WO2015129351A1 - Ultrasound imaging apparatus - Google Patents

Abstract

　Provided is an ultrasound imaging apparatus whereby artifacts in a generated image can be reduced even when the imaging subject moves during spatially encoded transmission/reception. In the present invention, spatially encoded ultrasonic waves are transmitted three or more times toward a predetermined position from at least two transmission regions of an ultrasonic probe simultaneously. A reception unit in the present invention includes a decoding unit and a synthesizing unit, and the decoding unit performs decoding corresponding to the spatial encoding and generates a decoded reception signal (H_A1) using two or more of three or more reception signals (R1, R2, R3) outputted by the reception regions in corresponding fashion to the three or more transmissions of ultrasonic waves. This processing is performed for each of two or more different combinations of the two or more reception signals used, and a plurality of decoded reception signals (H_A1, H_A2) are thereby generated. The synthesizing unit adds the plurality of decoded reception signals (H_A1, H_A2) and obtains a decoded reception signal (H_A') in which an unwanted signal (19b) is suppressed.

Description

Ultrasonic imaging device

The present invention relates to a technique for improving an S / N ratio using encoding in an ultrasonic imaging apparatus.

The imaging method using ultrasonic waves is configured by transmitting ultrasonic waves to an object, receiving echoes reflected by the object as electrical signals, and displaying the received signals on a monitor as image data. Ultrasound is generated by inputting an electrical signal to a transducer (electroacoustic transducer or vibrator) provided in the apparatus. The ultrasonic wave emitted from the transducer is partially reflected at the boundary where the acoustic impedance is different while traveling through the object to make an echo. The echo is received by the electroacoustic transducer, and a reception signal is generated. Thereby, the boundary surface of the object can be displayed as a tomographic image of the object. Such an imaging technique is widely used as a non-destructive inspection of a structure or a diagnostic apparatus for imaging a tomographic image of a living body with minimal invasiveness.

Normally, transducers are arranged in a channel array, and ultrasonic waves are transmitted as ultrasonic beams by array beam forming. The ultrasonic imaging apparatus scans an object with an ultrasonic transmission beam and receives an echo generated by each transmission. Then, reception beam forming is performed on the reception signal of each channel to generate small area data in a region on the beam axis. Then, the tomographic image of the entire object is created by combining (summing) the small area data.

The frame rate can be improved by reducing the number of transmissions for creating one tomographic image. However, as a result, the amount of signal obtained decreases and the SN ratio decreases. Spatial encoding transmission / reception is known as an imaging method that enables high frame rate imaging while improving the SN ratio (Patent Document 1). In spatial encoding transmission / reception, the S / N ratio is improved by transmitting to a target object simultaneously from a plurality of directions instead of unidirectional transmission and unidirectional reception. Specifically, in the spatial encoding transmission / reception method, ultrasonic waves transmitted from any direction are transmitted by simultaneously transmitting encoded ultrasonic waves from multiple directions to an object, receiving echoes, and then decoding the received signal. The received signal is distinguished and separated. For example, when the directions (or positions) of transmitting the ultrasonic beam to the object are the A direction and the B direction, transmission / reception is performed twice. In the first transmission, 1 and 1 are encoded for the transmission waveforms of ultrasonic beams in the A direction and the B direction, respectively, and in the second transmission, 1 and −1 are respectively encoded. The received signals obtained by receiving the echoes generated by the two transmissions are each stored in the state of channel data before being subjected to receive beamforming. By performing decoding processing using the first received signal and the second received signal, the received signal transmitted in the A direction and the received signal transmitted in the B direction are separated. Specifically, by summing the first received signal and the second received signal at the same time, the received signal due to transmission in the B direction is canceled, and only the received signal due to transmission in the A direction remains. On the other hand, the subtraction process cancels the reception signal due to transmission in the A direction and leaves only the reception signal due to transmission in the B direction.

JP-A-11-155867

Spatial encoding transmission / reception requires multiple transmissions / receptions. The performance of the decoding process is exhibited on the assumption that each received signal is an echo signal from the same part. When a movement such as the imaging target approaches or moves away from the transducer during multiple transmissions / receptions, the propagation distance of the echo varies. As a result, since the time axes of the plurality of received signals are shifted from each other, when the summation process or the subtraction process is performed in the decoding process, a signal to be canceled remains, and an artifact (false image) on the image is generated. This causes image quality degradation.

An object of the present invention is to provide an ultrasonic imaging apparatus capable of reducing artifacts in a generated image even when a motion occurs in an imaging target when performing spatial encoding transmission / reception.

In order to achieve the above object, according to the present invention, at least two transmission areas of the ultrasonic probe are simultaneously transmitted with the spatially encoded ultrasonic wave three times or more toward a predetermined position. The receiving unit includes a decoding unit and a synthesizing unit, and the decoding unit performs spatial encoding using two or more of three or more received signals output by the receiving region in response to transmission of three or more ultrasonic waves. Is decoded to generate a received signal after decoding. This process is performed for two or more different combinations of two or more received signals to be used, thereby generating a plurality of decoded received signals. The synthesizer performs addition processing on the plurality of decoded received signals.

According to the present invention, it is possible to reduce artifacts in a generated image even when a motion occurs in an imaging target when performing spatial encoding transmission / reception.

1 is a block diagram showing a configuration of an ultrasonic imaging apparatus according to a first embodiment of the present invention. Explanatory drawing which shows the principle of unnecessary signal suppression of this invention. 1 is a block diagram showing a configuration of an ultrasonic imaging apparatus according to a first embodiment. The block diagram of the receiving part of 1st embodiment. (A) Explanatory drawing which shows the position of the transmission area (aperture) of the ultrasonic probe of 1st embodiment, and the imaging target 120, (b) Explanatory drawing which shows the position of the small area data corresponding to a transmission area (opening) (C) Explanatory drawing which shows the image of the imaging target 120 obtained by arranging small area data. Explanatory drawing which shows repeating the scan which transmits in order from the group of the transmission opening of 1st embodiment. (A) Explanatory drawing which shows the reference waveform used for transmission, (b) Explanatory drawing which shows the inversion waveform used for transmission. (A) An explanatory diagram showing codes of transmission waveforms transmitted from two transmission apertures by spatial encoding, (b) an explanatory diagram showing a reception signal waveform of spatial encoding and the principle of decoding processing, and (c) a decoded signal Explanatory drawing which shows the state in which the unnecessary component has arisen. The block diagram which shows the whole structure of the specific example of the ultrasonic imaging apparatus of 1st embodiment. Explanatory drawing which shows the example of arrangement | positioning of the reception area | region (channel) and transmission area | region (opening) of the ultrasonic probe of 1st embodiment. The block diagram which shows the structure of the receiving part 105 of the ultrasonic imaging device of FIG. The block diagram which shows the structure of the 1st memory | storage part (channel memory) 40 and the decoding part 41 for every channel of the ultrasonic imaging device of FIG. The block diagram which shows the structure of the 2nd memory | storage part 24 and the synthetic | combination part 25 of the ultrasonic imaging device of FIG. 10 is a flowchart showing transmission / reception operations of the ultrasonic imaging apparatus of FIG. The block diagram which shows the structure of the 2nd memory | storage part 24 and the synthetic | combination part 25 of the ultrasonic imaging device of 2nd embodiment. Explanatory drawing which shows the principle of unnecessary signal suppression of 2nd embodiment. (A) Explanatory drawing which shows the waveform which synthesize | combined the received signal without weighting, (b) Explanatory drawing which shows the waveform which weighted and synthesized the received signal in 2nd embodiment. The block diagram which shows the structure of the 1st memory | storage part (channel memory) 40 and the decoding part 41 for every channel of the ultrasonic imaging device of 3rd embodiment. Explanatory drawing which shows the time code | symbol (Golay code | symbol) X1, X2, and the principle of a decoding process. (A) Explanatory drawing which shows the example of the waveform of Golay code | cord X1, X2, and the waveform of a received signal, (b) Explanatory drawing which shows the decoding process and waveform of Golay code | cord | chord. The block diagram which shows the structure of the 1st memory | storage part (channel memory) 40, the decoding part 41, and the 2nd decoding part 141 of the ultrasonic imaging device of 4th embodiment. Explanatory drawing which shows the code | symbol of the transmission which combined the time coding of 4th embodiment, and space coding, and the decoding process of a received signal. The flowchart which shows the operation | movement of transmission / reception of the ultrasonic imaging apparatus of 4th embodiment. FIG. 16 is a block diagram showing a first storage unit (channel memory) 40, decoding units 41 and 141, and weighting units 61 to 64 of the ultrasonic imaging apparatus according to the fifth embodiment. Explanatory drawing which shows the structure of 2nd decoding part 141 grade | etc., Of the ultrasonic diagnosing device which transmits simultaneously from four transmission area | regions (opening) of 6th embodiment.

