JPH074368B2 - Non-linear parameter measuring device - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention relates to an apparatus for imaging the spatial distribution of a nonlinear parameter B / A of a medium, which is used for medical diagnosis by ultrasonic waves.

[Background of the Invention]

It is effective in the field of medical diagnosis to acquire the spatial component as an image by using the nonlinear parameter B / A, which is a characteristic quantity that expresses the magnitude of the nonlinear interaction between a sound wave and a medium. Volume 8 (1983), pages 521-530. The apparatus conventionally proposed for obtaining such an image is an image method by a transmission method as in the above-mentioned document. Therefore, when it is considered to be applied to the diagnosis of the human body, it is considered difficult to measure in vivo (ex vivo measurement) without removing the organ to be imaged except the breast outside the body.

On the other hand, when the measurement by the reflection method is applied to a non-linear parameter imaging device, multiple reflected waves from various parts of the body are mixed with the reflected waves that have passed through the target organ and are reflected. Accurate measurement is hindered by the phase error due to.

[Object of the Invention]

Therefore, an object of the present invention is to provide a non-linear parameter measuring device by a reflection method, in which a phase error due to multiple reflections that adversely affects the non-linear parameter B / A spatial distribution is removed.

[Outline of Invention]

In the reflection imaging method, using a sinusoidal probe wave with a constant frequency may make it difficult to obtain an accurate phase shift of the received signal in a specific time interval that correlates with the spatial distribution of B / A. . When a chap wave is used as the probe wave, the reflected chap wave interacts with a pump wave opposite thereto and a wave of a single frequency different at each point in space. As a result, an accurate image of the spatial distribution of the nonlinear parameter B / A can be obtained without the adverse effect of multiple reflection.

FIG. 1 shows the principle of the reflection imaging method using the chap wave. An acoustic wave in which a short pump pulse wave having an intensity of 22 is connected to the trailing edge of the high frequency (1 MHz or more) chirp wave probe wave shown by 20 in FIG. 1b is transmitted from the transmitting / receiving probe. The chirp probe wave is reflected by the wall (x = 1). At this time, in order to image all the lines of the propagation path from x = 0 to x = 1, the time length of the probe wave 20 is required to be τd = 2l / co. Therefore, the time length of the probe wave 20 is at least twice as long as the signal transmission time between the transmitting / receiving probe and the reflecting wall. FIG. 1b shows that the time t =
The situation of τd is shown. According to it, the pump wave P
(T, x) is the probe wave S (t, x) and x reflected by the reflecting wall
It is clear that each point on all image lines from = 0 to x = 1 interacts with a different single frequency waveform. If B / A changes in space as shown in FIG. 1a, the probe wave S (t, x) undergoes phase fluctuations over the entire time length τd = 2l / co. In FIG. 1c, the time t3τd /
It shows the situation at 2 = 3l / 2. Eventually, 4 l / co = 2τd elapses from the start of the transmission of the probe wave 20 (t = 0) to the reception of the trailing edge of the probe wave.

The principle diagram of FIG. 2 relates to signal processing. It is drawn that the actually-reflected reflected signal is composed of the necessary reflected wave shown in b and the unnecessary reflected wave shown in a. However, when the received signal is divided into time intervals T ₁ , T ₂ , ... Tn, the spectrum of the reflected wave existing in each time interval is known a priori. Therefore, the unnecessary reflection wave from the reflection wall existing far from the necessary reflection wave is outside the band of the spectrum of the necessary reflection wave. Therefore, by using an appropriate filter, the unnecessary reflection spectrum existing in each time section can be easily removed.

When B / A changes in space as shown in FIG. 3a, the phase distribution spectrum shown in FIG. 3b is obtained by the above-described principle signal processing. Therefore, the phase fluctuation distribution caused by the nonlinear interaction between the pump wave and the chirp wave probe wave is proportional to the B / A at each point in space and the probe wave frequency. By Fourier transforming the received reflected probe wave, a phase distribution spectrum including information on the spatial distribution of B / A can be obtained. The phase difference distribution spectrum representing the absolute amount is obtained using the spectrum of the difference between the reflected chap wave probe wave with the pump wave and the reflected chap wave probe wave without the pump wave.

