JP3268943B2 - Ultrasonic reception processing method and ultrasonic diagnostic apparatus - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an ultrasonic reception processing method and an ultrasonic diagnostic apparatus.

[0002]

2. Description of the Related Art An ultrasonic diagnostic apparatus transmits ultrasonic waves to a subject, receives echoes from boundaries having different acoustic impedances in a living body, detects the echoes as electrical signals, and displays the signals on a display device. Used for medical diagnosis. FIG. 8 is a conceptual diagram of the ultrasonic diagnostic apparatus. In the figure, reference numeral 1 denotes an ultrasonic probe (probe) that transmits an ultrasonic wave to the subject 2 and receives an echo from the subject. In the figure, the ultrasonic probe 1
Are transmitted and received via water without directly contacting the subject 2. Ultrasonic probe 1 and subject 2
The reason why water is interposed is to avoid direct contact of the ultrasonic probe 1 with the subject 2 (for example, when the subject is a pregnant woman) and to facilitate transmission of the ultrasonic wave to the subject. Yes (ultrasonic waves are difficult to propagate in air).

[0003] The ultrasonic pulse output from the transmission / reception circuit 4 is applied to the ultrasonic probe 1. At this time, the scanning of the ultrasonic probe 1 is performed by the scanner 3. And
When an ultrasonic wave is transmitted to the subject 2, an echo (reflection) is generated from a boundary at which the acoustic impedance of the subject 2 differs, as shown in the figure. This echo is received by the same ultrasonic probe 1, converted into an electric signal, and sent to the transmission / reception circuit 4. The transmission / reception circuit 4 amplifies and detects the received electric signal and supplies the signal to the z-axis of the display device 7 as a luminance modulation signal. On the other hand, the synchronization signal generation circuit 5 generates a synchronization signal,
The transmission / reception circuit 4 and the xy sweep generation circuit 6 are provided.
The xy sweep circuit 6 receives signals from the synchronizing signal generating circuit 5 and the scanner 3 and provides a synchronizing signal in the x and y directions to the display device 7. Thereby, the display device (for example, CR
The corresponding position (position determined by the x and y coordinates) of (T) is luminance-modulated by the z-axis signal, and an image in each mode as shown in the figure is obtained.

Here, in the A mode, the depth is displayed in the direction of the vertical axis (time axis), and the reflection intensity is displayed in the horizontal axis. The B mode scans an ultrasonic wave in a living body using a scanner, and performs display according to the scan while performing luminance modulation on a reflection signal obtained on a display device to display an ultrasonic tomographic image of the living body. It was done.

[0005]

In the above-described conventional apparatus, the main purpose is to display an ultrasonic image in each mode, and the S / N ratio and the bandwidth are optimized according to the operation mode. It was not configured. Further, in this type of conventional device, an A / D converter is used to convert a received electric signal into digital data.
As a method of the D conversion, a parallel type and a successive approximation type are mainly used. However, this type of A / D conversion method requires a sample-and-hold circuit, and it is difficult to reduce the size when integrating.

SUMMARY OF THE INVENTION The present invention has been made in view of such problems, and an ultrasonic diagnostic apparatus capable of miniaturizing a circuit and optimizing an S / N ratio and a bandwidth according to an operation mode. It is intended to provide.

[0007]

According to a first aspect of the present invention, there is provided an ultrasonic reception processing method for transmitting and receiving ultrasonic waves to obtain an ultrasonic image. The wave signal is quantized by a 1-bit oversampling A / D converter, and when the quantized data is applied to a decimation filter, the cutoff frequency of the decimation filter is made variable according to the type of shooting mode. It is characterized by the following.

The decimation filter may be divided into a part commonly used for each photographing mode and a part individually used for each photographing mode, and the part used individually for each photographing mode may be switched. preferable.

Further, the decimation filter is divided into a portion commonly used for each photographing mode and a portion individually used for each photographing mode, and the commonly used portion is constituted by hardware, and the separately used portion is constituted by software. It is preferable that the individually used portion is switched according to the type of shooting mode.

According to a second aspect of the present invention, a 1-bit oversampling type A for quantizing a signal received from an ultrasonic probe in an ultrasonic diagnostic apparatus which obtains an ultrasonic image by transmitting and receiving an ultrasonic wave. / D converter and a decimation filter for removing high-frequency components, which receives data quantized by the over-sampling A / D converter and varies the cutoff frequency according to the type of shooting mode. It is characterized by having.

