JPH01195846A - Ultrasonic diagnoser - Google Patents

Abstract

PURPOSE:To make an unnecessary signal due to a side lobe eliminable by sampling an echo signal with high frequency, delaying a sampling signal secured at each vibrator by specified delay time, and reading it out on the time base successively. CONSTITUTION:Each echo signal out of vibrators 10-1-10-n is inputted into a sampling hold circuit 38 via electronic focus delay circuits 36-1-36-n, sampling it with higher frequency than ultrasonic frequency. This sampling signal is delayed at specified delay time by a delay line 40 and read out on a timing axis successively. This output is taken out via an adder 42, a band passing filter 44, an integrator 46, and a sample hold circuit 48.

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention is an ultrasonic diagnostic device, in particular, an ultrasonic diagnostic device that controls electronic focus using a probe in which several transducers are arranged, emits an ultrasonic beam into a subject, and processes reflected echoes. The present invention relates to an ultrasonic diagnostic apparatus that 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 the 'WslO diagram, an arbitrary point F within the subject is focused. An electronic focusing technique is well known in which excitation control is performed such that each vibrator 10 in a group of vibrators has a delay time. The ultrasonic beam obtained by this electronic focus control is a composite wave (secondary wave) of a plurality of ultrasonic waves emitted from a plurality of transducers, and is a composite wave (secondary wave) of a plurality of ultrasonic waves emitted from a plurality of transducers. The sound waves interfere with each other to form a composite wave with maximum interference at the focal point. The ultrasonic waves formed by a transducer group consisting of a plurality of transducers 10 are reflected by a reflector in the living body and received as an echo signal. The reflected echo is received by the vibrator 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 can be controlled, the more sharp an image can be obtained. Problems to be solved by the invention C]. However, if a strong reflector exists near the focal position of the subject, a false echo (artifact) is generated by this strong reflector, and unnecessary echo signals due to side lobes are mixed into the signal from the focal position. 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 in order to reduce unnecessary echo signals caused by such side lobes, 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. OBJECTS 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 first object, the present invention transmits and receives an ultrasonic pulse wave into a subject by electronic focusing control of a plurality of arranged transducers. In ultrasonic diagnostic equipment that displays information inside a specimen as an image, echo signals from reflectors at predetermined points obtained by each transducer are used as ultrasonic waves (carrier).
A sample-and-hold circuit that samples and holds at a frequency higher than the frequency, and a predetermined delay time for each output from this sample-and-hold circuit, and the sample-and-hold output signals obtained from each vibrator are sequentially read out on the time axis. A spatial frequency conversion circuit that converts the echo signal from a reflector at a predetermined point and the echo signal from a reflector other than the predetermined point into a signal with a spatial frequency, and the signal output from this spatial frequency conversion circuit is input. It is characterized by comprising a filter for removing spatial frequency signal components of echo signals from reflectors other than predetermined points and extracting only fundamental ultrasonic frequency signals. That is, in the present invention, an echo signal coming from a focal position of a predetermined point has the same amplitude no matter which transducer in the transducer group is used, but the amplitude of an echo signal coming from a position other than the focal point is not the same. Rather, the focus is on the fact that when looking at the group of oscillators as a whole, they have a spatial frequency. For example, as shown in FIG. 11, if we consider the case where the focal point is located far away, if an unnecessary echo signal from the force near the focal point is input to the vibrator 10 from the direction of the angle θ, then , the unnecessary echo signal waves are aligned at a line 100 at an angle θ from the transducer arrangement direction. Therefore,
If the received signals obtained by the n transducers 10 are echo signals from the focal position, the amplitude of the signal from each transducer 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 lined up during time Td. , a signal having a spatial frequency is 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. Ultrasonic continuous wave C
If OSωt is the origin and the vibrator 10-n is the origin, then the voltage at this origin is sinω. At the time of tl, the voltage at the vibrator 10-6, which is separated by a distance of Xl from the vibrator 10-n, is as follows. However, Jl-x, sin θ, and λ are the wavelengths of the ultrasonic waves. Further, the voltage distribution g (x. 1,) on the X axis at time t1 can be expressed by the following equation. sinθ g (x, t) = cos (2yr −x
+ω. tt ) l λ ; When 0≦X≦a, or g (X, tl) - 0; In other cases... (2) Read out this spatial voltage distribution function g (x, t) at high speed in T1 time. If so, it becomes a waveform on the time axis, which can be expressed by the following equation. g (t, τj) ... (3) where τ, ≦t τ, , D is the aperture of the vibrator, J
3+1 Td-τj+l-τj, C is the speed of sound, and fo is the frequency of the ultrasonic wave. Therefore, when the echo signal is sampled every time Td and the respective voltage distribution waveforms are transferred, the time waveform f(t)
