Ultrasonic imaging system and photoacoustic image generation method

Abstract

To generate a photoacoustic image in which an influence of a synchronization shift between an optical pulse period and a reception period is removed.SOLUTION: A vibrator array 22 receives a photoacoustic wave from a light absorption element 18a in a state that an insertion member 18 is inserted into a living body 16. An analyzer 50 calculates a synchronization shift on the basis of an acquired reception signal string. A plurality of correction devices 32 correct a plurality of reception signals on the basis of the synchronization shift. The plurality of reception signals after correction are subjected to phasing addition. A photoacoustic image is generated on the basis of the reception information after correction generated by the phasing addition. The synchronization shift may be calculated on the basis of a pseudo-reception signal string.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to an ultrasound imaging system and a photoacoustic image generating method, and more particularly to a technique for displaying the position of an insertion member inserted into a living body. [Background technology]

[0002] An ultrasonic imaging system is a system for treating or examining a living body, i.e., a patient, using an ultrasonic imaging device. More specifically, an ultrasonic imaging system generates and displays an image showing the position of an insertion member inserted into the living body. Treatment or the like of the living body is performed while referring to such an image. From this perspective, an ultrasonic imaging system is a system that supports treatment or the like of the living body.

[0003] In an ultrasound imaging system, an ultrasound diagnostic device is typically used as the ultrasound imaging device. The insertion member inserted into a living body is, for example, a catheter inserted into a blood vessel. Generally, a guide wire is inserted into the blood vessel prior to insertion of the catheter. The guide wire is also an insertion member. An ultrasound imaging system that images an insertion member inserted into a blood vessel using an ultrasound probe abutted against the surface of the living body is also called an EVUS (extra-vascular ultrasound) system.

[0004] An advanced ultrasound imaging system has been proposed that uses the photoacoustic effect to image an insertion member. In this ultrasound imaging system, an optical absorbing element is provided at the tip of the insertion member. Optical pulses generated by an optical pulse generator are guided into the insertion member through an optical fiber, and the optical pulses are irradiated onto the optical absorbing element. Photoacoustic waves are generated within the living body when the optical pulses are absorbed by the optical absorbing element. The photoacoustic waves are received by an ultrasound probe placed in contact with the surface of the living body. Based on the received information, an image (hereinafter referred to as a photoacoustic image or PA image) representing the position of the optical absorbing element (i.e., the sound source) is formed. For example, the photoacoustic image is synthesized with an ultrasound image (hereinafter also referred to as a US image) generated by transmitting and receiving ultrasound waves. The synthesized image is then displayed. By observing the synthesized image, the position of the tip of the insertion member can be clearly identified while observing the living tissue.

[0005] In the above-mentioned advanced ultrasound imaging system, it is basically necessary to synchronize the optical pulse period of the optical pulse generator with the reception period of the ultrasound probe. If synchronization is not established, receive beamforming will not be performed properly, resulting in a deterioration in the quality of the photoacoustic image. Furthermore, in order to accurately represent the depth position of the sound source in the photoacoustic image, in addition to matching the optical pulse period with the reception period, it is also necessary to match the generation timing of the optical pulse with the start timing of the reception period in the probe.

[0006] Patent Document 1 discloses the above-mentioned advanced ultrasound imaging system. Patent Document 1 does not disclose a technique for correcting a received signal sequence. In the ultrasound diagnostic device disclosed in Patent Document 2, Fourier transform (also called Fourier phasing) and inverse Fourier transform (also called inverse Fourier phasing) are performed in stages. These staged data transformations are for sound speed correction and are unrelated to photoacoustic images. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Patent No. 5819387 [Patent Document 2] Japanese Patent Publication No. 2020-137876 Summary of the Invention [Problem to be solved by the invention]

[0008] An object of the present disclosure is to generate a photoacoustic image similar to a photoacoustic image obtained without synchronization even when there is a synchronization error between an optical pulse period and a reception period, or to display a sound source at a correct position in a photoacoustic image even when there is a synchronization error between an optical pulse period and a reception period. [Means for solving the problem]

[0009] The ultrasound imaging system according to the present disclosure is characterized by including: a light source that generates optical pulses; an insertion member that is inserted into a living body and has a light absorbing element that converts the optical pulses into photoacoustic waves; a probe having a plurality of transducers that receive the photoacoustic waves; an analyzer that calculates a synchronization deviation between the optical pulse period in the light source and the reception period in the probe based on a reception signal sequence consisting of a plurality of reception signals output in parallel from the plurality of transducers or a pseudo reception signal sequence equivalent thereto; a processor that applies correction to the reception signal sequence or the pseudo reception signal sequence to eliminate position deviation resulting from the synchronization deviation and phasing addition for reception beam formation, thereby outputting corrected reception information; and a generator that generates a photoacoustic image that represents the position of the light absorbing element in the living body based on the corrected reception information.

