JP4320157B2 - Ultrasonic device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an ultrasonic imaging apparatus that captures an image of a subject using ultrasonic waves, an ultrasonic apparatus including a thrombus lysis apparatus using ultrasonic waves, and the like.
[0002]
[Prior art]
Transcranial ultrasonic Doppler measurement has already been established as a means for easily observing blood flow in the brain. It has also been proposed that transcranial ultrasonic Doppler measurement is performed during thrombolysis treatment using tPA (tissue plasminogen activator) (for example, see Non-Patent Document 1). The ultrasonic wave for Doppler measurement uses a frequency of about 2 MHz in consideration of resolution and attenuation.
[0003]
Regarding the effect of promoting the dissolution of thrombus by application of ultrasonic waves, a frequency of about 500 kHz is considered desirable from the effects of cavitation and temperature rise (see Non-Patent Document 2, for example).
[0004]
However, as described above, in order to use a relatively low frequency of about 500 kHz for treatment and a relatively high frequency of about 2 MHz for Doppler measurement, are both provided with separate transducers (for example, Patent Document 1)? 2), or by making the frequency of the monitoring ultrasonic wave an odd multiple of the frequency of the therapeutic ultrasonic wave, it is necessary to perform two roles with one transducer (see, for example, Patent Document 3).
[0005]
[Non-Patent Document 1]
AVAlexander, et al., “High Rate Complete Recanalization and Dramatic Clinical Recovery During tPA Infusion When Continuous ly Monitored With 2-MHz Transcranial Doppler Monitoring”, Stroke, 2002, vol.31, p.610-614
[Non-Patent Document 2]
T. Ishibashi, et al., “Can Transcranial Ultrasonication Increa se Recanalization Flow With Tissue Plasminogen Activator?”, Stroke, 2002, vol. 33, p.1399-1404
[Patent Document 1]
Japanese Patent Laid-Open No. 5-220152 [Patent Document 2]
JP 2001-327495 A [Patent Document 3]
JP-A-6-269448 [0006]
[Problems to be solved by the invention]
FIG. 1 is a diagram showing a cross section around a temple of a skull that transmits and receives ultrasonic waves and an element array of an ultrasonic transducer (ultrasonic transducer) 1 for the skull. The most part of the skull 20 has a structure in which a perforated interlaminar layer 21 is sandwiched between them as shown on both sides of FIG. 1, and the interlaminar layer 21 has a large attenuation of ultrasonic waves. It has been known. On the other hand, the temple portion has no interlamellar layer 21 or is very thin, so that it is known that the attenuation of the ultrasonic wave is less than that of the portion with the interlaminar layer 21, and the inside of the skull is imaged with ultrasonic waves. Or it is used as an acoustic window for treatment.
[0007]
However, since the size of the acoustic window area through which ultrasonic waves pass relatively well is limited to a few cm square, separate transducers are used side by side for monitoring and treatment in this narrow area. It has the problem that it is difficult.
[0008]
On the other hand, a single transducer serves both for monitoring and for treatment because the vibration of the transducer is actually coupled with a transverse mode in addition to the thickness resonance, and the acoustic matching layer When this is taken into consideration, there is a problem that designing to optimize for two frequencies is extremely difficult.
[0009]
An object of the present invention is to provide an ultrasonic device that can use ultrasonic waves in the same frequency band for ultrasonic irradiation in monitoring by transcranial ultrasonic Doppler and ultrasonic irradiation that promotes the thrombolytic effect of tPA. Accordingly, an object of the present invention is to provide an ultrasonic device capable of enhancing the thrombolytic effect of tPA by ultrasonic irradiation under ultrasonic blood flow monitoring.
[0010]
[Means for Solving the Problems]
In order to achieve the above object, in the present invention, a transducer for transmitting / receiving ultrasonic waves to a subject, a plurality of electric ultrasonic transducer elements (hereinafter referred to as elements) constituting the transducer, and a transducer are connected. An ultrasonic device (transcranial ultrasonic imaging device) that includes a transmitting beamformer and a receiving beamformer and capable of imaging a blood flow image, and transmitting and receiving ultrasonic pulses to determine the thickness distribution of the skull A means for measuring is provided, and a means for selecting a transmission frequency at which the transmittance is maximized for each element based on the thickness distribution is provided to optimize the enhancement of the effect of the thrombus dissolving agent by ultrasound.
