JP2009153945A - Bone thickness measurement apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a bone thickness measurement apparatus by which bone thickness can be stably measured. <P>SOLUTION: The bone thickness measurement apparatus includes an ultrasonic transceiver 2 to transmit an incoming pulse 40 almost perpendicularly to a cortical bone 60 and receive a first reflection wave 41 from a cortical bone surface 63 and a second reflection wave 42 from a cortical bone backside face 64, and a bone thickness calculation part to calculate thickness D of a cortical bone by the ultrasonic transceiver 2 based on the difference between times when the first reflection wave and the second reflection wave are respectively received. Further, the ultrasonic transceiver 2 has a plurality of ultrasonic oscillators 21-24 for performing both of transmission and reception of ultrasonic waves and an ultrasonic oscillator 25 for performing only transmission of ultrasonic waves placed on an identical plane. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a bone thickness measuring apparatus that measures the thickness of bone using ultrasonic waves, particularly the thickness of cortical bone.

  Conventionally, various apparatuses for diagnosing bone strength are known for diagnosis of osteoporosis, diagnosis of an implant (artificial tooth root) before surgery, and the like. As such a device, there is a device using X-rays. However, the device becomes large and there is a problem of radiation exposure.

  Therefore, as a safe device that does not cause such a problem, a device for diagnosing bone strength using ultrasonic waves has been developed. As an apparatus using such an ultrasonic wave, for example, there is a bone density measuring apparatus disclosed in Patent Document 1. The evaluation index of bone strength includes bone density, bone thickness (cortical bone thickness), etc., but the apparatus of Patent Document 1 diagnoses bone strength by paying particular attention to bone density. In this bone density measuring apparatus, both sides of a subject are sandwiched between an ultrasonic wave transmitter and an ultrasonic wave receiver, and bone density is calculated from the passing speed of ultrasonic waves in the subject. In this bone density measuring apparatus, for example, a rib that can be easily sandwiched between a transmitter and a receiver is a measurement target.

JP-A-10-43180

  However, the device disclosed in Patent Document 1 described above is a device that measures bone density to the last, and is not a device that measures bone thickness. Moreover, in the apparatus of Patent Document 1 described above, it is necessary to sandwich both sides of the subject with an ultrasonic transmitter and an ultrasonic receiver. Therefore, for example, it is not suitable for measurement of a part that is difficult to be sandwiched from both sides, such as a jawbone, and the measurement target is limited.

  Accordingly, the inventors of the present application pay attention to bone thickness, which is one of the indices of bone strength, and provide an object of the present invention to provide a bone thickness measuring device that can stably measure bone thickness. .

Means for Solving the Problems and Effects of the Invention

  The bone thickness measuring device according to claim 1 transmits an ultrasonic wave to a bone, and receives a first reflected wave from the surface of the bone and a second reflected wave from the back surface of the bone. A bone thickness calculator that calculates the thickness of the bone based on a difference in time at which the first reflected wave and the second reflected wave are received by the ultrasonic transmitting / receiving unit, and the ultrasonic transmitting / receiving unit; The ultrasonic transmission / reception unit includes a plurality of ultrasonic transducers arranged on the same plane and capable of both transmitting and receiving ultrasonic waves.

  When ultrasonic waves are transmitted to the bone, a first reflected wave reflected on the surface of the bone and a second reflected wave propagated through the bone and reflected on the back surface of the bone are generated. The ultrasonic wave transmitting / receiving unit receives the first reflected wave and the second reflected wave after transmitting the ultrasonic wave to the bone. The second reflected wave returns with a delay from the first reflected wave by the amount reciprocating between the front surface and the back surface of the bone. That is, the time difference between the two reflected waves corresponds to the time for the ultrasonic wave to reciprocate between the bone surface and the bone back surface. Therefore, the bone thickness calculation unit can calculate the bone thickness based on the difference between the reception times of the first reflected wave and the second reflected wave. In this way, in the bone thickness measuring apparatus, since the measurement is performed using the reflected wave, a device that transmits and receives an ultrasonic wave is arranged on one side of the bone. Therefore, the bone thickness of various parts can be measured.

  The ultrasonic transmission / reception unit includes a plurality of ultrasonic transducers that can both transmit and receive ultrasonic waves. The ultrasonic transmission / reception unit transmits ultrasonic waves to the bone simultaneously by a plurality of ultrasonic transducers, and receives the reflected wave that has bounced out of the plurality of ultrasonic transducers. Receive by. Therefore, it is desirable for the ultrasonic wave transmitting / receiving unit to receive the ultrasonic wave substantially perpendicularly to the bone in order to reliably receive the reflected wave. However, since the bone is covered with soft tissues such as fat and muscle, the incident direction to the bone is difficult to understand from the outside. As a result, ultrasonic waves may be incident on the bone obliquely.

  When both ultrasonic wave transmission and reception are performed by one ultrasonic transducer, the reflected wave can be received even if the ultrasonic wave is incident obliquely on the bone in order to solve the above problem. In order to achieve this, it is conceivable to increase the transmission surface for transmitting ultrasonic waves (vibration surface of the ultrasonic transducer). However, generally, when the vibration surface is enlarged, the directivity at the time of reception is narrowed. Therefore, even if the transmission surface is enlarged, the reflected wave can be received only within a narrow directivity range.

  On the other hand, in the ultrasonic transmission / reception unit of the present invention, the ultrasonic wave transmission surface is constituted by the vibration surfaces of a plurality of ultrasonic transducers. The reception of the reflected wave is performed independently for each ultrasonic transducer that receives the wave among the plurality of ultrasonic transducers. Therefore, compared to the case where both ultrasonic wave transmission and reception are performed by one ultrasonic transducer, the directivity at the time of wave reception can be widened, and at the same time the wave transmission surface can be enlarged. Therefore, even when an ultrasonic wave is incident obliquely on the bone, the reflected wave can be received, and the thickness of the bone can be measured stably.

  A bone thickness measurement apparatus according to a second aspect of the present invention is the apparatus according to the first aspect, further comprising: a wave receiving transducer determining unit that determines an ultrasonic transducer that performs wave reception among the plurality of ultrasonic transducers.

  According to this configuration, the ultrasonic transmission / reception unit transmits the ultrasonic wave to the bone simultaneously with the plurality of ultrasonic transducers, and receives the reflected wave that has rebounded among the plurality of ultrasonic transducers. A wave is received by the ultrasonic transducer determined by the transducer determining means. In order to calculate the thickness of the bone, it is not necessary to receive all the reflected waves generated by the transmitted ultrasonic waves, as long as a part of the reflected waves can be received. Therefore, the ultrasonic wave receiving surface may be smaller than the wave transmitting surface. And, it is unnecessary compared with the case where receiving is performed by some ultrasonic transducers among a plurality of ultrasonic transducers, and receiving is performed by all ultrasonic transducers. In addition, since there are few ultrasonic transducers that receive ultrasonic waves, the electrical configuration for processing the received signals can be simplified, and the cost can be reduced. In addition, depending on the shape of the bone, it may be possible that the ultrasonic wave is obliquely incident on the bone no matter how the ultrasonic transmission / reception unit is installed. By setting the position of the wave receiving surface that receives the sound wave to a position where the reflected wave returns, the reflected wave can be reliably received.

