Ultrasonic imaging system and synchronization control method

Abstract

To cause a light pulse period and a reception period to synchronize with each other correctly in an ultrasonic imaging system for imaging the position of an inserted object using a photoacoustic effect.SOLUTION: An inserted member inserted into a living body 16 includes a light absorption element 18a for absorbing a light pulse and generating a photoacoustic wave. An analyzer 52 calculates a synchronization shift on the basis of a photoacoustic wave signal string included in a reception signal string prior to phasing addition. A synchronization controller 54 changes a light pulse period or a reception period on the basis of the synchronization shift. The synchronization shift may be calculated on the basis of a pseudo reception signal string equivalent to the reception signal string.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present disclosure relates to an ultrasonic imaging system and a synchronization control method, and particularly to a technique for displaying the position of an insert inserted into a living body.

Background Art

[0002] An ultrasonic imaging system is a system for treating or examining a living body of a patient using an ultrasonic imaging device. More specifically, in an ultrasonic imaging system, an image representing the position of an insertion member inserted into a living body is generated and displayed. Treatment of the living body and the like are performed while referring to such an image. From such a viewpoint, the ultrasonic imaging system is a system for assisting treatment of the living body and the like.

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

[0004] An advanced ultrasonic imaging system that images an insertion member using the photoacoustic effect has been proposed. In such an ultrasonic imaging system, a light absorption element is provided at the tip of the insertion member. A light pulse generated by a light pulse generator is guided through an optical fiber into the interior of the insert, and the light pulse is irradiated onto the light absorption element. Absorption of the light pulse by the light absorption element generates a photoacoustic wave in the living body. The photoacoustic wave is received by an ultrasonic probe that is in contact with the body surface. Based on the received information thus obtained, an image (hereinafter referred to as a photoacoustic image or a PA image) representing the position of the light absorption element (i.e., the sound source) is formed. For example, a photoacoustic image is synthesized with an ultrasonic image (hereinafter also referred to as a US image) generated by transmitting and receiving ultrasonic waves. The synthesized image thus generated is displayed. Through observation of the synthesized image, the position of the tip of the insertion member can be clearly identified while observing the biological tissue.

[0005] In the above-described advanced ultrasonic imaging system, it is necessary to precisely synchronize the light pulse period in the light pulse generator and the reception period in the ultrasonic probe. For example, even when the sound source is located below the ultrasonic probe, if the timing at which the photoacoustic wave from the sound source reaches the ultrasonic probe is outside the reception period, the sound source will not be imaged. Also, if synchronization is not established, reception beamforming will not be properly executed, and the quality of the image will deteriorate.

[0006] Patent Document 1 discloses the above-described advanced ultrasonic imaging system. In that system, a method of electrically synchronizing reception and the light pulse is adopted, that is, it is necessary to provide a special dedicated circuit for synchronization. Therefore, it can be pointed out that the system configuration becomes complicated. Note that Patent Document 2 describes a photoacoustic diagnostic apparatus. That photoacoustic diagnostic apparatus does not image the position of an insert inserted into a living body.

Prior Art Documents

Patent Documents

[0007] [Patent Document 1] Japanese Patent No. 5819387 [Patent Document 2] Japanese Unexamined Patent Application Publication No. 2012-29715 [Summary of the Invention] [Problems to be Solved by the Invention]

[0008] An object of the present disclosure is to correctly synchronize the optical pulse period and the reception period while avoiding or reducing the complexity of the system configuration in an ultrasonic imaging system that images the position of an insertion member using the photoacoustic effect. [Means for Solving the Problems]

[0009] The ultrasonic imaging system according to the present disclosure includes a light source that generates an optical pulse, an insertion member inserted into a living body and having a light absorption element that converts the optical pulse into a photoacoustic wave, a probe including a plurality of vibrators that receive the photoacoustic wave, a receiver that applies coherent summation to a reception signal sequence including a plurality of reception signals output in parallel from the plurality of vibrators, a generator that 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, an analyzer that analyzes the reception signal sequence or a pseudo-reception signal sequence corresponding to the reception signal sequence to calculate a synchronization deviation between the optical pulse period in the light source and the reception period in the probe, and a controller that changes at least one of the optical pulse period and the reception period based on the synchronization deviation.

[0010] The synchronization control method according to the present disclosure includes a step of receiving, by a plurality of oscillators in the probe, an optoacoustic wave from the photoabsorber while an insertion member having a photoabsorber that converts an optical pulse from a light source into an optoacoustic wave is inserted into an acoustic propagation medium and the probe is in contact with the acoustic propagation medium; a step of analyzing a received signal sequence composed of a plurality of received signals output in parallel from the plurality of oscillators or a pseudo-received signal sequence corresponding to the received signal sequence, thereby calculating a synchronization deviation between an optical pulse period at the light source and a reception period at the probe; and a step of changing at least one of the optical pulse period and the reception period based on the synchronization deviation.

