JP2003079619A - Ultrasonic diagnostic system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To eliminate such problems that a contrast by a speckle pattern is displayed on an ultrasonic image, and the image quality deteriorates. SOLUTION: A uniform ultrasonic wave of a broad band is transmitted to respective scanning lines from a broad band probe 110. Then, at the time of receiving, different bands between scanning lines or the like are filtered by a variable band pass filter 116, and the imaging process is performed. In a sector type scanning surface of an odd number frame, the central frequency of the filer 116 is switched to f1 for the scanning lines at odd numbers, and the central frequency is switched to f2 for the scanning lines at even numbers, and the receipt is performed. In the sector type scanning surface of an even number frame, the central frequency of the filter 116 is switched to f2 for the scanning lines at odd numbers, and the central frequency is switched to f1 for the scanning lines at even numbers, and the receipt is performed. Thus, differences are generated in the interference conditions of reflective waves between the scanning lines and frames, and the speckle pattern is dispersed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ultrasonic diagnostic apparatus for transmitting and receiving ultrasonic waves to obtain ultrasonic images, and more particularly to reducing speckle patterns.

[0002]

2. Description of the Related Art Ultrasonic wave transmission / reception systems in ultrasonic diagnostic equipment include linear electronic scanning using an ultrasonic transducer array and sector scanning using an electronic focusing method, which uses mechanical movement of the transducer. There are methods such as mechanical sector scanning. In any of these, an ultrasonic pulse having a predetermined time width is transmitted in the direction of each scanning line, and a reflected wave generated according to the acoustic impedance on the scanning line is received. Conventionally, ultrasonic pulses of the same frequency have been used regardless of the frame of the ultrasonic image or the direction of the scanning line. FIG. 7 is a diagram schematically showing this, and shows even and odd frames in electronic scanning by the convex type probe and frequencies of scanning lines forming the frames. The sector-type scanning surface 150 represents an odd-numbered frame and the sector-type scanning surface 152 represents an even-numbered frame. When forming the respective scanning lines 154 constituting them, ultrasonic pulses of frequency f are all used.

[0003]

The ultrasonic pulse has a space length according to the transmission time width. Reflected waves from two points at different depths overlap each other when the difference in the round-trip path length of ultrasonic waves is less than or equal to this space length. That is, when the distance between the two points is less than half of this space length, the reflected waves from these points interfere with each other. Since the distribution of acoustic impedance will not change so much between adjacent scan lines and between consecutive frames, the light and shade due to interference will continue in the direction in which the scan lines are arranged,
As a result, an interference fringe having an intensity different from the actual reflection intensity at each point can be generated. This interference fringe is called a speckle pattern. For example, in the simplest case,
When reflections of similar intensity occur at two points shifted by four wavelengths, the intensity is weakened to each other, and conversely, if they are shifted by a half wavelength, they are strengthened.

These interference fringes are visually conspicuous, and it is difficult to judge whether they are significant patterns or speckle patterns when performing image data processing. Therefore, if a striped noise due to the speckle pattern is displayed in the vicinity of a diagnosis target such as an organ whose acoustic impedance changes spatially on the ultrasonic image, there is a problem that accurate diagnosis is hindered.

An object of the present invention is to provide an ultrasonic diagnostic apparatus capable of obtaining a good ultrasonic image with reduced speckle pattern and improved image quality.

[0006]

An ultrasonic diagnostic apparatus according to the present invention forms an ultrasonic image by changing the frequency of a received signal in at least one of adjacent scanning lines or frames of continuous ultrasonic images. Is characterized by. This makes it possible to form an ultrasonic image in which the same speckle pattern is not spatially or temporally continuous. The present invention uses a method of differentiating the pass band of the reception filter in order to make the frequency of the received signal different.

That is, in the ultrasonic diagnostic apparatus according to the present invention, in forming each scanning plane, ultrasonic waves having a wide band frequency are transmitted in each scanning line direction, and a receiving filter having a different pass band between adjacent scanning lines is used. Then, the received signal is filtered.

In the present invention, signals in different frequency bands are extracted from the received signal between adjacent scanning lines. This allows
The conditions of interference of reflected waves used to form an ultrasonic image are
An ultrasonic image that changes between adjacent scanning lines and whose speckle pattern is not continuous in the direction in which the scanning lines are arranged is obtained. Therefore, the speckle patterns are dispersed to make them visually inconspicuous, and it is easy to distinguish from a real image in image processing.