  The bone thickness measuring device according to claim 3 transmits an ultrasonic wave to the bone, and receives a first reflected wave from the surface of the bone and a second reflected wave from the back surface of the bone. A bone thickness calculator that calculates the thickness of the bone based on a difference in time at which the first reflected wave and the second reflected wave are received by the ultrasonic transmitting / receiving unit, and the ultrasonic transmitting / receiving unit; The ultrasonic transmission / reception unit is disposed on the same plane, and transmits / receives an ultrasonic transducer for both transmission and reception of ultrasonic waves, and a transmission / reception unit that transmits only ultrasonic waves. It has a wave-dedicated ultrasonic transducer.

  The ultrasonic wave transmitting / receiving unit transmits an ultrasonic wave to the bone, and receives the first reflected wave reflected from the surface of the bone and the second reflected wave reflected from the back surface of the bone. The time difference between the two reflected waves corresponds to the time for the ultrasonic wave to reciprocate between the bone surface and the bone back surface. Therefore, the bone thickness calculation unit can calculate the bone thickness based on the difference between the reception times of the first reflected wave and the second reflected wave. In this way, in the bone thickness measuring apparatus, since the measurement is performed using the reflected wave, a device that transmits and receives an ultrasonic wave is arranged on one side of the bone. Therefore, the bone thickness of various parts can be measured.

  The ultrasonic transmission / reception unit includes a transmission / reception ultrasonic transducer that performs both transmission and reception of ultrasonic waves and a dedicated ultrasonic transducer for transmission that performs only transmission of ultrasonic waves. The ultrasonic transmission / reception unit transmits ultrasonic waves to the bone at the same time by the ultrasonic transducer for transmission / reception and the ultrasonic transducer for transmission, and reflects the reflected wave by the ultrasonic transducer for transmission / reception. Receive a wave. Therefore, it is desirable for the ultrasonic wave transmitting / receiving unit to receive the ultrasonic wave substantially perpendicularly to the bone in order to reliably receive the reflected wave. However, since the bone is covered with soft tissues such as fat and muscle, the incident direction with respect to the bone is difficult to understand from the outside, and as a result, the ultrasonic wave may be obliquely incident on the bone.

  In the ultrasonic transmission / reception unit, the ultrasonic wave transmission surface is constituted by the vibration surfaces of the ultrasonic transducer for transmission / reception and the ultrasonic transducer dedicated for transmission. Further, the reflected wave is received by an ultrasonic transducer for transmitting and receiving waves. Therefore, compared with the case where both ultrasonic wave transmission and reception are performed by one ultrasonic transducer, the wave transmission surface can be enlarged without narrowing the directivity during reception. Therefore, even when an ultrasonic wave is incident obliquely on the bone, the reflected wave can be received, and the thickness of the bone can be measured stably. In order to calculate the thickness of the bone, it is not necessary to receive all the reflected waves generated by the transmitted ultrasonic waves, and it is sufficient that a part of the reflected waves can be received. Therefore, the ultrasonic wave receiving surface may be smaller than the wave transmitting surface. Therefore, compared with the case where the ultrasonic transmission / reception unit is configured by a plurality of ultrasonic transducers capable of both transmitting and receiving ultrasonic waves, the ultrasonic transducers that receive unnecessary ultrasonic waves Since the number is small, the electrical configuration for processing the received signal can be simplified, and the cost can be reduced.

  The bone thickness measuring device according to claim 4 transmits ultrasonic waves to the cortical bone of the jawbone, and includes a first reflected wave from the surface of the cortical bone of the jawbone and a back surface of the cortical bone of the jawbone. Based on the difference between the time when the first reflected wave and the second reflected wave are received by the ultrasonic wave transmitting / receiving unit receiving the second reflected wave and the ultrasonic wave transmitting / receiving unit, A transmission / reception ultrasonic transducer for performing both transmission and reception of ultrasonic waves, the ultrasonic transmission / reception unit being arranged on the same plane, and a bone thickness calculation unit for calculating the thickness of cortical bone And a transmission-dedicated ultrasonic transducer that performs only ultrasonic transmission.

  The ultrasonic wave transmitting / receiving unit transmits an ultrasonic wave to the cortical bone of the jawbone, and then reflects the first reflected wave reflected on the surface of the cortical bone of the jawbone and the second reflected wave reflected on the back surface of the cortical bone of the jawbone. Is received. The time difference between the two reflected waves corresponds to the time for the ultrasonic wave to reciprocate between the front surface and the back surface of the cortical bone of the jawbone. Therefore, the bone thickness calculation unit can calculate the thickness of the cortical bone of the jawbone based on the difference between the reception times of the first reflected wave and the second reflected wave. In this way, in the bone thickness measurement apparatus, since the measurement is performed using the reflected wave, a device for transmitting and receiving ultrasonic waves may be arranged on one side of the jawbone. Therefore, the thickness of the cortical bone of the jawbone can be easily measured.

  The ultrasonic transmission / reception unit includes a transmission / reception ultrasonic transducer that performs both transmission and reception of ultrasonic waves and a dedicated ultrasonic transducer for transmission that performs only transmission of ultrasonic waves. The ultrasonic transmission / reception unit simultaneously transmits ultrasonic waves to the jawbone by the ultrasonic transducer for transmission / reception and the ultrasonic transducer for transmission, and reflects the reflected wave by the ultrasonic transducer for transmission / reception. Receive a wave. In order to receive the reflected wave reliably, it is desirable that the ultrasonic waves be incident almost perpendicular to the cortical bone of the jawbone, but the direction of incidence on the jawbone is difficult to understand from the outside, and as a result, the jawbone In some cases, ultrasonic waves are incident obliquely on the cortical bone.

  In the ultrasonic transmission / reception unit, the ultrasonic wave transmission surface is constituted by the vibration surfaces of the ultrasonic transducer for transmission / reception and the ultrasonic transducer dedicated for transmission. Further, the reflected wave is received by an ultrasonic transducer for transmitting and receiving waves. Therefore, compared with the case where both ultrasonic wave transmission and reception are performed by one ultrasonic transducer, the wave transmission surface can be enlarged without narrowing the directivity during reception. Therefore, even when ultrasonic waves are incident obliquely on the cortical bone of the jawbone, the reflected wave can be received, and the thickness of the cortical bone of the jawbone can be measured stably. In order to calculate the thickness of the cortical bone of the jawbone, it is not necessary to receive all the reflected waves generated by the transmitted ultrasonic waves, and it is sufficient that a part of the reflected waves can be received. Therefore, the ultrasonic wave receiving surface may be smaller than the wave transmitting surface. Therefore, compared with the case where the ultrasonic transmission / reception unit is configured by a plurality of ultrasonic transducers capable of both transmitting and receiving ultrasonic waves, the ultrasonic transducers that receive unnecessary ultrasonic waves Since the number is small, the electrical configuration for processing the received signal can be simplified, and the cost can be reduced.

  The bone thickness measuring device according to claim 5 is the ultrasonic transducer according to any one of claims 1 to 4, wherein the ultrasonic transmitting / receiving unit includes at least two ultrasonic transducers for receiving ultrasonic waves, An incident direction detection unit that detects an incident direction of the ultrasonic wave with respect to the bone based on a phase difference between the first reflected wave and the second reflected wave respectively received by two or more ultrasonic transducers It is characterized by providing.

