JPH082357B2 - Ultrasonic Doppler blood flow meter - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ultrasonic Doppler blood flow meter capable of simultaneously performing ultrasonic imaging and pulse Doppler velocity measurement.

2. Description of the Related Art Recently, an ultrasonic Doppler blood flow meter that simultaneously displays a Doppler sonargram and a tomographic image in real time by using ultrasonic Doppler measurement method and pulse reflection method has been actively used for diagnosis of biological circulatory organs. It has come to be used. This ultrasonic Doppler blood flow meter is known to have a structure described in, for example, JP-A-55-54941. The conventional ultrasonic Doppler blood flow meter will be described below with reference to FIG.

FIG. 4 is a diagram showing the basic principle of the ultrasonic Doppler blood flow meter. In FIG. 4, 40 is a probe, 41 is a transmission scanning circuit, 42 is a reception scanning circuit, 43 is a phase detection circuit, 44 is a frequency analyzer, 45 is an amplitude detection circuit, 46 is a display section, and 47 is a control section. .

Next, the operation of the above conventional example will be described. The drive pulse generated by the transmission scanning circuit 41 is applied to the probe 40, and a sound wave is transmitted in the directions of directivity m ₁ , m ₂ , ..., M _n .
Receiving scanning circuit 42 transmits the same directivity m _1, m _2, the receiving sensitivity in the direction of ... is controlled to be higher. In the Doppler mode, the directivity is fixed in a fixed direction, for example, the directivity is fixed in the m _d direction, transmission and reception are repeated, and the I and Q signals, which are Doppler shift data obtained by phase detection of the received signal, are subjected to frequency analysis. The moving speed of the blood flow in the sample is calculated and displayed on the display unit. In the B mode, transmission / reception is sequentially performed in the directivities m ₁ , m ₂ , ..., And the obtained reception signal is subjected to envelope detection by the detection circuit and displayed as a tomographic image on the display unit. Doppler mode,
The control unit 47 determines which of the B modes is selected. In order to simultaneously obtain blood flow information and B-mode tomographic image of the sample volume S in the m _d direction, m _J (j
= 1 to n) direction, the control unit 47 alternately performs the Doppler operation in the m _d direction after the B mode operation. Hereinafter, such an operation mode is referred to as a B / D mode. When the repetition frequency of the transmitted ultrasonic pulse in the Doppler mode is fr, the repetition frequency of the Doppler operation decreases to fr / 2 in the B / D mode, which causes a problem that the measurable maximum blood flow velocity becomes half.

In order to solve this problem, a method for obtaining a B-mode image without lowering the Doppler sampling frequency has been devised. As an example of such a method, the method described in JP-A-61-25534 is known. In this method, for example, in a device having a configuration as shown in FIG. 4, transmission / reception in the Doppler mode is repeated three times, transmission / reception in the B mode is performed once, and interpolation is performed on the Doppler shift data of the phase detection output that has passed once. This is based on the principle that the sampling frequency of the Doppler shift data is not lowered apparently by performing.

However, the interpolation method used in this method was devised for the processing of speech signals and includes frequency components approaching 1/2 of the sampling frequency like Doppler shift data. It was not suitable for signal interpolation. In Fig. 5, the transmission in the Doppler mode is repeated twice, and then the transmission in the B mode is set to 1.
FIG. 7 shows the state of interpolation by the conventional method in the case of Doppler shift data having a frequency component close to 1/2 of the repetition frequency fr of the transmission pulse.

As shown in FIG. 5, the interpolated result is completely different from the expected value, and there is a problem that the frequency shifts to a low frequency and correct frequency analysis cannot be performed.

The present invention solves the above problems of the prior art, and it is possible to reduce the repetition frequency of the Doppler mode transmission pulse.
The purpose is to enable accurate interpolation even for Doppler shift data approaching 1/2.

Means for Solving the Problems In order to solve the above problems, the present invention considers Doppler shift data of phase detection output as complex data, obtains declination difference data between adjacent Doppler complex data, and calculates the declination difference. The above object is achieved by providing data interpolation means for generating interpolation data based on the data.

Action The present invention has the above-described configuration to enable accurate data interpolation in the B / D mode even for Doppler shift data having a frequency close to 1/2 of the sample frequency in the Doppler mode.

First Embodiment A first embodiment of the present invention will be described below with reference to the drawings.

