JP2014004488A - Measuring apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a technique for suppressing inflowing system noise in a measuring apparatus when switching a probe in receiving a photoacoustic wave and an ultrasound wave.SOLUTION: A measuring apparatus to be used comprises: a first probe that includes a first acoustic conversion element 1 for transmitting an ultrasound wave, receiving the ultrasound wave reflected by a subject and converting the received ultrasound wave into an electric signal; a second probe that includes a second acoustic conversion element for receiving a photoacoustic wave generated when the subject absorbs light emitted from a light emission part, and converting the received photoacoustic wave into an electric signal; a receiving part that receives the electric signals converted by the first and second acoustic conversion elements and converts the received signals into digital signals; and switching means switching the acoustic conversion elements so that the receiving part receives either one of the electric signals.

Description

  The present invention relates to a measuring apparatus that measures biological information.

Research on measuring devices using optical imaging technology that obtains in-vivo information by propagating light irradiated on a living body using a light source such as a laser has been actively promoted in the medical field. As one of the optical imaging, there is a technique called PAT (Photo Acoustic Tomography) called photoacoustic imaging. In this method, a living body is irradiated with pulsed light generated from a light source, and photoacoustic waves (typically ultrasonic waves) generated by the absorption of pulsed light energy propagated and diffused in the living body are detected. To do. By analyzing this detection signal, an optical characteristic distribution in the living body, in particular, a light energy absorption density distribution can be obtained.

  A photoacoustic imaging apparatus is used to measure a substance concentration in a living body because an optical characteristic value distribution with high resolution can be obtained. On the other hand, a general ultrasonic measurement apparatus is widely used for determining the presence of morphological features in a living body. Therefore, by combining functional imaging that expresses material distribution in living tissue and morphological imaging that expresses morphological features, it is possible to characterize the tissue more precisely and to diagnose malignant tumors more accurately. It has become.

The measuring device of Patent Document 1 is configured to detect photoacoustic waves generated based on light energy irradiated inside a subject in addition to ultrasonic echoes and to image biological information of the subject.
A conventional example will be described with reference to FIG. The light irradiation unit 310 included in the apparatus irradiates light to the living body. The probe 305 is a 1D probe in which 256 acoustic transducers that detect photoacoustic waves are arranged one-dimensionally (1D). This acoustic conversion element is a piezoelectric element such as PZT (lead zirconate titanate), for example, and photoacoustic waves generated from an in-vivo light absorber that absorbs part of the light energy irradiated by the light irradiation unit. Can be received and detected. At the same time, the acoustic transducer has a function of outputting an ultrasonic wave under the control of a high-voltage transmission pulser circuit (64-CH transmission unit 303). Therefore, in the conventional example, it is also used as an acoustic transducer that transmits and receives ultrasonic waves.

Further, in the conventional example, when performing linear scanning using a 1D probe, a high-voltage analog switch circuit (high-voltage SW circuit 314) for linear scanning that operates by connecting only a necessary opening to a transmission / reception circuit. Was used. As shown in FIG. 4, this switch circuit connects a 256-element 1D probe and a 64-channel transmission / reception circuit, and performs linear scanning by switching ON / OFF so that each element is shifted to the right.
Next, the weak electrical signal detected by the acoustic transducer is subjected to signal processing by the 64CH receiver 304. That is, after being amplified by the reception amplifier circuit, digital sampling is performed by the A / D converter. The digital signal is sent to an image processing unit 311 that calculates optical characteristic value distribution information of a living body.

  The apparatus of the conventional example is configured to simultaneously acquire a photoacoustic image and an ultrasonic image of almost the same region as the tissue to be examined by using a 1D probe in which the light irradiation unit and the acoustic conversion element are integrated. It was. That is, by superimposing the photoacoustic image generated from the light energy irradiated on the subject to be inspected and the ultrasonic image generated from the ultrasonic wave irradiated on the subject to be inspected, the morphology of the subject's tissue It was possible to know the distribution of substance concentration for various characteristics.

  On the other hand, as described in Patent Document 2, there is a conventional example in which acoustic transducer elements are arranged in a two-dimensional (2D) array on a substrate. That is, as shown in FIG. 3B, by using a 2D probe 306 having acoustic conversion elements configured in a two-dimensional array, a photoacoustic wave corresponding to a three-dimensional region is detected by a single light irradiation. I can do it. Thereby, it was comprised so that the photoacoustic image of 3D structure could be produced | generated by one light irradiation.

