JPWO2014087776A1 - Measuring apparatus and measuring method - Google Patents

Abstract

A measuring apparatus capable of measuring the sound velocity and BUA of cortical bone in a living body is provided. A transfer function setting unit models a difference between a propagation path 27 of a reference signal R (jω) and a propagation path 28 of a reception signal Fn (jω) by modeling SOS and BUA of cortical bone as parameters. The function Hn (jω) is set. The signal synthesis unit applies a plurality of transfer functions Hn (jω) in which the combinations of SOS and BUA of the cortical bone are different from each other to the reference signal R (jω), so that the synthesis corresponding to the combination of the SOS and BUA is performed. A signal Gn (jω) is generated. The coincidence calculation unit calculates the inner product <Fn, Gn> as the coincidence between each composite signal Gn (jω) and the received signal Fn (jω). The parameter selection unit obtains a combination of SOS and BUA when the inner product shows the maximum value. [Selection] Figure 5

Description

  The present invention mainly relates to a technique for simultaneously measuring sound velocity and absorption (BUA) in a measuring apparatus using ultrasonic waves.

  A measuring device that measures the speed of sound of cortical bone using ultrasonic waves is known. By measuring the sound velocity of cortical bone, the soundness of bone can be evaluated. This type of diagnostic apparatus is described in Patent Document 1, for example.

  When ultrasonic waves propagate through cortical bone, absorption (broadband ultrasonic attenuation, BUA) is generated by the cortical bone. Due to this BUA, the waveform of the ultrasonic signal received by the measuring apparatus is distorted, which may cause an error in deriving the sound speed. In this regard, the measuring device described in Patent Document 1 does not consider BUA when deriving the sound velocity, and cannot measure BUA.

  Non-Patent Document 1 shows that there is a correlation between BUA and cortical bone quality. Therefore, it is considered that it can be used as a useful index for bone diagnosis by measuring the BUA of cortical bone. For this reason, in the clinical field, the technique which can measure BUA of the cortical bone in the living body is desired.

  Non-Patent Document 2 discloses a method of measuring the sound speed and BUA in the bone by modeling a received signal when a Gaussian pulse is transmitted toward the bone and optimizing each parameter.

JP 2010-246692 A

Magali Sasso, Salah Naili, Guillaume Haiat, Mami Matsukawa, Yu Yamato.'Broadband Ultrasonic Attenuation in femoral bovine cortical bone is an indicator of bone properties'. 2007 IEEE Ultrasonics Symposium. Pages 2167-2170. Stefanie Dencks, Reinhard Barkmann.'Model-Based Estimation of Quantitative Ultrasound Variables at the Proximal Femur'.IEEE TRANSACTIONS ON ULTRASONICS, FERROELECTRICS, AND FREQUENCY CONTROL, VOL. 55, NO. Reinhard Barkmann, Pascal Laugier, Urs Moser, Stefanie Dencks, Michael Klausner, Frederic Padilla, Guillaume Haiat, Martin Heller, Claus.-C. Gluer.'In Vivo Measurements of Ultrasound Transmission Through the Human Proximal Femur '. , Volume34, Issue 7, July 2008, Pages 1186-1190. <URL: http: //www.umbjournal.org/article/S0301-5629%2807%2900652-7/abstract>.

  Non-Patent Document 1 measures BUA for a cut cortical bone sample and does not measure the BUA of cortical bone in vivo. Therefore, Non-Patent Document 1 has not yet proposed a method capable of measuring BUA in the clinical field.

  Non-Patent Document 2 is not a measurement of bone in a living body but a measurement of a bone sample in a water tank. Non-Patent Document 2 suggests the possibility of being applicable to the measurement of bone in a living body, but in order to do so, it is necessary to consider the influence of soft tissue around the bone. Further, when the bone sound speed is derived in Non-Patent Document 2, information on the bone thickness is required. However, since Non-Patent Document 2 assumes that the bone thickness is d = 30 mm, the sound speed in the actual bone is assumed. Is not calculated.

  Non-Patent Document 2 arranges a bone sample between two ultrasonic transducers to transmit and receive an ultrasonic signal, and derives the bone sound speed and BUA based on the signal transmitted through the bone.

  Non-Patent Document 3 discloses a technique for measuring bones in a living body. In Non-Patent Document 3, similarly to Non-Patent Document 2, a bone to be measured is sandwiched between two ultrasonic transducers, and bone sound speed and BUA are derived based on a signal transmitted through the bone. Although the technique using transmitted waves can be used to measure cancellous bone inside the bone, it cannot be used to measure cortical bone on the bone surface.

  As described above, the conventional ultrasonic measurement apparatus cannot measure the sound velocity and BUA of cortical bone in a living body.

  The present invention has been made in view of the above circumstances, and a main object thereof is to provide a measuring apparatus capable of measuring the sound velocity and BUA of cortical bone in a living body.

Means and effects for solving the problems

  The problems to be solved by the present invention are as described above. Next, means for solving the problems and the effects thereof will be described.

  According to the first aspect of the present invention, the following measuring apparatus is provided. That is, the measurement apparatus includes a transmission unit, a reception unit, a transfer function setting unit, a signal synthesis unit, a coincidence calculation unit, and a parameter selection unit. The transmission unit transmits a signal toward the measurement object. The receiving unit propagates the first signal, which is incident on the measured object, propagates through the measured object and is radiated to the outside of the measured object again, and propagates along a different path from the first signal. And a second signal radiated out of the measurement body. The transfer function setting unit sets a transfer function in which a difference between propagation paths of the first signal and the second signal is modeled including at least a first parameter. The signal synthesis unit generates a synthesized signal corresponding to each first parameter by applying a plurality of transfer functions having different values of the first parameter to the first signal. The coincidence calculation unit calculates the coincidence between each of the combined signals and the second signal. The parameter selection unit obtains a value of the first parameter when the degree of coincidence is maximized.

  Thus, the validity of the transfer function set by the transfer function setting unit is determined by generating a synthesized signal by applying the transfer function to the first signal and determining the degree of coincidence between the synthesized signal and the second signal. Can be judged. Then, by searching for a parameter that maximizes the degree of coincidence, the value of the parameter can be determined. Since the transfer function only needs to model the difference between the propagation path of the first signal and the propagation path of the second signal, the transfer function becomes simpler and the measurement accuracy is improved compared to modeling the entire propagation path. To do.

