Ultrasonic imaging system and synchronization control method

Abstract

To maintain a synchronization state or a state near the same when detection of photoacoustic waves is interrupted in an ultrasonic imaging system that uses photoacoustic effects to image a position of an object to be inserted.SOLUTION: An insertion member inserted in a living organism has a light absorbing element which absorbs optical pulse and generates photoacoustic waves. A computing unit 202 computes an actually measured value of synchronization shift on the basis of a reception signal column before phasing addition or a pseudo reception signal column equivalent to the same. An estimator 206 estimates estimated value of synchronization shift history. A synchronization controller 212 changes optical pulse frequency or reception frequency on the basis of actually measured value when the photoacoustic waves are detected, and changes the optical pulse frequency or reception frequency on the basis of the estimated value when no photoacoustic waves are detected.SELECTED DRAWING: Figure 2

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 that supports 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 representing the position of the light absorption element (hereinafter referred to as a photoacoustic image or a PA image) 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. By observing 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. This is because if the timing at which the photoacoustic wave from the sound source reaches the ultrasonic probe is outside the reception period even when the sound source is located below the ultrasonic probe, the sound source will not be imaged. Also, if synchronization is not established, reception beamforming will not be properly executed and the image quality will deteriorate. For the same reason, it is desirable to prevent the relationship between the light pulse period and the reception period from deteriorating when the detection of the photoacoustic wave is interrupted for some reason during the synchronization establishment process or after synchronization has been established.

[0006] Patent Document 1 discloses the above-described advanced ultrasonic imaging system. Patent Document 1 does not disclose a technique for dealing with the interruption of the detection of the photoacoustic wave. Patent Document 2 describes a photoacoustic diagnostic apparatus. The 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 provide an ultrasonic imaging system capable of coping with interruption of detection of photoacoustic waves. Alternatively, an object of the present disclosure is to avoid or reduce deterioration in the relationship between the optical pulse period and the reception period when detection of photoacoustic waves is interrupted in an ultrasonic imaging system. [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 that has an optical absorption element that converts the optical pulse into a photoacoustic wave and is inserted into a living body, a probe that receives the photoacoustic wave, a determiner that determines detection or non-detection of the photoacoustic wave based on first reception information generated by a reception operation of the probe, an arithmetic unit that calculates, as a measured value, a synchronization deviation between the optical pulse period in the light source and the reception period in the probe based on second reception information generated by the reception operation of the probe when detection of the photoacoustic wave is determined, a memory that stores a synchronization deviation history including a plurality of measured values sequentially calculated by the arithmetic unit, an estimator that estimates the synchronization deviation as an estimated value based on the synchronization deviation history when non-detection of the photoacoustic wave is determined, and a controller that changes at least one of the optical pulse period and the reception period based on the estimated value when non-detection of the photoacoustic wave is determined.

[0010] The synchronization control method according to the present disclosure includes a step of performing a reception operation by a probe provided for receiving the photoacoustic wave in a state where an insertion member having a photoabsorption element that converts an optical pulse from a light source into a photoacoustic wave is inserted into a living body; a step of determining whether the photoacoustic wave is detected or not based on first reception information generated by the reception operation of the probe; a step of calculating, as a measured value, a synchronization deviation between the optical pulse period in the light source and the reception period in the probe based on second reception information generated by the reception operation of the probe when it is determined that the photoacoustic wave is detected; a step of estimating the synchronization deviation as an estimated value based on a synchronization deviation history including a plurality of sequentially calculated measured values when it is determined that the photoacoustic wave is not detected; and a step of changing at least one of the optical pulse period and the reception period based on the measured value when it is determined that the photoacoustic wave is detected, and changing the at least one of the periods based on the estimated value when it is determined that the photoacoustic wave is not detected.

Advantages of the Invention

[0011] According to the present disclosure, in an ultrasonic imaging system, when the detection of a photoacoustic wave is interrupted, deterioration in the relationship between the optical pulse period and the reception period can be avoided or reduced.

Brief Description of the Drawings

[0012]

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Mode 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 detector, an arithmetic unit, a memory, an estimator, and a controller. The light source generates optical pulses. The insertion member has a light absorption element that converts optical pulses into photoacoustic waves and is a member inserted into a living body. The probe receives photoacoustic waves. The detector determines whether a photoacoustic wave is detected or not based on first reception information generated by the reception operation of the probe. When it is determined that a photoacoustic wave is detected, the arithmetic unit calculates, as an actual measurement value, the synchronization deviation between the optical pulse period at the light source and the reception period at the probe based on second reception information generated by the reception operation of the probe. A synchronization deviation history including a plurality of actual measurement values sequentially calculated by the arithmetic unit is stored in the memory. When it is determined that a photoacoustic wave is not detected, the estimator estimates the synchronization deviation as an estimated value based on the synchronization deviation history. When it is determined that a photoacoustic wave is not detected, the controller changes at least one of the optical pulse period and the reception period based on the estimated value.