JP 2005-021380 A JP 2009-031268 A

  However, the conventional example described in Patent Document 1 has a problem in that the characteristics of the acoustic transducer cannot be used separately for photoacoustic wave reception and ultrasonic wave transmission / reception by using an integrated probe. there were. For example, in the case of the conventional probe, a 2D sector probe having a rough element pitch of about 1.0 to 2.0 mm is used for receiving a photoacoustic wave in order to acquire an acoustic wave of a wide area at a time. On the other hand, a 1D linear probe with a fine element pitch of about 0.2 to 0.3 mm is used for ultrasonic wave transmission and reception in order to acquire acoustic waves in a shallow region with high resolution. Could not select the probe.

  In the integrated probe, photoacoustic waves and ultrasonic waves are received by a common circuit. However, since the ultrasonic wave transmitter is generally composed of a high-voltage-driven pulser circuit, the pulser circuit In some cases, system noise generated in the standby state flows into the receiver. As a result, the inflow of this system noise has been a problem when detecting a photoacoustic wave that is weaker than the ultrasonic wave (ultrasonic echo) reflected in the subject.

  Furthermore, when a 2D probe is used for receiving photoacoustic waves, a transmission / reception circuit having the same number of channels as the number of elements of the probe is required, which increases the circuit scale and reduces the cost and size of the apparatus. There was also a problem that it was difficult to suppress. Furthermore, even if the probes are different, inflow of system noise is unavoidable when the transmitter is shared.

  The present invention has been made in view of the above circumstances, and an object thereof is to provide a technique for suppressing inflow of system noise when a probe is switched by receiving a photoacoustic wave and an ultrasonic wave in a measurement apparatus. There is.

In order to achieve the above object, the present invention adopts the following configuration. That is, a transmission unit that determines the timing of transmitting an ultrasonic wave, and a first acoustic conversion element that transmits an ultrasonic wave according to an instruction from the transmission unit, receives an ultrasonic wave reflected by a subject, and converts the ultrasonic wave into an electrical signal. A first probe including a light irradiator, and a second acoustic conversion element that receives a photoacoustic wave generated by absorption of light irradiated from the light irradiator and is converted into an electrical signal. A second probe;
A receiving unit that receives the electrical signals converted by the first and second acoustic transducers and converts them into digital signals, and the receiving unit is one of the first acoustic transducer or the second acoustic transducer. Switching is performed so as to receive an electrical signal, and during the period in which the receiving unit is receiving from one acoustic transducer, there is a switching means for preventing the electrical signal from the other acoustic transducer from being received. This is a characteristic measuring device.

  According to the present invention, in the measurement apparatus, when the probe is switched by receiving a photoacoustic wave and an ultrasonic wave, inflow of system noise can be suppressed.

It is a block diagram which shows the structure of a measuring apparatus. It is a figure explaining operation | movement of the apparatus in Example 1. FIG. It is a figure explaining the process of the reception data in a prior art example. It is a figure which shows the linear scanning using a switch circuit. It is a figure explaining operation | movement of the apparatus in Example 2. FIG. It is a timing chart of time division control. It is a figure which shows the switching pattern of time division control.

The present invention relates to a measurement device that combines a measurement device that receives an ultrasonic echo reflected in a subject by transmission of ultrasonic waves and a measurement device that receives a photoacoustic wave generated in the subject by light irradiation. Applies to The received ultrasound or photoacoustic wave can be used for imaging within the subject. In the present invention, an acoustic wave (elastic wave) generated by light irradiation is referred to as a “photoacoustic wave”, and the acoustic wave transmitted from the acoustic transducer or the transmitted acoustic wave is reflected within the subject. The reflected wave is called “ultrasonic wave” or “ultrasonic echo”.
Hereinafter, each example will be described in detail with reference to the drawings.

