JPH06225880A - Ultrasonic bloodstream imaging device - Google Patents

Abstract

PURPOSE:To observe the low-velocity bloodstream without reducing image quality, the number of frames and the maximum visual field depth by changing the ultrasonic scanning order, and reducing the sampling frequency of the Doppler information without changing the ultrasonic repetition frequency. CONSTITUTION:A control circuit 35 changes the ultrasonic scanning order of a sector electronic scanning device analog section 12. When an ultrasonic transmission beam is scanned from the right end of a probe 11, scanning is performed among three independent scanning lines in turn. The repetition frequency of the ultrasonic transmission beam in the same direction becomes three times the ultrasonic pulse repetition frequency, and the lower limit of the measurable flow velocity is improved to 1/3 of the conventional system. If the ultrasonic transmission times in the same direction are set to four, four data are read out from multiple line memories 34a, 34b on each scanning line when the fourth data are extracted for each scanning line. The phase detection output is added to an MTI calculation section 27 and sent to a color monitor 23 to remove unnecessary reflected signal from an object having slow movement such as the wall of a heart.

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. There is known an ultrasonic blood flow imaging device that displays color in real time. 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] 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 which is Doppler-shifted and reflected by 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 the DSC (Dig
It is sent to the ital scan converter 5 and scan-converted there, and then sent to the display unit 6 to display the blood flow distribution image in the A direction as a two-dimensional image in real time.

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.

[0009]

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) number of frames FN is 2 It is related to the real-time property of the three-dimensional blood flow image, and is usually a value of 8 to 30.
Up to 30 images can be seen.

[0012] As shown in FIG. 6, when the sector electronic scanning, the scanning line number m = 32, the ultrasonic pulse repetition frequency (PRF) fr' = 4KH _Z, if the sampling number n = 8, the number of frames FN about Become 16. Further, the maximum depth of field 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. Further, if the number of scanning lines m is reduced, the scanning line density becomes coarser, resulting in deterioration of image quality.

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 low-velocity blood flow without deteriorating the maximum depth of field, the number of frames, and the image quality. There is.

[0015]

According to the present invention, an object is subjected to ultrasonic scanning at an ultrasonic pulse repetition frequency fr ', and received data of a predetermined number of ultrasonic pulses obtained for each scanning line is obtained. In an ultrasonic blood flow imaging apparatus that obtains blood flow information in the subject based on the information and displays the distribution, a scanning unit that transmits and receives an ultrasonic pulse at an ultrasonic pulse repetition frequency fr ', and Sampling frequency fr of ultrasonic pulse in scan line
Control means for changing the scanning line of the ultrasonic pulse for each transmission / reception between a plurality of scanning lines so that fr <fr ′, and at least the reception data obtained by the scanning means for each scanning line. Storage means for holding a predetermined number, detection means for detecting blood flow information for each scanning line from the received data held in the storage means, and display means for displaying the blood flow information detected by the detection means It is characterized by having.

[0016]

The control means controls the scanning means to change the ultrasonic scanning order, thereby lowering the sampling frequency fr in each scanning line with respect to the ultrasonic pulse repetition frequency fr 'to the subject. As a result, low flow velocity can be observed without changing the maximum depth of field, the number of frames, and the image quality.

[0017]

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 the subject, and 12 is an analog section of the 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 DSC (Digital Scan Converte
r), 20 is a color processing circuit, 21 is a D / A converter, 22
Is a VTR, 23 is a color monitor, and 35 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).

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 f0 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 is applied to the low-pass filters 26a and 26b.
And (2f0 + fd) signal are input, high frequency components are removed by the low pass filters 26a 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 (Mov
ing Target Indicator) The calculation unit 27 is added.

The MTI calculator 27 is used in the A / D converter 2
8a, 28b, plural line memories 34a, 34b, MT
It is composed of I 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 plurality of line memories 34a and 34b can hold Doppler information for a plurality of scanning lines according to ultrasonic scanning order control.

FIG. 3 shows an example of the structure of the MTI filter. 1 / Z is a delay of 1 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.

[0029]

[Equation 2] The variance calculator 32 calculates the variance σ ² based on the following equation.

[0030]

[Equation 3] The power calculator 33 calculates the total power T based on the following equation.
Find P.

[0031]

[Equation 4] This total power TP is proportional to the intensity of the scattered echo 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 calculated for each point (blood flow information) is input to the DSC 19, the data is interpolated, and then 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 control of changing the ultrasonic scanning order is performed as follows.

As shown in FIG. 7, when the ultrasonic transmission beam is scanned from the right end of the probe 11, the scanning order is as follows: the rightmost scanning line (No. 1) → the second scanning line (N
o.2) → 3rd scan line (No. 3) → 1st right scan line (N
o.1) → ..., N (N is an integer of 2 or more. In this case, N = 3) independent scan lines (scan lines)
The scanning is performed alternately between them.