[0015] According to the above configuration, when the detection of the photoacoustic wave stops, the synchronization deviation is estimated as an estimated value based on the synchronization deviation history. At least one of the optical pulse period and the reception period (target period) is changed based on the estimated value. Therefore, even if the detection of the photoacoustic wave stops, the deterioration of the relationship between the optical pulse period and the reception period is avoided or reduced. Generally, by executing the above processing during the period when the photoacoustic wave is not detected, the time required to re-establish the synchronization state is shortened after the situation is improved.

[0016] An estimated value may be stored as part of the synchronization deviation history, and a new estimated value may be calculated based on the synchronization deviation history including the estimated value. Synchronization control based on the synchronization deviation history may be executed in a situation where a photoacoustic wave is detected. Note that the reception operation of the probe is an operation executed within a reception period. When a photoacoustic wave is detected, reception information including a photoacoustic wave component is obtained by the reception operation. When a photoacoustic wave is not detected, reception information corresponding to noise is obtained by the reception operation.

[0017] In an embodiment, the second received information is a received signal sequence composed of a plurality of received signals output from a plurality of oscillators in a probe, or a pseudo-received signal sequence corresponding to the received signal sequence. The received signal sequence is constituted by, for example, a plurality of received signals before coherent addition. The pseudo-received signal sequence is, for example, recognizable as the received signal sequence from the viewpoint of synchronization deviation calculation. The pseudo-received signal sequence may be calculated from the beam data sequence, or may be calculated from image data generated based on the beam data sequence.

[0018] In an embodiment, the first received information is the same received information as the second received information, or is different received information from the second received information. Generally, by making the first received information and the second received information the same, the handling of the received information becomes easy.

[0019] In an embodiment, when it is continuously determined that no photoacoustic wave is detected and thus the cumulative error condition is satisfied, the controller switches the method for changing the period. For example, from the time when no photoacoustic wave is detected for the first time, at each time point, an error (period correction error) is calculated and the error is accumulated to obtain a cumulative error. The error is obtained, for example, from the magnitude of the estimated value. When the cumulative error becomes large, it is highly likely that the synchronization control based on the estimated value is not appropriate. Therefore, the method for changing the period is switched.

[0020] In an embodiment, when it is continuously determined that no photoacoustic wave is detected and until the cumulative error condition is satisfied, the controller changes at least one of the periods by a first method based on the synchronization deviation history. On the other hand, when it is continuously determined that no photoacoustic wave is detected and after the cumulative error condition is satisfied, the controller changes at least one of the periods by a second method different from the first method. For example, the first method is synchronization control based on an estimated value, and the second method is synchronization control not based on an estimated value. Examples of the second method include addition of a constant value to the target period, subtraction of a constant value from the target period, temporary fixing of the target period, and the like.

[0021] The ultrasonic diagnostic apparatus according to the embodiment includes a discriminator that discriminates the contact state of the probe based on third reception information generated by receiving acoustic waves. The controller changes at least one of the periods based on the contact state of the probe.

[0022] When the transmission / reception surface of the probe is separated from the surface of the living body, photoacoustic waves cannot be observed in the probe. In such a state, there is little need to change the period for establishing synchronization. Alternatively, in such a state, appropriate period change cannot be performed. Therefore, in the above configuration, the contact state is referred to during synchronization control. The period may be changed only when the contact state is appropriate. The third reception information is the same information as the first reception information or different information from the first reception information, or is the same information as the second reception information or different information from the second reception information. Whether the contact state is good or bad may be determined based on the ultrasonic image.

[0023] The synchronization control method according to the embodiment includes a reception step, a determination step, a calculation step, an estimation step, and a control step. In the reception step, while an insertion member having a photoabsorption element that converts an optical pulse from a light source into a photoacoustic wave is inserted into the living body, a probe provided for detecting the photoacoustic wave performs a reception operation. In the determination step, based on the first reception information generated by the reception operation of the probe, it is determined whether the photoacoustic wave is detected or not. In the calculation step, when it is determined that the photoacoustic wave is detected, based on the second reception information generated by the reception operation of the probe, the synchronization deviation between the optical pulse period at the light source and the reception period at the probe is calculated as an actual measurement value. In the estimation step, when it is determined that the photoacoustic wave is not detected, based on the synchronization deviation history including a plurality of sequentially calculated actual measurement values, the synchronization deviation is estimated as an estimated value. In the control step, when it is determined that the photoacoustic wave is detected, at least one of the optical pulse period and the reception period is changed based on the actual measurement value, and when it is determined that the photoacoustic wave is not detected, at least one of the optical pulse period and the reception period is changed based on the estimated value.