  <Example 1>

  FIG. 1 is a block diagram of the measuring apparatus according to the first embodiment. The CPU 1 manages the main control of the measuring device. The transmission / reception control unit 2 performs beam forming control related to transmission / reception of ultrasonic waves. The transmitter 3 is driven by giving an instruction to the probe to generate ultrasonic waves. The receiving unit 4 processes received data detected by the probe. The ultrasonic 1D probe (first probe) 5 has a mechanism for generating ultrasonic waves and detecting ultrasonic echoes as reflected waves. A plurality of acoustic transducer elements (first acoustic transducer elements) included in the ultrasonic 1D probe are elements that are arranged one-dimensionally and are suitable for detecting ultrasonic waves. The photoacoustic 2D probe (second probe) 6 is used exclusively for photoacoustic signal detection. A plurality of acoustic transducers (second acoustic transducers) included in the photoacoustic 2D probe are two-dimensionally arranged elements suitable for detecting photoacoustic waves. The bridge circuit (T / R) 7 limits the high voltage signal output from the transmitter to a voltage value that can be detected by the receiver. A changeover switch circuit (SW) 8 switches between the ultrasonic 1D probe 5 and the photoacoustic 2D probe 6. The light irradiation unit 9 performs light irradiation on the living body. The light source unit 10 drives and controls the light irradiation unit. The image processing unit 11 calculates density information from photoacoustic waves and morphological information from ultrasonic echoes, and generates image data. The display control unit 12 performs scan conversion. The display 13 displays an image.

  The basic operation of imaging with ultrasound will be described. When the user contacts the subject (living body) with the probe and starts the operation, the transmission unit 3 determines the timing of ultrasonic transmission and gives an instruction to drive the ultrasonic 1D probe 5. The probe generates ultrasonic waves in the living body. The ultrasonic wave travels through the living body in a short time, and an ultrasonic echo returns when it hits a hard object. The probe detects the ultrasonic echo, calculates the distance from the time it takes the ultrasonic echo to return, and visualizes the internal state. That is, it is possible to form a morphological image representing the substance distribution of the living tissue.

The basic operation of imaging with photoacoustic waves will be described. First, the light irradiation unit 9 irradiates the living body with pulsed light. Subsequently, the photoacoustic 2D probe 6 detects an acoustic wave generated by the living tissue absorbing the energy of the pulsed light that has propagated and diffused in the living body. By analyzing this detection signal by the image processing unit 11, an optical characteristic distribution in the living body, in particular, a light energy absorption density distribution can be obtained. The image processing unit generates image data based on this data. That is, it is possible to image a functional image representing the substance distribution of the living tissue.

FIG. 2 is a diagram for explaining the operation of the apparatus according to the first embodiment. The transmission unit 3 is a high-voltage driven pulsar circuit composed of HV-CMOS. The transmitting unit 3 determines the timing for driving the ultrasonic 1D probe based on the pulse, issues an instruction, and generates an ultrasonic wave. The receiving unit 4 amplifies the ultrasonic echo detected by the probe and the weak signal of the photoacoustic wave by the preamplifier circuit (Amp), performs digital sampling in synchronization with the clock CLK by the A / D converter circuit (ADC), and performs digital sampling. The signal is generated.
Since the high voltage signal 100 output from the transmission unit to the probe exceeds the allowable voltage value of the detection signal 101 input to the reception unit, it is necessary to apply a limiter. In this embodiment, a diode bridge circuit (T / R) and the voltage value is within ± 5V. At this time, since the transmitter is a high-voltage drive circuit, it is necessary to keep a holding current flowing in order to keep the CMOS circuit operating at the ± 100 V level always operable. As a result, the system noise 102 at the time of holding the operation is generated while being minute.

  Particularly in this embodiment, since the receiving unit 4 is commonly used for ultrasonic and photoacoustic signal detection, even in the detection of photoacoustic waves, the system noise 102 generated in the transmitting unit is detected from the photoacoustic probe. The detection signal 101 may be mixed. Since the photoacoustic wave is weaker than the ultrasonic echo, the influence of the system noise is increased.

  Therefore, in this embodiment, a changeover switch circuit (SW) 8 that selects and switches between the ultrasonic probe 5 and the photoacoustic probe 6 is provided at the input end of the receiving unit. The changeover switch circuit 8 switches the detection source of the detection signal 101 input to the receiving unit between a period for detecting the photoacoustic wave and a period for detecting the ultrasonic echo of the ultrasonic wave. That is, during the period for detecting the photoacoustic wave, only the signal detected by the photoacoustic 2D probe 6 is used as a detection signal, and the signal detected by the ultrasonic 1D probe 5 is not input. As a result, while one of the electrical signals derived from the ultrasonic wave and the photoacoustic wave is received by the receiving unit, the other is not received.