  In the measurement apparatus, the receiving unit receives the first signal after a first time has elapsed after the signal is transmitted, and after a second time longer than the first time, A second signal is received.

  Since the first signal is received earlier in time than the second signal, the distance propagated through the measured object is shorter than the second signal. Therefore, the first signal is less affected by the measured object than the second signal. Therefore, by modeling the difference in propagation path between the first signal and the second signal on the basis of the first signal, the parameter can be obtained with high accuracy.

  The measurement apparatus is preferably configured as follows. That is, the measurement apparatus includes a shape detection unit that transmits a signal toward the measurement object and detects the shape of the measurement object based on a reflected signal reflected by the measurement object. The transfer function setting unit sets the transfer function based on the shape of the measured object detected by the shape detection unit.

  Thus, since the propagation path of the first signal and the second signal can be obtained by detecting the shape of the measurement object in advance, the transfer function can be set accurately.

  In the measurement apparatus, the signal may be an ultrasonic signal, and the first parameter may be a sound speed of the measured object.

  With this measuring device, the sound speed of the object to be measured can be measured.

  In the measurement apparatus, the signal may be an ultrasonic signal, and the first parameter may be a broadband ultrasonic attenuation coefficient of the measurement object.

  With this measuring device, the broadband ultrasonic attenuation coefficient of the object to be measured can be measured.

  The measurement apparatus is preferably configured as follows. That is, the coincidence calculation unit calculates an inner product of each of the combined signals and the second signal. The parameter selection unit obtains the first parameter when the inner product shows a maximum value.

  That is, if the two signals match, the inner product of the two becomes the maximum, and if they do not match, the inner product of the two becomes smaller. Therefore, the value of the inner product of both can be used as an index of the degree of coincidence between the synthesized signal and the second signal.

  The above measuring apparatus can also be configured as follows. That is, the transfer function includes a second parameter that is different from the first parameter. The signal synthesizing unit applies a plurality of transfer functions in which combinations of the first parameter and the second parameter are different from each other to each of the first signals, thereby generating a synthesized signal corresponding to each of the combinations. Generate.

  In this way, by applying the transfer function with different combinations of the two parameters, it is possible to calculate a synthesis function corresponding to each combination.

  In the measurement apparatus, the signal is an ultrasonic signal, the first parameter is a sound velocity of the measured object, and the second parameter is a broadband ultrasonic attenuation coefficient of the measured object. it can.

  Thereby, a plurality of composite functions obtained by different combinations of the sound velocity of the measurement object and the broadband ultrasonic attenuation coefficient can be obtained.

  The measurement apparatus is preferably configured as follows. That is, the coincidence calculation unit calculates an inner product of each of the combined signals and the second signal. The parameter selection unit obtains a combination of the first parameter and the second parameter when the inner product shows a maximum value.

  As described above, according to the configuration of the present invention, it is possible to simultaneously measure the sound velocity in the body to be measured and the broadband ultrasonic attenuation (BUA) coefficient.

  In the measurement apparatus, the measurement object may be cortical bone in soft tissue.

  Thereby, the sound speed of a cortical bone in a living body, a broadband ultrasonic attenuation coefficient, etc. can be measured with the measuring apparatus of the present invention.

  In the measurement apparatus, it is preferable that the signal transmitted from the transmission unit propagates near the surface of the cortical bone and is received by the reception unit.

  Thus, based on the signal propagated through the surface of the cortical bone, the sound velocity of the cortical bone, the broadband ultrasonic attenuation coefficient, and the like can be measured.

  According to the second aspect of the present invention, the following measurement method is provided. That is, this measurement method includes a transmission step, a reception step, a transfer function setting step, a signal synthesis step, a coincidence calculation step, and a parameter selection step. In the transmission step, a signal is transmitted toward the measured object. In the receiving step, the signal incident on the device to be measured propagates through the device to be measured and is radiated to the outside of the device to be measured again, and propagates along a path different from the first signal and is again measured. And a second signal radiated out of the measurement body. In the transfer function setting step, a transfer function is set in which a difference between propagation paths of the first signal and the second signal is modeled including at least a first parameter. In the signal synthesizing step, a plurality of transfer functions having the first parameters different from each other are applied to the first signal, thereby generating a synthesized signal corresponding to each first parameter. In the coincidence degree calculating step, the coincidence degree between each composite signal and the second signal is calculated. In the parameter selection step, the value of the first parameter when the degree of coincidence is maximized is obtained.

  In the measurement method, in the reception step, after the signal is transmitted, the first signal is received after a first time has elapsed, and after a second time longer than the first time, A second signal is received.

  The measurement method is preferably as follows. That is, this measurement method includes a shape detection step of transmitting a signal toward the measurement object and detecting the shape of the measurement object based on a reflected signal reflected by the measurement object. In the transfer function setting step, the transfer function is set based on the shape of the measurement object detected in the shape detection step.

  In the measurement method, the signal may be an ultrasonic signal, and the first parameter may be a sound speed of the measured object.

  In the above measurement method, the signal may be an ultrasonic signal, and the first parameter may be a broadband ultrasonic attenuation coefficient of the measured object.

  The above measurement method can also be performed as follows. That is, in the coincidence calculation method, the inner product of each combined signal and the second signal is calculated. In the parameter selection step, the first parameter when the inner product shows a maximum value is obtained.

  The above measurement method can also be performed as follows. That is, the transfer function includes a second parameter that is different from the first parameter. In the signal synthesizing step, a plurality of transfer functions in which combinations of the first parameter and the second parameter are different from each other are applied to the first signal, respectively, so that a synthesized signal corresponding to each of the combinations is obtained. Generate.

  The above measuring method can be performed as follows. That is, the signal is an ultrasonic signal, the first parameter is a sound velocity of the measured object, and the second parameter is a broadband ultrasonic attenuation coefficient of the measured object.

  The measurement method is preferably as follows. That is, in the coincidence calculation step, inner products of the respective synthesized signals and the second signal are calculated. In the parameter selection step, a combination of the first parameter and the second parameter when the inner product shows the maximum value is obtained.

  In the above measurement method, the object to be measured can be cortical bone in soft tissue.

  In the measurement method, it is preferable that the signal transmitted in the transmitting step is propagated near the surface of the cortical bone and received in the receiving step.

