JPH0771557B2 - Ultrasonic blood flow imaging device - Google Patents

Description

Detailed Description of the Invention

[0001]

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

[0002]

2. Description of the Related Art Blood flow information and tomographic image (B-mode image) information are obtained by one ultrasonic probe by using the ultrasonic Doppler method and the pulse reflection method together, and the blood flow information is superposed on the tomographic image in real time. There is known an ultrasonic blood flow imaging device that displays in color. The principle of operation when measuring the blood flow velocity with such a device is as follows.

That is, when an ultrasonic pulse is transmitted to a blood flow flowing in a living body as a subject, the center frequency fc of this ultrasonic beam is scattered by flowing blood cells and undergoes Doppler shift to generate a frequency. By changing by fd, the received frequency f becomes f = fc + fd. At this time the frequency f
c and fd are expressed by the following equations.

[0004]

[Equation 1] Where v: blood flow velocity θ: angle between ultrasonic beam and blood vessel c: speed of sound

Therefore, the blood flow velocity v can be obtained by detecting the Doppler shift fd.

The two-dimensional image display of the blood flow velocity v thus obtained is performed as follows. First, as shown in FIG. 10, the ultrasonic probe 1 sequentially transmits ultrasonic pulses in the A, B, C, ...
In performing the scan, the ultrasonic blood flow imaging apparatus having the configuration shown in FIG. 11 controls the scanning of the ultrasonic pulse.

When the ultrasonic pulse is first transmitted several times in the direction A, the echo signal reflected by the Doppler shift due to the blood flow in the subject is received by the same probe 1 and converted into an electric signal. It is sent to the receiving circuit 2.

Next, the phase detection circuit 3 detects the Doppler shift signal. This Doppler shift signal is captured for every 256 sample points set in the ultrasonic pulse transmission direction. The Doppler shift signal captured at each sample point is frequency-analyzed by the frequency analyzer 4, and D.P. S.
C. After being sent to the (digital scan converter) 5 and scanned and converted there, the blood flow velocity distribution image in the direction A is displayed as a two-dimensional image in real time on the display unit 6.

The same operation is repeated for each of the directions B, C, ... Then, the blood flow image (flow velocity distribution image) corresponding to each scanning direction is displayed.

[0010]

By the way, the detectability of a low flow velocity depends on the length of data for frequency analysis. If the sampling frequency of the Doppler signal is fr and the number of samplings is n, the data length Td of the wave for frequency analysis is Td = n / fr (1), and the frequency resolution Δfd at this time is Δfd = 1 / Td becomes (2). Therefore, the lower limit fd min of the measurable flow velocity can also be expressed as fd min = 1 / Td = fr / n (3) Therefore, in order to detect a blood flow having a low flow velocity, the sampling frequency fr of the Doppler signal may be reduced or the number of data n may be increased (see FIGS. 4 and 5).

However, in two-dimensional Doppler blood flow imaging, the following relational expression holds.

FN.n.m. (1 / Fr ') = 1 (4) where FN: number of frames, m: number of scanning lines fr'; ultrasonic transmission pulse repetition frequency (PRF)

The number of frames F N is related to the real-time property of a two-dimensional blood flow image, and is usually a value of 8 to 30, whereby 8 to 30 images can be viewed in one second.

As shown in FIG. 6, in the case of sector electronic scanning, the number of scanning lines m = 32, the ultrasonic pulse repetition frequency (P
If RF) fr '= 4 KHz and the sampling number n = 8, the frame number FN becomes about 16. Further, the maximum field depth D max and the PRF fr ′ have a relationship of D max = c / (2 · fr ′) (5). Therefore, if PRFfr ′ is increased in order to improve the detectability of low flow velocity, the maximum depth of field D
There is a drawback that max cannot be large. The number of scanning lines is m
If is smaller, the scanning line density becomes coarser and the image quality is deteriorated.

As described above, if the low flow velocity detection capability is improved,
It has the disadvantage of having to sacrifice something.

