WO2015198824A1 - Ultrasound imaging apparatus - Google Patents

Abstract

Provided is an ultrasound imaging apparatus capable of reducing image artifacts generated during spatially encoded transmission/reception even when movement of the object being imaged occurs. To each of (at least two) transmitting aperture groups (110, 111) of an ultrasound probe (108) in order, a transmitting unit (102) causes the action of transmitting spatially encoded ultrasonic waves toward a prescribed location of an object that is being imaged (120) simultaneously from at least two transmitting apertures contained in the transmitting aperture group to be performed at least one time. A receiving unit (105) obtains a received signal by performing decoding and phasing of the output of a reception region (109). When doing so, the transmitting unit (102) inverts the spatially encoded code of the ultrasonic waves transmitted by some of the two or more transmitting aperture groups with respect to the spatially encoded code of the ultrasonic waves transmitted by the other transmitting aperture groups. An aperture synthesis unit (25) performs aperture synthesis of the reception signal obtained with the transmission of the transmitting aperture group (110) and the reception signal obtained with the transmission of the other transmitting aperture group (111).

Description

Ultrasonic imaging device

The present invention relates to a high frame rate technology using coding and an SN ratio improving technology 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 is improved by reducing the number of transmission events for creating one tomographic image. Spatial encoding transmission / reception is known as an imaging method that enables high frame rate imaging (Patent Document 1). In spatially encoded transmission / reception, the required number of transmissions is reduced by transmitting to the 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. Also, by subtracting the first received signal and the second received signal, the received signal due to transmission in the A direction is canceled, and only the received signal due to transmission in the B direction remains. This process is equivalent to canceling the reception signal by one transmission in the A direction and the B direction and simultaneously adding the reception signal by the other transmission. For this reason, the amplitude of the received signal in each direction obtained after the post-decoding processing is twice the amplitude of the received signal obtained by the conventional one-way transmission and one-way reception, and the SN ratio is improved.

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 the present invention, the transmission unit performs the operation of transmitting the spatially encoded ultrasonic wave simultaneously from two or more transmission apertures included in the transmission aperture group for one or more rounds (one scan) in order for each of the plurality of transmission aperture groups. Make it. The reception unit performs a decoding process and a phasing process on the output of the reception area that has received the echo of the ultrasonic wave from the imaging target, and obtains a reception signal for a desired reception focus of the imaging target. At this time, the transmission unit changes the spatial encoding code of the ultrasonic wave transmitted by some of the transmission aperture groups to the ultrasonic spatial encoding code transmitted by the other transmission aperture groups. Invert it. The aperture synthesis unit transmits a reception signal for a desired reception focus obtained by the reception unit from an echo generated by an ultrasonic wave transmitted from one transmission aperture group among a plurality of transmission aperture groups, and another transmission aperture group. Addition processing is performed on the reception signals for the same reception focus obtained by the reception unit from echoes generated by ultrasonic waves.

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. (a) Explanatory drawing which shows transmission by the transmission aperture group of 1st embodiment, (b) Explanatory drawing which shows receiving beam forming of 1st embodiment, (c) Explanatory drawing which shows aperture synthesis of 1st embodiment. Explanatory drawing which shows suppression of the unnecessary signal by aperture synthesis of 1st embodiment. Explanatory drawing which shows the basic waveform used for the space coding transmission of 1st embodiment. Explanatory drawing which shows Hadamard space encoding transmission of 1st embodiment, and a decoding process. Explanatory drawing which shows that an unnecessary signal arises by body movement in space coding transmission / reception. (A) Explanatory drawing which shows the spatial encoding of the transmission aperture group 110 of 1st embodiment, and the phase of the unnecessary signal after decoding, (b) Spatial encoding of the transmission aperture group 111, and the phase of the unnecessary signal after decoding FIG. The block diagram which shows the structure of the ultrasonic imaging device of 2nd embodiment. The block diagram which shows the channel 109 of the probe 108 of 2nd embodiment, the transmission aperture pair 110 grade | etc.,. The block part which shows the structure of the receiving part 105 of the ultrasonic probe of 2nd embodiment. The block diagram which shows the structure of the 1st memory | storage part (channel memory) 20 of 2nd embodiment, and the structure of the decoding part 41. FIG. Explanatory drawing which shows receiving beam forming of 2nd embodiment, and arrangement | positioning of a receiving focus. The block diagram which shows the structure of the 2nd memory | storage part 24 and opening synthetic | combination part 25 of 2nd embodiment. 9 is a flowchart showing transmission / reception operations of the ultrasonic imaging apparatus according to the second embodiment. Explanatory drawing which shows the arrangement pattern (transmission order) of the transmission scanning line (transmission opening pair) of 2nd embodiment. (A) Explanatory drawing which shows receiving beam forming of 2nd embodiment, (b) Explanatory drawing which shows selection of the receiving signal after phasing addition of the same receiving focus, (c) Explanatory drawing which shows an aperture synthetic image. Explanatory drawing which shows another example of the arrangement pattern (transmission order) of the transmission scanning line (transmission opening pair) of 2nd embodiment. Explanatory drawing which shows another example of the arrangement pattern (transmission order) of the transmission scanning line (transmission opening pair) of 2nd embodiment. The block diagram which shows the structure which has arrange | positioned the storage part 124 which stored the arrangement pattern of the transmission scanning line in the ultrasonic imaging apparatus of 2nd embodiment. The block diagram which shows the structure which has arrange | positioned the decoding part 41 in the back | latter stage of the phasing addition part 22 in 2nd embodiment. Explanatory drawing which shows the structure which carries out aperture synthesis weighted to the received signal after decoding of 3rd embodiment. The block diagram which shows the structure of the opening synthetic | combination part 25 of 3rd embodiment. (A) Explanatory diagram showing receive beamforming of the third embodiment, (b) Explanatory diagram showing weighting after selection of received signals after phasing addition of the same reception focus, (c) Aperture composite image Illustration. (A) In 3rd embodiment, explanatory drawing which shows the waveform which added the several decoding reception signal as it is, (b) Explanatory drawing which shows the waveform added after weighting the several decoding reception signal. (A) Explanatory drawing which shows giving a weight to the receiving signal after the phasing addition of the receiving focus of the receiving scanning line for every receiving scanning line of 3rd embodiment, (b) Adjustment of the receiving focus given the weight. Explanatory drawing which shows carrying out aperture synthesis of the received signal after phase addition. Explanatory drawing which shows the structure of the opening synthetic | combination part 25 of 3rd embodiment. Explanatory drawing which shows the spatial encoding transmission by the orthogonal Golay code of 1st embodiment, and a decoding process. Explanatory drawing which shows another example of the arrangement pattern (transmission order) of the transmission scanning line (transmission opening pair) of 2nd 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 according to the first embodiment includes an ultrasonic probe 108, a transmission unit 102, a reception unit 105, and an aperture synthesis unit 25. The ultrasonic probe 108 has a plurality of transmission aperture groups 110 and 111 and one or more reception areas 109. A transmission aperture group (eg, 110) includes two or more transmission apertures 110A, 110B, and the like. The transmission aperture group (for example, 111) includes two or more transmission apertures 111A, 111B, and the like.

As shown in FIG. 2A, the transmission unit 102 transmits ultrasonically spatially encoded simultaneously from two or more transmission apertures (110A, 110B, etc.) included in a transmission aperture group (for example, 110). This operation is performed one round (one scan) or more in order for each of the transmission aperture groups 110, 111, and the like. Ultrasonic waves transmitted from two or more transmission apertures (110A, 110B, etc.) may be transmitted toward a predetermined position (transmission focal point) of the imaging target 120, or transmitted in different directions. Good. At this time, the ultrasonic wave may be transmitted in focus or defocused. In the case of focus transmission, the transmission focus may be different for each transmission aperture group (110, 111, etc.) or may overlap.

