JPH0550942B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an ultrasonic diagnostic device, and particularly an ultrasonic diagnostic device that performs an electronic focus circle using a probe in which a plurality of transducers are arranged, and emits an ultrasonic beam into a subject. The present invention relates to an ultrasonic diagnostic apparatus that processes reflected echoes and displays information such as tomographic images inside a subject.

[Prior Art] In recent years, devices that electronically scan the inside of a subject have been widely used as ultrasonic diagnostic devices, and as shown in FIG. Each oscillator 1 of the oscillator group is
Electronic focus technology that performs excitation control with a delay time at 0 is well known. The ultrasound beam obtained by this electronic focus control is a composite wave (secondary wave) of multiple ultrasound waves emitted from multiple transducers.
The ultrasonic waves from each transducer 10 of the transducer group interfere with each other to form a composite wave with maximum interference at the focal position.

The ultrasonic waves formed by the transducer group consisting of a plurality of transducers 10 are reflected by a reflector inside the living body and received as an echo signal, but in this case as well, each vibration used to form the ultrasonic beam The reflected echo is received at the child 10 with a delay time.

In this way, when the echo signals obtained by each transducer 10 of the transducer group are combined, an ultrasonic reception signal having information on the position of the focus point F is obtained.

On the other hand, echo signals from points other than point F are also subjected to the same phase control as described above, and may become a composite wave with considerable force. This is called an echo signal due to side lobes.

Furthermore, by scanning the ultrasonic beam obtained by electronic focus control multiple times in the depth direction of the object and in the direction of the transducer arrangement, it is possible to display images inside the object in B mode, etc. The sharper the ultrasonic beam is controlled, the more sharp the image can be obtained.

[Problems to be Solved by the Invention] However, if there is a strong reflector near the focal position of the subject, a false echo (artifact) will occur due to this strong reflector, and unnecessary echo signals due to side lobes will be added to the signal from the focal position. is mixed in. In this case, an image is displayed as if a reflector that does not actually exist is present due to the pseudo echo, and an unclear image is formed.

In recent years, there has been a trend to increase the number of transducers to reduce unnecessary echo signals caused by such sidelobes, but with this method, even if the number of transducers is doubled, the maximum improvement in principle is 6 dB. Further, this method of increasing the number of transducers has the problem that the circuit becomes complicated, there is a limit in the size of the probe that accommodates the group of transducers, and manufacturing costs are increased.

Purpose of the Invention The present invention has been made in view of the above-mentioned conventional problems, and its purpose is to provide an ultrasonic diagnostic apparatus that can significantly reduce unnecessary echo signals due to side lobes that cause the generation of pseudo echoes. It is in.

[Means for Solving the Problems] In order to achieve the above object, the present invention includes a plurality of arrayed ultrasonic transducers, which transmit and receive ultrasonic waves of a predetermined frequency to generate a plurality of received signals. a focus delay circuit that delays each of the received signals according to the distance from the focal position to each of the ultrasonic transducers in order to perform electronic focusing; a sample hold circuit that samples and holds each received signal output from the focus delay circuit at a sampling frequency higher than the predetermined frequency; a spatial frequency conversion circuit that serially outputs a plurality of signals output in parallel from the hold circuit in the order in which the ultrasonic transducers are arranged; It is characterized by comprising a filter that passes nearby components and removes the spatial frequency component, and an integrating circuit that integrates the signal output from the filter at the sampling period.

That is, in the present invention, the amplitude of the echo signal coming from the focal position of a predetermined point is the same no matter which transducer in the transducer group is used, but the amplitude of the echo signal coming from a position other than the focal point is the same. The focus is on the fact that the amplitude is not the same, but when looking at the whole group of oscillators, it has a spatial frequency.

For example, as shown in FIG. 11, if the focal point is located far away, if an unnecessary echo signal from near the focal point is input to the transducer 10 from the direction of the angle θ, then , the unnecessary echo signal wave is located at a line 100 at an angle θ from the transducer array direction.
The waves become aligned at the position. Therefore, when electronic focusing is performed on the received signals obtained by n transducers 10, in the case of an echo signal from the focal position,
The amplitude of the signal from each vibrator of the waveform sampled and held at a certain time is constant. However, in the case of an unnecessary echo signal input from the direction of angle θ, the amplitude of the sampled and held waveform shown by waveform 200 fluctuates, and the signals obtained from all n transducers are arranged in the order in which the transducers are arranged. When juxtaposed, a signal having a spatial frequency will be formed.