  In this way, by providing a changeover switch circuit to separate the detection signal of the photoacoustic wave and the ultrasonic echo, the signal from the ultrasonic transmission unit is transmitted to the reception unit during the period of detecting the photoacoustic wave. It will not flow in. As a result, it is possible to suppress system noise caused by the operation of the transmission unit and improve measurement accuracy.

  <Example 2>

  In the apparatus configuration of the first embodiment, the number of probe elements and the number of transmitter / receiver circuits must be the same. However, recent devices using multi-element 1D linear probes and 2D array probes have a large number of probe elements, which increases the size and cost of the device, and reduces the number of transmitter / receiver circuits. There was a need to devise to do this.

With a 1D linear probe, as described above with reference to FIG. 4, the number of circuits can be reduced from 1/4 to 256 channels, for example, by a method using a high-voltage switch circuit for linear scanning. It is. However, a 2D array probe cannot take the same method.
In this embodiment, therefore, a measurement apparatus configured to reduce the circuit scale in addition to suppressing system noise will be described.

FIG. 5 is a diagram for explaining the measurement apparatus according to the second embodiment. The apparatus configuration will be described focusing on the differences from the apparatus of the first embodiment shown in FIG. The transmission unit 3 and the reception unit 4 are configured to perform 64 CH transmission / reception. On the ultrasonic 1D probe 5, 256 acoustic transducer elements are arranged one-dimensionally. In the 2D probe 6 for photoacoustics, 256 acoustic transducer elements are two-dimensionally arranged. A high voltage switch circuit (high voltage SW circuit) 14 is arranged between the bridge circuit (T / R) 7 and the ultrasonic 1D probe 5. A high-speed switch circuit (high-speed SW circuit) 15 is disposed between the changeover switch circuit (SW) 8 and the photoacoustic 2D probe 6.

Here, as described above with reference to FIG. 3, when both probe characteristics are compared, a 1D linear probe for transmitting and receiving ultrasonic waves is 0.25 mm in order to acquire an acoustic wave in a shallow region with high resolution. The element pitch is fine. Therefore, the center frequency is 8 MHz as the frequency characteristic of the probe. On the other hand, a 2D array probe for receiving photoacoustic waves has a rough element pitch of about 1.0 mm so that a large area of acoustic waves can be acquired at one time, and the center frequency is 2 MHz as the frequency characteristics of the probe. ing.
The optimum sampling frequency of the receiving unit is said to be about 8 to 10 times the center frequency of the probe. Here, the sampling frequency of 80 MHz is input to CLK1 in the 1D probe and the sampling clock of 20 MHz is input to CLK2 in the 2D probe as 10 times the center frequency.

  When receiving a photoacoustic signal in the second embodiment, the high-speed switch circuit 15 operates with a clock of 80 MHz that is four times as high as 20 MHz of the 2D probe 6 for photoacoustics. The A / D converter of the receiving unit 4 is also operated at 80 MHz. Accordingly, it is possible to detect the photoacoustic wave signals for four elements at the timing of 20 MHz of the photoacoustic 2D probe 6. Further, when transmitting and receiving ultrasonic echoes using the ultrasonic 1D probe 5, if the high-voltage switch circuit 14 for linear scanning is provided, the number of circuits can be reduced as described with reference to FIG. 4. it can.

  As the high withstand voltage switch circuit 14, since the operating voltage of the signal output from the transmitter is high, a switch device that can increase the operating frequency only to several MHz is used as a general specification of the high withstand voltage switch. On the other hand, as the high-speed switch circuit 15, since the operating voltage is limited by the bridge circuit 7, a switch device capable of high-speed operation up to several GHz can be selected. Further, the number of probe elements, the number of channels at the time of transmission / reception, and the operation clock can be selected as necessary without being limited to the present embodiment.

  FIG. 6 shows a timing chart of time division control. FIG. 6A shows an example of sampling at 20 MHz without using a high-speed switch circuit, and output data is for one element. On the other hand, in the example using the high-speed switch circuit shown in FIG. 6B, sampling is performed at 80 MHz, and the output data is for four elements. That is, the switching clock of the high-speed switch circuit 15 and the sampling clock of the A / D converter circuit of the receiving unit 4 are driven at 80 MHz of the same CLK1 to perform time division control. As a result, the number of circuits in the receiving unit can be reduced to 1/4 from 256 channels to 64 channels.