The reception area 109 receives an ultrasonic echo from the imaging target 120 and outputs an electrical signal. The receiving unit 105 performs a decoding process and a phasing process on the output of the reception area, and a desired reception focus (for example, 52) to be imaged as illustrated in FIG. The received signal is obtained.

The transmission unit 102 transmits the spatial encoding code of the ultrasonic wave transmitted by some of the transmission aperture groups (eg, 111) out of the plurality of transmission aperture groups (110, 111, etc.) to another transmission aperture group (eg, 110). ) Is inverted with respect to the spatial encoding code of the ultrasonic wave transmitted. As a result, when body motion occurs in the imaging target 120, unnecessary signals 18-1b and 18-2b generated in the reception signals 18-1 and 18-2 in the decoding process of the decoding unit 41 as shown in FIG. The phase is inverted for two transmission aperture groups (110, 111) having different spatial encoding at the time of transmission. On the other hand, the phases of the original reception signals 18-1a and 18-2a from the reception focal point 52 are not inverted.

The aperture synthesizing unit 25 is obtained for a desired reception focal point 52 obtained by the receiving unit 105 from echoes generated by ultrasonic waves transmitted from one transmission aperture group 110 among two or more transmission aperture groups (110, 111, etc.). The reception signal 18-1 and the reception signal 18-2 for the same reception focal point 52 obtained by the reception unit 105 from the echo generated by the ultrasonic wave transmitted from another transmission aperture group 111 are added. Among some of the plurality of transmission aperture groups (110, 111, etc.), some of the transmission aperture groups (for example, 110) have spatial encoding codes inverted with respect to the other transmission aperture groups (111). As described above, the unnecessary signals 18-1b and 18-2b generated by the body movement of the imaging target 120 can be canceled and reduced by the addition process. Further, the original reception signals 18-1a and 18-2a from the reception focal point 52 can be added and strengthened.

Therefore, the ultrasonic imaging apparatus according to the present embodiment, when performing spatially encoded transmission / reception, causes artifacts in an image due to unnecessary signals 18-1b and 18-1b even when movement occurs in the imaging target. Can be suppressed.

Note that a known method can be used as the spatial encoding method by the transmission unit 102. For example, Hadamard spatial coding, spatial coding using orthogonal Golay codes, or the like can be used.

Next, the principle of spatial encoding and decoding processing will be described below.

(Principle of spatial encoding and decoding)
The principle of ultrasonic imaging will be described in which spatial coding is used to simultaneously transmit to a plurality of regions and distinguish and separate the echo signal from which region.

Spatial encoding is an imaging technique that uses spatially encoded transmission events. By using an inverse matrix of a matrix used for encoding, signals transmitted simultaneously in a plurality of directions can be separated as received signals when transmitted independently. For example, a 2-by-2 Hadamard matrix shown in Equation (1) can be used as an encoding matrix.

The inverse of the matrix of equation (1) is a scaled matrix H ⁻¹ = 1 / 4H. By using this matrix, it is possible to easily perform generation of a spatially encoded transmission signal and decoding of a reception signal. For example, when the transmission signals of the transmission apertures 110A and 110B of the transmission aperture group 110 are spatially encoded, the transmission apertures 110A and 110B are used in the first round transmission (first scan) by using the matrix row vector [1 1]. Each encodes a transmission waveform to be transmitted. Thereby, the sound wave waveform of the same phase is simultaneously transmitted from the transmission openings 110A and 110B. That is, assuming that the waveform 71 of FIG. 4 is a reference waveform, the waveform 71 is used to transmit from the transmission apertures 110A and 110B. In the second round transmission (second scan), the transmission vectors transmitted by the transmission apertures A and B are encoded using the row vector [1 −1]. That is, the sign of one of the transmission apertures 110A and 110B is set to the opposite phase with respect to the other transmission waveform, and transmission is performed in the same two directions as those transmitted in the first round transmission (first scan). The waveform 72 shown in FIG. 4 is used as the antiphase waveform.

When the reception signal obtained for each transmission is Rx = [y1 y2] ^t , the reception signal x1 for one transmission aperture (110A) and the reception signal x2 for the other transmission aperture (110B) Can be obtained by the decoding operation.

Note that scaling of the inverse matrix was ignored here.

Therefore, when the received signals y1 and y2 received in each transmission event are added at the same time, the received signal x1 can be extracted. On the other hand, when subtracted, the received signal x2 can be extracted. The calculation process of this received signal is a decoding process.

This concept of spatial coding will be further explained with reference to FIG. The ultrasonic waves are transmitted twice from the two transmission openings 110A and 110B by performing the above-described encoding. The echo is generated from the point scatterer 11 of the imaging target 120. Two transmissions (the first transmission Tx1, the second transmission Tx) subjected to the above encoding are performed. The reception area (channel) 109 receives reception signals R1 and R2 for each transmission event. The reception signal 18a included in each of the reception signals R1 and R2 is an echo signal due to transmission through the transmission aperture 110A, and the reception signal 18b is an echo signal due to transmission through the transmission aperture 110B. Therefore, when the received signals R1 and R2 are added by the adder 14, the received signal 18b transmitted by the transmission aperture 110B is canceled, and only the received signal 18a transmitted by the transmission aperture 110A remains. When the received signals R1 and R2 are subtracted by the subtractor 15, the received signal 18a transmitted by the transmission aperture 110A is canceled, and only the received signal 18b transmitted by the transmission aperture 110B remains. Therefore, a reception signal in a state where echoes due to simultaneous transmission from the two transmission openings 110A and 110B are mixed can be separated as a reception signal when each transmission is performed independently.

Here, in the above decoding process, if the body movement of the imaging target 120 occurs between two transmissions or the ultrasonic probe 108 moves relative to the imaging target 120, the propagation distance of the echo in each transmission changes. To do. As a result, the received signals are shifted from each other in time. For example, FIG. 6 illustrates 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. In this case, undeleted unnecessary signals 18b and 18a are generated in the received signals H _A 1 and H _B 1 after decoding.

(Principle of unnecessary signal suppression)
In the present embodiment, as shown in FIG. 3 and FIGS. 7A and 7B, reception of the reception focus 52 corresponding to transmission of one transmission aperture group 110 out of a plurality of transmission aperture groups 110, 111, etc. The signal 18-1 and the reception signal 18-2 for the reception focal point 52 corresponding to the transmission in which the sign of the spatial encoding of the other transmission aperture group 111 is inverted are added. Thereby, as shown in FIG. 3, unnecessary signals 18-1b and 18-2b generated by the body movement of the imaging target 120 are canceled and reduced, and at the same time, the original received signals 18-1a and 18- Add 2a and strengthen.

As shown in FIG. 7 (a), the spatial encoding code is [1 1] in the first transmission Tx1 and [1 -1] in the second transmission Tx2. Refers to that. The spatial coding obtained by inverting the spatial coding code refers to a code in which [1 1] and [1 -1] are interchanged. In the first transmission Tx1 as shown in FIG. [1-1], indicating that it is [1 1] in the second transmission Tx2. Inversion of the spatial coding code can also be performed by changing the coding order from [1 1] to [1 -1] from [1 -1] to [1 1]. equal.

The principle of suppressing unnecessary signals will be further explained using mathematical expressions. As shown in FIG. 7 from the transmission aperture group 110, the received signals R1 and R2 received by the channel 109 after two spatially encoded transmissions are complex numbers exp (jωt) using arbitrary frequencies ω. Is expressed as the following expression (3). According to the above equation (2), these received signals R1 and R2 are added by the adder 14, and the decoded received signal H1 (18-1) obtained by decoding the one transmission aperture (110A) is expressed by the following equation ( 3).

Here, a and b are arbitrary coefficients.

In the decoded received signal H1 (18-1) after the expression (3), the original received signal 18-1a corresponding to the transmission aperture 110A is the first term of the expression (3), and the undesired unnecessary signal 18- 1b is the second term (see FIG. 7A).