An ultrasonic imaging apparatus according to an embodiment of the present invention will be described with reference to the drawings.

<< First Embodiment >>
As shown in FIG. 1, the ultrasonic imaging apparatus 100 of the present invention includes an ultrasonic probe 108, a transmission unit 102, and a reception unit 105. The ultrasonic probe 108 has at least two transmission areas 110A and 110B and at least one reception area 109, each composed of a transducer. The transmitting unit 102 transmits the spatially encoded ultrasonic waves from the predetermined two transmission areas 110A and 110B of the ultrasonic probe 108 at least three times toward the predetermined position (120). The reception area 109 receives and outputs an ultrasonic echo from the position (120). The receiving unit 105 processes this received signal.

The receiving unit 105 includes a decoding unit 41 and a combining unit 25. As shown in FIG. 2, the decoding unit 41 receives the reception signals (R1, R2, R3,..., Where the reception area 109 sequentially outputs in response to three or more times of transmission of ultrasonic waves. The received signal (H1) after decoding is obtained by performing decoding corresponding to the spatial encoding at the time of transmission using two or more of the signals). By performing this processing for each of two or more different combinations of two or more received signals to be used (for example, a set of R1 and R2, a set of R2 and R3), a plurality of received signals after decoding (H _A 1, H _A2 , ..., where subscript A indicates a received signal corresponding to transmission from transmission area 110A). Synthesizing unit 25, a plurality of decoded received signal _{(H A 1, H A 2} , ···) and the addition processing to obtain the summed decoded received signal (H _A '). The decoding unit generates a decoded reception signal (H _B 1, H _B 2,...) Corresponding to transmission from the transmission area 110B, and obtains an added decoded reception signal (H _B ′). Of course it is also possible.

As described above, by adding a plurality of decoded reception signals (H _A 1, H _A 2,...), Reception after decoding is performed when movement occurs in the imaging target 120 when performing spatial encoding transmission / reception. Unnecessary signals 16b and 17b (FIG. 2) generated in the signals (H _A 1, H _A 2,...) Can be canceled and reduced. The reason is that when the movement of the imaging target 120 between a plurality of transmissions / receptions is substantially constant speed, it is obtained from a set of received signals (a set of R1 and R2, a set of R2 and R3, etc.) obtained by sequentially combining received signals This is because the received decoded signals (H _A 1, H _A 2,...) Sequentially invert the phases of the unnecessary signals 16b and 17b. On the other hand, the original received signals 16a and 17a have the same phase between the decoded received signals (H _A 1, H _A 2,...), And are strengthened by the adding process of the synthesizer 25. Therefore, it is possible to obtain a decoded received signal (H _A ′) 19a after synthesis in which the unnecessary component 19b is suppressed and the original received signal 19a is strengthened, and by using this to generate an image, Artifacts can be reduced.

A publicly known method can be used as the spatial encoding method by the transmission unit 102 and the decoding method by the decoding unit 41. An example of known spatial encoding and decoding processing will be described in detail later.

Decoding processing by the decoding unit 41 separates echo reception signals generated by ultrasonic waves for each transmission region from ultrasonic reception signals transmitted simultaneously from two or more transmission regions 110A and 110B, for each transmission region. Is a process for obtaining a received signal (decoded received signal) corresponding to. The synthesizer 25 adds and synthesizes a plurality of decoded received signals (H _A 1, H _A 2,...) Obtained for the same transmission region (for example, 110A), thereby combining these received signals. The unnecessary signals 16b and 17b are suppressed.

As shown in FIG. 3, the receiving unit 105 is a first storage unit that sequentially stores at least one of received signals (R1, R2, R3,...) Sequentially received corresponding to three or more transmissions. 40 and a second storage unit 24 that stores at least one of the decoded reception signals (H _A 1, H _A 2,...) Generated by the decoding unit 41 may be provided. The decoding unit 41 can sequentially perform the decoding process by performing the decoding process using the received signal stored in the first storage unit 40 and the received signal received next. The synthesizer 25 can reduce unnecessary signals by adding one or more decoded received signals stored in the second storage unit 24 and the decoded received signal generated next.

For example, the first storage unit 40 has two storage areas for sequentially storing the two most recent reception signals, and the decoding unit 41 performs a decoding process using the reception signals stored in the two storage areas. By performing the above, it is possible to have a configuration for generating a reception signal after decoding in time series. The second storage unit 24 is configured to sequentially store the latest two or more decoded reception signals, and the combining unit 25 adds the two or more decoded reception signals stored in the second storage unit 24. By doing so, the added decoded received signals can be sequentially generated in time series.

Further, as shown in FIG. 4, the ultrasonic probe 108 includes a plurality of (for example, P) receiving areas 109 ₁ ,... 109 _P (where the subscript indicates the number of the receiving area). You may comprise. Receiving section 105, the receiving area ₁₀₉ 1, the · · · 109 _P, the received signal _{(e.g., R 1 1, R 2 1} ... R P 1, where the subscript indicates the number of the receiving area) Receive. In addition, the reception unit 105 includes a phasing addition unit 22. The decoding unit 41 decodes the reception signal for each of the reception areas 109 ₁ ,... 109 _P , and receives the decoded reception signals (H _1A 1, H _2A 1... H corresponding to the transmission area (for example, 110A). _PA 1, where the subscript number and P indicate the number of the reception area, and the subscript A indicates a received signal after decoding corresponding to transmission from the transmission area 110A). Phasing addition unit 22, the receiving area ₁₀₉ 1,..., Decoded received signal for each of 109 _P a _{(H 1A 1, H 2A 1} ... H PA 1) is added after the phasing. As a result, a decoded received signal (H _sumA 1) after phasing addition can be generated. This process is repeated a plurality of times in time series, and a plurality of decoded received signals (H _sumA 1, H _sumA 2...) After phasing addition are generated and added by the synthesizer 25. _A received signal (H _A ′) after decoding can be obtained.

As shown in FIG. 4, by which the synthesis section 25 is disposed downstream than phasing addition unit 22, the combining unit 25 to the receiving area ₁₀₉ 1, ..., it is not necessary to place every 109 _P, phasing addition It suffices to arrange one combining unit 25 after the unit 22. Therefore, compared with the case where the synthesizing unit 25 is arranged for each decoding unit 41, the apparatus configuration can be simplified and an increase in the calculation amount of the synthesizing unit 25 can be suppressed.

As shown in FIG. 5 (a), the ultrasound probe 108 includes a plurality of transmission areas (111A and B sets, 112A and B sets, 113A and 113A, in addition to the transmission areas 110A and 110B. B set) can be provided. At this time, as shown in FIG. 6, the order of transmission from each set of transmission areas is such that the operation (scanning operation) of sequentially transmitting from each set of transmission areas is repeated three times or more. It is preferable. Thereby, it is possible to obtain reception signals for all sets of transmission areas for each scanning operation. Therefore, after the second scan, the received signal obtained can be combined with the received signal obtained in the previous scan and decoded. Therefore, when there are two reception signals used for the decoding process, a decoded reception signal can be generated for the entire transmission region for each scan after the second scan.

As shown in FIG. 5B, each decoded reception signal for each transmission area indicates data of a small area (small area data) of the imaging target 120 irradiated with the ultrasonic wave transmitted from the transmission area. . That is, the decoded reception signal in the transmission area 110A is data in the small area 211A, and the decoded reception signal in the transmission area 110B is data in the small area 211B. Therefore, by generating a decoded reception signal for each entire transmission area for each scan, an entire image (FIG. 5C) of the imaging target 120 in which these small area data are arranged is generated for each scan. can do. This makes it possible to output images sequentially in substantially real time.

Further, in the present invention, it may be configured to further include a receiving unit that receives the setting of the number of received signals after decoding to be added by the combining unit 25 from the operator. In this case, the transmission unit 102 can transmit a number N of ultrasonic waves that is one or more greater than the accepted number, and the synthesis unit can add the received number of received reception signals after decoding.

It should be noted that the transmission areas 110A and 110B of the ultrasonic probe 108 may be the same size as the reception areas 109 ₁ ,..., 109 _P or may be different sizes. In addition, the transmission area and the reception area are set at the time of transmission and reception, respectively, and are not set at the same time. Therefore, the transmission area and the reception area may be entirely or partially overlapped.

<Principle of spatial coding>
Here, the principle of spatial encoding will be described. Spatial encoding is a known technique for encoding spatial dimensions. In this embodiment, Hadamard space coding is used as an example, and a case where ultrasonic waveforms are transmitted simultaneously from two transmission regions will be described.