[0024] (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 part 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 purposes.

[0025] The ultrasonic imaging system includes an optical pulse generator 10, an ultrasonic diagnostic device 12, a synchronization control 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 within the distal end portion of the insertion member 18.

[0026] 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. An optical absorption element 18a made of an optical absorption material is provided within the distal end portion of the insertion member 18. By irradiating the optical absorption element 18a with an optical pulse, the optical absorption 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.

[0027] 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. An oscillator array 22 composed of a plurality of oscillators is provided within the ultrasonic probe 21.

[0028] When forming a normal tomographic image, ultrasonic waves are transmitted into the living body 16 by the oscillator array 22, and the reflected waves from the living body 16 are received by the oscillator array 22. More specifically, a transmission beam and a reception beam are formed, and they are electronically scanned.

[0029] When forming a photoacoustic image, the oscillator array 22 performs only a receiving operation without performing a transmitting operation. That is, the photoacoustic wave 20 generated in the living body 16 is received by the oscillator array 22. More specifically, on the time axis, a plurality of reception periods are set according to the reception cycle. Each reception period is a period for receiving or detecting a photoacoustic wave. In other words, it corresponds to a reception beam forming period.

[0030] Note that a plurality of reception beams may be formed simultaneously and in parallel in each reception period. All of the received signal sequences obtained from the oscillator array 22 may be used as reception information for synchronization deviation analysis, or a part of the received signal sequence may be used as reception information for synchronization deviation analysis. In general, the transmission / reception process for tomographic image formation and the reception process for photoacoustic image formation are alternately executed.

[0031] 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.

[0032] 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 plurality of amplified reception signals (analog signals) into a plurality of digital signals, and an addition unit 31 that applies coherent addition to the plurality of converted reception signals. Coherent addition is a process of generating reception beam data from a plurality of reception signals.

[0033] More specifically, the coherent addition unit 31 includes a plurality of memories 32 that temporarily store a plurality of received signals, 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 read 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 focusing is performed, and if necessary, so-called parallel reception is performed.

[0034] The receiving circuit 26 outputs 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.

[0035] 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.

[0036] 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 functions such as a coordinate conversion function and a pixel interpolation function.

[0037] 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.

[0038] 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, etc.

[0039] 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.

[0040] The transmission / reception control unit 59 controls the operations of the transmission circuit 24 and the reception circuit 26. The reception cycle and the time length 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.

[0041] In the ultrasonic diagnostic apparatus 12 according to the first embodiment, the reception signal sequence before coherent addition is taken out from the reception circuit 26. The reception signal sequence is composed of a plurality of reception signals output from a plurality of ADCs 30. In the illustrated configuration example, the plurality of taken-out reception signals are temporarily stored in the memory 50 via the processing circuit 48. Each reception signal read from the memory 50 is sent to the synchronization control device 14. Each reception signal may be output from the processing circuit 48 to the synchronization control device 14. Each reception signal may be directly output from the reception circuit 26 to the synchronization control device 14.

[0042] 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 synchronization control device 14 (see reference numeral 14A).

[0043] The synchronization control device 14 is constituted by an information processing device, specifically, a computer having a CPU that executes a program. The synchronization control device 14 calculates a synchronization deviation between the optical pulse period and the reception period based on the received signal sequence that has been transferred, and establishes synchronization by changing the optical pulse period or the reception period based on the calculated synchronization deviation. Further, when the detection of the photoacoustic wave stops, the synchronization control device 14 estimates the synchronization deviation based on the synchronization deviation history, and changes the optical pulse period or the reception period based on the estimated synchronization deviation, thereby maintaining the synchronization state or a state close thereto, or suppressing an increase in the synchronization deviation.

[0044] When changing the optical pulse period, a control signal 56 is sent from the synchronization control device 14 to the light source 17. The light source 17 changes the optical pulse period based on the control signal 56. On the other hand, when changing the reception period, a control signal 58 is sent from the synchronization control device 14 to the transmission / reception control unit 59. The transmission / reception control unit 59 changes the reception period based on the control signal 58.

[0045] FIG. 2 shows a configuration example of the synchronization control device 14 shown in FIG. 1. The synchronization control device 14 has a CPU and a memory. In FIG. 2, a plurality of functions exerted by the CPU are represented by a plurality of blocks. Specifically, the synchronization control device 14 has a determiner 200, a calculator 202, an estimator 206, an accumulator 208, a discriminator 210, and a synchronization controller 212. Each of them may be constituted by a processor. The synchronization control device 14 also has a history memory 204 constituted by a semiconductor memory or the like. The synchronization controller 212 has a method switch 214.