Advantages of the Invention

[0011] According to the present disclosure, in an ultrasonic imaging system that images the position of an insertion member using the photoacoustic effect, it is possible to correctly synchronize the optical pulse period and the reception period while avoiding or reducing the complexity of the system configuration.

Brief Description of the Drawings

[0012]

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Embodiments for Carrying Out the Invention

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

[0014] (1) Outline of the Embodiment The ultrasonic imaging system according to the embodiment includes a light source, an insertion member, a probe, a receiver, a generator, an analyzer, and a controller. The light source generates optical pulses. The insertion member is inserted into a living body and has a light absorption element that converts optical pulses into photoacoustic waves. The probe includes a plurality of vibrators that receive photoacoustic waves. The receiver applies coherent addition to a reception signal sequence composed of a plurality of reception signals output in parallel from the 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 sequence or a pseudo-reception signal sequence corresponding to the reception signal sequence, and thereby calculates a synchronization deviation between the optical pulse period at the light source and the reception period at the probe. The controller changes at least one of the optical pulse period and the reception period based on the synchronization deviation.

[0015] According to the above configuration, it is possible to identify the synchronization deviation by analyzing the reception signal sequence generated by receiving the photoacoustic wave or a pseudo-reception signal sequence corresponding thereto. Moreover, based on the identified synchronization deviation, it is possible to correctly synchronize the optical pulse period and the reception period without using expensive or complex equipment.

[0016] One or both of the parser and the controller may be disposed in an ultrasonic imaging device, an information processing device, or an optical pulse generation device including a light source. When changing the pulse period based on the synchronization deviation, the pulse period is adjusted to the reception period. When changing the reception period based on the synchronization deviation, the reception period is adjusted to the pulse period.

[0017] The synchronization deviation may be measured in a state where the insertion member is inserted into a living body, or may be measured in a state where the insertion member is inserted into an acoustic propagation medium other than the living body. The insertion member is a member for treatment or a member for examination. The pseudo-reception signal sequence can be regarded as the above reception signal sequence from the viewpoint of calculating the synchronization deviation. For example, a pseudo-reception signal may be generated by applying an operation opposite to the integral addition to the reception information output from the receiver.

[0018] In an embodiment, the parser detects a plurality of photoacoustic wave signals included in the reception signal sequence or the pseudo-reception signal sequence, and calculates the synchronization deviation based on the plurality of detection timings of the plurality of photoacoustic wave signals. According to this configuration, the synchronization deviation is calculated based on the timing at which the photoacoustic wave reaches each vibrator. In each reception signal or each pseudo-reception signal, the photoacoustic wave signal appears as a peak or pulse having a large amplitude. It is relatively easy to identify individual photoacoustic wave signals.

[0019] In an embodiment, the parser calculates a plurality of apparent propagation times from the reception period start timing to the plurality of detection timings, and calculates the synchronization deviation based on the plurality of apparent propagation times. Specifically, the parser calculates the synchronization deviation by giving a 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 corresponding to the phase deviation.

[0020] The synchronization deviation may be calculated by a method other than the method using the mathematical model. For example, the synchronization deviation may be calculated based on the shape described by the photoacoustic wave signal sequence in the reception signal sequence or the pseudo-reception signal sequence.

[0021] In an embodiment, the analyzer analyzes the received signal sequence taken out from the receiver. The received signal sequence to be taken out is the received signal sequence before coherent addition. Alternatively, the analyzer analyzes the pseudo-received signal. In that case, based on the received information, a restorer for generating a pseudo-received signal sequence corresponding to the received signal sequence is provided.

[0022] In an embodiment, when the received signal sequence or the pseudo-received signal sequence does not include the photoacoustic wave signal sequence, the controller tentatively changes at least one of the optical pulse period and the reception period until the received signal sequence or the pseudo-received signal sequence includes the multi-photoacoustic wave signal sequence within the optical pulse period and the reception period. For example, a new optical pulse period or a new reception period may be tentatively determined by adding a certain time to the pulse period or the reception period, or by subtracting a certain time from the pulse period or the reception period.

[0023] In an embodiment, in the preparation step before the step of treating or examining a living body, the controller changes at least one of the optical pulse period and the reception period based on the synchronization deviation. The preparation step is a synchronization establishment step. In the preparation step, an acoustic propagation medium other than the living body is used as necessary. This step is a treatment step or an examination step. In this step, the calculation of the synchronization deviation and the control for maintaining synchronization may be executed.