First, the concept of Hadamard space coding will be explained. The waveform 71 in FIG. 7A is set as a reference waveform. A waveform 72 in FIG. 7B is an inverted waveform of the reference waveform. As shown in FIG. 8A, as the first transmission Tx1, the ultrasonic waves of the reference waveform 71 are simultaneously transmitted from the two transmission areas 110A and 110B toward a predetermined position (imaging target 120). Next, as the second transmission Tx2, the reference waveform 71 is obtained from one of the two transmission areas (here, the left transmission area 110A in FIG. 8A) and the other (the right transmission area 110B in FIG. 8A). ) To transmit the inverted waveform 72 simultaneously. When the reference waveform 71 is 1, the inverted waveform 72 is -1, and the position of the transmission area is represented as a row vector column, the first transmission is a row vector [1 1] and the second transmission is [1 -1]. Each is represented. Assuming that the transmission order is a matrix row, the first transmission and the second transmission are represented by the matrix of Expression (1).

The matrix of equation (1) is called a second-order Hadamard matrix. A transmission event obtained by encoding a transmission waveform with this matrix is called Hadamard space coding.

The echoes of the ultrasonic waves transmitted from the two transmission areas 110A and 110B by Hadamard space coding are received by the reception area 109, whereby reception signals R1 and R2 are obtained, respectively. The calculation process of separating the reception signal H _A 1 by the ultrasonic wave transmitted from the transmission area 110A and the reception signal H _B 1 by the ultrasonic wave transmitted from the transmission area 110B from the reception signals R1 and R2 is called Hadamard decoding processing.

As shown in FIG. 8B, the reception signals R1 and R2 include an ultrasonic reception signal 13a transmitted from the transmission area 110A and an ultrasonic reception signal 13b transmitted from the transmission area 110B, respectively. The decoding unit 41 includes an adder 14 and a subtracter 15. When the reception signal R1 by the first transmission and the reception signal R2 by the second transmission are added at the same time by the adder 14 in the decoding unit 41, the addition of the row vector
[1 1] + [1 -1] = [2 0]
Thus, the right column can be led to 0. That is, as shown in FIG. 8B, the reception signal 13b by the transmission in the right column (right transmission area 110B) can be canceled, and the reception signal 13a of the echo generated by the transmission in the left transmission area can be superimposed. The received signal 16a (decoded received signal H _A 1) can be extracted.

On the other hand, when the received signal R1 and the received signal R2 are subtracted by the subtracter 15 in the decoding unit 41,
[1 1]-[1 -1] = [0 2]
Thus, the received signal 13a by the transmission in the left column (left transmission area 110A) can be canceled, and the received signal 18b (decoded received signal H _B 1) on which the reception signal 13b by the transmission in the right transmission area 110B is superimposed is obtained. Can be extracted.

By this decoding process, received signals equivalent to the case where each transmission is performed independently from the received signals R1 and R2 received in a state where echoes due to simultaneous transmission from the two transmission areas 110A and 110B are mixed (after decoding) The received signals H _A 1 and H _B 1) can be separated.

However, in the above decoding process, if the imaging target 120 moves between two transmissions / receptions or the ultrasonic probe 108 moves with respect to the imaging target 120, the propagation distance of the echo in each transmission varies. As a result, the received signals are shifted from each other in time. For example, FIG. 8C shows a state in which the imaging target 120 approaches the ultrasonic probe 108 during two transmissions and the signal appearance time of the reception signal R2 is shifted with respect to the reception signal R1. Yes. In this case, the Hadamard decoding received signals H _A 1, H _B 1, remaining unnecessary signals 16b, 18a occurs canceled. Therefore, in the present invention, when the movement of the imaging target 120 is substantially constant, the unnecessary signal 16b remaining after cancellation of the decoded received signal H _A 1 obtained by adding the received signals R1 and R2, and the received signal R2 By utilizing the fact that the unnecessary signal 17b (FIG. 2) remaining after cancellation in the decoded signal H _A 2 obtained by adding R3 has an inverted waveform, the synthesizer 25 receives the decoded received signal H _A 1. And the decoded signal H _A 2 are added to suppress unnecessary signals 16b and 17b. Similarly, with respect to the decoded received signal H _B 1 and the decoded signal H _B 2 obtained for the transmission signal from the transmission area 110B, the synthesizer 25 similarly adds unnecessary signals to be suppressed.

In the above example, an example in which there are two transmission areas has been described. However, since the number of transmission areas is determined by the number of Hadamard code columns, it is possible to have two or more transmission areas. In addition, the plurality of transmission areas may overlap each other.

Hereinafter, a specific example of the ultrasonic imaging apparatus according to the first embodiment will be described in detail.

<Overall configuration of device>
The overall configuration of the ultrasonic imaging apparatus 100 of the present embodiment will be described. FIG. 9 is a block diagram showing a schematic configuration of a specific example of the ultrasonic imaging apparatus 100 of the present embodiment. The ultrasonic imaging apparatus 100 includes a control unit 106, a user interface (UI) 121, a transmission / reception switching unit 101, and an image processing unit 107, in addition to the ultrasonic probe 108, the transmission unit 102, and the reception unit 105 described above. And a display unit 122. The UI 121 is an interface that accepts the number of decoded received signals added by the synthesis unit 25 described above, instructions from the user, input of various parameters, and the like. The control unit 106 controls the overall operation.

The ultrasonic probe 108 includes a plurality of transducers arranged one-dimensionally or two-dimensionally in a predetermined arrangement. The transducer is an electroacoustic conversion element (vibrator) having a function of converting an electric signal into a sound wave and a sound wave into an electric signal. The ultrasonic probe 108 is tailored to have an outer shape suitable for use by bringing the surface on which the transducer is disposed (ultrasonic transmission / reception surface) into contact with the imaging target 120.

As shown in FIG. 10, the plurality of arranged transducers are virtually or physically divided into a plurality of (P) receiving areas (hereinafter referred to as channels) 109 ₁ to 109 _P. Each channel 109 ₁ to 109 _P is constituted by one or a plurality of transducers. Transmission region 110A or the like to be set at the time of transmission may be the same size as the channel 109 _1, etc., it may be different. In the following description, an example in which an area equivalent to a plurality of adjacent (four in FIG. 10) channels is used as one transmission area 110A will be described. In the following description, the transmission area is referred to as a transmission aperture. The transmission opening 110A and the transmission opening 110B may be formed at positions separated from each other, or may be formed so as to partially overlap. In the following description, when the plurality of channels 109 ₁ to 109 _P are not distinguished, they are also simply referred to as channels 109.

In addition, as shown in FIG. 11, the receiving unit 105 uses the channel signal processing unit 20 including the first storage unit 40 (hereinafter referred to as channel memory) and the decoding unit 41 for each of the channels 109 ₁ to 109 _P. It is the arranged configuration. The receiving unit 105 includes the phasing / adding unit 22, the second storage unit 24, and the combining unit 25 described above.

The transmission unit 102 determines the type of waveform to be transmitted, the delay time for each transmission aperture (for example, 110A, 110B), amplitude modulation, weighting, and the like in accordance with an instruction from the control unit 106, and generates a transmission signal corresponding thereto. In the present invention, the operation in which the transmitting unit 102 simultaneously transmits the spatially encoded ultrasonic waves from two predetermined transmission openings of the ultrasonic probe is repeated three or more times. The position where the transmission of ultrasonic waves is directed from each transmission aperture is the same among three or more transmissions. The transmission signal passes through the transmission / reception switching unit 101 and is transferred to the transducers forming the transmission openings 110A and 110B. The transducers in the transmission apertures 110A and 110B receive transmission signals and generate ultrasonic waves (ultrasonic pulses and ultrasonic beams).

The control unit 106 causes the transmission unit 102 to perform the first transmission Tx1 from the transmission openings 110A and 110B, and causes echoes to be received by the reception region (channel) 109 of the ultrasonic probe 108. As the channels used for reception, all the channels 109 _{1 to} 109 _P of the ultrasonic probe 108 may be used, or only channels within a predetermined reception opening may be used. The control unit 106 receives the received signals R ₁ 1, R ₂ 1 ... R _P 1 of each channel 109 ₁ ... 109 _P (subscript indicates the channel number, and 1 is obtained in the first transmission. The received signal) is passed to the receiving unit 105.

As shown in FIG. 12, the channel memory 40 includes two storage areas 40-1 and 40-2 for each set of transmission apertures. Control unit 106 transmits the opening 110A, the received signal R ₁ 1 to channel 109 ₁ was obtained by the first transmission Tx1 from 110B, transmission opening 110A, is stored in the storage area 40-1 for 110B. Similarly, the reception signals R ₂ 1... R _P 1 obtained by the other channels 109 ₂ ... 109 _P are also used for the transmission openings 110A and 110B of the channel memory 40 connected to the respective channels. It is stored in the storage area 40-1.

