JP2000175911A - Method and instrument for measuring bone strength - Google Patents

Abstract

PROBLEM TO BE SOLVED: To more correctly grasp the state of bone and to easily and safely execute measurement by grasping the state of the bone by the level of an acoustic bone strength value which is obtained by means of multiplying an ultrasonic wave attenuating value obtained in the case of irradiating the bone to be measured with ultrasonic wave by a bone frequency characteristic value obtained in the case of analyzing a vibration intrinsic to the bone. SOLUTION: A foot 5 is placed on a measuring instrument, a heel 32 is irradiated with ultrasonic wave from a ultrasonic wave emitting transducer 6, an ultrasonic wave receiving transducer 7 receives it and its strength is outputted as an electric signal and amplified in an amplifier circuit 24. Then, it is frequency-analyzed by an FFT analyzer 25, inputted to a computer 27, specified as an ultrasonic attenuation(BUA) value and stored. Then a cuneiform is hit by a keying hammer, the number of the vibration of a calcaneus is measured by an piezoelectric element 1, the vibration strength is outputted as the electric signal and amplified in the amplifier circuit 24 and, then, it is inputted to the computer 27 after being frequency-analyzed by the FFT analyzer 25. The computer 27 multiplies the obtained BUA value by a bone frequency characteristic(BFC) value, calculates an deoustic bone strength(ABS) value, obtains a numerical value as it is or makes it into a graph and displays it in a display 26.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a bone strength measuring method for grasping bone properties from an acoustic bone strength value obtained by multiplying an ultrasonic attenuation value and a bone frequency characteristic value of a bone to be measured. Related to the device.

[0002]

2. Description of the Related Art It is desirable to know the degree of aging in advance for aging of bone as seen in osteoporosis and to perform appropriate aging prevention and treatment. From such a viewpoint, various measurement methods have been proposed. Use radiation for typical ones
There are DXA method, SXA method, QCT method, and QUS method using ultrasound. Among them, the measurement method using ultrasonic waves has recently become the mainstream in the measurement method using radiation because young people and pregnant women may be exposed to radiation. There are various utilization forms of the ultrasonic wave, and there are many methods of irradiating the ultrasonic wave and measuring the ultrasonic wave which has passed or reflected the bone. For example, JP-A-9-62056
The “bone density measuring device” corrects the propagation speed of the ultrasonic wave propagating in the bone from the ultrasonic wave propagating in the air, and measures the bone density with high accuracy. Further, Japanese Patent Application Laid-Open No. 9-313483, “Osteoporosis Diagnosis Apparatus” determines acoustic impedance from reflected waves of ultrasonic waves applied to bones, and measures bone density.

[0003]

The conventional measuring method using ultrasonic waves has a problem that it is difficult to grasp the aging rate of the measured value. If the aging rate of the measured value is small, it is difficult to set a cutoff value for discriminating between a normal person and an abnormal person, and it becomes impossible to accurately grasp the properties of the bone. In particular, the rate of decline over time in men is small, and it is difficult to determine the presence of a vertebral fracture or a femoral neck fracture based on minor trauma due to a fall or the like by a conventional measurement method. Therefore, we developed a measurement method that can easily grasp the aging rate of the measured value and can more accurately grasp the properties of the bone, and studied to provide an easy and safe measurement device.

[0004]

[MEANS TO SOLVE THE PROBLEMS] A BUA obtained by irradiating ultrasonic waves to the bone to be measured is developed as a result of the examination.
The value (Broadband Ultrasonic Attenuation: Ultrasonic attenuation value, unit dB / MHz) is multiplied by the BFC value (Bone Frequency Characetristic: bone frequency characteristic value, unit Hz) obtained by analyzing the natural frequency of this bone. Obtained ABS value (Aco
ustic Bone Strength: This is a bone strength measurement method for grasping the properties of the bone based on the magnitude of the acoustic bone strength value (unit: μdB).
The bone to be measured may be freely selected, but it is desirable to measure the calcaneus as seen in the conventional measuring method.

