JP4263575B2 - Ultrasonic transmitter and ultrasonic apparatus using the same - Google Patents

Description

  The present invention relates to an ultrasound imaging technique for capturing an image in a subject using ultrasound.

  Transcranial ultrasonic Doppler measurement has already been established as a means for easily observing blood flow in the brain. In addition, it has been reported that the thrombolytic effect is enhanced when transcranial ultrasonic Doppler monitoring is performed during thrombolytic treatment using a thrombolytic agent such as tPA (tissue plasminogen activator) (for example, see Non-Patent Document 1). .

  An ultrasonic wave for Doppler monitoring has a frequency of about 2 MHz in consideration of resolution and attenuation. Regarding the effect of promoting the dissolution of thrombus by applying ultrasonic waves, as already reported, a frequency of about 500 kHz is considered desirable from the effects of cavitation and temperature rise (for example, see Non-Patent Document 2).

  However, as described above, in order to transmit ultrasonic waves having a relatively low frequency of about 500 kHz for treatment and to transmit and receive frequencies of about 2 MHz for Doppler monitoring, transducers for treatment and Doppler monitoring are used. Are separately provided, or the frequency of the monitoring ultrasonic wave is set to an odd multiple of the frequency of the therapeutic ultrasonic wave so that one transducer plays a dual role (for example, see Patent Document 1). .

"High Rate of Complete Recanalization and Dramatic Clinical Recovery During tPA Infusion When Continuously Monitored With 2-MHz Transcranial Doppler Monitoring", Stroke vol.31, (2000) pp.610-614

"Can Transcranial Ultrasonication Increase Recanalization Flow With Tissue Plasminogen Activator", Stroke vol.33, (2002) pp.1399-1404 JP-A-6-269448

  FIG. 2 shows a sectional view around the temple of the skull and an element array (transducer array) 101 of the ultrasonic transducer. The ultrasonic wave transmitted from the element array 101 is focused on the ultrasonic irradiation focus 122 through the skull 120. As shown on both sides (left and right) of FIG. 2, most of the skull 120 has a structure in which a perforated interlaminar layer 121 is sandwiched therebetween, and this part has a large attenuation of ultrasonic waves. It has been known. The temple part has no interlamellar layer or is very thin, so it is known that the attenuation of ultrasonic waves is less than that of the interlaminar layer, and the sound when imaging or treating the inside of the skull with ultrasound It is used as a typical window (acoustic window). However, since the size of the acoustic window region is limited to a narrow range of several cm square, it is difficult to use separate transducers side by side for imaging and treatment. On the other hand, if the frequency of the monitoring ultrasonic wave is set to an odd multiple of the frequency of the therapeutic ultrasonic wave, the freedom of frequency selection is lost, and the pulse width on the time axis when used in the higher frequency mode, that is, monitoring, is reduced. There was a problem that it could not be narrow enough.

  Therefore, in order to effectively use the limited acoustic window of the skull, an object of the present invention is to promote the thrombolytic effect of the thrombolytic agent by ultrasonic monitoring and the ultrasonic thrombolytic agent from one opening. It is an object to provide an ultrasonic transmitter that can be obtained, and to provide an ultrasonic device using the same.

  In order to achieve the above object, in the present invention, a transducer array for transmission (therapeutic transducer array) for irradiating thrombolysis ultrasonic waves for enhancing the effect of a thrombolytic agent, and the state of thrombolysis are monitored. For this reason, a limited acoustic window in the skull is effectively utilized by using a configuration in which a monitoring transducer array for stacking is laminated.

  By simply laminating, when the monitoring transducer array is driven, ultrasonic waves transmitted from the monitoring transducer array and directed in the direction opposite to the subject are converted into ultrasound for thrombus dissolution. Reflecting and returning at the interface behind the transducer array to be irradiated deteriorates the pulse characteristics. In the present invention, this problem is solved by arranging a frequency selective separation layer between the two transducer arrays. The frequency selective separation layer has an acoustic impedance smaller than the acoustic impedance of the above two transducer arrays, and its thickness is approximately half or less of the wavelength at the center frequency of the transmitted ultrasonic wave in the monitoring mode. It is desirable. Furthermore, considering the ultrasonic wave transmission efficiency for thrombolysis, the thickness of the frequency-selective separation layer is about one-fourth of the wavelength at the central frequency of the monitoring ultrasonic wave to about one-fourth. A thickness range is desirable. From the viewpoint of acoustic impedance, the function becomes effective by using a polymer-based material smaller than about one third of the acoustic impedance of the transducer array.