  By detecting the incident direction of the ultrasonic wave to the bone by the incident direction detecting unit, the direction in which the ultrasonic wave is transmitted from the ultrasonic wave transmitting / receiving unit can be adjusted according to the detected incident direction. Thereby, an ultrasonic wave can be incident more perpendicularly to the bone. Therefore, measurement can be performed more stably and measurement accuracy is improved.

  The bone thickness measuring device according to claim 6 is the bone thickness measuring device according to claim 3 or 4, wherein the ultrasonic transducer for transmitting and receiving is surrounded by the ultrasonic transducer dedicated to transmission, and vibration surfaces of all ultrasonic transducers The outer edge shape of the combined surface is a circular shape or a polygonal shape, and the combined shape of the vibration surfaces of all the transmitting / receiving ultrasonic transducers is a circular shape or a polygonal shape. . It is an example of a structure of the ultrasonic transducer | vibrator which an ultrasonic transmission / reception part has.

  A bone thickness measurement apparatus according to a seventh aspect of the present invention is the bone thickness measurement apparatus according to any one of the first to sixth aspects, wherein the bone thickness calculation unit uses the difference between the received times and the assumed value of the speed of ultrasonic waves propagating through the bone. Then, the thickness of the bone is calculated.

  The thickness of the bone can be calculated from the difference between the sound velocity of the ultrasonic wave propagating through the bone in the thickness direction and the time when the first reflected wave and the second reflected wave are received. Both the sound speed in the bone and the bone thickness have individual differences, but the variation due to the individual difference in the sound speed in the bone is smaller than the variation due to the individual difference in the bone thickness. Therefore, by calculating the bone thickness assuming that the sound speed in the bone is a constant value, the bone thickness can be calculated easily.

  The bone thickness measuring apparatus according to an eighth aspect is characterized in that, in the seventh aspect, the assumed value is in a range of 3000 to 3300 m / s. By setting the assumed value of the sound velocity in the bone within the above-described range, the bone thickness can be calculated with high accuracy.

<First Embodiment>
Hereinafter, a first embodiment of the present invention will be described.
As shown in FIG. 1, the bone thickness measuring apparatus 1 of the present embodiment transmits ultrasonic waves almost perpendicularly to the cortical bone at the measurement site, and reflects reflected waves from the surface of the cortical bone and the back surface of the cortical bone. This is a device that measures the thickness of the cortical bone based on the time difference between the two reflected waves received by receiving the waves. As shown in FIG. 1, the bone thickness measuring apparatus 1 uses the cortical bone of the mandible as a measurement site. Further, the cortical bone of the maxilla can be used as the measurement site.

  As shown in FIG. 2, the bone is composed of cortical bone 60 and reticulated cancellous bone 61 existing inside cortical bone 60. The surface 63 of the cortical bone is covered with a soft tissue 62 such as fat or muscle. Here, the surface opposite to the surface 63 of the cortical bone, that is, the interface between the cancellous bone 61 and the cortical bone 60 is defined as the cortical bone back surface 64. The cortical bone surface 63 is parallel or slightly inclined with respect to the cortical bone back surface 64. The thickness D of the cortical bone 60 is the length of the cortical bone 60 that is substantially perpendicular to the cortical bone surface 63 and the cortical bone back surface 64.

  As shown in FIG. 1, the bone thickness measuring apparatus 1 includes an ultrasonic transducer 2, a pulse generator 3, a transmission / reception separating unit 4, a receiving unit 5, a signal processing unit 6, a control device 7, and a display. Part 8 is provided. The ultrasonic transducer 2 is connected to the pulse generator 3 and the receiving unit 5 via the transmission / reception separating unit 4. The receiving unit 5 is connected to the signal processing unit 6. The control device 7 is connected to the pulse generator 3, the signal processing unit 6, and the display unit 8. In the following description of the bone thickness measuring apparatus 1, the vertical direction shown in FIG. 1 is defined as the vertical direction, and the horizontal direction shown in FIG.

  As shown in FIG. 2, the ultrasonic transducer 2 has a contact surface 2 a that contacts the skin surface 65. The ultrasonic transducer 2 is disposed on the skin surface 65 of the measurement site so that the abutment surface 2 a is substantially parallel to the cortical bone 60.

  The ultrasonic transducer 2 receives an ultrasonic pulse (incident pulse) 40 substantially perpendicular to the cortical bone 60 at the measurement site in accordance with the electric pulse signal sent from the pulse generator 3 via the transmission / reception separator 4. To transmit. In addition, the ultrasonic transducer 2 receives the first reflected wave 41 in which the incident pulse 40 is reflected by the cortical bone surface 63 and the second reflected wave 42 in which the incident pulse 40 is reflected by the cortical bone back surface 64. . Then, when receiving the first reflected wave 41 and the second reflected wave 42, the ultrasonic transducer 2 transmits the received signal to the receiving unit 5 via the transmission / reception separating unit 4.

  As shown in FIG. 3A, the ultrasonic transducer 2 has a transducer group 20. The transducer group 20 includes four ultrasonic transducers (hereinafter referred to as transducers for transmission / reception) 21 to 24 that are arranged on the same plane and perform both transmission and reception of ultrasonic waves, It is composed of one ultrasonic transducer (hereinafter referred to as a dedicated transducer for transmission) 25 that performs only transmission. As shown in FIG. 3A, the transmission surface 20 a that transmits ultrasonic waves is composed of the vibration surfaces of the transducers 21 to 24 and the dedicated transducer 25 for transmission. Further, as shown in FIG. 3B, the wave receiving surface 20b for receiving the ultrasonic waves is constituted by the vibration surfaces of the transducers 21 to 24 for transmitting and receiving.

  All of the four transducers 21 to 24 have the same shape, and each is formed in a square flat plate shape with one side length W. The transmission / reception transducers 21 to 24 are arranged in a lattice pattern. More specifically, the transmission / reception transducers 21 and 23 are arranged side by side, and the transmission / reception transducers 22 and 24 are respectively disposed above the transmission / reception transducers 21 and 23. The transmission / reception transducers 21 to 24 are configured to be able to receive ultrasonic waves independently. The transmitting / receiving transducers 21 to 24 are respectively connected to four receiving circuits built in the receiving unit 5 in parallel. The four receiving circuits of the receiving unit 5 transmit the received signal to the signal processing unit 6. Further, the signal processing unit 6 once stores the received signal in the storage device, detects the peak value of the received signal in the signal processing circuit, and transmits it to the control device 7.

  The dedicated transmission transducer 25 is formed in a flat plate shape surrounding the four transmission / reception transducers 21 to 24. The transmission dedicated transducer 25 has a square outer shape, and the transmission / reception transducers 21 to 24 are arranged at the center thereof. That is, the outer edge shape of the dedicated transducer for transmitting 25 and the shape of the surface (the receiving surface 20b) obtained by combining the vibration surfaces of the transmitting and receiving transducers 21 to 24 are square.

  As the transmission / reception transducers 21 to 24 and the dedicated transmission transducer 25, for example, a PZT (lead titanium zirconate) piezoelectric element or a so-called composite piezoelectric element made of PZT and a synthetic resin can be used. In particular, it is preferable to use a composite piezoelectric element.

