Ultrasonic imaging system and synchronization control method

Abstract

The invention provides an ultrasonic imaging system and a synchronization control method. In an ultrasonic imaging system that images the position of an insert using a photoacoustic effect, an optical pulse period and a reception period are correctly synchronized. An insertion member inserted into a living body (16) has a light absorbing element (18a) that absorbs a light pulse and generates a photoacoustic wave. The analyzer (52) calculates a synchronization deviation from the photoacoustic wave signal sequence included in the received signal sequence before the phasing addition. The synchronization controller (54) changes the optical pulse period or the reception period in accordance with the synchronization deviation. The synchronization deviation may also be calculated on the basis of a pseudo received signal column corresponding to the received signal column.

Description

Technical Field

[0001] The present invention relates to an ultrasonic imaging system and a synchronous control method, and more particularly to a technology for displaying the position of an insertion object inserted into a living body. Background Art

[0002] An ultrasonic imaging system is a system for treating or examining a patient, i.e., a living body, using an ultrasonic imaging device. More specifically, in the ultrasonic imaging system, an image showing the position of an insertion component inserted into the living body is generated and displayed. The living body is treated, etc., while referring to this image. From this point of view, the ultrasonic imaging system is a system that supports the treatment of the living body, etc.

[0003] In an ultrasonic imaging system, an ultrasonic diagnostic device is generally used as an ultrasonic imaging device. An insertion component inserted into a living body is, for example, a catheter inserted into a blood vessel. Usually, a guide wire is inserted into the blood vessel before inserting the catheter. The guide wire is also an insertion component. An ultrasonic imaging system that uses an ultrasonic probe that abuts against the surface of a living body to image an insertion component inserted into a blood vessel is also called an EVUS (Extra-vascular ultrasound) system.

[0004] An advanced ultrasonic imaging system that uses the photoacoustic effect to image an insertion component has been proposed. In this ultrasonic imaging system, a light absorbing element is provided at the front end of the insertion component. The light pulse generated by the optical pulse generator is guided to the inside of the insertion object through an optical fiber, and the light pulse is irradiated to the light absorbing element. Photoacoustic waves are generated in the living body by the absorption of the light pulse in the light absorbing element. The photoacoustic waves are received by the ultrasonic probe abutting against the surface of the living body. Based on the received information thus obtained, an image (hereinafter referred to as a photoacoustic image or PA image) is formed to represent the position of the light absorbing element (i.e., the sound source). For example, a photoacoustic image is synthesized with an ultrasonic image (hereinafter also referred to as a US image) generated by the transceiver waves of the ultrasonic wave. The synthesized image thus generated is displayed. By observing the synthesized image, the position of the front end of the insertion component can be clearly determined while observing the living tissue.

[0005] In the above-mentioned advanced ultrasonic imaging system, it is necessary to accurately synchronize the optical pulse cycle in the optical pulse generator with the receiving cycle in the ultrasonic probe. For example, even if the sound source is located below the ultrasonic probe, if the time when the photoacoustic wave from the sound source reaches the ultrasonic probe is out of the receiving period, the sound source will not be imaged. In addition, if synchronization is not established, the receiving beamforming cannot be properly performed, resulting in reduced image quality.

[0006] The above-mentioned advanced ultrasonic imaging system is disclosed in Patent Document 1. In this system, a method of electrically synchronizing reception and optical pulses is adopted, that is, a special dedicated circuit for synchronization is required. Therefore, it can be pointed out that the system structure is complicated. In addition, Patent Document 2 describes a photoacoustic diagnostic device. This photoacoustic diagnostic device does not image the position of an insert inserted into a living body.

[0007] Patent Document 1: Japanese Patent No. 5819387

[0008] Patent Document 2: Japanese Patent Application Publication No. 2012-29715 Summary of the invention

[0009] An object of the present invention is to accurately synchronize a light pulse cycle and a reception cycle in an ultrasonic imaging system that uses the photoacoustic effect to image the position of an inserted component while avoiding or reducing the complexity of the system configuration.

[0010] The ultrasonic imaging system according to the present invention is characterized by comprising:

[0011] a light source, generating light pulses;

[0012] an insertion member, which is inserted into a living body and has a light absorbing element for converting the light pulse into a photoacoustic wave;

[0013] A probe having a plurality of vibrators for receiving the photoacoustic waves;

[0014] A receiver that applies phase addition to a reception signal train composed of a plurality of reception signals output in parallel from the plurality of transducers;

[0015] a generator that generates a photoacoustic image indicating a position of the light absorbing element in the living body based on the reception information output from the receiver;

[0016] an analyzer that analyzes the received signal sequence or a pseudo received signal sequence equivalent to the received signal sequence, thereby calculating a synchronization deviation between a light pulse period in the light source and a receiving period in the probe; and

[0017] The controller changes at least one of the optical pulse period and the receiving period according to the synchronization deviation.