If this signal with a certain spatial frequency is removed from the received signal, unnecessary echo signals can be effectively removed.

The above spatial frequency will be explained using a mathematical formula. If the ultrasonic wave is a continuous wave cos ω ₀ t and the origin is the transducer 10-n, then when the voltage at this origin is sin ω ₀ t ₁ , the transducer 10-n is separated by a distance of x ₁ . 10-6
The voltage at is cos(2πl/λ+ω ₀ t ₁ )...(1). However, l=x ₁ sin θ, λ is the wavelength of the ultrasonic wave.

Also, the voltage distribution on the X axis at time t ₁ g (x, t ₁ )
can be expressed by the following formula.

g(x, t ₁ )=cos(2πsinθ/λx+ω ₀ t ₁ ); when o≦x≦a, or g(x, t ₁ )=0; in other cases...(2) This spatial voltage distribution function g If (x, t ₁ ) is read out at high speed in T _d time, it becomes a waveform on the time axis, which can be expressed by the following equation.

g(t, τ _j ) = cos2πf ₀ (D/CT _d sinθ・t+τ _j ) …(3) However, τ _j ≦t<τ _j+1 , D is the aperture of the vibrator, Td=τ _j+1 − τ _j and C are the speed of sound, and f ₀ is the frequency of the ultrasonic wave.

Therefore, the time waveform f(t) [curve 200] when the echo signal is sampled every time T _d and each voltage distribution waveform is transferred is: f(t)= _∞ 〓 ^j=0 …(4) It can be expressed as

[Operation] According to the above configuration, if the ultrasonic frequency (carrier frequency) is 3.5MHz, for example, 10M
The echo signal from the focal position will be sampled at a sampling frequency of Hz. Then, the sampled echo signals for each vibrator are sequentially read out on the time axis, and this readout is repeated at every sampling period. As a result, echo signals from the focal position are not significantly affected, but unnecessary echo signals due to side lobes from positions other than the focal position appear as spatial frequency signals considerably higher than the carrier frequency.

Next, the signals read out sequentially on the time axis are supplied to a filter that passes only the carrier frequency signal, and the spatial frequency signal is removed by this filter.

[Embodiments] Hereinafter, preferred embodiments of the present invention will be described based on the drawings.

FIG. 1 shows a schematic configuration of characteristic parts of an ultrasonic diagnostic apparatus according to a first embodiment of the present invention, and a second embodiment of the present invention is shown in FIG.
The figure specifically shows the overall configuration of the ultrasonic diagnostic apparatus.

In FIG. 2, a probe 14 is brought into contact with the subject 12, and a group of transducers within the probe 14 emit an ultrasonic beam with electronic focus to the subject 12.
radiated towards. Radiation control of this ultrasonic beam is performed by a scanner 16, to which a transmitting circuit 18 and a high frequency oscillator 20 are connected.

Therefore, the high frequency output from the high frequency oscillator 20 is converted into a repetitive pulse signal which is repeated at a predetermined period at a frequency of 3.5 MHz (carrier frequency), for example, by the transmitting circuit 18, and this high frequency pulse signal having a predetermined repetition is sent to the scanner 16. Transducer 1 through
4, and by controlling this scanner 16, the object 12 can be scanned with the ultrasonic beam.

The echo reflected from the subject 12 is received by the transducer 10 within the probe 14 and supplied to the electronic focus delay circuit 22 via the scanner 16. This electronic focus delay circuit 22
At the time of reception, delay control is performed to receive only the signal from the focal position, and the probe 14
A delay time corresponding to the distance to the focal position is given to each input signal of each vibrator 10 in the oscillator 10. Note that the operation of this electronic focus delay circuit 22 is based on the output 300 of the timing generation circuit 24.

The characteristic feature of the present invention is that the unnecessary echo signal due to the side lobe is converted into a signal with a spatial frequency, and this signal is removed from the echo signal (received signal).For this purpose, a spatial frequency filter is used. A section 26 is provided, which will be described later.

The output of the spatial frequency filter section 26 is logarithmically amplified by a logarithmic amplifier 28 at a predetermined rate, and is supplied to a digital scan converter (DSC) 32 via a detector 30. This DSC
32 performs signal processing for displaying ultrasound information as an image on the CRT display 34, thereby making it possible to display a tomographic image of the subject 12 in a good condition without flickering or the like.