In FIG. 1, a solid line indicates a signal flow, a dotted line indicates a control flow, 1 is a probe, 2 is a transmission scanning circuit, 3 is a reception scanning circuit, 4 is a control unit, 5 is a switch, 6 is a detection unit, 7,8 is a mixer, 9 is an oscillator, 10 is a phase shifter, 11,12
Is a sample and hold circuit, 13 is an interpolation unit, 14 is a frequency analysis unit, and 15 is a display unit. The operation of the configuration shown in FIG. 1 will be described below. The probe 1 receives the drive pulse from the transmission scanning circuit 2, transmits an ultrasonic pulse to the subject, converts the scattered ultrasonic waves from the subject into an electric signal, and sends the electrical signal to the reception scanning circuit 3. Transmission scanning circuit 2,
The reception scanning circuit 3 performs B-mode scanning and Doppler scanning in time division according to an instruction from the control unit 4. The switch 5 sends an ultrasonic echo signal from the reception scanning circuit 3 to the detection unit 6 during the B mode scanning and to the mixers 7 and 8 during the Doppler scanning according to an instruction from the control unit 4. The mixer 7 mixes the ultrasonic echo signal from the switch 5 and the signal from the oscillator 9, and the mixer 8 mixes the ultrasonic echo signal from the switch 5 and the oscillator 9.
The Doppler signal is detected by mixing the signal from (1) with the signal whose phase is shifted by 90 ° by the phase shifter (10). The sample hold circuits 11 and 12 receive a gate signal corresponding to the Doppler inspection region from the control unit 4 and sample the Doppler signals from the mixers 7 and 8. Interpolator 13 is a sample and hold circuit
Based on the Doppler signals from 11 and 12, the Doppler data in the Doppler transmission / reception pause period instructed by the control unit 4 is obtained by interpolation calculation, and is inserted into the Doppler signal in the Doppler transmission / reception period to obtain the Doppler signal at equal time intervals. Generate a data string,
It is sent to the frequency analysis unit 14. The frequency analysis unit 14 performs Fourier analysis, etc., and displays the result as a Doppler image signal in the display unit.
Send to 15. The display unit 15 simultaneously displays the B-mode image signal from the detection unit 6 and the Doppler image signal from the frequency analysis unit 14 under the control of the control unit 4.

The operation timing of each of the above parts will be described with reference to FIG. FIG. 2 shows an example of operation timing in which Doppler scanning is repeated twice and B-mode scanning is repeated once. In the figure, (A) shows the transmission pulse of the transmission scanning circuit 2, (A) shows the connection state of the switch 5, and D shows that the input is connected to the mixers 7 and 8, and B shows the connection to the detection unit 6. (C) is the output of the detection unit 6,
(D) is a Doppler gate signal from the control unit 4 for controlling the sample and hold circuits 11 and 12, (E) is a diagram in which the outputs of the sample and hold circuits 11 and 12 are represented by real and imaginary parts, respectively. FIG. 3 is a diagram showing the output of the interpolation unit 13 as a vector.

The transmission scanning circuit 2 sends the Doppler scanning pulse D or the B-mode scanning pulse B to the probe 1 at the timing indicated by the transmission pulse (a). As shown in (a), the switch 5 sends the output of the transmission scanning circuit 3 to the mixers 7 and 8 during the periods P ₁ and P ₃ (Doppler scanning period), and detects the output during the period P ₂ (Doppler scanning rest period). It is sent to the unit 6. In the period P ₂ , as shown in (c), the information of the two scanning lines forming the B-mode tomographic image is collected, and the detection unit 6 performs envelope detection. In the Doppler scanning periods P ₁ and P ₃ , the quadrature detection outputs from the mixers 7 and 8 are output to the Doppler sampling time t _{1 as} shown by (e) by the sample and hold circuits 11 and 12 controlled by the Doppler gate signal (d). , T ₂ , t ₄ , and t ₅ are sampled. As shown in (f), the interpolating unit 13 calculates the Doppler signal Z ₃ at the Doppler sampling time t ₃ when the B-mode scanning period P ₂ is assumed to be the Doppler scanning period as t ₁ , t ₂
Interpolation based on the Doppler data in.