[0024] The synchronization control method according to the embodiment includes a reception step, a calculation step, and a change step. In the reception step, an insertion member having a photoabsorption element that converts an optical pulse from a light source into a photoacoustic wave is inserted into an acoustic propagation medium, and in a state where a probe is in contact with the acoustic propagation medium, a plurality of vibrators in the probe receive the photoacoustic wave from the photoabsorption element. In the calculation step, a received signal sequence composed of a plurality of received signals output in parallel from the plurality of vibrators or a pseudo-received signal sequence corresponding to the received signal sequence is analyzed, whereby the synchronization deviation between the optical pulse period at the light source and the reception period at the probe is calculated. In the change step, at least one of the optical pulse period and the reception period is changed based on the synchronization deviation.

[0025] (2) Details of the Embodiment FIG. 1 shows an ultrasonic imaging system according to the first embodiment. The ultrasonic imaging system is a medical system installed in a medical institution such as a hospital. Specifically, it is a system used when sending the tip of an insertion member to the affected area while observing a photoacoustic image (PA image) representing the position of the tip of the insertion member. The ultrasonic imaging system may be used for other applications.

[0026] The ultrasonic imaging system includes an optical pulse generator 10, an ultrasonic diagnostic device 12, an information processing device 14, and an insertion member 18. The optical pulse generator 10 includes 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 inside the distal end portion of the insertion member 18.

[0027] 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. Inside the distal end portion of the insertion member 18, a photoabsorbing element 18a made of a photoabsorbing material is provided. By irradiating the photoabsorbing element 18a with an optical pulse, the photoabsorbing element 18a absorbs the optical pulse. At that time, a photoacoustic wave 20 is generated by the photoacoustic effect. The photoacoustic wave 20 propagates through the living body 16 as a pulsed wave.

[0028] Next, the ultrasonic diagnostic device 12 as an ultrasonic imaging device will be described. An 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. Inside the ultrasonic probe 21, an oscillator array 22 composed of a plurality of oscillators is provided.

[0029] When forming a normal tomographic image, ultrasonic waves are transmitted into the living body 16 by the oscillator array 22, and reflected waves from the living body 16 are received by the oscillator array 22. More specifically, transmission beams and reception beams are formed, and they are electronically scanned.

[0030] When forming a photoacoustic image, the oscillator array 22 does not perform a transmission operation but only a reception operation. That is, the photoacoustic wave generated in the living body 16 is received by the oscillator array 22. More specifically, a plurality of reception periods are set according to the reception cycle on the time axis. Each reception period is a period for receiving or detecting a photoacoustic wave, in other words, it corresponds to a reception beam forming period.

[0031] Note that a plurality of reception beams may be formed simultaneously and in parallel in each reception period. The reception signal sequence obtained from the entire oscillator array 22 may be used as reception information for synchronization deviation analysis, and a part of the reception signal sequence may be used as reception information for reception beam formation. Generally, the transmission and reception process for tomographic image formation and the reception process for photoacoustic image formation are alternately executed.

[0032] 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 oscillators in parallel during transmission.

[0033] The reception circuit 26 is a reception beamformer and corresponds to a receiver or a reception unit. Specifically, the reception circuit 26 is an electronic circuit that processes a plurality of reception signals output in parallel from a plurality of oscillators during reception. The reception circuit 26 includes a plurality of amplifiers 28 that amplify a plurality of reception signals, an ADC 30 that converts the amplified plurality of reception signals (analog signals) into a plurality of digital signals, and an addition unit 31 that applies coherent addition to the converted plurality of reception signals. Coherent addition is a process of generating reception beam data from a plurality of reception signals.

[0034] More specifically, the coherent addition unit 31 includes a plurality of memories 32 that temporarily store a plurality of received signals after conversion, an adder 34 that adds the plurality of received signals read from the plurality of memories, and a controller 36 that controls the writing of the plurality of received signals to the plurality of memories 32 and also controls the reading of the plurality of received signals from the plurality of memories 32. By controlling the reading timing of the plurality of received signals from the plurality of memories 32, the phases of the plurality of received signals are aligned. During coherent addition, so-called reception dynamic focus is implemented, and if necessary, so-called parallel reception is implemented.

[0035] The receiving circuit 26 outputs the received beam data generated by coherent addition. By one-time electronic scanning of a received beam, a plurality of received beam data arranged in the electronic scanning direction are generated. The plurality of received beam data constitute received frame data corresponding to the beam scanning surface. Each received beam data is composed of a plurality of echo data arranged in the depth direction. Note that in the receiving circuit 26, the received beam data may be generated by software processing.