[0010] The photoacoustic image generating method according to the present disclosure is characterized by including the steps of: receiving the photoacoustic waves with a plurality of transducers while an insertion member having a light absorbing element that converts light pulses into photoacoustic waves is inserted into a living body; calculating a synchronization deviation between the light pulse period and the reception period based on a reception signal sequence consisting of a plurality of reception signals output in parallel from the plurality of transducers or a pseudo reception signal sequence equivalent thereto; applying correction to the reception signal sequence or the pseudo reception signal sequence to eliminate the position deviation resulting from the synchronization deviation and phasing addition for reception beam formation, thereby generating corrected reception information; and generating a photoacoustic image representing the position of the light absorbing element in the living body based on the corrected reception information. [Effects of the Invention]

[0011] According to the present disclosure, even if there is a synchronization error between the optical pulse period and the reception period, a photoacoustic image similar to a photoacoustic image obtained without the synchronization error can be generated. Alternatively, according to the present disclosure, even if there is a synchronization error between the optical pulse period and the reception period, a sound source is displayed at the correct position in the photoacoustic image. [Brief explanation of the drawings]

[0012] [Figure 1] 1 is a block diagram showing an ultrasound imaging system according to a first embodiment. [Figure 2] FIG. 2 is a diagram illustrating an example of a received signal including a photoacoustic wave signal. [Figure 3] FIG. 10 is a diagram illustrating correction of a received signal sequence before phasing and summation. [Figure 4] FIG. 1 illustrates the spatial relationship between a sound source and an array of transducers. [Figure 5] FIG. 10 is a diagram illustrating the relationship between synchronization deviation, actual propagation time, and apparent propagation time. [Figure 6] FIG. 10 is a diagram illustrating an example of a synchronization deviation calculation method. [Figure 7] FIG. 10 is a block diagram showing a first modified example. [Figure 8] FIG. 10 is a block diagram showing a second modified example. [Figure 9]FIG. 10 is a block diagram showing an ultrasound imaging system according to a second embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0013] Hereinafter, an embodiment will be described with reference to the drawings.

[0014] (1) Overview of the embodiment An ultrasound imaging system according to an embodiment includes a light source, an insertion member, a probe, an analyzer, a processor, and a generator. The light source generates optical pulses. The insertion member is inserted into a living body. The insertion member has a light absorbing element that converts the optical pulses into photoacoustic waves. The probe includes multiple transducers that receive photoacoustic waves. The analyzer calculates a synchronization error between the optical pulse period at the light source and the reception period at the probe based on a reception signal sequence consisting of multiple reception signals output in parallel from the multiple transducers or a pseudo reception signal sequence equivalent thereto. The processor applies correction to the reception signal sequence or the pseudo reception signal sequence to eliminate positional errors resulting from the synchronization error and phasing addition for reception beam formation, thereby outputting corrected reception information. The generator generates a photoacoustic image representing the position of the light absorbing element in the living body based on the corrected reception information.

[0015] According to the above configuration, a correction is applied to the received signal sequence or the pseudo received signal sequence to eliminate positional deviations resulting from synchronization deviations. Therefore, even if there is synchronization deviation between the optical pulse period and the reception period, the influence of the synchronization deviation does not appear on the photoacoustic image, or the influence of the synchronization deviation that appears on the photoacoustic image is reduced. Therefore, the sound source is displayed at the correct position or a position close to the correct position in the photoacoustic image. From another perspective, according to the above configuration, there is no need to strictly control the optical pulse period and / or the reception period, and therefore the configuration of the ultrasound imaging system can be simplified. Note that the above configuration may function during a temporary period until synchronization is established or during a temporary period when synchronization is lost.

[0016] From the viewpoint of calculating the synchronization error, the pseudo received signal sequence can be considered to be a received signal sequence similar to the received signal sequence output from a plurality of transducers. For example, the pseudo received signal sequence may be generated by performing a restoration process on the received frame data or the displayed frame data. The corrected received information is the received frame data or the displayed frame data to which correction has been applied to eliminate the positional error resulting from the synchronization error.

[0017] In the embodiment, the synchronization deviation is the time difference between the generation timing of the optical pulse and the start timing of the reception period in the probe. The start timing of the reception period is the reference timing in receive beamforming. When the generation timing of the photoacoustic wave coincides with this reference timing, the depth of the sound source is correctly identified. Conversely, by eliminating the position deviation due to the time difference in the received signal sequence or the pseudo received signal sequence, the depth of the sound source can be correctly represented.

[0018] In an embodiment, the processor includes a correction unit and a delay-and-sum unit. The correction unit shifts a photoacoustic wave signal sequence included in the received signal sequence or the pseudo received signal sequence in a depth direction based on a synchronization deviation. The delay-and-sum unit applies delay-and-sum to the corrected received signal sequence or the pseudo received signal sequence output from the correction unit, thereby generating corrected reception information.