The decimation filter is divided into a portion that uses the same in each shooting mode and a portion that is used individually in each shooting mode, and switches between the portions used individually according to the type of the shooting mode. It is preferred that

It is preferable that the individual part of the decimation filter is switched to a wide band in the B mode, a medium band in the pulse Doppler mode, and a narrow band in the CW Doppler mode.

Further, the decimation filter is divided into a part commonly used for each photographing mode and a part individually used for each photographing mode. The commonly used part is constituted by hardware, and the individually used part is constituted by software. It is preferable that the individually used portion can be switched in accordance with the type of shooting mode.

[0014]

[Action]

(First invention) When an ultrasonic wave reception signal is quantized by a 1-bit oversampling type A / D converter and the quantized data is applied to a decimation filter, the data of the decimation filter is used in accordance with the type of imaging mode. The cutoff frequency is made variable. Since the decimation filter is a kind of low-pass filter, the bandwidth is determined by the cutoff frequency. On the other hand, the ultrasonic diagnostic apparatus has various modes such as a B mode, a pulse Doppler mode, and a CW Doppler mode, and each has a different frequency band.

In the pulse Doppler mode, blood flow velocity information is obtained from outside the body non-invasively using the Doppler effect of ultrasonic waves. In the CW Doppler mode, blood flow velocity information is obtained by using a continuous wave as an ultrasonic wave to be used.

Therefore, if the cutoff frequency is changed according to each mode, the S / N ratio is changed according to the operation mode.
The ratio and bandwidth can be optimized. Further, since a 1-bit oversampling A / D converter that is easy to integrate is used, the circuit can be downsized.

(Second Invention) A 1-bit oversampling A / A for quantizing a signal received from an ultrasonic probe
A D-converter and a decimation filter for removing high-frequency components configured to receive data quantized by the over-sampling A / D converter and to vary a cutoff frequency according to a type of a shooting mode. I did it.

Since the decimation filter is a kind of low-pass filter, the bandwidth is determined by the cutoff frequency. On the other hand, the ultrasonic diagnostic apparatus has various modes such as a B mode, a pulse Doppler mode, and a CW Doppler mode, and each has a different frequency band. Therefore, if the cutoff frequency is changed according to each mode, the S / N ratio and the bandwidth can be optimized according to the operation mode. Further, since a 1-bit oversampling A / D converter that is easy to integrate is used, the circuit can be downsized.

[0019]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 is a flowchart showing the principle of the method of the present invention, and FIG. 2 is a block diagram showing a main part of an embodiment of the present invention. In the method of the present invention, as shown in FIG. 1, a signal received from an ultrasonic probe is quantized by a 1-bit oversampling type A / D converter (S1), and the quantized data is applied to a decimation filter. The cut-off frequency of the decimation filter is varied according to the type of shooting mode (S2).

In the present invention, an A / D converter using an ΔＡ modulation system (oversampling type A / D
D converter). This A / D converter has recently been used in the audio field, and includes a 1-bit A / D converter and a decimation filter (Deci filter).
motion filter).
For example, 16-bit or 18-bit high-speed / high-resolution A /
A D converter can be realized. This A / D converter does not require a sample-and-hold circuit, and also includes a 1-bit A / D converter (abbreviated as ADC) and a decimation filter, and is suitable for integration because of its simple circuit configuration. . Moreover, since the decimation filter is a kind of low-pass filter, its cutoff frequency can be adjusted externally.

The apparatus shown in FIG. 2 is a block diagram showing a main part of an embodiment of the present invention, and is an ultrasonic diagnostic apparatus which obtains a tomographic image of a soft tissue of a living body using ultrasonic pulses. . In the figure, the same components as those in FIG. 8 are denoted by the same reference numerals. 1 is an ultrasonic probe for transmitting and receiving ultrasonic waves, 10 is an echo transmitting / receiving unit which gives an ultrasonic pulse to the ultrasonic probe 1 and receives an echo signal from the ultrasonic probe 1, and 20 is an echo transmitting / receiving unit A 1-bit oversampling A / D converter (Δ) that receives a signal from the unit 10 and quantizes a received signal from the ultrasonic probe 1
Σmodulation type A / D converter). Numeral 30 denotes a decimation filter for removing high-frequency components, which receives the data quantized by the oversampling A / D converter 20 and varies its cutoff frequency in accordance with the type of shooting mode, and 40 denotes the decimation. Filter 30
Is a post-processing circuit that receives the output of. The post-processing circuit 40
In the case of the B mode, detection processing and luminance modulation signal creation are performed, and in the case of the pulse Doppler mode, fast Fourier transform (FFT) processing and the like are performed. Although not shown, the output of the post-processing circuit 40 is given to a display device such as a CRT and displayed. The operation of the device configured as described above will be described below.