1 is a block diagram showing a configuration of an ultrasonic diagnostic apparatus according to an embodiment of the present invention. The flowchart of the measuring method which concerns on this invention. Continuation of the flowchart of FIG. The schematic diagram explaining a shape detection process. (A) The typical sectional view showing signs that an ultrasonic beam was transmitted to cortical bone. (B) A schematic cross-sectional view showing how a leakage wave is received by each transducer. BUA-t ₀ the inner product plotted on the coordinate <F _n, G _n> diagram illustrating a 3-dimensional curved surface of. BUA-SOS inner product plotted on the coordinate <F _n, G _n> diagram illustrating a 3-dimensional curved surface of.

  Next, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram of an ultrasonic diagnostic apparatus 1 as a measuring apparatus according to an embodiment of the present invention.

  The ultrasonic diagnostic apparatus 1 according to the present embodiment uses a human cortical bone 10 as a diagnosis target. The ultrasonic diagnostic apparatus 1 according to the present embodiment transmits an ultrasonic signal toward the cortical bone 10, and based on the ultrasonic signal returned from the cortical bone 10, the speed of sound (SOS: Speed Of) in the cortical bone 10. Sound and Broadband Ultrasonic Attenuation (BUA) coefficients are measured. The measured SOS and BUA can be used as an index of bone health.

  As shown in FIG. 1, the ultrasonic diagnostic apparatus 1 includes an ultrasonic transducer 2 and an apparatus main body 3.

  The ultrasonic transmitter / receiver 2 transmits and receives ultrasonic waves. The ultrasonic transducer 2 includes an abutment surface 2 a that abuts on the surface (skin) of the soft tissue 11 at the measurement site, and a transducer array 22. The transducer array 22 includes a plurality of transducers 24 arranged in a line at equal intervals along the contact surface 2a.

  When an electric signal is given, the vibrator 24 vibrates its surface to generate an ultrasonic wave, and generates and outputs an electric signal when receiving an ultrasonic wave on the surface. That is, each transducer 24 is configured to be able to transmit and receive ultrasonic waves.

  The apparatus main body 3 is connected to the ultrasonic transducer 2 by a cable, and is configured to be able to transmit and receive signals to and from the ultrasonic transducer 2. The apparatus main body 3 includes a transmission circuit 31, a plurality of reception circuits 33, a transmission / reception separation unit 34, a calculation unit 35, and a display unit 32.

  The transmission circuit 31 is configured to generate an electrical pulse signal for generating an ultrasonic wave by vibrating the transducers 24 of the transducer array 22 and to apply the electrical pulse signal to the transducers 24. Yes. The center frequency of the electric pulse signal is, for example, about 1 to 10 MHz.

  The vibrator 24 to which the electric pulse is applied vibrates according to the electric pulse signal and generates an ultrasonic wave. The transmission circuit 31 is configured to apply an electrical pulse signal at an arbitrary timing to each of the plurality of transducers 24 of the transducer array 22. Thereby, it is possible to control to transmit ultrasonic waves from a plurality of transducers 24 all at once or at individual timing.

  The plurality of receiving circuits 33 are respectively connected to the plurality of transducers 24 constituting the transducer array 22. Each receiving circuit 33 receives an electrical signal output by the transducer 24 receiving an ultrasonic wave, and receives the electrical signal subjected to amplification processing, filter processing, digital conversion processing, and the like. A signal is generated and transmitted to the calculation unit 35.

  The transmission / reception separation unit 34 is connected between the transducer array 22 and the transmission circuit 31 and the reception circuit 33. The transmission / reception separating unit 34 prevents an electrical signal (electrical pulse signal) sent from the transmission circuit 31 to the transducer array 22 from flowing directly to the reception circuit 33, and also sends electricity sent from the transducer array 22 to the reception circuit 33. This is to prevent a signal from flowing to the transmission circuit 31 side.

  The calculation unit 35 is configured as a computer including hardware such as a CPU, RAM, and ROM, and is configured to calculate the SOS and BUA of the cortical bone 10 based on the signals received by the transducers 24. Yes. Details of the processing performed by the calculation unit 35 will be described later.

  The SOS and BUA derived by the calculation unit 35 are appropriately displayed on the display unit 32. With the ultrasonic diagnostic apparatus 1 configured as described above, the BUA and SOS of the cortical bone 10 can be measured.

Next, the transfer function H _n (jω) will be described as a premise for explaining the operation of the ultrasonic diagnostic apparatus 1 of the present embodiment.

  Consider a case where an ultrasonic beam in an oblique direction is transmitted toward the cortical bone 10 as indicated by a thick arrow in FIG. In the ultrasonic diagnostic apparatus 1 of the present embodiment, the transmission circuit 31 applies an electrical pulse signal with a predetermined time difference applied to two adjacent transducers 24, as shown in FIG. Transmitting an ultrasonic beam in an oblique direction. At this time, the two transducers 24 that transmit ultrasonic beams are referred to as a beam transmission pair (transmission unit) 25. The direction in which the ultrasonic beam is transmitted from the beam transmission pair 25 is preferably set so that the beam is incident on the surface of the cortical bone 10 at a critical angle or an angle close to the critical angle.

  The ultrasonic signal incident on the surface of the cortical bone 10 at an angle close to the critical angle propagates near the surface in the cortical bone 10. Thus, the ultrasonic signal propagating through the cortical bone 10 travels at the speed of sound SOS of the cortical bone 10 and is affected by broadband ultrasonic attenuation (BUA) by the cortical bone 10. Further, when the ultrasonic signal propagates near the surface in the cortical bone 10, the ultrasonic signal is reradiated from the surface of the cortical bone 10 into the soft tissue 11 (FIG. 5B). An ultrasonic signal re-radiated from the surface of the cortical bone 10 to the soft tissue 11 is called a leaky wave.

The beam transmission pair 25 and the transducers 24 other than the beam transmission pair 25 are located on the same side as viewed from the cortical bone 10. Therefore, at least one of the transducers 24 can receive a leaky wave re-radiated from the surface of the cortical bone 10 into the soft tissue 11. This leaky wave is not received by the transducer 24 near the beam transmission pair 25, but is received by the transducer 24 at a certain distance from the beam transmission pair 25 (see FIG. 5B). Therefore, among the vibrator 24 that has received the leaky waves from the cortical bone 10, the closest resonator 24 to the beam transmit pair 25, reference receiving section (first receiving unit) and 24 _0. Further, the other transducers 24 that have received the leaky wave 26 are referred to as receiving units 24 ₁ , 24 ₂ ... In order from the side closer to the reference receiving unit 24 ₀ .