Therefore, the present invention eliminates the above-mentioned drawbacks, and an object of the present invention is to provide an ultrasonic blood flow imaging apparatus capable of observing a low flow velocity blood flow without deteriorating the maximum depth of field, the number of frames, and the image quality. .

[0017]

According to the present invention, ultrasonic scanning is performed on a subject, blood flow information in the subject is obtained based on the received data of the obtained ultrasonic pulses, and its distribution is displayed. In the ultrasonic blood flow imaging apparatus, the ultrasonic pulse repetition frequency fr 'is set and n is set for each scan line.
Scanning means for transmitting and receiving individual ultrasonic pulses, storage means for holding the received data obtained by the scanning means for each scanning line, and blood for each scanning line from the data stored in the storage means. A detecting means for detecting the flow information, a sampling frequency fr of n ultrasonic pulses for each scanning line so that fr <fr ', and the receiving means collects n receiving data for each scanning line. It has a control means for performing ultrasonic scanning order control on the scanning means so that the completion interval is substantially constant.

[0018]

By controlling the ultrasonic scanning order by the control means, the sampling frequency fr of the Doppler information is lowered below the ultrasonic pulse repetition frequency fr ', and
Since the Doppler information is obtained through the storage means while keeping the data collection interval substantially constant, it is possible to observe the low flow velocity blood flow without deteriorating the maximum depth of field, the number of frames, and the image quality.

[0019]

EXAMPLES The present invention will be specifically described below with reference to examples.

FIG. 1 is a block diagram of an apparatus according to an embodiment of the present invention.

Reference numeral 11 is an ultrasonic probe for transmitting and receiving ultrasonic pulses to and from an object, and 12 is an analog section of a sector electronic scanning device, which includes a preamplifier 13, a pulser 14, and an oscillator 1.
5, delay line 16, adder 17, and detector 18. 19 is D.I. S. C. (Digital scan converter), 20 is a color processing circuit, 21 is a D / A converter, 22 is a VTR, 23 is a color monitor, 3
Reference numeral 5 is a control circuit.

The control circuit 35 controls the change of the ultrasonic scanning order in the analog section 12 of the sector electronic scanning device. In this change control, the sampling frequency of the Doppler information is lowered without changing the ultrasonic pulse repetition frequency. (This will be described in detail later).
The control circuit 35 corresponds to the control means in the present invention.

One of the signals output from the adder 17 is sent to the D.V. S. C. It is sent to 19 and is used for displaying a tomographic image (black and white B-mode image). The other is sent below line 39 and is used to display the blood flow image. The signal applied from line 39 is divided into two and applied to mixers 24a and 24b, respectively.
A reference signal fo from the oscillator 15 is added to each of the mixers 24a and 24b by a 90 ° phase shifter 25 with a 90 ° phase difference, and multiplication is performed. As a result, the Doppler shift signal fd and the (2fo + fd) signal are input to the low pass filters 26a and 26b, and the low pass filter 2
The high frequency components are removed by 6a and 26b, and only the Doppler shift signal fd is obtained. This becomes the phase detection output signal for the blood flow image.

FIGS. 2A to 2C show respective signal waveforms. FIG. 2A is a transmission pulse transmitted from the ultrasonic probe 11 to the subject, and FIG. 2B is a reflection from the subject. The received pulse (received echo) thus generated, (c) is a phase detection output.

The phase detection output signal includes not only blood flow information but also an unnecessary reflection signal (called clutter) from a slow-moving object such as the wall of the heart.
In order to remove this clutter, the phase detection output is MTI (Mo
ving Target Indicator) calculation unit 27.

The MTI calculator 27 is an A / D converter 28.
a, 28b, plural line memories 34a, 34b, MTI
It is composed of filters 29a and 29b, an autocorrelator 30, an average velocity calculator 31, a variance calculator 32, and a power calculator 33.

The A / D converters 28a and 28b convert the outputs of the low-pass filters 26a and 26b into digital signals, and the converted outputs are sent to a plurality of line memories 34a and 34b arranged in the subsequent stage. . The plural line memories 34a and 34b can hold the Doppler information of plural scanning lines according to the change of the ultrasonic scanning order, and this corresponds to the storage means in the present invention.