[0046] The discriminator 200 determines whether or not a photoacoustic wave is detected based on the received signal sequence. Specifically, when the received signal sequence contains a photoacoustic wave signal sequence, the discriminator 200 determines that a photoacoustic wave is detected, while when the received signal sequence does not contain a photoacoustic wave signal sequence, the discriminator 200 determines that no photoacoustic wave is detected.

[0047] In the illustrated configuration example, the determination result of the discriminator 200 is sent to the arithmetic unit 202, the estimator 206, the accumulator 208, and the synchronization controller 212. The discriminator 200 may determine the presence or absence of a photoacoustic wave based on other received information instead of the above-described received signal sequence. Examples of other received information include a pseudo-received signal sequence described later.

[0048] When it is determined that a photoacoustic wave is detected, the arithmetic unit 202 calculates a synchronization deviation based on the photoacoustic wave signal sequence included in the received signal sequence. The method of calculating the synchronization deviation will be described in detail later. The arithmetic unit 202 may calculate the synchronization deviation based on other received information instead of the above-described received signal sequence. Examples of other received information include a pseudo-received signal sequence described later. When a photoacoustic wave is continuously detected, the arithmetic unit 202 sequentially calculates the synchronization deviation. Hereinafter, each synchronization deviation is expressed as an actual measurement value.

[0049] A plurality of sequentially calculated actual measurement values are stored in the history memory 204. The stored plurality of actual measurement values constitute a synchronization deviation history. The history memory 204 is a memory that stores the synchronization deviation history, and it is constituted by a semiconductor memory or the like. An estimated value of the synchronization deviation described below may be stored in the history memory 204.

[0050] Note that the stored content in the history memory 204 may be erased at the time of synchronization recovery or after a certain period of time has elapsed after synchronization recovery. The stored content in the history memory 204 may be maintained until an explicit erase command is input.

[0051] When it is determined that the photoacoustic wave is not detected, the estimator 206 estimates the current synchronization deviation as an estimated value based on the synchronization deviation history, that is, based on a series of past synchronization deviations. For example, the estimated value may be calculated by averaging a plurality of performance values within a certain past period. Instead of the simple averaging method, a weighted averaging method or an extrapolation method may be adopted. Examples of filters applied to the synchronization deviation history for estimating the synchronization deviation include a simple averaging filter, a low-pass filter, and a mode filter. The reference interval on the synchronization deviation history may be adaptively changed.

[0052] The accumulator 208 accumulates the calculated error within the period during which it is continuously determined that the photoacoustic wave is not detected, and obtains the accumulated error. For example, the error is calculated by multiplying the estimated value by a certain coefficient. The certain coefficient is, for example, 0.2. The accumulated error is sent to the method switch 214.

[0053] The discriminator 210 discriminates the contact state of the probe based on the received signal sequence, and specifically determines the suitability of the contact state. For example, when the transmitting and receiving wavefronts of the probe are separated from the surface of the living body, the amplitude of each received signal as a whole decreases significantly. Even when a part of the transmitting and receiving wavefronts floats from the surface of the living body, the amplitude of some of the received signals decreases. From such an amplitude change, the suitability of the contact state of the probe is determined. The discriminator 210 may discriminate the contact state based on other received information instead of the above received signal sequence. Examples of other received information include a pseudo-received signal sequence described later. The contact state may be discriminated based on an ultrasonic image.

[0054] When it is determined that the photoacoustic wave is detected, the synchronization controller 212 performs synchronization control based on the measured value. Specifically, based on the measured value, at least one of the optical pulse period at the light source and the reception period at the probe (the target period) is changed. Thereby, it becomes possible to synchronize the optical pulse period and the reception period with high precision.

[0055] In the initial stage of synchronous control, in quite a few cases, no photoacoustic waves are detected and no synchronization deviation history is generated. In such a situation, the synchronous controller 212 changes the target period by adding a constant value to or subtracting a constant value from the target period. By repeating such changes to the target period, photoacoustic waves come to be detected, and subsequently synchronization is established.

[0056] The method switch 214 switches the synchronous control method when the determination of non-detection of photoacoustic waves is repeated and the cumulative error exceeds the threshold value. Specifically, it switches from the period change based on the estimated value to the period change using a constant value. In that case, for example, a new target period is calculated and set by adding a constant value to the target period or subtracting a constant value from the target period.

[0057] When the discriminator 210 determines a defect in the contact state, the synchronous controller 212 temporarily suspends the period change. That is, it maintains the last period before the determination of a defect in the contact state. When an appropriate contact state is restored, synchronous control, that is, the period change, is resumed. In that case, for example, after the period change by addition or subtraction of a constant value is performed, the period change based on the measured value may be performed.

[0058] Fig. 3 shows an example of the synchronization deviation history. The synchronization deviation history is composed of a plurality of synchronization deviations corresponding to a plurality of times. The time ta indicates the timing when the detection of the photoacoustic signal ceased. The period 250 is the period during which the determination of detection of photoacoustic waves is repeated, and the period 252 is the period during which the determination of non-detection of photoacoustic waves is repeated.