FIG as shown in 5 (b), leaky wave received in the reference receiver 24 _0, compared to the leaky wave 26 received by the other receiving unit 24 _1, 24 ₂ ..., propagate cortical bone 10 medium The shortest distance. Therefore, the signal received by the reference receiving section 24 ₀ is said to influence due to the propagation through the cortical bone 10 is the smallest signal. Therefore, the signal received by the reference receiving section 24 _0, the reference signal R (jω). After an ultrasonic beam is transmitted from the beam transmission pair 25, the time taken until the reference receiving section 24 ₀ reference signal R (j [omega]) is received and the first hour. On the other hand, the signals received by the other receivers 24 ₁ , 24 ₂ ... Are assumed to be received signals F ₁ (jω), F ₂ (jω). In the following description, a frequency domain expression is used when describing a signal unless otherwise specified.

An arbitrary receiving unit is selected as the target receiving unit (second receiving unit) 24 _n among the receiving units 24 ₁ , 24 ₂ ... That have received the leaky wave other than the reference receiving unit 24 ₀ . Further, the signal received by the target receiving unit 24 _n is represented by a received signal F _n (jω). Incidentally, n subscript represents what number of the receiving portion counted from the reference receiver 24 _0. The time taken from when the ultrasonic beam is transmitted from the beam transmission pair 25 to when the reception signal F _n (jω) is received by the target reception unit 24 _n is defined as a second time. Attention receiving unit 24 _n, so than the reference receiving section 24 ₀ is farther from beam transmission pair 25, the second time is longer than the first hour.

Here, as shown in FIG. 5B, the propagation path of the reference signal (first signal) R (jω) is the first propagation path 27 and the propagation path of the reception signal (second signal) F _n (jω) is. The second propagation path 28 is assumed. As shown in FIG. 5B, the distance that the ultrasonic signal propagates in the cortical bone 10 in the first propagation path 27 is x ₀ , and the distance that the ultrasonic signal propagates in the cortical bone 10 in the second propagation path 28. _Xn . Further, the distance that the leaky wave propagates in the soft tissue 11 in the first propagation path 27 is x _0soft , and the distance that the leaky wave propagates in the soft tissue 11 in the second propagation path 28 is x _nsoft .

  The longer the distance that the ultrasonic signal propagates through the cortical bone 10, the greater the influence received from the cortical bone 10. Similarly, the longer the distance that the ultrasonic signal propagates through the soft tissue 11, the greater the influence received from the soft tissue 11. In the first propagation path 27 and the second propagation path 28, the distance that the ultrasonic signal propagates through the cortical bone 10 is different from the distance that the ultrasonic signal propagates through the soft tissue 11. And the magnitude of the influence received from the soft tissue 11 is also different.

For example, the received signal F _n received by the second propagation path 28 focused reception unit 24 _n to propagate (j [omega]) is the reference signal R received by the reference receiving section 24 ₀ propagated through the first propagation path 27 Compared to (jω), the difference in the distance propagated through the cortical bone 10 (x _n −x ₀ ) is more affected by the cortical bone 10 and the difference in the distance propagated through the soft tissue 11 (x _nsoft −x _0soft ). Only affected by the soft tissue 11.

Considering the above points, the relationship between the reference signal R (jω) and the received signal F _n (jω) can be described as follows using the transfer function H _n (jω). The transfer function H _n (jω) models the difference between the propagation path 27 of the reference signal R (jω) and the propagation path 28 of the received signal F _n (jω).

By the way, when the surface of the cortical bone 10 and the direction in which the transducers 24 are arranged (the horizontal direction in FIG. 5) can be regarded as parallel, the distance x _0soft at which the ultrasonic signal propagates through the soft tissue 11 through the first propagation path 27. And the distance x _nsoft at which the ultrasonic signal propagates through the soft tissue 11 in the second propagation path 28 can be regarded as the same. In this way, it can be considered that the difference between the first propagation path 27 and the second propagation path 28 is only the difference in distance (x _n −x ₀ ) at which the signal propagates through the cortical bone 10. In this case, since the transfer function H _n (jω) does not need to consider the influence of the soft tissue 11, the transfer function H _n (jω) is simplified. Specifically, the transfer function H _n (jω) is the difference between the sound velocity SOS [m / s] of the cortical bone 10, the broadband ultrasonic attenuation coefficient BUA [dB / Hz / m] of the cortical bone 10, and the propagation distance. Using (x _n −x ₀ ) [m], the following equation can be used.

Here, the part (a) in Equation 2 represents frequency attenuation due to BUA in the cortical bone 10, and the part (b) in Equation 2 propagates through the cortical bone 10 at the speed of sound SOS. This represents the signal phase delay. Note that t _{0 in} Equation 2 is a phase delay due to a delay of the arithmetic circuit or the like.

  Next, the measurement principle of SOS and BUA in the ultrasonic diagnostic apparatus 1 of the present embodiment will be described.

As described above, the transfer function H _n (jω) includes four parameters (SOS, BUA, (x _n −x ₀ ), and t ₀ ). By assuming these parameters, a provisional transfer function H _n (jω) can be set. The calculation unit 35 of the present embodiment has a function as the transfer function setting unit 41 that sets the temporary transfer function H _n (jω) in this way.

The calculation unit 35 has a function as the signal synthesis unit 42. The signal synthesis unit 42 generates the synthesized signal G _n (jω) by applying the temporary transfer function H _n (jω) set by the transfer function setting unit 41 to the reference signal R (jω). Specifically, the signal synthesizer 42 generates a synthesized signal G _n (jω) according to Equation 3 below. Note that the denominator of Equation 3 is for normalizing the composite signal G _n (jω).

If the transfer function H _n (jω) in Equation 3 is an appropriately modeled difference between the propagation path 27 and the propagation path 28, the combined signal G _n (jω) and the received signal F _n (jω) match. . However, since the transfer function H _n (jω) in Expression 3 is a temporary transfer function set by the transfer function setting unit 41, the combined signal G _n (jω) and the received signal F _n (jω) are not always the same. Absent. Therefore, the calculation unit 35 has a function as a coincidence degree calculation unit 43 that obtains a coincidence degree between the combined signal G _n (jω) and the received signal F _n (jω).