[0036] The processing circuit 38 is an electronic circuit that processes each received 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 received 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 received beam data output from the processing circuit 38 is sent to the PA image generation unit 42.

[0037] The US image generation unit 40 is a module that has a digital scan converter (DSC) and generates display frame data from the 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, etc.

[0038] 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 the received frame data. The sound source identification unit identifies 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 marker representing the position of the sound source within the beam scanning plane. The marker is, for example, a point having high brightness or a predetermined color.

[0039] 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.

[0040] The US image generation unit 40, the PA image generation unit 42, and the display processing unit 44 are each constituted by a processor. The CPU that controls the operation of the ultrasonic diagnostic apparatus 12 may function as the US image generation unit 40, the PA image generation unit 42, and the display processing unit 44.

[0041] The transmission / reception control unit 59 controls the operations of the transmission circuit 24 and the reception circuit 26. The reception cycle and the duration of the reception period are determined by the transmission / reception control unit 59. The above CPU may function as the transmission / reception control unit 59.

[0042] In the ultrasonic diagnostic apparatus 12 according to the first embodiment, the received signal sequence before coherent addition is extracted from the reception 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 plurality of received signals extracted 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 apparatus 14. Each received signal may be directly output from the reception circuit 26 to the information processing apparatus 14.

[0043] 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 processing, and the like. The processing circuit 48 and the memory 50 may be provided in the information processing apparatus 14 (see reference numeral 14A).

[0044] The information processing apparatus 14 is constituted by, for example, a computer. The information processing apparatus 14 includes an analyzer 52 and a synchronization controller 54. They are constituted by a processor. The CPU in the information processing apparatus 14 may function as the analyzer 52 and the synchronization controller 54. Note that the analyzer 52 and the synchronization controller 54 may be provided in the optical pulse generation apparatus 10 or the ultrasonic diagnostic apparatus 12.

[0045] The analyzer 52 detects an optoacoustic wave signal train included in the received signal train before coherent addition, and calculates a synchronization deviation (synchronization deviation amount) between the optical pulse period and the reception period based on the optoacoustic wave signal train. The synchronization deviation can also be referred to as a phase deviation. The method for calculating the synchronization deviation will be described in detail later.

[0046] The synchronization controller 54 has a function (synchronization control function) of changing or correcting at least one of the optical pulse period and the reception period based on the calculated synchronization deviation, thereby synchronizing the optical pulse period and the reception period. In addition, the synchronization controller 54 has a function (trial change function) of tentatively changing the optical pulse period or the reception period. When the optoacoustic wave cannot be observed because the optoacoustic wave has reached the oscillator array 22 during a period other than the reception period, the synchronization controller 54 tentatively changes at least one of the optical pulse period and the reception period.

[0047] When changing the optical pulse period among the optical pulse period and the reception period, a control signal 56 is output from the synchronization controller 54 to the optical pulse generation apparatus 10. When changing the reception period among the optical pulse period and the reception period, a control signal 58 is output from the synchronization controller 54 to the transmission / reception control unit 59. Here, the reception period is the reception period for PA image generation.

[0048] As will be described later, in the preparation process, synchronization is established between the optical pulse period and the reception period. In this process (treatment process, inspection process) following the preparation process, the optical pulse period and the reception period are maintained. However, in this process following the preparation process, control for maintaining the synchronization established state may be continuously performed.

[0049] In FIG. 2, a first example of synchronization control is shown as a timing chart. (A) shows an optical pulse train generated by a light source. The optical pulse train is composed of a plurality of optical pulses 70 arranged on the time axis. The width of the optical pulse is, for example, 100 ns, and the optical pulse period is, for example, 1 ms.

[0050] (B) shows a plurality of photoacoustic wave signal trains 72 arranged on the time axis. In FIG. 2, 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 a plurality of oscillators receiving the photoacoustic wave generated by one optical pulse. The photoacoustic wave signal train 72 is composed of a plurality of photoacoustic wave signals. d indicates the propagation time of the photoacoustic wave.

[0051] (C) shows a plurality of reception periods 74 arranged on the time axis. Each reception period 74 is a period during which a photoacoustic wave can be received. Each reception period 74 is set in the ultrasonic probe, in other words, set for the reception circuit. For example, a reception aperture is set for the entire oscillator array, and the reception signal train corresponding to the reception aperture is analyzed.

[0052] In the first example shown in FIG. 2, based on the calculated synchronization deviation, the optical pulse period is changed within the optical pulse period and the reception period. TA1, TA2, TA2 + δ1 respectively indicate the optical pulse period. TB indicates the reception period. The reception period TB is fixed. The time length of each reception period 74 is T1. Incidentally, T2 is the time length of the blank period.