On the other hand, from the transmission aperture group 111 different from the transmission aperture group 110, the received signals R1 and R2 when the transmission is performed twice by reversing the spatial encoding code from the two transmissions of the transmission aperture group 110, respectively. The decoded received signal H1 ⁻ (18-2) obtained by adding these signals is expressed by the following equation (4).

Wherein decoded received signal (4) H1 ^- in (18-2), the original received signal 18-2a corresponding to the transmission opening 110A is the first term of the equation (4), canceling the remaining unwanted signal 18 -2b is the second term (see FIG. 7B).

From the equations (3) and (4), the original received signals 18-1a and 18-2a obtained by transmitting from the different transmission aperture groups 110 and 111 are in-phase waveforms, while unnecessary signals are obtained. 18-1b and 18-2b have phases inverted from each other. Therefore, if the decoded received signals H1 and H1 ⁻ obtained by two transmissions of different transmission aperture groups 110 and 111 are added, unnecessary components cancel each other, and only necessary components can be left.

It should be noted that the reception signal for two transmissions performed by changing the order of the spatial encoding (inverting the spatial encoding code) from the transmission aperture group 111 to the transmission aperture group 110 described above is Rx = [y1 y2 ] ^t , the decoding process for obtaining the received signal x1 for one transmission aperture (111A) and the received signal x2 for the other transmission aperture (111B) can be expressed by equation (5) (see equation (2)) ).

As described above, when the transmission is performed twice while changing the order of the codes of the spatial coding, the reception signals R2 and R1 are added by the adder 14 when the reception signals R1 and R2 for the two transmissions are used. As a result, only the reception signal 13a transmitted by the transmission aperture 111A remains. When the received signals R2 and R1 are subtracted by the subtractor 15, only the received signal 13b transmitted by the transmission aperture 111B remains.

In the spatial coding using orthogonal Golay codes, unnecessary components cancel each other out, and only necessary components can be left. Spatial coding using orthogonal Golay codes uses a matrix represented by the following equation (6).

Here, X1 and X2 are Golay codes that are complementary pairs, and Y1 and Y2 are Golay codes that are different types of complementary pairs. 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, and a Golay code having an orthogonal combination of Golay codes having such a relationship Call. For example, there are combinations of Golay codes of X1 = [1 1] and X2 = [1 −1], Y1 = [− 1 1] and Y2 = [− 1 −1].

When spatial coding by this Golay code is used, the decoding process is as shown in the following equation (7). In Equation (7), let R1 and R2 be the received signals obtained in each transmission event in the spatially coded transmission using the Golay code.

By this calculation, the echo from the transmission direction using the Golay code X and the echo from the transmission direction using the Golay code Y are separated. FIG. 27 shows spatial encoding transmission and decoding processing when orthogonal Golay codes are used. R1 is input to a correlation processing unit 54-1 that performs cross-correlation processing with X1 and a correlation processing unit 55-1 that performs cross-correlation processing with Y1. R2 is input to a correlation processing unit 54-2 that performs cross-correlation processing with X2 and a correlation processing unit 55-2 that performs cross-correlation processing with Y2. Addition processing 56 is obtained, respectively, and decoded reception signals H _A 1 and H _B 1 are obtained.

In this decoding process, when body motion occurs and each received signal is in a time-shifted state, there remains a cancellation of the time side lobe generated by the autocorrelation function of the Golay code, which is the same as the unnecessary component generated by Hadamard space coding In addition, it becomes an unnecessary component that causes artifacts. Similar to the unnecessary component cancellation method using Hadamard space coding shown in FIG. 3, the Golay code also corresponds to the transmission of one transmission aperture group 110 out of a plurality of transmission aperture groups 110, 111, etc. The reception signal 18-1 for the reception focal point 52 and the reception signal 18-2 for the reception focal point 52 corresponding to the transmission in which the spatial encoding of the other transmission aperture group 111 is inverted are added. As a result, the unnecessary signals 18-1b and 18-2b generated by the body movement can be canceled and reduced, and at the same time, the original received signals 18-1a and 18-2a from the reception focal point 52 can be added and strengthened.

In the case of spatial coding using orthogonal Golay codes, only the decoding process is different, and the other forms are the same as those using Hadamard spatial coding. In the following, description will be made using Hadamard space coding.

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

The basic configuration of the ultrasonic imaging apparatus of the second embodiment is the same as that of the apparatus of the first embodiment, but in the second embodiment, there are two transmission aperture groups (110, 111, etc.), respectively. Includes transmission apertures (eg, 110A, 110B). Therefore, in the following description, the transmission aperture group is referred to as a transmission aperture pair. The transmission unit 102 transmits ultrasonic waves in order for every two or more transmission aperture pairs (110, 111, etc.). At this time, the order of the spatial encoding codes is reversed alternately.

In addition, the transmission unit 102 repeatedly performs an operation of sequentially transmitting each transmission aperture pair (110, 111, etc.) two or more times. In the second transmission, a plurality of transmission aperture pairs (110, 111, etc.) are transmitted. Each spatial encoding code is set to a code different from the first round. The decoding unit 41 of the reception unit 105 performs a decoding process using the output of the transmission area pair (for example, 110) from the first round transmission and the output from the second round transmission in the reception area 109.

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

<Overall configuration of device>
The overall configuration of the ultrasonic imaging apparatus 100 according to the second embodiment will be described in detail. FIG. 8 is a block diagram showing a schematic configuration of a specific example of the ultrasonic imaging apparatus 100 of the present embodiment. In FIG. 8, the same components as those of the first embodiment shown in FIG. The ultrasonic imaging apparatus 100 includes an ultrasonic probe 108, a transmission unit 102, a reception unit 105, and an aperture synthesis unit 25. In addition to these, a control unit 106, a user interface (UI) 121, a transmission / reception switching unit 101, an image processing unit 107, and a display unit 122 are provided. The UI 121 is an interface that receives 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.

The plurality of arranged transducers are virtually or physically divided into a plurality of (P) channels 109 ₁ to 109 _P determined in advance as shown in FIG. Each channel 109 ₁ to 109 _P is composed of one or more transducers. Transmission apertures 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 a plurality of adjacent channels (four in FIG. 9) are used as one transmission aperture 110A will be described. The transmission aperture 110A and the transmission aperture 110B that constitute each of the transmission aperture pairs 110 will be described below as an example where they are separated from each other on the ultrasonic probe 108 by a predetermined distance. Good. The same applies to the other transmission aperture pairs 111, 112, 113, and 114. Moreover, you may form so that all the transmission aperture pairs may overlap.

In the following description, each of the channels 109 ₁ to 109 _P is used as the reception area 109. Of course, it is possible to use two or more channels as one reception area 109.

The transmission unit 102 selects a predetermined transmission aperture pair (for example, 110) of the ultrasonic probe 108 in accordance with an instruction from the control unit 106, and transmits the transmission to the transmission apertures 110A and 110B of the selected transmission aperture pair 110. Generate a signal. Specifically, the waveform type, delay time for each of the transmission apertures 110A and 110B, amplitude modulation, weighting, and the like are determined, and a transmission signal corresponding to the delay time is generated. At this time, the transmission signal is spatially encoded with the Hadamard spatial code described later.

The transmission unit 102 passes the generated transmission signals to the transducers of the channels constituting the transmission apertures 110A and 110B, respectively, and causes the transmission apertures 110A and 110B to simultaneously transmit ultrasonic waves spatially encoded with Hadamard spatial codes in different directions. . This operation is sequentially executed by all of the plurality of transmission aperture pairs 110 to 113 and the like. The ultrasonic wave may be transmitted in focus or defocused. In the case of focus transmission, the transmission focus for each of the transmission aperture pairs 110 to 113 may be different. The transmitter 102 inverts Hadamard's spatial code alternately when transmitting ultrasonic waves in order to the transmission aperture pairs 110 to 113 and the like. Repeat this two or more times. However, in the second round, the transmission aperture pairs 110 to 113 and the like are reversed so that the spatial coding is different from the first round.