In the present embodiment, the coincidence calculation unit 43 calculates the inner product <F _n , G _n > of both the combined signal G _n (jω) and the received signal F _n (jω) as an index of the coincidence according to the following Equation 4. Ask. When the synthesized signal G _n (jω) and the received signal F _n (jω) are standardized, the inner product <F _n , G _n > is 1 if the two match, and the inner product < F _n , G _n > is smaller than 1. As described above, the inner product <F _n , G _n > can be used as an index of the degree of coincidence between the combined signal G _n (jω) and the received signal F _n (jω).

If the temporary transfer function H _n (jω) set by the transfer function setting unit 41 can appropriately model the difference between the propagation path 27 and the propagation path 28, the combined signal G _n (jω) and the received signal F _n Since (jω) matches, the inner product <F _n , G _n > is 1. On the other hand, if the model is not properly modeled, the synthesized signal G _n (jω) and the received signal F _n (jω) do not match, so the inner product <F _n , G _n > is smaller than 1. Therefore, when the inner product <F _n , G _n > is maximized, it can be determined that the transfer function H _n (jω) can appropriately model the difference between the propagation path 27 and the propagation path 28.

  Based on the above, a method for measuring SOS and BUA using the ultrasonic diagnostic apparatus 1 of the present embodiment will be described with reference to the flowcharts of FIGS. 2 and 3.

  When measuring the BUA and SOS of the cortical bone 10 with the ultrasonic diagnostic apparatus of the present embodiment, first, the surface shape of the cortical bone 10 that is the object to be measured is detected (step S101, shape detection step). The operator performs a predetermined measurement start operation in a state where the contact surface 2a of the ultrasonic transducer 2 is in contact with the surface of the human body (skin) that is the object of diagnosis. When the measurement start operation is performed, the transmission circuit 31 applies an electrical pulse signal to each transducer 24 of the transducer array 22 at the same timing. As a result, ultrasonic waves are transmitted from the transducers 24 toward the body at the same timing, so that plane waves traveling in a direction orthogonal to the direction in which the transducers 24 are arranged are transmitted (FIG. 4A).

  The plane wave transmitted from the transducer array 22 travels through the soft tissue 11 and is reflected by the surface of the cortical bone 10 to generate a reflected wave (FIG. 4B). This reflected wave is received by at least some of the transducers 24 included in the transducer array 22. The signal received by each transducer 24 is subjected to appropriate processing such as filtering and sampling by the receiving circuit 33 and is output to the arithmetic unit 35.

  The calculation unit 35 has a function as a shape detection unit 40 that detects the surface shape of the cortical bone 10. The shape detection unit 40 detects the arrival angle of the signal received by each transducer 24 and detects the surface shape of the cortical bone 10 based on this. In addition, since the structure which detects the surface shape of the cortical bone 10 is described in patent document 1, detailed description is abbreviate | omitted.

  Subsequently, the transmission circuit 31 transmits an ultrasonic beam toward the cortical bone 10 as shown in FIG. 5A (step S102, transmission step). The ultrasonic beam propagates in the vicinity of the surface of the cortical bone 10, and a leakage wave (FIG. 5B) re-radiated from the surface of the cortical bone 10 into the soft tissue 11 is received by the vibrator 24 (step). S103, receiving step).

When the leakage wave is received by the plurality of transducers 24, the calculation unit 35 selects the reference reception unit (first reception unit) ₂₄₀ and the attention reception unit (second reception unit) from the plurality of transducers 24. ) 24 _n is selected (step S104). As described above, the reference receiving unit ₂₄₀ is the transducer closest to the beam transmission pair 25 among the transducers 24 that have received the leaky wave. The target receiving unit may be any one of the other receiving units 24 ₁ , 24 ₂ .

The calculation unit 35 standardizes the reception signal F _n (jω) received by the target reception unit 24 _n (step S105).

As described above, in parallel with the process of acquiring the received signal F _n (jω) (steps S102 to S105), the computing unit 35 generates the plurality of synthesized signals G _n (jω) (steps S106 to S108). )I do.

In order to generate a plurality of combined signals G _n (jω), first, the transfer function setting unit 41 sets a plurality of temporary transfer functions H _n (jω). As described above, the transfer function setting unit 41 sets the temporary transfer function H _n (jω) by assuming four parameters (SOS, BUA, (x _n −x ₀ ), and t ₀ ). be able to.

By the way, in this embodiment, since the surface shape of the cortical bone 10 is detected in step S101, the propagation path of the ultrasonic beam can be simulated by applying Snell's law. By this simulation, the difference in propagation distance (x _n −x ₀ ) can be obtained.

In order to simulate the propagation path of the ultrasonic beam by applying Snell's law, the value of the sound velocity SOS _soft in the soft tissue 11 and the value of the sound velocity SOS in the cortical bone 10 are necessary. Empirical values may be used for the sound velocity SOS _soft in the soft tissue 11. However, the speed of sound SOS in the cortical bone 10 is exactly what the ultrasonic diagnostic apparatus 1 is trying to measure, so that the value cannot be known in advance. Therefore, the transfer function setting unit 41 performs the above simulation using the assumed SOS value as a parameter of the transfer function H _n (jω), and obtains the propagation distance difference (x _n −x ₀ ).

The transfer function setting unit 41 substitutes the difference (x _n −x ₀ ) of the propagation distance obtained by the simulation and the assumed three parameters (SOS, BUA, and t ₀ ) into Equation 2 to A transfer function H _n (jω) is set. Since the difference (x _n −x ₀ ) in the propagation distance depends on the parameter SOS, the temporary transfer function H _n (jω) has three independent parameters (SOS, BUA, and t ₀ ). .

Of the above three parameters, information useful as the ultrasound diagnostic apparatus 1 is the values of SOS and BUA, and t ₀ is not useful information. Therefore, it is preferable to determine t ₀ at an early stage from the viewpoint of reducing the calculation load.

Therefore, in the present embodiment, two-stage processing is performed such that t ₀ is first determined and then SOS and BUA are obtained. First, the transfer function setting unit 41 fixes the SOS to an appropriate value among the above three parameters (step S106), and sets a plurality of transfer functions H _n ( _where the combinations of the values of BUA and t ₀ are different from each other. jω) is set (step S107).