[0018] The synchronization control method involved in the present invention is characterized in that it includes the following steps: when an insertion component having a light absorption element that converts light pulses from a light source into photoacoustic waves is inserted into an acoustic propagation medium and a probe is in contact with the acoustic propagation medium, a plurality of vibrators in the probe receive the photoacoustic waves from the light absorption element; a reception signal train composed of a plurality of reception signals output in parallel from the plurality of vibrators or a pseudo reception signal train equivalent to the reception signal train is analyzed, thereby calculating a synchronization deviation between the light pulse period in the light source and the reception period in the probe; and at least one of the light pulse period and the reception period is changed according to the synchronization deviation.

[0019] Effects of the Invention

[0020] According to the present invention, in an ultrasonic imaging system for imaging the position of an insertion member using the photoacoustic effect, it is possible to accurately synchronize the optical pulse cycle and the reception cycle while avoiding or reducing the complexity of the system configuration. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is a block diagram showing the ultrasonic imaging system according to the first embodiment.

[0022] Figure 2 This is a timing chart showing the first example of the synchronous control method.

[0023] Figure 3 FIG. 1 is a diagram showing an example of a received signal before phasing and addition.

[0024] Figure 4 This is a diagram showing an example of a received signal sequence before phasing and addition.

[0025] Figure 5 This is a diagram showing the spatial relationship between the sound source and the transducer array.

[0026] Figure 6 This is a graph showing the relationship between synchronization deviation, actual propagation time, and apparent propagation time.

[0027] Figure 7 This is a diagram showing an example of a synchronization deviation calculation method.

[0028] Figure 8 This is a flowchart showing a first example of the synchronous control method.

[0029] Fig. 9 This is a timing chart showing the second example of the synchronous control method.

[0030] Fig.10 This is a flowchart showing a second example of the synchronous control method.

[0031] Fig.11This is a block diagram showing an ultrasonic imaging system according to the second embodiment.

[0032] Fig.12 It is a diagram showing the first modified example.

[0033] Fig.13 It is a diagram showing a second modified example.

[0034] Fig.14 This is a flowchart showing the operation of the ultrasonic imaging system.

[0035] Explanation of symbols

[0036] 10-light pulse generating device, 12-ultrasonic diagnostic device, 14-information processing device, 17-light source, 18-insertion component, 18a-light absorbing element (sound source), 20-photoacoustic wave, 21-ultrasonic probe, 22-transducer array, 26-receiving circuit, 31-phase addition unit, 40-US image generating unit, 42-PA image generating unit. DETAILED DESCRIPTION

[0037] Hereinafter, embodiments will be described with reference to the drawings.

[0038] (1) Overview of implementation methods

[0039] The ultrasonic imaging system involved in the embodiment has a light source, an insertion component, a probe, a receiver, a generator, an analyzer and a controller. The light source generates a light pulse. The insertion component is inserted into a living body and has a light absorption element that converts the light pulse into a photoacoustic wave. The probe has a plurality of vibrators that receive the photoacoustic wave. The receiver applies phase addition to a reception signal column composed of a plurality of reception signals output in parallel by a plurality of vibrators. The generator generates a photoacoustic image representing the position of the light absorption element in the living body based on the reception information output from the receiver. The analyzer analyzes the reception signal column or a pseudo reception signal column equivalent to the reception signal column, thereby calculating the synchronization deviation between the light pulse period in the light source and the reception period in the probe. The controller changes at least one of the light pulse period and the reception period based on the synchronization deviation.

[0040] According to the above structure, the received signal sequence generated by receiving the photoacoustic wave or the pseudo received signal sequence equivalent to the received signal sequence can be analyzed to determine the synchronization deviation. Then, based on the determined synchronization deviation, the optical pulse period and the receiving period can be correctly synchronized without using expensive or complicated equipment.

[0041] One or both of the analyzer and the controller may be configured in an ultrasonic imaging device, an information processing device, or an optical pulse generating device including a light source. When the pulse period is changed according to the synchronization deviation, the pulse period is aligned with the receiving period. When the receiving period is changed according to the synchronization deviation, the receiving period is aligned with the pulse period.

[0042] The synchronization deviation can be measured when the insertion component is inserted into a living body, or when the insertion component is inserted into a sound propagation medium other than a living body. The insertion component is a component for treatment or a component for inspection. From the perspective of calculating the synchronization deviation, the pseudo reception signal sequence can be regarded as the above-mentioned reception signal sequence. For example, the pseudo reception signal can also be generated by applying an operation opposite to the phase addition to the reception information output from the receiver.

[0043] In an embodiment, the analyzer detects a plurality of photoacoustic wave signals included in a received signal column or a pseudo received signal column, and calculates synchronization deviations based on a plurality of detection times of the plurality of photoacoustic wave signals. According to this structure, the synchronization deviation is calculated based on the time when the photoacoustic wave reaches each oscillator. In each received signal or each pseudo received signal, the photoacoustic wave signal appears in the form of a peak or pulse with a large amplitude. It is relatively easy to determine a single photoacoustic wave signal.

[0044] In an embodiment, the analyzer calculates a plurality of apparent propagation times from the start time of the reception cycle to a plurality of detection times, and calculates synchronization deviation based on the plurality of apparent propagation times. Specifically, the analyzer calculates synchronization deviation by assigning the plurality of apparent propagation times to a mathematical model including a synchronization deviation parameter as an unknown parameter. The apparent propagation time is a time including a delay time equivalent to a phase deviation.