FIG. 1 shows the internal configuration of the spatial frequency filter section 26. In the figure, first, n pieces of transducers 10, 64 pieces in the embodiment, are arranged inside the probe 14. Electronic focus delay circuit 22
There are n pieces (64
) delay lines 36 are provided. This delay line 36 gives each vibrator 10 a delay amount corresponding to the distance from the focal position F, so that only the echo signal from the focal position F is received. The amount of delay is increased in order from the vibrator 10 to the vibrator 10 closest to it.

The spatial frequency filter unit 26, which is a characteristic component of the present invention, includes a sampling circuit that samples the signal at a predetermined point (point F in the figure) in the subject 12, which is the output of the delay line 36. However, in the embodiment, a sample and hold device 38 is used as this circuit. This sample hold device 38 is connected to the output 3 of the timing generation circuit 24.
01, for example, the gate circuit is opened for a predetermined period of time at a period of the reciprocal of the frequency of 10 MHz, a signal is taken in, and the signal is held for a period of Δt.

Additionally, there is a delay line 40 for aligning the respective outputs from the sample and hold device 38 in the order of the transducer arrangement and serially reading them out within the Td period, and this delay line 4
The delay line 40 and the adder 42 constitute a spatial frequency conversion circuit that converts an unnecessary echo signal due to a side lobe into a signal with a spatial frequency.

That is, the output of each sample and hold device 38 is delayed by the hold time Δt by the delay line 40, and then added, so that the output of each vibrator 1 is
The echo signals of the focal position F obtained at 0 can be sequentially read out and arranged on the time axis. In this case, the echo signal from the focal position F will be a signal that does not change at all based on the carrier frequency, but
Unnecessary echo signals due to side lobes captured at the same time become signals having a spatial frequency. In addition,
The delay line 40 can also be replaced by a storage circuit that stores and holds the input signal for a predetermined period of time.

Further, the adder 42 includes a band pass filter 44 as a filter for removing the spatial frequency signal.
is connected, and this bandpass filter 44
is the center frequency f ₀ as shown in Fig. 3.
It has filter characteristics of 3.5MHz. Therefore, this means that frequency components of 7MHz or higher are removed.

FIG. 4 conceptually shows a carrier signal 400 and a spatial frequency signal 401. here,
The horizontal axis is time and the vertical axis is voltage.

The carrier signal is represented as a 3.5 MHz sine wave, and the spatial frequency signal is represented as a higher frequency sine wave. Therefore, the spatial frequency signal, which is a high frequency signal, can be removed by passing the echo signal through the band pass filter 44 whose center frequency is the ultrasonic carrier frequency of 3.5 MHz. In Figure 12,
The output signal from one side of delay line 40 is specifically shown. Here, 301 is an output waveform when no unnecessary echo occurs, and is a rectangular wave.

This rectangular wave is caused by the fact that the levels of each output from the sample and hold circuit 38 are the same, in other words, the phases are matched by electronic focus. On the other hand, 302 is
This is an output waveform when unnecessary echo components are superimposed, and as shown in the figure, spatial frequency components appear as dashed lines.

In the present invention, as is clear from FIG. 4, the echo signals obtained by each transducer 10 are sequentially read out on the time axis, but in the conventional ultrasonic diagnostic apparatus, the echo signals are read out by 64 vibrations. The output of the child 10 is added in the voltage (vertical axis) direction for subsequent processing.
Therefore, in the present invention, an integrator 46 is provided to integrate the output of the bandpass filter 44.
Next, the output of this integrator 46 is further sampled by a sample-and-hold device 48, and is output to the logarithmic amplifier 28 in FIG. Note that the integrator 46 and sample hold device 48 are driven based on the outputs 302 and 303 of the timing generation circuit 24.

The first embodiment has the above configuration, and its operation will be explained below.

The ultrasonic wave radiated toward the focal position F is reflected from a reflector depending on the focal position F, and is received by each transducer 10 as an echo signal. The echo signals are each given a predetermined amount of delay by a delay line 36, and are supplied to a sample and hold device 38 in the spatial frequency filter section 26. Then,
The echo signal with a carrier frequency of 3.5MHz is sampled with a sampling frequency of 10MHz.