[0011]
The ultrasonic apparatus of the present invention includes a plurality of electric ultrasonic transducers, an ultrasonic transducer for transmitting / receiving ultrasonic pulses to / from a subject, and a transmission / reception for switching between transmission and reception of ultrasonic waves to the element. A switch beam, a transmission beamformer connected to the transmission / reception wave changeover switch for controlling the transmission focal position of the ultrasonic wave in the subject, a reception beamformer for controlling the reception focal position in the subject, and reception A detector that receives the output of the beamformer, a flow velocity calculation unit that measures the blood flow in the subject from the output of the detector, and a display unit that displays the blood flow. The device transmits and receives ultrasonic pulses for each element, and measures the thickness of the skull in front of the element, and selects the transmission frequency that maximizes the intensity of ultrasonic waves that pass through the skull for each element, based on the thickness of the skull. Means and selected transmission Means for irradiating the inside of the skull with an ultrasonic pulse of a wave number from the ultrasonic transducer, and in the second configuration, the ultrasonic pulse is transmitted and received for each of a plurality of elements, and the skull in front of the elements Means for measuring the frequency characteristics of the ultrasound transmission rate, means for selecting the transmission frequency that maximizes the intensity of the ultrasound transmitted through the skull, and irradiating the selected transmission frequency to the inside of the skull from the ultrasonic transducer Means.
[0012]
Further, in the first and second configurations described above, there is provided means for controlling the amplitude of the transmission waveform for each element based on the thickness of the skull, and the product of the transmittance distribution of the skull and the transmission amplitude distribution for each element is The transmission amplitude distribution for each element is determined so that the amplitude distribution after passing through the skull is obtained.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
The present invention provides an ultrasonic device capable of enhancing the thrombolytic effect of tPA by ultrasonic irradiation under ultrasonic blood flow monitoring without incising the skull. An ultrasonic imaging device (transcranial ultrasonic wave) that includes an ultrasonic transducer composed of a plurality of elements and alternately repeats ultrasonic irradiation for enhancing the effect of tPA in the brain and monitoring of blood flow imaging of the effect of treatment. An imaging device) that measures the thickness of the skull in front of each element constituting the ultrasonic transducer with ultrasonic waves in advance and determines the frequency at which the transmittance is maximized for each element, or directly By obtaining the frequency at which the transmittance of the skull in front of each element is maximized by sound waves, the enhancement of the therapeutic effect of tPA can be optimized.
[0014]
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
[0015]
In the present invention, ultrasonic waves in the same frequency band are used for ultrasonic irradiation in monitoring by transcranial ultrasonic Doppler and ultrasonic irradiation for promoting the thrombolytic effect of tPA. For this purpose, the frequency dependence of the transmittance of the ultrasonic wave with and without the interlaminar layer was simulated using the FDTD method (time-resolved finite element method).
[0016]
FIG. 2 is a diagram showing the frequency characteristics of the ultrasonic transmittance of the skull obtained by the present invention. FIG. 2 shows an ultrasonic transmission intensity curve 40 with an inter-plate layer and an ultrasonic transmission intensity curve 41 without an inter-plate layer. From the results shown in FIG. 2, in the case where there is an interlaminar layer, the lower the frequency, the higher the transmissivity, but the portion without the interlaminar layer may have a maximum transmittance near 1 MHz, 2 MHz, and 3 MHz. Recognize. By selecting a place where there is no interlaminar layer and using a frequency corresponding to the maximum point, it is possible to promote the effect of tPA within the frequency band (usually 2 MHz to 5 MHz) of the ultrasonic transceiver for transcranial topola monitoring. Ultrasonic waves can also be transmitted.
[0017]
Since this maximum point corresponds to a resonance point that is an odd multiple of wavelength / 2, the frequency with the maximum transmittance varies with the thickness of the bone. As shown in FIG. 1, when transmitting / receiving ultrasonic waves to / from the transmission focal point 22, the thickness of the bone on the front surface is different for each element of the ultrasonic transducer, so it is necessary to adjust the optimum frequency for each element. is there.
[0018]
Hereinafter, the apparatus of the first embodiment for realizing therapeutic transmission with the frequency optimized for each element will be described.
[0019]
FIG. 3 is a diagram showing an apparatus configuration of the first embodiment of the present invention, and FIG. 4 is a flowchart showing operations (processes) in the apparatus of the first embodiment of the present invention.
[0020]
First, with respect to a subject not shown in FIG. 3, the ultrasonic transducer 1 composed of a plurality of ultrasonic elements is searched from the top of the skull 20 shown in FIG. , Fix in place. This location can be found by changing the location of the ultrasonic transducer 1 while observing a B-mode image or a Doppler image.