In another ultrasonic diagnostic apparatus according to the present invention, reception is performed in the same scanning line direction by using reception filters having different pass bands even between consecutive frames of ultrasonic images displayed on the same screen. Filter the signal.

According to the present invention, the pass frequency of the reception filter is changed between adjacent scan lines and also between frames for each scan line. As a result, the conditions of interference of the reflected waves in the ultrasonic images displayed on the same screen are temporally changed, and the dispersion action of the speckle pattern is further improved.

In the ultrasonic diagnostic apparatus according to the preferred embodiment of the present invention, the frequencies of the pass bands of the reception filter in two adjacent scanning lines are not in a multiple relationship, and the ultrasonic waves are in the same scanning line direction. The frequencies of the pass band of the reception filter between two consecutive frames of the image are set so as not to have a multiple relationship. The fact that the frequencies of the passbands of the two reception filters are not in a multiple relationship means that the representative value of each of the two passbands, for example, the smaller value of the center frequencies is not a divisor of the larger value. This makes it difficult for the light and dark positions due to interference to match between adjacent scanning lines or between frames. Therefore, the speckle pattern is significantly reduced.

An ultrasonic diagnostic apparatus according to another aspect of the present invention transmits wideband ultrasonic waves in forming each scanning plane,
The reception signal is filtered using reception filters having different pass bands between consecutive frames of the ultrasonic image displayed on the same screen.

In the present invention, the pass frequency of the reception filter is changed between successive frames of the ultrasonic image displayed on the same screen. With this, regardless of the difference in the pass frequency of the reception filter between the adjacent scanning lines in the same frame,
Even if the passing frequency in the frame is uniform, the speckle pattern can be reduced by the temporal dispersion action of the speckle pattern.

In the ultrasonic diagnostic apparatus of the preferred embodiment of the present invention, the frequencies of the pass band of the reception filter between two consecutive frames of the ultrasonic image are set so as not to have a multiple relationship. This makes it difficult for the positions of light and dark due to interference to match between consecutive frames. Therefore, the speckle pattern is significantly reduced.

The ultrasonic images to which the present invention is applied include B-mode images. In the M-mode image, reflected waves at spatially continuous time for one scanning line are displayed side by side. However, since the frame is configured by arranging a plurality of lines and is not different from the B mode in that the frames are sequentially displayed, the present invention can be applied to the M mode image.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, an example of a basic configuration on which the present invention is based will be described, and then a preferred embodiment of the present invention will be described with reference to the drawings.

[Basic Configuration Example] FIG. 1 is a block diagram of an ultrasonic diagnostic apparatus of a basic configuration example on which the present invention is premised. The frame / line counter 2 counts the order of scanning lines to be transmitted and received in the frame and the order of the frame to which the scanning line belongs. Frequency switching signal generator 4
Obtains these two orders from the frame / line counter 2 and switches the frequency of the ultrasonic wave transmitted / received to / from the scanning line according to the even / odd of these. This frequency switching operation will be described later.

The transmitter 6 receives the transmission frequency setting signal 8 output from the frequency switching signal generator 4, and drives the convex type transducer array of the probe 10 with a rectangular electric pulse having a time width designated by the transmission frequency setting signal 8. To do. The wider the time width of the rectangular electric pulse, the lower the center frequency of the ultrasonic wave emitted from the transducer.

An ultrasonic pulse is transmitted from the probe 10 in a predetermined direction by an electronic scanning method. The reflected wave of the ultrasonic pulse is received by the broadband probe 10 and converted into an electric signal for each transducer.
It is amplified by 2. Subsequently, the focus adder 14 adds and synthesizes the electric signals for each transducer by the reception dynamic focus method to obtain reception signals from each point on the designated scanning line.

The variable band pass filter 16 receives the pass band setting signal 18 from the frequency switching signal generator 4,
A pass band including the center frequency at the time of transmitting the received ultrasonic pulse is set. The band of the received signal output from the focus adder 14 is selected by the variable bandpass filter 16, and then the detector 20 and the analog image processor 22 are selected.
Is converted into an analog reception signal corresponding to the acoustic impedance distribution.