Next, the control unit 106 causes the transmission unit 102 to perform the second transmission Tx2 from the transmission apertures 110A and 110B, and the obtained reception signal R ₁ 2 of the channel 109 ₁ is stored in the storage area 40-2 in the channel memory 40. To store. Similarly, with respect to the received signals R ₂ 2... R _P 2 obtained by the other channels 109 ₂ ... 109 _P , the transmission openings 110A of the first storage unit 40 connected to the respective channels. The data is stored in the storage area 40-2 for 110B.

The control unit 106 reads the received signals R ₁ 1 and R ₁ 2 from the storage areas 40-1 and 40-2 for the transmission openings 110A and 110B and inputs them to the adder 14 and the subtracter 15 in the decoding unit 41, respectively. . Received signal H _1A 1 after decoding by transmission from the transmission aperture 110A by the addition process of the adder 14 (subscript indicates the channel number, and subscript A is the decoded received signal corresponding to the transmission aperture 110A. 1 indicates that it is the first received signal obtained after decoding). Received signal H _1B 1 after decoding by transmission from transmission aperture 110B by subtracting process by subtracter 15 (subscript number indicates channel number, subscript B is received signal after decoding corresponding to transmission aperture 110B) 1 indicates that it is the first received signal obtained after decoding). Similarly, the control unit 106 also inputs the received signal to the decoding unit 41 for the channel memories 40 connected to the other channels 109 ₂ ... 109 _P , respectively, and receives the decoded reception signal and transmission from the transmission aperture 110A. A decoded reception signal by transmission from the opening 110B is calculated.

Decoded received signals H _1A 1, H _2A 1, H _3A 1... Corresponding to the transmission aperture 110A output from each channel signal processing unit 20, and decoded signals H _1B 1, H corresponding to the transmission aperture 110B. _2B 1, H _3B 1... Are transferred to the phasing addition processing unit 22. The control unit 106 gives a delay time suitable for each of the decoded signals H _1A 1, H _2A 1, H _3A 1... Of each channel to the phasing addition processing unit 22 to perform summation processing (receive beam forming). ). Thus, decoded signals H _1A 1, H _2A 1, the received signal and the H _3A 1 · · · to phasing addition _H sumA 1 (sum indicates that a post-delay-and-sum, the A subscript, It indicates that the received signal corresponds to the transmission aperture 110A, and 1 indicates that it is the first received signal). The reception signal _HsumA1 after the phasing addition is small area data 210A (see FIG. 5B) corresponding to the transmission aperture 110A. Similarly, to obtain a decoded signal _{H 1B 1, H 2B 1,} H 3B 1 received signal to phasing addition the ··· H _sumB 1 (small area data 210B corresponding to the transmission openings 110B).

As shown in FIG. 13, the second storage unit 24 has storage areas 24A-1 to 24A- (N−1) for storing two sets of N−1 small area data for each set of transmission apertures. ) And 24B-1 to 24B- (N-1). Here, N is the number of transmissions required to obtain one post-combination small area data, and here N = 3. The received signal H _sumA 1 (small area data 210A) after the phasing addition corresponding to the transmission aperture 110A generated by the phasing addition processing unit 22 is stored in the storage area 24A-1. Similarly, the post-phasing addition received signal _HsumB1 (small area data 210B) corresponding to the transmission aperture 110B is stored in the storage area 24B-1.

The control unit 106 causes the transmission unit 102 to execute the third transmission Tx3 that is spatially encoded in the same manner as the first transmission Tx1. The reception signal R ₁₃ obtained by the channel 109 ₁ is overwritten and stored in the storage area 40-1 for the transmission openings 110A and 110B. That is, the received signal R ₁ 1 stored in the storage area 40-1 by the first transmission Tx1 is deleted, and the received signal R ₁₃ of the third transmission Tx3 is stored. Similarly, for the received signals R ₂ 3... R _P 3 obtained by the other channels 109 ₂ ... 109 _P , the storage areas 40 of 110A and 110B of the channel memory 40 connected to the respective channels. Save to -1.

The control unit 106 reads the received signals R ₁ 2 and R ₁₃ from the storage areas 40-1 and 40-2 for the transmission openings 110A and 110B, and inputs them to the adder 14 and the subtracter 15 in the decoding unit 41, respectively. Then, a decoded reception signal H _1A 2 for the transmission aperture 110A and a decoded reception signal H _1B 2 for the transmission aperture 110B are obtained. Similarly, the control unit 106 also inputs the received signal to the decoding unit 41 for the channel memories 40 connected to the other channels 109 ₂ ... 109 _P , respectively, and receives the decoded reception signal and transmission from the transmission aperture 110A. A decoded reception signal by transmission from the opening 110B is calculated.

Decoded received signals H _1A 2, H _2A 2, H _3A 1... Corresponding to the transmission aperture 110A from each channel signal processing unit 20, and decoded signals H _1B 2 and H _2B 2 corresponding to the transmission aperture 110B. , H _3B 2... _Are transferred to the phasing addition processing unit 22 and received signal H _sumA 2 after phasing addition (small area data 210A corresponding to transmission aperture 110A) and received signal H after phasing addition. _sumB 2 (small area data 210B corresponding to the transmission aperture 110B) is generated.

The received signal _HsumA2 after phasing addition (small area data 210A corresponding to the transmission aperture 110A) and the received signal _HsumB2 after phasing addition (small area data 210B corresponding to the transmission aperture 110B) are stored in the second memory. The data is stored in the storage areas 24A-2 and 24B-2 of the unit 24, respectively.

The control unit 106 stores, in the storage area 24A-1, two time-series small area data 210A (received signals H _sumA 1 and H _sumA 2 after phasing addition) for the transmission aperture 110A obtained by three transmissions. , 24A-2 and transferred to the combining unit 25. The addition processing unit 33 in the synthesizing unit 25 adds two small area data 210A (received signals H _sumA 1 and H _sumA 2 after phasing addition) for the transmission aperture 110A, and _combines the small area data 210A ( A combined received signal H _A ′) is obtained. Similarly, the control unit 106 reads out the small area data 210A (received signals H _sumB 1 and H _sumB 2 after phasing addition) for the transmission aperture 110B from the storage areas 24B-1 and 24B-2, and combines the data 25 Pass to. The addition processing unit 33 of the synthesizing unit 25 adds the two small area data 210B (the received signals H _sumB 1 and H _sumB 2 after phasing addition) for the transmission aperture 110B, and _combines the small area data 210B (synthesized). After receiving signal H _B ′) is obtained. In these small area data 210 </ b> A, B (combined received signals H _A ′, H _B ′), unnecessary signals due to the movement of the imaging target 120 are suppressed. The small area data H _A ′ and H _B ′ are stored in storage areas 24A-T and 24B-T provided in the second storage unit 24.

The control unit 106 repeats the same process as described above for each set of transmission apertures. At this time, in the above description, it has been described that transmission is performed three times (N times) continuously from one set of transmission apertures 110A and 110B. However, as shown in FIG. It is desirable to repeat the scan to be performed three times (N times).

Therefore, as shown in the flow of FIG. 14, when the number of scans is represented by n, in the first scan (step 141), the first transmission is sequentially performed for each set of transmission apertures (steps 142 to 148). At this time, when the number of scans n is an odd number, transmission is performed by encoding (first spatial encoding) in the first row of equation (1) (step 144), and the obtained reception signal is stored in the channel memory 40. The data is stored in the storage area 40-1 for each set of transmission apertures. When the number of scans n is an even number, transmission is performed by encoding (first spatial encoding) in the first row of equation (1) (step 146), and the obtained reception signal is set to a set of transmission apertures in the channel memory 40. Each of them is stored in the storage area 40-2 (step 147).

The control unit 106 transfers the received signals in the storage areas 40-1 and 40-2 to the decoding unit 41 for each set of transmission apertures (steps 151 and 156) after the second scan number n (step 149). The decoded received signals H _A and H _B are generated (steps 152 and 153). Further, the received signals H _A and H _B after decoding are _phased and added by the phasing adder 22 respectively, and the obtained small area data H _sumA and H _sumB are stored in the storage areas 24A-1 and _24B− of the second storage unit 24, respectively. 1 (that is, storage areas 24A- (n-1), 24B- (n-1)) is stored for each set of transmission apertures (step 155).

Thereafter, the process returns to step 142 to perform the third scan (steps 157 and 150). In the third scan, each transmission aperture set of the third transmission by the first spatial encoding is sequentially performed, and the obtained reception signal is overwritten and stored in the storage area 40-1 for each transmission aperture set of the channel memory 40. (Steps 142 to 148). Then, the process proceeds to steps 151 to 156, and the control unit 106 sequentially passes the received signals of the storage areas 40-1 and 40-2 to the respective decoding units 41 for each set of transmission apertures, and for each set of transmission apertures, After decoding, reception signals H _A and H _B are generated. The decoded reception signals H _A and H _B are _phased and added by the phasing and adding unit 22 respectively, and the obtained small area data H _sumA and H _sumB are stored in the storage areas 24A-2 and 24B-2 of the second storage unit 24, respectively. (That is, storage areas 24A- (n-1), 24B- (n-1)) are stored for each set of transmission apertures.

