JPH0568983B2 - - Google Patents

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to an ultrasonic continuous wave Doppler blood flow diagnostic device, and in particular, as a display format of an analysis spectrum,
The present invention relates to a device that adopts a folded display format. Folding display is data that does not originally fit into the display frequency band at the sampling frequency due to a large Doppler transition frequency, but is placed within the display frequency band by using folding based on the sampling theorem. This is a display format that allows you to display the spectrum on the same screen along with the data that can be displayed on the screen.

(Prior art) When a continuous wave Doppler blood flow diagnostic device transmits a continuous wave of ultrasound into a subject, the reflected wave from the blood flow undergoes a Doppler transition caused by the blood flow and changes to the transmission frequency. This device uses waves received at different frequencies to determine the radial velocity of blood flow from the transition frequency.

The _{Doppler transition} frequency _D1 (0
< _D1 < _s / 2), _D2 ( _s / 2 < _D2 < _s ), intensity A _D1
=A _D2 signal is input, and the noise contained in the signal and processing system is white noise, and the noise intensity in the frequency range from _-s /2 to _s /2 is assumed to be white noise.
It is assumed that the noise of A _N is also included. Here, the signal with the transition frequency _D1 is the _S1 signal, and the signal with the transition frequency _D2 is the _S2 signal.

With conventional ultrasound continuous wave Doppler blood flow diagnostic equipment,
The received signal is orthogonally detected using a reference signal with a transmission frequency _c , then passed through a low-pass filter (hereinafter referred to as LPF) with a cutoff frequency _s , and then sampled with a sampling frequency _s in an AD converter.
Analog signals are converted into digital signals, and the data is calculated using a fast Fourier transform analyzer (hereinafter referred to as an FFT analyzer) to display a Doppler image. FIG. 3 is a diagram showing spectra at each stage obtained by processing as described above. In the figure, figure A is the spectrum of the transmitting frequency _c , figure B is the spectrum of the received signal, and the intensity is A _D1 =
A _D2 is the spectrum of a signal with reflected waves due to two velocity streams, the S ₁ signal with frequency _c + _D1 and the S ₂ signal with frequency _c + _D2 . Figure C shows a received signal with the spectrum shown in Figure B at a frequency equal to the transmitting frequency.
This is the spectrum of the signal obtained by orthogonal detection at _c , the intensity does not change between A _D1 and A _D2 , and the frequencies are _D1 and _D2 . Figure 2 shows the characteristics of an LPF with a cutoff frequency of _s . The reason why the cutoff frequency was set to _s instead of _s /2 is to fold back and display the _S2 signal, which has a high blood flow velocity and a large Doppler transition frequency, without being cut. In this way, even high-velocity blood flow can be obtained and displayed as a folded signal.
Figure E is the signal passed through the LPF in Figure D, and the frequency - _s
In the range of ~ _s , the spectrum is similar to the spectrum in Figure C. Figure F is a spectrum obtained by AD converting and FFT analysis of the signal that passed through the LPF in Figure E. In this case, since the sampling frequency is _s , − _s ~
The signals in _{the -s} /2 and _s /2~ ₂ frequency ranges are folded back into the 0~ _s /2 and _-s /2~0 frequency ranges, respectively.

(Problem to be solved by the invention) However, when doing this, as mentioned above, folding occurs in the frequency domain, so although the signal size does not change, the noise is uniformly constant over the entire frequency domain. Since the noise is distributed by intensity, the noise intensity is doubled as shown in Figure F. Therefore, the SN ratio deteriorates compared to when an LPF with a cutoff frequency of _s /2 is used.

The present invention has been made based on such consideration, and its purpose is to provide a device that can display folded Doppler signals without deteriorating SN.