[0053] When the above-described synchronization controller cannot observe the photoacoustic wave signal train 72 within the reception period 74, it tentatively changes the optical pulse period. Specifically, the next optical pulse period TA2 is set by adding or subtracting a certain period from the optical pulse period TA1.

[0054] In the example shown in FIG. 2, within the reception period 74A, the photoacoustic wave signal train 72A is being observed. By analyzing the photoacoustic wave signal train 72A, a synchronization deviation δ1 has been calculated (see reference numeral 76), and by adding the synchronization deviation δ1 to the current optical pulse period TA2, a new optical pulse period TA2 + δ1 has been set. As a result, synchronization has been established between the optical pulse period and the reception period. Specifically, within the reception period 74B, the photoacoustic wave signal train 72B is being correctly observed. Thereafter, as necessary, in order to maintain the synchronization established state, the calculation of the synchronization deviation and the control based on the synchronization deviation are continuously performed.

[0055] FIG. 3 illustrates the received signal before coherent addition. The received signal 77 includes a photoacoustic wave signal 78 generated due to the reception of the photoacoustic wave. The photoacoustic wave signal 78 has a peak-like or pulse-like form with a large amplitude. For example, the photoacoustic wave signal 78 can be detected or extracted by threshold processing. In that case, the portion exceeding the threshold α is specified as the photoacoustic wave signal 78. The threshold α may be set according to the magnitude of the noise included in the received signal. For example, when the standard deviation of the received signal is expressed as σ, the threshold α may be set according to α = 6σ. Prior to the threshold processing, filtering, envelope detection, etc. may be applied to the received signal.

[0056] By detecting the photoacoustic wave signal 78, for each received signal, the timing (detection timing) td at which the photoacoustic wave was detected is specified. The period pi from the reception period start timing ts to the detection timing td includes the propagation time of the photoacoustic wave and the time corresponding to the synchronization deviation. From such a viewpoint, hereinafter, the period pi will be referred to as the apparent propagation time.

[0057] FIG. 4 illustrates a received signal sequence before coherent addition. The received signal sequence is composed of a plurality of received signals 80 corresponding to a plurality of oscillators constituting the oscillator array. In FIG. 4, the x direction is the oscillator array direction, and the y direction is the depth direction. The y direction corresponds to the time axis.

[0058] The received signal sequence includes a photoacoustic wave signal sequence 84. In the illustrated example, the x coordinate (xc) of the center of the oscillator array coincides with the x coordinate of the sound source, and the x coordinate of the apex of the photoacoustic wave signal sequence 84 coincides with the x coordinate (xc) of the center of the oscillator array.

[0059] The photoacoustic wave signal sequence 84 is composed of a plurality of photoacoustic wave signals. Focusing on a specific photoacoustic wave signal 82 received by the i-th oscillator, an apparent propagation time pi is specified based on its detection timing. The specific photoacoustic wave signal 82 occurs at a point with a depth yi.

[0060] The photoacoustic wave signal sequence 84 has a parabolic form. The form of the photoacoustic wave signal sequence 84 is constant regardless of the magnitude of the synchronization deviation. The position where the photoacoustic wave signal sequence 84 occurs changes depending on the spatial relationship between the oscillator array and the sound source. For example, when the position of the sound source is shifted in the x direction from the center position xc of the oscillator array, a photoacoustic wave signal sequence 90 is generated. The x coordinate (xc1) of its apex 90a corresponds to the x coordinate of the sound source. Even in that case, the form of the photoacoustic wave signal sequence 90 is the same as the form of the photoacoustic wave signal sequence 84.

[0061] Based on the photoacoustic wave signal sequence 84, the synchronization deviation is calculated, and at least one of the optical pulse period and the reception period is changed based on the synchronization deviation. As a result, in the coordinate space shown in FIG. 4, the photoacoustic wave signal sequence 84 is translated in the depth direction (see reference numeral 86). Reference numeral 88 indicates the photoacoustic wave signal sequence observed when the synchronization deviation is eliminated.

[0062] The method for calculating the phase difference will be described below. Fig. 5 shows the spatial relationship between the oscillator array 92 and the sound source 96. The x direction is the oscillator array direction, and the y direction is the depth direction. The center of the oscillator array 92 is the origin (0,0), and the position of the i-th oscillator 94 is represented by (xi, yi). However, 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 oscillator is calculated by the following equation (1). In equation (1), c is the speed of ultrasonic waves in the medium.

Number

[0063] The apparent propagation time pi is the time obtained by adding the phase difference δ and the propagation time di. That is, the apparent propagation time pi is expressed as in the following equation (2).