Then, it is determined whether the number of transmissions is N times (three times) or more (step 157). In the case of N times (three times) or more, the control unit 106 sets the data in the storage areas 24A-1 to 24A- (N-1) of the second storage unit 24 for each set of transmission apertures (steps 158 and 163). Is transferred to the synthesizing unit 25, and the synthesizing unit 25 adds to obtain one small area data H _A ′ (steps 159 and 160). Next, the control unit 106 reads out the data in the storage areas 24B-1 and 24B- (N-1) and transfers the data to the combining unit 25, and the addition processing unit 33 of the combining unit 25 adds the other small area data. H _B ′ is obtained (steps 161 and 162). The obtained small area data H _A ′ and H _B ′ are stored in the storage areas 24A-T and 24B-T provided in the second storage unit 24 for each transmission aperture. Thus, a total of eight small area data 210A to 213A and 210B to 213B are stored in the storage areas 24A-T and 24B-T in FIG. 13, two for each set of transmission apertures shown in FIG. The control unit 106 transfers the small area data of the storage areas 24A-T and 24B-T to the synthesis unit 25, and the image construction unit 34 of the synthesis unit 25 arranges these small area data at predetermined positions, respectively. An image of the imaging target 120 is constructed (step 164).

Thereafter, returning to step 142, the fourth and subsequent n-th scans are performed. The processing of the fourth and subsequent scans is the same as in the above steps, but in step 155, the storage area of the second storage unit 24 that stores the small area data H _sumA and H _sumB is the storage area 24A- ( n-1- (N-1)) and 24B- (n-1- (N-1)), and the storage areas after the (N-1) th time are sequentially overwritten and saved. Thereby, the image of the imaging target 120 using the small area data synthesized by the synthesis unit 25 can be constructed every n-th scan.

Note that the number of scans N until the composition unit 25 performs composition is not limited to three, and can be any number. For example, the setting of the number of scans N can be accepted from the operator via the UI 121. Further, the number (N−1) of decoded received signals to be combined by the combining unit 25 can be received from the operator via the UI 121, and transmission can be performed by a number one or more larger than that number. Furthermore, the control unit 106 can also set an appropriate number of scans N according to the set imaging conditions. In this case, an appropriate number of scans N is obtained in advance for each settable imaging condition, and this is stored in a memory in the control unit 106 or an external memory, and the control unit 106 reads and uses it. Can do.

In steps 143, 144, and 146 in FIG. 14, the control unit 106 causes the first spatial coding to be transmitted when the number of scans is an odd number, and the second spatial coding to be performed when the number of scans is an even number. Thus, decoding can be performed for each scan using the two most recently received signals, and small area data for each set of transmission apertures can be obtained in time series. Therefore, it is possible to display an image to be imaged almost in real time for each scan. However, the present invention is not limited to this, and if it is possible to prepare a large number of storage areas in the scan memory 40, it is also possible to perform decoding using two received signals that are not the most recent. .

Note that the small area data need not be mutually exclusive in the imaging region of the imaging target 120 and may partially overlap each other. At this time, the overlapping small area data is combined and added coherently or incoherently as the same area data in the combining unit 25.

As described above, in the present embodiment, the combining unit 25 adds a plurality of time-series small area data, thereby obtaining small area data in which unnecessary data resulting from the movement of the imaging target is suppressed. At this time, since the second storage unit 24 and the combining unit 25 are arranged in the subsequent stage of the phasing addition unit 22, even if the device has 100 or more reception channels, the second storage unit is stored in the entire device. Only one unit 24 and one synthesis unit 25 need be arranged. Therefore, the hardware configuration does not increase in proportion to the number of channels, and the increase in hardware cost according to the present embodiment can be minimized. Since the phasing addition is a linear addition process, the phase of the unnecessary component in the signal before and after the phasing addition is maintained.

Note that the artifact can be further reduced as the number of time-series small area data to be added by the synthesizing unit 25 increases. However, when the movement of the imaging target is fast, the image quality may be deteriorated. Therefore, the control unit 106 may be configured to determine the number of small area data to be added by the synthesis unit 25 according to the speed of movement of the imaging target. In this case, the control unit 106 separately performs image processing, obtains the speed of movement of the imaging target by calculation, and determines the number of addition processes from the relationship between a predetermined speed and the number of addition processes. it can.

<< Second Embodiment >>
An ultrasonic imaging apparatus according to the second embodiment will be described with reference to FIGS.

In the ultrasonic imaging apparatus according to the second embodiment, as illustrated in FIG. 15, the combining unit 25 has a plurality of decoded received signals (small area data) H _sumA 1, H _sumA 2... H _sumA (N−1 .., 32- (N−1). The decoded received signals H _sumA 1, H _sumA 2... H _sumA (N−1) weighted by the weighting _{units 32-1} , _32-2,. Will add. At this time, the weighting units 32-1, 32-2,..., 32- (N-1) weights the received signal that is closer to the center time of the time series among the received signals generated in the time series. Is desirable. As a result, as shown in FIG. 16, the original received signal 119a is further strengthened, and small area data (decoded received signal after synthesis) H _A ′ in which the unnecessary signal 119b is further suppressed can be obtained. In the ultrasonic imaging apparatus, a weight data storage unit 86 in which weight coefficient values are stored in advance is provided. Other configurations are the same as those of the ultrasonic imaging apparatus of the first embodiment.

The second embodiment will be further described. As also described in the first embodiment, the decoded received signals H _A 1 the decoding unit 41 generates a time series, H _A 2, H _A 3 included in ..., original received signal 16a, 17a, 18a .. Are always in-phase waveforms as shown in FIG. These received signals are in a state in which the time is gradually shifted by the movement of the imaging target 120 as shown in FIG. Therefore, as shown in FIG. 17A, the signal appearance time center (the center of the time series) is closer than the small area data (decoded received signal after synthesis) H _A ′ obtained by simply adding these received signals. The smaller area data (decoded received signal after synthesis) H _A ′, which is weighted after increasing the weight, is less spread in the time axis direction of the signal and the spatial resolution is improved. .

On the other hand, the unnecessary signals 16b to 18b included in the decoded received signals H _A 1, H _A 2, H _A 3... Generated by the decoding unit 41 in time series alternately have waveforms with opposite phases. Since these signals are also time-shifted little by little, unnecessary signals are obtained by adding together signals having a small time shift ( unnecessary signals 16b and 17b, unnecessary signals 17b and 18b), rather than adding all signals together. If the addition results are added to each other after minimizing the error, the entire unnecessary signal component can be suppressed. This is equivalent to increasing the weighting and adding the signals closer to the center of the time series of the received signals H _A 1, H _A 2, H _A 3.

In this way, by increasing the weight of the decoded received signal that is closer to the center time of the time series, the spatial resolution is improved by suppressing the spread of the original received signal 119a in the time axis direction, and the unnecessary signal 119b is further suppressed. can do.

The method of performing weighting and performing addition is similar to the method of high quality image processing using a Gaussian filter. For example, when the three signals H _A 1, H _A 2, and H _A 3 shown in FIG. 16 are summed, the signals are summed after weighting coefficients α, β, and γ are multiplied. Β multiplied by the signal of H _A 2 which is the center of the time series is set to a value larger than α and γ before and after that. For example, the maximum amplitude value at the center of the Gaussian function is used for β, and the values corresponding to any two points before and after that are used for α and γ. In addition to the Gaussian function, the binomial coefficient value [1 2 1] based on the binomial distribution may be assigned to the weighting coefficients α, β, and γ, respectively.

The configuration and operation of the synthesis unit 25 in the second embodiment will be further described with reference to FIG. In step 159 of FIG. 14 of the first embodiment, the control unit 106 reduces the small area data H _sumA 1, H _sum stored in the storage areas 24A-1 to 24A- (N−1) of the second storage unit 24. _sumA 2... H _sumA (N−1) is read and transferred to the synthesis unit 25. The weighting units 32-1 to 32- (N−1) of the combining unit 25 weight the waveform amplitudes of H _sumA 1, H _sumA 2... H _sumA (N−1). The weight data storage unit 86 stores weight data in advance according to the number of data to be weighted (N-1). The control unit 106 selects an appropriate weighting coefficient value from the weight data storage unit 86 according to the number of data to be weighted (N−1), and assigns weighting units 32-1, 32-2,. Set to -1). As a result, the weight coefficient is increased as the time closer to the center of the time series of H _sumA 1, H _sumA 2... H _sumA (N−1). After the weighting, the small area data is added by the addition processing unit 33 of the synthesis unit 25 to become small area data (decoded received signal after synthesis) H _A ′, and the storage areas 24A-T of the second storage unit (Step 160). As a result, the unnecessary signal is further suppressed, and small area data in which the spatial resolution of the original received signal is increased can be generated. Similarly, in step 162, after weighting, addition processing is performed.