  In addition, the ultrasonic transducer including the transducer array for transmitting ultrasonic waves for thrombolysis and the transducer array for transmitting and receiving monitoring ultrasonic waves transmits and transmits at different time phases on the time axis. In addition, the influence of noise on the monitoring image can be minimized by performing transmission and reception, but by providing a mechanism for analyzing the reception signal during irradiation of therapeutic ultrasound, it is separate from blood flow monitoring It is possible to monitor cavitation. Cavitation monitoring is an effective method for controlling damage to the brain caused by ultrasonic irradiation.

  Furthermore, by providing the frequency-selective separation layer of the present invention, it is not necessary to attenuate the multiple reflection of ultrasonic waves in the backing material, so that the configuration of the backing material can be optimized for thrombolytic ultrasound treatment. It becomes. That is, the back material can be optimized for heat transfer for cooling the vibrator, rather than matching the acoustic impedance. Instead of conventional polymer-based materials, it is possible to select materials such as metals that have large acoustic impedance but also have high thermal conductivity. Considering the transmission efficiency of ultrasound for thrombolysis, it is also desirable to achieve both thermal conductivity and transmission efficiency from the transducer array by using a multilayer film as a part of the backing material.

  Hereinafter, typical configuration examples of the present invention will be listed.

  (1) In the ultrasonic wave transmitter according to the present invention, at least two or more layers of transducers composed of a plurality of electric ultrasonic transducers are stacked, and the acoustic impedance of the transducer is interposed between the stacked transducer layers. It has a structure in which layers with lower acoustic impedance are arranged, and is configured to transmit ultrasonic waves to the subject independently and electrically driven with a frequency suitable for each layer of the transducer It is characterized by that.

  (2) In the ultrasonic transmitter of (1), a resonance frequency of the transducer (monitoring transducer) at a position close to the subject among the plurality of transducer layers is located at a far position. It is characterized by being configured to be higher than the resonance frequency of the vibrator (therapeutic vibrator).

  (3) In the ultrasonic wave transmitter according to (2), an acoustic impedance of the layer disposed between the plurality of transducer layers may be a transducer close to the subject in the plurality of transducer layers. It is configured to be smaller than approximately one third of the acoustic impedance.

  (4) In the ultrasonic wave transmitter of (2), the transducer having a thickness close to the subject in the plurality of transducer layers is arranged between the plurality of transducer layers. It is characterized by being configured to be smaller than about half of the wavelength at the center frequency of the electric signal to be driven.

  (5) In the ultrasonic wave transmitter according to (1), the plurality of transducer layers are each composed of a transducer array and arrayed in a direction substantially orthogonal to each other.

  (6) In the ultrasonic transmitter of (1), the ultrasonic transducer is a two-dimensional array in which at least one transducer layer is arrayed in two directions among the plurality of transducer layers.

  (7) In the ultrasonic wave transmitter of (2), the material of the layer opposite to the subject side of the transducer layer located farthest from the subject among the plurality of transducer layers is: It is a metal or a metal oxide.

  (8) In the ultrasonic wave transmitter of (2), a part of the plurality of transducer layers out of layers opposite to the subject side of the transducer layer farthest from the subject is A structure in which two or more materials are alternately stacked with a period of half the wavelength at the center frequency of the electrical signal that drives the transducer layer farthest from the subject among the plurality of transducer layers. It is characterized by having.