By repeating the transmission two or more times in this way, the Hadamard spatial code can be decoded by combining the received signal obtained by the first round transmission and the received signal obtained by the second round transmission. In the case of focus transmission, the transmission focus for each of the transmission aperture pairs 110 to 113 is the same in at least the first and second round transmissions.

An echo is generated in the imaging target 120 by the ultrasonic waves sequentially transmitted to the imaging target 120 from the transmission aperture pairs 110 to 113 and the like. The echo is received by the reception area (channel) 109 of the ultrasonic probe 108. As channels used for reception, all the channels 109 ₁ ... 109 _P of the ultrasonic probe 108 may be used, or only channels within a predetermined reception opening (active channel) 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 indicates a certain transmission aperture pair. The received signal obtained by the first round transmission (hereinafter also referred to as the first scan) is transferred to the receiving unit 105.

As shown in FIG. 10, the receiving unit 105 includes a channel signal processing unit 20 including a first storage unit (hereinafter referred to as a channel memory) 40 and a decoding unit 41 that decodes a Hadamard spatial code as a channel 109 _1. It is provided for every 109 _P. The receiving unit 105 includes the phasing / adding unit 22 and the second storage unit 24 described above.

As shown in FIG. 11, the channel memory 40 includes two storage areas 40-1 and 40-2 for each of the transmission aperture pairs 110 to 113. Control unit 106 transmits the opening 110A of the transmission aperture pairs 110, the received signal R ₁ 1 to channel 109 ₁ is obtained by transmission from 110B, transmission opening 110A, it is stored in the storage area 40-1 for 110B. Similarly, the control unit 106 determines that the other channels 109 ₂ ... 109 _P are received signals R ₂ 1... R _P 1 obtained by transmission from the transmission apertures 110A and 110B of the transmission aperture pair 110, respectively. The data is stored in the storage area 40-1 for the transmission aperture 110 of the channel memory 40 connected to each channel.

Thereafter, the control unit 106, each time to be transmitted sequentially from the transmitting pair of openings 111-113, etc., channel _{109 1,} 109 2 ... 109 received signal R ₁ 1 _{where P} is obtained, respectively, R ₂ 1 ... R _P 1 is stored in the storage area 40-1 for the corresponding transmission aperture pair in the channel memory 40 connected to each channel.

Next, the control unit 106 causes the transmission unit 102 to perform the second round transmission (second scan) in order from the transmission aperture pairs 110 to 113, and the obtained channels 109 ₁ , 109 ₂ ... 109 _P Received signals R ₁ 2, R ₂ 2..R _P 2 are sequentially stored in the corresponding storage areas 40-2 in the channel memory 40 connected to the respective channels.

The decoding unit 41 includes an adder 14, a subtractor 15, a transfer unit 16, and first and second receiving units 17-1 and 17-2 for decoding the Hadamard space code. When the second round of transmission (second scan) is completed, under the control of the control unit 106, the decoding unit 41 receives the received signal R ₁ 1 from the storage areas 40-1 and 40-2 for the transmission aperture pair 110. , R ₁ 2 are read out and input to the transfer unit 16 in the decoding unit 41. In the case of a received signal obtained by transmission in which the order of the spatial encoding codes is not reversed, the control unit 106 receives the received signal R ₁ 1 as the first receiving unit 17-1 of the decoding unit 41. And the received signal R ₁ 2 is input to the second receiving unit 17-2. On the other hand, in the case of a received signal obtained by transmission in which the order of codes of spatial coding is reversed, the received signal R ₁ 1 is input to the second receiving unit 17-2 and the received signal R ₁ 2 is received first. Input to section 17-1. As shown in FIG. 11, the control unit 106 inputs the signals of the first receiving unit 17-1 and the second receiving unit 17-2 to the adder 14 and the subtracter 15, respectively. When the reception signal is input from the storage areas 40-1 and 40-2 for the transmission aperture pair 110 described above, the reception signal obtained by the transmission from the transmission aperture 110A by the addition process of the adder 14 ( Hereinafter, it is referred to as a received signal after decoding. H _1A 1 (The subscript number indicates the channel number, the subscript A indicates the decoded received signal corresponding to the transmission aperture 110A, and the half-width 1 is Indicating the first received signal after decoding). Received signal H _1B 1 after decoding obtained by transmission from the transmission aperture 110B by subtraction processing by the subtractor 15 (the subscript number indicates the channel number, and the subscript B indicates the decoding corresponding to the transmission aperture 110B) It indicates that the received signal is a post-received signal, and the half-width 1 indicates that it is the first received signal 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.

The phasing / adding unit 22 focuses the decoded reception signals H _1A 1, H _2A 1, H _3A 1... Corresponding to the transmission aperture 110A output from each channel signal processing unit 20 on a predetermined reception focus. Delay time is given, and the summing process is performed (receive beam forming). Thus, decoded signals H _1A, H _2A, the received signal is phased and added to H _3A ··· Hsum _A (sum indicates that a post-delay-and-sum, the A subscript, the transmission apertures 110A Indicating the corresponding received signal).

At this time, the phasing adder 22 performs parallel beam forming, and as shown in FIG. 12, the ultrasonic irradiation region of the transmission aperture 110A is M-numbered at a predetermined spread angle centered on the transmission aperture 110A. Reception scanning lines (beams # 1 to #M) are set, and G reception focal points 31-1 to 31-G are set on the respective reception scanning lines at predetermined intervals. In order to focus the reception signals H _1A 1, H _2A 1, H _3A 1... After decoding for each reception focus, delay curves 32a, 32b, 34a, 34b, etc. according to the position of the reception focus are provided. Set the corresponding delay time and obtain the received signal Hsum _A after phasing addition. That is, the phasing addition unit 22 receives the signals after the phasing addition for G × M reception focal points from the decoded reception signals H _1A 1, H _2A 1, H _3A 1... Corresponding to the transmission aperture 110A. Each signal Hsum _A is obtained. Thereby, the delay phasing data of the reception focus of the sector area 35-110A where the plurality of reception scanning lines of FIG. 12 are arranged can be generated. That is, an image of the sector area 35-110A (that is, a set of reception focal points) is generated by the decoded reception signal for the transmission aperture 110A.

Note that the number of reception scanning lines can be about 2 to 8 with the central axis of the transmission beam of the transmission aperture 110A as the center of the ultrasonic wave, or within the directivity angle 30 (eg, 90 °) of the transmission aperture 110A. In addition, a large number of reception scanning lines such as 32 lines, 64 lines, 128 lines, etc. can be generated in parallel.

FIG. 12 shows an example in which the delay time curves 32a, 32b, 34a, and 34b are obtained by the delay method in which the center of the transmission aperture 110A is set to time zero, but the delay method in which the transmission focal point position is set to time zero. Of course, the (virtual sound source method) can also be used.

The shape of the aggregate of reception beams may be a fan shape or a reception beam shape in which the beam direction is selected in the normal vector direction of the surface layer surface of the channel 109 in the probe 108. Further, it may be an aggregate of arbitrary plural beams that cover the range of the transmission beam to be transmitted. In FIG. 12, the probe 108 has a linear shape arranged on a straight line, but may have a convex shape with a curved element arrangement. Further, the transmission beam scanning method may be a sector type.

Similarly, the phasing addition unit 22 performs phasing addition on the decoded signals H _1B , H _2B , H _3B ... Corresponding to transmission from the transmission aperture 110B output from each channel signal processing unit 20. Get Hsum _B. At this time, the phasing addition unit 22 performs parallel beam forming, and M reception scanning lines (beam # 1) with a predetermined spread angle centered on the transmission aperture 110A in the ultrasonic irradiation region of the transmission aperture 110B. To #M) and G reception focal points 31-1 to 31-G are set on the respective reception scanning lines at predetermined intervals. For each reception focus, delay times 32a, 32b, 34a, 34b, etc. for setting the focus of the decoded received signals H _1B 1, H _2B 1, H _3B 1. Receive signal Hsum _B is obtained. That is, the phasing addition unit 22 receives the signals after phasing addition for G × M reception focal points from the decoded reception signals H _1B 1, H _2B 1, H _3B 1... Corresponding to the transmission aperture 110B. Each of the signals Hsum _B is obtained. As a result, an image of the sector area 35-110B is formed as shown in FIG.