Other configurations are the same as those in the first embodiment, and thus description thereof is omitted.

<< Third embodiment >>
A third embodiment of the present invention will be described. In the ultrasonic imaging apparatus according to the third embodiment, the transmission unit 102 causes the transmission aperture to transmit the spatial encoding combined with the temporal encoding having an orthogonal relationship, that is, the spatio-temporal encoded ultrasonic. The receiving unit 105 includes filters 54-1 to 54-2, 55-1 to 55-2 that perform decoding corresponding to time coding, and an adding unit 56 in the decoding unit 41 as shown in FIG. The synthesizer 25 adds the plurality of decoded received signals decoded by the decoder 41.

Time coding is a method of coding an ultrasonic waveform and distributing ultrasonic energy in the time direction and applying a compression filter at the time of reception. As a result, the energy of the dispersed sound waves is compressed, and a decoded signal having a high amplitude can be generated, so that imaging with an improved SN ratio can be performed. By applying temporal encoding to spatial encoding and applying it to the present invention, artifacts in the generated image can be reduced and the S / N ratio can be improved even when motion occurs in the imaging target. it can.

The details will be described below. Spatio-temporal coding transmission / reception itself in which temporal coding is added to spatial coding is a known technique described in, for example, US Pat. No. 6,048,315. The configuration of generating and synthesizing the post-reception signal is unique to the present invention.

(Principle of time coding)
First, the principle of time encoding will be described using an example of using a Golay code. The Golay code is known as a code in which an unnecessary signal called a time side lobe does not remain before and after the compressed pulse waveform in the time direction. The Golay code is a binary code that is a pair of complementary sequences having the same code length. _Assuming that the autocorrelation functions of the pair of codes X1 and X2 are ψ _X1X1 and ψ _X2X2 , the sum χ _x1x2 (k) of those k-th elements is expressed by the equation (2).

In Expression (2), L is the code length of the Golay code. As is clear from equation (2), the sum χ _x1x2 (k) of the k-th elements is always 0 except in the case of k = 0 (time shift 0 state). It can be seen that by performing transmission, performing autocorrelation processing on each received signal, and performing addition processing, time coding in which the time side lobe is completely canceled can be performed. Hereinafter, this arithmetic processing is referred to as Golay decoding.

For example, when a code X1 = [1 1] and X2 = [1 −1] with L = 2 is used as a pair of Golay codes as shown in FIG. 19, the waveform of the first transmission Tx1 subjected only to time encoding Is a waveform representing X1 as shown in FIG. 20A, and the waveform of the second transmission Tx2 is a waveform representing X2. However, the reference waveform 71 in FIG. 7A is assigned to reference numeral 1 and the inverted waveform 72 in FIG. 7B is assigned to reference numeral -1. The received signals R1 and R2 obtained by each transmission have the same waveform as the transmission waveform assuming an echo from one scatterer. Actually, the received signal has a waveform in which various echoes are overlapped by a medium scatterer. For the Golay decoding process, first, autocorrelation filters 54 and 55 of codes X1 and X2 used for each transmission are applied to the two received signals R1 and R2 (FIGS. 19 and 20B). . The autocorrelation filters 54 and 55 are matched filters using coefficients obtained by inverting the transmitted code coefficients (1 or −1) with respect to the time axis. Thereby, the compression pulses C1 and C2 are generated. The compression pulses C1 and C2 are composed of a central main lobe and time side lobes appearing before and after the time direction, and the time side lobes are in an inverted relationship with each other with the compression pulses C1 and C2. Therefore, the time side lobe is canceled by adding them at the same time by the adding unit 56, and the main lobe signals are added and output.

Next, spatial coding combined with temporal coding having an orthogonal relationship, that is, space-time coding will be described. In addition to the above Golay code pair X1 and X2, another Golay code pair Y1 and Y2 is used. The codes Y1 and Y2 are codes such that the sum of the cross-correlation functions of Y1 and Y2 with respect to X1 and X2 is zero at all points. When the cross-correlation function of the X1 and Y1 [psi _X1Y1, X2 and Y2 cross correlation of the number of the [psi _X2Y2, sum between their k-th element is represented by the formula (3).

In Expression (3), L is the code length of the Golay code. Therefore, even when the X and Y codes are transmitted simultaneously, if the cross-correlation processing is performed on the received signal, it can be separated as an echo signal transmitted with each code.

When the Golay pair with L = 2 is X1 = [1 1] and X2 = [1 −1], the codes of the Golay pairs Y1 and Y2 having an orthogonal relationship are Y1 = [− 1 1] and Y2 = [ -1 -1].

In space-time coded transmission / reception in which the operation of performing transmission from two transmission apertures at the same time is performed twice, space-time coded transmission as shown in Equation (4) is performed. In equation (4), the row vector indicates the order of transmission, and the column vector indicates the position of the transmission aperture. Therefore, in Expression (4), the first transmission is [X1 Y1], and a waveform time-coded with X1 from one of the two transmission apertures and a waveform time-coded with Y2 from the other are simultaneously transmitted. . The second transmission is [X2 Y2], and a waveform time-coded by X2 from one of the two transmission apertures and a waveform time-coded by Y2 from the other are simultaneously transmitted.

Decoding according to space-time coding is performed using the first received signal and the second received signal received for each transmission of Expression (4). Both Golay decoding by the X code and Golay decoding by the Y code are performed to separate the Golay code X echo from the Y echo. Accordingly, assuming that the received signals of each transmission are R1 and R2, the decoding process of space-time coding is expressed by Expression (5).

In such space-time encoding transmission / reception, the unnecessary signal generated by the movement of the imaging target is the remaining cancellation of the time side lobe generated in the compressed pulse of FIG. That is, when the imaging target moves between two transmissions / receptions, the signal appearance time of the reception signal R2 is shifted with respect to the reception signal R1, so that the time side lobes of C1 and C2 do not cancel each other. Become complete. Similarly, the signal appearance time of the received signal R2 with respect to the received signal R1 is also the signal that should be 0 when the signals _ψX1Y1 and _ψX2Y2 signals after cross-correlation processing with the Golay pair in the orthogonal relationship are added. Since it is in a shifted state, an unneeded unnecessary signal is generated.

In the third embodiment, on the basis of the same principle as in the first embodiment, the synthesizer 25 adds a plurality of decoded reception signals obtained for the same transmission aperture, so that an unnecessary signal is generated even when the imaging target moves. Can be suppressed.

As in the first embodiment, in this embodiment, as shown in FIG. 18, the channel memory 40 is provided with two storage areas 40-1 to 40-2 for each set of transmission openings. Further, the decoding unit 41 in the present embodiment includes a correlation filter 54-1 with a code X1, a correlation filter 54-2 with a code X2, a correlation filter 55-1 with a code Y1, a correlation filter 55-2 with a code Y2, and an addition unit. 56 is provided as shown in FIG.

The decoded reception signal H _1A 1 and the decoded reception signal H _1B 1 obtained after the processing of the adder 56 are respectively received from the decoded reception signal and the transmission opening 110B by transmission from the transmission aperture 110A, as in the first embodiment. Is a received signal after decoding. As in the first embodiment, the subscript number indicates the channel number, the alphabetic character indicates the decoded received signal corresponding to the transmission aperture, and 1 indicates the first obtained decoded signal. Show.

Therefore, the configuration other than the first spatial encoding [X1 Y1] which is the first temporal encoding and the second spatial encoding [X2 Y2] which is the second space-time encoding is the control at the time of transmission and reception. The operation of the unit 106 is the same as that in FIG.

<< Fourth Embodiment >>
A fourth embodiment of the present invention will be described. In the ultrasonic imaging apparatus of the fourth embodiment, the transmission unit 102 transmits not only the spatial encoding described in the first embodiment but also the temporally encoded ultrasonic wave from the transmission aperture. The receiving unit 105 includes a second decoding unit 141 that performs decoding corresponding to time coding in addition to the decoding unit 41 as illustrated in FIG. The synthesizer 25 adds the plurality of decoded received signals decoded by the decoder 41 and the second decoder 141.

As shown in FIG. 21, the second decoding unit 141 can be configured to perform decoding corresponding to temporal encoding on the received signal after decoding performed by the decoding unit 41 corresponding to spatial encoding.