[0005] In the measurement method of the present invention, the BUA value and the BFC value, each having an aging rate, are individually multiplied to obtain an ABS value having a large aging rate, and the ABS value is used to easily and accurately determine the properties of bone. To figure out. The BUA value is an index for evaluating bone quality, and reflects the number of trabecular bones including cortical bone and marine bone. The BFC value reflects the Young's modulus of the bone.
It is known that both values peak at the age of 20 to 30 years and then decline with age, but it is difficult to grasp the secular decline alone. The ABS value is an index that amplifies each aging by multiplying both values and makes it easier to grasp the change. The larger the value, the higher the bone strength can be determined. Also,
Although the BUA value and the BFC value each have the ability to determine the presence or absence of a vertebral compression fracture, the ABS value, which is the product of the two, has improved the discrimination ability.

When implementing the measurement method of the present invention, BUA
Value and BFC value may be measured by a single measuring device, and the ABS value may be obtained by multiplying the BUA value and BFC value that have been digitized by a separate computer, etc., but the BUA value and BFC value may be obtained in a series of operations. The following device may be configured so that measurement can be performed. That is, an ultrasonic measuring unit composed of ultrasonic transmitting and receiving transducers facing each other with a bone to be measured interposed therebetween, a natural vibration measuring unit composed of a piezoelectric element and a vibrating tool in close contact with the bone, and each measuring unit An analysis unit that converts the measured value of the bone into a frequency, and the BUA value and BFC
A bone strength measuring device comprising a calculating unit for specifying a value and calculating an ABS value by multiplying the obtained values.

The ultrasonic measuring section transmits ultrasonic waves from the ultrasonic transmitting transducer toward the bone, receives the ultrasonic waves attenuated by passing through the bone, and receives the ultrasonic waves with the receiving transducer, and measures the energy loss of the ultrasonic waves. I do. The BUA value can be specified by performing frequency conversion on the measurement value of the ultrasonic measurement unit. The natural vibration measurement unit applies vibration to the bone without pain using a vibration tool,
This vibration is detected by the piezoelectric element. The BFC value can be specified by converting the value measured by the natural vibration measuring unit into a frequency. As a vibration tool, a key hammer or a vibration machine for hitting a bone can be used. The piezoelectric element is preferably brought into close contact with the skin covering the bone, and when the bone to be measured is the calcaneus, it is brought into close contact with the calcaneus directly above the Achilles tendon attachment.

The analysis section analyzes the frequency of the measurement value obtained by each measurement section. An FFT is preferable for this frequency analysis, and the measurement value sent to the analysis unit is preferably amplified by an amplifier circuit in advance. The calculation unit specifies the BUA value and the BFC value of the bone based on the result of the analysis unit, and calculates the ABS value by multiplying both the quantified values. It is preferable to use a computer for this arithmetic unit and display the ABS value as a numerical value or a graph on a display.

[0009]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a side view showing a use state of the bone strength measuring device of the present invention, FIG. 2 is a partially broken front view of an ultrasonic measuring unit for obtaining a measurement value serving as a basis of a BUA value, and FIG. FIG. 4 is a cross-sectional view of a piezoelectric element 1 constituting a natural vibration measuring unit for obtaining a measured value, and FIG. 4 is a block diagram of the present device. In this example, the calcaneus and B
The FC value is a device that measures the calcaneus when the supra-wedge is hit with a keying hammer, and finally specifies the ABS value as the bone properties and grasps the bone strength.

First, the structure of the apparatus will be described with reference to FIGS. The measuring table 2 is mounted on the base 3 at an angle, and the foot 5 is placed on the measuring table 2 so that the shin is directed to the foot guide 4 raised by the measuring table 2. With respect to the foot 5, the ultrasonic transmission / reception transducers 6 and 7 constituting the ultrasonic measurement unit sandwich the calcaneus, and the piezoelectric element 1 constituting the natural vibration measurement unit is placed on the skin immediately above the calcaneus Achilles tendon attachment part. They are arranged so as to be in close contact with each other.

[0011] As shown in FIG.
The ultrasonic transmission / reception transducers 6 and 7 are opposed to each other in a positional relationship sandwiching the calcaneus, and approach and separate from each other by an equal amount. Both transducers 6, 7 have an equivalent configuration. An ultrasonic element 10 is mounted in a housing 9 in which a urethane rubber 8 is mounted on an opposing surface. One of the ultrasonic elements 10 is an ultrasonic transmitting transducer that transmits an ultrasonic wave by applying a voltage, and the other is an ultrasonic receiving transducer that receives the ultrasonic wave and measures the ultrasonic wave that has passed through the bone.
Each housing 9, 9 is supported by stands 12, 12, which stand on a box 11 extending in the direction opposite to the transducers 6, 7, and both stands 12, 12 slide with respect to the box 11. The two stands 12, 12 approach and separate by expansion and contraction of an air cylinder 13 controlled by a precision regulator (only the air cylinder 13 is shown with respect to the right stand 12 in FIG. 2). Thereby, at the time of measurement, each transducer 6, 7 can always hold the heel with a constant pressure,
Measurement reproducibility can be ensured. Further, in order to reduce a measurement error due to the difference in the size of the subject's foot, the box 11 is supported on the base 3 by the bracket 14, and the distance of the box 11 to the base 3 is adjusted so that the transducers 6, 7 Height adjustment is possible.