[0045] The synchronization mismatch may be calculated by a method other than the method using a mathematical model. For example, the synchronization mismatch may be calculated based on the shape drawn by the photoacoustic wave signal sequence in the reception signal sequence or the pseudo reception signal sequence.

[0046] In an embodiment, the analyzer analyzes the received signal sequence taken out from the receiver. The received signal sequence taken out is the received signal sequence before phasing and addition. Alternatively, the analyzer analyzes the pseudo received signal. In this case, a restorer is provided to generate a pseudo received signal sequence equivalent to the received signal sequence based on the received information.

[0047] In an embodiment, when the photoacoustic wave signal column is not included in the received signal column or the pseudo received signal column, the controller tentatively changes at least one of the light pulse period and the receiving period until the photoacoustic wave signal column is included in the received signal column or the pseudo received signal column. For example, a new pulse period or a new receiving period can be tentatively determined by adding a certain time to the pulse period or the receiving period, or by subtracting a certain time from the pulse period or the receiving period.

[0048] In an embodiment, the controller changes at least one of the light pulse period and the receiving period according to the synchronization deviation in a preparatory process before the present process of treating or inspecting a living body. The preparatory process is a synchronization establishment process. In the preparatory process, an acoustic propagation medium other than the living body is used as needed. This process is a treatment process or an inspection process. In this process, the calculation of the synchronization deviation and the control for maintaining synchronization can be performed.

[0049] The synchronous control method involved in the embodiment includes a receiving step, a calculation step, and a changing step. In the receiving step, when an insertion component having a light absorbing element that converts a light pulse from a light source into a photoacoustic wave is inserted into an acoustic propagation medium and the probe is in contact with the acoustic propagation medium, a plurality of vibrators in the probe receive the photoacoustic waves from the light absorbing element. In the calculation step, a reception signal train consisting of a plurality of reception signals output in parallel from a plurality of vibrators or a pseudo reception signal train equivalent to the reception signal train is analyzed, thereby calculating the synchronization deviation between the light pulse period in the light source and the reception period in the probe. In the changing step, at least one of the light pulse period and the reception period is changed according to the synchronization deviation.

[0050] (2) Details of implementation methods

[0051] exist Figure 1 , an ultrasonic imaging system according to the first embodiment is shown. The ultrasonic imaging system is a medical system installed in a medical institution such as a hospital, and is specifically a system used when the front end of the insertion member is delivered to the affected part while observing a photoacoustic image (PA image) indicating the position of the front end of the insertion member. The ultrasonic imaging system can also be used for other purposes.

[0052] The ultrasonic imaging system includes an optical pulse generating device 10, an ultrasonic diagnostic device 12, an information processing device 14, and an insertion member 18. The optical pulse generating device 10 includes a light source 17. The light source 17 is a laser that generates a pulse train of a laser beam. The base end of an optical fiber 19 is connected to the light source 17. The front end of the optical fiber 19 is located in the front end portion of the insertion member 18.

[0053] The insertion member 18 is, for example, a catheter inserted into a blood vessel in the living body 16. As another example of the insertion member 18, a guide wire, a puncture needle, etc. can be cited. A light absorbing element 18a made of a light absorbing material is provided in the front end portion of the insertion member 18. When a light pulse is irradiated to the light absorbing element 18a, the light absorbing element 18a absorbs the light pulse. At this time, a photoacoustic wave 20 is generated due to the photoacoustic effect. The photoacoustic wave 20 propagates in the living body 16 as a pulsed wave.

[0054] Next, the ultrasonic diagnostic apparatus 12 as an ultrasonic imaging apparatus will be described. The ultrasonic probe 21 is in contact with the surface 16A of the living body 16. The ultrasonic probe 21 is held by an examiner or a robot. A transducer array 22 composed of a plurality of transducers is provided in the ultrasonic probe 21.

[0055] When forming a normal tomographic image, ultrasonic waves are transmitted into the living body 16 by the transducer array 22, and reflected waves from the living body 16 are received by the transducer array 22. More specifically, a transmission beam and a reception beam are formed and electronically scanned.

[0056] When forming a photoacoustic image, the transducer array 22 does not perform a transmission operation, but only a reception operation. That is, the transducer array 22 receives the photoacoustic waves generated in the living body 16. More specifically, a plurality of reception periods are set on the time axis according to the reception cycle. Each reception period is a period for receiving or detecting photoacoustic waves, in other words, it is equivalent to a reception beam forming period.

[0057] In addition, multiple receiving beams may be formed in parallel at the same time during each receiving period. The receiving signal sequence obtained from the entire transducer array 22 may be used as receiving information for synchronization deviation analysis, and a part of the receiving signal sequence may be used as receiving information for receiving beam forming. Usually, the transmitting and receiving process for forming a tomographic image and the receiving process for forming a photoacoustic image are performed alternately.

[0058] The transmission circuit 24 is a transmission beamformer. That is, the transmission circuit 24 is an electronic circuit that outputs a plurality of transmission signals to a plurality of transducers in parallel during transmission.