Then, the delay line 40 reads out the output of the sample and hold device 38 in order from the first sample and hold device 38 to the nth sample and hold device 38 while sequentially shifting the output by a predetermined delay amount (Δt). In the example, the 1st, 2nd, 3rd
At the same time, the signals are read out from the sample-and-hold device 38 in the order of the n-th, . Then, the adder 42 outputs a signal that is the sum of the signals read from both sides, and this output includes the signals read from one side because the ultrasonic beam is scanned left and right. The spatial frequency will appear more prominently than in the case of

In this way, n=64 signals are arranged on the time axis by the adder 42, and this scanning is performed every sampling period, and the focus position F
The echo signal from is a signal as shown in waveform 401 in FIG. At the same time, the spatial frequency signal extracted by the processing from the sample and hold unit 38 to the adder 42 has a waveform 402 in FIG.
The signal is shown as .

Then, by supplying the output of the adder 42 to the band pass filter 44, only the carrier frequency signal (ultrasonic frequency signal) 401 is extracted.
Spatial frequency signal 402 will be removed. In this case, the carrier frequency signal 401 is a rectangular wave at the output stage of the adder 42, but after passing through the band pass filter 44, it becomes a signal close to a rounded sine wave.

The output of the bandpass filter 44 is then input to an integrator 46, where the conventional 64 oscillators 10
Integration corresponding to the addition of the voltage signals in is performed, and the indicating characteristic of the voltage distribution waveform in the signal output from the integrator 46 becomes as shown in FIG. In the figure, the vertical axis is the signal level, and the horizontal axis is the angle of the sidelobe seen from the center line, assuming that the focal point is on the center line drawn perpendicular to the transducer row from the center position of the arrayed transducer group. ing.

Here, before explaining the indication characteristics of the present invention, we will explain the indication characteristics of the voltage distribution waveform obtained with the conventional device and the output of the adder 42 to the integrator 46 without using the bandpass filter 44 in the present invention. Compare the indicated characteristics of the voltage distribution waveform when directly integrated.

Figure 5 shows the conventional method, for example, the frequency is 3.5M.
Hz, the number of oscillators is 32, and the pitch (d) between the oscillators is
The indicating characteristics in the case of 0.5 mm are shown in Figure 6.
The indication characteristic of the output of the integrator 46 is shown when the bandpass filter 44 is removed in the embodiment. Comparing both Fig. 5 and Fig. 6, it is found that the indicating characteristics are almost the same, and as a result, the echo signals obtained from each transducer 10 are sampled and held, and a predetermined delay is applied. It is proven that the same signal processing as the conventional method can be performed even when reading out sequentially over time and then integrating.

Next, the directional characteristics in Figure 7 are based on the sampling period
Td is 125n (nano) sec, band pass filter 4
4 is a Gaussian filter with a center frequency of 3.5MHz. As is clear from a comparison between FIG. 7 and FIG. 5, the side lobe at a position a predetermined angle away from the center line of the transducer array is suppressed by a maximum of 20 dB.

Attempting to achieve this 20 dB suppression using conventional methods would require increasing the number of transducers ten times, which is virtually impossible. In addition, in Figure 7, the angle is 30 degrees ~
The larger the sidelobe angle in the 60 degree range, the higher the signal level, but in reality, by adjusting the transducer array spacing d, the side lobe at 60 degrees in the figure becomes larger than 90 degrees. Since the design is such that the signal level of the side lobe increases does not become a problem.

In the present invention, since the echo signal is sampled at a high speed of 10 MHz, digital processing requires an A/D converter capable of high-speed processing, and other calculations must also be processed at high speed. Therefore, it is currently preferable to process the echo signal by reducing it to a low frequency band, and next, second and third embodiments related to this will be described.

FIG. 8 shows a second embodiment using the heterodyne system, in which n mixers 50 and n low-pass filters 52 are connected between the delay line 36 and the spatial frequency filter section 26. shall be.
Then, by multiplying the echo signal by a local signal of a sine wave (cosine wave) or a rectangular wave, which is a signal with a frequency different from the center frequency of the ultrasonic pulse wave, in the mixer 50, the echo signal is reduced to an intermediate frequency. By passing this through the low-pass filter 52, the carrier frequency of the echo signal, 3.5 MHz, can be reduced to 1 MHz or less.