In order to accurately measure only the vibration of the calcaneus in the natural vibration measuring section, it is necessary to isolate the piezoelectric element 1 from unnecessary external vibration. For this reason, as shown in FIG.
, The mounting flange 16 is elastically supported by a spring 18 with respect to the casing body 17, and the casing body 17 is further connected to the base 3 of the measuring device via urethane rubber 19.
It is attached to the upper bracket 20 (see FIG. 1). Each of the urethane rubbers 15 and 19 exerts a vibration damping action against external vibrations, so that the piezoelectric element 1 can accurately measure only the vibration of the calcaneus. In this example, a thin film 23 is attached to a casing head 22 in a cover 21 cut out in an arc shape so that a foot does not directly touch the piezoelectric element 1. The subject makes the heel adhere to the piezoelectric element 1 via the film 23 while bending the film 23 so as to cover the heel to the cover 21.

In addition, as shown in FIG. 1, the measuring device includes amplification circuits 24, 24 for amplifying electric signals from the ultrasonic receiving transducers 6, 7 and the piezoelectric element 1.
FFT as analysis unit for frequency analysis of amplified electric signal
A computer 27 that digitizes signals from the analyzers 25 and 25 and the FFT analyzer 25, calculates BFC values, BUA values, and ABS values, and displays the results on a display 26, and a power supply circuit
28, an ultrasonic transmission device 29, an air compressor 30 for an air cylinder, a keying hammer 31, and the like. FIG. 4 is a block diagram showing these relationships. Hereinafter, the measurement procedure will be described with reference to this block diagram. In the present example, the amplifier circuit 24 and the FFT analyzer 25 are illustrated for each system, however, in actual devices, there are not many devices having two systems of inputs and outputs, and they may be shared.

FIG. 5 is a block diagram showing a state in which an ultrasonic wave is applied to the calcaneus in the ultrasonic measuring unit and an ultrasonic wave passing through the calcaneus is measured. FIG. 6 is a key tap in the natural vibration measuring unit. FIG. 7 is a block diagram showing a state in which vibration of the calcaneus vibrated by the hammer 31 is measured. FIG. 7 shows the obtained BFC value and BUA.
FIG. 7 is a block diagram showing a state in which an ABS value is calculated from a value, and the ABS value is displayed as a result. The measurement order for BUA value and BFC value is free. In this example, the description will be made in the order of the ultrasonic measurement unit and the natural vibration measurement unit.

When the foot 5 is placed on the measuring device, first, as shown in FIG. 5, the ultrasonic oscillator 29 is operated to move the ultrasonic wave from the ultrasonic wave transmitting transducer 6 toward the heel (calcaneus) 32. And received by the opposed ultrasonic wave receiving transducer 7. Each transducer 6, 7 is brought into close contact with the heel 32 in order to suppress the loss due to the propagation of the ultrasonic wave in the air. The intensity of the received ultrasonic wave is output as an electric signal from the ultrasonic wave receiving transducer 7, and the amplified circuit
After amplification at 24, frequency analysis is performed by the FFT analyzer 25 and input to the computer 27. The computer specifies the BUA value from the input signal and stores it. The ultrasonic wave used for the measurement is determined in the range of 200 to 500 kHz.

In this example, the BUA value is specified as follows. Ultrasonic waves propagate while attenuating at different attenuation rates depending on the propagation medium. Therefore, examining this decay rate
There is nothing more than examining the propagation medium, here the calcaneus. Further, the attenuation rate becomes more remarkable as the frequency becomes higher. Therefore, the ultrasonic wave received by the ultrasonic wave receiving transducer is captured as an electric signal, and the electric signal is converted into a power spectrum by FFT, whereby an attenuation rate (sound pressure: dB) for each frequency can be obtained. Here, if the absolute value of the gradient of the attenuation rate with respect to the frequency is obtained, this becomes the BUA value.