The second storage unit 24 of FIG. 10 includes a storage area for storing the reception signal Hsum after the phasing addition of G × M reception focal points as shown in FIG. 13 for each transmission aperture of the transmission aperture pair. ing. The phasing addition unit 22 stores the reception signal Hsum _A after phasing addition of the G × M reception focal points obtained for the transmission aperture 110A in the storage area 24A for the transmission aperture pair 110 in FIG. Further, the reception signal Hsum _B after the phasing addition for the G × M reception focal points obtained for the transmission aperture 110B is stored in the storage area 24B for the transmission aperture 110B in FIG.

Similarly, for the transmission aperture pairs 111 to 113, the phasing addition unit 22 receives the decoded received signals H _1A 1, H _2A 1, H _3A 1 for one transmission aperture output from each channel signal processing unit 20. From the received signal Hsum _A after phasing addition for G × M reception focal points. Similarly, for the other transmission aperture, a reception signal Hsum _B after phasing addition for G × M reception focal points is obtained. Then, the received signals Hsum _A and Hsum _B after the phasing addition are stored in the storage areas 24A and 24B for each of the transmission aperture pairs 111 to 113 in the second storage unit 24, for example.

Since the transmission aperture pairs 111 to 113 are at positions slightly shifted from each other on the ultrasonic probe 108, the irradiation area is partially different between different transmission aperture pairs 110 to 113 as shown in FIG. The fan-shaped region 35 (collection of reception focal points) shown in FIG. 2B also partially overlaps with different transmission aperture pairs 110 to 113. For this reason, a part of the reception focus of the sector areas 35-110A, B of a certain transmission aperture pair 110 coincides with the reception focus of the sector areas 35-111A, B of the adjacent transmission aperture pair 111 and the like. The aperture synthesis unit 25 uses the reception signal Hsum after the phasing addition of the reception focal points (for example, 52-1 and 52-2 in FIG. 3) at the same position to all the storage areas 24A and 24B of the second storage unit 24. Is read out and added (synthesized).

In this embodiment, since the spatial encoding codes at the time of transmission of the plurality of transmission aperture pairs 111 to 113 are alternately inverted, unnecessary signals included in the received signal after decoding due to the body movement of the imaging target 120 Are reversed for each transmission aperture pair. Therefore, the aperture synthesis unit 25 synthesizes the reception signal after phasing addition between different transmission aperture pairs, so that it is included in the reception signal after decoding due to the body movement of the imaging target 120 as shown in FIG. The unnecessary signals 18-1b and 18-2b generated can be canceled and reduced, and artifacts caused by body movement can be suppressed.

The ultrasonic imaging apparatus 100 according to the present embodiment can output images of the imaging target 120 continuously by performing two or more rounds of transmission (scanning) using a plurality of transmission aperture pairs 110 to 113 and the like. This operation will be described below with reference to FIGS.

In the following description, transmission is performed in order using four transmission aperture pairs 110 to 113. Transmission from the transmission aperture pair is referred to as a transmission scanning line, and transmission from the transmission aperture pairs 110, 111, 112, and 113 is referred to as transmission scanning line k = 1, 2, 3, 4, respectively. In addition, the spatial coding of the row vector [1 1] in Equation (1) for transmitting signals of the same phase from the two transmission apertures of the transmission aperture pair is the first spatial encoding, and the signals having opposite phases are transmitted. The spatial encoding of the row vector [1−1] to be called is the second spatial encoding. Further, transmission in order from the transmission aperture pairs 110 to 113 is referred to as scanning, and transmission in the nth cycle (nth scan) is referred to as scan number n.

As shown in the flow of FIG. 14, the control unit 106 sequentially transmits the transmission aperture pairs 110 to 113 in the first transmission (scan n = 1) (steps 141 to 148). At this time, the code of spatial encoding is alternately inverted for each transmission aperture pair.

Specifically, first, the control unit 106 selects the transmission scanning line k = 1 (transmission aperture pair 110) (step 142), and determines whether the scan number n is an odd number (step 143). Since the scan number n is 1 (transmission in the first round), it is an odd number, and the process proceeds to step 144. Then, it is determined whether or not the transmission scanning line k (= 1) is an odd number (step 144). Since the transmission scanning line k = 1 is an odd number, transmission by the first spatial encoding is performed by the transmission aperture pair 110 (step). 145) (see k = 1 in FIG. 15). The control unit 106 stores the received signal obtained for each channel 109 in the storage area 40-1 for the transmission aperture pair 110 of the channel memory 40 of FIG. 11 connected to each channel 109 (step 146).

Next, the control unit 106 increments the transmission scanning line number k to k = 2 (step 156), returns to step 142, selects the transmission aperture pair 111 of the transmission scanning line k = 2, and k = 2 Since it is an even number (step 144), the transmission aperture pair 111 is caused to transmit by the second spatial encoding (step 147) (see k = 2 in FIG. 15). The control unit 106 stores the received signal obtained for each channel 109 in the storage area 40-1 for the transmission aperture pair 111 of the channel memory 40 of FIG. 11 connected to each channel 109 (step 148).

Similarly, for the transmission scanning line k = 3 (transmission aperture pair 112), the first spatially encoded transmission is performed, and for k = 4 (transmission aperture pair 113), the second spatially encoded transmission is performed, They are stored in the storage areas 40-1 for the transmission aperture pairs 112 and 113, respectively.

Thus, k = K (K = 4) in step 155 is reached, and the scan number n = 1 (transmission in the first round) is completed (step 155). As a result, the reception signal is stored in the storage area 40-1 for all the transmission aperture pairs 110 to 113. However, when the scan number n = 1, the received signal is not yet stored in the storage area 40-2, so that the decoding process cannot be performed. Therefore, the scan number n is incremented to 2 (step 158), and the process returns to step 142.

Scan number n = 2 (transmission in the second round) is performed by replacing the spatial encoding code with n = 1. Specifically, since n is an even number in Steps 143 and 149, the control unit 106 proceeds to Step 150. For the transmission aperture pairs 111 and 113 in which the transmission scanning line k is an odd number (k = 1, 3), Two-space-encoded transmission is performed (step 151) (see transmission scanning line k = 1, 3 with scan number n = 2 in FIG. 15). The control unit 106 stores the received signal obtained for each channel 109 in the storage area 40-2 for the transmission aperture pairs 110 and 112 of the channel memory 40 of FIG. 11 connected to each channel 109 (step 152). . Further, the control unit 106 performs the first spatial encoding for the transmission aperture pairs 110 and 112 whose transmission scanning line k is an even number (k = 2, 4) (step 153) (scan number n in FIG. 15). = 2 transmission scan lines k = 2, see 4). The control unit 106 stores the received signal obtained for each channel 109 in the storage area 40-2 for the transmission aperture pairs 111 and 113 of the channel memory 40 of FIG. 11 connected to each channel 109 (step 154). .

As described above, k = K (K = 4) in step 155 in the scan number n = 2 is reached, and the scan number n = 2 (transmission in the second round) is completed. The reception signal is stored in the storage area 40-2 for all the transmission aperture pairs 110 to 113. As a result, since the received signals are stored in the storage areas 40-1 and 40-2 of all the transmission aperture pairs 110 to 113, decoding processing becomes possible. Therefore, the process proceeds to step 159 in step 157 and the decoding process is performed.