In this case, the repetition frequency (= sampling frequency of the Doppler signal) f of the ultrasonic transmission beam in the same direction f
r becomes fr = fr '/ 3 (6), that is, the period T of fr (the ultrasonic beam scanning interval in the same direction) is 3 of the period T' (ultrasonic beam scanning interval) of the ultrasonic pulse repetition frequency fr '. Doubled and above (3)
As is clear from the formula, the lower limit of measurable flow velocity fd min
Is improved to 1/3 as compared with the conventional method, that is, the method in which the ultrasonic transmission beam is continuously transmitted n times in the same direction and then the adjacent scanning line is similarly performed 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. Ultrasonic waves are alternately transmitted and received on a plurality of scanning lines in accordance with the ultrasonic wave transmission / reception order, and Doppler information is stored in the plural line memory
4a and 34b are sequentially written in the corresponding lines. Then, when the fourth data (according to n = 4) is fetched for each scanning line, the four data for the scanning line are read from the plural line memories 34a, 34b.

At this time, the output timing of the four pieces of data is not constant in the case of FIG. To make the output timing constant, scanning may be performed as shown in FIG. That is, when scanning is performed from the right end of the probe 11, the scanning order is as follows: scan line (No. 1) → scan line (No.m-1) → scan line (No.m) → scan line (No.1) ) → scanning line (No.2) → scanning line (No.m) → scanning line (No.1) → scanning line (No.2) → scanning line (No.3) → scanning line (No.1) → ... By doing so, similarly to the case of FIG. 7, the repetition frequency (sampling frequency of the Doppler signal in the same scanning line) fr of the ultrasonic transmission beam in the same direction is ⅓.
And the data output timing can be set to 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 scanning order control of FIG. 7, each data is displayed on one scanning display screen. It is possible to obtain 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.

Generally, considering the repetition frequency fr of the same direction ultrasonic transmission beam, the ultrasonic transmission pulse repetition frequency fr ', and the low flow velocity detectability improvement ratio P (the number of alternating steps), fr = fr' / P expressed. 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.

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

However, in the case of the embodiment of FIG. 9 as well, the data output timing between each scanning line can be set to a substantially constant interval, so that 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 scan-converted in the DSC 19 together with the B-mode image information, and the color processing circuit 20 and the D / A converter 2 are used.
1 is sent to the color monitor 23 and is visualized there. Also, it is recorded in the VTR 22 as needed.

As described above, in the apparatus according to the embodiment of the present invention, the sampling frequency fr of the Doppler information is lowered without changing the ultrasonic repetition frequency fr 'by changing and controlling the ultrasonic scanning order. Field of view D m
A low flow velocity can be observed without degrading ax, the number of frames FN, and the image quality.

The present invention is not limited to the above embodiment, and various modifications can be made within the scope of the claims.

[0046]

As described above in detail, according to the present invention, it is possible to provide an ultrasonic blood flow imaging apparatus capable of observing low flow blood flow without deteriorating the maximum depth of field, the number of frames, and the image quality. You can

[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 a main part of an apparatus according to an embodiment of the present invention.

FIG. 3 is a block diagram of a main part of an apparatus according to an embodiment 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 operation explanatory view of the apparatus according to the embodiment of the present invention.

FIG. 8 is an explanatory view of the operation of the apparatus according to another embodiment of the present invention.

FIG. 9 is an explanatory view of the operation of the apparatus according to another embodiment of the present invention.

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 multiple line memory 35 control circuit

Claims (2)

[Claims] 1. A blood flow in a subject based on received data of a predetermined number of ultrasound pulses obtained for each scanning line by performing ultrasonic scanning on the subject at an ultrasonic pulse repetition frequency fr '. In an ultrasonic blood flow imaging apparatus for obtaining information and displaying the distribution, scanning means for transmitting and receiving ultrasonic pulses at an ultrasonic pulse repetition frequency fr ', and sampling of ultrasonic pulses in each scanning line with respect to the scanning means. Control means for changing the scanning line of the ultrasonic pulse for each transmission / reception between a plurality of scanning lines so that the frequency fr becomes fr <fr ', and the reception data obtained by the scanning means for each scanning line. Storage means for holding at least the predetermined number, detection means for detecting blood flow information for each scanning line from the received data held in the storage means, Ultrasonic blood flow imaging apparatus characterized by having a display means for displaying the blood flow information detected by means out. 2. The control means transmits ultrasonic waves to the scanning means for each transmission / reception between P scanning lines so that the sampling frequency fr of the ultrasonic pulse in each scanning line becomes fr = fr ′ / P. The ultrasonic blood flow imaging apparatus according to claim 1, wherein the scanning line of the pulse is changed.