FIG. 9 shows a third embodiment using the orthogonal detection method, in which two spatial frequency filter sections 2
6a, 26b are provided, and two mixers 54a, 54b (n each) and two low pass filters 56a, 56b (n each) are provided between the spatial frequency filter sections 26a, 26b and the delay line 36. ). And mixer 5
4a is supplied with a local signal as a cosine wave (cos) signal, and mixer 54b is supplied with a local signal as a sine wave (sin) signal with a phase difference of 90 degrees from the local signal, and these local signals are echoed. By multiplying the echo signal by the signal, the echo signal can be reduced to a low frequency signal as in the second embodiment.
In this case, the spatial frequency filter sections 26a, 26b
The output is the relationship between the real part and the imaginary part of the complex signal, and these outputs are combined and processed later as a complex signal.

According to the second and third embodiments, there is an advantage that sampling in the spatial frequency filter unit 26 can be easily performed, and that hardware such as an A/D converter can be easily designed.

[Effects of the Invention] As explained above, according to the present invention, an echo signal is sampled at a frequency higher than the ultrasonic frequency, and the sampling signal obtained by each transducer is delayed by a predetermined delay time on the time axis. By reading out sequentially, unnecessary echo signals from reflectors other than the predetermined points are converted into signals with spatial frequency, so the echo signals from the focal position and unnecessary echo signals from other than the focal position can be well separated. This makes it possible to effectively remove unnecessary signals due to side lobes.

Therefore, the occurrence of false echoes is eliminated, and it becomes possible to obtain ultrasonic diagnostic images with high sharpness.

[Brief explanation of drawings]

FIG. 1 is a schematic configuration diagram showing a first embodiment of the ultrasonic diagnostic apparatus according to the present invention, FIG. 2 is an overall configuration diagram of the ultrasonic diagnostic apparatus according to the present invention, and FIG. A graph showing the filter characteristics of
FIG. 4 is a waveform diagram explaining the adder output of the spatial frequency filter section, FIG. 5 is a diagram showing the indication characteristic of the voltage distribution waveform in the echo signal received and processed by the conventional device, and FIG. 6 is the waveform diagram in the present invention. FIG. 7 is a diagram showing the indication characteristics of the voltage distribution waveform in the echo signal received and processed without using a bandpass filter. FIG. 7 is a diagram showing the indication characteristic of the voltage distribution waveform in the echo signal received and processed by the apparatus of the present invention. The figure is a schematic configuration diagram showing a second embodiment using a heterodyne system,
Fig. 9 is a schematic configuration diagram showing the third embodiment using the orthogonal detection method, and Fig. 10 shows the array transducer and the focal position F.
11 is an explanatory diagram showing the relationship between unnecessary echo signals due to side lobes and spatial frequency signals, and FIG. 12 is a waveform diagram showing the output of the delay line 40. 10... vibrator, 16... skyana, 18...
Transmission circuit, 20... High frequency oscillator, 22... Electronic focus delay circuit, 26... Spatial frequency filter section, 28... Logarithmic amplifier, 36, 40... Delay line, 38, 48... Sample hold device, 42
... Adder, 44 ... Bandpass filter, 46 ...
...Integrator, 50, 54a, 54b...Mixer, 5
2, 56a, 56b...Low pass filter.

Claims (1)

[Claims] 1. A plurality of arranged ultrasonic transducers,
A group of ultrasonic transducers that transmit and receive ultrasonic waves of a predetermined frequency and output a plurality of received signals in parallel; , a focus delay circuit that delays each received signal; a sample hold circuit that samples and holds each received signal output from the focus delay circuit at a sampling frequency higher than the predetermined frequency; a spatial frequency conversion circuit that aligns the plurality of signals output in parallel from the sample hold circuit in the order in which the ultrasonic transducers are arranged and outputs them serially in order to extract the echo component of the ultrasonic transducer as a spatial frequency component; a filter that passes components around the predetermined frequency and removes the spatial frequency components of the signal output from the spatial frequency conversion circuit; and an integration circuit that integrates the signal output from the filter at the sampling period. An ultrasonic diagnostic device characterized by comprising the following. 2. The apparatus according to claim 1, wherein a heterodyne circuit converts the center frequency of the received signal to a lower frequency by multiplying the received signal by a signal having a frequency different from the center frequency of the transmitted ultrasonic pulse. An ultrasonic diagnostic apparatus characterized in that: is provided upstream of the sample hold circuit. 3. In the device according to claim 1, the frequency is the same as the center frequency of the transmitted ultrasonic pulse;
A circuit that multiplies two signals with a phase difference of 90 degrees to the received signal, performs orthogonal detection, and converts the received signal into a low-frequency complex signal is provided in the preceding stage of the sample and hold circuit, and complex signal processing is performed. Ultrasonic diagnostic equipment.