In step 159, the control unit 106 selects the transmission aperture pair 110, and passes the reception signal stored in the storage areas 40-1 and 40-2 for the transmission aperture pair 110 to the decoding unit 41. The decoding unit 41 generates decoded reception signals H _A and H _B (steps 160 and 161). Further, the decoded reception signals H _A and H _B are phased and added by the phase adjusting and adding unit 22 by parallel beam forming, respectively (step 162). As a result, fan-shaped areas 35-110A and 35-110B are set for the two transmission apertures as shown in FIGS. 2B and 16A, respectively, and predetermined M reception scanning lines (beam # About 1 ~ # M) each G number of receive focal point 31-1 ~ 31-G on, obtaining the reception signal H _SumA after phasing addition, the H _sumB. Control unit 106, resulting Sector Region 35-110A, after phasing addition of 35-110B received signal H _SumA, the H _sumB, storage area 24A for transmission aperture pairs 110 of the second storage unit 24 of FIG. 13 , 24B (step 163).

For all of the transmission of the above steps 159 to 163 pair of openings 111-113, phasing addition received signals H _SumA of G × M pieces of receive focal point of each sector area, with the H _sumB, each transmission pair of openings 111-113 The process is repeated until it is stored in the storage areas 24A and 24B (step 164).

For one position among a plurality of predetermined positions M, the control unit 106 receives the received signal after phasing addition of the reception focus at the same coordinates as that position, as shown in FIG. Reading is performed from the storage areas 24A and 24B for the transmission aperture pairs 110 to 113 (step 165). As shown in FIGS. 2 (c) and 16 (c), the aperture synthesizing unit 25 synthesizes by adding a plurality of readout signals after phasing addition of the same coordinates, and stores the storage unit 34 in FIG. (Steps 167 and 168). Steps 165 to 168 are repeated until completion for all positions M (step 169). If the synthesis has been completed for all positions M, the image processing unit 107 constructs an image by arranging the post-composition phasing addition received signals stored in the storage unit 34 for each position (step 170). ). The constructed image is displayed on the display unit 122.

Thereafter, the control unit 106 returns to Step 158, increments the scan number n, and performs scan number n = 3 (transmission in the third round). In the third transmission, the control unit 106 stores the received signal in the storage areas 40-1 and 40-2 in steps 146 and 148. Therefore, in step 157, by proceeding to steps 159 to 170, the received signal obtained with scan number n = 3 (transmission in the third round) stored in the storage area 40-1 and the storage area 40-2 are stored. An image can be constructed by performing a decoding process using the received signal obtained with the stored scan number n = 2 (transmission in the second round) to obtain a decoded received signal. Thereby, after the scan number n = 2, an image of the imaging target 120 can be constructed and displayed sequentially for each scan.

In this manner, in steps 165 to 169, the received signals after phasing addition obtained by a plurality of transmissions having different spatial encoding codes can be added by synthesizing the received signals after phasing addition at the same position. it can. Therefore, unnecessary signals 18-1b and 18-2b caused by body movement of the imaging target 120 can be canceled and suppressed, and artifacts are suppressed in the image constructed at step 170.

Note that in steps 141 to 157 in FIG. 14, the control unit 106 transmits the first spatial coding when the scanning number k is an odd number and the transmission scanning line k is an odd number and the second spatial code when the scanning number n is an even number. When the scan number n is an even number, the transmission scan line k is an even number and the first spatial encoding transmission is performed. When the scan number n is an even number, the second spatial encoding transmission is performed. However, the first spatial encoding and the second spatial encoding can be interchanged.

Also, the overlapping state of the fan-shaped regions 35 for each of the transmission aperture pairs 110 to 113 differs depending on the position of the reception focus. For this reason, the number of received signals after phasing addition selected in step 165 differs depending on the position of the reception focal point, but may be combined while remaining different. It is also possible to perform processing for correcting the intensity of the signals 18-1a, 18-2a and the like that should be received according to the number of received signals after phasing addition to be combined.

Here, the principle that the unnecessary signal is suppressed by synthesizing the reception signal after phasing addition in step 167 will be further described using mathematical expressions. The received signal (echo) obtained at the time of transmission scan line number k = 1 of scan number n = 2 in FIG. 15 (assumed to be transmission number K + 1) is the transmission scan line number k = 1 of scan number n = 1. It is assumed that the appearance time is shifted by ΔT with respect to transmission 1 (transmission number 1). In this case, when the scan number n = 2, the signal H1 obtained for the transmission aperture 110A in the decoding process (addition process) in step 161 is as expressed by the above-described equation (3). This signal is a signal at the reception focal point 52-1 in FIG.

On the other hand, the signal at the reception focal point 52-2 of the transmission aperture 111A is transmitted at the time of the transmission scanning line number k = 2 with the scan number n = 1 (transmission number 2) and the transmission scanning with the scan number n = 1. It is generated by a received signal (echo) obtained by transmission at the time of line number k = 2 (transmission number K + 2). For this reason, if the body movement is uniform while the scan is repeated, the time shift due to the body movement occurring between transmissions of transmission number 1 and transmission number 2 is simply expressed as Δτ = ΔT / K. . In addition, the appearance times of the reception signals transmitted by the transmission number 2 and the transmission number K + 2 are shifted by ΔT. Therefore, the signal H2 obtained for the transmission aperture 111A in the decoding process (addition process) by echo in the transmission of the transmission number 2 and the transmission number K + 2 is expressed by the following equation (8) using the above equation (4). Can be expressed as: This signal corresponds to the signal at the reception focal point 52-2 in FIG.

K is the number of transmission scanning lines (transmission aperture pairs). Considering the size of a general probe 108, the number of transmission scanning lines (transmission aperture pairs) of the ultrasonic diagnostic apparatus is 100 or more. become. Therefore, Δτ is sufficiently small with respect to ΔT and can be regarded as almost zero. Therefore, the signal H2 of receive focal point 52-2 of the formula (8), signals H1 of the formula (4) ^- is almost equivalent to. When the signals of the reception focal point 52-1 and the focal point 52-2 are added by aperture synthesis processing, unnecessary signals corresponding to the second item of the equations (3) and (4) cancel each other, and an image in which artifacts are suppressed is generated. be able to.

In the example shown in FIG. 15, the control unit 106 sets the transmission aperture 110A of the transmission aperture pair 110 at the end of the probe 108, sets the transmission aperture 110B at the center of the probe 108, and others. The transmission apertures of the transmission aperture pairs are set so as to be adjacent to each other sequentially. In this case, the A-side transmission aperture (transmission scanning line #aK) of the transmission aperture pair of the transmission scanning line k = K is adjacent to the transmission aperture 110B (transmission scanning line # b1). If the codes of the spatial encoding of ultrasonic waves transmitted from adjacent transmission apertures are different, unnecessary signals can be further reduced.

In addition, this embodiment is not limited to arrangement | positioning of the transmission aperture pair (transmission scanning line) of FIG. In the arrangement of FIG. 15, as described above, the scanning line #aK and the scanning line # b1 are adjacent to each other, and the adjacent position is the central portion of the probe 108. As described above, the time difference ΔT of the received signal due to the transmission of k = 1 and k = K is larger than the above-described Δτ, and the remainder of the cancellation of the unnecessary signal is less than the combination of other transmission scanning lines even if aperture synthesis is performed. Can also be large. Therefore, if the position where the scanning line #aK and the scanning line # b1 are adjacent to each other is in the center portion of the probe 108, there is a possibility that artifacts of unneeded unwanted signals appear near the center of the image. Therefore, in order to avoid artifacts at the center of the image, the arrangement of the transmission aperture pairs (transmission scanning lines) may be configured as follows.

For example, as shown in FIG. 17, a region where transmission scanning lines are continuously transmitted is positioned at the center of the probe 108. Specifically, the position of the transmission aperture 110 </ b> A with k = 1 is not the end of the probe 108, but a position shifted from the end. Specifically, as shown in FIG. 17, when the transmission aperture 110A with k = 1 is arranged at a position shifted by about ¼ of the length of the probe 108, adjacent scanning lines are arranged in the central region of the probe 110. Can be consecutive. Further, the transmission scanning lines may be arranged as shown in FIG.