Number

[0064] The relationship among the apparent propagation time pi, the phase difference δ, and the propagation time (actual propagation time) di expressed in the above equation (2) is shown in Fig. 6. 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 optical pulse 98 is the phase difference δ. The propagation time from the generation timing of the optical pulse 98 (the generation timing of the photoacoustic wave) to the reception of the photoacoustic wave by the i-th oscillator is di. The reference numeral 100 indicates the photoacoustic wave signal generated by the reception of the photoacoustic wave.

[0065] When the photoacoustic wave reaches n oscillators, n detection timings td corresponding to the n oscillators are specified. Based on the n detection timings td, n apparent propagation times pi are specified. From the positions xi of the n oscillators and the n apparent propagation times pi, n data pairs (xi, pi) are defined (where i = 1, ···, n).

[0066] By substituting n data pairs (xi, pi) into the above equation (2), which is a mathematical model, it is possible to identify the unknown parameters δ, xb, and yb. In this case, 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 identified.

[0067] The method described above is schematically shown in FIG. 7. In the analyzer 52, 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. From the coordinates xi of the n vibration elements in the x direction and the n apparent propagation times pi, n data pairs (xi, pi) 132 are defined. In block 134, by substituting the n data pairs (xi, pi) 122 into the above equation (2), the synchronization deviation δ, which is an unknown parameter, is calculated. 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).

[0068] The analyzer shown in FIG. 1 calculates the synchronization deviation δ by analyzing a plurality of received signals. The synchronization controller shown in FIG. 1 changes one of the optical pulse period or the reception period based on the synchronization deviation δ. When changing the optical pulse period, the reception period can be maintained, so the advantage is obtained that there is no need to change the transmission / reception sequence in the ultrasonic diagnostic apparatus. When changing the reception period, communication between the information processing apparatus (or ultrasonic diagnostic apparatus) and the optical pulse generation apparatus becomes unnecessary, so the configuration of the ultrasonic imaging system can be simplified.

[0069] Regarding |xi - xb| in the above equation (2), in many cases, |xi - xb| << yb holds. Therefore, the following equation (3) holds for the above equation (2).

Equation

[0070] The above formula (3) indicates that in the above xy coordinate system, a plurality of photoacoustic wave signals form a parabola. The synchronization deviation δ may be specified using the above formula (3). In addition, a photoacoustic image may be generated using the coordinates (xb, yb) of the specified sound source, or the operation of the ultrasonic imaging system may be controlled based on the coordinates (xb, yb) of the specified sound source.

[0071] Incidentally, in synchronization control, instead of directly referring to the synchronization deviation calculated at each time point, a smoothed synchronization deviation may be referred to. In that case, for example, a smoothed synchronization deviation may be calculated according to the following formula (4). [Number]

[0072] In the above formula (4), δ j represents the j-th synchronization deviation. PRT j+1 represents the (j + 1)-th optical pulse period calculated based on the j-th optical pulse period. In formula (4), N synchronization deviation amounts are averaged, and the average value of the synchronization deviation amounts is added to the j-th optical pulse period. A smoothed optical pulse period may be calculated based on other calculation formulas.

[0073] A certain coefficient (for example, 0.8) may be multiplied by the calculated synchronization deviation or the smoothed synchronization deviation, and the optical pulse period or the reception period may be corrected based on the synchronization deviation obtained by the multiplication.

[0074] Fig. 8 shows a first example of the synchronization control method as a flowchart. In S10, it is determined whether the received signal sequence before integral addition includes a photoacoustic wave signal sequence. That is, it is determined whether a photoacoustic wave signal has been received. For example, based on the result of threshold processing for each received signal, the presence or absence of the photoacoustic wave signal sequence is determined.

[0075] As cases where no photoacoustic wave signal is received, a first case and a second case can be considered. The first case is when there is no sound source within the observation region of the ultrasonic probe. The second case is when there is a sound source within the observation region of the ultrasonic probe, but due to a timing deviation, the reception timing of the photoacoustic wave is shifted from the reception period.

[0076] S12 is a process for dealing with the second case. In S12, for example, a certain time is added to the optical pulse period TA, thereby setting a new optical pulse period. Then, S10 is executed again. For example, when the sound source approaches the ultrasonic probe, a predetermined input by the user may be received and S12 may be executed. In that case, when the sound source is not approaching the ultrasonic probe, unnecessary changes to the optical pulse period TA can be avoided. As will be described later, when the sound source is positioned directly below the ultrasonic probe to establish synchronization, S12 may be executed from the beginning.