Then, the signal synthesizing unit 42, a transfer transfer function function setting unit 41 has set H _n (j [omega]), the selected reference signal receiving unit 24 ₀ is received in step S104 (reference signal R (j [omega])) By applying this, a composite signal G _n (jω) is generated (step S108). Since a plurality of transfer functions H _n (jω) are set in step S107 described above, the signal synthesis unit 42 applies each of the plurality of transfer functions H _n (jω) to the reference signal R (jω). Thus, a plurality of synthesized signals G _n (jω) are generated. As a result, a combined signal G _n (jω) corresponding to each combination of BUA and t ₀ is obtained.

The coincidence calculation unit 43 calculates inner products <F _n , G _n > of the received signal F _n (jω) and the plurality of combined signals G _n (jω) generated by the signal combining unit 42 (step S109). ). As a result, inner products <F _n , G _n > corresponding to the combinations of BUA and t ₀ described above are obtained. A plurality of <F _n , G _n > values obtained in this way are plotted at each point of the BUA-t ₀ coordinate, whereby a three-dimensional curved surface as shown in FIG. 6 is obtained.

The calculation unit 35 has a function as the parameter selection unit 44. The parameter selection unit 44 obtains a t ₀ coordinate when the inner product <F _n , G _n > shows the maximum value on the three-dimensional curved surface. It is considered that the value of t ₀ at this time coincides with the actual t ₀ (phase delay caused by delay of the arithmetic circuit). Therefore, the parameter selection unit 44 adopts the value of t ₀ when the inner product <F _n , G _n > is maximum as the measured value of t ₀ (step S110). As described above, an unnecessary t ₀ value among the three parameters of the transfer function H _n (jω) can be determined.

  Subsequently, the calculation unit 35 obtains values of SOS and BUA.

The transfer function setting unit 41 fixes the value of t ₀ among the three parameters of the transfer function H _n (jω) to the value obtained in step S110, and sets SOS (first parameter) and BUA (second parameter). A plurality of transfer functions H _n (jω) with different combinations of values are set (step S111, transfer function setting step).

Subsequently, the signal synthesizing unit 42 applies the plurality of transfer functions H _n (jω) set by the transfer function setting unit 41 to the reference signal R (jω), respectively, to thereby generate a plurality of synthesized signals G _n (jω). Is generated (step S112, signal synthesis step). As a result, a combined signal G _n (jω) corresponding to each combination of SOS and BUA is obtained.

The coincidence calculation unit 43 calculates inner products <F _n , G _n > of the received signal F _n (jω) and the plurality of combined signals G _n (jω) generated by the signal combining unit 42 (step S113). , Coincidence calculation step). As a result, inner products <F _n , G _n > corresponding to the combinations of SOS and BUA described above are obtained. A plurality of <F _n , G _n > values obtained in this way are plotted at each point of the SOS-BUA coordinates to obtain a three-dimensional curved surface as shown in FIG.

In the above processing, since the values of the inner product <F _n , G _n > are plotted while changing the values of BUA and SOS, only a discrete and rough three-dimensional curved surface can be obtained. Therefore, in the present embodiment, the parameter selection unit 44 is configured to perform Gaussian interpolation of the three-dimensional curved surface obtained as described above (step S114). For example, the parameter selection unit 44 uses a Levenberg-Marquardt method or the like to obtain a two-dimensional Gaussian function that is fitted to the inner product <F _n , G _n > of each point of the BUA-SOS coordinates.

Then, the parameter selection unit 44 calculates BUA-SOS coordinates that maximize the value of the inner product <F _n , G _n > based on the two-dimensional Gaussian function obtained as described above. The parameter selection unit 44 employs the combination of BUA and SOS at this time as the measured values of SOS and BUA (step S115, parameter selection step).

  As described above, the ultrasonic diagnostic apparatus 1 of the present embodiment can measure the values of the sound velocity SOS (first parameter) and the broadband ultrasonic attenuation BUA (second parameter) of the cortical bone 10.

As described above, the ultrasonic diagnostic apparatus 1 according to the embodiment includes the beam transmission pair 25, the reference reception unit ₂₄₀ , the attention reception unit _24n , the transfer function setting unit 41, the signal synthesis unit 42, A coincidence calculation unit 43 and a parameter selection unit 44 are provided. The beam transmission pair 25 transmits a signal toward the cortical bone 10. Reference receiving section 24 ₀ receives a reference signal the signal is radiated again to the outer cortical bone 10 and propagates the cortical bone 10 which enters the cortical bone 10 R (jω). The attention receiving unit 24 _n receives the received signal F _n (jω), which is emitted from the cortical bone 10 again after the signal incident on the cortical bone 10 propagates through the cortical bone 10 through a path different from the reference signal R (jω). ). The transfer function setting unit 41 models the difference between the propagation path 27 of the reference signal R (jω) and the propagation path 28 of the received signal F _n (jω) by including the SOS and BUA of cortical bone as parameters. _n (jω) is set. The signal synthesizer 42 applies a plurality of transfer functions H _n (jω) in which the combinations of SOS and BUA of the cortical bone are different from each other to the reference signal R (jω), thereby corresponding to the combination of the SOS and BUA. The synthesized signal G _n (jω) is generated. The coincidence calculation unit 43 calculates inner products <F _n , G _n > of the respective synthesized signals G _n (jω) and received signals F _n (jω). The parameter selection unit 44 obtains a combination of SOS and BUA when the inner product shows the maximum value.

In this way, by obtaining the inner product <F _n , G _n > of the combined signal G _n (jω) and the received signal F _n (jω), H _n (jω) of the transfer function set by the transfer function setting unit 41 is appropriate. Can determine gender. Then, by searching for a parameter that maximizes the inner product <F _n , G _n >, the value of the parameter can be determined. Since the transfer function only needs to model the difference between the propagation path 27 and the propagation path 28, the transfer function is simplified and the measurement accuracy is improved as compared with the case of modeling the entire propagation path.

  Next, a first modification of the above embodiment will be described.

In the above embodiment, a plurality of receiving portions _{24 1, 24 2 ... 24 n} ... of the, in terms of selecting one of the reception unit 24 _n as a target receiver, the received signal F _n for the attention receiving unit 24 _n has received and (j [omega]), the reference signal the reference receiver 24 ₀ receives R (jω), is derived the BUA and SOS based on. That is, in the above embodiment, only information of signals received by the two transducers (the attention receiving unit 24 _n and the reference receiving unit 24 ₀ ) is used.

However, according to the transducer array 22 to the ultrasonic diagnostic apparatus 1 of this embodiment comprises a plurality of receiving portions _{24 1, 24 2 ... 24 n} ... in the reception signal _{F 1 (jω), F 2} (jω) ... F _{Since n} (jω)... can be obtained, it is considered that SOS and BUA can be obtained more stably by using information of a plurality of signals obtained by the plurality of receiving units.