FIG. 3 shows a block diagram of an embodiment of the interpolation unit 13. 3
Reference numerals 1 and 32 denote AD converters, 33 denotes deviation angle difference data calculation means, and 34 denotes interpolation data generation means. The AD converters 31 and 32 perform A / D conversion on the outputs from the sample hold circuits 11 and 12, respectively. Since the outputs of the sample and hold circuits 11 and 12 can be treated as complex numbers, the outputs of the A / D converters 31 and 32 will be referred to as complex Doppler shift data. Calculates the polarization angle difference data Δθ data Z ₂ in the complex Doppler shift data Z ₁ and t ₂ at the sampling time t ₁ in polarization angle difference data calculation means 33. Arithmetic unit
In 34, the interpolation data Z ₃ is calculated based on the deviation angle difference data Δθ and the complex Doppler shift data, and the directly measured Doppler shift data Z ₁ and Z ₂ and the interpolated data Z ₃ are arranged in the correct time order. Output.

An example of the interpolation calculation is shown below. Complex Doppler shift data
Z ₁ and Z ₂ can be expressed as x ₁ + jy ₁ and x ₂ + jy ₂ , respectively. The deviation angle θ ₁ of Z ₁ can be calculated as θ ₁ = tan ⁻¹ (y ₁ / x ₁ ) ... (1). Similarly, the deviation angle θ ₂ of Z ₂ can be obtained, and the deviation angle difference data Δθ Δθ = θ ₂ −θ ₁ (2) can be obtained using the above. When the Doppler signal is viewed as a complex number, its absolute value and declination difference data usually rarely change abruptly. Therefore, the argument θ of the interpolation data Z can be approximated by the following equation.

θ = θ ₂ + Δθ (3) If the interpolation data Z and the complex displacement data Z ₂ are approximated to have the same absolute value, the interpolation data Z can be expressed by the following equation.

Z = r ₂ × (cos θ + j sin θ) (4) where r ₂ = | x ₂ + jy ₂ | This interpolation calculation uses the fact that the absolute values of complex Doppler displacement data and declination difference data do not change rapidly. Various methods are possible. For example, Z = Z ₂ · Z ₂ / Z ₁ is also possible.

As described above, even for Doppler deviation data approaching 1/2 of the repetition frequency of the Doppler mode transmission pulse, it is correct based on the deviation angle data (in this case, it approaches ± 180 °) and the absolute value. Interpolation data can be obtained, and accurate interpolation can be performed even during the Doppler pause period.

As is apparent from the above embodiment, the present invention generates interpolation data based on deviation angle difference data between complex Doppler displacement data, so that, for example, B mode and Doppler mode are switched alternately. In D mode, it becomes possible to correctly obtain the interpolation data during the Doppler pause period.

The present invention can accurately interpolate Doppler deviation data approaching 1/2 of the repetition frequency of the transmission pulse of the Doppler mode.

[Brief description of drawings]

FIG. 1 is a block diagram of a Doppler blood flow meter in one embodiment of the present invention, FIG. 2 is a timing diagram showing operation timing of the block diagram shown in FIG. 1, and FIG. 3 is a main part of the Doppler blood flow meter. FIG. 4 is a block diagram of a certain data interpolating means, FIG. 4 is a block diagram of a conventional ultrasonic Doppler blood flow meter, and FIG. 5 is a diagram showing an example of conventional data interpolation. 1 ... probe, 2 ... transmission scanning circuit, 3 ... reception scanning circuit, 13 ... interpolator, 33 ... declination difference data calculation means.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor, Yunao Nakanaka, 4-3-1, Tsunashima-higashi, Kohoku-ku, Yokohama-shi, Kanagawa Matsushita Communication Industrial Co., Ltd. (56) Reference JP-A-61-25534 A)

Claims (2)

[Claims] 1. An ultrasonic Doppler blood flow meter for obtaining moving speed information of a scatterer in the subject based on ultrasonic waves scattered from the subject by transmitting and receiving ultrasonic pulses in the subject,
Control means for generating a pause period for the Doppler transmission / reception sequence, means for obtaining deviation angle difference data between continuously obtained complex Doppler shift data, and the pause period based on the deviation angle difference data. An ultrasonic Doppler blood flow meter equipped with data interpolation means for generating interpolation data. 2. The ultrasonic Doppler blood flow meter according to claim 1, further comprising a data interpolating means for extrapolating the deviation angle data.