When an image is displayed using the output of the analog image processor 22, the speckle pattern is smoothed due to human vision and the afterimage effect and the spatial resolution limit of the display device. However, in this ultrasonic diagnostic apparatus, in order to obtain a more reliable smoothing effect of the speckle pattern, the output of the analog image processor 22 is image-processed by the digital scan converter (DSC) 24, and the ultrasonic waves are displayed on the display monitor 26. The image is displayed.

Image processing in the DSC 24 will be described. The analog-digital (A / D) converter 28 temporarily converts the analog reception signal into digital reception data. The line correlator 33 arithmetically averages the latest one scan line data 32 sent from the A / D converter 28 and the scan line data 31 one line before read from the line memory 30 to obtain one line. While the digital video signal is generated and sequentially output while performing the processing for generating the new scanning line data, the data in the line memory 30 is updated. This is line correlation. By the line correlation processing, the spatial smoothing of the speckle pattern is realized by the electronic circuit, the roughness on the image is suppressed, and the degree of high quality is improved.
This line correlation processing can be used alone without being used together with the frame correlation processing described below, and the smoothing effect of the speckle pattern can be obtained. However, in this ultrasonic diagnostic apparatus, the image quality is further enhanced by using the frame correlation processing together.

The frame correlation processing will be described below. First, a case where the main memory 36 has a storage area for two frames will be described. In the frame correlator 34, the received data is arithmetically averaged with the received data of the previous frame stored in the storage area for one frame of the main memory 36.
This is called frame correlation. The frame-correlation data obtained by the averaging is stored in the storage area of the remaining one frame of the main memory 36.

The frame correlation processing can be performed using the main memory 36 having a storage capacity for one frame. In this case, the frame correlation data is stored in the main memory 36, and the new frame correlation data is
It is obtained by averaging the received data and the old frame correlation data in the main memory 36 with appropriate weighting. The contents of the main memory 36 are updated with this new frame correlation data. In this method, the frame correlation data is not only the reception data of two consecutive frames but also the old reception data before that is cumulatively added. However, the older the received data component is, the more it is reduced as it is older, so that it is possible to obtain an effect similar to the case where the memory for two frames is used.

After the above frame correlation processing, this digital video signal is converted into an analog video signal in a digital-analog (D / A) converter 38, and the display monitor 26
Is displayed in.

The above frame correlation processing may be carried out independently and displayed on the display monitor 26. In this case, since the smoothing of the speckle pattern with time is realized by the electronic circuit, flicker on the image is suppressed and a high-quality image can be obtained.

FIG. 2 is an explanatory diagram showing the frequency switching operation. The sector scan plane 40 is an odd frame and the sector scan plane 42 is an even frame. Sector type scanning plane 4
0 is configured by alternately arranging odd-numbered scanning lines 44 and even-numbered scanning lines 46. Similarly, the sector-type scan plane 42 has an odd scan line 48 and an even scan line 50.
And are arranged alternately. These scanning surfaces 40 and 42 are sequentially scanned from the scanning line on the left side in the drawing. The frequency switching signal generator 4 shown in FIG. 1 obtains the frame order and the scanning line order from the frame / line counter 2 as described above. The transmission frequency setting signal 8 and the pass band setting signal 18 are
When the order of frames is an odd number, specifies the frequency f ₁ for the odd-numbered scanning lines 44, and specifies the frequency f ₂ for the even-numbered scanning lines 46, and when the frame order is an even number, odd The frequency f ₂ is designated for the scanning line 48 and the frequency f ₁ is designated for the scanning line 50 at even number. That is, ultrasonic waves having different transmission frequencies are transmitted / received between adjacent scanning lines, and ultrasonic waves having different transmission frequencies are transmitted / received between consecutive frames in the same scanning line direction.

[0028] The transmitter 6 any frequency f _1, f ₂ is designated by the transmission frequency setting signal 8, the pulse time width tau ₂ is the pulse duration tau _1, f ₂ for f ₁ Generates a rectangular electrical pulse. The probe 10 generates an ultrasonic pulse having a band having a center frequency of f ₁ and f ₂ by the rectangular electric pulse having the pulse time widths τ ₁ and τ ₂ , respectively. The amplitude levels of both rectangular pulses are determined so that the intensities of the transmitted ultrasonic waves at both central frequencies become equal.