[0019] Due to synchronization deviation, a positional deviation occurs in the photoacoustic wave signal train on the time axis. The above configuration shifts the photoacoustic wave signal train along the time axis to eliminate the positional deviation. The delay-and-sum process after the shift has the advantage that it is not necessary to set special delay-and-sum conditions.

[0020] In an embodiment, the processor simultaneously applies correction and delay-and-sum to the received signal sequence or the pseudo received signal. This configuration simplifies the configuration of the receiver. For example, simultaneous application of correction and delay-and-sum to the received signal sequence can be realized by controlling the read timing of each received signal from each memory.

[0021] An ultrasound imaging system according to an embodiment includes a restoration processor that generates a pseudo received signal sequence by applying restoration processing to reception information generated from a received signal sequence. An analyzer calculates a synchronization deviation based on the pseudo received signal sequence. This configuration makes it possible to eliminate positional deviation without changing the configuration of the receiving unit. The restoration processing is processing that restores the received signal sequence before delay-and-sum from the reception information after delay-and-sum. The restored received signal sequence is the pseudo received signal sequence.

[0022] In an embodiment, the analyzer calculates the synchronization deviation based on a photoacoustic wave signal sequence included in a received signal sequence or a pseudo received signal sequence. In an embodiment, the photoacoustic wave signal sequence is composed of a plurality of photoacoustic wave signals corresponding to a plurality of transducers. The analyzer calculates the synchronization deviation based on a plurality of propagation times corresponding to the plurality of photoacoustic wave signals.

[0023] The photoacoustic wave signals constituting the photoacoustic wave signal train are arranged in a two-dimensional space defined by the time direction (depth direction) and the electronic scanning direction in a manner that reflects the magnitude of the synchronization deviation. That is, the magnitude of the synchronization deviation is reflected in the multiple propagation times corresponding to the multiple photoacoustic wave signals. Using this, the synchronization deviation is calculated from the multiple propagation times.

[0024] A photoacoustic image generating method according to an embodiment includes a receiving step, an analyzing step, a processing step, and a generating step. In the receiving step, a photoacoustic wave is received by a plurality of transducers while an insertion member having a light absorbing element that converts light pulses into photoacoustic waves is inserted into a living body. In the analyzing step, a synchronization error between the light pulse period and the reception period is calculated based on a reception signal sequence consisting of a plurality of reception signals output in parallel from the plurality of transducers or a pseudo reception signal sequence equivalent thereto. In the processing step, correction is applied to the reception signal sequence or the pseudo reception signal sequence to eliminate positional deviations resulting from the synchronization error, and phasing addition is performed to form a reception beam, thereby generating corrected reception information. In the generating step, a photoacoustic image representing the position of the light absorbing element in the living body is generated based on the corrected reception information.

[0025] (2) Details of the embodiment 1 shows an ultrasound imaging system according to a first embodiment. The illustrated ultrasound imaging system is a medical system installed in a medical institution such as a hospital, and specifically, is a system used when sending the tip of an insertion member to an affected area while observing a photoacoustic image (PA image) that shows the position of the tip of the insertion member. The ultrasound imaging system may also be used for other purposes.

[0026] The ultrasound imaging system includes an optical pulse generating device 10, an ultrasound diagnostic device 12, and an insertion member 18. The ultrasound diagnostic device 12 functions as an ultrasound imaging device. In the illustrated configuration example, no device is provided for establishing synchronization between the optical pulse generating device 10 and the ultrasound diagnostic device 12.

[0027] The optical pulse generating device 10 has a light source 17. The light source 17 is a laser that generates a pulse train of laser light. The proximal end of an optical fiber 19 is connected to the light source 17. The distal end of the optical fiber 19 is located within the distal end portion of the insertion member 18.

[0028] The insertion member 18 is, for example, a catheter inserted into a blood vessel in the living body 16. Other examples of the insertion member 18 include a guide wire, a puncture needle, etc. A light absorbing element 18a made of a light absorbing material is provided in the tip of the insertion member 18. When a light pulse is irradiated onto the light absorbing element 18a, the light pulse is absorbed by the light absorbing element 18a. At this time, a photoacoustic wave 20 is generated by the photoacoustic effect. The photoacoustic wave 20 propagates within the living body 16 as a pulsed wave. The light absorbing element 18a functions as a sound source within the living body 16. By imaging the sound source, the position of the tip of the insertion member 18 can be identified in real time.

[0029] Next, a description will be given of the ultrasonic diagnostic device 12. The ultrasonic diagnostic device 12 has a B mode for displaying a B-mode tomographic image (US image) and a PA mode for displaying a photoacoustic wave image (PA image).

