JP4473388B2 - Ultrasonic diagnostic equipment - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an ultrasonic diagnostic apparatus, and more particularly to an ultrasonic diagnostic apparatus to which a frequency compound method is applied.
[0002]
[Prior art]
In the B-mode image (black and white tomographic image) displayed in the ultrasonic diagnostic apparatus, there is an artifact called speckle with a granular pattern generated by interference of the wavefront of the ultrasonic wave regardless of the structure in the living body. As a method for reducing this, a frequency compound method described in the following literature is known.
[0003]
1) GETrahey, JW Allison, SWSmith, and OTvon Ramm, A Quantitative Approach to Speckle Reduction via Frequency Compounding, Ultrasonic Imaging 8151-164 (1986)
2) Steve M. Gehlbach, F. Graham Sommer, Frequency Diversity Speckle Processing, Ultrasonic Imaging 9,92-105 (1987)
3) Yoshida, Nakajima, Oilfield, Real time reduction method of speckle noise in ultrasonic tomogram, Jpn J Med Ultrasonics Vol.13, No.5, 305-314, (1986)
This frequency compound method is a method of reducing speckle noise by dividing a received signal into a plurality of bands, independently detecting each band, and then superimposing the results. That is, the speckle nozzle is made inconspicuous by changing the interference condition for each band.
[0004]
In the conventional method, a plurality of band pass filters (BPF) are used for dividing a plurality of bands.
[0005]
[Problems to be solved by the invention]
However, according to the conventional frequency compound method, although speckle noise is reduced, there is a problem in image quality deterioration that the distance resolution is lowered and the image is blurred.
[0006]
The present invention has been made in view of the above-described conventional problems, and an object of the present invention is to provide an ultrasonic diagnostic apparatus capable of improving a decrease in distance resolution while reducing speckle noise.
[0007]
[Means for Solving the Problems]
(1) In order to achieve the above-described object, the present invention provides transmission / reception means for transmitting / receiving ultrasonic waves and outputting a reception signal, and separating signal components from the reception signal for a plurality of different frequency bands. An individual band extracting unit that performs extraction; a wideband extracting unit that extracts a wideband signal component covering the plurality of frequency bands from the received signal; and a signal component for each of the plurality of frequency bands and the wideband signal component. Adding means for adding.
[0008]
According to the above configuration, the speckle reduction effect can be obtained simultaneously by adding the plurality of narrowband signal components extracted by the individual band extraction unit and the wideband signal component extracted by the wideband extraction unit. The spatial resolution in the distance direction (depth direction) can be improved.
[0009]
Preferably, the adding means performs weighted addition. Each weighting factor can be appropriately adjusted depending on whether the speckle reduction is emphasized or the spatial resolution is emphasized. For example, the weighting coefficient switching setting may be performed artificially or automatically based on factors such as a diagnosis part and a constitution.
[0010]
Preferably, the individual band extracting unit includes a plurality of band pass filters provided in parallel for each band, and the wide band extracting unit includes a band pass filter corresponding to the wide band. Preferably, the characteristic of each bandpass filter is variably set according to the diagnostic distance. Since the frequency characteristics of the echo change according to the depth, if the characteristics of the bandpass filter are varied accordingly, a more appropriate effect can be exhibited.
[0011]
Preferably, the individual extraction means includes a plurality of first quadrature detectors and a plurality of narrowband lowpass filters provided in parallel for each band, and the wideband extraction means is a second quadrature detection corresponding to the wideband. And a broadband low-pass filter. As described above, a desired band component can be extracted even if the quadrature detection method is used.
[0012]
Preferably, a first reference signal output unit that supplies a plurality of first reference signals having different frequencies corresponding to the respective bands to the plurality of first quadrature detectors, and the second quadrature detector. And a second reference signal output unit for supplying a second reference signal having a frequency corresponding to the broadband. Preferably, each frequency of the first reference signal and the second reference signal is variably set according to a diagnostic distance.
[0013]
(2) Note that transmission / reception means for transmitting and receiving ultrasonic waves and outputting a reception signal, individual band extraction means for separating and extracting signal components for each of a plurality of different frequency bands from the reception signal, It is also possible to provide a signal component for each of a plurality of frequency bands and an adding means for weighted addition of the received signals .
[0014]
According to this configuration, it is possible to obtain a speckle reduction effect and a spatial resolution improvement effect by weighting and adding the actual wideband signal.
[0015]
DETAILED DESCRIPTION OF THE INVENTION
DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, preferred embodiments of the invention will be described with reference to the drawings.
[0016]
FIG. 1 shows a preferred embodiment of an ultrasonic diagnostic apparatus according to the present invention, and FIG. 1 is a block diagram showing the overall configuration thereof.
[0017]
The probe 10 is an ultrasonic probe that is used in contact with a body surface or inserted into a body cavity. An array transducer is accommodated in the probe 10, and a scanning plane which is a two-dimensional data capturing area can be formed by applying electronic linear scanning or electronic sector scanning to the array transducer. The transmitter 12 is a circuit that supplies a transmission signal to the probe 10.