  The connection pattern of the switch to the 2D array probe at this time will be described below. As shown in FIG. 6, the detection signals of the four elements acquired by the time division control are sampled in a state where the phases are shifted from each other, so that an interpolation process for matching the phases before sending them to the image processing unit 11 Will be needed. Linear interpolation or the like is used for the interpolation processing. However, when the number of probe elements is large, the interpolation processing needs to be simplified in order to shorten the processing time.

FIG. 7 is a diagram illustrating a switching pattern of time division control. FIG. 7 (a) is a pattern diagram in which a switch circuit of one set of four elements is arranged in a staggered manner so as to constitute a proximity group, and FIG.
) Is a pattern diagram in the case of radial layout.
In FIG. 7A, the switch circuit for four elements is divided into adjacent groups, so that simplification is possible by performing arithmetic processing using a common interpolation formula for each group of four elements. . Since FIG. 7B has a radial layout, the first element, the second element, the third element, and the fourth element are divided into groups, and arithmetic processing using a common interpolation formula is performed for each group. By doing so, simplification is possible.

  As described above, in the measuring apparatus according to the present embodiment, by providing the high-voltage switch circuit 14 for linear scanning and the high-speed switch circuit 15 for time division control, the number of channels can be reduced and the circuit scale can be suppressed. It becomes possible. Therefore, the scale and cost of the apparatus can be reduced. At this time, the changeover switch circuit 8 operates in the same manner as in the first embodiment. Thereby, while one of the electrical signals derived from the ultrasonic wave and the photoacoustic wave is received by the receiving unit, the other is not received. That is, while the photoacoustic wave is received, the transmission unit 3 and the reception unit are not connected, so that inflow of system noise from the transmission unit can be prevented.

  3: Transmitter, 4: Receiver, 5: Ultrasonic 1D probe, 6: Photoacoustic 2D probe, 8: Changeover switch circuit, 10: Light irradiation unit

In order to achieve the above object, the present invention adopts the following configuration. That is, a transmission unit that outputs a signal for transmitting an ultrasonic wave, and an ultrasonic wave is transmitted based on the signal from the transmission unit, and the ultrasonic wave reflected in the subject is received and converted into a first signal. A first acoustic transducer, a light irradiator, and a second acoustic transducer that receives a photoacoustic wave generated in the subject by the light emitted from the light irradiator and converts it into a second signal And a receiving unit that performs signal processing on the first and second signals, and a switching unit, wherein the switching unit is configured to receive the first signal during a period in which the receiving unit is receiving the first signal. The output from the second acoustic transducer is not received, and the output from the first acoustic transducer and the output from the transmitter are received during the period in which the receiver receives the second signal. It is a measuring device characterized by not doing .

Claims (4)

A transmission unit for determining the timing of transmitting an ultrasonic wave;
A first probe including a first acoustic transducer that transmits an ultrasonic wave according to an instruction of the transmission unit, receives an ultrasonic wave reflected by a subject, and converts the ultrasonic wave into an electrical signal;
A light irradiation unit;
A second probe including a second acoustic transducer that receives a photoacoustic wave generated when the light irradiated from the light irradiation unit is absorbed by the subject and converts the photoacoustic wave into an electrical signal;
A receiving unit that receives the electrical signals converted by the first and second acoustic transducers and converts them into digital signals;
The receiving unit performs switching so as to receive an electrical signal from one of the first acoustic transducer or the second acoustic transducer, and the period during which the receiver is receiving from one acoustic transducer is the other Switching means for preventing the electrical signal from the acoustic transducer from being received,
A measuring apparatus comprising: The first probe is a one-dimensional array of a plurality of the first acoustic transducer elements,
The measuring apparatus according to claim 1, wherein the second probe is a two-dimensional array of a plurality of the second acoustic transducer elements. The number of channels through which the receiving unit can receive electrical signals is less than the number of elements of the first acoustic transducer element,
A switch circuit that connects a channel of the first acoustic conversion element and the receiving unit and enables reception of an electrical signal through the channel, the first acoustic conversion element connected to the channel of the receiving unit The measuring apparatus according to claim 2, further comprising a switch circuit that sequentially switches the two. The number of channels through which the receiving unit can receive an electrical signal is less than the number of elements of the second acoustic conversion element,
A switch circuit that connects a channel of the second acoustic transducer and the receiving unit and enables reception of an electrical signal by the channel, and the second acoustic transducer that sends a signal to the channel of the receiving unit The measuring apparatus according to claim 2, further comprising a switch circuit that switches between the two in a time division manner.

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