[0030] An ultrasonic probe 21 is placed in contact with the surface 16A of the living body 16. The ultrasonic probe 21 is usually held by an examiner. The ultrasonic probe 21 may be held by a fixing tool, a robot arm, or the like. A transducer array 22 composed of a plurality of transducers is provided within the ultrasonic probe 21.

[0031] When B-mode is performed, ultrasound waves transmitted from the transducer array 22 are emitted into the living body 16, and reflected waves from within the living body 16 are received by the transducer array 22. More specifically, a transmission beam and a reception beam are formed, and these are electronically scanned.

[0032] When the PA mode is executed, the transducer array 22 does not perform a transmission operation but performs only a reception operation. In other words, only a reception beam is formed and electronically scanned. More specifically, the photoacoustic waves 20 generated within the living body 16 are received by the transducer array 22. On the time axis, multiple reception periods are set according to the reception cycle. Each reception period is a period for receiving or detecting photoacoustic waves, and corresponds to a reception beam formation period.

[0033] In addition, multiple receive beams may be formed simultaneously in parallel during each receive period. The receive signal sequence obtained from the entire transducer array 22 may be used as receive information for synchronization deviation analysis, or a portion of the receive signal sequence may be used as receive information for receive beam formation. In general, transmit / receive operations according to B mode and receive operations according to PA mode are performed alternately.

[0034] The transmitter 24 is a transmit beamformer. That is, during transmission, the transmitter 24 outputs multiple transmit signals in parallel to multiple transducers. The transmitter 24 is configured, for example, by a processor. The processor can be configured by a programmable device, an electronic circuit, etc.

[0035] The receiving unit 26 is a receiving beamformer. Specifically, during reception, the receiving unit 26 processes a plurality of received signals output in parallel from a plurality of transducers. The receiving unit 26 is configured by a processor. The processor functions as an analyzer 50, a correction unit 200, and a phasing adder 35, which will be described below. The analyzer 50, the correction unit 200, and the phasing adder 35 may each be configured by a processor.

[0036] Specifically, the receiving unit 26 has a plurality of amplifiers 28, a plurality of ADCs 30, a plurality of memories (first memories) 31, a plurality of correctors 32, a plurality of memories (second memories) 33, an adder 34, a read controller 36, an analyzer 50, etc. The plurality of memories 33, the adder 34, and the read controller 36 configure a phasing addition unit 35.

[0037] The multiple amplifiers 28 amplify the multiple received signals that are input. The multiple ADCs 30 convert the multiple amplified received signals (analog signals) into multiple digital signals. The multiple received signals output from the multiple ADCs 30 are temporarily stored in multiple memories 31. The multiple correctors 32 apply correction processing to the multiple received signals output from the multiple memories 31. The correction processing is processing to eliminate position shifts resulting from synchronization errors, which will be described in detail later. The multiple received signals output from the multiple correctors 32 are temporarily stored in multiple memories 33.

[0038] A plurality of reception signals are read from a plurality of memories 33 under read control of the read controller 36. The read reception signals are added together by an adder 34, thereby generating reception beam data. In other words, the read controller 36 dynamically assigns a delay time to each reception signal so that reception beam data is generated, i.e., so that reception focal points are formed at each depth on the sound ray.

[0039] The receiver 26 outputs the receive beam data generated by the delay-and-sum process. A single electronic scan of the receive beam generates multiple receive beam data aligned in the electronic scan direction. These multiple receive beam data constitute receive frame data corresponding to the beam scan plane. Each receive beam data is composed of multiple echo data aligned in the depth direction.

[0040] The receiving unit 26 according to the embodiment has a plurality of memories 31, a plurality of correctors 32, and an analyzer 50 in order to eliminate positional deviations resulting from synchronization deviations. These components do not function when the B mode is being executed, but function when the PA mode is being executed. The plurality of correctors 32 constitute a correction unit 200.

[0041] The analyzer 50 calculates a synchronization deviation (amount of synchronization deviation) based on the plurality of received signals stored in the plurality of memories 31, i.e., the received signal sequence before phasing and summing. The synchronization deviation can also be called a phase deviation. The analyzer 50 can be configured by, for example, a processor.

[0042] Generally, when there is no synchronization deviation, the temporal relationship between the optical pulse period and the reception period is constant. When there is a synchronization deviation, the temporal relationship between the optical pulse period and the reception period changes from moment to moment. In an embodiment, the synchronization deviation is calculated to display the sound source at the correct depth on the displayed image. Specifically, when the temporal relationship between the optical pulse period and the reception period is constant, the time difference between the generation timing of each optical pulse and the start timing of each reception period is calculated as the synchronization deviation. In a two-dimensional space defined by the depth direction and the electronic scanning direction, the synchronization deviation appears as a positional deviation in the depth direction. The method of calculating the synchronization deviation will be described in detail later. Note that, in the process in which the temporal relationship between the optical pulse period and the reception period is changing, the time difference may be repeatedly calculated as the synchronization deviation.