The number of transmissions of the transmission unit 102 is 5 or more. The decoding unit 41 and the second decoding unit 141 perform decoding using four received signals among the received signals obtained by five or more transmissions, and generate a decoded received signal. By performing this process for two or more different combinations of four received signals to be used, a plurality of decoded received signals can be generated. The combining unit 25 combines these.

Therefore, in the first storage unit 40 of the receiving unit 105, four storage areas 40-1 to 40-4 that sequentially store the latest four received signals among the received signals for each transmission of five or more ultrasonic waves. 40-4 is provided. The decoding unit 41 and the second decoding unit 141 perform different decoding processes using the four received signals respectively stored in the four storage areas 40-1 to 40-4, so that the combinations of received signals are different. The decoded received signal can be generated in time series.

(Combination of space coding and time coding)
Generation of a transmission signal in which space coding is further time-coded can be realized by applying the time-coded transmission described above to the element of Equation (1). The time encoding by the code X1 is the first time encoding, and the time encoding by the code X2 is the second time encoding. For example, as shown in FIG. 22, the first transmission Tx1 ultrasonic wave is subjected to first spatial encoding and first time encoding, and the second transmission Tx2 ultrasonic wave is subjected to the first spatial encoding and the first temporal encoding. Two-time encoding is performed. The second transmission Tx3 is subjected to the second spatial encoding and the first temporal encoding, and the fourth transmission Tx4 is subjected to the second spatial encoding and the second temporal encoding. In this case, a spatial encoding matrix combined with temporal encoding is expressed by Expression (6).

In the decoding process, as shown in FIG. 22, Hadamard decoding is first performed by the decoding unit 41 on the four received signals R1 to R4 obtained by four transmissions. At this time, two received signals that have been subjected to the same time-coded transmission are used in combination. Thereby, the echo by the transmission from a some transmission opening is isolate | separated. Thereafter, the Golay decoding unit 141 applies the above-described Golay decoding process to generate a signal with a high S / N ratio.

This decoding process is expressed by Equation (7), and thereby, a decoded reception signal _HA from one transmission aperture (for example, 110A) is generated.

Also, the decoded received signal H _B corresponding to the other transmission aperture (for example, 110B) is obtained by Expression (8).

The decoding processing of equations (7) and (8) is referred to as Golay-Hadamard decoding.

In the third embodiment, unnecessary signals can be suppressed even when the imaging target moves by adding a plurality of decoded reception signals obtained for the same transmission aperture by Golay-Hadamard decoding, by the synthesis unit 25.

As shown in FIG. 21, the channel memory 40 is provided with four storage areas 40-1 to 40-4 for each set of transmission openings. In addition, the decoding unit 41 includes two adders 14 and two subtracters 15 and can decode the spatial encoding of the four received signals. The second decoding unit 141 includes autocorrelation filters 54 and 55 and an addition unit 56 as shown in FIG. 21 for Golay time-coding decoding.

The operation of the control unit 106 during transmission / reception will be described with reference to FIG.

First, when the number of scans n = 1, the control unit 106 transmits an ultrasonic wave subjected to the first spatial coding and the first time coding (X1) (step 172). The control unit 106 stores the obtained reception signal R1 in the storage area 40-1 of the channel memory 40 (step 173). This is sequentially performed for all sets of transmission apertures (steps 142 and 148).

When the number of scans n = 2, the ultrasonic wave subjected to the first spatial coding and the second time coding (X2) is transmitted (step 175). The control unit 106 stores the obtained reception signal R2 in the storage area 40-2 of the channel memory 40 (step 176). This is sequentially performed for all sets of transmission apertures (steps 142 and 148).

When the number of scans n = 3, the ultrasonic waves subjected to the second spatial encoding and the first temporal encoding (X1) are transmitted (step 178). The control unit 106 stores the obtained reception signal R3 in the storage area 40-3 of the channel memory 40 (step 179). This is sequentially performed for all sets of transmission apertures (steps 142 and 148).

When the number of scans n = 4, the ultrasonic waves subjected to the second spatial encoding and the second temporal encoding (X2) are transmitted (step 181). The control unit 106 stores the obtained reception signal R4 in the storage area 40-4 of the channel memory 40 (step 182). This is sequentially performed for all sets of transmission apertures (steps 142 and 148).

If the number of scans n is 4 or more, the control unit 106 proceeds to step 152 and transfers the received signals R1 to R4 in the storage areas 40-1 to 40-4 to the decoding unit 41 in FIG. The decoding unit performs an addition process by the adder 14 and a subtraction process by the subtracter 15 on the reception signal R1 obtained by the transmission of the first spatial coding and the reception signal R3 obtained by the transmission of the second spatial coding. To decrypt. Similarly, the received signals R2 and R4 are decoded by addition processing and subtraction processing.

The four received signals obtained by decoding the spatial coding obtained by the decoding unit 41 are applied with autocorrelation filters 54 and 55 in the second decoding unit 141 to generate compressed pulses, respectively. By receiving two sets of different Golay codes X1 and X2 at the time of transmission and adding them by the adder 56, decoded received signals H _1A 1 and H _1B 1 are obtained (step 153). This process is performed for each set of transmission apertures (step 151).

The obtained decoded received signals H _1A 1 and H _1B 1 are subjected to the following steps 154 to 156 to obtain small area data after phasing addition. Since these steps 154 to 156 are the same as those in the first embodiment, description thereof will be omitted.

When the number of scans is n = 5, the transmission unit 102 performs transmission with the first spatial coding and the first time coding performed in step 171 as in the case of n = 1 (step 172). The control unit 106 overwrites and stores the received signal R5 obtained by this transmission in the storage area 40-1 of the channel memory 40 (step 173). Therefore, when performing the decoding process in step 152, the control unit 106 reads the received signals R5, R2, R3, and R4 from the four storage areas 40-1 to 40-4 and passes them to the decoding unit 41. Subsequent steps 153 to 156 provide small area data after phasing addition.

In steps 158 to 164, similarly to the first embodiment, the combining unit 25 obtains the combined small area data H _A ′ and H _B ′ and constructs an image. In this image, an unnecessary signal generated by moving the imaging target is suppressed. Thereafter, one image is constructed for each scan.

Other configurations are the same as those in the first embodiment, and thus description thereof is omitted.

<< Fifth Embodiment >>
The ultrasonic diagnostic apparatus of the fifth embodiment has a configuration in which weighting units 61 to 64 are arranged between the channel memory 20 and the decoding unit 41 as shown in FIG. Other configurations are the same as those of the fourth embodiment. The control unit 106 sets the weights of the weighting units 61 to 64.

In the space-time coding according to the fourth embodiment, when the imaging target 120 moves between a plurality of transmissions, the received signals are shifted in time from each other. Since the time side lobe generated in the compression pulse of the Golay code cannot be completely canceled if the time axis of the two compression pulses is shifted, a time side lobe remaining after cancellation occurs. This remaining cancellation time side lobe is also an unnecessary signal that causes an artifact on the image. Therefore, in this embodiment, weighting in Golay decoding is given in order to suppress unnecessary signals due to Golay coding. The weighting coefficient values set in the weighting units 61 to 64 are set so that the centered value becomes larger when the reception signals stored in the storage areas 40-1 to 40-4 are arranged in the order of reception. . For example, it is desirable that the weighting coefficient value is selected and set by the control unit 106 from the weight data storage unit 87 in which values corresponding to Gaussian functions, binomial coefficient values, and the like are stored in advance.

By weighting the reception signal in this way, it is possible to suppress time side lobes that occur in the Golay code compression pulse.

Other configurations are the same as those in the fourth embodiment, and thus description thereof is omitted.

<< Sixth Embodiment >>
In the space-time coded transmission / reception of the fourth embodiment, since transmission is performed simultaneously from two transmission apertures, four transmissions are necessary to obtain two small area data. In the sixth embodiment, in order to improve the frame rate, space-time encoded transmission / reception is performed in which transmission is performed four times from four directions (four transmission apertures) at the same time.

¡When transmitting from four transmission apertures at the same time, use the Golay code set that is orthogonal. For example, the Golay code pairs Y1 and Y2 described in the third embodiment are used.

In space-time coded transmission / reception in which transmission is performed simultaneously from four transmission apertures, a transmission aperture for performing space-time coding of the following equation (9) is added to the transmission aperture of space-time coding performed by equation (6).

To summarize the four transmission apertures, the space-time coding is as shown in Equation (10).

Hadamard decoding is performed on a received signal that has been subjected to the same time-coded transmission. In the case of Expression (9), decoding is performed using the first received signal and the second received signal, and decoding is performed using the second received signal and the fourth received signal. Then, Golay decoding is applied. At this time, both Golay decoding by the X code and Golay decoding by the Y code are performed, and the Golay code X echo and the Y echo are separated. Therefore, assuming that the received signals for each transmission are R1 to R4, the Hadamard decoding process is expressed by Expression (11).