  (9) An ultrasonic apparatus according to the present invention includes a plurality of electric ultrasonic transducers, an ultrasonic transducer that transmits and receives ultrasonic pulses to a subject, and transmission and reception of ultrasonic waves to the elements. A transmission / reception changeover switch, a transmission beamformer connected to the transmission / reception changeover switch for controlling the transmission focal position of the ultrasonic wave in the subject, and a received beam for controlling the reception focal position in the subject An ultrasonic apparatus comprising a former, the transmission / reception changeover switch, the transmission beam former, and a control system that controls the reception beam former, wherein the ultrasonic transducer includes the plurality of electric ultrasonic transducers A structure in which at least two or more layers of the vibrator are laminated, and a layer having an acoustic impedance smaller than the acoustic impedance of the vibrator is arranged between the laminated vibrator layers. A and electrically driven independently with a frequency suitable for each layer of the vibrator, characterized in that it is configured to transmit the ultrasonic waves to the subject.

  (10) In the ultrasonic device according to (9), the frequency analysis of the signal connected to the ultrasonic transmitter and received by the ultrasonic transmitter during ultrasonic transmission is performed in the subject. A cavitation monitoring unit for monitoring the occurrence of cavitation is provided.

  (11) In the ultrasonic transmission device of (9), connected to the transmission beamformer, evaluates the stability of the output of the transmission beamformer during ultrasonic transmission, and generates cavitation in the subject. It is characterized by having a cavitation monitoring unit for monitoring the above.

  According to the present invention, in order to effectively use the limited acoustic window of the skull, monitoring from a transcranial ultrasonic blood flow image and the thrombolytic effect of a thrombolytic agent by ultrasound can be promoted from one opening. An acoustic wave transmitter and an ultrasonic device using the same can be realized.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 1 shows a cross section of an ultrasonic transmitter according to an embodiment of the present invention. In this embodiment, a transcranial ultrasonic tomographic transducer array (monitoring transducer array) 11 and a therapeutic ultrasonic transmission array, each of which is composed of an electric ultrasonic transducer of a piezoelectric ceramic material (for example, PZT). (Treatment transducer array) 12 is laminated. In order to provide a tomographic image and a blood flow image having a spatial resolution suitable for monitoring, it is important that the ultrasonic array for ultrasonic tomography 11 has a short pulse width as well as good sensitivity. On the other hand, it is important that the therapeutic ultrasonic wave transmission array 12 can transmit ultrasonic power for assisting in thrombolysis. Regarding therapeutic ultrasound transmission, the importance of the short pulse width is not as important as in the case of the transducer array 11.

  On the transducer array 11 (subject side), an acoustic lens 14 for focusing the beam in a direction orthogonal to the arraying direction, and an acoustic matching layer 13 is laminated between the acoustic lens 14 and the transducer array 11. Has been. On the other hand, with respect to the back surface of the transducer array 11, in order to reduce the influence of ultrasonic waves reflected and returned from the back surface side of the therapeutic transducer array 12, the frequency selective separation layer 15 which is a feature of the present invention is provided. Is disposed between the therapeutic transducer array 12 and the imaging transducer array 11. A back material 16 is arranged on the back surface of the therapeutic transducer array 12. The transducer arrays 11 and 12 are arrayed at different intervals, and each element of the array is separated by the fillers 17 and 18 including the electrodes 19-1 to 19-4.

  Hereinafter, description will be given by showing specific numerical values. For example, if the center frequency of the transducer array 11 is 2 MHz and the center frequency of the transducer array 12 is 500 kHz, the thickness of the transducer array 11 is about 1 mm and the thickness of the transducer array 12 is about 3 mm. Here, the center frequency refers to a frequency that takes a maximum value in the frequency space by converting the waveform transmitted from the transducer array into the frequency space. A center frequency may be obtained by using an average value of two frequencies that are generally used and energy is halved before and after the maximum value. It is preferable to use a material having a low mechanical Q for the transducer array 11 and a material having a high mechanical Q for the transducer array 12. This is because it is desirable that the imaging transducer array 11 has a wide band for pulse driving, and the therapeutic transducer array 12 has a narrow band for performing continuous wave operation. As the matching layer 13 and the back material 16, those in which acoustic impedance is adjusted with a mixture of a polymer material and metal powder are used. In the present embodiment, the matching layer 13 is shown as a single layer. However, the matching of the acoustic impedance between the transducer and the subject is improved by using a matching layer in which a plurality of layers having different acoustic impedances are stacked. It is also possible. Further, with respect to the vibrator, it is possible to make the capacitance and electric resistance appropriate by using a known laminated vibrator.