[0021]
After the ultrasonic transducer 1 is fixed to the skull 20, A-mode imaging (A-mode imaging step 100 shown in FIG. 4) is performed for each element, thereby measuring the bone thickness in front of each element. . Under the control of the control system 2, a pulse output is sent from the bone thickness measuring unit 3 to one element in the ultrasonic transducer 1 selected by the transmission / reception wave changeover switch 5 (also serving as an element selection switch) The reflected signal is returned to the bone thickness measuring unit 3 again via the transmission / reception wave changeover switch 5, and the reflected signal is measured.
[0022]
At this time, the first large reflected signal is a reflected signal from the acoustic lens provided on the ultrasonic transducer 1 and the skull surface, and the second reflected signal is reflected from the back side of the skull. From the time difference, the thickness of the skull in front of the element can be measured (skull thickness measuring step 101 in FIG. 4). Strictly speaking, the speed of sound of the bone varies from person to person, but is about 3300 m / s. From this value, the resonance frequency that is an odd multiple of a half wavelength, that is, the maximum point of the transmittance of ultrasonic waves can be obtained. . There may be a plurality of maximum points of the transmittance, and among them, the one having the lowest frequency within the effective frequency band of the ultrasonic transducer 1 may be selected. This is because the attenuation rate of ultrasonic attenuation in a living body increases as the frequency increases, and the attenuation is changed to heat. In the brain, excessive temperature rise is strictly prohibited, so it is better to choose a lower frequency for thrombolysis. This operation is repeated for each element. From this result, in the treatment frequency setting step 102 shown in FIG. 4, the ultrasonic frequency of each element in the treatment mode is determined.
[0023]
Next, an operation of a conventionally known color flow image capturing (blood flow image capturing) step 103 is performed. This is because, under the control of the control system 2, an ultrasonic pulse is transmitted from the transmission beam former 4 to the subject via the transmission / reception wave changing switch 5, and reflection and scattering signals in the subject are as described above. Is input to the receiving beamformer 11 via the ultrasonic transducer 1 and the transmission / reception change-over switch 5 in the reverse path. The receiving beam former 11 adjusts and adds the delay time for each element so as to maximize the signal at a predetermined focal position. The detector 12 performs quadrature detection on the output of the receiving beam former 11, and the MTI filter 13, the autocorrelation calculator 14, the flow velocity / dispersion calculator 15 display the flow velocity at each location in the subject on the display 16. The When this blood flow image capturing step 103 is performed for a certain time, the treatment ultrasonic wave irradiation step 104 is switched.
[0024]
It is assumed that tPA has been administered into the patient's body by the operator before this. In the therapeutic ultrasonic wave irradiation step 104, a transmission signal having an optimal frequency (maximum transmittance) is transmitted from the transmission beamformer 4 to the transmission / reception switching unit for each element based on the output of the bone thickness calculation unit 3 from the control system 2. The wave is transmitted into the subject via the switch 5 and the ultrasonic transducer 1. After repeating this therapeutic ultrasound irradiation step 104 for a certain time, the process returns to the blood flow image capturing step 103 again, and after confirming the therapeutic effect, if the effect is insufficient, the therapeutic ultrasonic irradiation step 104 again treats. Ultrasonic irradiation is performed. When it is confirmed that the therapeutic effect is sufficient in the blood flow image capturing step 103, the therapeutic ultrasonic wave irradiation ends (treatment end determination step 105).
[0025]
The time of the blood flow image capturing step 103 and the time of the treatment ultrasound irradiation step 104 may be set in advance as default values in units of seconds, or may be input from the user interface 17 by the operator before the treatment. It may be possible to change it appropriately during treatment.
[0026]
If the frequency is changed for each element in this way, the beam shape is affected. However, the treatment ultrasonic wave irradiation does not need to squeeze the beam to the maximum, so that there is no problem in the method of the first embodiment. Although the above description has been made when a bone thickness measurement pulse signal is sent from the bone thickness measurement unit 3, based on the same idea, the pulse signal may be transmitted only from the transmission beamformer for one element. The effect is the same.