  Each time the ultrasonic transducer 2 receives an electrical pulse signal transmitted from the pulse generator 3 at a constant period, the ultrasonic transducer 2 has a predetermined frequency band from the transducers 21 to 24 for transmission and the transducer 25 dedicated to transmission. The incident pulse 40 is transmitted simultaneously. The period of the electric pulse signal is set to a time sufficiently longer than the time from when the incident pulse 40 is transmitted until the reflected wave returns.

  The incident pulse 40 transmitted from the ultrasonic transducer 2 almost perpendicularly to the cortical bone 60 propagates as a plane wave in the soft tissue 62, and a part thereof is reflected by the cortical bone surface 63. Thereby, the 1st reflected wave 41 arises. Further, a part of the incident pulse 40 that has propagated through the cortical bone 60 without being reflected by the cortical bone surface 63 is reflected by the cortical bone back surface 64 of the cortical bone 60, and the second reflected wave 42 is generated.

  The first reflected wave 41 (second reflected wave 42) is incident on the wave receiving surface 20b at an angle within the directivity range of the transmitting / receiving transducers 21 to 24, whereby the first reflected wave 41 (first reflected wave 41). The two reflected waves 42) are received by the transmitting / receiving transducers 21 to 24, respectively. When the transducers 21 to 24 receive the first reflected wave 41 (second reflected wave 42), the ultrasonic transducer 2 converts the electrical signal (received signal) into an electrical signal. The data is transmitted to the receiving unit 5 through the transmission / reception separating unit 4.

  Note that the directivity of the ultrasonic transducer when receiving ultrasonic waves refers to the extent of the angular range in which ultrasonic waves can be detected. The directivity is determined by the area of the vibration surface of one ultrasonic transducer, the wavelength of the ultrasonic wave, and the like. For example, when an ultrasonic wave is incident obliquely on a vibration surface having a large area, the phase is shifted at the receiving position, and the amplitude is weakened by interference. Therefore, the directivity becomes wider as the area of the vibration surface is smaller and the wavelength is longer.

  In order for the ultrasonic transducer 2 to reliably receive the reflected waves 41 and 42, it is desirable that the incident pulse 40 be incident substantially perpendicularly to the cortical bone surface 63 and the cortical bone back surface 64. However, since the bone is covered with the soft tissue 62, the incident direction with respect to the cortical bone 60 is difficult to understand from the outside. Therefore, as a result, the incident pulse 40 may be incident on the cortical bone 60 obliquely.

  In the case of an ultrasonic transducer having only one ultrasonic transducer that performs both transmission and reception of ultrasonic waves, the reflected waves can be received even if the ultrasonic waves are incident obliquely on the bone. In order to achieve this, it is conceivable to increase the transmission surface for transmitting ultrasonic waves (vibration surface of the ultrasonic transducer). However, generally, when the vibration surface is enlarged, the directivity is narrowed. Therefore, even if the transmission surface is enlarged, the reflected wave can be received only within a narrow directivity range.

  However, in the ultrasonic transducer 2 of the present embodiment, the transmission surface 20a is composed of the vibration surfaces of the transmission / reception transducers 21 to 24 and the dedicated transducer 25, and the reception of the reflected wave is as follows. This is performed independently by the transducers 21 to 24 for transmitting and receiving. Therefore, compared with the case where both ultrasonic wave transmission and reception are performed by one ultrasonic transducer, the wave transmission surface 20a can be enlarged without narrowing the directivity during reception. Therefore, even when the incident pulse 40 is obliquely incident on the cortical bone surface 63 or the cortical bone back surface 64, the reflected waves 41 and 42 can be received, and the cortical bone 60 can be stably received. Thickness can be measured.

  Furthermore, since the wave receiving surface 20b is composed of the vibration surfaces of the transducers 21 to 24 for transmitting and receiving, the vibration surface is made smaller than when the wave receiving surface is composed of one transducer for transmitting and receiving waves. Therefore, the directivity during reception can be widened. Therefore, even when the incident pulse 40 is incident on the cortical bone 60 more obliquely, the reflected waves 41 and 42 can be received.

  In order to calculate the thickness of the cortical bone 60, it is not necessary to receive all the reflected waves 41 and 42 generated by the transmitted incident pulse 40, and it is only necessary to receive a part of the reflected waves 41 and 42. . Therefore, the ultrasonic wave receiving surface 20b may be smaller than the wave transmitting surface 20a. Therefore, compared with the case where the ultrasonic transducer 2 is composed of a plurality of ultrasonic transducers capable of both transmitting and receiving ultrasonic waves, ultrasonic waves that receive unnecessary ultrasonic waves. Since the number of vibrators is small, the electrical configuration for processing the received signal can be simplified, and the cost can be reduced.

  In addition, since the transmitting / receiving transducers 21 to 24 are arranged at the center of the dedicated transmitting transducer 25, the receiving surface 20b is located at the central portion of the transmitting surface 20a. Therefore, regardless of whether the incident pulse 40 transmitted from the transmission surface 20a is inclined in the vertical direction or the horizontal direction with respect to the cortical bone surface 63 and the cortical bone back surface 64, the wave receiving surface 20b It is easy to receive reflected waves.

  Further, in order to perform the measurement using the reflected wave in this way, one ultrasonic transducer 2 may be disposed on the skin surface 65 on the cortical bone surface 63 side. Therefore, the thickness of the jawbone that is the measurement target can be easily measured.

  The pulse generator 3 transmits an electrical pulse signal to the ultrasonic transducer 2 through the transmission / reception separation unit 4 at a constant period by receiving a signal from an ultrasonic control unit 10 described later of the control device 7.

  The transmission / reception separating unit 4 is disposed between the ultrasonic transducer 2, the pulse generator 3 and the receiving unit 5. The transmission / reception separating unit 4 prevents the electrical pulse signal (transmitted signal) sent from the pulse generator 3 to the ultrasonic transducer 2 from being sent to the receiving unit 5 and receives it from the ultrasonic transducer 2. The electrical signal (received signal) sent to the unit 5 is prevented from being sent to the pulse generator 3.

  The receiving unit 5 is disposed between the transmission / reception separating unit 4 and the signal processing unit 6. The receiving unit 5 includes four receiving circuits arranged in parallel, and these four receiving circuits are connected to the transducers 21 to 24 of the ultrasonic transducer 2, respectively. The receiving unit 5 amplifies the electrical signal (received signal) sent from the ultrasonic transducer 2 via the transmission / reception separating unit 4 with a predetermined amplification degree and converts it into a digital signal, and then the signal processing unit 6 Send to.

  The signal processing unit 6 includes a storage unit and a signal processing circuit. After the digital signal received from the reception unit 5 is temporarily stored in the storage unit, the peak value of the received signal shown in FIG. It is detected and transmitted to the bone thickness calculator 12 and the incident direction detector 13 of the control device 7.

  The control device 7 includes a CPU, a ROM, a RAM, and the like, and includes an ultrasonic control unit 10 and a calculation unit 11 as shown in FIG. 1. The calculation unit 11 includes a bone thickness calculation unit 12, And an incident direction detector 13.

  The ultrasonic control unit 10 transmits a signal for transmitting the incident pulse 40 from the ultrasonic transducer 2 to the pulse generator 3.

