JPH0236103B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a pulse Doppler apparatus, and more particularly to a pulse Doppler apparatus in which optimization of a Doppler filter portion is automated.

(Prior Art) A pulsed Doppler device is a medical diagnostic device that uses the Doppler effect related to acoustic signals. It irradiates a subject with ultrasound and collects the resulting reflected Doppler signals (i signal, q signal) for each signal. For example, frequency analysis is performed using a frequency analyzer such as a fast Fourier analyzer (hereinafter referred to as FFT), and the resulting spectrum image is monitored on a display device such as a CRT to obtain various information. According to the pulsed Doppler apparatus, it is possible to obtain information regarding a moving subject, such as the heart or blood circulation system.

FIG. 8 is a block diagram showing a conventional example of a pulsed Doppler apparatus. A Doppler signal obtained from the subject enters a Doppler filter 1 and unnecessary frequency components are removed. The output of the Doppler filter 1 enters a frequency analyzer (for example, FFT) 2 where frequency analysis is performed at high speed, and the analysis results are displayed as a spectrum image on the CRT 3. The operator should
By observing the spectrum image displayed on the CRT 3, or by transmitting the signal after passing through the Doppler filter 1 to the spooker 5 via the buffer amplifier 4.
Various information can be obtained by listening to the audio signal. Frequency band of Doppler filter 1,
The gain and the like are controlled by the operator operating the operating section 6.

In this type of device, it is desirable that the frequency characteristics of the path of the Doppler signal input to the FFT 2 be flat in a desired region. This is because if the gains are not equal at each frequency, noise may occur in the FFT2 analysis result, which is undesirable. Also, when performing frequency analysis of Doppler signals, if there are components that occur in soft tissues other than blood flow that are slow moving and have strong signal levels, the signal level will be much lower than that and the Doppler shift will occur. A problem arises in that components with a large width (ie, high Doppler frequency) are masked and cannot be recognized or analyzed. For this reason, the Doppler filter 1 includes a strong low-cut filter for removing fixed reflections (clutter), regardless of whether it is a CW Doppler or a pulsed Doppler, and cuts out the peak components in the low frequency range described above.

(Problems to be Solved by the Invention) Conventionally, the low-frequency cut characteristic of the Doppler filter 1 described above has been determined by an operator manually operating the operating section 6 to a value according to the purpose (for example, when the carrier frequency is 3MHz, 100, 200, 400, 800Hz). Then, the operator changes the filter characteristics of the Doppler filter 1 by operating the operating section 6 while monitoring the spectrum image on the CRT 3 or listening to the sound from speed 5. For example, if there are too many low frequency components, or if the low frequency components are so strong that they mask the high frequency components, or if interference is caused by saturation or distortion due to the low frequency components, Perform operations such as strengthening the cut or raising the cut frequency even higher.

The reason for performing this operation is that the Doppler signal is
This is because generally, the lower the frequency, the higher the level, including Kuratsuta. However, if you blindly cut out the low frequency range, there will be a problem that it will also be cut when another signal hits the low frequency range.
FIG. 9A is a diagram showing the characteristics of a conventional filter. In the figure, the vertical axis represents gain, and the horizontal axis represents frequency. Since the filter characteristics of the conventional Doppler filter have an extremely steep rise as shown in the figure, there is a high risk that effective signal components will be cut out. Therefore, if the filter characteristics can be made to have a gentle slope as shown in FIG. 9B, there is a possibility that effective signal components can be picked up.

The present invention was made in view of these points, and its purpose is to automate the optimization of the Doppler filter, which had conventionally been manually operated, and to adjust the characteristics of the low frequency cut in particular to the current state of the signal. The object of the present invention is to realize a pulsed Doppler device that can be adjusted to an appropriate level.

(Means for Solving the Problems) The present invention, which solves the above-mentioned problems, receives an ultrasonic Doppler signal obtained from a subject, and externally calculates the gain of each band divided into a large number of frequency bands. A Doppler filter section whose overall frequency characteristics can be controlled by increasing or decreasing the frequency characteristics using a control signal from the Doppler filter section, a frequency analysis section which performs high-speed frequency analysis based on the output of the Doppler filter section, and a frequency analysis section that performs high-speed frequency analysis based on the output of the Doppler filter section. The present invention is characterized by comprising a feedback control section that increases or decreases the gain of each band of the Doppler filter section based on the feedback control section.