[0059] For example, based on a plurality of timing deviations (a plurality of actual values) belonging to period 254, a timing deviation (estimated value) 256 at time t4 is estimated. Next, for example, based on a plurality of timing deviations (a plurality of measured values) belonging to period 258A, a timing deviation (estimated value) 260 at time t5 is calculated. Based on a plurality of timing deviations (a plurality of measured values and one estimated value) belonging to period 258B, the timing deviation (estimated value) 260 at time t5 may be calculated. When performing such calculations, each calculated estimated value is stored in the history memory. Within period 252, the timing deviation is repeatedly estimated based on the timing deviation history. However, the estimation of the timing deviation is stopped when the cumulative error condition is satisfied.

[0060] FIG. 4 shows an example of synchronization control. The horizontal axis is the time axis, and the vertical axis indicates the magnitude of the timing deviation. Each point represents the timing deviation (measured value or estimated value) calculated at each time. Period 234 is a non-detection period of the photoacoustic wave. Note that FIG. 4 is for easily explaining the synchronization control according to the embodiment, and its content is exaggerated or different from the actual one.

[0061] For example, based on the measured value 230a of the timing deviation, the target period is changed so that the timing deviation decreases or the timing deviation is eliminated (see reference numeral 232a). Such processing is repeated. When the detection of the photoacoustic wave stops, that is, within the non-detection period 234, an estimated value 230b is calculated based on the timing deviation history, and the target period is changed based on the estimated value 230c (see reference numeral 232b). Within the non-detection period 234, such processing is repeated. After the elapse of the non-detection period 234, the change of the target period based on the measured value is restarted.

[0062] FIG. 5 shows another example of synchronization control. In the upper part, the horizontal axis is the time axis, and the vertical axis indicates the magnitude of the timing deviation. In the lower part, the horizontal axis is the time axis, and the vertical axis indicates the magnitude of the cumulative error. Note that FIG. 5 is for easily explaining the synchronization control according to the embodiment, and its content is exaggerated or different from the actual one.

[0063] At time t1, the detection of the photoacoustic wave has ceased. Period 236 is a period during which the photoacoustic wave is not detected. In period 238 within period 236, a cycle change based on an estimated value, that is, the first method, is implemented. Specifically, an estimated value 240a is calculated based on the synchronization deviation history, and the target cycle is changed based on the estimated value 240a (reference numeral 242a). This is repeated. An error is calculated by multiplying a constant coefficient to each calculated estimated value, and a cumulative error is calculated by accumulating each error. The cumulative error gradually increases within period 238.

[0064] At time t2, the cumulative error 244A exceeds the threshold value Eth, that is, the cumulative error condition is satisfied. Accordingly, the cycle change method is switched from the first method to the second method. Period 246 is a period during which the second method is implemented. The second method determines a new target cycle, for example, by adding a constant value to the target cycle or subtracting a constant value from the target cycle. Under the new target cycle, a synchronization deviation 240b has occurred. Within period 246, the cycle change based on the second method is repeated. As the second change method, a method other than the above may be adopted. Instead of the cumulative error, the elapsed time from the point in time when the detection of the photoacoustic wave has ceased may be referred to.

[0065] FIG. 6 shows synchronization control executed after a certain number of measured values have been acquired (that is, during the transition process before synchronization establishment or after synchronization establishment). In S10, it is determined whether the photoacoustic wave is detected or not detected. When detection is determined, based on S12, a synchronization deviation (measured value) is calculated based on the photoacoustic wave signal train included in the received signal train.

[0066] On the other hand, in S10, when non-detection is determined, in S14, it is determined whether the cumulative error E exceeds the threshold value Eth. When the cumulative error E does not exceed the threshold value Eth, in S16, the first method is implemented. That is, a synchronization deviation (estimated value) is calculated based on the synchronization deviation history. In S18, the target cycle is corrected based on the synchronization deviation (measured value or estimated value).

[0067] In S14, when it is determined that the cumulative error E exceeds the threshold value Eth, in S20, a second method different from the first method is implemented, that is, the target period is corrected by the second method. In S22, it is determined whether to continue this process. If it is to continue, each step after S10 is executed again.

[0068] Hereinafter, the calculation method of the phase difference will be described with reference to FIGS. 7 to 13. FIG. 7 shows a first example of control for establishing synchronization 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.

[0069] (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, it is represented as a single pulse wave. A plurality of photoacoustic wave signals are generated in parallel when a plurality of vibrators receive the photoacoustic wave generated by one optical pulse. The photoacoustic wave signal train 72 is composed of those plurality of photoacoustic wave signals. d indicates the propagation time of the photoacoustic wave.