  The bone thickness calculator 12 of the calculator 11 calculates the thickness D of the cortical bone 60 based on the time difference ΔT when the first reflected wave 41 and the second reflected wave 42 are received by the ultrasonic transducer 2. Is calculated. Specifically, the bone thickness calculator 12 calculates the thickness D of the cortical bone 60 using this time difference ΔT and the assumed value of the sound velocity Vb in the cortical bone 60.

  Hereinafter, a method for calculating the thickness D by the bone thickness calculator 12 will be described in detail. The bone thickness calculator 12 first calculates a time difference ΔT based on the received signal sent from the signal processor 6.

  As a method for deriving the time difference ΔT, as shown in FIG. 4A, a time domain graph is shown in which the horizontal axis is time and the vertical axis is the intensity (amplitude) of the received ultrasonic wave (reflected wave). There is a method of using and a method of using a frequency domain graph as shown in FIG. 4B, in which the horizontal axis is frequency and the vertical axis is power spectrum. The graphs shown in FIG. 4A and FIG. 4B are derived by the bone thickness calculator 12 based on the signal transmitted from the signal processor 6.

  As a method of calculating the time difference ΔT using the time domain graph, a so-called peak time difference method for calculating the time difference ΔT1 of the maximum peaks of the first reflected wave 41 and the second reflected wave 42 can be used. Alternatively, a so-called zero-cross method may be used in which a time difference ΔT2 of the intersection between the rising portion of the maximum peak of each of the first reflected wave 41 and the second reflected wave 42 and the horizontal axis (a line with zero amplitude) is calculated.

  However, when the thickness D of the cortical bone 60 is thin, the time-domain graph as shown in FIG. 4A is such that the waveform of the first reflected wave 41 and the waveform of the second reflected wave 42 partially overlap. It becomes difficult to calculate the time difference ΔT using the graph of the region. In such a case, it is preferable to calculate the time difference ΔT using the frequency domain graph shown in FIG. Hereinafter, a method of calculating the time difference ΔT using a frequency domain graph will be described.

  Assuming that the functions of the time t of the first reflected wave 41 and the second reflected wave 42 are R1 (t) and R2 (t), and the amplitude ratio of the second reflected wave 42 to the first reflected wave 41 is k, The ultrasonic wave R (t) received by the wave receiving surface 20b is represented by R (t) = R1 (t) + R2 (t) = R1 (t) + k · R1 (t−ΔT). Further, the Fourier spectrum F [R2 (t)] of the second reflected wave 42 is expressed by the following Equation 1.

[Equation 1]
F [R2 (t)] = k · F [R1 (t−ΔT)]
= K · exp (−j2πfΔT) · F [R1 (t)]
However, f: frequency and j: imaginary unit.

  Therefore, the power spectrum | P (f) | of the ultrasonic wave R (t) received by the wave receiving surface 20b is expressed by the following formula 2.

[Equation 2]
P (f) = | F [R1 (t) + R2 (t)] | ²
= | F [R1 (t)] | ² · | 1 + k · exp (−j2πfΔT) | ² ·
= | F [R1 (t)] | ² · (1 + k ² + 2k · cos 2πfΔT) ·

  From Equation 2, P (f) has a peak when cos2πfΔT = 1, and a drop when cos2πfΔT = −1. If the frequency interval at which the peak occurs is Δf1, and the frequency interval at which the drop occurs is Δf2, Δf1 = Δf2 = 1 / ΔT. Therefore, if Δf1 or Δf2 is calculated from the frequency domain graph shown in FIG. 4B, ΔT can be obtained.

  Next, a method for calculating the thickness D of the cortical bone 60 using the time difference ΔT calculated as described above will be described. As shown in FIG. 2, the path from when the wave is transmitted until it is received as the first reflected wave 41, and the path from when the incident pulse 40 is transmitted until it is received as the second reflected wave 42 Is a distance 2D in which the ultrasonic waves reciprocate in the cortical bone 60 in the thickness direction. That is, the ultrasonic wave travels through the cortical bone 60 by the distance 2D during the time ΔT. Therefore, if the velocity of the ultrasonic wave traveling in the thickness direction in the cortical bone 60 is Vb, the thickness D of the cortical bone 60 is expressed by D = Vb · ΔT / 2. Therefore, the sound velocity Vb in the cortical bone 60 is assumed to be a constant value, and the thickness D of the cortical bone 60 is calculated by substituting this assumed value into the above equation. The assumed value of the sound velocity Vb is preferably set within a range of 3000 to 3300 m / s, for example.

  Although the sound velocity Vb in the cortical bone 60 and the thickness D of the cortical bone 60 are both individual differences, the variation due to the individual difference in the sound velocity Vb in the cortical bone 60 is due to the individual difference in the thickness D of the cortical bone 60. Smaller than Therefore, by calculating the thickness D of the cortical bone 60 on the assumption that the sound velocity Vb in the cortical bone 60 is a constant value, the calculated thickness D substantially matches the actual thickness of the cortical bone 60.

  As described above, by calculating the thickness D of the cortical bone 60 on the assumption that the sound velocity Vb in the cortical bone 60 is a constant value, the thickness D of the cortical bone 60 can be easily calculated.

  Hereinafter, the reason why it is preferable to set the assumed value of the sound velocity Vb within the range of 3000 to 3300 m / s will be described.

  In general, it is known that the speed of sound in cortical bone varies depending on the propagation direction. The speed of sound in the cortical bone is relatively fast in the direction in which the load acts, and is around 3900 m / s. The direction in which the load acts is usually the direction along the cortical bone surface.

  On the other hand, the speed of sound in a direction substantially perpendicular to the cortical bone surface (cortical bone thickness direction) is relatively slow, about 3000 to 3500 m / s. Specifically, for example, as a result of measuring the ultrasonic velocity in the thickness direction of the cortical bone of the femurs of 17 men and women of 70 to 94 years old, as shown in FIG. 5, the distribution is in the range of 3125 to 3565 m / s. The average value was about 3300 m / s, and the standard deviation value was 91 m / s. This measurement was performed according to the following procedure. That is, a bone sample is taken out from a position 3 cm below the femoral small trochanter in the long tube direction, a rectangular parallelepiped bone block having a side of 1 cm or less is produced, and the bone block is sandwiched between two ultrasonic transducers. The ultrasonic sound velocity was measured by transmitting ultrasonic waves through the bone block.

  Further, it was verified as follows that the thickness D of the cortical bone calculated assuming the sound velocity Vb substantially coincided with the actual thickness. As shown in Table 1, the thicknesses of the mandibles of three subjects were measured using the bone thickness measuring apparatus 1 and the X-ray CT apparatus of the present embodiment, respectively. In the measurement by the bone thickness measuring apparatus 1, the assumed value of the sound velocity Vb was set to 3000 m / s.

  In the measurement using the bone thickness measuring apparatus 1, the thickness D of the cortical bone was calculated as shown in Table 1 while adjusting the inclination of the ultrasonic transducer 2 in contact with the subject to be measured. Further, in the measurement using the X-ray CT apparatus, the thickness of the cortical bone to be measured from the photographed CT image was measured.

  As a result, as shown in Table 1, the average value of the cortical bone thickness D measured using the bone thickness measuring apparatus 1 and the cortical bone thickness measured using the X-ray CT apparatus substantially coincide. It was confirmed.