FIG. 3 shows an example of the structure of the MTI filter. 1 / Z is a delay of one rate, Σ is an adder, and K1 and K2.
Indicates the coefficient.

The autocorrelator 30 is a kind of frequency analysis method, and is used because it is necessary to perform two-dimensional multipoint frequency analysis in real time.

The average speed calculator 31 calculates the average Doppler shift frequency fd based on the following equation.

[0031]

[Equation 2]

The variance calculator 32 calculates the variance σ based on the following equation.
Ask for ² .

[0033]

[Equation 3]

The power calculator 33 calculates the total power TP based on the following equation.

[0035]

[Equation 4]

This total power TP is proportional to the intensity of the echo scattered from the blood cells, but the echo from the moving object corresponding to the cutoff frequency of the MTI filter or less is excluded.

The value (blood flow information) calculated for each point is D. S. C. The data is input to 19, and after interpolating the data, it is converted into color information by the color processing circuit 20. In the case of the display by the average blood flow velocity and the blood flow velocity dispersion, the flow approaching the probe is converted to red and the flow moving away from the probe is converted to blue. The magnitude of the average speed is expressed by the difference in brightness, and the speed dispersion is expressed by the hue (mixing green).

In the apparatus having the above-mentioned structure, the ultrasonic scanning order changing control is performed as follows.

As shown in FIG. 7, when scanning the ultrasonic transmission beam from the right end of the probe 11, the scanning order is as follows: the rightmost scanning line (No. 1) → the second scanning line (No. 2) → third scanning line (No.3) → first rightmost scanning line (No.1) → ... N (N is an integer of 2 or more. In this case, N = 3). ) Independent scanning lines are alternately scanned. In this case, the repetition frequency of the ultrasonic beam transmitted in the same direction (the sampling frequency of the Doppler signal) fr is: fr = fr ′ / 3 (6), that is, the period T of fr (the ultrasonic beam scanning interval in the same direction) is fr. 3'of period T '(ultrasonic scanning interval)
As is clear from the above equation (3), the lower limit fd min of the measurable flow velocity is the conventional method, that is, the ultrasonic transmission beam is transmitted n times consecutively in the same direction, and then the next scanning line. Is improved to 1/3 as compared with the method of performing n times.

If the number of ultrasonic waves transmitted in the same direction (the number of Doppler signal samplings) is n, then n = 4 in the case of FIG. The ultrasonic waves are alternately transmitted / received to a plurality of scanning lines in accordance with the ultrasonic wave transmission / reception order, and the Doppler information is stored in the plural line memory 34.
It is sequentially written in the corresponding lines of a and 34b. Then, when the fourth data (according to n = 4) is fetched for each scanning line, four data for the scanning line are read from the plural line memories 34a and 34b.

At this time, the output timings of the four pieces of data are not at regular intervals in the case of FIG. To make the output timing constant, scanning may be performed as shown in FIG. That is, when scanning from the right end of the probe 11, the scanning order is as follows: scanning line No. 1 → scanning line No. m-1 →
Scan line No.m → Scan line No. 1 → Scan line No. 2 → Scan line No. m → Scan line No. 1 → Scan line No. 2 → Scan line No. 3 → Scan line No. 1 →… To do. By doing so, as in the case of FIG. 7, the repetition frequency (sampling frequency of the Doppler signal) fr of the ultrasonic transmission beam in the same direction can be lowered to 1/3, and the data output timing can be set at a constant interval. .

Therefore, according to the embodiment shown in FIG. 8, since the data output timing between the scanning lines becomes a constant interval,
Unlike the case of the ultrasonic scan order control of FIG. 7, an ultrasonic blood flow imaging image in which the time difference between scan lines is constant and the time difference between scan lines is small is obtained on one scan display screen. be able to.