[0077] In S14, the timing deviation is calculated based on the photoacoustic wave signal sequence included in the received signal sequence before coherent addition. In S16, it is determined whether the timing deviation is greater than a predetermined threshold. When the timing deviation is less than or equal to the predetermined threshold, the optical pulse period TA is maintained. When the timing deviation is greater than the predetermined threshold, the optical pulse period TA is changed in S18. In S20, it is determined whether to continue this process. When it is determined to continue this process, each step after S10 is executed again.

[0078] In FIG. 9, a second example of the synchronization control method is shown as a timing chart. In FIG. 9, the same elements as those shown in FIG. 2 are denoted by the same reference numerals, and the description thereof is omitted.

[0079] In FIG. 9, TB1, TB2, and TB2+δ2 respectively indicate reception periods. The optical pulse period TA is fixed. If no photoacoustic wave signal train 72 is detected during the reception period 74, the reception period is tentatively changed. Specifically, the next reception period TB2 is set by adding a certain period to the reception period TB1.

[0080] During the reception period 74A, a photoacoustic wave signal train 72A is being observed. By analyzing the photoacoustic wave signal train 72A, a synchronization deviation δ2 has been calculated (see reference numeral 76A), and a new reception period TB2+δ2 is set by adding the synchronization deviation δ2 to the current reception period TB2. As a result, synchronization is established between the optical pulse period and the reception period. Specifically, a photoacoustic wave signal train 72B is being observed during the reception period 74B.

[0081] FIG. 10 shows a second example of the synchronization control method as a flowchart. In FIG. 10, the same process numbers are assigned to the processes identical to those shown in FIG. 8, and the description thereof is omitted. In this second example, in S12A, the reception period TB is tentatively changed. Also, in S18A, the reception period TB is corrected based on the synchronization deviation.

[0082] FIG. 11 shows an ultrasonic imaging system according to the second embodiment. In FIG. 11, the same reference numerals are assigned to the elements identical to those shown in FIG. 1, and the description thereof is omitted.

[0083] In the second embodiment, the reception information 60 output from the processing circuit 38 is transferred to the information processing apparatus 14B. The reception information 60 is a plurality of received beam data that have undergone a certain process. The reception information output from the reception circuit 26A may also be transferred to the information processing apparatus 14B. By transferring the plurality of received beam data after envelope detection, the amount of transferred data can be significantly reduced.

[0084] The information processing apparatus 14B includes a restorer 62, a memory 50A, an analyzer 52, and a synchronization controller 54. The restorer 62 applies an operation reverse to the integral addition to the received information 60. The reverse operation is also called an inverse Fourier transform or an inverse integral addition. The restorer 62 generates a pseudo-received signal sequence corresponding to the received signal sequence before the integral addition. The pseudo-received signal sequence is temporarily stored in the memory 50A.

[0085] When the pseudo-received signal sequence is mapped into the xy coordinate space, an optoacoustic wave signal sequence similar to the optoacoustic wave signal sequence shown in FIG. 4 is generated. The analyzer 52 calculates a synchronization deviation based on the optoacoustic wave signal sequence included in the pseudo-received signal sequence using the method described above. The synchronization controller 54 changes the optical pulse period or the reception period based on the synchronization deviation.

[0086] According to the second embodiment, an advantage is obtained in that it is easy to extract transfer information from the ultrasonic diagnostic apparatus. The received information or the PA image after the coordinate transformation may be transferred to the information processing apparatus. Alternatively, the information output from the display processing unit 44 may be transferred to the information processing apparatus 14B. In those cases, a pseudo-received signal sequence is generated based on the transferred information. All or part of the configuration from the restorer 62 to the synchronization controller 54 may be provided in the ultrasonic diagnostic apparatus 12A.

[0087] Control for establishing synchronization may be performed using an acoustic propagation medium other than the living body. In this regard, a first modification example is shown in FIG. 12, and a second modification example is shown in FIG. 13.

[0088] In the first modification example shown in FIG. 12, the inside of the water tank 108 is a container that stores water 110 as an acoustic propagation medium. The transmission / reception surface of the ultrasonic probe 104 is in contact with the surface of the water 110, or the tip of the ultrasonic probe 104 is inserted into the water 110. In that state, the insertion member 112 is inserted into the water 110, and the sound source 114 is positioned directly below the ultrasonic probe 104, specifically, directly below the oscillator array in the ultrasonic probe 104. In that state, a photoacoustic wave is generated. The photoacoustic wave is detected by a plurality of oscillators constituting the oscillator array 106. Based on the received signal sequence thus obtained, a timing deviation is calculated, and the optical pulse period or the reception period is corrected based on the calculated timing deviation.