Hereinafter, the effect of the frequency selective separation layer 15 will be described with reference to FIG. FIG. 3A shows a simulation result of a transmission waveform when a pulse waveform is applied between the electrodes 19-1 to 19-2 when there is no separation layer. In the simulation, in order to accurately estimate the influence of the size below the wavelength, the space was finitely differentiated, and the propagation of the wave equation between each difference point was also differentiated on the time axis. FIG. 3B shows a simulation result of a transmission waveform when a pulse waveform is given between the electrodes 19-1 to 19-2 when the separation layer is also provided. At this time, an epoxy resin having a density of 1000 kg / m ³ , a sound velocity of 2500 m / s, and a thickness of 300 μm was used for the separation layer. This corresponds to a thickness of approximately one quarter of the wavelength at 2 MHz. Signals of about 3 μs seen in both (A) and (B) of FIG. 3 are ultrasonic waves transmitted directly forward from the transducer array 11. A large peak of 5 μs, which is noticeable in FIG. 3A, is reflected between the transducer array 12 and the back material 16 and again passes through the transducer arrays 12 and 11 and returns to the front surface. It is a waveform. It is confirmed that the signal in the same time zone is greatly suppressed in FIG. 3B by inserting the frequency selective separation layer.

  By changing the thickness of the frequency separation layer, the magnitude of the reverberant sound of the ultrasonic pulse transmitted from the transducer array 11 and the transmission energy at 500 kHz of the ultrasonic wave transmitted from the transducer array 12 are simulated. The calculated results are shown in FIG. The horizontal axis in FIG. 4 represents the energy of the 500 kHz component of the ultrasonic waveform transmitted to the front surface through the separation layer 15 when the transducer array 12 is driven. The case where there is no separation layer is represented as 0 dB, and the relative value is shown. On the other hand, the vertical axis in FIG. 4 represents the peak intensity of the reverberant sound of the ultrasonic pulse transmitted from the transducer array 11 to the front surface, and the pulse transmitted directly from the transducer 11 at each thickness. The maximum value of the reverberant sound normalized with the maximum value of the amplitude of the reverberant sound was evaluated. This is also displayed as a relative value with respect to the value when there is no separation layer 15. The numbers in FIG. 4 represent the thickness of the separation layer 15 compared to the wavelength at 2 MHz.

  As evaluated from this figure, first, as the thickness of the separation layer 15 is increased, the transmission energy at the time of driving at 500 kHz is reduced. On the other hand, the magnitude of the reverberant sound when driven at 2 MHz is minimum when the thickness of the separation layer is 1/12 of the wavelength (λ) at 2 MHz, and the separation layer 15 is between 1/2 and 1/48. It turns out that it can suppress to less than half of the case where there is no. Thus, there is a great advantage in practice that there is a width in the thickness that can be used as the separation layer 15. That is, as will be described later, a plurality of modes, that is, modes such as a tomographic image, a blood flow image, a pulse Doppler image, and a continuous wave Doppler image are appropriately selected and used depending on the situation. In general, these modes do not always have the same center frequency. Even if the frequency is 2 MHz in the Doppler mode, 3 to 4 MHz may be used in the tomographic image mode. Even if it is limited to one tomographic mode, frequency dependence attenuation can be avoided by changing the center frequency from higher to lower according to the already known dynamic frequency shift method, that is, according to the reception timing. Therefore, there are many cases where a method of receiving a signal is taken where the signal-to-noise ratio is the best. In such a case, if the separation layer has a thickness of 1 / 24th of the wavelength at 2 MHz, it corresponds to 1 / 12th of the wavelength at 4 MHz. It can be realized at any frequency.