Here, generally, the repetition frequency fr of the ultrasonic transmission beam in the same direction and the repetition frequency f of the ultrasonic transmission pulse.
Considering r ′ and the low flow velocity detectability improvement ratio P (the number of alternating stages), it is expressed as fr = fr ′ / P. 7 and 8 show the case where P = 3.

It should be noted here that even in the case of FIG. 8, when P is an integer multiple of n, the data output timing cannot be set to a constant interval.

For example, FIG. 9 shows the case where n = 4 and P = 2. Data output timing interval is 3 / fr ', 5 / f
r ', 3 / fr', 5 / fr ', ...

However, even in the case of the embodiment shown in FIG. 9, since the data output timing between the scanning lines can be set at a substantially constant interval, one scanning is different from the case of the ultrasonic scanning sequence control of FIG. It is possible to obtain an ultrasonic blood flow imaging image in which the time difference between the scanning lines on the display screen is substantially constant and the time difference between the scanning lines is small.

The blood flow information obtained by the ultrasonic scanning as described above is D. S. C. Scan conversion is performed in 19 and is sent to the color monitor 23 via the color processing circuit 20 and the D / A converter 21 to be visualized there. Also, it is recorded in the VTR 22 as needed.

As described above, in this embodiment, by changing and controlling the ultrasonic scanning order, the ultrasonic repetition frequency f
Since the sampling frequency fr of the Doppler information is lowered without changing r ', the low flow velocity blood flow can be observed without lowering the maximum field depth Dmax, the number of frames FN, and the image quality.

Needless to say, the present invention is not limited to the above-mentioned embodiment, and various modifications can be made.

[0050]

As described in detail above, according to the present invention, the data collection interval for each scanning line can be made substantially constant, and the maximum depth of field, the number of frames, and the image quality can be reduced. An ultrasonic blood flow imaging device capable of observing low-velocity blood flow can be provided.

[Brief description of drawings]

FIG. 1 is a block diagram of an apparatus according to an embodiment of the present invention.

FIG. 2 is a waveform diagram of the main part of the device of the present invention.

FIG. 3 is a block diagram of a main part of the device of the present invention.

FIG. 4 is an explanatory diagram of the number of data

FIG. 5 is an explanatory diagram of frequency resolution.

FIG. 6 is an explanatory diagram of sector electronic scanning.

FIG. 7 is an explanatory view of the operation of the device of this embodiment.

FIG. 8 is an explanatory view of the operation of another embodiment.

FIG. 9 is an explanatory view of the operation of another embodiment of the device.

FIG. 10 is a scan pattern diagram showing a conventional example.

FIG. 11 is a block diagram of a conventional example.

[Explanation of symbols]

 12 sector electronic scanning device analog section 34a, 34b plural line memory (storage means) 35 control circuit (control means)

Claims (3)

[Claims] 1. An ultrasonic blood flow imaging apparatus that performs ultrasonic scanning on a subject, obtains blood flow information in the subject based on the received data of the obtained ultrasonic pulses, and displays the distribution thereof. , A scanning means having an ultrasonic pulse repetition frequency fr ′ and transmitting / receiving n ultrasonic pulses to / from each scanning line, and a memory for holding the reception data obtained by the scanning means for each scanning line Means, detecting means for detecting blood flow information for each scanning line from the data stored in the storage means, and sampling frequency fr of n ultrasonic pulses for each scanning line so that fr <fr '. In addition, in the storage means, n for each scan line
An ultrasonic blood flow imaging apparatus, comprising: a control unit that performs ultrasonic scanning order control on the scanning unit so that an interval at which collection of individual pieces of reception data is completed is substantially constant. 2. The control means alternately scans a plurality of scanning lines based on the number of alternating steps P, and the sampling frequency fr of n ultrasonic pulses for each scanning line becomes fr = fr '/ P. 2. The ultrasonic blood flow imaging apparatus according to claim 1, wherein the scanning means controls the scanning order of ultrasonic waves. 3. The ultrasonic blood flow imaging apparatus according to claim 2, wherein the control means performs ultrasonic scan order control on the scanning means based on the set values of n and P.