[0043] A plurality of received signals output from a plurality of memories 31 are input to a plurality of correctors 32. Each corrector 32 corrects each received signal based on the synchronization deviation calculated by the analyzer 50. Specifically, the position of the photoacoustic wave contained in each received signal is shifted in the time axis direction. This shift corresponds to eliminating the synchronization deviation, that is, eliminating the position deviation. The corrected plurality of received signals are sent to a phasing addition unit 35. Therefore, with the configuration shown in FIG. 1, a received signal sequence that indicates the correct sound source position is obtained.

[0044] If photoacoustic waves cannot be observed because they reach the transducer array 22 at times other than the reception period, at least one of the optical pulse period and the reception period may be changed automatically or trially by the user. For example, the analyzer 50 may determine whether or not a photoacoustic wave component is included in the reception signal sequence stored in the multiple memories 31. If it is determined that a photoacoustic wave component is not included, at least one of the optical pulse period and the reception period may be changed.

[0045] The data processing unit 38 is composed of a processor that processes each receive beam data. The data processing unit 38 includes an envelope detection circuit, a filter circuit, a logarithmic conversion circuit, etc. When generating an ultrasound image (US image), each receive beam data output from the data processing unit 38 is sent to a US image generation unit 40. When generating an acoustic wave image (PA image), each receive beam data output from the data processing unit 38 is sent to a PA image generation unit 42.

[0046] The US image generator 40 functions during B-mode imaging. The US image generator 40 has a digital scan converter (DSC) and is a module that generates display frame data from received frame data. Specifically, the US image generator 40 generates a tomographic image (B-mode tomographic image) representing tissue structure as a US image. The DSC has a coordinate conversion function, a pixel interpolation function, etc.

[0047] The PA image generation unit 42 functions when the PA mode is executed. The PA image generation unit 42 is a module that has a DSC and a sound source identification unit and generates display frame data from received frame data. The sound source identification unit identifies the position of the sound source within the living body by detecting or extracting the sound source signal contained in the display frame data generated by the DSC. The PA image includes a marker that represents the position of the sound source within the beam scanning plane. The marker is, for example, a point with high brightness or a predetermined color. Since the positional deviation caused by synchronization deviation has already been eliminated by the correction process in the receiving unit 26, the marker is displayed in the correct position in the PA image.

[0048] The display processing unit 44 generates a composite image by superimposing the PA image on the US image (tomographic image). The composite image is displayed on the display unit 46. The display unit 46 is configured with an organic EL display device, a liquid crystal display, or the like.

[0049] The US image generating unit 40, the PA image generating unit 42, and the display processing unit 44 may each be configured by a processor. A CPU, which will be described below, may function as the US image generating unit 40, the PA image generating unit 42, and the display processing unit 44.

[0050] The main controller 52 controls the operation of each element constituting the ultrasound diagnostic apparatus 12. The main controller 52 is configured, for example, by a CPU that executes a program. The main controller 52 may function as all or part of the elements shown in FIG.

[0051] FIG. 2 illustrates an example of a received signal before correction. The received signal 77 includes a photoacoustic wave signal 78 resulting from the reception of photoacoustic waves. The photoacoustic wave signal 78 has a peak-like or pulse-like form with a large amplitude. For example, the photoacoustic wave signal 78 may be detected or extracted by threshold processing. In this case, a portion exceeding a threshold α is identified as the photoacoustic wave signal 78. The threshold α may be set according to the magnitude of noise contained in the received signal. For example, if the standard deviation of the received signal is represented as σ, the threshold α may be set according to α=6σ. Prior to threshold processing, filtering, envelope detection, etc. may be applied to the received signal 77. The photoacoustic wave signal 78 may be identified by detecting a local maximum value, comparing with a reference waveform (e.g., cross-correlation calculation), etc.

[0052] The detection timing td is determined by detecting the photoacoustic wave signal 78. The period pi from the reception period start timing ts to the detection timing td includes the propagation time of the photoacoustic wave and a time corresponding to a synchronization error. From this perspective, the period pi will be referred to as the apparent propagation time hereinafter.

[0053] Fig. 3 shows an example of a received signal sequence referenced by the analyzer. The received signal sequence is composed of a plurality of received signals 80 corresponding to a plurality of transducers that make up the transducer array. In Fig. 3, the x direction is the transducer array direction (electronic scanning direction), and the y direction is the depth direction. The y direction corresponds to the time axis.

[0054] The received signal sequence includes a photoacoustic wave signal sequence 84. In the illustrated example, the x-coordinate (xc) of the center of the transducer array and the x-coordinate of the sound source coincide, and the x-coordinate of the vertex of the photoacoustic wave signal sequence 84 coincides with the x-coordinate (xc) of the center of the transducer array.