Here, for example, f ₁ = 3.5 MHz, f ₂
= 5.0 MHz, and they are not in a multiple relationship. That is, the least common multiple of these f ₁ and f ₂ is 35 MHz, and the ultrasonic wave of the frequency f _{1 and} the ultrasonic wave of the frequency f ₂ are in phase with each other only every 7 cycles and 10 cycles. On the other hand, there are f ₁ = 2.5 MHz and f ₂ = 5.0 MHz as a case where f ₁ and f ₂ are in a multiple relationship in a combination of frequencies close to the above combination of frequencies. In this case, the ultrasonic wave of the frequency f _{1 has} the same phase as the ultrasonic wave of the frequency f ₂ in each cycle. That is, f ₁ = 3.5 MHz,
In the ultrasonic diagnostic apparatus adopting f ₂ = 5.0 MHz, the frequency at which the position of the speckle pattern matches between adjacent scanning lines or continuous frames is estimated to be about 1/7 as compared with the case of the above multiple relation, Therefore, the image quality can be expected to improve.

FIG. 3 is a conceptual diagram for explaining the line correlation processing. In FIG. 1, the line correlator 33 is a line for the one-line delay data 31, which is the previous scan line data stored in the line memory 30, and the latest scan line data 32 obtained without passing through the memory. Perform correlation processing. In FIG. 3, the line correlator 33 outputs the k-th scanning line data e _k (n), which is the one-line delay data 31, and the (k + 1) -th scanning line data e, which is the latest scanning line data 32.
_{It is shown that k + 1} (n) is added and averaged to output the line correlation data d _{k + 1} (n) corresponding to the (k + 1) th scanning line. That is, d _{k + 1} (n) = _{[e k (n) + e k} + 1 (n) ] / 2 (where _{d 1 (n) = e 1} (n)) ......... (1). The difference in the acoustic impedance distribution between these two adjacent scan lines is small and can be ignored, and the scan line data e _k (n) and e _{k + 1} (n) are scanned with f _{1 on} the one hand and f ₂ on the other hand. Since it is the data, the speckle pattern is smoothed by this arithmetic mean and the image quality is improved.

In FIG. 4, the main memory 36 described above has two frames.
A frame correlation process having a memory capacity for memory is explained.
It is a conceptual diagram for. From the line correlator 33 to the nth frame
Digital data 60 (represented by the sector type scanning plane)
It ) Is output, the main menu
In the memory area 62 for one frame of the memory 36, the (n-
1) Digital data 64 of frame, remaining 1 frame
Minute storage area 66, the (n−2) th frame and the (n−th) frame
-1) Frame correlation data 68 with the frame is stored
ing. The kth of each of the data 60, 64, 68
Scan line data is d _k(n), d_k(n-1), g_kTable with (n-1)
is doing. Each scanning line data g of the frame correlation data 68
_kThe area where (n-1) is stored is for each scan line data of the data 60.
Data d_kEach scan line of data 64 updated by (n)
Data d_kThe area where (n-1) is stored is d_k(n-1) and d
_k(n) is the new frame correlation data that is averaged
G_kUpdated by (n). here,   g_k(n) = [d_k(n-1) + d_k(n)] / 2 (however g_k(1) = d_k(1)) ……… (2) Is.

The data d _k (n) and d _k (n-1) of the data 60 and the data 64 in the same scanning line direction are line-correlated data, and have different frequencies f ₁ and f ₂ , respectively.
It contains the components obtained by ultrasonic waves. Since the speckle patterns of these components are different, in the frame correlation data g _k (n) obtained by adding and averaging these components, the speckle pattern is smoothed and the image quality is improved similarly to the above line correlation. In the case of the frame correlation processing in which the main memory 36 has a storage capacity of one frame, although not shown, the frame correlation data of the (n-1) th frame in the main memory 36 and the nth correlation from the line correlator 33. The digital data of the frame is added and averaged to generate frame correlation data g _k (n) of the nth frame, and the content of the main memory 36 is updated. Here, _gk (n) = [ _gk (n-1) + _dk (n)] / 2 (where _gk (1) = _dk (1)) (3). The equation (2) in the line correlation or the frame correlation using the main memory 36 for the above two frames can be said to be the simple addition average, whereas the equation (3) is the cumulative addition or the sequential addition average. , Because the components of the old frame are gradually reduced, so regarding the speckle pattern smoothing,
It is possible to obtain an effect similar to that obtained by the equation (2).