[0059] The receiving circuit 26 is a receiving beam former, which is equivalent to a receiver or a receiving unit. Specifically, the receiving circuit 26 is an electronic circuit that processes a plurality of receiving signals outputted in parallel from a plurality of transducers during reception. The receiving circuit 26 includes a plurality of amplifiers 28 that amplify a plurality of receiving signals, an ADC 30 that converts the amplified plurality of receiving signals (analog signals) into a plurality of digital signals, and a phasing addition unit 31 that applies phasing addition to the converted plurality of receiving signals. Phasing addition is a process of generating receiving beam data from a plurality of receiving signals.

[0060] More specifically, the phasing and adding section 31 includes a memory 32 for temporarily storing the converted multiple received signals, an adder 34 for adding the multiple received signals read from the multiple memories, and a controller 36 for controlling the writing of the multiple received signals into the multiple memories 32 and the reading of the multiple received signals from the multiple memories 32. The phases of the multiple received signals are aligned by controlling the timing of reading the multiple received signals from the multiple memories 32. When performing the phasing and adding, so-called dynamic focusing of reception is performed, and so-called parallel reception is performed as needed.

[0061] The receiving circuit 26 outputs the receiving beam data generated by phasing and addition. A plurality of receiving beam data arranged in the electronic scanning direction are generated by electronic scanning of the receiving beam once. The receiving frame data corresponding to the beam scanning surface is formed by these plurality of receiving beam data. Each receiving beam data is composed of a plurality of echo data arranged in the depth direction. In addition, in the receiving circuit 26, the receiving beam data can be generated by software processing.

[0062] The processing circuit 38 is an electronic circuit that processes each reception beam data. The processing circuit 38 includes an envelope detection circuit, a filter circuit, a logarithmic conversion circuit, etc. When generating an ultrasonic image (US image), each reception beam data output from the processing circuit 38 is sent to the US image generation unit 40. When generating a photoacoustic image (PA image), each reception beam data output from the processing circuit 38 is sent to the PA image generation unit 42.

[0063] The US image generation unit 40 is a module having a digital scan converter (DSC) and generating display frame data from received frame data. Specifically, the US image generation unit 40 generates a tomographic image (B-mode tomographic image) representing the tissue structure as a US image. The DSC has a coordinate conversion function, a pixel interpolation function, and the like.

[0064] The PA image generation unit 42 is a module that includes a DSC and a sound source identification unit and generates display frame data from received frame data. The sound source identification unit determines the position of the sound source in the living body by detecting or extracting the sound source signal included in the display frame data generated by the DSC. The PA image includes a mark indicating the position of the sound source in the beam scanning plane. The mark is, for example, a point with high brightness or a specified color.

[0065] 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 46. The display 46 is composed of an organic EL display device, a liquid crystal display, or the like.

[0066] The US image generator 40 , the PA image generator 42 , and the display processor 44 are each configured by a processor. A CPU that controls the operation of the ultrasonic diagnostic apparatus 12 may function as the US image generator 40 , the PA image generator 42 , and the display processor 44 .

[0067] The transmission and reception control unit 59 controls the operations of the transmission circuit 24 and the reception circuit 26. The reception cycle and the length of the reception period are determined by the transmission and reception control unit 59. The CPU described above may function as the transmission and reception control unit 59.

[0068] In the ultrasonic diagnostic apparatus 12 according to the first embodiment, a received signal sequence before phasing and addition is taken out from the receiving circuit 26. The received signal sequence is composed of a plurality of received signals output from a plurality of ADCs 30. In the illustrated configuration example, the taken out plurality of received signals are temporarily stored in the memory 50 via the processing circuit 48. Each received signal may be output from the processing circuit 48 to the information processing device 14. Each received signal may be directly output from the receiving circuit 26 to the information processing device 14.

[0069] The processing circuit 48 is an electronic circuit that applies necessary signal processing to each received signal. The necessary signal processing may include envelope detection, noise removal, etc. The processing circuit 48 and the memory 50 (reference symbol 14A) may be provided in the information processing device 14 .

[0070] The information processing device 14 is constituted by, for example, a computer. The information processing device 14 has an analyzer 52 and a synchronization controller 54. These are constituted by a processor. The CPU in the information processing device 14 may also function as the analyzer 52 and the synchronization controller 54. In addition, the analyzer 52 and the synchronization controller 54 may also be provided in the optical pulse generating device 10 or in the ultrasonic diagnostic device 12.

[0071] The analyzer 52 detects the photoacoustic wave signal sequence contained in the received signal sequence before phase addition, and calculates the synchronization deviation (synchronization deviation amount) between the light pulse period and the received period based on the photoacoustic wave signal sequence. The synchronization deviation can also be called phase deviation. The calculation method of the synchronization deviation will be described in detail later.

[0072] The synchronization controller 54 has a function of changing or correcting at least one of the optical pulse period and the receiving period according to the calculated synchronization deviation, thereby synchronizing the optical pulse period with the receiving period (synchronization control function). In addition, the synchronization controller 54 has a function of tentatively changing the optical pulse period or the receiving period (trial change function). In the case where the photoacoustic wave cannot be observed because the photoacoustic wave reaches the transducer array 22 during a period other than the receiving period, the synchronization controller 54 tentatively changes at least one of the optical pulse period and the receiving period.