  Next, FIG. 5 shows a calculation result when the thickness of the separation layer 15 is fixed to ¼ of the wavelength at 2 MHz and the acoustic impedance is changed. The horizontal axis represents the acoustic impedance of the separation layer 15 in MRay units, and the vertical axis represents the magnitude of reverberant sound when driven at 2 MHz compared to the case without the separation layer. From this result, the magnitude of the reverberant sound is the minimum when the acoustic impedance of the separation layer 15 is 5 to 7 MRay, that is, about √ (Zpzt × Ztissue), and gradually gradually shifts to either the larger side or the smaller side. The reverberation becomes louder. Here, Zpzt and Ztissue are the acoustic impedances of PZT and the living body, respectively. Considering other parameters such as the influence on the manufacturing process, it is practical to select a region having an acoustic impedance of about 10 MRay or less as a region where the effect of the separation layer is effective. In other words, the acoustic impedance of the separation layer 15 may be selected to be smaller than about one third of the acoustic impedance of the monitoring vibrator.

  Up to this point, the case where the separation layer is made of a homogeneous material has been described as an example. However, when the separation layer such as an electrical wiring is made of a plurality of materials in the separation layer, the structure of the separation layer It can be considered that the separation layer is made of a uniform material having an average acoustic impedance of the material. This is because the overall thickness of the separation layer is smaller than the wavelength, and the dimensions of the material constituting the interior of the separation layer are inevitably smaller than the wavelength, so there is no significant difference even when discussed with the average value. It is.

  Next, FIG. 6 shows a configuration example of an ultrasonic device connected to a transmitter when thrombolysis treatment is performed using the ultrasonic transmitter (two-frequency transmitter) described so far. . In this figure, the transmitter described so far is shown as an ultrasonic transmitter / receiver 31. The ultrasonic wave irradiation for thrombus dissolution and the transmission / reception wave for monitoring image pickup are alternately performed on the wave transmitter / receiver 31. The control system 32 performs control for that purpose.

  First, at the time of ultrasonic irradiation for thrombolysis, a signal is transmitted from the control system 32 to the therapeutic transmission beamformer 33 so as to drive the ultrasonic transducer 31 with a delay time for focusing on a predetermined position. It is done. This focal position is appropriately scanned within the subject, so that therapeutic ultrasonic waves are applied to the entire treatment area. In the treatment mode, no reception is performed. As for the transmission power, as reported in the above-described conventional examples (Non-Patent Documents 1 and 2), a value lower than the safety reference value of the diagnostic transmission power is used. Next, when the monitoring mode is entered, a signal is sent from the control system 32 to the imaging transmission beamformer 34, and from the transmission beamformer 34 via the transmission / reception changeover switch 35, from the ultrasonic transmitter / receiver 31. An ultrasonic wave for monitoring is transmitted to a specimen (not shown). The signal reflected and scattered by the ultrasonic signal in the subject is converted again into an electrical signal by the ultrasonic transducer 31, and beam forming is performed by the reception beam former 36 via the transmission / reception switch 35. It is.

  In the monitoring mode, the following four modes are selected and used according to the situation. (1) A tomographic image display mode in which reflected signal intensity is converted into luminance information. (2) The blood flow velocity is estimated by repeating a plurality of transmission / reception waves with respect to the same portion and obtaining a correlation between the signals, and the spatial distribution of the blood flow velocity is displayed by scanning this portion. Blood flow image display mode. (3) A pulse Doppler mode in which a pulse signal is transmitted / received only to a specific site and displayed as a horizontal time axis and vertical blood flow velocity dispersion. (4) Continuous wave Doppler mode that transmits and receives a continuous wave in a specific direction and displays a temporal change in blood flow rate with high accuracy.

  The tomographic image can be displayed at the highest speed because only one transmission / reception wave is required to obtain the luminance information at one place. However, as information relating to the blood flow, only the shape of the blood vessel can be displayed when the blood vessel diameter is relatively large, and the blood flow information is not useful when the blood vessel diameter is small. However, the relative positional change between the ultrasonic transducer and the object that affects the Doppler information can also be determined from the tomographic image. In addition, even if the blood vessel itself cannot be observed, the tissue structure can be understood, which can be useful for determining whether the blood flow image is a true blood flow or a false image due to noise. For blood flow images, pulse Doppler, and continuous wave Doppler, blood flow velocity measurement accuracy increases in order, but spatial information decreases in order. Thus, since these four modes have different characteristics, in the monitoring mode, imaging is performed by appropriately using the four modes according to the purpose of the user.