[Curve 200] can be expressed as follows. [Operations] According to the above configuration, if the ultrasonic frequency (carrier frequency) is 3.5 MHz, the echo signal from the focal position is sampled at a sampling frequency of 10 MHz, for example. 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 FIG. 2 specifically shows the overall configuration of the ultrasonic diagnostic apparatus. There is. In FIG. 2, a probe 14 is brought into contact with a subject 12, and a group of transducers within the probe 14 emit an electronic focus-controlled ultrasound beam toward the subject 12. 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 (carrier frequency) of, for example, 3.5 MHz by the transmitting circuit 18, and this predetermined repeated high frequency pulse signal is sent to the scanner 16. The ultrasonic beam is supplied to the probe 14 through the
can be scanned. The echo reflected from the object 12 is transmitted to the probe 14.
The signal is received by the transducer 10 in the camera and supplied to the electronic focusing delay circuit 22 via the scanner 16. In this electronic focus delay circuit 22, delay control is performed to receive only the signal from the focal position during reception, and for each input signal of each transducer 10 in the probe 14. Give a delay time corresponding to the distance to the focal point. 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). A filter 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 then sent to a digital scan converter (DSC) 32 via a detector 30.
is supplied to This DSC32 transmits ultrasound information to CR7.
Signal processing is performed to display the image on the display 34, and as a result, the tomographic image of the subject 12 can be displayed 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. In the electronic focusing delay circuit 22, n (64) delay lines 36 corresponding to the number of the vibrators 10 are provided. This delay line 36 gives each transducer 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 delay amount is increased in order from the first oscillator 10 that is farthest from the oscillator 10 to the oscillator 10 that is closest to the oscillator 10. 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. Based on the output 301 of the timing generation circuit 24, the sample and hold device 38 opens the gate circuit for a predetermined period of time, for example, at a period of the reciprocal of the frequency of 10 MHz, takes in the signal, and holds the time signal of Δt. Further, a delay line 40 that gives a predetermined delay time, Δt in the embodiment, to each output from the sample and hold device 38, and an adder 42 that adds the outputs from this delay line 40 are provided. The delay line 40 and the adder 42 constitute a spatial frequency conversion circuit that converts an unnecessary echo signal due to side lobes into a signal with a spatial frequency. That is, the output of each sample hold ri3g is delayed by the hold time Δt by the delay line 4G, and then added, so that the echo signals at the focal position F obtained by each vibrator 10 are sequentially read out on the time axis. You can line them up. Then, the echo signal from the focal position F becomes a signal that does not change at all with reference to the carrier frequency, but the unnecessary echo signal due to the side lobe that is captured at the same time becomes a signal that has a spatial frequency. Note that the delay line 40 may be replaced by a storage circuit that stores and holds the input signal for a predetermined period of time. Furthermore, a band pass filter 44 is connected to the adder 42 as a filter for removing the spatial frequency signal, and this band pass filter 44 has a center frequency f of 3.5 MHz as shown in FIG. It has certain filter characteristics. Therefore, frequency components of 7 MHz or higher are thereby removed. FIG. 4 shows the output waveform of the adder 3!1L 642, where the horizontal axis represents time and the vertical axis represents voltage, and the ultrasonic carrier signal waveform 400 is converted into a sine wave signal with a frequency of 3.5 MHz. Then, the rectangular wave 401 becomes the output waveform of the adder 42, and the sampling frequency is 10 by the 64 oscillators 10.
The echo signal obtained at each period of 1/1MHz is plotted at 1/106 seconds on the time axis (sampling frequency - 10MHz
Therefore, the signal is arranged between -Td. This waveform 40
Although the signal No. 1 becomes a rectangular wave, it becomes a carrier frequency signal having the same frequency as the carrier signal 400, and the information contained in the echo signal is not lost. Further, the spatial frequency signal is represented by a waveform 402, which is a signal with a frequency much higher than the frequency of the carrier signal 400. Therefore, the spatial frequency signal, which is a high frequency signal, is passed through a band pass filter 44 whose center frequency is the ultrasonic carrier frequency of 3.5 M and the center frequency of the echo signal.
can be removed by passing through it. In the present invention, as is clear from FIG.
The echo signals obtained at 0 are sequentially read out on the time axis, but in conventional ultrasonic diagnostic equipment, the echo signals are read out by adding the outputs of 64 transducers 10 in the voltage (vertical axis) direction. Processing is in progress. Therefore, in the present invention, an integrator 46 is provided to integrate the output of the band-pass filter 44, and then the output of the integrator 46 is further sampled in a sample-and-hold device 48, and the logarithmic amplifier shown in FIG. 28. Note that the integrator 46 and sample-hold device 48 are driven based on timing and outputs 302 and 303 of the generation circuit 24. The first embodiment has the above configuration, and its operation will be explained below. The ultrasonic wave emitted toward the focal position F is reflected from the reflector present at the focal position F, and is transmitted to each transducer 1 as an echo signal.