[0027]
If the thickness of the bone is known by this method, the effect can also be used for blood flow imaging. As described above, the sound velocity of the bone is about 3300 m / s, which is more than twice the sound velocity of the living body. Therefore, the ultrasonic wave obliquely incident on the bone is refracted at the front and back interfaces of the bone. This causes blurring of the focus, causing a decrease in sensitivity and a major factor that degrades the blood flow image and the B-mode image. In order to prevent this, it is only necessary to perform a focus calculation with an effect of refraction, and this can be achieved by measuring the thickness. As a method of not directly calculating refraction, there is a known adaptive image reproduction technique. However, if the thickness of the bone is known, it can be used as a first approximation value of adaptive image reproduction as a starting point, and the adaptive image is reproduced. This can contribute to the improvement of reproduction accuracy or calculation speed.
[0028]
FIG. 5 is a diagram showing an apparatus configuration of the second embodiment of the present invention, and FIG. 6 is a flowchart showing an operation <process> in the apparatus of the second embodiment of the present invention.
[0029]
In the first embodiment, the bone thickness measuring unit 3 can transmit and receive a signal in the same manner as in the A mode, and the bone thickness can be measured from the reflected pulse interval. Can also be measured. In the second embodiment, the frequency dependency of the transmittance is directly measured, and the optimum frequency for each element is selected. That is, the configuration of the apparatus of the second embodiment is a configuration in which the bone thickness measuring unit 3 is replaced with the transmittance measuring unit 8 and the frequency determining unit 9 in the configuration of the apparatus of the first example. Further, in place of the A-mode imaging step 100 shown in FIG. 4, a transmittance measuring step 108 is executed in FIG.
[0030]
The transmittance measuring unit 8 sweeps the center frequency of the transmission pulse within the sensitivity range of the ultrasonic transducer, and the frequency determining unit 9 selects the frequency with the maximum transmittance. When there are a plurality of maximum points of transmittance, the one with the lowest frequency is selected in consideration of the temperature rise in the brain as in the first embodiment. After this frequency is determined, treatment and monitoring of its effect can be performed alternately by the same method as in the first embodiment as shown in FIGS.
[0031]
If the transmittance is known, the amplitude of each element within the transmission aperture of the ultrasonic transducer 1 can be optimized. In order to prevent the temperature rise, the transmission energy of the element facing the bone with low transmittance is reduced, and the transmission energy of the element facing the bone with high transmittance is increased, so that it is possible to suppress the excessive temperature rise near the skull. Become.
[0032]
On the other hand, when it is desired to optimize the beam shape, the method shown in FIG. 7 is effective.
[0033]
FIG. 7 shows a transmission amplitude distribution 33, a transmission amplitude distribution 31 after passing through the skull, and a reciprocal distribution 32 of the transmittance of the skull in the device according to the second embodiment of the present invention. It is a figure showing a relation typically.
[0034]
The amplitude distribution of the ultrasonic wave after passing through the skull in the direction along the arrangement of the elements of the ultrasonic transducer 1 is similar to the apodization for each element on the conventionally known ultrasonic transducer. By controlling so as to have a shape, it is possible to minimize the effect that the ultrasonic beam shape deteriorates due to the transmission of the skull. That is, the transmission amplitude distribution for each element is determined so that the product of the reciprocal distribution 32 of the skull transmittance and the transmission amplitude distribution 33 for each element shown in FIG. 7 becomes the amplitude distribution 31 after passing through the skull. Just do it. In any case, by knowing the transmittance of the skull, it is possible to meet the user's needs whether to give priority to the control of the temperature rise or the beam shape according to the guideline of the ultrasonic transmission method. It becomes possible.
[0035]
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.
[0036]
As described above, according to the present invention, the means for irradiating the transcranial bone with the ultrasonic wave for enhancing the effect of tPA by optimizing the acoustic window for ultrasonic wave transmission / reception of the subject head, and the thrombolytic effect are obtained. It is possible to have a means for monitoring. Further, it is possible to prevent an excessive temperature rise in the brain and in the vicinity of the skull.
[0037]
In the ultrasonic device of the present invention, using a limited acoustic window of the skull, monitoring by transcranial ultrasonic Doppler and ultrasonic irradiation for promoting the thrombolytic effect of tPA by ultrasonic waves are performed using ultrasonic waves in the same frequency band. Can be used and executed.
[0038]
【The invention's effect】
According to the present invention, there is provided an ultrasonic apparatus capable of using ultrasonic waves in the same frequency band for ultrasonic irradiation in monitoring by transcranial ultrasonic Doppler and ultrasonic irradiation for promoting the thrombolytic effect of tPA. And an ultrasonic device capable of enhancing the thrombolytic effect of tPA by ultrasonic irradiation under ultrasonic blood flow monitoring.