(Example) Hereinafter, an example of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a block diagram showing an embodiment of the present invention. Components that are the same as those in FIG. 3 are designated by the same numbers. In the figure, 11 is a graphic equalizer that receives ultrasound Doppler signals, and 12 is a graphic equalizer that receives ultrasound Doppler signals.
This is a feedback control section that provides an optimal amount of feedback to the graphic equalizer 11 based on the analysis results of the FFT2. The graphic equalizer 11 is divided into a large number of frequency bands, and the overall frequency characteristics can be controlled by increasing or decreasing the gain of each band using an external control signal. The operation of the circuit configured as described above will be explained as follows.

The ultrasound signal obtained from the subject enters a graphic equalizer 11. Here, the input ultrasonic Doppler signal is LSB (Low Side Band) after direction separation of the ultrasonic Doppler signal, or
USB (Upper Side Band) is selected. The graphic equalizer 11 transmits the frequency characteristics and gain of the input Doppler signal to the feedback controller 12.
The optimum values are set based on the feedback signals (control signals) from the

FIG. 2 is an electrical circuit diagram showing a specific example of the configuration of the graphic equalizer 11. The circuit shown in the figure shows a 7-band graphic equalizer. Each band can be switched to side a (boost side) or side b (cut side) by switches _SW1 to _SW7 . The switches SW ₈ and SW ₉ operate in conjunction, and the gain variable range can be set in two ways, ±6 dB or ±12 dB, depending on whether the contact is turned on or off. Ra ₀ , Ra ₁ , Rab, and Rac are resistors that determine the gain, and Rb ₁ to Rb ₇ and Rc ₁ to Rc ₇ are resistors that constitute an attenuator. Z ₁ to Z ₇ are resonant circuits in which the common contact of switches SW ₁ to _{SW 7} is grounded at one end and the other end is grounded, and each resonant circuit is composed of a series circuit of a capacitor, a coil, and a resistor. . U ₁ is the input signal Vin
The operational amplifier _U2 that receives the signal is an operational amplifier that constitutes a buffer amplifier.

In the circuit configured in this way, it is assumed that the switches SW ₁ to SW ₇ are now connected to the boost side. Considering the case of only the first band, the circuit shown in the figure becomes as shown in FIG. 3. If the identification signal is used as is as the resistance value of the resistor and the impedance value of the impedance shown in FIG. 3, the gain Ab ₁ of the circuit shown in the figure is given by the following equation.

Ab ₁ =1+{Ra ₀ /(Rb ₁ +Z ₁ )} (1) The frequency characteristics of Ab ₁ are as shown in FIG. 4, where f ₁ is the center frequency.

Next, assume that switches SW ₁ to SW ₇ are connected to the cut side. Considering the case of only the first band, the circuit shown in FIG. 2 becomes as shown in FIG. 5. When the gain of the circuit shown in the figure is determined in the same manner as in the case of FIG. 3, the gain Ac ₁ is given by the following equation.

Ac ₁ =1/{1+(Ra ₂ /(Rc ₁ +Z ₁ ))}(2) The frequency characteristics of Ac ₁ are as shown in FIG. 6, where f ₁ is the center frequency.

FIG. 7 is a diagram showing the overall frequency characteristic of the circuit shown in FIG. 2 obtained by repeating the above-described operation. In the figure, the horizontal axis represents frequency (Hz), and the vertical axis represents gain (dB). A waveform drawn in a region where the gain is positive is a boost waveform, and a waveform drawn in a region where the gain is negative is a cut waveform. Both exhibit 7-band frequency characteristics, f ₁ , f ₂
indicates the sum of the respective waveforms. Note that the characteristics shown in the figure are for the case where the gain variable range is ±12 dB. In this way, according to the graphic equalizer shown in FIG _.
By controlling the switching state of SW ₉ ,
Any band can be set to boost or cut mode. Therefore, the graphic equalizer shown in the figure can arbitrarily vary its frequency characteristics and gain using external control signals.