[0070] (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 for the ultrasonic probe, or in other words, it is set for the reception circuit. For example, a reception aperture is set for the entire array of vibrators, and the reception signal train corresponding to the reception aperture is analyzed.

[0071] In the first example shown in FIG. 7, 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 periods. 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.

[0072] When the photoacoustic wave signal train 72 cannot be observed within the reception period 74, the optical pulse period is tentatively changed. Specifically, the current optical pulse period TA2 is set by adding a certain period to the previous optical pulse period TA1 or subtracting a certain period from the optical pulse period TA1.

[0073] In the example shown in FIG. 7, in the reception period 74A, the photoacoustic wave signal train 72A is observed. By analyzing the photoacoustic wave signal train 72A, the synchronization deviation δ1 is calculated (see reference numeral 76). For example, by adding the synchronization deviation δ1 to the current optical pulse period TA2, a new optical pulse period TA2 + δ1 is set. As a result, synchronization is established between the optical pulse period and the reception period. That is, the magnitudes of the optical pulse period and the reception period become the same, and the photoacoustic wave signal train 72B is correctly observed within the reception period 74B. 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. Incidentally, when establishing synchronization, the generation timing of the optical pulse and the start timing of the reception period may be made to coincide.

[0074] FIG. 8 illustrates the received signal before coherent addition. The received signal 77 includes a photoacoustic wave signal 78 generated due to the reception of a 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.

[0075] By detecting the photoacoustic wave signal 78, for each received signal, the timing (detection timing) td at which the photoacoustic wave is 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.

[0076] FIG. 9 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 array oscillator. 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.

[0077] The received signal sequence includes a photoacoustic wave signal sequence 84. In the illustrated example, the x coordinate (xc) of the center of the vibrating 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 vibrating array.

[0078] 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, the apparent propagation time pi is specified based on the detection timing. The specific photoacoustic wave signal 82 is generated at a point with a depth yi.

[0079] The photoacoustic wave signal train 84 has a parabolic form. The form of the photoacoustic wave signal train 84 is constant regardless of the magnitude of the timing deviation. The position where the photoacoustic wave signal train 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 shifts in the x direction from the center position xc of the array oscillator, a photoacoustic wave signal train 90 is generated. The x coordinate (xc1) of its vertex 90a corresponds to the x coordinate of the sound source. Even in that case, the form of the photoacoustic wave signal train 90 is the same as the form of the photoacoustic wave signal train 84.

[0080] Based on the photoacoustic wave signal train 84, the timing deviation is calculated, and at least one of the optical pulse period and the reception period is changed based on the timing deviation. As a result, in the coordinate space shown in FIG. 9, the photoacoustic wave signal train 84 moves parallel in the depth direction (see reference numeral 86). Reference numeral 88 indicates the photoacoustic wave signal train observed when the timing deviation is eliminated.

[0081] Hereinafter, the method for calculating the timing deviation will be described in more detail. FIG. 10 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 expressed as (xi, yi). However, yi = 0. The position of the sound source 96 is expressed as (xb, yb). The propagation time di of the photoacoustic wave from the sound source 96 to the i-th oscillator is calculated by the following equation (1). c in equation (1) is the speed of sound of ultrasonic waves (photoacoustic waves) in the medium.

Equation

[0082] The apparent propagation time pi is the time obtained by adding the timing deviation δ and the propagation time di. That is, the apparent propagation time pi is expressed as in the following equation (2).

Equation

[0083] The relationship among the apparent propagation time pi, the synchronization deviation δ, and the propagation time (actual propagation time) di expressed in the above formula (2) is shown in FIG. 11. The reception period 102 is a 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 synchronization deviation δ. The propagation time from the generation timing of the optical pulse 98 (the generation timing of the photoacoustic wave) until the photoacoustic wave is received by the i-th vibrator is di. The reference numeral 100 indicates a photoacoustic wave signal generated by the reception of the photoacoustic wave.

[0084] When the photoacoustic wave reaches n vibrators, n detection timings td corresponding to the n vibrators are specified. Based on the n detection timings td, n apparent propagation times pi are specified. n data pairs (xi, pi) are defined by the positions xi of the n vibrators and the n apparent propagation times pi (where i = 1, ···, n).

[0085] By substituting the n data pairs (xi, pi) into the above formula (2) which is a mathematical model, it is possible to specify δ, xb, and yb which are unknown parameters. In that 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 specified.

[0086] FIG. 12 schematically shows the method described above. In block 130, n photoacoustic wave signals included in the n reception signals before coherent addition are detected, and n apparent propagation times pi from the reception period start timing to the n detection timings are calculated. n data pairs (xi, pi) 132 are defined by the coordinates xi of the n vibrating elements in the x direction and the n apparent propagation times pi. In block 134, by substituting the n data pairs (xi, pi) 132 into the above formula (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 a certain condition among the n data pairs (xi, pi) 132 may be substituted into the above formula (2).