(Means for Solving the Problems) The present invention for solving the above-mentioned problems detects a received signal, passes the detected signal through a low-pass filter, samples it with a sampling means, and processes the detected signal based on the sampling data. , perform frequency analysis using frequency analysis means, display the analysis result in frequency band ( _s ), and use the following as the display format:
Folded display format, that is, data that does not originally fall within the display frequency band at the sampling frequency due to the large Doppler transition frequency (A _D2 )
is placed within the display frequency band ( _s ) using folding based on the sampling theorem, and a display format that can be displayed on the same screen is adopted along with data that can originally be displayed within the display frequency band (A _D1 ). In the ultrasonic continuous wave Doppler blood flow diagnostic apparatus, the sampling frequency of the sampling means is at least twice the upper limit frequency ( _s ) of the display frequency band, that is, a frequency that does not cause aliasing. , and the spectrum analyzed by the frequency analysis means is divided into a band ( _s /
2) Spectrum storage means 5A to 5D for storing data in each division, and sequentially outputting data from each of the divisions stored in the spectrum storage means;
Comparators 6A and 6B compare the magnitudes of the corresponding data values for each set of frequency segments in a relationship where aliasing may occur, and select the larger one, and the frequency spectrum data output from these comparators is set to the zero point on the display. It has spectrum data storage means 7A and 7B that separately store data on the positive side and negative side centered on , and synthesizes the spectrum data on the positive side and the negative side outputted from the spectrum data storage means. ,
This method is characterized by creating a spectrum equivalent to a spectrum using folding based on the sampling theorem.

(Function) The present invention is a device that adopts a folding display format, in which signal analysis processing is performed to prevent folding, and when displaying, an artificial process of spectrum synthesis is performed to prevent folding from occurring. It reproduces a spectrum equivalent to that of , and displays it in a folded display format.

Restoration of the folded format after analysis is performed by the following electrical processing.

In other words, data after FFT analysis is divided and stored in units of ( _s /2), and data is sequentially output from the low frequency side from each of a set of bands in which aliasing may occur, and real-time data is stored. By holding (comparing) the peak at , Doppler shift frequency component data can be extracted. Next, the data after comparison is stored in RAM sequentially starting from the low frequency side.
If you write data into the buffer and decide that the side containing the high shift component is the negative side data buffer, the high shift component will automatically be located at the same spectrum position in the negative side buffer as when there is aliasing. is memorized.

(Example) Hereinafter, an example of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a block diagram of an apparatus according to an embodiment of the present invention. In the figure, 1A converts the input received _signal to cos ωt (ω=
2π _c ), 1B is a detector of the same frequency.
The detector demodulates by sin ωt, and the detectors 1A and 1B perform orthogonal detection and output an i signal (in-phase signal) and a q signal (orthogonal signal), respectively. 2A,
2B is an LPF that cuts signals having a frequency higher than the frequency _s of the i and q signals, and 3A and 3B are AD converters that sample the i and q signals at a sampling frequency of 2 _s . The outputs of the AD conversions 3A and 3B are subjected to spectrum analysis by an FFT analyzer 4. 5A to 5D are
A spectrum line buffer that equally divides and stores the spectrum of the output of the FFT analyzer 4 into four frequency regions, 5A is _−s − ~ _s /2, 5B
is _−s /2~0, 5C is 0~ _s /2, 5D is _s /
Stores data in the frequency domain of 2 to _s . 6A is _−s /2 to 0 frequency domain data and _s /2 to _s
6B is a comparator that compares the data in the frequency domain of and selects the data with the larger signal strength as the data in the frequency domain of _{-s /} 2 to 0.
This is a comparator that compares data in the frequency domain of _s /2 and data in the frequency domain of 0 to _s /2, and selects the data with greater signal strength as data in the frequency domain of 0 to _s /2. . 7A is a spectrum line in-buffer that stores data in the frequency domain from _-s /2 to 0 of the output of the comparator 6A, and 7B is a spectrum line buffer that stores data in the frequency domain of _-s /2 to 0 of the output of the comparator 6B.
This is a spectrum line buffer that stores data in the frequency domain.

Next, the operation of the apparatus of the embodiment configured as described above will be explained with reference to FIG. The Doppler transition signals of transition frequencies _D1 and _D2 received by the ultrasonic probe (not shown) are detected by the detector 1A.
detected by a signal with a reference frequency of cos ωt,
It is output as an i signal (in-phase signal). In addition, the received signal input to the detector 1B is detected by a signal with a reference frequency of sin ωt, and a q signal (orthogonal signal) is generated.
It is output as The i signal and the q signal pass through LPFs 2A and 2B having a cutoff frequency _s . This output signal has a spectrum shown in FIG. 2A. This figure is a diagram of the same spectrum as FIG. 1(e). The signal passing through LPF2A and 2B is AD
Sampling frequency in converters 3A and 3B
The signal is sampled at 2 _s , converted to a digital signal, and input to the FFT analyzer 4. The FFT analyzer 4 performs Fourier transform on the input signal to generate a frequency space signal. This output signal has the spectrum shown in the diagram. This spectrum is sampled at a sampling frequency of 2 _s , so the S ₂ signal is not folded back.

