed among the multiple points by comparing the result and a predetermined threshold value, by blanking the output of the blood flow information computing means based on this blank information, An ultrasonic blood flow imaging device capable of displaying a blood flow distribution image in which noise signals are not mixed can be provided.

[Brief description of drawings]

FIG. 1 is a block diagram showing the configuration of a first embodiment of the present invention.

FIG. 2 is a block diagram showing a configuration of a blank processing means shown in FIG.

FIG. 3 is a diagram showing sector scanning.

FIG. 4 is a diagram for explaining the principle of discriminating ability improvement according to the present embodiment.

FIG. 5 is a conceptual diagram illustrating an operation of a blank processing unit according to the present exemplary embodiment.

FIG. 6 is a diagram for explaining the principle by which the maximum value detection processing of the blank processing means of the second embodiment improves the discrimination ability.

FIG. 7 is a diagram for explaining the principle that the change speed calculation process of the blank processing means of the third embodiment improves the discrimination ability.

FIG. 8 is a diagram showing another embodiment in which the arrangement of the blank processing means in the first to third embodiments is changed.

FIG. 9 is a block diagram showing a schematic configuration of a conventional ultrasonic blood flow imaging device.

FIG. 10 is a diagram illustrating a problem development of the ability to discriminate between a blood flow signal and a noise signal in a conventional ultrasonic blood flow imaging device.

[Explanation of symbols]

11 ... Ultrasonic probe, 12 ... Electronic scanning device analog part, 24 ... Mixer, 25 ... 90 degree phase shifter, 26 ... Low pass filter, 27 ... MTI calculation part, 28 ... A / D conversion means, 29 ... MTI filter, 30 ... Autocorrelator, 3
1, 32, 33 ... Operation part, 34, 35 ... Scan conversion means,
36 ... Color information changing means, 37 ... Multiplexer, 3
8 ... D / A conversion means, 39 ... Display means, 40 ... Blank processing means.

Claims (4)

[Claims] 1. An ultrasonic beam is transmitted and received while scanning an ultrasonic beam in a subject to obtain a reflected wave signal, a Doppler signal is detected using the reflected wave signal, and a multipoint frequency analysis processing is performed on the Doppler signal. Means for performing a predetermined blood flow information calculation processing, and predetermined inter-frame processing for a plurality of frames of information continuously output from the blood flow information calculation means, and compare the processing result with a predetermined threshold value. By means of obtaining blank information representing a point that should not be displayed among the multiple points, and performing a blank process on the output of the blood flow information calculation means based on the blank information, and the result as a blood flow distribution image. An ultrasonic blood flow imaging apparatus comprising: a means for displaying. 2. The blank information means inputs power information for a plurality of frames from the blood flow information computing means, performs an averaging process on each point of the plurality of frames, and based on an averaging process result of the respective points, The ultrasonic blood flow imaging apparatus according to claim 1, wherein blank information indicating a point that should not be displayed among the multiple points is obtained. 3. The blank information means inputs the power information for a plurality of frames from the blood flow information computing means, performs processing for detecting the power information indicating the maximum at each point of the plurality of frames, and outputs the maximum power information. The ultrasonic blood flow imaging apparatus according to claim 1, wherein blank information indicating a point that should not be displayed among the multiple points is obtained based on the above. 4. The blank information means inputs the average flow velocity information for a plurality of frames from the blood flow information calculation means, calculates the change velocity of the average flow velocity at each point of the plurality of frames, and based on the change velocity. The ultrasonic blood flow imaging apparatus according to claim 1, wherein blank information indicating a point that should not be displayed among the multiple points is obtained.