In the ultrasonic diagnostic apparatus, even if the ultrasonic frequency for each scanning line in the same frame is the same and the frequency is alternately switched only between frames, and the frame correlation processing is performed on the received signal, The speckle pattern is temporally smoothed to improve the image quality.

The transducer array forming the probe 10 may be a linear transducer array or another structure. The scanning method may be any scanning means such as electronic scanning or mechanical scanning, and the scanning shape may be linear, sector, convex, arc or the like. The order of scanning within one scanning plane may be such that the scanning is performed from the right side or the right and left sides are alternately alternated toward the center.

[Embodiment] FIG. 5 is a block diagram of an ultrasonic diagnostic apparatus embodying the present invention. The components having the same functions as those of the ultrasonic diagnostic apparatus of the above basic configuration are shown in FIG.
The reference numeral will be added with 100 and will be described below, focusing on the points different from the basic configuration example.

The frequency switching signal generator 104 obtains the order of the next scanning line in the frame and the order of the frame to which the next scanning line belongs from the frame / line counter 102, and the variable band pass filter 116 is supplied to the variable band pass filter 116 in accordance with these even and odd. A pass band setting signal 118 is sent to the device.

The variable bandpass filter 116 has a structure such as having two filters which can be switched by switching in the inside thereof.
The pass band setting signal 118 from 4 sets one of the two pass bands having different center frequencies f ₁ and f ₂ .

Unlike the transmitter 6 of the first embodiment, the transmitter 106 transmits a constant ultrasonic wave from the broadband probe 110 regardless of the order of frames and lines. The broadband probe 110 can transmit ultrasonic waves in a wider band than the probe 10 of the basic configuration example.

FIG. 6 is a conceptual diagram for explaining the filtering of a wideband ultrasonic wave received signal by the variable bandpass filter 116. 6 (a) shows the variable band-pass filter 116, the center frequency f ₁ of the passband 140, the passband 142 of the center frequency f _2, and the respective frequency characteristics of the received signal 144 caused by the broadband ultrasound. FIG. 6B shows frequency characteristics 146 and 148 of the received signal output from the variable bandpass filter 116. The output frequency characteristics 146 and 148 are respectively assigned to the variable bandpass filter 11
It corresponds to 6 pass bands 140 and 142, and only one of them can be obtained at one time point. Both output frequency characteristics 146, 14
If the intensities of 8 are different between the adjacent scanning lines and the inter-frame scanning lines displayed by using the received signals of different bands at the time of displaying the image, the image quality deteriorates. Therefore, in this ultrasonic diagnostic apparatus, the output frequency characteristics 146 and 148 are aligned, and the transmittance of the pass bands 140 and 142 and the received signal 144 are obtained.
The relationship with the spectrum is defined so as to realize the uniformity of both frequency characteristics. In the figure, pass band 140,
The characteristics of 142 are illustrated as being equal except for the center frequency. At this time, the received signal 144 is adjusted so that the received signal strengths become equal at the center frequencies f ₁ and f ₂ of both pass bands 140 and 142. When the spectrum shape of the received signal 144 is asymmetrical with respect to the peak position f _S for the reason that the oscillator is driven by the rectangular pulse to obtain the transmitted ultrasonic wave, the time width of the rectangular pulse shown on the left is adjusted. By adjusting the peak position f _S of the signal 144 between f ₁ and f ₂ , a balance of received signal strength at both center frequencies can be achieved.

As described above, by changing the frequency for each frame with respect to the same scanning line or alternately between the scanning lines within the same frame, a part of the band of the received signal is cut out and processed. As in the basic configuration example, the speckle pattern is smoothed to improve the image quality.