Subsequently, as shown in FIG.
Then, the frequency of the calcaneus vibrating by the vibration is measured by the piezoelectric element 1. Unlike the ultrasonic measurement unit, it is necessary to confirm reproducibility in the measurement by the natural vibration measurement unit where the measurer vibrates with the keying hammer 31.
For this reason, measurement is repeated several times, and the obtained BFC value (Hz)
It is good to confirm that the deviation of is less than a certain value. For example, the measurement is repeated three times, and the deviation of the BFC value within 15 Hz is one measure of reproducibility. Tests have shown that the error by the operator is up to 3%. The detected vibration intensity is output as an electric signal from the piezoelectric element 1, amplified by an amplifier circuit 24, analyzed in frequency by an FFT analyzer 25, and input to a computer 27.

In the computer 27, the electric signal is digitized in proportion to the level of the input signal, and this is stored as a BFC value. The calculation based on the algorithm of is used. The so-called natural frequency fc of the porous material varies depending on the material, size, presence or absence and number of holes, fixing conditions at the time of measurement, etc., but a rod-shaped porous material having both ends fixed.
Fc of the (elastic body) can be obtained by the following equation.

[0019]

## EQU1 ## fc = (n / 2L) * (E / ρ) ^1/2

N is a natural number, L is the length of the elastic body, E is the Young's modulus, and ρ is the density. If the length L is constant, fc
Is proportional to the square root of the Young's modulus and inversely proportional to the square root of the density. The following equation is given as an empirical equation for the Young's modulus of the porous substance.

[0021]

E = E ₀ * exp (-d * P)

D is a constant, P is the porosity of the porous material, and E ₀ is the Young's modulus at P = 0. When the equation of E is substituted into the equation of fc, it can be seen that fc is approximately inversely proportional to the porosity. That is, if the size and density of the porous material (elastic body) are constant, fc reflects P.

In general, a frequency measurement value including a vibration of a substance obtained by measurement can be decomposed into a power spectrum by Fourier analysis. Of this power spectrum,
The first peak represents the first harmonic frequency fp of the material. In addition, the amplitude of the vibration of the substance decreases when it receives resistance against the restoring force, and at the same time, the cycle becomes long, that is, the frequency attenuates. At this time, the natural frequency fc of the substance and the first harmonic frequency fp have the following relationship.

[0024]

Fp = ((2πfc) ² −k ² ) ^1/2 / 2π

[0025]

[Expression 4] -ln ( _{Xn + 2} / _Xn ) = (2πk) / ((2πfc) ² −k ² ) ^1/2

K is a constant decay rate and constant, and -ln (X
_{n + 2} / _Xn ) is the logarithmic decay rate. If the constant k is eliminated from both equations, the natural frequency fc of this substance can be obtained by applying the first harmonic frequency fp to the following equation.

[0027]

Fc = fp * (1+ (2π) ⁻² * (ln (X _{n + 2} / X _n )) ² ) ^1/2

As described above, the natural frequency fc of the substance is obtained by reading the damping rate X _{n + 2} / X _n from the vibration waveform, obtaining the first harmonic frequency fp from the power spectrum, and substituting it into the above equation. You can ask. The attenuation rate _{Xn + 2} / _Xn and the first harmonic frequency fp required for the calculation of the natural frequency fc can all be specified by analyzing the vibration waveform detected by the piezoelectric element by a power spectrum obtained by FFT. . For this reason,
In this example, the FFT analyzer 25 is used.

In general, bone is considered to be a kind of porous substance composed of trabecular bone and bone marrow, and it is considered that the natural frequency of bone can be measured by applying the above concept. This seems to be generally valid, as experiments have shown that fc is less susceptible to soft tissue. As described, the natural frequency is inversely proportional to the porosity of a substance, so knowing the natural frequency of a bone means knowing the porosity of the bone, that is, the bone strength.

Here, since fc is inversely proportional to the size of the substance, the calculation result must be corrected based on the size of the bone when using it as an index of bone strength. In this example,
The following equation is used as a correction based on height, and the result of this equation is used as the finally obtained BFC value. ht is height (cm),
Experimentally, it is corrected in a linear proportional relationship with 161 cm as a standard.