[0089] In the second modification example shown in FIG. 13, the ultrasonic probe 116 is held so that the transmission / reception surface thereof faces upward. A large amount of acoustic jelly 120 is provided on the transmission / reception surface. For example, the acoustic jelly 120 is introduced so that a bulge of the acoustic jelly 120 occurs on the transmission / reception surface. Thereafter, the light absorption element of the insertion member 122, that is, the sound source 124, is inserted into the acoustic jelly 120. In that state, a photoacoustic wave is generated. The photoacoustic wave is detected by a plurality of oscillators constituting the oscillator array 118. Based on the received signal sequence thus obtained, a timing deviation is calculated, and the optical pulse period or the reception period is corrected based on the calculated timing deviation.

[0090] FIG. 14 shows the operation of the ultrasonic imaging system. S30 is a preparation step. In S30, synchronization between the optical pulse period and the reception period is established using the method described above. S32 is the main step. In S32, the living body is treated or examined using the insertion member. In S32, the optical pulse period and the reception period may be fixed, or the above-described method may be continuously applied to maintain the synchronized state.

[0091] As described above, according to the ultrasonic imaging system according to the embodiment, it is possible to correctly synchronize the optical pulse period and the reception period while avoiding or reducing the complication of the system configuration.

Description of Symbols

[0092] 10 Optical pulse generator, 12 Ultrasonic diagnostic device, 14 Information processing device, 17 Light source, 18 Insertion member, 18a Light absorption element (sound source), 20 Photoacoustic wave, 21 Ultrasonic probe, 22 Transducer array, 26 Receiving circuit, 31 Coherent addition unit, 40 US image generation unit, 42 PA image generation unit.

Claims

1. a light source generating 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 having a plurality of transducers for receiving the photoacoustic waves; a receiver that applies delay-and-sum to a received signal sequence including a plurality of received signals output in parallel from the plurality of transducers; a generator that generates a photoacoustic image representing a position of the light absorbing element in the living body based on the reception information output from the receiver; an analyzer for analyzing the received signal sequence or a pseudo received signal sequence corresponding to the received signal sequence, thereby calculating a synchronization deviation between an optical pulse period in the light source and a receiving period in the probe; a controller that changes at least one of the optical pulse period and the reception period based on the synchronization deviation; 1. An ultrasound imaging system comprising:

2. 2. The ultrasound imaging system of claim 1, The analyzer includes: Detecting a plurality of photoacoustic wave signals included in the received signal sequence or the pseudo received signal sequence; calculating the synchronization deviation based on a plurality of detection timings of the plurality of photoacoustic wave signals; 1. An ultrasound imaging system comprising:

3. 3. The ultrasound imaging system of claim 2, The analyzer includes: Calculating a plurality of apparent propagation times from a reception cycle start timing to the plurality of detection timings; calculating the synchronization deviation based on the plurality of apparent propagation times; 1. An ultrasound imaging system comprising:

4. 4. The ultrasound imaging system of claim 3, the analyzer calculates the synchronization deviation by applying the plurality of apparent propagation times to a mathematical model including a synchronization deviation parameter as an unknown parameter; 1. An ultrasound imaging system comprising:

5. 2. The ultrasound imaging system of claim 1, The analyzer analyzes the received signal sequence extracted from the receiver.

1. An ultrasound imaging system comprising:

6. 2. The ultrasound imaging system of claim 1, a restorer for generating the pseudo received signal sequence corresponding to the received signal sequence based on the received information, The analyzer analyzes the pseudo received signal sequence.

1. An ultrasound imaging system comprising:

7. 2. The ultrasound imaging system of claim 1, When the photoacoustic wave signal sequence is not included in the reception signal sequence or the pseudo reception signal sequence, the controller trial-changes at least one of the optical pulse period and the reception period until the photoacoustic wave signal sequence is included in the reception signal sequence or the pseudo reception signal sequence.

1. An ultrasound imaging system comprising:

8. 2. The ultrasound imaging system of claim 1, the controller changes at least one of the optical pulse period and the reception period based on the synchronization deviation in a preparation step prior to a main step of performing a treatment or examination of a living body.

1. An ultrasound imaging system comprising:

9. A step of inserting an insertion member having a light absorbing element that converts a light pulse from a light source into a photoacoustic wave into an acoustic propagation medium, and in a state where a probe is in contact with the acoustic propagation medium, a plurality of transducers in the probe receive the photoacoustic wave from the light absorbing element; a step of analyzing 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 to the reception signal sequence, thereby calculating a synchronization deviation between an optical pulse period in the light source and a reception period in the probe; changing at least one of the optical pulse period and the reception period based on the synchronization deviation; A synchronization control method comprising:

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