Therefore, the received signal a plurality of receiving portions _{24 1, 24 2 ... 24 n} ... received _{F 1 (jω), F 2} (jω) ... F n (jω) ... and, combined signal G ₁ calculated for each receiver The average inner product <F, G> _ave of (jω), G ₂ (jω),... G _n (jω).

Similar to the above embodiment, the combination of SOS and BUA values is made different from each other to obtain the average inner product <F, G> _ave , and the combination of SOS and BUA when <F, G> _ave shows the maximum value. Ask for. As described above, by using a plurality of signals obtained by the plurality of receiving units 24 ₁ , 24 ₂ ... 24 _n .

  Next, a second modification of the above embodiment will be described.

In the above embodiment, the surface of the cortical bone 10 is described as being parallel to the direction in which the transducers 24 are arranged. Thereby, the transfer function can be simplified. However, when the surface of the cortical bone 10 is curved, the leaky wave arrival angle φ ₀ with respect to the reference receiver 24 ₀ and the leaky wave arrival angle φ _{n with} respect to the target receiver 24 _n are different (FIG. 5B). reference). Since the vibrator 24 has directivity, the influence of directivity may not be negligible when the arrival angles φ ₀ and φ _n are greatly different.

If the direct function _{,? N} (jω) is a transfer function representing the influence of the received signal F _n (jω) on the reference signal R (jω) due to the difference in the arrival angle, the effect of _directivity is incorporated. The transfer function H ′ _n (jω) can be defined by Equation 6 below. Note that the transfer function H _{directivity,? N} (jω) is determined by the reception characteristics of the transducer 24 and the arrival angle φ _n of the leaky wave with respect to the target reception unit 24 _n . The calculation unit 35 can calculate the arrival angle φ _n based on the propagation path of the signal, and can determine the transfer function H _{directivity,? N} (jω) based on this.

Further, when the surface of the cortical bone 10 is not parallel to the direction in which the transducers 24 are arranged, the propagation distance of the leaky wave in the soft tissue 11 may not be considered the same in the first propagation path 27 and the second propagation path. is there. For example, in the case of FIG. 5B, the second propagation path 28 has a shorter distance (x _nsoft −x _0soft ) through which the leaky wave propagates in the soft tissue 11 than the first propagation path 27. When the difference in the distance propagating through the soft tissue 11 (x _nsoft −x _0soft ) is large, the influence of the BUA (soft tissue BUA) of the soft tissue 11 and the SOS (soft tissue SOS) in the soft tissue 11 cannot be ignored.

A transfer function representing the influence of the soft tissue BUA received signal F _n (jω) received by the difference (x _nsoft −x _0soft ) of the propagation distance of the leaky wave in the soft tissue 11 with respect to the reference signal R (jω) is H _{SoftAbsorption ,? n} (jω), where the transfer function representing the influence of soft tissue SOS is H _{SoftSpeed, n} (jω), the transfer function H ″ _n (jω) incorporating the influence of soft tissue BUA and soft tissue SOS is It can be defined by Equation 7. Note that BUA _{soft in} Equation 7 is the BUA in the soft tissue 11, and an experience value can be used. However, this BUA _soft may be used as a parameter. SOS _{soft in} Equation 7 is the SOS in the soft tissue 11, and an empirical value can be used. However, this SOS _soft may be used as a parameter. The calculation unit 35 calculates the distance x _nsoft −x _0soft by simulating the propagation path of the ultrasonic beam based on the shape of the cortical bone 10 detected by the shape detection unit 40, and based on this, calculates the transfer function H _{SoftAbsorption, ? n} (jω) and transfer function H _{SoftSpeed, n} (jω) can be obtained.

Furthermore, a transfer function H ′ ″ _n (jω) that incorporates both the influence of directivity and the influence of soft tissue BUA and soft tissue SOS can also be defined by Equation 8 below.

Incorporating effects of directional transfer functions H _'n (jω) and the transfer incorporating the effects of the soft tissue function H'_'n (jω), or transmission incorporating the influence of both the function H''' _n (jω) Can be used instead of the transfer function H _n (jω) of Equation 2. Thereby, even when the surface of the cortical bone 10 is greatly curved, SOS and BUA can be accurately measured.

  The preferred embodiments and modifications of the present invention have been described above, but the above configuration can be modified as follows, for example.

  In the above embodiment, a beam transmission pair 25 including two adjacent transducers 24 is used as a transmission unit for transmitting a beam to the cortical bone 10. For example, sound velocity measurement described in Patent Document 1 is used. A dedicated transducer (transmitting unit) for transmitting a beam may be provided as in the apparatus.

In the above embodiment, of the vibrator 24 that has received the leaky wave, reference receiving section closest vibrator 24 to the beam transmit pair 25 (first reception unit) was 24 _0, leaky waves from the cortical bone 10 Any of the transducers 24 that have received the signal can be used as a reference receiving unit (first receiving unit).

  In the above embodiment, SOS and BUA are measured simultaneously, but only SOS or BUA may be measured.

In the above embodiment, the process of acquiring the received signal F _n (jω) (steps S102 to S105) and the process of generating a plurality of combined signals G _n (jω) (steps S106 to S108) are performed in parallel. However, these processes may be executed sequentially.

  In the above embodiment, Gaussian interpolation is performed in step S114, but other interpolation methods may be used as long as the interpolation method can be applied to a three-dimensional curved surface. However, the interpolation in step S114 can be omitted.

In the above embodiment, the inner product is obtained as an index of the degree of coincidence between the combined signal G _n (jω) and the received signal F _n (jω), but another index other than the inner product is used as the degree of coincidence of the two signals. Also good.

  In the description of the above embodiment, the frequency domain expression is used in the mathematical expression, but each mathematical expression can also be expressed in the time domain. Therefore, the actual calculation processing in the calculation unit 35 may be performed in the frequency domain or in the time domain.

In the above embodiment, SOS and BUA in the cortical bone 10 are measured. However, the measurement target that is the measurement target of the measurement apparatus of the present invention is not limited to the cortical bone 10. For example, the soft tissue 11 can be measured, and the sound velocity SOS _{soft of} the soft tissue 11 and BUA _{soft of the} soft tissue 11 can be measured by the measuring apparatus of the present invention.