[0073] When the optical pulse cycle is changed between the optical pulse cycle and the receiving cycle, the synchronous controller 54 outputs a control signal 56 to the optical pulse generating device 10. When the receiving cycle is changed between the optical pulse cycle and the receiving cycle, the synchronous controller 54 outputs a control signal 58 to the transmission and reception control unit 59. Here, the receiving cycle is a receiving cycle for generating a PA image.

[0074] As described later, in the preparation process, synchronization between the light pulse cycle and the receiving cycle is established. In the process (treatment process, inspection process) after the preparation process, the light pulse cycle and the receiving cycle are maintained. Of course, in the process after the preparation process, control for maintaining the synchronization establishment state can also be continuously implemented.

[0075] exist Figure 2 , a first example of synchronization control is shown as a timing chart. (A) shows a light pulse train generated by a light source. The light pulse train is composed of a plurality of light pulses 70 arranged on a time axis. The width of the light pulse is, for example, 100 ns, and the light pulse period is, for example, 1 ms.

[0076] (B) shows a plurality of photoacoustic wave signal trains 72 arranged on the time axis. Figure 2 In FIG. 7 , each photoacoustic wave signal train 72 is schematically represented, that is, represented as a single pulse wave. A plurality of photoacoustic wave signals are generated in parallel by receiving a photoacoustic wave generated by one light pulse by a plurality of oscillators. The photoacoustic wave signal train 72 is composed of a plurality of photoacoustic wave signals. d represents the propagation time of the photoacoustic wave.

[0077] (C) shows a plurality of receiving periods 74 arranged on the time axis. Each receiving period 74 is a period during which photoacoustic waves can be received. Each receiving period 74 is set in the ultrasonic probe, in other words, in the receiving circuit. For example, a receiving aperture is set for the entire transducer array, and a receiving signal sequence corresponding to the receiving aperture is analyzed.

[0078] exist Figure 2 In the first example shown, the optical pulse period is changed in the optical pulse period and the receiving period according to the calculated synchronization deviation. TA1, TA2, and TA2+δ1 represent the optical pulse period, respectively. TB represents the receiving period. The receiving period TB is fixed. The time length of each receiving period 74 is T1. Incidentally, T2 is the time length of the blank period.

[0079] When the synchronization controller described above cannot observe the photoacoustic wave signal train 72 within the reception period 74, the light pulse cycle is tentatively changed. Specifically, the next light pulse cycle TA2 is set by adding or subtracting a certain period from the light pulse cycle TA1.

[0080] exist Figure 2In the example shown, the photoacoustic wave signal train 72A is observed during the receiving period 74A. By analyzing the photoacoustic wave signal train 72A, the synchronization deviation δ1 (reference symbol 76) is calculated, and by adding the synchronization deviation δ1 to the current light pulse period TA2, a new light pulse period TA2+δ1 is set. As a result, synchronization between the light pulse period and the receiving period is established. Specifically, during the receiving period 74B, the photoacoustic wave signal train 72B is correctly observed. Then, as needed, in order to maintain the synchronization establishment state, the calculation of the synchronization deviation and the control based on the synchronization deviation are continuously implemented.

[0081] exist Figure 3 The example in FIG. 7 shows a received signal before phase addition. The received signal 77 includes a photoacoustic wave signal 78 generated by receiving the photoacoustic wave. The photoacoustic wave signal 78 has a peak-shaped or pulse-shaped form with a large amplitude. For example, the photoacoustic wave signal 78 can be detected or extracted by threshold processing. In this case, the portion exceeding the threshold value α is determined as the photoacoustic wave signal 78. The threshold value α can also be set according to the size of the noise contained in the received signal. For example, when the standard deviation of the received signal is expressed as σ, the threshold value α can also be set according to α=6σ. Before threshold processing, filtering processing, envelope detection, etc. can also be applied to the received signal.

[0082] By detecting the photoacoustic wave signal 78, the time (detection time) td at which the photoacoustic wave is detected is determined for each received signal. The period pi from the start time ts of the reception period to the detection time td includes the time equivalent to the propagation time of the photoacoustic wave and the synchronization deviation. From this point of view, in the following, the period pi is referred to as the apparent propagation time.

[0083] exist Figure 4 exemplifies a received signal sequence before phasing and addition. The received signal sequence is composed of a plurality of received signals 80 corresponding to a plurality of transducers constituting the transducer array. Figure 4 In the diagram, the x direction is the direction of the transducer arrangement, and the y direction is the depth direction. The y direction is equivalent to the time axis.

[0084] The received signal train includes the photoacoustic wave signal train 84. In the example shown in the figure, the x coordinate (xc) of the center of the transducer array coincides with the x coordinate of the sound source, and the x coordinate of the vertex of the photoacoustic wave signal train 84 coincides with the x coordinate (xc) of the center of the transducer array.

[0085] The photoacoustic wave signal train 84 is composed of a plurality of photoacoustic wave signals. If attention is paid to the specific photoacoustic wave signal 82 received by the i-th transducer, the apparent propagation time pi is determined based on the detection time. The specific photoacoustic wave signal 82 is generated at a location at a depth yi.