  In FIG. 6, when displaying a tomogram, the RF signal of the receiving beam former 36 is converted into a video signal by the detector 37, passes through the digital scan converter 39, and is displayed on the display unit 40 in the user interface 41. An image is displayed. When displaying a blood flow image, the blood flow velocity estimation unit 38 including a correlator and a body motion removal filter obtains the blood flow velocity and its dispersion from the RF signal of the receiving beam former 35. An image is displayed on the display unit 40 via a converter (DSC) 39. Normally, this blood flow velocity image is displayed superimposed on the previous tomographic image. Based on this tomographic image and blood flow velocity image, pulse Doppler information or continuous wave Doppler information is acquired and monitored for a target site where thrombolysis is performed. By repeatedly switching between this monitoring and ultrasonic irradiation for thrombolysis, treatment is performed while monitoring.

  FIG. 7 shows another configuration example of the ultrasonic apparatus according to the present invention. In this example, the received signal of the ultrasonic transducer 31 is intermittently acquired in the thrombolysis mode. The received signal is Fourier transformed to monitor the occurrence of cavitation in the brain, such as the treatment area or the interface with the skull. Cavitation can damage tissue due to the high pressure that occurs locally when bubbles collapse, and when cavitation occurs, it is twice the transmission frequency or an odd number of half the transmission frequency. There is a feature that a signal of a frequency is generated. In particular, a frequency that is an integral multiple of the transmission frequency is already generated by the generation of bubbles before the bubbles are crushed, so that there is a possibility that the signs may be caught before cavitation is reached. Therefore, by monitoring the ultrasonic waves of these frequencies in the cavitation monitoring unit 42, immediately after the cavitation is generated or in advance, the ultrasonic waves for treatment are turned off or the output thereof is reduced, thereby eliminating unnecessary intracerebral It is possible to prevent damage to the tissue.

  The cavitation monitoring can also be performed by monitoring the output of the high output amplifier in the therapeutic transmission beam former 33 connected to the ultrasonic transducer 31 with the cavitation monitoring unit 43. Monitoring is possible by using the fact that the fluctuation of the voltage of the high-power amplifier at the time of cavitation generation becomes larger than the fluctuation of the voltage of the high-power amplifier before the cavitation generation. The apparatus configuration in that case is shown in FIG.

  The configuration of the ultrasonic transducer 31 used in the configuration examples of the ultrasonic apparatus of FIGS. 6 to 8 described so far is not limited to the configuration of FIG. 1, and has the configuration described below. It is also possible to change.

  FIG. 9 shows an example of an ultrasonic transducer in the case where the treatment transducer array 12 is used without being arrayed for the purpose of irradiating ultrasonic waves over the entire treatment area without scanning the beam in the treatment mode. Also in this structure, the frequency selective separation layer 15 functions effectively, and the ultrasonic pulse waveform transmitted from the transducer array 11 and the transmission power from the treatment transducer 12 are suitable for the purpose of the present invention. Can be.

  FIG. 10 shows another example of the ultrasonic transducer, in which two transducer arrays are arrayed in directions substantially orthogonal to each other. This can prevent the efficient arraying from being hindered by the situation of the transducer array 12 as a base when the transducer array 11 is arrayed.

  As still another example of the ultrasonic transducer, as shown in FIG. 11, each transducer array can be a two-dimensional array. In a two-dimensional array, wiring extraction becomes a problem. That is, the wiring of the transducer array 12 can be taken from the back material side, but the wiring method for the transducer array 11 becomes a problem. However, in the present invention, as shown in FIG. 5, the acoustic impedance of polyimide, which is the main material of the flexible printed circuit board, is sufficient as a frequency selective separation layer. Therefore, this transducer array 11 can be made into a two-dimensional array, and its wiring can be incorporated into the separation layer.