[0031]

[Equation 6] BFC = fc * ht / 161 (Hz)

In the computer 25, as shown in FIG. 7, the ABS value is calculated by multiplying the BUA value and the BFC value obtained by the above measurement and calculation based on the algorithm. The calculation result may be displayed on the display 26 as a numerical value, or more visually, in comparison with the average value or the normal value. The measurement for obtaining the BUA value and the BFC value is non-invasive to the body as well as being free from radiation exposure, and the measurement time is short. However, the calculation of the ABS value in a form that amplifies the degree of aging is a more accurate indicator of bone strength and provides useful information for prevention and treatment.

[0033]

EXAMPLES Next, the effectiveness of the present invention was confirmed through specific measurements. In this test, the BUA value and the BFC value were measured with separate measuring devices, respectively, and the ABS values were obtained by multiplying both values quantified by a separate computer. The BUA value was measured for the right calcaneus using CUBA clinical (MuCue). For BFC value, see Bone VibrationAnaly
Using a zer (manufactured by Shoei Technica), measurements were also made on the right calcaneus. The calculated value is a ratio between the annual change rate indicating the secular change of the measured value and the YAM of 80% or less and the YAM of 70% or less calculated from the measured value for each age of the subject from 20 to 44 years old. In addition, 680 men who can walk independently (22 to 89 years old,
Among the average age (55.3 years), 197 patients were examined for the presence or absence of vertebral fractures based on the diagnostic criteria of the Japanese Society for Bone Metabolism from Th11 to L5, and the risk for vertebral fractures was calculated for each measurement value.
Further, with respect to 230 cases, the BMD value in the anterior-posterior direction of the third lumbar vertebra was measured by QDR1000W (manufactured by HOLOGIC), and the data was used as verification data of chronological decline.

From the results of all the tests, the annual rate of change tended to be slightly larger in the early 50s.
Specifically, the BUA value was 1.19% and the BFC value was 0.77%, whereas the ABS value was 1.89%. This decline was most pronounced in the early 70s, with a BUA of 2.1.
The BFC value was 8%, the BFC value was 1.33%, and the ABS value was 3.91%. B
The MD value showed a slight increase with age. In addition, the BAM value, BFC value, and ABS value for 50-54 year olds are each 24.
4%, 7.8%, and 40.4%, respectively, 6.7%, 2.2%, and 22.5% of the total below 70% YAM
Met. From 60 to 64 years old, YA at each value
M80% or less accounted for 43.1% and 13.
They were 9% and 64.8%, respectively, and the percentage of the total of YAM 70% or less was 16.7%, 1.4% and 45.1%, respectively. The risk of vertebral fracture calculated from these factors is BUA value 3.63 times (95% CI, 1.18 to 11.1) and BFC value 1.33 times.
Times (95% CI, 1.22-46.0), and the ABS value is 3.91 times (95% C
I, 1.70-36.5).

From the above results, it can be understood that the ABS value is effective as an index for sensitively detecting the change in bone of a man due to aging. BU by CUBA clinical (MuCue) used this time
The A value is also a sensitive value, but not as high as the ABS value, which proves its effectiveness. In addition, the comparison with the change in the BMD value shows that the ABS value also reflects the presence or absence of a vertebral fracture in men. As described above, according to the present invention, it is possible to more clearly grasp the secular decrease of the bone of a man who could not measure bone strength with high accuracy by the conventional measurement.

Subsequently, with the same configuration of the test apparatus as described above,
The test was performed on the right calcaneus of a woman. The calculated value is
YAM of 80% or less and Y calculated from the measured values of 18-44 years old for each age of the measured person
It is a ratio of 70% or less AM. In addition, as for cases of 4785 women who can walk independently (18-93 years old, average age 54.3 years), Th11
The presence or absence of a vertebral body fracture based on the diagnostic criteria of the Japanese Society for Bone Metabolism from to to L5 was examined, and the risk for the vertebral body fracture for each measurement value was calculated.