Returning again to the explanation of the operation in FIG. The ultrasonic Doppler signal given a predetermined frequency characteristic and gain by the graphic equalizer 11 enters the FFT 2.
The ultrasound Doppler signal entering FFT2 is, for example, the 7th
By passing through the graphic equalizer 11 section with cut characteristics as shown in _FIG . Therefore, on the FFT2 side, even if there is a component with a strong amplitude level in the low frequency range, it is removed by the filter effect of the graphic equalizer 11, so the high frequency signal component is not masked, and the accurate frequency Analysis can be performed.

Furthermore, according to the present invention, as shown in FIG. 7, the slope part of the filter characteristic can be made considerably smooth by setting the circuit constants of the impedances Z ₁ to _{Z 7} of the resonant circuit part to predetermined values. It can be made to have certain characteristics. Therefore, the originally effective signal component, which would have been lost in the case of the conventional device, is saved and applied to the FFT2 as a useful signal. As a result, FFT2 can perform more accurate frequency analysis than conventional equipment, and the spectrum image on CRT3 also provides more accurate information.

The output of FFT2 is simultaneously sent to feedback control section 12. The feedback control section 12
compares the sent FFT2 analysis data with internal standard data or externally input standard data. The comparison results are integrated using an integrator,
Alternatively, the integral calculation is performed by a microprocessor. The feedback control section 12 determines the amount of feedback based on the comparison result and provides it to the graphic equalizer 11. The graphic equalizer 11 receives a control signal from the feedback control section 12 and determines optimal frequency characteristics and gain. Taking the circuit shown in FIG. 2 as an example, this operation means switching the switches _SW1 to _SW9 to predetermined states. Graphic equalizer 11
Given the optimal frequency characteristics and gain,
The input ultrasonic Doppler signal has its low frequency components removed and is converted into a signal containing only necessary frequency components.
Therefore, as described above, FFT2 can perform accurate frequency analysis and obtain accurate information.

In the above explanation, a graphic equalizer was used as a means to vary the frequency characteristics and gain, but other types of means, such as an active filter combination circuit, may be used as long as they produce the same effect. good. Furthermore, when processing ultrasound Doppler signals of multiple channels, this can be handled by increasing the number of channels in the graphic equalizer section and using FFT in a time-division manner. Further, the number of bands of the graphic equalizer 11 does not need to be seven as shown in FIG. 2, but may be any number. Increasing the number of bands is advantageous because it allows the frequency characteristics and gain to be varied over a wider range.

(Effects of the Invention) As explained in detail above, according to the present invention,
The output of the Doppler filter section, whose overall frequency characteristics can be controlled by increasing or decreasing the gain of each band divided into many frequency bands using an external control signal, is analyzed by the frequency analysis section, and based on the analysis results. Since the feedback control unit increases or decreases the gain of each band of the Doppler filter unit, it is possible to automatically set the frequency characteristics and gain to optimal values.

[Brief explanation of drawings]

FIG. 1 is a configuration block diagram showing one embodiment of the present invention, FIG. 2 is an electric circuit diagram showing a specific example of the configuration of a graphic equalizer, FIGS. 3 and 5 are equivalent circuit diagrams thereof, and FIG. 4, 6, and 7 are diagrams showing filter characteristics, FIG. 8 is a block diagram showing a conventional example, and FIG. 9 is a diagram showing filter characteristics. 1...Doppler filter, 2...FFT, 3...
CRT, 4...Buffer amplifier, 5...Speaker,
6...Operation unit, 11...Graphic equalizer, 12...Feedback control unit, _Rb1 to _Rb7 ,
Rc ₁ ~ Rc ₇ , Ra ₀ , Ra ₁ , Rab, Rac...Resistance,
SW ₁ to _{SW 9} ... switch, Z ₁ to _{Z 7} ... resonant circuit,
U ₁ , U ₂ ... operational amplifier.

Claims (1)

[Claims] 1 A Doppler filter section that receives the ultrasonic Doppler signal obtained from the subject, and whose overall frequency characteristics can be controlled by increasing or decreasing the gain of each band divided into a large number of frequency bands using an external control signal. and a frequency analysis section that performs high-speed frequency analysis upon receiving the output of the Doppler filter section;
An ultrasonic Doppler apparatus comprising: a feedback control section that increases or decreases the gain of each band of the Doppler filter section based on the analysis result of the frequency analysis section.