Received as 0. This echo signal is then transmitted to the delay line 36.
A predetermined amount of delay is applied to each of the signals, and the signals are supplied to a sample and hold unit 38 in the spatial frequency filter section 26. Then, the echo signal with a carrier frequency of 3.5 MHz is sampled at a sampling frequency of 10 MHz. 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 port (Δt). In the example,
At the same time, signals are read out from the sample and hold device 38 in the order of the first port, the second port, the third port, and so on.
-1st. Port n-2... sample holder 38 in the order of 1st
I am trying to read the output of . Then, the adder 42 outputs a signal that is the sum of the signals read from both sides, and since the ultrasonic beam is scanned left and right, this output includes the signals read from the C side. The spatial frequency will appear more prominently than in the case of In this way, the adder 42 arranges n-64 signals on the time axis, and this scanning is performed every sampling period, and the echo signal from the focal position F is A signal as shown in waveform 401 is obtained. At the same time, the spatial frequency signal extracted by the processing from the sample-and-hold device 38 to the adder 42 becomes a signal shown by a waveform 402 in FIG. 4. Then, by supplying the output of the adder 42 to the bandpass filter 44, only the carrier frequency signal (ultrasonic frequency signal) 401 is extracted, and the spatial frequency signal 402
will be removed. In this case, the carrier frequency signal 401 was a rectangular wave at the output stage of the adder 42;
By passing the signal, the signal becomes a rounded sine wave. Then, the output of the bandpass filter 44 is inputted to an integrator 46, where integration equivalent to the conventional addition of voltage signals in 64 vibrators 10 is performed, and the voltage in the signal output from this integrator 46 is The indicated characteristics of the distribution waveform are as shown in FIG. In the figure, the vertical axis is the signal level, and the horizontal axis is the center line drawn perpendicular to the transducer row from the center position of the arranged transducer group, and the focal point is the angle of the sidelobe seen from this center line. It shows. Here, before explaining the indicating characteristics of the present invention, we will explain the indicating 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 a conventional method, for example, a frequency of 3.5MHz.
, the number of transducers is 32, and the pitch between transducers (d) is 0.5 m.
The indicating characteristic in the case of m is shown, and FIG. 6 shows the integrator 4 when the bandpass filter 44 is removed in the embodiment.
The indication characteristics of the output of 6 are shown. And this fifth
Comparing both Fig. 6 and Fig. 6, the indicating characteristics are almost the same, which means that the echo signals obtained from each transducer 10 can be sampled and held and sequentially read out at a predetermined delay time. It is proven that the same signal processing as the conventional method can be performed even if integration is performed after that. Next, the directional characteristics in FIG.
25n (nano) sec, and the bandpass filter 44 is a Gaussian filter with a center frequency of j and 5 MHz. 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. If you try to achieve this 20dB suppression using the conventional method,
The number of oscillators must be increased by 10 times, which is a fact-L
It's impossible. In addition, in Figure 7, the larger the sidelobe angle in the range of 30 degrees to 60 degrees, the higher the signal level, but in reality, the transducer array spacing d was adjusted to 60 degrees as shown in the figure. Since the design is such that the side lobe at 90 degrees or more is shifted, the increase in the signal level of the side lobe does not pose 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 reduce the echo signal to a low frequency band and process it. A third embodiment will be explained. FIG. 8 shows a second embodiment using the heterodyne system, in which n mixers 50 and n low-pass filters 52 are each connected between the delay line 36 and the spatial frequency filter section 26. composition. Then, by multiplying the echo signal by a local signal such as a sine wave (cosine wave) or a rectangular wave, which has a frequency different from the center frequency of the ultrasonic pulse wave, in the mixer 50, the echo signal is converted to an intermediate frequency. By passing this through the low-pass filter 52, the carrier frequency of the echo signal of 3.5 MHz can be adjusted to below IMHz. A third embodiment using the orthogonal detection method is shown in FIG. two mixers 54a, 54b (n each) and two low-pass filters 56a, 56b.
(n each) are connected. The mixer 54a receives the local signal as a cosine wave (COS) signal, and the mixer 54b receives the local signal and 9.
By supplying local signals in the form of sine wave (sln) signals with a phase difference of 0 degrees, and multiplying these local signals with the echo signal, the echo signal can be reduced to a low frequency signal as in the second embodiment. Can be done. In this case, the outputs of the spatial frequency filter sections 26a and 26b have a relationship between the real part and the imaginary part of the complex signal, and these outputs are combined and processed later as a guard signal. This second. According to the third embodiment, there is an advantage that sampling in the spatial frequency filter section 26 can be easily performed, and that hardware such as an A/D converter can be easily designed.