[0018]
Received signals output from the probe 10 (specifically, a plurality of received signals output from the respective vibration elements) are respectively amplified by the receiving amplifier 14 and then input to the AD converter 16 where the analog signals are converted into digital signals. Converted to a signal. The plurality of reception signals converted into digital signals are input to the phasing adder 18 where the phasing addition for forming the reception beam is executed to generate a reception signal after the phasing addition. The received signal is input to the speckle reduction circuit 20. The speckle reduction circuit 20 includes n narrow band pass filters 22 _{1 to} 22 _n connected in parallel to each other and n envelope detections provided for the respective narrow band pass filters 22 _{1 to} 22 _n. Units 26 _{1 to} 26 _n , the wide band pass filter 24, the envelope detector 28 provided in the subsequent stage, and the received signals after detection output from the envelope detectors 26 _{1 to} 26 _n and 28 are weighted. And an adder 30 for adding. Here, FIG. 3 shows the frequency characteristics of each bandpass filter. Incidentally, FIG. 2 shows the frequency characteristics of each band-pass filter included in the conventional speckle reduction circuit.
[0019]
Conventionally, a plurality of narrow bands 102 to 108 are set so that received signals do not overlap each other as much as possible with respect to 100 spectra, and a process of adding signal components for each narrow band has been performed.
[0020]
On the other hand, in the present embodiment, as shown in FIG. 3, the plurality of narrow bands 102 to 108 are set in the same manner as in the prior art, but further, a wide band 110 that covers them is set. Here, the narrow bands 102 to 108 correspond to the frequency characteristics of the narrow band pass filters 22 _{1 to} 22 _n shown in FIG. 1, and the wide band 110 is the frequency characteristic of the wide band pass filter 24 shown in FIG. It corresponds to.
[0021]
Therefore, in the conventional example, although speckle is surely reduced, there is a problem of a decrease in spatial resolution in the distance direction. However, according to the present embodiment, signal addition can be performed by compensating for a broadband component. There is an advantage that a decrease in the spatial resolution in the distance direction can be reduced.
[0022]
Incidentally, FIG. 6 shows, as a general theory, the relationship between the bandwidth of the filter and the spatial resolution in the distance direction, and the spatial resolution in the distance direction deteriorates as the bandwidth becomes narrower as shown in the figure. .
[0023]
Incidentally, in the filter characteristics shown in FIG. 3, the effect of reducing speckles is enhanced by reducing the cross-correlation value of signals in each band as much as possible. Therefore, adjacent narrow bands should be set so as not to overlap each other. Is desirable.
[0024]
As described above, the detected received signals output from the envelope detectors 26 _{1 to} 26 _n and 28 are weighted and added in the adder 30. Here, each weighting coefficient can be arbitrarily set. For example, if priority is given to the speckle reduction effect, a larger weighting value may be given to the received signal component corresponding to a plurality of narrow bands, If priority is given to the time resolution in the distance direction, a larger weighting value may be given to a wideband received signal component.
[0025]
The processed received signal output from the speckle reduction circuit 20 is input to the signal compressor 32 as before, and after logarithmic compression there, only the low-frequency component is extracted by the low-pass filter 34. Is done. Then, the received signal having the low frequency component is input to the scan converter 36. Here, the scan converter 36 is configured as a digital scan converter (DSC), and the scan converter 36 performs coordinate conversion, interpolation processing, and the like as in the prior art, and an ultrasonic image formed thereby is displayed. Displayed on the instrument 38.
[0026]
Incidentally, in the present embodiment, the frequency characteristics of the narrow band pass filters 22 _{1 to} 22 _n and the wide band pass filter 24 are variably set by a band control unit (not shown). Specifically, the center frequency of the band pass filter is continuously variably set as a function of the depth as shown in FIG. Specifically, reference numeral 202 represents the center frequency of the wide band pass filter 24, and reference numerals 200, 201, 203, and 204 represent the center frequencies of the narrow band pass filters 22 _{1 to} 22 _n , respectively. As is well known, it is known that the high frequency component of ultrasonic echoes decreases as the depth increases. According to the continuous variation of the center frequency as shown in FIG. There is an advantage that appropriate filtering can be performed in accordance with the specific properties of the sound wave.
[0027]
As described above, according to the above-described embodiment, it is possible to reduce the phenomenon of specific speckles that occur in an ultrasonic image, and to deal with the problem of a decrease in resolution in the distance direction due to the speckle reduction. Become. Therefore, there is an advantage that the image quality of the ultrasonic image can be remarkably improved.