The ultrasonic probe 1 has an echo transmitting / receiving unit 10
And ultrasonic waves are transmitted toward a subject (not shown). At this time, scan control of the ultrasonic probe 1 is performed by a scanner driver (not shown). Then, echoes reflected from portions of the subject having different acoustic impedances are received by the ultrasonic probe 1.

The reflected echo signal received by the ultrasonic probe 1 is converted into a digital signal by an oversampling type A / D converter 20 which passes through an echo transmitting / receiving unit 10 (details will be described later). The reflected echo signal converted into the digital signal enters the decimation filter 30, and after the high-frequency component is removed at a specified cutoff frequency according to the photographing mode, enters the post-processing circuit 40, where predetermined signal processing is performed. . Here, the decimation filter 30 includes a digital filter having a function as a low-pass filter and a decimation unit (details will be described later).

The cut-off frequency of this digital filter can be set externally.
The cutoff frequency can be set arbitrarily according to the shooting mode. Therefore, if the cutoff frequency is set according to the shooting mode (operation mode), the S / N ratio and the bandwidth can be optimized.

For example, when the ultrasonic frequency given to the ultrasonic probe 1 is 3.5 MHz, the B mode has a wide bandwidth of 2 to 5 MHz with emphasis on the impulse response. In this case, the cutoff frequency f
Set c1 wide. On the other hand, in the case of the pulse Doppler mode, the bandwidth is required to be 3 to 4 due to the need to settle the transmission frequency.
MHz and middle band. In this case, the cutoff frequency fc2 is set narrower than fc1. On the other hand, C
In the case of W Doppler (continuous wave Doppler), the S / N ratio is emphasized and the band becomes narrower. In this case, the cutoff frequency fc3 is, for example, 2.5 MHz ± 50 kHz.
Set to about.

FIG. 3 is a block diagram showing an example of a detailed configuration of a main part of the present invention. In the figure, reference numeral 20 denotes an oversampling A / D converter for quantizing an input signal, and 30 a decimation filter for receiving the output of the oversampling A / D converter 20.
1 and a decimation unit 32. Now, the sampling frequency is set to, for example, 32 kHz, and the oversampling frequency of the oversampling A / D converter 20 (hereinafter simply referred to as 1-bit ADC) is set to 25 kHz of 32 kHz.
Six times, that is, 8.192 MHz.

Although the total quantization noise of the 1-bit ADC 20 is very large, noise shaping (Noise
(Shaping) to cancel out the quantization noise. FIG. 4 is a block diagram showing a configuration example of the 1-bit ADC 20. The 1-bit ADC 20 includes a 1-bit quantizer 21, a subtractor 22, and a filter 23, as shown in FIG.
And an adder 24. As the filter 23, a second-order FIR (Finite Impulse)
Response) filter, and the delay unit 23
a and 23b, amplifiers 23c and 23d, and an adder 23e. The output of the filter 23 is
And is added to the input X. The output Yo of the 1-bit quantizer 21 enters the subtractor 22 and is subtracted from the input Y1 of the 1-bit quantizer 21. And the subtracter 2
2 is in the filter 23.

In the circuit thus constructed, the relationship between the input Y1 and the output Yo of the 1-bit quantizer 21 is given by the following equation. If Y1 ≧ 0, Yo = + 1 (1) If Y1 <0, Yo = −1 (2) This equation shows that even if the input Y1 is a sine wave, Yo becomes a square wave. Generates large distortion. However, this distortion is an error uncorrelated with the signal when the input signal is in a voice band, and is considered as white noise. If this noise (quantization noise) is set to Nq, it can be expressed as Yo = Y1 + Nq (3). This Nq is output Y2 by subtraction of the subtractor 22.
Is expressed as follows: Y2 = Y1-Yo = Y1- (Y1 + Nq) =-Nq (4)
become. Therefore, if the output of the filter 23 is Y3 and its transfer function (Y3 / Y2) is H (jω), then Y1 = X + H (jω) · Y2 (5). By transforming equation (5) using equation (4), Y1 = X + H (jω) · (−Nq) (6) When Y1 is eliminated from equations (3) and (6), then Yo = X + H (jω) (−Nq) + Nq (7) In the equation (7), the output Yo is the signal X and the quantization noise H (j
ω) · (−Nq) + Nq.