[0087] As described above, the synchronization deviation δ is calculated by analyzing a plurality of received signals. Based on the synchronization deviation, at least one of the optical pulse period and the reception period is changed. When changing the optical pulse period, the reception period can be maintained, so that the advantage of not having to change the transmission / reception sequence in the ultrasonic diagnostic apparatus is obtained. When changing the reception period, communication between the information processing apparatus (or ultrasonic diagnostic apparatus) and the optical pulse generation apparatus becomes unnecessary, so that the configuration of the ultrasonic imaging system can be simplified.

[0088] 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

[0089] The above equation (3) indicates that a plurality of photoacoustic wave signals draw a parabola in the xy coordinate system. The synchronization deviation δ may be specified using the above equation (3). Note that 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.

[0090] Incidentally, in synchronization control, instead of referring to the synchronization deviation calculated at each time point as it is, a smoothed synchronization deviation may be referred to as the measured value. In that case, for example, a smoothed synchronization deviation is calculated according to the following equation (4), and based on that, the next cycle PRT j+1 may be determined.

Equation

[0091] In the above equation (4), δ j represents the j-th synchronization deviation. PRT j+1indicates the (j + 1)-th optical pulse period calculated based on the j-th optical pulse period. In equation (4), N amounts of synchronization deviation are averaged, and the average value of the amounts of synchronization deviation is added to the j-th optical pulse period. An optical pulse period smoothed based on other calculation formulas may be calculated.

[0092] A constant 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 measured value of the synchronization deviation obtained by the multiplication.

[0093] FIG. 13 shows, as a timing chart, a second example of control for synchronization establishment. In FIG. 13, elements identical to those shown in FIG. 7 are denoted by the same reference numerals, and the description thereof is omitted.

[0094] In FIG. 13, TB1, TB2, and TB2 + δ2 indicate reception periods, respectively. The optical pulse period TA is fixed. When the photoacoustic wave signal train 72 is not detected during the reception period 74, the reception period is tentatively changed. Specifically, for example, the next reception period TB2 is set by adding a certain period to the reception period TB1.

[0095] During the reception period 74A, the photoacoustic wave signal train 72A is being observed. By analyzing the photoacoustic wave signal train 72A, the synchronization deviation δ2 has been calculated (see reference numeral 76A). In the illustrated example, 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, the photoacoustic wave signal train 72B is being observed within the reception period 74B.

[0096] FIG. 14 shows an ultrasonic imaging system according to the second embodiment. In FIG. 14, elements identical to those shown in FIG. 1 are denoted by the same reference numerals, and the description thereof is omitted.

[0097] 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 reception beam data that has undergone a certain process. The reception information output from the reception circuit 26A may be transferred to the information processing apparatus 14B. The PA image described later may be transferred to the information processing apparatus 14B as reception information. Note that by transferring a plurality of reception beam data after envelope detection, the amount of transferred data can be significantly reduced.

[0098] FIG. 15 shows a configuration example of the information processing apparatus 14B. In FIG. 15, elements similar to those shown in FIG. 2 are denoted by the same reference numerals, and the description thereof is omitted.

[0099] The converter 216 applies an operation inverse to the coherent addition to the plurality of transferred beam data. The inverse operation is also called an inverse Fourier transform or an inverse coherent addition. Focusing on this point, the converter 216 is a restoration device. A pseudo-reception signal sequence corresponding to the reception signal sequence before coherent addition is output from the converter 216. The pseudo-reception signal sequence is temporarily stored in the memory 218.

[0100] When the pseudo-reception signal sequence is mapped to the xy coordinate space, an optoacoustic wave signal sequence similar to the optoacoustic wave signal sequence shown in FIG. 9 is generated. In FIG. 15, the determiner 200 determines whether or not an optoacoustic wave is detected based on whether or not the optoacoustic wave signal sequence is included in the pseudo-reception signal sequence. The calculator 202 calculates the synchronization deviation as an actual measurement value based on the optoacoustic wave signal sequence included in the pseudo-reception signal sequence. The discriminator 220 discriminates the contact state of the probe based on the reception information (a plurality of beam data) transferred from the ultrasonic diagnostic apparatus. That is, it determines the quality of the contact state.

[0101] Other received information instead of the pseudo-received signal sequence may be input to the discriminator 200. For example, a PA image may be input. In that case, based on the luminance information in the PA image, specifically, based on the presence or absence of an image or a group of pixels having a luminance value exceeding a certain threshold value, detection or non-detection of the photoacoustic wave can be determined. Other received information instead of the pseudo-received signal may be input to the identifier 220. For example, similarly to the above, a PA image may be input. In that case, based on the luminance information in the PA image, for example, based on the average luminance, the quality of the probe contact state can be determined.