[0028]
FIG. 5 shows another embodiment. The speckle reduction circuit 20A shown in FIG. 5 corresponds to the speckle reduction circuit 20 shown in FIG. In the speckle reduction circuit 20A, a plurality of orthogonal detection units 39 are provided. Specifically, a quadrature detection unit is provided for each of a plurality of narrow bands, and one quadrature detection unit is provided corresponding to the wide band. Here, in FIG. 5, reference numerals 40 and 42 denote mixers that mix the reference signal with the received signal. The mixers 40 and 42 have phases different from each other by 90 degrees due to the action of the phase shifter 41. A reference signal is supplied. The reception signals output from the two mixers 40 and 42 are input to the computing unit 48 via low pass filters (LPF) 44 and 46. The low-pass filters 44 and 46 are circuits for extracting signal components in the baseband region. The low-pass filters 44 and 46 are narrow-band low-pass filters, and the low-pass filters 64 and 66 described later are wide-band low-pass filters.
[0029]
The computing unit 48 is a circuit that performs a predetermined computation on the received signal output from each low-pass filter, specifically, a complex signal, adds the square of the real part and the square of the imaginary part, and further adds the result Is a circuit that calculates the amplitude of the received signal by calculating the square root. The amplitude information is weighted by the weighting circuit 50 and then output to the adder 52.
[0030]
On the other hand, for wideband processing, two reference signals having different phases from each other are mixed in the mixers 60 and 62 with respect to the received signal as described above. Here, reference numeral 61 represents a phase shifter. As described above, the received signals output through the low-pass filters 64 and 66 for the wide band are input to the calculator 68, and the amplitude of the broadband component is calculated by executing the same calculation as the calculator 48. The information is weighted by the weighting circuit 70 and then sent to the adder 52.
[0031]
The adder 52 performs addition for each signal component and outputs the addition result to the computing unit 54. Here, the computing unit 54 performs normalization by dividing the addition result by the total number of weight values. Incidentally, the weighting value to be multiplied to each signal component in FIG. 5 is represented by a ₁ ~a _n and a _w.
[0032]
Also in the speckle reduction circuit 20A shown in FIG. 5, it is desirable to continuously vary a plurality of narrowband and wideband center frequencies according to the depth of the echo. In that case, according to the characteristics shown in FIG. The center frequency is variably set.
[0033]
【The invention's effect】
As described above, according to the present invention, there is an advantage that the resolution in the distance direction can be improved while reducing speckle peculiar to an ultrasonic image. Further, according to the present invention, it is possible to obtain better image quality in the depth direction by continuously varying the center frequency of the band.
[Brief description of the drawings]
FIG. 1 is a block diagram of an ultrasonic diagnostic apparatus according to an embodiment.
FIG. 2 is a diagram for explaining band setting according to a conventional frequency compound method.
FIG. 3 is a diagram for explaining band setting according to a frequency compound system according to the present embodiment.
FIG. 4 is a diagram for explaining continuous variation of the center frequency of the band-pass filter.
FIG. 5 is a diagram illustrating a configuration example of a speckle reduction circuit according to another embodiment.
FIG. 6 is a diagram showing the relationship between bandwidth and spatial resolution in the distance direction.
[Explanation of symbols]
10 probes, 12 transmitters, 14 reception amplifiers, 16 AD converters, 18 phasing adders, 20 speckle reduction circuits, 32 signal compressors, 34 low-pass filters, 36 scan converters, 38 displays.

Claims (2)

A transmission / reception means for transmitting / receiving ultrasonic waves and outputting a reception signal;
A means for separating and extracting signal components for each frequency band from a plurality of different frequency bands from the received signal, and a plurality of bandpass filters for individual band extraction provided corresponding to the plurality of frequency bands An individual band extraction means comprising:
Means for extracting a wideband signal component covering the plurality of frequency bands from the received signal, the wideband extraction means comprising a wideband extraction bandpass filter corresponding to the wideband ;
Adding means for weighted addition of a plurality of signal components for the plurality of frequency bands and the wideband signal components;
The characteristics of the plurality of bandpass filters for individual band extraction constituting the individual band extraction means are variably set according to the diagnostic distance, and the characteristics of the bandpass filter for wideband extraction constituting the wideband extraction means are set according to the diagnostic distance. A bandwidth control unit to variably set;
An ultrasonic diagnostic apparatus comprising: A transmission / reception means for transmitting / receiving ultrasonic waves and outputting a reception signal;
A means for separating and extracting signal components for each frequency band from a plurality of different frequency bands from the received signal, the plurality of first orthogonal detectors provided corresponding to the plurality of frequency bands, and a plurality of Individual band extraction means composed of a narrow band low pass filter,
Means for extracting a wideband signal component covering the plurality of frequency bands from the received signal, the wideband extraction means comprising a second quadrature detector corresponding to the wideband and a wideband low-pass filter;
Adding means for weighted addition of a plurality of signal components for the plurality of frequency bands and the wideband signal components;
A first reference signal output unit that supplies a plurality of first reference signals having different frequencies corresponding to the plurality of frequency bands to the plurality of first quadrature detectors;
A second reference signal output unit for supplying a second reference signal having a frequency corresponding to the wide band to the second quadrature detector;
A bandwidth control unit that variably set in accordance with the diagnostic distance frequency of the second reference signal with variably set in accordance with the frequency of the plurality of first reference signal to the diagnostic distance,
An ultrasonic diagnostic apparatus comprising:

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