[0086] The photoacoustic wave signal train 84 has a parabolic shape. The shape of the photoacoustic wave signal train 84 is constant regardless of the size of the synchronization deviation. The position at which the photoacoustic wave signal train 84 is generated varies according to the spatial relationship between the transducer array and the sound source. For example, when the position of the sound source is displaced in the x direction from the center position xc of the transducer array, a photoacoustic wave signal train 90 is generated. The x coordinate (xc1) of the vertex 90a is equivalent to the x coordinate of the sound source. Even in this case, the shape of the photoacoustic wave signal train 90 is the same as the shape of the photoacoustic wave signal train 84.

[0087] The synchronization deviation is calculated based on the photoacoustic wave signal train 84, and at least one of the light pulse period and the reception period is changed based on the synchronization deviation. Figure 4 In the coordinate space shown, the photoacoustic wave signal train 84 moves in parallel along the depth direction (reference symbol 86 ). Reference symbol 88 denotes the photoacoustic wave signal train observed when the synchronization deviation is eliminated.

[0088] The following describes the calculation method of synchronization deviation. Figure 5 The spatial relationship between the transducer array 92 and the sound source 96 is shown in the figure. The x direction is the direction of arrangement of the transducers, 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 represented by (xi,yi). Where yi=0. The position of the sound source 96 is represented by (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 formula (1). In formula (1), c is the sound velocity of the ultrasonic wave in the medium.

[0089] [Formula 1]

[0090]

[0091] The apparent propagation time pi is the time obtained by adding the synchronization error δ to the propagation time di. That is, the apparent propagation time pi is expressed as in the following formula (2).

[0092] [Formula 2]

[0093]

[0094] Figure 6 The relationship between the apparent propagation time pi, the synchronization deviation δ and the propagation time (actual propagation time) di represented in the above formula (2) is shown. The receiving period 102 is the period from the start time ts to the end time te. The synchronization deviation of the time between the start time ts and the generation time of the light pulse 98 is δ. The propagation time from the generation time of the light pulse 98 (the generation time of the photoacoustic wave) to the reception of the photoacoustic wave by the i-th oscillator is di. Symbol 100 represents the photoacoustic wave signal generated by receiving the photoacoustic wave.

[0095] The photoacoustic waves reach n oscillators, and n detection times td corresponding to the n oscillators are determined. Based on the n detection times td, n apparent propagation times pi are determined. Based on the positions xi of the n oscillators and the n apparent propagation times pi, n data pairs (xi, pi) (where i = 1, ..., n) are defined.

[0096] By substituting n data pairs (xi, pi) into the above formula (2) as a mathematical model, the unknown parameters δ, xb, and yb can be determined. At this time, a solution search method such as the least squares method is used. In this method, in addition to the synchronization deviation δ, the coordinates (xb, yb) of the sound source are also determined.

[0097] exist Figure 7 The method described above is schematically represented in . In the analyzer 52, n photoacoustic wave signals contained in the n received signals before phase addition are detected in box 130, and n apparent propagation times pi from the start time of the receiving period to the n detection times 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 box 134, the synchronization deviation δ as an unknown parameter is calculated by substituting the n data pairs (xi, pi) 122 into the above formula (2). Secondly, the coordinates (xb, yb) of the sound source are also calculated. Among the n data pairs (xi, pi) 122, as long as multiple data pairs (xi, pi) 122 that meet certain conditions are substituted into the above formula (2).

[0098] Figure 1 The analyzer shown calculates the synchronization deviation δ by analyzing a plurality of received signals. Figure 1 The synchronization controller shown changes one of the light pulse period or the reception period according to the synchronization deviation δ. When the light pulse period is changed, the reception period can be maintained, so that the advantage of not having to change the transmission and reception sequence in the ultrasonic diagnostic apparatus can be obtained. When the reception period is changed, communication between the information processing apparatus (or ultrasonic diagnostic apparatus) and the light pulse generating apparatus is not required, so the structure of the ultrasonic imaging system can be simplified.

[0099] Furthermore, if we focus on |xi-xb| in the above formula (2), |xi-xb|<<yb holds true in most cases. Therefore, the following formula (3) holds true for the above formula (2).

[0100] [Formula 3]

[0101]

[0102] The above formula (3) indicates that in the above xy coordinate system, a plurality of photoacoustic wave signals describe a parabola. The above formula (3) can also be used to determine the synchronization deviation δ. In addition, the photoacoustic image can be generated using the coordinates (xb, yb) of the determined sound source, and the operation of the ultrasonic imaging system can be controlled according to the coordinates (xb, yb) of the determined sound source.

[0103] Incidentally, when performing synchronization control, the smoothed synchronization deviation calculated at each time point may be referred to instead of directly referring to the synchronization deviation. In this case, for example, the smoothed synchronization deviation may be calculated according to the following equation (4).

[0104] [Formula 4]

[0105]

[0106] In the above formula (4), δ j Indicates the jth synchronization deviation. PRT j+1 = represents the j+1th optical pulse period calculated from the jth optical pulse period. In formula (4), N synchronization deviations are averaged, and the average synchronization deviation is added to the jth optical pulse period. The optical pulse period smoothed by other calculation formulas may also be calculated.