As another method of achieving the balance between the scanning lines displayed by using the reception signals of different bands, the amplification factor switching signal is obtained from the frequency switching signal generator 104 to set the amplification factor of the preamplifier 112. Switching is performed by adjusting the intensity difference between the two passbands, or weighted addition / averaging processing is performed by the frame correlator 134, and the weighting coefficient is switched by the switching signal from the frequency switching signal generator 104. There is a method by processing.

In the ultrasonic diagnostic apparatus, the pass band of the variable band pass filter 116 is the same for each scanning line in the same frame, the frequency is alternately switched only between frames, and the received signal is received. On the other hand, even if the frame correlation process is performed, the speckle pattern is temporally smoothed and the image quality is improved.

[0043]

According to the ultrasonic diagnostic apparatus of the present invention, by transmitting or receiving ultrasonic waves of different frequencies, the speckle patterns are made different for scanning lines that are temporally or spatially close to each other. The effect is that the speckle pattern on the ultrasonic image can be smoothed.

[Brief description of drawings]

FIG. 1 is a block diagram of an ultrasonic diagnostic apparatus having a basic configuration example.

FIG. 2 is an explanatory diagram showing a frequency switching operation.

FIG. 3 is a conceptual diagram for explaining line correlation processing.

FIG. 4 is a conceptual diagram for explaining frame correlation processing.

FIG. 5 is a block diagram of an ultrasonic diagnostic apparatus according to an embodiment of the present invention.

FIG. 6 is a conceptual diagram illustrating filtering of a received signal by a variable bandpass filter.

FIG. 7 is a conceptual diagram showing an ultrasonic image forming method in a conventional ultrasonic diagnostic apparatus.

[Explanation of symbols]

40, 42 sector scan planes, 44, 48 odd scan lines, 46, 50 even scan lines, 60 nth frame digital data, 62, 66 storage area, 64
(N-1) th frame digital data, 68 frame correlation data, 102 frame / line counter, 1
04 frequency switching signal generator, 106 transmitter, 110
Wideband probe, 114 focus adder, 116 variable bandpass filter, 118 passband setting signal, 1
24 digital scan converter, 126 display monitor, 128 analog-digital converter, 130 line memory, 131 1 line delay data, 132 latest scan line data, 133 line correlator, 134 frame correlator, 136 main memory, 138 digital-analog Converter, 150 odd frame sector scanplanes, 152 even frame sector scanplanes, 154
Scan line.

Claims (6)

[Claims] 1. An ultrasonic diagnostic apparatus for obtaining an ultrasonic image by transmitting and receiving ultrasonic waves in each direction of a plurality of scanning lines forming a scanning surface, wherein a wide band frequency is applied to each scanning line direction when forming each scanning surface. The ultrasonic diagnostic apparatus is characterized in that the received signal is filtered using a reception filter having a different pass band between adjacent scanning lines. 2. The ultrasonic diagnostic apparatus according to claim 1, wherein reception is performed in the same scanning line direction by using reception filters having different pass bands even between consecutive frames of ultrasonic images displayed on the same screen. An ultrasonic diagnostic apparatus characterized by performing filtering on a signal. 3. An ultrasonic diagnostic apparatus for transmitting and receiving ultrasonic waves in each direction of a plurality of scanning lines forming a scanning plane to obtain an ultrasonic image, wherein ultrasonic waves having a wide band frequency are transmitted when forming each scanning plane. An ultrasonic diagnostic apparatus is characterized in that a received signal is filtered using a receiving filter having a different pass band between successive frames of ultrasonic images displayed on the same screen. 4. The ultrasonic diagnostic apparatus according to claim 1 or 2, wherein the frequencies of the pass bands of the reception filter on two adjacent scanning lines are set so as not to have a multiple relationship. And ultrasonic diagnostic equipment. 5. The ultrasonic diagnostic apparatus according to claim 2, wherein the frequencies of the passbands of the reception filter in two adjacent scanning lines are not in a multiple relationship and the ultrasonic image of the ultrasonic image is in the same scanning line direction. An ultrasonic diagnostic apparatus characterized in that frequencies of a pass band of the reception filter between two consecutive frames are also set so as not to have a multiple relationship. 6. The ultrasonic diagnostic apparatus according to claim 3, wherein the frequencies of the pass band of the reception filter between two consecutive frames of the ultrasonic image are set so as not to have a multiple relationship. Ultrasonic diagnostic equipment.