  Furthermore, by using the frequency selective separation layer of the present invention, the degree of freedom in selecting the material of the backing material 16 is improved. Normally, the acoustic impedance of the backing material is selected to match the transducer to reduce reflection at the backing material interface, and the influence of the ultrasonic pulse reflected back on the opposite side of the backing material is affected. In order to eliminate it, the absorption coefficient is required to be above a certain level. However, in the present invention, since there is a frequency selective separation layer, the influence of the back material on the pulse waveform of the transducer array 11 is reduced. Therefore, when the sensitivity of the transducer array 12 is desired to be increased, the acoustic impedance of the back material can be reduced as much as possible.

  On the other hand, when the cooling of the entire transmitter is more important than the sensitivity, it is possible to select a material having a high thermal conductivity such as metal or metal oxide for the backing material 16 shown in FIG.

  When both sensitivity and thermal conductivity are important, a frequency selective reflection heat transport layer 22 can be used as shown in FIG. The frequency selective reflection heat transport layer 22 is formed by alternately laminating a plurality of layers of metal and polymer material, and uses a well-known Bragg reflection condition 2dsinθ = λ, and a specific frequency (in this case, a super therapeutic layer). (Sound wave frequency). Here, d is the period of the plurality of layers, and λ is the wavelength at the monitoring center frequency. θ is 90 degrees-incident angle, but under this monitoring condition, it can be considered to be almost 90 degrees, so the above equation can be described as 2d = λ. Further, by using a metal in this material, heat conduction can be performed efficiently, and the average density can be lowered as compared with the case where the whole is a metal, so the load on the vibrator 11 can be reduced. It is. In particular, the transport of heat is important because the brain is sensitive to heat, so it is necessary to minimize the heat transmitted from the transmitter. After transporting heat from the vicinity of the vibrator by the above-described method, the heat is finally radiated by a method such as a Peltier element or an air cooling fan.

  Furthermore, the method of transmitting two different frequencies using two layers has been described so far, but if the concept of frequency selective separation layer is used, three or more different frequencies can be obtained in three or more layers. It is possible to manufacture a transmitter that transmits waves.

  The present invention is not limited to the specific embodiments described above, and various modifications can be made without departing from the scope of the technical idea thereof. In particular, in the above-described embodiments, the case where the center frequency of the monitoring ultrasonic wave is 2 MHz and the center frequency of the thrombus dissolving ultrasonic wave is 500 kHz has been described as an example. Of course, these frequencies are not limited to those values. In particular, when the relationship between the two frequencies is different, the optimum thickness of the frequency selective separation layer is different. If it has the technical idea of invention, the deformation | transformation suitable for each condition is possible.

  As described above in detail with reference to the examples, the present invention optimizes the ultrasonic wave for enhancing the effect of the thrombolytic agent in the transcranial bone to the acoustic window for ultrasonic wave transmission / reception of the subject's head. It is possible to combine a means for irradiating and a means for monitoring the thrombolytic effect. In addition, an excessive temperature increase in the brain and in the vicinity of the skull can be suppressed.

1 is a cross-sectional view showing an ultrasonic transmitter according to an embodiment of the present invention. The schematic diagram of the element of a skull cross section and an ultrasonic transducer. The figure which shows the pulse characteristic of the case (A) with and without the separated layer by this invention (B). The figure which shows the evaluation result of the permeation | transmission characteristic in 500 kHz and the magnitude | size of a reverberation sound by the thickness of a separated layer. The figure which shows the evaluation result of the reverberation sound by the acoustic impedance of a separated layer. The figure explaining the example of 1 structure of the ultrasonic device using the ultrasonic transmitter by this invention. The figure explaining another structural example of the ultrasonic device using the ultrasonic transmitter by this invention. The figure explaining the further another structural example of the ultrasonic device using the ultrasonic transmitter by this invention. Sectional drawing which shows another Example of the ultrasonic transmitter of this invention. Sectional drawing which shows another Example of the ultrasonic transmitter of this invention. Sectional drawing which shows another Example of the ultrasonic transmitter of this invention. Sectional drawing which shows another Example of the ultrasonic transmitter of this invention.