[0107] The calculated synchronization deviation or the smoothed synchronization deviation may be multiplied by a certain coefficient (for example, 0.8), and the optical pulse period or the reception period may be corrected based on the synchronization deviation obtained by the multiplication.

[0108] exist Figure 8 The first example of the synchronous control method is shown as a flowchart. In S10, it is determined whether the received signal sequence before phase adjustment and addition contains a photoacoustic wave signal sequence. In other words, it is determined whether a photoacoustic wave signal is received. For example, it is determined whether there is a photoacoustic wave signal sequence based on the result of threshold processing for each received signal.

[0109] As the case where the photoacoustic wave signal is not received, the first case and the second case can be considered. The first case refers to the case where there is no sound source in the observation area of ​​the ultrasonic probe. The second case refers to the case where there is a sound source in the observation area of ​​the ultrasonic probe, but the reception time of the photoacoustic wave deviates from the reception period due to synchronization deviation.

[0110] S12 is a process for dealing with the second situation. In S12, for example, a certain time is added to the light pulse period TA, thereby setting a new light pulse period. Then, S10 is executed again. For example, when the sound source is close to the ultrasonic probe, S12 can be executed by receiving a specified input from the user. In this case, when the sound source is not close to the ultrasonic probe, meaningless changes in the light pulse period TA can be avoided. As described later, when the sound source is positioned directly below the ultrasonic probe and synchronization is established, S12 can be executed from the beginning.

[0111] In S14, the synchronization deviation is calculated based on the photoacoustic wave signal column contained in the received signal column before phase addition. In S16, it is determined whether the synchronization deviation is greater than a specified threshold. When the synchronization deviation is below the specified threshold, the light pulse period TA is maintained. When the synchronization deviation is greater than the specified threshold, the light pulse period TA is changed in S18. In S20, it is determined whether to continue the present process. When it is determined that the present process is to be continued, the steps after S10 are executed again.

[0112] exist Fig. 9 In FIG. 1 , a second example of the synchronous control method is shown as a timing diagram. Fig. 9 In, with Figure 2 The same elements as those shown are denoted by the same reference numerals, and description thereof will be omitted.

[0113] exist Fig. 9 In , TB1, TB2, and TB2+δ2 represent reception cycles respectively. The light pulse cycle TA is fixed. When the photoacoustic wave signal train 72 is not detected in the reception period 74, the reception cycle is tentatively changed. Specifically, the next reception cycle TB2 is set by adding a certain period to the reception cycle TB1.

[0114] During the receiving period 74A, the photoacoustic wave signal train 72A is observed. By analyzing the photoacoustic wave signal train 72A, the synchronization deviation δ2 (reference symbol 76A) is calculated, and by adding the synchronization deviation δ2 to the current receiving period TB2, a new receiving period TB2+δ2 is set. As a result, synchronization between the light pulse period and the receiving period is established. Specifically, during the receiving period 74B, the photoacoustic wave signal train 72B is observed.

[0115] exist Fig.10 A second example of the synchronous control method is shown as a flow chart. Fig.10 In, with Figure 8 The same steps as those shown are denoted by the same step numbers, and their descriptions are omitted. In this second example, in S12A, the reception cycle TB is tentatively changed. And in S18A, the reception cycle TB is corrected according to the synchronization deviation.

[0116] exist Fig.11 FIG. 2 shows an ultrasonic imaging system according to a second embodiment. Fig.11 In, with Figure 1 The same elements as those shown are denoted by the same reference numerals, and description thereof will be omitted.

[0117] In the second embodiment, the reception information 60 output from the processing circuit 38 is transmitted to the information processing device 14B. The reception information 60 is a plurality of reception beam data that has been processed in a certain manner. The reception information output from the reception circuit 26A may also be transmitted to the information processing device 14B. By transmitting a plurality of reception beam data after envelope detection, the amount of transmission data can be greatly reduced.

[0118] The information processing device 14B includes a restorer 62, a memory 50A, an analyzer 52 and a synchronization controller 54. The restorer 62 applies an operation opposite to the phase addition to the received information 60. This opposite operation is also called inverse Fourier transform or inverse phase addition. The restorer 62 generates a pseudo received signal sequence equivalent to the received signal sequence before the phase addition. The pseudo received signal sequence is temporarily stored in the memory 50A.

[0119] When the pseudo received signal sequence is mapped to the xy coordinate space, the same as Figure 4 The analyzer 52 calculates the synchronization deviation from the photoacoustic wave signal sequence included in the pseudo reception signal sequence using the above-mentioned method. The synchronization controller 54 changes the optical pulse period or the reception period according to the synchronization deviation.

[0120] According to the second embodiment, the advantage of being able to easily extract the transmitted information from the ultrasonic diagnostic apparatus can be obtained. The received information or PA image after coordinate transformation can also be transmitted to the information processing apparatus. Alternatively, the information output from the display processing unit 44 can also be transmitted to the information processing apparatus 14B. In these cases, a pseudo received signal sequence is generated based on the transmitted information. All or part of the structure from the restorer 62 to the synchronization controller 54 can be set in the ultrasonic diagnostic apparatus 12A.