[0055] The photoacoustic wave signal sequence 84 is composed of multiple photoacoustic wave signals. Focusing on a specific photoacoustic wave signal 82 received by the i-th transducer, the apparent propagation time pi is determined based on the detection timing. The specific photoacoustic wave signal 82 is generated at a point of depth yi.

[0056] The photoacoustic wave signal sequence 84 has a parabolic shape. The shape of the photoacoustic wave signal sequence 84 depends on the depth of the sound source. This shape is constant regardless of the magnitude of the synchronization error. The position at which the photoacoustic wave signal sequence 84 is generated changes depending on the spatial relationship between the transducer array and the sound source, and also changes depending on the synchronization error. For example, when the position of the sound source shifts in the x direction from the center position xc of the transducer array, a photoacoustic wave signal sequence 90 is generated. The x coordinate (xc1) of its vertex 90a corresponds to the x coordinate of the sound source. Even in this case, the shape of the photoacoustic wave signal sequence 90 is the same as that of the photoacoustic wave signal sequence 84.

[0057] The synchronization deviation is calculated based on the photoacoustic wave signal sequence 84. The synchronization deviation is a deviation of the generation timing of the photoacoustic wave relative to the start timing of the reception period on the time axis. The synchronization deviation appears as a positional deviation in the depth direction of the photoacoustic wave signal sequence 84 in the two-dimensional coordinate system shown in FIG.

[0058] As will be described later, the plurality of received signals 80 are corrected based on the synchronization deviation. Specifically, the position of the photoacoustic wave signal sequence 84 is changed in the depth direction. In this case, a process is applied in which the photoacoustic wave signal sequence 84 is translated in the depth direction relative to the photoacoustic wave signal sequence 84 on the two-dimensional coordinate system shown in FIG. 3 (see reference numeral 86). Reference numeral 88 denotes a photoacoustic wave signal sequence in which the position deviation caused by the synchronization deviation has been eliminated.

[0059] The method for calculating the synchronization deviation will be explained below. Figure 4 shows the spatial relationship between the transducer array 92 and the sound source 96. The x direction is the transducer arrangement direction, and the y direction is the depth direction. The center of the transducer array 92 is the origin (0,0), and the position of the i-th transducer 94 is expressed as (xi, yi), where yi = 0. The position of the sound source 96 is expressed as (xb, yb). The propagation time di of the photoacoustic wave from the sound source 96 to the i-th transducer is calculated by the following equation (1). In equation (1), c is the sound speed of ultrasound in biological tissue.

number

[0060] The apparent propagation time pi is the sum of the synchronization deviation δ and the propagation time (actual propagation time) di. That is, the apparent propagation time pi is expressed as in the following equation (2).

number

[0061] The relationship between the apparent propagation time pi, synchronization shift δ, and propagation time di expressed in the above equation (2) is shown in Figure 5. The reception period 102 is the period from the start timing ts to the end timing te. The time between the start timing ts and the generation timing of the light pulse 98 is the synchronization shift δ. The propagation time from the generation timing of the light pulse 98 (the generation timing of the photoacoustic wave) to the reception of the photoacoustic wave by the i-th transducer is di. Reference numeral 100 denotes a photoacoustic wave signal generated by receiving the photoacoustic wave.

[0062] When the photoacoustic waves reach n transducers, n detection times td corresponding to the n transducers are identified. Based on the n detection times td, n apparent propagation times pi are identified. N data pairs (xi, pi) are defined by the positions xi of the n transducers and the n apparent propagation times pi (where i = 1, . . . , n).

[0063] By substituting n data pairs (xi,pi) into the mathematical model (2), it is possible to identify the unknown parameters δ, xb, and yb. A solution search method such as the least squares method is used for this purpose. This method identifies the coordinates (xb,yb) of the sound source in addition to the synchronization offset δ.

[0064] The processes described above are schematically shown in FIG. 6. In the analyzer 50, in block 130, n photoacoustic wave signals included in the n received signals before coherent addition are detected, and n apparent propagation times pi from the reception period start timing to the n detection timings are calculated. n data pairs (xi, pi) 132 are defined by the coordinates xi of the n vibration elements in the x direction and the n apparent propagation times pi. In block 134, the synchronization deviation δ, which is an unknown parameter, is calculated by substituting the n data pairs (xi, pi) 122 into the above equation (2). Secondarily, the coordinates (xb, yb) of the sound source are also calculated. Only a plurality of data pairs (xi, pi) 122 that satisfy certain conditions among the n data pairs (xi, pi) 122 may be substituted into the above equation (2).

[0065] Regarding |xi - xb| in the above equation (2), in many cases, |xi - xb| << yb holds. Therefore, the following equation (3) holds based on the above equation (2).