Here, if H (jω) = 1,
The expression (7) becomes Yo = X + (− Nq) + Nq = X, and the quantization noise is completely canceled (noise shaping method).

Returning to the description of FIG. FIG. 5 is a diagram showing a waveform and a frequency spectrum of each part in FIG. Now, FIG.
Assuming that the input shown in FIG. 3A enters the 1-bit ADC 20, the spectrum consists of only the spectrum of the original signal as shown in FIG. The output waveform of the 1-bit ADC 20 at this time is as shown in (c) (PDM (Pulse Density Modul).
ation) wave). The frequency spectrum is as shown in FIG. 1-bit ADC2
Although the quantization noise of 0 is very large, since the spectrum of the quantization noise is reconstructed as shown in FIG.
The following quantization noise spectrum is very small.

When the output of the 1-bit ADC 20 shown in FIG. 5C is filtered by a digital low-pass filter 31 having, for example, a cutoff frequency fc = 16 kHz, the output waveform becomes as shown in FIG. The spectrum is as shown in (f). The output waveform of the digital low-pass filter 31 has a normal 18-bit quantization sampling frequency fs = 8.19 as shown in FIG.
2 MHz (256 times oversampling of 32 kHz)
It is equivalent to an A / D converter. In the spectrum shown in (f), it can be seen that the quantization noise component is largely removed by the filter.

Finally, the digital low-pass filter 31
The output digital data of
If the signal data is sampled at a rate of one out of every six, the digital data waveform becomes the sampling data of the original sampling frequency as shown in (g). here,
When 18-bit data is rounded to 16 bits, the normal 16
It becomes a digital signal of bit quantization and sampling frequency fs = 32 kHz.

The digital low-pass filter 31
As described above, the cut-off frequency fc can be varied by an external mode setting signal. In the above-described embodiment, the case where fc = 16 kHz has been described. However, an arbitrary frequency such as fc = 24 kHz can be set. Therefore, as described above, the cutoff frequency of the digital low-pass filter portion is varied according to various imaging modes (operation modes) of the ultrasonic diagnostic apparatus, so that S is determined according to the operation mode.
/ N ratio and bandwidth can be optimized. Also, A
Since a 1-bit oversampling A / D converter that is easily integrated is used for the / D converter, the circuit can be downsized.

FIG. 6 is a block diagram showing a main part of another embodiment of the present invention. The same components as those in FIG. 2 are denoted by the same reference numerals. In the embodiment shown in the figure, the decimation filter 30 is divided into a part (common part) 33 that uses it commonly for each shooting mode and a part (individual part) 34 that uses it individually for each shooting mode. The individual unit 34 is switched by a switch SW in accordance with the type of the photographing mode. The switch SW is included in the post-processing circuit 40.

Here, the common section 33 is a section commonly used in each photographing mode, and corresponds to, for example, a digital low-pass filter section having a cutoff frequency fc1 having the widest bandwidth. On the other hand, in the figure, the individual section 34 is composed of a digital low-pass filter and a decimation section each having a bandwidth smaller than that of fc1. In the drawing, the cutoff frequency is fc for each of the individual units 34.
2, fc3, fc4 (fc2>fc3> fc4) are illustrated as three, but the number of individual units 34 is not limited to this, and may be any number. The output of each individual unit 34 is connected to a switch SW, and the contact of this switch can be switched according to the shooting mode setting. Since the bandwidth may be fc1 in some cases, the output of the common unit 33 is connected to the switch SW via the decimation unit 35 in this case.

In the device configured as above, the signal quantized by the 1-bit ADC 20 is first sent to the common unit 33.
And a low-pass filter with a cutoff frequency fc1 is applied. Thereafter, each individual unit 34 functions as a low-pass filter of each cutoff frequency, and thereafter, data extracted by a decimation unit (not shown) is connected to the switch SW. On the other hand, common area 3
The output of the switch SW3 is output to the switch SW via the decimation unit 35.
Connected to.

Here, the contact of the switch SW is switched to the optimum individual unit or the decimation unit 35 according to the mode setting (for example, B mode, pulse Doppler mode, CW Doppler mode, etc.). As a result, the image data that has been optimally filtered according to the photographing mode is output to the post-processing
It will enter 0. That is, the signal band-limited at the cutoff frequency fc1 by the common unit 33 is transmitted to the subsequent individual unit 34.
Then, the band is further limited by the respective cutoff frequencies. For example, in the B mode, the bandwidth is set to a wide band with emphasis on the impulse response, in the pulse Doppler mode, the bandwidth is set to the middle band due to the need for stabilization of the transmission frequency, and in the CW Doppler mode, the S / N ratio is emphasized. To set the bandwidth to a narrow band. As a result, it is possible to optimize the S / N ratio and the bandwidth according to the operation mode while reducing the size of the circuit.