【Effect of the invention】

As explained above, according to the present invention, echo signals are sampled at a frequency higher than the ultrasonic frequency, and the sampling signals obtained by each transducer are delayed by a predetermined delay time and read out sequentially on the time axis. Since unnecessary echo signals from reflectors other than the predetermined points are converted into signals with spatial frequency, the echo signals from the focal position and unnecessary echo signals from other than the focal position can be separated well. 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 the drawing]

FIG. 1 is a schematic configuration diagram showing a first embodiment of an ultrasonic diagnostic apparatus according to the present invention, FIG. 2 is an overall configuration diagram of an ultrasonic diagnostic apparatus according to the present invention, and FIG. 3 is a band-pass filter according to the present invention. 4 is a waveform diagram illustrating the adder output of the spatial frequency filter section. FIG. 5 is a diagram illustrating the indication characteristics of the voltage distribution waveform in the echo signal received and processed by the conventional device. , FIG. 6 is a diagram showing the indication characteristics of the voltage distribution waveform in the echo signal received and processed without using a bandpass filter in the present invention, - FIG. 7 is a diagram showing the voltage distribution waveform in the echo signal received and processed by the device of the present invention 8 is a schematic diagram showing the second embodiment using the heterodyne method, FIG. 9 is a schematic diagram showing the third embodiment using the orthogonal detection method, and FIG. FIG. 11 is an explanatory diagram showing the relationship between the array transducer and the focal position F. FIG. 11 is an explanatory diagram showing the relationship between unnecessary echo signals due to side lobes and spatial frequency signals. 10... Vibrator 16... Scanner 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 and hold device 42 ...
- Adder 44...Bandpass filter 46...Integrator 50.54a, 54b...=Mixer 52, 56
a, 56 b...Low pass filter. Applicant Aloka Co., Ltd. Company Agent Patent Attorney Yoshi1) Kenji [8-451kon*'p -
1', 3rd person! 2 → Kini Nishir 7th drawing toko - Mutsugame Jun]

Claims (3)

[Claims] (1) In an ultrasonic diagnostic device that transmits and receives ultrasonic pulse waves into a subject and displays information inside the subject as an image by controlling an array of multiple transducers with electronic focus, each transducer obtains information. A sample-and-hold circuit samples and holds the echo signal from the reflector at a predetermined point at a frequency higher than the ultrasonic frequency, and a sample-and-hold circuit that samples and holds the echo signal from the reflector at a predetermined point, and a predetermined delay time is given to each output from this sample-and-hold circuit, and the signal obtained from each transducer is a spatial frequency conversion circuit that converts an echo signal from a reflector at a predetermined point and an echo signal from a reflector other than the predetermined point into a signal with a spatial frequency by sequentially reading out the sample-and-hold output signals on the time axis; A filter for inputting the signal output from the spatial frequency conversion circuit, removing spatial frequency signal components of echo signals from reflectors other than predetermined points, and extracting only the fundamental ultrasonic frequency signal. An ultrasonic diagnostic device featuring: (2) In the device according to claim (1), the center frequency of the echo signal is lowered by multiplying the echo signal from the reflector at the predetermined point by a frequency signal different from the center frequency of the ultrasonic pulse wave. An ultrasonic diagnostic apparatus characterized in that a heterodyne converting circuit is provided at a stage upstream of a spatial frequency filter section. (3) In the device according to claim (1), two signals having the same frequency as the center frequency of the ultrasonic pulse wave and having a phase shift of 90 degrees are applied to the echo signal from the reflector at the predetermined point. 1. An ultrasonic diagnostic apparatus characterized in that a circuit for orthogonal detection and converting an echo signal into a low-frequency complex signal is provided in a stage upstream of a spatial frequency filter section to perform complex signal processing.