From the late 40s to the early 60s, the annual rate of change showed the largest decrease with a BUA value of 2.57%, a BFC value of 1.09%, and an ABS value of 3.49%. This decrease rate is 65 ~
At the age of 75, it slowed down a bit, and in the late 70s, the BUA was 1.81%, the BFC was 1.21%, and the ABS was 3.08%. The BAM, BFC, and ABS values for those aged 50 to 54 years each accounted for 36.
7%, 17.3%, and 52.4%, respectively, and the percentage of total YAM 70% or less was 16.0%, 3.1%, and 33.6%, respectively.
%Met. At the age of 60-64, each value
The percentage of the total of YAM 80% or less is 82.5% and 3
It was 4.0% and 89.4%, respectively, and the percentage of the total of less than 70% YAM was 58.9%, 9.4% and 78.2%, respectively. The risk of vertebral fracture calculated from the above is that the BUA value is 6.45 times (95% CI, 4.37 to 9.51) and the BFC value is 11.8 times (95% C
I, 8.28-16.9), and the ABS value was 14.9-fold (95% CI, 7.59-
29.2).

[0038] Values such as YAM80% and YAM70% are cut-off values for judging bone properties from so-called measured values, but it has been difficult to set a cut-off value by a conventional measuring method. It can be considered that this is because the change in the speed of the ultrasonic wave was only a slight increase or decrease in the speed of the ultrasonic wave under water, irrespective of the deterioration of the bone properties, because the living body was a property close to water. . In addition, in the measurement method for examining the bone properties using many ultrasonic waves, the decrease in the measured value with aging has made it difficult to set the YAM value. In contrast, A
The BS value was sensitive to chronological decline, and it was found that setting the YAM value was relatively easy at aging up to the age of 40 because the decrease was small. Thus, according to the measurement method of the present invention, it was found that even more accurate and favorable measurement of bone strength can be performed for women.

[0039]

According to the method for measuring bone strength of the present invention, it is possible to measure the bone strength of a woman with higher accuracy than before, and it is possible to measure the bone strength of a man with difficulties in the past. , Fracture prevention and prediction. Various methods have already been proposed for ultrasonic measurement for obtaining a BUA value, and results have been achieved. The present invention can utilize such a method. Also, BFC
The measurement method for obtaining the value has been logically and empirically validated, and has high reproducibility. That is, the method for measuring bone strength according to the present invention has high reliability.

The measurement of the BUA value and the BFC value are both simple, and the measuring unit for realizing each measurement is, as described above,
It can be put together by an integrated device configuration. Such a measuring device is useful for performing a series of operations related to the measurement in a well-ordered manner and increasing the measurement efficiency. Further, the integrated devices are convenient to handle, and they have a function of further enhancing the effect of the present invention.

[Brief description of the drawings]

FIG. 1 is a side view showing a use state of a bone strength measuring device of the present invention.

FIG. 2 is a partially broken front view of an ultrasonic measurement unit for obtaining a measurement value serving as a basis of a BUA value.

FIG. 3 is a cross-sectional view of a piezoelectric element constituting a natural vibration measuring unit for obtaining a measurement value serving as a basis of a BFC value.

FIG. 4 is a block diagram of the present apparatus.

FIG. 5 is a block diagram showing a state in which the ultrasonic measurement unit irradiates the calcaneus with ultrasonic waves and measures the ultrasonic waves passing through the calcaneus.

FIG. 6 is a block diagram showing a state in which the natural vibration measuring unit measures the vibration of the calcaneus vibrated by the keying hammer.

FIG. 7 calculates an ABS value from the obtained BFC value and BUA value,
FIG. 6 is a block diagram showing a state in which the ABS value is displayed as a result.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Piezoelectric element 6 Transducer for ultrasonic transmission 7 Transducer for ultrasonic reception 25 FFT analyzer 26 Display 27 Computer 32 Heel (calcaneus)

Continuation of the front page F term (reference) 4C301 AA06 DD15 DD18 DD30 EE11 EE19 GA11 JB34 JB50 JC16 KK40 LL20

Claims (2)

[Claims] 1. An acoustic device obtained by multiplying an ultrasonic attenuation value obtained by irradiating an ultrasonic wave to a bone to be measured with a bone frequency characteristic value obtained by analyzing a natural frequency of the bone. A bone strength measuring method characterized by ascertaining the properties of a bone based on the magnitude of a target bone strength value. 2. An ultrasonic measuring unit comprising ultrasonic transmitting and receiving transducers facing each other with a bone to be measured interposed therebetween, and a natural vibration measuring unit comprising a piezoelectric element and a vibrator in close contact with the bone. An analysis unit that converts the measured value of each measurement unit into a frequency, and an ultrasonic attenuation value and a bone frequency characteristic value of the bone are specified from the result of the analysis unit, and the obtained values are multiplied to obtain an acoustic bone strength value. And a calculation unit for calculating the bone strength.