Equation

[0066] The above equation (3) indicates that a plurality of photoacoustic wave signals draw a parabola in the above xy coordinate system. The synchronization deviation δ may be specified using the above equation (3). In addition, a photoacoustic image may be generated using the specified coordinates (xb, yb) of the sound source, or the operation of the ultrasonic imaging system may be controlled based on the specified coordinates (xb, yb) of the sound source.

[0067] Incidentally, in the correction process for eliminating the positional deviation due to the synchronization deviation, instead of the synchronization deviation calculated at each time point, a smoothed synchronization deviation may be referred to. In that case, for example, the smoothed synchronization deviation may be calculated according to the following equation (4).

Equation

[0068] In the above equation (4), δj represents the j-th synchronization deviation. The equation (4) corresponds to a moving average process, and the most recent N synchronization deviations are averaged by the equation (4).

[0069] A first modified example of the first embodiment is shown in Fig. 7. Fig. 7 shows a part of a receiving unit 26A. A plurality of received signals are stored in a plurality of memories 31A. An analyzer 50 analyzes the stored plurality of received signals and thereby identifies synchronization deviation.

[0070] A plurality of correctors 32A are connected to a plurality of memories 31A. Each corrector 32A reads the received signal from its corresponding memory 31A, corrects the received signal based on the synchronization deviation, and writes the corrected received signal to that memory 31A. In each memory 31A, the corrected received signal is overwritten on the uncorrected received signal.

[0071] Under the control of the read controller 36, a plurality of corrected received signals are read from the plurality of memories 31A, and the read plurality of received signals are added by the adder 34. This results in corrected received information. The plurality of memories 31A, the adder 34, and the read controller 36 form a phasing adder 35A. According to the first modification, the number of memories in the receiving unit 26A can be reduced.

[0072] A second modified example of the first embodiment is shown in Fig. 8. Fig. 8 shows a part of a receiving unit 26B. A plurality of received signals are stored in a plurality of memories 31A. An analyzer 50 analyzes the stored plurality of received signals and thereby identifies synchronization deviation.

[0073] The read controller 36A has a delay control function for phasing and summing and a delay control function for position error correction. In Fig. 8, the latter delay control function is represented as a correction unit 36Aa. An actual delay amount determined from a first delay amount for phasing and summing and a second delay amount for position error correction is applied to each received signal. Whether the second delay amount is added to or subtracted from the first delay amount is determined according to the polarity (positive / negative) of the synchronization error.

[0074] Under the control of the read controller 36A, a plurality of reception signals are read from a plurality of memories 31A. The reception signals are added by an adder 34. This results in corrected reception information. The plurality of memories 31A, the adder 34, and the read controller 36A form a phasing adder 35B. According to the second modification, the configuration of the receiving unit 26B is simplified. Instead of performing phasing addition on a plurality of reception signals, phasing addition may be performed on a plurality of photoacoustic wave signals extracted from the plurality of reception signals.

[0075] An ultrasound imaging system according to the second embodiment is shown in Fig. 9. In Fig. 9, the same elements as those shown in Fig. 1 are given the same reference numerals, and the description thereof will be omitted.

[0076] In the second embodiment, when the B mode is executed, the reception information (reception frame data after phasing addition) output from the data processing unit 38 is sent to the US image generation unit 40. When the PA mode is executed, the reception information (reception frame data after phasing addition) output from the data processing unit 38 is sent to the processor 59. The receiving unit 26C has a general configuration.

[0077] The processor 59 includes an inverse transformer 60, an analyzer 62, a correction unit 64, and a converter 66. The inverse transformer 60 is a reconstruction processor or restorer that applies reconstruction processing to received information. The reconstruction processing is processing that generates a received signal sequence before delay and summation from received information after delay and summation. From this perspective, the reconstruction processing is an inverse transform (inverse delay and summation) corresponding to delay and summation. The reconstruction processing may also be an inverse Fourier transform (inverse Fourier phasing). In this way, the inverse transformer 60 generates a pseudo received signal sequence equivalent to the received signal sequence before delay and summation.

[0078] When the pseudo reception signal sequence is mapped onto the xy coordinate space, a photoacoustic wave signal sequence similar to the photoacoustic wave signal sequence 84 shown in FIG. 3 is generated. In FIG. 9, the analyzer 62 calculates the synchronization deviation based on the photoacoustic wave signal sequence included in the pseudo reception signal sequence using the method described above. The synchronization deviation is the time difference between the generation timing of the optical pulse and the start timing of the reception period in the probe. The correction unit 64 corrects the pseudo reception signal sequence based on the synchronization deviation. Specifically, the photoacoustic wave signal sequence included in the pseudo reception signal sequence is shifted in the depth direction so that the synchronization deviation appears to be eliminated. This shift corresponds to the elimination of the position deviation caused by the synchronization deviation.