  Therefore, in the measurement using the bone thickness measuring apparatus 1, it is preferable to set the assumed value of the sound velocity Vb to 3000 m / s. However, for example, when the cortical bone thickness is calculated on the assumption that the sound velocity Vb is 3300 m / s, it is about 10% larger than the case where the cortical bone thickness is assumed to be 3000 m / s, but the tendency of the actual cortical bone thickness is almost grasped. be able to. Therefore, the assumed value of the sound speed Vb is not limited to 3000 m / s.

  From the above, it is preferable to set the assumed value of the sound velocity Vb propagating in the cortical bone 60 in the thickness direction within a range of 3000 to 3300 m / s. By setting the assumed value of the sound velocity Vb within this range, the cortical bone thickness can be calculated with high accuracy.

  Next, the incident direction detection unit 13 of the calculation unit 11 will be described. The incident direction detector 13 receives the incident pulse 40 on the cortical bone 60 based on the phase difference between the first reflected wave 41 and the second reflected wave 42 received by the transducers 21 to 24, respectively. Calculate the corner.

  Hereinafter, the calculation method of the incident angle of the incident pulse 40 with respect to the cortical bone surface 63 by the incident direction detection unit 13 will be specifically described. The incident angle of the incident pulse 40 with respect to the cortical bone surface 63 is determined by the incident angle in the vertical direction and the incident angle in the horizontal direction.

  As shown in FIG. 6, when the incident pulse 40 is perpendicularly incident on the cortical bone surface 63, the first reflected wave 41 is perpendicularly incident on the transmitting / receiving transducers 21 to 24. At this time, the wave surface 41a of the first reflected wave 41 is parallel to the vibration surfaces of the transducers 21 to 24 for transmitting and receiving. Therefore, the phases of the first reflected wave 41 at the receiving position are all the same, and the four transducers 21 to 24 receive the first reflected wave 41 simultaneously. In such a case, the incident direction detection unit 13 determines the incident angle as 0 °.

  On the other hand, as shown in FIG. 7, when the incident pulse 40 is incident on the cortical bone surface 63 at an incident angle θ in the vertical direction, the first reflected wave 41 is transmitted to the transducers 21 to 24 for transmitting and receiving waves. Incident at an incident angle of 2θ. At this time, the wavefront 41a of the first reflected wave 41 is inclined 2θ with respect to the vibration surfaces of the transducers 21 to 24 for transmission and reception. Therefore, a phase difference occurs in the first reflected wave 41 received by the two transmitting / receiving transducers 21 and 22 (or transmitting / receiving transducers 23 and 24) arranged in the vertical direction. Accordingly, a time lag occurs when the transmitting / receiving transducers 21 and 22 (or transmitting / receiving transducers 23 and 24) receive the first reflected wave 41. This time difference is represented by Δt.

  In this case, the incident direction detection unit 13 first calculates the time difference Δt based on the received signal transmitted from the signal processing unit 6. As shown in FIG. 7, the difference between the path of the first reflected wave 41 received by the transmitting / receiving transducer 21 and the path of the first reflected wave 41 received by the transmitting / receiving transducer 22 is as follows. Only the distance W · sin2θ in the soft tissue 62 is present. That is, the first reflected wave 41 travels through the soft tissue 62 by the distance W · sin 2θ during the time Δt. Therefore, when the sound velocity in the soft tissue 62 is Vs, Δt is expressed by Δt = (W · sin 2θ) / Vs. From this equation, the incident angle θ in the vertical direction with respect to the cortical bone surface 63 can be calculated. it can.

  Also, the incident angle in the left-right direction with respect to the cortical bone surface 63 is the same based on the received signals of the two transducers 21 and 23 (or the transducers 22 and 24) arranged in the left-right direction. Can be calculated.

  Also, the incident angle with respect to the cortical bone back surface 64 can be calculated in the same manner as the incident angle with respect to the cortical bone surface 63 is calculated.

  As described above, the ultrasonic transducer 2 includes the four transducers 21 to 24 that receive ultrasonic waves, and the transducers 21 to 24 transmit and receive the vertical and horizontal directions. Two are arranged in each. Therefore, the incident direction detection unit 13 can calculate the incident angles in the vertical direction and the horizontal direction of the incident pulse 40 with respect to the cortical bone 60 based on the reception signals from the transmission / reception transducers 21 to 24.

  The calculated incident angle of the incident pulse 40 with respect to the cortical bone surface 63 and the cortical bone back surface 64 is immediately displayed on the display unit 8. While measuring the incident angle displayed on the display unit 8, the measurer moves the ultrasonic transducer 2 in the vertical direction or the horizontal direction with the contact surface 2a in contact with the skin surface 65 as a fulcrum. Since the ultrasonic transducer 2 continues to transmit the incident pulse 40 at a constant period, the measurer can transmit and receive the ultrasonic wave so that the incident angle newly displayed on the display unit 8 approaches 0 °. The inclination of the wave generator 2 is adjusted.

  Thus, by calculating the incident angle of the ultrasonic wave with respect to the cortical bone 60 by the incident direction detecting unit 13, the inclination of the ultrasonic transducer 2 can be adjusted according to the calculated incident angle. Thereby, ultrasonic waves can be incident on the cortical bone 60 more perpendicularly. Therefore, it is possible to perform measurement stably and improve measurement accuracy.

  Further, in particular, when the cortical bone surface 63 and the cortical bone back surface 64 are not parallel, in order to receive both the first reflected wave 41 and the second reflected wave 42, it is incident as perpendicular to the cortical bone back surface 64 as possible. The pulse 40 is preferably incident. This is because the cortical bone back surface 64 has a long distance to the wave receiving surface 20b, and therefore the second reflected wave 42 does not return to the wave receiving surface 20b when the incident angle increases.

  The first embodiment has been described above as a preferred embodiment of the present invention, but the first embodiment can be implemented with the following modifications.

  That is, the number of transducers dedicated to transmission included in the transducer group 20 of the ultrasonic transducer 2 is not limited to one, and may be two or more. For example, as illustrated in FIG. 8, the transducer group 20 </ b> A may include four dedicated transmission transducers 25 </ b> A to 28 </ b> A.

  Further, the number of transducers for transmitting and receiving included in the transducer group 20 of the ultrasonic transducer 2 is not limited to four. For example, as shown in FIG. 9, the transducer group 20B may have a configuration having only one transducer 21B for transmitting and receiving waves. In this case, the transmitting / receiving transducer 21B may be connected to one receiving circuit among the plurality of receiving circuits of the receiving unit 5, but the receiving unit 5 is configured by one receiving circuit, and this one receiving circuit May be connected.

  Further, for example, the transducer group may have a configuration including nine transducers for transmission and reception that are arranged three by three in the vertical direction and the horizontal direction. However, if the number of transducers for transmitting and receiving is too large (if the number of divisions of the receiving surface 20b is too large), the vibration surface of one transducer for transmitting and receiving becomes too small, and the sensitivity to receive ultrasonic waves is low. The measurement accuracy decreases.

