JPH0655209B2 - Ultrasonic diagnostic equipment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Outline] In a two-dimensional tomography apparatus that performs a fast Fourier transform (FFT) analysis on an ultrasonic reflection signal obtained from a subject, the fast Fourier transform (FFT) analysis is performed with an odd number. By performing the data length (the number of points), the obtained maximum frequencies in the positive direction and the negative direction are made the same.

[Industrial application field]

The present invention relates to an ultrasonic diagnostic apparatus, and particularly to a fast Fourier transform.
An ultrasonic wave that performs a fast Fourier transform (FFT) analysis with an odd data length in a two-dimensional tomography device using (FFT) analysis so that the maximum blood flow velocity that can be detected is the same in the positive direction and the negative direction. The present invention relates to an analysis method for reflected signals.

When performing Doppler measurement in a recent ultrasonic diagnostic apparatus, a so-called color Doppler blood flow meter, which displays blood flow dynamics in a living body by coloring it in two dimensions, is rapidly used because of its good visibility. It is spreading.

This color Doppler blood flow meter used a method that used an analysis method based on autocorrelation at first, but due to the drawback that low-speed blood flow is difficult to display, it has recently been analyzed by fast Fourier transform (FFT). Method has been devised.

Under these circumstances, a fast Fourier transform (FFT) analysis method suitable for a color Doppler blood flow meter with good visibility has been required.

[Problems to be solved by conventional technology and invention]

FIG. 4 is a diagram showing a configuration example of a conventional FFT Doppler blood flow meter.

Conventionally, when frequency analysis is performed on a given signal, an analysis method using a fast Fourier transform (FFT) is known as a method for significantly reducing the calculation time.

Generally, when frequency analysis by the above fast Fourier transform (hereinafter referred to as FFT) is performed on an arbitrary number of data N = 2 ^r (where N and r are positive integers), for example, FF of radix 2 is used.
When the calculation by the T algorithm is used, Log ₂ N stages of calculation are performed, and the calculation at each stage is called a butterfly calculation because of its calculation form.

^Similarly , when the number of data N = 3 ^r is expressed,
For example, when the radix-3 FFT operation is used, the number of operation steps at this time is Log ₃ N steps.

In the calculation by the FFT, the number N of data is called the data length N.

Since many documents are known about the FFT operation itself, the FFT analysis for the case where the data length N is an even number is more orderly in terms of algorithms, though not particularly mentioned here. Often used for signal analysis.

FIG. 4 shows an example of the FFT analysis device when the data length is an even number.

First, set the number of transmissions to "8" in the number of times setting section 61,
When the scan controller 6 is started,
The drive signal is sent eight times in one direction,
From 1 to the subject, the ultrasonic signal is transmitted eight times in this direction.

At that time, when the transmission / reception unit 2 receives the reflected signals of the ultrasonic signals from the subject 8 times through the probe 1 and sends them to the analog processing unit 3, the analog processing unit 3 In the above, a predetermined process is performed, and for each reflection signal, 128 signals sampled and held by 128 sampling signals are obtained, and the A / D converter (A / D) After being converted to a digital signal by 4, it is sent to the even-numbered FFT analyzer 5.

As a result, input signals of 128 points in the depth direction of the subject and 8 points in the time axis direction are obtained, and FFT analysis is performed on 8 data in each depth direction.

After that, the same operation is repeated while changing the sending direction of the ultrasonic signal to obtain a two-dimensional tomographic image regarding the blood flow velocity.

FIG. 5 is a diagram showing an example of a radix-2 butterfly operation diagram of an 8-point FFT, and shows a flow of operation when FFT analysis is performed on the data length of 8 points (even number). Here, fr indicates the repetition frequency of ultrasonic transmission.

FIG. 6 is a diagram showing an example of the solution result of the 8-point FFT, in which the vertical axis shows the power spectrum (P) and the horizontal axis shows the frequency (f).

Generally, the DC component always exists in the frequency analysis result by FFT. Therefore, in the FFT analysis for an even data length of 8 points, the maximum frequencies in the positive and negative directions are different as shown in the figure. In the above-mentioned color Doppler blood flow meter, if the positive and negative blood flow velocities are displayed in shades of color, there is a problem that the concentrations cannot be the same for the same blood flow velocity.

In addition, in the two-dimensional tomographic analysis in the ultrasonic diagnostic apparatus, in addition to the above-mentioned FFT analysis, the above-mentioned autocorrelation analysis method is also known. The autocorrelation analysis method is a time-axis function analysis method. Therefore, the high-pass filter cannot remove the low-speed region such as the heart wall.

Therefore, there is a problem that the obtained analysis result cannot remove the influence of the reflection signal from the heart wall of the heart, and it is difficult to detect a low blood flow velocity.

In view of the above conventional drawbacks, the present invention has an object to provide an ultrasonic diagnostic apparatus in which the maximum blood flow velocity that can be detected does not vary depending on the flow velocity direction by setting the data length of the FFT analysis to an odd number. Is.

[Means for solving problems]

FIG. 1 is a block diagram showing an embodiment of the present invention.