FIG. 7 is a block diagram showing a configuration of a main part of another embodiment of the present invention. 6 are denoted by the same reference numerals. In this embodiment, the decimation filter 30 is divided into a part (common part) 35 that uses it commonly for each shooting mode, and a part (individual part) 36 that uses it individually for each shooting mode. The individual unit 36 includes a DSP (digital signal processor) 36a, an SRAM (static RAM) 36b, and a PROM 36c. Moreover, the common unit 33 is configured by hardware, and the individual unit 36 is realized by software.

A software sequence for performing an individual filter operation is stored in the PROM 36c, and is stored in the SRAM 36b.
Is used as a work area for calculations performed by the DSP 36a. The mode setting signal is input to the DSP 36a.

In the device configured as above, the signal quantized by the 1-bit ADC 20 is first sent to the common unit 33.
And a low-pass filter with a cutoff frequency fc1 is applied. Thereafter, the individual unit 36 executes a low-pass filter operation and decimation of each cutoff frequency. Here, DS is set according to the mode setting (for example, B mode, pulse Doppler mode, CW Doppler mode, etc.).
P36a executes a low-pass filter operation and a decimation of a target cutoff frequency. As a result, image data that has been optimally filtered according to the shooting mode enters the post-processing circuit 40. As a result, it is possible to optimize the S / N ratio and the bandwidth according to the operation mode while reducing the size of the circuit.

[0041]

As described above in detail, according to the present invention, a received signal from an ultrasonic probe is quantized by a 1-bit oversampling type A / D converter, and the quantized data is decimation. In applying the filter, by varying the cutoff frequency of the decimation filter according to the type of shooting mode, the circuit can be downsized, and the S / N ratio and the bandwidth can be optimized according to the operation mode. An ultrasonic reception processing method and an ultrasonic diagnostic apparatus can be provided.

[Brief description of the drawings]

FIG. 1 is a flowchart showing the principle of the method of the present invention.

FIG. 2 is a configuration block diagram showing a main part of one embodiment of the present invention.

FIG. 3 is a block diagram showing a detailed configuration example of a main part of the present invention.

FIG. 4 is a block diagram illustrating a configuration example of an oversampling type A / D converter.

FIG. 5 is a diagram showing a waveform and a frequency spectrum of each unit.

FIG. 6 is a block diagram showing a main part of another embodiment of the present invention.

FIG. 7 is a configuration block diagram showing a main part of another embodiment of the present invention.

FIG. 8 is a conceptual diagram of an ultrasonic diagnostic apparatus.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 ultrasonic probe 10 echo transmitting / receiving section 20 oversampling type A / D converter 30 decimation filter 40 post-processing circuit

Continuation of front page (58) Field surveyed (Int.Cl. ⁷ , DB name) A61B 8/00-8/15

Claims (4)

(57) [Claims] An ultrasonic reception processing method in which an ultrasonic image is obtained by transmitting and receiving an ultrasonic wave, wherein a received signal from an ultrasonic probe is quantized by a 1-bit oversampling A / D converter. An ultrasonic reception processing method characterized in that, when applying quantized data to a decimation filter, a cutoff frequency of the decimation filter is varied according to a type of a photographing mode. 2. A 1-bit oversampling A / D converter for quantizing a signal received from an ultrasonic probe in an ultrasonic diagnostic apparatus for obtaining an ultrasonic image by transmitting and receiving ultrasonic waves. And a decimation filter for removing high-frequency components that receives data quantized by the oversampling A / D converter and varies its cutoff frequency according to the type of shooting mode. Ultrasound diagnostic device characterized by the following. 3. The decimation filter is divided into a portion which uses the same in each shooting mode and a portion which is used individually in each shooting mode, and switches between the portions which are used individually according to the type of the shooting mode. The ultrasonic diagnostic apparatus according to claim 2, wherein: 4. An individual part of the decimation filter is adapted to switch to a wide band in the B mode, to a middle band in the pulse Doppler mode, and to a narrow band in the CW Doppler mode. The ultrasonic diagnostic apparatus according to claim 3, wherein