In this embodiment, if the positions of the transmission apertures from which the two reception signals used for the decoding process are obtained are the same position, the transmission scanning lines do not have to be aligned in order along the probe 108. . That is, as long as the positions of the transmission areas of the transmission aperture A and the transmission aperture B are the same in each scan, the positions of the transmission scanning lines on the probe 108 may not be aligned. Therefore, as shown in FIG. 18, the transmission scanning line may be set at random.

The arrangement pattern of these transmission scanning lines (transmission aperture pairs) on the probe 108 may be appropriately selected by the control unit 106 according to the imaging conditions, or may be selected by the user. May be. For example, as shown in FIG. 19, a storage unit 124 storing a plurality of types of transmission scanning line arrangement patterns is arranged in the ultrasonic imaging apparatus 100, and the control unit 106 selects an appropriate pattern, or A selection from the user is accepted via the UI 121. This is performed in step 142 of the flowchart of FIG. The control unit 106 controls the operations of the transmission unit 102 and the reception unit 105 according to the selected pattern.

Note that, as shown in FIG. 10, the ultrasonic imaging apparatus of the present embodiment has a configuration in which the phasing addition unit 22 is arranged after the decoding unit 41 and performs the phasing addition process after the decoding process. The phasing addition process may be performed before the decoding process. In that case, since the decoding unit 41 may be arranged after the phasing addition unit 22, it is not necessary to arrange the decoding unit 41 for each reception channel 109, and the circuit scale of the reception unit 105 can be reduced. Note that the decoding unit 41 needs to use the received signal for each transmission received by each channel twice for decoding processing. Therefore, it is possible to adopt a configuration in which the phasing / adding unit 22 reads the data twice from the first storage unit (channel memory) 40 and delivers it to the decoding unit 41 after the phasing process. Alternatively, as shown in FIG. 20, a duplicator 21 is arranged for each channel 109 instead of the first storage unit 40, and the received signal of each channel obtained by one transmission event is transmitted by the duplicator 21. Two replicated signals R ₁ 1, R ₁ 1 '(subscript indicates channel number, dash indicates second read (or after replication) signal, 1 is first round It is also possible to output the received signal obtained by transmission (first transmission). The phasing addition unit performs phasing addition processing on the two signals R ₁ 1 and R ₁ 1 ′ separately. Further, the beam memory 23 is arranged after the phasing addition section 22, and the decoding section 41 is arranged at the subsequent stage.

Two identical received signals R ₁ 1 and R ₁ 1 ′ generated by the duplicator 21 are delivered to the phasing addition processing unit 22. The control unit 106 gives a delay time for focusing each point in the region on the transmission beam axis from the transmission aperture A to the reception signal R ₁ 1 of each channel to the phasing addition processing unit 22 to obtain R _sumA 1, The data is stored in the storage area 23A-1 of the beam memory 23. Similarly, the control unit 106 gives a delay time for focusing each point in the region on the transmission beam axis from the aperture B to the received signal R ₁ 1 ′ of each channel to the phasing addition processing unit 22, and R _sumB 1 Is stored in the storage area 23B-1 of the beam memory 23.

In the second round transmission (second transmission), the control unit 106 similarly _obtains R _sumA 2 and R _sumB 2 and stores them in the storage areas 23A-2 and 23B-2 of the beam memory 23, respectively.

The control unit 106 reads the received signals R _sumA 1 and R _sumA 2 from the storage areas 23A-1 and 23A-2 and inputs them to the adder 14 of the decoding unit 41. _Decoded received signal _HsumA after phasing by transmission from transmission aperture 110A by the addition process of adder 14 (sum indicates that after phasing addition, subscript A indicates the phasing corresponding to transmission aperture 110A. Indicating that it is a post-phase decoded received signal). In addition, the control unit 106 reads the received signals R _sumB 1 and R _sumB 2 from the storage areas 23B-1 and 23B-2 and inputs them to the subtracter 15 of the decoding unit 41. _Decoded received signal _HsumB after phasing by transmission from transmission aperture 110B by subtraction processing of subtractor 15 (sum indicates that it is after phasing addition, and subscript B indicates phasing corresponding to transmission aperture 110B. Indicating that it is a post-phase decoded received signal).

Received signal H _SumA and H _sumB each transmission aperture 110A after the phasing addition, a data reception focus with sector area 35 corresponding to 110B.
<Third embodiment>
An ultrasonic imaging apparatus according to the third embodiment will be described with reference to FIGS.

The third embodiment has the same configuration as the second embodiment, but the second embodiment is different from the second embodiment in that the aperture synthesis unit 25 weights and adds a plurality of post-phased reception signals for the same reception focus. Is different. Specifically, the aperture synthesizer 25 sets the weights of the plurality of reception signals for the same reception focus to be heavier as the reception signal is closer to the center of the time variation at which the plurality of reception signals are obtained.

As shown in FIG. 21, the received signals 18-1 to 18-K after phasing addition for the same reception focal points 52-1 to 52-K obtained by the transmission scanning lines (k = 1 to K) are as follows. The original received signals 18-1a to 18-Ka have the same phase, and the unnecessary signals 18-1b to 18-Kb have inverted phases alternately.

In the third embodiment, as shown in FIG. 21, the weighting unit 32 is arranged in the aperture synthesis unit 25. The weighting unit 32 weights the amplitudes of the reception signals 18-1 to 18-K and then adds them. It is desirable that the weighting units 32-1, 32-2,..., 32-K weight the reception signals 18-1 to 18-K generated in time series closer to the center time in the time series. . As a result, as shown in FIG. 21, it is possible to obtain an image after aperture synthesis in which the original received signal 119a is further strengthened and the unnecessary signal 119b is further suppressed.

A specific configuration will be described with reference to FIG. In this embodiment, a weight table storage unit 86 is arranged in the ultrasonic diagnostic apparatus 100 of the second embodiment as shown in FIG. The control unit 106 _obtains weight data (w (m, σ, k)) for the received signals 18-1 to 18-K (H _sumA (m, σ, k)) at each reception focus from the weight table storage unit 86. The reading and weighting units 32-1, 32-2,..., 32-K are installed (FIGS. 23A and 23B). Here, m is the number of the reception scanning line, σ is the number of the reception focus in the reception scanning line, and k is the number of the transmission scanning line. The weighting units 32-1, 32-2,..., 32-K multiply the received signals 18-1 to 18-K by weight data (w (m, σ, k)), respectively. Thereafter, the synthesizer 25 synthesizes the weighted reception signals (FIG. 23 (c)). Other configurations are the same as those of the ultrasonic imaging apparatus of the second embodiment.

The third embodiment will be further described. The original reception signals 18-1a to 18-Ka included in the reception signals 18-1 to 18-K after phasing addition for the reception focus 52 generated by the decoding unit 41 in time series are as shown in FIG. In addition, the waveform is always in phase. These received signals are in a state of being gradually shifted in the time direction due to the movement of the imaging target 120 as shown in FIG. Therefore, the center of the signal appearance time (reception time) (the center of the time series) as shown in FIG. 24B, rather than the data after aperture synthesis in which these received signals are simply added as shown in FIG. The closer the data to (), the greater the weighting, and the data after aperture synthesis by the aperture synthesis unit 25 has a smaller spread of the signal in the time axis direction and the spatial resolution is improved.

On the other hand, the unnecessary signals 18-1b to 18-Kb included in the reception signals 18-1 to 18-K after the phasing addition for the reception focal point 52 generated by the decoding unit 41 in time series are alternately inverted in waveform. It becomes. Since these signals are also time-shifted little by little, signals that have a smaller time shift (unnecessary signals 18-1b and 18-2b, unnecessary signals 18-2b and 18-3b) than the sum of all the signals. It is possible to suppress the unnecessary signal components as a whole by adding the addition results after minimizing the unnecessary signals. This is equivalent to increasing the weighting of signals closer to the center of the time series of time series delay phasing data and adding them.

In this way, by decoding and decoding received signals that are closer to the center time of the time series, the spatial resolution is improved by suppressing the spread in the time axis direction of the original received signal 119a after synthesis, and unnecessary. The signal 119b can be further suppressed.