[Brief description of the drawings]
FIG. 1 is a diagram showing a cross section around a temple of a skull that transmits and receives ultrasonic waves in the present invention, and an element array of an ultrasonic transducer for the skull.
FIG. 2 is a diagram showing the frequency characteristics of the ultrasonic transmission rate of the skull obtained by the study of the present invention.
FIG. 3 is a diagram showing an apparatus configuration of a first embodiment of the present invention.
FIG. 4 is a flowchart showing processing in the apparatus of the first embodiment of the present invention.
FIG. 5 is a diagram showing a device configuration of a second embodiment of the present invention.
FIG. 6 is a flowchart showing processing in the apparatus of the second embodiment of the present invention.
FIG. 7 schematically shows the relationship between the transmission amplitude distribution, the transmission amplitude distribution after passing through the skull, and the inverse distribution of the transmittance of the skull in the second embodiment of the present invention. Figure representing.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Ultrasonic transmitter / receiver, 2 ... Control system, 3 ... Bone thickness measurement part, 4 ... Transmission beam former, 5 ... Transmission / reception wave changeover switch, 8 ... Transmittance measurement part, 9 ... Frequency determination part, 11 ... Reception Wave beam former, 12 ... detector, 13 ... MTI filter, 14 ... autocorrelation calculator, 15 ... flow velocity, dispersion calculation unit, 16 ... display unit, 17 ... user interface, 20 ... skull, 21 ... interplate layer, 22 ... Transmission focal point, 31... Transmission amplitude distribution after passing through the skull with respect to the element arrangement position, 32... Distribution of reciprocal number of skull transmittance with respect to the element arrangement position, 33... Transmission amplitude distribution with respect to the element arrangement position, 40. Ultrasonic transmission intensity curve when there is a layer, 41 ... Ultrasonic transmission intensity curve when there is no interplate layer, 100 ... A-mode imaging step, 101 ... Skull thickness measurement step, 102 ... Treatment frequency setting step, 103 ... Flow imaging step, 104 ... treatment ultrasonic irradiation step, 105 ... end of treatment determination, 108 ... transmittance measurement step.

Claims (7)

An ultrasonic transducer comprising a plurality of electric ultrasonic transducers, and transmitting / receiving ultrasonic pulses to / from a subject, a transmission / reception switching switch for switching between transmission and reception of ultrasonic waves to the element, and the transmission / reception A transmission beamformer connected to a changeover switch for controlling a transmission focal position of an ultrasonic wave in the subject, a reception beamformer for controlling a reception focal position in the subject, and a reception beamformer A detector that receives an output; a flow velocity calculation unit that measures blood flow in the subject from the output of the detector; a display unit that displays the blood flow; and an ultrasonic pulse for each of the plurality of elements. Means for transmitting and receiving, measuring the frequency characteristics of the ultrasound transmittance of the skull in front of the element, means for selecting a transmission frequency based on the intensity of ultrasound transmitted through the skull, and the selected transmission frequency in front And a means for irradiating the ultrasonic transducer inside the skull,
The ultrasonic beam former controls an ultrasonic wave for thrombolysis and ultrasonic wave for blood flow measurement.   The ultrasonic apparatus according to claim 1, wherein the transmission beamformer controls an amplitude of a transmission waveform for each element based on a thickness of the skull.   2. The ultrasonic device according to claim 1, wherein the transmission beamformer alternately repeats transmission of ultrasonic waves for thrombolysis and ultrasonic waves for blood flow measurement. apparatus.   4. The ultrasonic device according to claim 1, wherein when there are a plurality of transmission frequencies that are candidates for selection of the transmitted ultrasonic intensity, the selecting unit selects the lowest frequency. 5. An ultrasonic device characterized by that.   5. The ultrasonic device according to claim 1, wherein the transmission beamformer uses ultrasonic waves in the same frequency band to measure the ultrasonic waves for thrombolysis and the blood flow measurement. An ultrasonic device characterized by performing ultrasonic waves.   6. The ultrasonic apparatus according to claim 1, wherein the transmission beamformer transmits the ultrasonic wave for thrombolysis and the ultrasonic wave for blood flow measurement for each element. An ultrasonic apparatus, wherein control is performed so that waveforms are different. 7. The ultrasonic apparatus according to claim 1, wherein the measuring means measures a transmittance at the time of bone propagation from a pulse intensity ratio.

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