Next, Golay decoding is performed with each code, and signals in each column are extracted.

More specifically, the control unit 106 sets four transmission apertures in the ultrasonic probe 108. Assuming that the transmission apertures are transmission apertures A, B, C, and D, respectively, the control unit 106 codes the time waveform in the order of X1, X2, X1, and X2 to the channel of the transmission aperture A according to Equation (10). The transmission signals that have been converted are sent sequentially. A transmission signal obtained by encoding a time waveform in the order of X1, X2, -X1, and -X2 is sequentially sent to the channel of the transmission aperture B. A transmission signal obtained by encoding a time waveform in the order of Y1, Y2, Y1, and Y2 is sequentially sent to the channel of the transmission aperture C. A transmission signal obtained by encoding a time waveform in the order of Y1, Y2, -Y1, and -Y2 is sequentially sent to the channel of the transmission aperture D.

As shown in FIG. 25, in addition to the configuration of FIG. 24, autocorrelation filters 57 and 58 using a Y code are added to the second decoding unit 141. The control unit 106 adds the received signals R1 and R3 by the adder 14 and subtracts it by the subtractor 15. The output is divided into two, and an X1 autocorrelation filter 54 and a Y1 autocorrelation filter 57 are applied. The received signals R2 and R4 are added by the adder 14 and subtracted by the subtractor 15, respectively. The output is divided into two parts, and the X2 autocorrelation filter 55 and the Y2 autocorrelation filter 58 are applied. Then, the addition is performed by the Golay code adding unit 56, so that the decoded reception signal H _A corresponding to the transmission of the transmission aperture A subjected to the Golay-Hadamard decoding, the decoded reception signal H _B corresponding to the transmission of the transmission aperture _B , The decoded reception signal H _C corresponding to the transmission of the transmission aperture C and the decoded reception signal HD corresponding to the transmission of the transmission aperture _D are output.

Since the subsequent processing is the same as that of the third embodiment including the synthesis processing of a plurality of decoded received signals (small area data) by the synthesis unit 25, description thereof will be omitted.

According to the sixth embodiment, since the small area data corresponding to the four transmission apertures can be generated by four scans as in the fourth embodiment, the frame rate is improved.

13a, 13b, 18b ... received signal, 15 ... subtractor, 16a, 17a, 19a ... original received signal, 16b, 17b, 18b, 19b ... unnecessary signal, 22 ... phasing addition, 24 ... second storage unit, 25 ... Synthesizer, 40 ... First memory, 41 ... Decoder, 100 ... Ultrasound imaging device, 102 ... Transmitter, 105 ... Receiver, 108 ... Ultrasound probe, 109 ... Receiving area, 109 ₁ , ... 109 _P ... reception area, 110A, 110B ... transmission area, 120 ... imaging target, 211A, 211B ... small area

Claims (15)

1. An ultrasound probe having at least two transmission areas and at least one reception area, each composed of a transducer;
   A transmitter that transmits spatially-encoded ultrasonic waves three or more times toward a predetermined position simultaneously from the at least two transmission regions;
   The reception area has a reception unit that processes a reception signal that receives and outputs the ultrasonic echo from the position;
   The receiving unit includes a decoding unit and a combining unit,
   The decoding unit performs decoding corresponding to the spatial coding using two or more of the three or more received signals output from the reception area in response to the transmission of the ultrasonic wave three times or more. A plurality of decoded received signals are generated by performing a process of generating a decoded received signal for each of two or more different combinations of two or more received signals to be used,
   The ultrasonic imaging apparatus, wherein the synthesizing unit performs addition processing on a plurality of the decoded reception signals.
2. 2. The ultrasonic imaging apparatus according to claim 1, wherein the decoding process by the decoding unit is performed by ultrasonic waves for each transmission region from reception signals of echoes transmitted by the ultrasonic waves simultaneously transmitted from the two or more transmission regions. The process of obtaining the received signal after decoding, which is a received signal corresponding to each transmission region, by separating the received signal of the generated echo,
   The ultrasound imaging apparatus, wherein the plurality of decoded reception signals that are added by the combining unit are the plurality of decoded reception signals obtained for the same transmission region.
3. 2. The ultrasonic imaging apparatus according to claim 1, wherein the reception unit is generated by the decoding unit and a first storage unit that sequentially stores at least one of the reception signals received in order corresponding to the transmission. A second storage unit for storing at least one received signal after decoding,
   The decoding unit performs a decoding process using the received signal stored in the first storage unit,
   The ultrasonic imaging apparatus, wherein the synthesizing unit performs the addition process using the decoded received signal stored in the second storage unit.
4. 4. The ultrasonic imaging apparatus according to claim 3, wherein the first storage unit sequentially stores the two most recent reception signals among the reception signals for each transmission of the three or more ultrasonic waves. Has two storage areas,
   The decoding unit sequentially generates decoding received signals having different combinations of the received signals in time series by sequentially performing decoding processing using the two received signals respectively stored in the two storage areas. An ultrasonic imaging apparatus characterized by the above.
5. The ultrasonic imaging apparatus according to claim 1, wherein the ultrasonic probe has a plurality of the reception areas,
   The receiving unit includes a phasing addition unit,
   The decoding unit generates the reception signal after decoding for each of the plurality of reception areas using each reception signal of the reception area corresponding to the transmission of the same ultrasonic wave,
   The phasing addition unit phasing the decoded received signal for each of the plurality of reception areas, and adding,
   The ultrasonic imaging apparatus, wherein the synthesizer adds a plurality of the decoded reception signals after the phasing addition.
6. The ultrasonic imaging apparatus according to claim 1, wherein the ultrasonic probe includes a plurality of sets of the transmission areas,
   The ultrasonic imaging apparatus, wherein the transmission unit repeats a scanning operation of sequentially transmitting ultrasonic waves from a plurality of sets of the transmission areas toward the position three times or more.
7. The ultrasonic imaging apparatus according to claim 1, further comprising: a receiving unit that receives a number of received signals after decoding that the combining unit performs addition processing from an operator;
   The transmitting unit causes one or more transmissions greater than the number received by the receiving unit, and the synthesizing unit performs addition processing on the received number of decoded reception signals. Sound imaging device.
8. 2. The ultrasonic imaging apparatus according to claim 1, wherein the synthesis unit includes a weighting unit that weights the plurality of decoded reception signals, and adds the plurality of decoded reception signals weighted by the weighting unit. An ultrasonic imaging apparatus.
9. 9. The ultrasonic imaging apparatus according to claim 8, wherein the decoding unit generates the decoded reception signal in time series using two or more recent reception signals, and the weighting unit is generated in time series. An ultrasonic imaging apparatus, wherein a weight closer to a central time among the plurality of decoded received signals is weighted more.
10. The ultrasonic imaging apparatus according to claim 1, wherein the transmission unit transmits time-encoded ultrasonic waves from the transmission region in addition to the spatial encoding,
    In addition to the decoding unit, the receiving unit includes a second decoding unit that performs decoding corresponding to the time encoding,
    The ultrasonic imaging apparatus, wherein the synthesizing unit performs addition processing on a plurality of decoded reception signals decoded by the decoding unit and the second decoding unit.
11. The ultrasound imaging apparatus according to claim 10, wherein the second decoding unit performs decoding corresponding to the temporal encoding for the received signal after decoding, in which the decoding unit performs decoding corresponding to the spatial encoding. An ultrasonic imaging apparatus characterized by performing:
12. The ultrasonic imaging apparatus according to claim 10, wherein the transmission unit transmits five or more times simultaneously from the two transmission areas,
    The decoding unit and the second decoding unit use a process of performing encoding using the four received signals among the received signals obtained by five or more transmissions to generate the decoded received signal An ultrasonic imaging apparatus that generates a plurality of the decoded reception signals by performing two or more different combinations of the four reception signals.
13. The ultrasonic imaging apparatus according to claim 12, wherein the reception unit 105 sequentially stores the latest four reception signals among the reception signals for every five or more ultrasonic transmissions. A first storage unit comprising:
    The decoding unit and the second decoding unit sequentially perform decoding processing using the four reception signals respectively stored in the four storage areas, so that the decoded reception signals having different combinations of the reception signals Are generated in time series.
14. The ultrasonic imaging apparatus according to claim 10, wherein the receiving unit includes a weighting unit that weights the received signal before being transferred to the decoding unit.
15. The ultrasonic imaging apparatus according to claim 10, wherein the ultrasonic probe includes at least four transmission regions,
    The ultrasonic imaging apparatus, wherein the transmission unit causes the spatially encoded and temporally encoded ultrasonic waves to be transmitted simultaneously from the four transmission regions.

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