The signal of the graph converted by FFT analyzer 4 is divided into four frequency regions _-s ~ _s /2, _-s /2~0,0~
Divide the data into _s /2, _s /2 to _s data and put them into spectrum line buffers 5A, 5B, and 5, respectively.
Store in C, 5D. The data stored in each spectrum line buffer 5A, 5B, 5C, and 5D is as shown in Figure C. Comparator 6B
successively compares the signal strength of each data of spectrum line buffers 5A and 5C. That is, the frequency -
_s and 0, frequency - _s + α and 0 + α, frequency - _s +
The signal intensities of signals at equivalent positions in each block, such as 2α and 0+2α, are compared. As a result of the comparison, the signal with the higher signal strength is stored in the spectrum line buffer 7B as data with a frequency of 0 to _s /2. Similarly, the comparator 6A successively compares the data of the spectrum line buffers 5B and 5D, and selects the data with the higher signal strength from the frequency
The data is stored in the spectrum line buffer 7A as _s /2-0 data. As a result of this comparison, the noise is approximately the same over the entire frequency band, so the signal level of the comparison result also hardly changes, and the S ₁ and S ₂ signal parts are A _D1 ,
It is output as is as the signal strength of A _D2 . The spectrum output obtained by combining the outputs of the spectrum line buffers 7A and 7B is as shown in Fig. E, and _S2 is displayed with the frequency folded back, but the noise level remains almost the same. Therefore, the SN ratio does not deteriorate.

(Effects of the Invention) As explained above, the present invention provides an ultrasonic continuous wave Doppler blood flow diagnostic device that can observe aliasing of high-speed blood flow, prevent aliasing of noise, and prevent SN deterioration. can be provided.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of an apparatus according to an embodiment of the present invention, FIG. 2 is a spectrum diagram of each part in this embodiment, and FIG. 3 is a spectrum diagram of a conventional Doppler apparatus. 1A, 1B...Detector, 2A, 2B...LPF,
3A, 3B...AD converter, 4...FFT analyzer,
5A, 5B, 5C, 5D, 7A, 7B... Spectrum line buffer, 6A, 6B... Comparator.

Claims (1)

[Claims] 1. Detect a received signal, pass the detected signal through a low-pass filter, sample it with a sampling means, and, based on the sampling data,
A frequency analysis means performs frequency analysis, and the analysis result is displayed in a predetermined frequency band ( _s ), and the display format is a folded display format, that is,
Because the Doppler transition frequency is large, the data (A _D2 ) that does not originally fall within the display frequency band at the sampling frequency is placed within the display frequency band ( _s ) using folding based on the sampling theorem, and the data that is originally displayed is In an ultrasonic continuous wave Doppler blood flow diagnostic apparatus that employs a display format that can be displayed on the same screen as well as data (A _D1 ) that can be displayed within a frequency band, the sampling frequency of the sampling means is set to the predetermined display. Upper limit frequency of frequency band ( _s )
, that is, a frequency that does not cause aliasing, and the spectrum analyzed by the frequency analysis means is divided into bands ( _s /2) that are half the upper limit frequency of the display frequency band. Spectrum storage means 5A to 5D are configured to output data sequentially from each of the sections stored in the spectrum storage means, and for each set of frequency sections in a relationship where aliasing may occur, the corresponding data value is output. Comparators 6A and 6B that compare sizes and select the larger one, and spectrum data storage that stores the frequency spectrum data output from these comparators divided into positive and negative data centered on the zero point on the display. means 7A and 7B, and generates a spectrum equivalent to a spectrum using folding based on the sampling theorem by synthesizing the positive side and negative side spectrum data output from the spectrum data storage means. Features: Ultrasonic continuous wave Doppler blood flow diagnostic device.