[0102] According to the second embodiment, an advantage that it is easy to extract transfer information from the ultrasonic diagnostic apparatus is obtained. All or part of the component group shown in FIG. 15 may be provided in the ultrasonic diagnostic apparatus. Alternatively, all or part of the component group shown in FIG. 15 may be provided in the optical pulse generation apparatus.

[0103] According to the ultrasonic imaging system according to the first embodiment and the second embodiment, when the detection of the photoacoustic wave is interrupted, the timing deviation is estimated as an estimated value based on the timing deviation history. At least one of the optical pulse period and the reception period is changed based on the estimated value. Therefore, even if the detection of the photoacoustic wave is interrupted, the synchronous state or a state close thereto is maintained. By continuously optimizing the target period during the period of non-detection of the photoacoustic wave, the time required to re-establish the synchronous state after the situation is improved is shortened.

Explanation of Reference Numerals

[0104] 10 Optical pulse generation apparatus, 12 Ultrasonic diagnostic apparatus, 14 Synchronization control apparatus, 17 Light source, 18 Insertion member, 18a Photoabsorbing element (sound source), 20 Photoacoustic wave, 21 Ultrasonic probe, 22 Transducer array, 26 Reception circuit, 31 Coherent addition unit, 40 US image generation unit, 42 PA image generation unit, 200 Discriminator, 202 Arithmetic unit, 204 History memory, 206 Estimator, 208 Accumulator, 210 Identifier, 212 Synchronization controller, 214 Method switcher.

Claims

1. A light source that generates light pulses, An insertion member that has a light absorption element for converting the light pulses into photoacoustic waves and is inserted into a living body, A probe that receives the photoacoustic waves, A determiner that determines whether the photoacoustic waves are detected or not based on first reception information generated by the reception operation of the probe, An arithmetic unit that, when it is determined that the photoacoustic waves are detected, calculates, as an actual measurement value, a synchronization deviation between a light pulse period in the light source and a reception period in the probe based on second reception information generated by the reception operation of the probe, A memory that stores a synchronization deviation history including a plurality of actual measurement values sequentially calculated by the arithmetic unit, An estimator that, when it is determined that the photoacoustic waves are not detected, estimates the synchronization deviation as an estimated value based on the synchronization deviation history, A controller that, when it is determined that the photoacoustic waves are not detected, changes at least one of the light pulse period and the reception period based on the estimated value, An ultrasonic imaging system, characterized by including the above.

2. In the ultrasonic imaging system according to Claim 1, The second reception information is a reception signal sequence composed of a plurality of reception signals output from a plurality of vibrators in the probe, or a pseudo-reception signal sequence corresponding to the reception signal sequence. An ultrasonic imaging system, characterized by the above.

3. In the ultrasonic imaging system according to Claim 2, The first reception information is the same reception information as the second reception information, or is different reception information from the second reception information. An ultrasonic imaging system, characterized by the above.

4. In the ultrasonic imaging system according to Claim 1, When the controller continuously determines that the photoacoustic wave is not detected, thereby satisfying the cumulative error condition, it switches the method for changing the at least one period. An ultrasonic imaging system characterized by this.

5. In the ultrasonic imaging system according to claim 4, The controller, When it is determined that the photoacoustic wave is not detected continuously and until the cumulative error condition is satisfied, the at least one period is changed by a first method based on the synchronization deviation history, When it is determined that the photoacoustic wave is not detected continuously and after the cumulative error condition is satisfied, the at least one period is changed by a second method different from the first method. An ultrasonic imaging system characterized by this.

6. In the ultrasonic imaging system according to claim 1, It includes a discriminator that discriminates the contact state of the probe based on the third reception information generated by the reception operation of the probe, The controller changes the at least one period based on the contact state of the probe. An ultrasonic imaging system characterized by this.

7. In a state where an insertion member having a photoabsorbing element that converts an optical pulse from a light source into a photoacoustic wave is inserted into a living body, a step of performing a reception operation by a probe provided for detecting the photoacoustic wave, A step of determining whether the photoacoustic wave is detected or not based on the first reception information generated by the reception operation of the probe, When it is determined that the photoacoustic wave is detected, a step of calculating the synchronization deviation between the optical pulse period in the light source and the reception period in the probe as a measured value based on the second reception information generated by the reception operation of the probe, When it is determined that the photoacoustic wave is not detected, estimating the synchronization deviation as an estimated value based on a synchronization deviation history including a plurality of measured values calculated sequentially; When it is determined that the photoacoustic wave is detected, changing at least one of the optical pulse period and the reception period based on the measured value, and when it is determined that the photoacoustic wave is not detected, changing the at least one period based on the estimated value; A synchronization control method characterized by including the above.

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