It is also possible to use a probe wave having a sharp wave whose frequency gradually increases with time. FIG. 3c shows the phase fluctuation distribution spectrum obtained at that time.

Example of Invention

An embodiment of the present invention will be described below with reference to FIG. When the sweep signal is repeatedly emitted from the sweep oscillator 2 with the period τd, the gate circuit 3 applies a gate having the time length τd to the chap signal to drive the amplifier 4 and the probe transmitting / receiving probe after amplification. A pump wave probe 6 and a pump pulse generator 5 are used so that a short pump wave of high intensity is connected to the trailing edge of the probe wave of the time length τd. A high frequency wave that changes from 5 MHz to 3 MHz is used as the chirp wave. Reference numeral 1 is a master oscillator which emits a reference frequency signal for generating such a chirp wave.

The reflected probe wave received by the probe wave transmitting / receiving probe 6 is detected by the wave receiving circuit 10 and converted into a digital signal by the AD converter 11. The sampling frequency used at this time is one that satisfies the Nyquist sampling theorem. The timing controller 8 controls the timing of transmitting / receiving ultrasonic waves, and controls the timing of gate application, the timing of pump pulse generation, and the timing of wave reception.

The bandpass filter 12 has a configuration in which the resonance frequency can be changed according to the delay time of the input signal. The resonance frequency is changed by transferring the coefficient of the digital band pass filter from the coefficient ROM 9 according to the delay time. It also controls the transfer timing of the timing controller 8. In this way, the bandpass filter 12 removes unnecessary signals. The fast Fourier transformer 13 Fourier transforms the filtered reflected signal and outputs a phase distribution proportional to the frequency. In order to smooth the noise in the phase distribution, the averaging circuit 14 is used to perform averaging. The coordinate conversion circuit 15 arranges the averaged phase distribution in reverse with respect to the frequency axis ω.

Since the waveform of the pump wave is already known, the deconvolution calculation circuit 16 executes the deconvolution calculation to obtain the nonlinear parameter distribution B / A.

When a probe wave whose frequency is gradually increased as the probe wave is used, the coordinate conversion circuit 15 is not necessary.

〔The invention's effect〕

According to the present invention, when obtaining the non-linear parameter B / A spatial distribution, it is possible to improve the phase error due to the multiple reflection, which has an adverse effect, so that an accurate B / A image can be obtained.

Although the above description has been made on the chirp waveform, it is natural that a similar effect can be obtained by performing correlated reception for a wideband signal.

[Brief description of drawings]

FIG. 1 is a principle diagram of the B / A reflection imaging method, where a is a spatial change of B / A, b is a situation at time tτd, and c is a situation at time t3 / 2τd. However, τd is the total time length of the probe wave. FIG. 2 is a principle diagram of signal processing. FIG. 3a shows the spatial variation of B / A, and FIGS. 3b and 3c show the phase distribution spectrum obtained by signal processing. FIG. 4 shows an embodiment according to the present invention. 1 ... Main oscillator, 2 ... Sweep oscillator, 3 ... Gate circuit, 4 ... Amplifier, 5 ... Pump pulse generator, 6 ...
Pump wave probe, 7 ... Probe wave transmission / reception probe, 8 ...
... Timing controller, 9 ... Coefficient ROM, 10 ... Reception circuit, 11 ... AD converter, 12 ... Digital band path converter, 13 ... Fast Fourier transformer, 14 ... Adding circuit, 15
...... Coordinate conversion circuit, 16 …… Deconvolution solution circuit.

Claims (1)

[Claims] 1. A pulse wave pump propagating in the opposite direction to a probe wave propagating by reflecting and propagating a reverberation wave in which a pulse wave pump having a relatively large power is connected to a trailing edge of a high frequency chirp wave probe wave. A transducer or an array of transducers that receives the waves, a means for removing unnecessary reflection signals by applying a bandpass filter having a different resonance frequency to the received probe wave according to the time interval, and a Fourier transform of the output of the bandpass filter. Means for obtaining a phase distribution proportional to frequency, means for adding and averaging the phase distributions to obtain an average phase distribution, means for arranging the average phase distributions in reverse on frequency, and pumping from the rearranged average phase distributions. A non-linear parameter measuring apparatus having means for obtaining a spatial distribution of non-linear parameters on a video line by means of deconvolution based on waves.