  Further, the shape of the outer edge of the dedicated transducer for transmitting 25 and the shape of the combined surface of the transducers 21 to 24 (the receiving surface 20b) are not limited to square shapes. For example, as shown in FIG. 10 (a), the surface (wave receiving surface 20b) of the outer edge shape of the dedicated transducer for transmitting 25C of the transducer group 20C and the vibration surfaces of the transmitting and receiving transducers 21C to 24C are combined. Each of the shapes may be formed in a circular shape. As shown in FIG. 10B, the transducer group 20D has only one transmission / reception transducer 21D, the outer edge shape of the dedicated transducer 25D, and the transmission / reception transducer 21D. These shapes may each be formed in a circular shape. Since the outer shape of the dedicated transducer for transmission 25C is circular, the ultrasonic transducer 2 can be made smaller than in the case of a square shape. Further, for example, the outer edge shape of the dedicated transmission transducer 25 and the shape of the surface (the receiving surface 20b) that combines the vibration surfaces of the transmission / reception transducers 21 to 24 are polygonal shapes such as a quadrangular shape and an octagonal shape, respectively. May be formed respectively.

  Further, the shape of the outer edge of the dedicated transducer for transmitting 25 and the shape of the surface (the receiving surface 20b) obtained by combining the vibrating surfaces of the transmitting and receiving transducers 21 to 24 may be different from each other. For example, the outer edge shape of the transmission dedicated transducer 25 may be a circular shape, and the shape of the wave receiving surface 20b may be a polygonal shape such as a square shape.

  Further, the dedicated transmission transducer 25 may not be formed so that the transmission / reception transducers 21 to 24 are arranged at the center thereof. For example, the transmission / reception transducers 21 to 24 may be disposed below the center portion in the vertical direction of the dedicated transmission transducer 25.

  Moreover, in the said embodiment, although the incident angle with respect to the cortical bone 60 of the incident pulse 40 is calculated by the incident direction detection part 13 of the calculating part 11, in order to detect the incident direction of the incident pulse 40, it is not necessarily incident angle. Need not be calculated. For example, the incident direction may be detected using a time domain graph shown in FIG. Specifically, the incident direction detection unit 13 derives a time-domain graph for each of the transmission / reception transducers 21 to 24 and compares the phase difference between the waveforms of adjacent transmission / reception transducers. If there is no phase difference, it is determined that the incident is perpendicular, and if there is a phase difference, there is a shift in the received time, so that it can be determined that the incident pulse 40 is obliquely incident on the cortical bone 60.

Second Embodiment
Next, a second embodiment of the present invention will be described. However, about the thing which has the structure similar to 1st Embodiment, the same code | symbol is attached | subjected and the description is abbreviate | omitted suitably.

  As shown in FIG. 11, the bone thickness measuring apparatus 201 of this embodiment includes an ultrasonic transducer 202, a transmission / reception separating unit 4, a switching circuit (received transducer determining means) 209, a receiving unit 5, and a signal. A processing unit 6, a control device 7, and a display unit 8 are provided. The switching circuit 209 is disposed between the transmission / reception separating unit 4 and the receiving unit 5.

  As shown in FIG. 12, the ultrasonic transducer 202 includes a transducer group 220. The transducer group 220 includes 16 ultrasonic transducers 221 to 236 arranged on the same plane and capable of both transmitting and receiving ultrasonic waves.

  The ultrasonic transducers 221 to 236 are each formed in a rectangular flat plate shape. The ultrasonic transducers 221 to 236 are arranged in a lattice form by four in the vertical direction and the horizontal direction.

  The ultrasonic transducers 221 to 236 are independently connected to the switching circuit 209 via the transmission / reception separating unit 4. The switching circuit 209 determines, for example, four ultrasonic transducers that perform wave reception from the 16 ultrasonic transducers 221 to 236. In the following description, an ultrasonic transducer that is determined to receive a wave by the switching circuit 209 is referred to as a wave receiving transducer. The reception signal generated by the ultrasonic transducer determined as the reception transducer by the switching circuit 209 is transmitted to the reception unit 5. The received signal generated by the ultrasonic transducer other than the received transducer is disconnected from the receiving unit 5 by the switching circuit 209. Therefore, the wave receiving surface that receives the ultrasonic waves is constituted by the vibration surfaces of the four wave receiving vibrators determined by the switching circuit 209. The wave transmission surface for transmitting ultrasonic waves is constituted by the vibration surfaces of 16 ultrasonic transducers 221 to 236.

  The receiving unit 5 includes four receiving circuits connected in parallel to the four receiving transducers selected by the switching circuit 209 in parallel. Further, the signal processing unit 6 temporarily stores the digital signals transmitted from the four receiving circuits of the receiving unit 5 in the storage unit, then detects the peak value and the like by the signal processing circuit and transmits them to the control device 7.

  The switching circuit 209 determines four ultrasonic transducers among the 16 ultrasonic transducers 221 to 236 as receiving transducers. Specifically, the switching circuit 209 may have a configuration in which the wave receiving vibrator is determined by a measurer switching a switch (not shown) provided in the switching circuit 209, or via a cable (not shown). A configuration may be adopted in which the receiving vibrator is determined by the switching circuit 209 receiving the receiving vibrator determination signal transmitted from the control device 7.

  When the switching circuit 209 determines, for example, that four ultrasonic transducers 226, 227, 230, and 231 arranged in the center are receiving transducers, the ultrasonic transducer 202 includes 16 ultrasonic vibrations. While the incident pulse 40 is simultaneously transmitted by the vibration surfaces (transmission surfaces) of the sub-elements 221 to 236, the reflected waves 41 and 42 that have bounced back are received by four receiving transducers (ultrasonic transducers 226, 227, and 230). 231) is received by the vibration surface (receiving surface). Note that the receiving transducer is not limited to the four ultrasonic transducers 226, 227, 230, and 231 described above, and any four ultrasonic transducers out of the 16 ultrasonic transducers 221 to 236 may be used. An oscillator can be selected.

  As described above, in the ultrasonic wave transmitter / receiver 202, the wave transmission surface is configured by the vibration surfaces of the plurality of ultrasonic transducers 221 to 236. In addition, the reception of the reflected wave is performed independently for each wave receiving vibrator determined by the switching circuit 209. Therefore, compared to the case where both ultrasonic wave transmission and reception are performed by one ultrasonic transducer, the directivity at the time of wave reception can be widened, and at the same time the wave transmission surface can be enlarged. Therefore, even when ultrasonic waves are incident obliquely on the cortical bone 60, the reflected waves can be received, and the thickness of the cortical bone can be measured stably.

  In addition, since some of the ultrasonic transducers 221 to 236 (four in the present embodiment) are switched to the receiving transducer, the ultrasonic receiving surface is smaller than the transmitting surface. However, in order to calculate the thickness of the cortical bone, it is not necessary to receive all of the reflected waves 41 and 42 generated by the transmitted incident pulse 40, and it is only necessary to receive a part of the reflected waves 41 and 42. Therefore, the ultrasonic wave receiving surface may be smaller than the wave transmitting surface. Therefore, by providing the switching circuit 209 and receiving the waves with a part of the plurality of ultrasonic transducers 221 to 236, it is unnecessary to compare with the case where the switching circuit is not provided. Since there are few ultrasonic transducers that receive sound waves, the electrical configuration for processing the received signals can be simplified, and the cost can be reduced.

  Further, depending on the shape of the cortical bone 60, for example, when the cortical bone surface 63 and the cortical bone back surface 64 are not parallel, the incident pulse 40 is applied to the cortical bone 60 no matter how the ultrasonic transducer 202 is installed. On the other hand, it may be incident obliquely. Even in such a case, the reflected wave can be reliably received by setting the position of the wave receiving surface to a position where the reflected wave returns.