In the present invention, a transmitting / receiving unit 2 that transmits and receives ultrasonic waves several times in a certain direction, an analog processing unit 3 that performs analog processing on a reception signal obtained by the transmitting / receiving unit 2, and a post-stage of the analog processing unit 3. Fast Fourier transform (FFT) analysis unit
In the ultrasonic diagnostic apparatus provided with 5 ', the transmitting / receiving unit 2
The number of transmissions of the ultrasonic wave is set to an odd number, and the data length in the fast Fourier transform (FFT) analysis unit 5'is configured to be the same as the number of transmissions.

[Action]

That is, according to the present invention, in a two-dimensional tomographic apparatus that performs a fast Fourier transform (FFT) analysis on an ultrasonic reflection signal obtained from a subject, the fast Fourier transform (FFT) analysis is performed with an odd data length. Since the maximum frequency in the positive direction and the maximum frequency in the negative direction that are obtained are made the same by performing with (number of points), even when the Doppler blood flow velocity is displayed in color, the shade of the color depending on the flow velocity direction is displayed. There is an effect that can be the same.

〔Example〕

Embodiments of the present invention will be described in detail below with reference to the drawings. FIG. 1 is a block diagram showing an embodiment of the present invention, FIG. 2 is a diagram showing an example of a radix-3 butterfly operation diagram of a 9-point FFT, and FIG. It is the figure which showed an example of the analysis result of point FFT, and odd number FF in FIG.
Transmitter / receiver 2 from T analyzer 5'and scan controller 6
An odd number of drive signals per direction (9 times in this example) is a necessary means for carrying out the invention. still,
The same reference numerals denote the same objects throughout the drawings.

First, when the number of times of transmission is set in the number of times setting section 61 to, for example, an odd number of '9' and the scan control section 6 is started, the drive signal is sent to the transmitting / receiving section 2 nine times in one direction. , 9 from the probe 1 to the subject
Ultrasonic signals are transmitted once.

At that time, when the transmission / reception unit 2 receives the reflection signal of the ultrasonic signal from the subject 9 times through the probe 1 and sends it to the analog processing unit 3, the analog processing unit 3 In the same manner as in the conventional method, the predetermined processing is performed, and for each reflection signal, 128 signals sampled and held by 128 sampling signals are obtained. D converter (A /
After being converted into a digital signal by D) 4, it is sent to the odd-numbered FFT analyzer 5 '.

As a result, input signals of 128 points in the depth direction of the subject and 9 points in the time axis direction are obtained, and the FFT analysis is performed on 9 pieces of data in each depth direction.
In this case, since the expressed by 9 = 3 ^2, the butterfly computation with a base 3 is performed.

FIG. 2 is a diagram showing an example of a radix-3 butterfly operation diagram of a 9-point FFT, and shows the flow of the operation operation when the FFT analysis is performed on the data length of 9 points (odd number).

FIG. 3 is a diagram showing an example of the analysis result of the 9-point FFT, which corresponds to an odd data length of 9 points.
The FFT analysis is characterized in that the maximum frequency in the positive direction and the maximum frequency in the negative direction are the same, as shown in the figure, even if the analysis result always includes a DC component.

Therefore, in a color Doppler blood flow meter that displays blood flow velocities in both positive and negative directions by coloring them as shades of red and blue, for example, the shades corresponding to the blood velocities of the two colors are the same. Can be

As described above, according to the present invention, in the ultrasonic diagnostic apparatus having the frequency analysis function by the FFT analysis, the number of transmissions of the ultrasonic signal in a certain direction to the subject is odd (for example, 9).
In addition, the data length in the FFT analysis unit is the same as the number of transmissions.

〔The invention's effect〕

As described above in detail, the ultrasonic diagnostic apparatus of the present invention is a two-dimensional tomographic apparatus that performs a fast Fourier transform (FFT) analysis on an ultrasonic reflection signal obtained from a subject, By performing the conversion (FFT) analysis with an odd number of data lengths (number of points), the maximum frequencies in the positive and negative directions obtained are the same, so when the Doppler blood flow rate is displayed in color. Also, there is an effect that the shades of colors depending on the direction of the flow velocity can be made the same.

[Brief description of drawings]

1 is a block diagram showing an embodiment of the present invention, FIG. 2 is a diagram showing an example of a radix-3 butterfly operation diagram of a 9-point FFT, and FIG. 3 is an analysis result of the 9-point FFT. Fig. 4 shows an example, Fig. 4 shows an example of the configuration of a conventional FFT Doppler blood flow meter, and Fig. 5 shows an example of a radix-2 butterfly operation diagram of an 8-point FFT, Fig. 6 Is a diagram showing an example of 8-point FFT analysis results. In the drawing, 1 is a probe, 2 is a transmitting / receiving unit, 3 is an analog processing unit, 4 is an A / D converter (A / D), 5 is an even FFT analysis unit, 5'is a radix FFT analysis unit, 6 is a scan control unit, and 61 is a frequency setting unit.

Claims (1)

[Claims] 1. A transmission / reception unit (2) for transmitting and receiving ultrasonic waves several times in a fixed direction, an analog processing unit (3) for analog-processing a reception signal obtained by the transmission / reception unit (2), Fast Fourier transform (FFT) after the analog processing unit (3)
An ultrasonic diagnostic apparatus provided with an analysis unit (5 ′), wherein the number of ultrasonic waves transmitted from the transmission / reception unit (2) is an odd number, and data from the fast Fourier transform (FFT) analysis unit (5 ′) An ultrasonic diagnostic apparatus having the same length as the number of transmissions.