As a specific method for weighting the received signal and performing addition, a method similar to the image quality enhancement image processing method using a Gaussian filter can be used. For example, when three received signals after phasing and addition for the same reception focus 52 are subjected to aperture synthesis, the signals are added after being multiplied by weighting coefficients α, β, and γ. Β that is multiplied by the signal that is the center of the time series is set to a value that is larger than α and γ that are multiplied by the preceding and succeeding signals. 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.

At this time, when the order of the transmission scanning lines to be transmitted is arranged in order from the end of the probe 108 as shown in FIG. 15, the weighting method is performed on the reception signal on one scanning line. This is equivalent to weighting along the position of the scanning line. For example, as shown in FIG. 25A, when nine reception scanning lines are set for one transmission scanning line, each reception scanning line is weighted with a binary coefficient of 1 to 70. Looking at the weighting coefficient for the reception focal point 52 of each transmission scanning line, as shown in FIG. 25B, the position of the reception focal point 52 moves to the inner reception scanning line as the transmission scanning line number increases. For this reason, the reception signal that is aperture-synthesized with respect to the reception focus 52 is weighted so that the amplitude of the reception signal of the reception scanning line closer to the center increases.

Therefore, as shown in FIG. 25 (b), a weighting unit that weights all the received signals after phasing stored in the second storage unit 24 so that the reception signal whose reception scanning line number is closer to the center is greater. 250 may be arranged in the synthesis unit 25 (see FIG. 26).

Note that FIG. 25B shows an example in which the transmission scanning line interval is exactly equal to the reception beam interval.

In the above-described embodiment, the operation of the ultrasonic imaging apparatus has been described with reference to the flowchart in FIG. 14. However, the control unit 106 reads the program predetermined by the CPU and executes it to realize the operation in FIG. 14. Or a hardware structure realized by the operation of a hardware circuit such as an ASIC (application specific integrated circuit) or a programmable hardware circuit such as an FPGA (field-programmable gate array). Also good. The operation of the aperture synthesis unit 25 is the same, and may be a structure realized by software or a structure that realizes the operation by a hardware circuit such as an ASIC or FPGA. The same applies to the transmission unit 102 and the reception unit 105.

DESCRIPTION OF SYMBOLS 25 ... Aperture synthetic | combination part, 41 ... Decoding part, 52 ... Reception focus, 100 ... Ultrasound imaging device, 101 ... Dual tree switching part, 102 ... Transmission part, 105 ... Reception part, 106 ... Control part, 107 ... Image processing part DESCRIPTION OF SYMBOLS 108 ... Ultrasonic probe, 109 ... Reception area, 110, 111 ... Transmission aperture group (transmission aperture pair), 110A, 110B, 111A, 111B ... Transmission aperture, 120 ... Imaging object, 121 ... User interface (UI) 122: Display unit

Claims (13)

1. An ultrasound probe having a plurality of transmission aperture groups, each including two or more transmission apertures, and one or more reception areas;
   An operation for transmitting the spatially encoded ultrasonic wave simultaneously from the two or more transmission apertures included in the transmission aperture group, one cycle or more in order for each transmission aperture group; and
   A receiving unit that performs a decoding process and a phasing process on the output of the reception area that has received the echo of the ultrasonic wave from the imaging target, and obtains a reception signal for a reception focus at a desired position of the imaging target When,
   An aperture synthesis section,
   The transmission unit is configured to transmit the spatial encoding code of the ultrasonic wave transmitted by a part of the transmission aperture groups among the plurality of transmission aperture groups, and the spatial encoding code of the ultrasonic wave transmitted from another transmission aperture group. Invert
   The aperture synthesizing unit is different from a reception signal for a reception focal point at the desired position obtained by the reception unit from the echo generated by ultrasonic waves transmitted from one transmission aperture group among the plurality of transmission aperture groups. An ultrasonic imaging apparatus characterized by performing an addition process on the reception signal for the same reception focus obtained by the reception unit from the echo generated by the ultrasonic wave transmitted by the transmission aperture group.
2. The ultrasonic imaging apparatus according to claim 1, wherein the transmission unit alternately reverses the codes of the spatial encoding when transmitting ultrasonic waves in order for each transmission aperture group. Sound imaging device.
3. The ultrasonic imaging apparatus according to claim 1, wherein the transmission unit repeatedly performs the operation of transmitting the transmission aperture groups in order for each of the transmission aperture groups two or more times. Make each spatial coding code different from the first round,
   The ultrasonic imaging apparatus, wherein the receiving unit performs a decoding process using an output of the transmission aperture group in a first round transmission and an output of a second round transmission in the reception area.
4. 2. The ultrasonic imaging apparatus according to claim 1, wherein two or more transmission apertures included in the transmission aperture group are located apart from each other on the ultrasonic probe.
5. The ultrasonic imaging apparatus according to claim 4, wherein the ultrasonic probe has a configuration in which a plurality of the transmission openings are arranged.
   The transmission unit sequentially selects two or more transmission apertures at a predetermined distance from the arranged transmission apertures, and transmits ultrasonic waves as the transmission aperture group. apparatus.
6. The ultrasonic imaging apparatus according to claim 5, wherein the transmission unit selects two or more transmission apertures positioned at a central portion of the ultrasonic probe as the transmission aperture of the transmission aperture group to be transmitted first. An ultrasonic imaging apparatus.
7. The ultrasonic imaging apparatus according to claim 4, wherein the ultrasonic probe has a configuration in which a plurality of the transmission openings are arranged.
   The ultrasonic imaging apparatus, wherein the transmission unit randomly selects two or more transmission apertures among the arranged transmission apertures and transmits ultrasonic waves as the transmission aperture group.
8. 2. The ultrasonic imaging apparatus according to claim 1, wherein the aperture synthesis unit weights the reception signal and adds the plurality of reception signals for the same reception focus obtained by the reception unit. 3. An ultrasonic imaging apparatus.
9. 9. The ultrasonic imaging apparatus according to claim 8, wherein the aperture synthesizer receives the weights of the plurality of reception signals for the same reception focal point near the center of variation in time at which the reception signals are respectively obtained. An ultrasonic imaging apparatus that is set to be heavier as a signal.
10. 9. The ultrasonic imaging apparatus according to claim 8, wherein the reception unit sets a plurality of reception scanning lines in a predetermined range around the transmission aperture, and each of the plurality of reception scanning lines is set on the reception scanning line. Set the reception focus;
    The ultrasonic imaging apparatus, wherein the aperture synthesizing unit sets the weight of the reception signal of the reception focal point located above the reception scanning line closer to the center among the plurality of reception scanning lines.
11. The ultrasonic imaging apparatus according to claim 1, wherein the ultrasonic probe has a plurality of the reception areas,
    The receiving unit includes a decoding unit that performs the decoding process, and a phasing addition unit that adds the outputs of the plurality of reception areas after phasing processing,
    The decoding unit is arranged for each of the plurality of reception areas, and the phasing addition unit adds the decoded signals output from the plurality of decoding units after phasing processing, and receives a reception signal for the reception focus An ultrasonic imaging apparatus characterized in that:
12. The ultrasonic imaging apparatus according to claim 1, wherein the ultrasonic probe has a plurality of the reception areas,
    The receiving unit includes a decoding unit that performs the decoding process, and a phasing addition unit that adds the outputs of the plurality of reception areas after phasing processing,
    The ultrasonic imaging apparatus, wherein the decoding unit is arranged at a subsequent stage of the phasing addition unit, and decodes the signal after the phasing processing and addition processing.
13. 13. The ultrasonic imaging apparatus according to claim 12, wherein a duplicator is disposed for each of the plurality of reception areas between the phasing adder and the ultrasonic probe, and the plurality of reception areas are output. An ultrasonic imaging apparatus, wherein two signals obtained by copying the obtained signals are output to the phasing addition unit, and the phasing addition unit performs phasing addition processing on the two signals separately.

Images