  The second embodiment has been described above as a preferred embodiment of the present invention. However, the second embodiment can be implemented with the following modifications.

  That is, the number of ultrasonic transducers included in the ultrasonic transducer 202 is not limited to 16. For example, the ultrasonic transducer 202 may have a configuration including nine ultrasonic transducers arranged three by three in the vertical direction and the horizontal direction.

  Further, the number of receiving vibrators determined by the switching circuit 209 is not limited to four, and may be nine or nine, for example, four or less.

  Further, reception may be performed by all the ultrasonic transducers 221 to 236 without providing the switching circuit 209. As a result, even if the incident pulse 40 is obliquely incident on the cortical bone 60, the reflected wave is easily received.

  As described above, in the first embodiment and the second embodiment described above, the measurement site is the mandible or the maxilla and the measurement is performed by placing the ultrasonic transducer outside the oral cavity. As shown in FIG. The bone thickness measuring device of the present invention can also be applied when measuring the thickness D3 of the cortical bone 360 of the alveolar bone (jaw bone) regenerated after tooth extraction. The cancellous bone 361 exists inside the cortical bone 360 of the alveolar bone, and the surface of the cortical bone 360 is covered with gingiva (soft tissue) 362. The ultrasonic transducer 302 transmits the incident pulse 340 substantially perpendicularly to the cortical bone 360, the first reflected wave 341 reflected by the cortical bone surface 363, and the second reflection reflected by the cortical bone back surface 364. Each of the waves 362 is received. In this case, the ultrasonic transducer 302 is formed in a size of about one tooth. In this case, as the ultrasonic transducer, one having a plurality of ultrasonic transducers may be used as in the first embodiment or the second embodiment described above. You may use what has only one ultrasonic transducer | vibrator which performs both receiving waves.

  Moreover, the measuring object of the bone thickness measuring apparatus of the present invention is not limited to the jawbone. For example, the bone thickness measuring apparatus of the present invention can also be used when measuring the thickness of cortical bones such as skulls (other than jaw bones) and tibias. In this case, the ultrasonic sound velocity Vb in the thickness direction of the cortical bone is set to an appropriate value according to the measurement site. Specifically, it is preferable to set the value within a range of 3000 to 3300 m / s.

It is a figure which shows the bone thickness measuring apparatus of 1st Embodiment. It is sectional drawing which shows the use condition of an ultrasonic transducer. It is a figure which shows arrangement | positioning of a vibrator group, (a) shows the ultrasonic vibrator which transmits an ultrasonic wave, (b) shows the ultrasonic vibrator which receives an ultrasonic wave. (A) is a graph which shows the amplitude for every receiving time of the received ultrasonic wave, (b) is a graph which shows the power spectrum of the received ultrasonic wave. It is a graph which shows the ultrasonic speed of sound in the cortical bone of a femur. It is sectional drawing which shows the state in which the ultrasonic wave was injected perpendicularly with respect to the cortical bone surface. It is sectional drawing which shows the state in which the ultrasonic wave was injected diagonally with respect to the cortical bone surface. It is a figure which shows the transducer group of a change form. It is a figure which shows the transducer group of a change form. It is a figure which shows the transducer group of a change form. It is a figure which shows the bone thickness measuring apparatus of 2nd Embodiment. It is a figure which shows arrangement | positioning of a vibrator group. It is sectional drawing which shows the other use condition of an ultrasonic transducer.

Explanation of symbols

1,201 Bone thickness measuring device 2, 202, 302 Ultrasonic transducer 12 Bone thickness calculator 13 Incident direction detector
20, 20A, 20B, 20C, 20D transducer group 20a transmitting surface 20b receiving surfaces 21-24, 21B, 21C, 21-24C, 21D transmitting / receiving transducers 25, 25A-28A, 25C, 25D dedicated transducers for transmitting 40 incident pulse 41 first reflected wave 42 second reflected wave 60, 360 cortical bone 61, 361 cancellous bone 62, 362 soft tissue 63, 363 cortical bone surface 64, 364 cortical bone back surface 221-236 ultrasonic transducer
209 switching circuit (received vibrator determining means)

Claims (8)

An ultrasonic transmission / reception unit for transmitting an ultrasonic wave to the bone, and receiving a first reflected wave from the surface of the bone and a second reflected wave from the back surface of the bone;
A bone thickness calculator that calculates the thickness of the bone based on a difference in time when the first reflected wave and the second reflected wave are received by the ultrasonic wave transmitting / receiving unit,
The ultrasonic transmission / reception unit is
A bone thickness measuring apparatus comprising a plurality of ultrasonic transducers arranged on the same plane and capable of both transmitting and receiving ultrasonic waves.   The bone thickness measuring apparatus according to claim 1, further comprising: a receiving transducer determining unit that determines an ultrasonic transducer that receives a wave among the plurality of ultrasonic transducers. An ultrasonic transmission / reception unit for transmitting an ultrasonic wave to the bone, and receiving a first reflected wave from the surface of the bone and a second reflected wave from the back surface of the bone;
A bone thickness calculator that calculates the thickness of the bone based on a difference in time when the first reflected wave and the second reflected wave are received by the ultrasonic wave transmitting / receiving unit,
The ultrasonic transmission / reception unit is
It has the ultrasonic transducer for transmission / reception that performs both transmission and reception of ultrasonic waves, and the ultrasonic transducer dedicated for transmission that transmits only ultrasonic waves, which are arranged on the same plane. Bone thickness measuring device. Ultrasound that transmits ultrasonic waves to the cortical bone of the jawbone and receives a first reflected wave from the cortical bone surface of the jawbone and a second reflected wave from the back surface of the cortical bone of the jawbone A transmission / reception unit;
A bone thickness calculator that calculates the thickness of the cortical bone of the jawbone based on the difference in time at which the first reflected wave and the second reflected wave are received by the ultrasonic wave transmitting / receiving unit,
The ultrasonic transmission / reception unit is
It has the ultrasonic transducer for transmission / reception that performs both transmission and reception of ultrasonic waves, and the ultrasonic transducer dedicated for transmission that transmits only ultrasonic waves, which are arranged on the same plane. Bone thickness measuring device. The ultrasonic transmission / reception unit has at least two ultrasonic transducers for receiving ultrasonic waves,
Incident direction detection for detecting an incident direction of the ultrasonic wave to the bone based on a phase difference between the first reflected wave and the second reflected wave respectively received by the two or more ultrasonic transducers The bone thickness measuring apparatus according to claim 1, further comprising a portion. The transmitting / receiving ultrasonic transducer is surrounded by the dedicated ultrasonic transducer for transmission,
The outer edge shape of the combined surface of all the ultrasonic vibrators is a circular shape or a polygonal shape,
5. The bone thickness measuring device according to claim 3, wherein a shape of a plane obtained by combining vibration surfaces of all the ultrasonic transducers for transmitting and receiving is a circular shape or a polygonal shape.   The bone thickness calculation unit calculates the bone thickness using the difference between the received times and an assumed value of sound velocity of ultrasonic waves propagating in the bone. The bone thickness measuring apparatus in any one of -6.   The bone thickness measuring apparatus according to claim 7, wherein the assumed value is within a range of 3000 to 3300 m / s.

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