[0079] The converter 66 applies delay-and-sum to the pseudo received signal sequence after correction. The delay-and-sum may be a Fourier transform (Fourier phasing). The converter 66 outputs a pseudo received signal sequence after correction and delay-and-sum. The pseudo received signal sequence is the corrected received frame data, and is corrected received information.

[0080] The PA image generation unit 42 generates a PA image based on the corrected receive frame data. The US image generation unit 40 generates a US image as a tomographic image based on the receive frame data output from the data processing unit 38. The display processing unit 44 synthesizes the PA image on the US image to generate a composite image. The composite image is displayed on a display 46.

[0081] In the second embodiment, the received frame data output from the data processing unit 38 may be directly provided to the PA image generating unit 42, and the uncorrected PA image output from the PA image generating unit 42 may be provided to the processor 59 (see reference numeral 68). In this case, a corrected PA image is generated by processing in the processor 59. The corrected PA image corresponds to corrected received information.

[0082] In the second embodiment, the CPU may function as the processor 59. According to the second embodiment, an advantage is obtained in that the receiving unit 26C having a general configuration can be used as is.

[0083] As described above, according to the ultrasound imaging system of the embodiment, even if there is a synchronization error between the light pulse period and the reception period, that is, even if there is a time difference between the light pulse generation timing and the start timing of the reception period, it is possible to display the sound source at the correct position. [Explanation of symbols]

[0084] 10 Optical pulse generator, 12 Ultrasound diagnostic device, 17 Light source, 18 Insertion member, 18a Light absorption element (sound source), 20 Photoacoustic wave, 21 Ultrasound probe, 22 Transducer array, 26 Receiver, 35 Phased addition unit, 32 Corrector, 40 US image generation unit, 42 PA image generation unit, 50 Analyzer.

Claims

1. a light source that generates light pulses; an insertion member to be inserted into a living body, the insertion member having a light absorbing element that converts the light pulse into a photoacoustic wave; a probe including a plurality of transducers for receiving the photoacoustic waves; an analyzer that calculates a synchronization deviation between an optical pulse period in the light source and a reception period in the probe based on a reception signal sequence consisting of a plurality of reception signals output in parallel from the plurality of transducers or a pseudo reception signal sequence equivalent thereto; a processor that applies correction to the received signal sequence or the pseudo received signal sequence to eliminate positional deviations resulting from the synchronization deviation and performs phasing addition for forming a receive beam, thereby outputting corrected received information; a generator that generates a photoacoustic image representing the position of the light absorbing element in the living body based on the corrected reception information; 1. An ultrasound imaging system comprising:

2. 2. The ultrasound imaging system of claim 1, The synchronization error is a time difference between the generation timing of the light pulse and the start timing of a reception period in the probe.

1. An ultrasound imaging system comprising:

3. 2. The ultrasound imaging system of claim 1, The processor includes: a correction unit that shifts a photoacoustic wave signal sequence included in the received signal sequence or the pseudo received signal sequence in a depth direction based on the synchronization deviation; a phasing addition unit that applies the phasing addition to the corrected received signal sequence or pseudo received signal sequence output from the correction unit, thereby generating the corrected received information; 1. An ultrasound imaging system comprising:

4. 2. The ultrasound imaging system of claim 1, the processor simultaneously applies the correction and the delay-and-sum to the received signal sequence or the pseudo received signal sequence.

1. An ultrasound imaging system comprising:

5. 2. The ultrasound imaging system of claim 1, a reconstruction processor that generates the pseudo received signal sequence by applying a reconstruction process to received information generated from the received signal sequence, the analyzer calculates the synchronization deviation based on the pseudo received signal sequence; 1. An ultrasound imaging system comprising:

6. 2. The ultrasound imaging system of claim 1, the analyzer calculates the synchronization deviation based on a photoacoustic wave signal sequence included in the received signal sequence or the pseudo received signal sequence.

1. An ultrasound imaging system comprising:

7. 7. The ultrasound imaging system of claim 6, the photoacoustic wave signal sequence is composed of a plurality of photoacoustic wave signals corresponding to the plurality of transducers, the analyzer calculates the synchronization deviation based on a plurality of propagation times corresponding to the plurality of photoacoustic wave signals.

1. An ultrasound imaging system comprising:

8. receiving the photoacoustic waves with a plurality of transducers in a state where an insertion member having a light absorption element that converts light pulses into photoacoustic waves is inserted into a living body; calculating a synchronization deviation between an optical pulse period and a reception period based on a reception signal sequence consisting of a plurality of reception signals output in parallel from the plurality of transducers or a pseudo reception signal sequence equivalent thereto; applying a correction to the received signal sequence or the pseudo received signal sequence to eliminate the position shift resulting from the synchronization shift and a delay-and-sum process for forming a receive beam, thereby generating corrected received information; generating a photoacoustic image representing the position of the light absorbing element in the living body based on the corrected reception information; A photoacoustic image generating method comprising:

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