  In addition, the measuring device of the present invention is not limited to use as a diagnostic device for diagnosing a human body. For example, the measuring device of the present invention can be used in the field of nondestructive inspection. For example, the presence or absence of cracks in the concrete can be determined by measuring the SOS and BUA of the concrete with the measuring device of the present invention.

1 Ultrasonic diagnostic equipment (measuring equipment)
10 Cortical bone (object to be measured)
24 vibrator 24 ₀ reference receiver (first receiver)
24 _n attention receiver (second receiver)
25 Beam transmission pair (transmitter)
40 shape detection unit 41 transfer function setting unit 42 signal synthesis unit 43 coincidence calculation unit

Claims (22)

A transmitter for transmitting a signal toward the device under test;
The signal incident on the measured object propagates through the measured object and is radiated again outside the measured object, and propagates along a different path from the first signal and is radiated again outside the measured object. A receiver for receiving the second signal;
A transfer function setting unit that sets a transfer function in which a difference between propagation paths of the first signal and the second signal is modeled by including at least a first parameter;
Applying a plurality of transfer functions having different values of the first parameter to the first signal, respectively, to generate a synthesized signal corresponding to each first parameter;
A degree of coincidence calculation unit for calculating the degree of coincidence between each synthesized signal and the second signal;
A parameter selection unit for obtaining a value of the first parameter when the degree of coincidence is maximum;
A measuring apparatus comprising: The measuring device according to claim 1,
The receiver is
Receiving the first signal after a lapse of a first time after the signal is transmitted;
The measurement apparatus receives the second signal after elapse of a second time longer than the first time. The measuring apparatus according to claim 1 or 2,
A shape detection unit that transmits a signal toward the object to be measured and detects the shape of the object to be measured based on a reflected signal reflected by the object to be measured;
The measurement function, wherein the transfer function setting unit sets the transfer function based on the shape of the measured object detected by the shape detection unit. A measuring device according to any one of claims 1 to 3,
The signal is an ultrasonic signal;
The measuring apparatus, wherein the first parameter is a sound velocity of the measured object. A measuring device according to any one of claims 1 to 3,
The signal is an ultrasonic signal;
The measuring apparatus according to claim 1, wherein the first parameter is a broadband ultrasonic attenuation coefficient of the object to be measured. A measuring device according to any one of claims 1 to 5,
The coincidence calculation unit calculates an inner product of each combined signal and the second signal,
The parameter selection unit obtains the first parameter when the inner product shows a maximum value. A measuring device according to any one of claims 1 to 3,
The transfer function includes a second parameter different from the first parameter;
The signal synthesizing unit applies a plurality of transfer functions in which combinations of the first parameter and the second parameter are different from each other to each of the first signals, thereby generating a synthesized signal corresponding to each of the combinations. A measuring device characterized by generating. The measuring device according to claim 7,
The signal is an ultrasonic signal;
The first parameter is a sound speed of the measured object,
The measuring apparatus, wherein the second parameter is a broadband ultrasonic attenuation coefficient of the object to be measured. The measurement device according to claim 7 or 8, wherein
The coincidence calculation unit calculates an inner product of each combined signal and the second signal,
The parameter selection unit obtains a combination of the first parameter and the second parameter when the inner product shows a maximum value. A measuring device according to any one of claims 1 to 9,
The measuring device is a cortical bone in soft tissue. The measuring device according to claim 10,
The measurement apparatus, wherein the signal transmitted by the transmission unit propagates near the surface of the cortical bone and is received by the reception unit. A transmission step of transmitting a signal toward the measurement object;
The signal incident on the measured object propagates through the measured object and is radiated again outside the measured object, and propagates along a different path from the first signal and is radiated again outside the measured object. Receiving a second signal; and
A transfer function setting step of setting a transfer function in which a difference between propagation paths of the first signal and the second signal is modeled including at least a first parameter;
Applying a plurality of transfer functions having different values of the first parameter to the first signal, respectively, to generate a synthesized signal corresponding to each first parameter;
A degree of coincidence calculating step for calculating the degree of coincidence between each of the combined signals and the second signal;
A parameter selection step for obtaining a value of the first parameter when the degree of coincidence is maximized;
A measurement method comprising: The measurement method according to claim 12, comprising:
In the receiving step,
Receiving the first signal after a lapse of a first time after the signal is transmitted;
The measurement method, wherein the second signal is received after the elapse of a second time longer than the first time. The measurement method according to claim 12 or 13,
Including a shape detection step of transmitting a signal toward the device under test and detecting the shape of the device under test based on a reflected signal reflected by the device under test;
In the transfer function setting step, the transfer function is set based on the shape of the measurement object detected in the shape detection step. A measurement method according to any one of claims 12 to 14, comprising:
The signal is an ultrasonic signal;
The measuring method according to claim 1, wherein the first parameter is a sound velocity of the measured object. A measurement method according to any one of claims 12 to 14, comprising:
The signal is an ultrasonic signal;
The measuring method according to claim 1, wherein the first parameter is a broadband ultrasonic attenuation coefficient of the object to be measured. The measurement method according to any one of claims 12 to 16, comprising:
In the coincidence degree calculating step, inner products of the respective synthesized signals and the second signal are calculated,
In the parameter selection step, the first parameter when the inner product shows a maximum value is obtained. A measurement method according to any one of claims 12 to 14, comprising:
The transfer function includes a second parameter different from the first parameter;
In the signal synthesizing step, a plurality of transfer functions in which combinations of the first parameter and the second parameter are different from each other are applied to the first signal, respectively, so that a synthesized signal corresponding to each of the combinations is obtained. The measuring method characterized by producing | generating. The measurement method according to claim 18, wherein
The signal is an ultrasonic signal;
The first parameter is a sound speed of the measured object,
The method according to claim 2, wherein the second parameter is a broadband ultrasonic attenuation coefficient of the object to be measured. The measurement method according to claim 18 or 19,
In the coincidence degree calculating step, inner products of the respective synthesized signals and the second signal are calculated,
In the parameter selection step, a combination of the first parameter and the second parameter when the inner product shows a maximum value is obtained. A measurement method according to any one of claims 12 to 20, comprising:
The measurement method, wherein the object to be measured is cortical bone in soft tissue. The measurement method according to claim 21, wherein
The measurement method characterized in that the signal transmitted in the transmitting step propagates near the surface of the cortical bone and is received in the receiving step.

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