[0121] It is also possible to use a sound propagation medium other than a living body to implement control to establish synchronization. Fig.12 The first variant is shown in Fig.13 A second variation is shown in FIG.

[0122] exist Fig.12In the first variant shown, the water tank 108 contains a container for storing water 110 as a sound propagation medium. The transceiver wave surface of the ultrasonic probe 104 is in contact with the surface of the water 110, or the front end of the ultrasonic probe 104 is inserted into the water 110. In this state, the insertion component 112 is inserted into the water 110, and the sound source 114 is positioned directly below the ultrasonic probe 104, specifically, directly below the transducer array in the ultrasonic probe 104. In this state, photoacoustic waves are generated. The photoacoustic waves are detected in the multiple transducers constituting the transducer array 106. The synchronization deviation is calculated based on the received signal train thus obtained, and the optical pulse period or the receiving period is corrected based on the calculated synchronization deviation.

[0123] exist Fig.13 In the second variant shown, the ultrasonic probe 116 is held in a manner in which the transceiver surface of the ultrasonic probe 116 faces upward. A large amount of acoustic gel 120 is provided on the transceiver surface. For example, the acoustic gel 120 is introduced in a manner in which a protrusion of the acoustic gel 120 is generated on the transceiver surface. Then, the light absorbing element of the insertion part 122, i.e., the sound source 124, is inserted into the acoustic gel 120. In this state, photoacoustic waves are generated. The photoacoustic waves are detected in the multiple transducers constituting the transducer array 118. The synchronization deviation is calculated based on the received signal train thus obtained, and the optical pulse period or the receiving period is corrected based on the calculated synchronization deviation.

[0124] exist Fig.14 The operation of the ultrasonic imaging system is shown in FIG. S30 is a preparation process. In S30, the above-mentioned method is used to establish synchronization between the light pulse period and the receiving period. S32 is the main process. In S32, an insertion component is used to treat or examine a living body. In S32, the light pulse period and the receiving period can be fixed, or the above-mentioned method can be continuously applied to maintain the synchronization establishment state.

[0125] As described above, according to the ultrasonic imaging system according to the embodiment, it is possible to accurately synchronize the optical pulse cycle and the reception cycle while avoiding or reducing the complexity of the system configuration.

Claims

1. An ultrasonic imaging system, characterized in that: include: a light source, generating light pulses; an insertion member, which is inserted into a living body and has a light absorbing element for converting the light pulse into a photoacoustic wave; A probe having a plurality of vibrators for receiving the photoacoustic waves; A receiver that applies phase addition to a reception signal train composed of a plurality of reception signals output in parallel from the plurality of transducers; a generator that generates a photoacoustic image indicating a position of the light absorbing element in the living body based on the reception information output from the receiver; An analyzer that analyzes the received signal sequence or a pseudo received signal sequence equivalent to the received signal sequence, thereby calculating a synchronization deviation between a light pulse period in the light source and a receiving period in the probe; and The controller changes at least one of the optical pulse period and the receiving period according to the synchronization deviation.

2. The ultrasonic imaging system according to claim 1, characterized in that: The analyzer performs the following processing: detecting a plurality of photoacoustic wave signals included in the received signal train or the pseudo received signal train; The synchronization deviation is calculated based on a plurality of detection times of the plurality of photoacoustic wave signals.

3. The ultrasonic imaging system according to claim 2, characterized in that: The analyzer performs the following processing: Calculating a plurality of apparent propagation times from the start time of the receiving period to the plurality of detection times; The synchronization offset is calculated based on the plurality of apparent propagation times.

4. The ultrasonic imaging system according to claim 3, characterized in that: The analyzer calculates the synchronization deviation by assigning the plurality of apparent propagation times to a mathematical model including a synchronization deviation parameter as an unknown parameter.

5. The ultrasonic imaging system according to claim 1, characterized in that: The analyzer analyzes the reception signal sequence obtained from the receiver.

6. The ultrasonic imaging system according to claim 1, characterized in that: A restorer is included, wherein the restorer generates the pseudo reception signal sequence corresponding to the reception signal sequence based on the reception information, The analyzer analyzes the pseudo received signal train.

7. The ultrasonic imaging system according to claim 1, characterized in that: When the photoacoustic wave signal train is not included in the received signal train or the pseudo received signal train, the controller tentatively changes at least one of the light pulse period and the receiving period until the photoacoustic wave signal train is included in the received signal train or the pseudo received signal train.

8. The ultrasonic imaging system according to claim 1, characterized in that: The controller changes at least one of the optical pulse period and the reception period according to the synchronization deviation in a preparatory process before a process of treating or examining a living body.

9. A synchronous control method, characterized in that: Including the following processes: When an insertion member having a light absorbing element that converts light pulses from a light source into photoacoustic waves is inserted into an acoustic propagation medium and the probe is in contact with the acoustic propagation medium, a plurality of transducers in the probe receive the photoacoustic waves from the light absorbing element; Analyzing a reception signal train composed of a plurality of reception signals outputted in parallel from the plurality of transducers or a pseudo reception signal train equivalent to the reception signal train, thereby calculating a synchronization deviation between a light pulse period in the light source and a reception period in the probe; and At least one of the optical pulse period and the reception period is changed according to the synchronization deviation.

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