Explanation of symbols

11 ... Monitoring transducer array, 12 ... Treatment transducer array, 13 ... Acoustic matching layer, 14 ... Acoustic lens, 15 ... Frequency selective separation layer, 16 ... Back material, 17 ... Filler, 18 ... Filler, DESCRIPTION OF SYMBOLS 19 ... Electrode, 21 ... Back material, 22 ... Frequency selective reflection heat transport layer, 31 ... Ultrasonic transducer, 32 ... Control system, 33 ... Treatment transmission beam former, 34 ... Imaging transmission beam former, 35 ... Transmission / reception Changeover switch, 36 ... received beam former, 37 ... detector, 38 ... blood flow velocity estimation unit, 39 ... digital scan converter, 40 ... display unit, 41 ... user interface, 42 ... cavitation monitoring unit, 43 ... cavitation monitoring unit 101 ... vibrator array, 120 ... skull, 121 ... interlaminar layer, 122 ... ultrasonic irradiation focus.

Claims (10)

  A structure in which at least two or more layers of transducers composed of a plurality of electric ultrasonic transducers are laminated, and a layer having an acoustic impedance smaller than the acoustic impedance of the transducer is arranged between the laminated transducer layers. In addition, an ultrasonic wave transmitter configured to be electrically driven independently at a frequency suitable for each layer of the vibrator and transmit ultrasonic waves to the subject.   The resonance frequency of the transducer at a position close to the subject among the plurality of transducer layers is configured to be higher than a resonance frequency of the transducer at a farther position. The ultrasonic transmitter according to 1.   The acoustic impedance of the layer disposed between the plurality of transducer layers is configured to be smaller than approximately one third of the acoustic impedance of the transducer at a position close to the subject in the plurality of transducer layers. The ultrasonic transmitter according to claim 2, wherein the ultrasonic transmitter is provided.   The thickness of the layer disposed between the plurality of transducer layers is smaller than about half of the wavelength at the center frequency of the electrical signal that drives the transducer close to the subject in the plurality of transducer layers. It is comprised so that it may become. The ultrasonic transmitter of Claim 2 characterized by the above-mentioned.   The ultrasonic transmitter according to claim 1, wherein each of the plurality of transducer layers includes a transducer array and is arrayed in a direction substantially orthogonal to each other.   2. The ultrasonic transmitter according to claim 1, wherein the ultrasonic transducer is a two-dimensional array in which at least one of the plurality of transducer layers is arrayed in two directions.   The material of the layer on the opposite side to the subject side of the transducer layer located farthest from the subject among the plurality of transducer layers is a metal or a metal oxide. The described ultrasonic transmitter.   Of the plurality of transducer layers, a portion of the transducer layer located farthest from the subject on the side opposite to the subject side is partly farthest from the subject among the plurality of transducer layers. The ultrasonic transmission according to claim 2, wherein the ultrasonic wave transmission has a structure in which two or more materials are alternately laminated at a period of half the wavelength at the center frequency of the electric signal for driving the transducer layer positioned. Waver.   An ultrasonic transducer comprising a plurality of electric ultrasonic transducers for transmitting / receiving ultrasonic pulses to / from a subject, a transmission / reception switch for switching between transmission and reception of ultrasonic waves to the element, and the transmission / reception switch A transmission beamformer for controlling a transmission focal position of ultrasonic waves in the subject, a reception beamformer for controlling a reception focal position in the subject, the transmission / reception changeover switch, and the transmission wave In the ultrasonic apparatus including a beam former and a control system that controls the receiving beam former, the ultrasonic transducer includes at least two or more layers of transducers composed of the plurality of electric ultrasonic transducers. And a layer having a lower acoustic impedance than that of the transducer is disposed between the stacked transducer layers, and the transducer Electrically driven independently with a frequency suitable for a layer of, respectively, ultrasound apparatus characterized by being configured to transmit the ultrasonic waves to the subject. A cavitation monitoring unit is provided that is connected to the ultrasonic transmitter, performs frequency analysis of the signal received by the ultrasonic transmitter during ultrasonic transmission, and monitors the occurrence of cavitation in the subject. The ultrasonic apparatus according to claim 9.

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