JPH09140703A - Method for diagnosing osteoporosis and device therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To exactly estimate the state of bone density and to easily perform high-reliability diagnosis. SOLUTION: An ultrasonic impulse is radiated toward the cortical bone, echo (almost not mixing noise) returned from the surface of the lower part of the tibia is received, and the echo level is measured by an A/D converter 8, etc., later. A CPU 11 extracts the maximum echo level among measured echo levels and calculates the coefficient of ultrasonic wave reflection on the interface between the soft tissue of an examinee and the lower part of the bone of the neck. Next, an acoustic impedance at the lower part of the tibia is calculated based on the calculated ultrasonic wave reflection coefficient, and the bone density of the examinee is calculated from the calculated acoustic impedance. Since the acoustic impedance at the lower part of the tibia is expressed by the square root of 'elastic modulus × density' of the cortical bone when the bone density is decreased and the elastic modulus is lowered, the acoustic impedance is remarkably decreased sensitively in response to the synergistic effect of these factors. Therefore, the acoustic impedance at the lower part of the tibia becomes a good index for judging the bone density.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an osteoporosis diagnosing method and osteoporosis for diagnosing osteoporosis by radiating an ultrasonic impulse toward a predetermined cortical bone of a subject and measuring an echo level from the surface of the cortical bone. Regarding diagnostic equipment.

[0002]

2. Description of the Related Art In recent years, with the advent of an aging society, a bone disease called osteoporosis has become a problem. this is,
It is a disease that causes calcium to escape from bones and becomes scuffed and easily broken with a slight shock, which is one of the causes of so-called bedridden elderly people. The physical diagnosis of osteoporosis is mainly performed by precisely measuring the bone density with a diagnostic device using X-rays such as DXA, but the physical diagnosis with X-rays requires a large-scale device. In addition, there is a troublesome problem in that it is subject to various restrictions from the viewpoint of preventing radiation exposure damage.

[0003] As a simple device that does not cause such inconveniences at all, diagnostic devices using ultrasonic waves have begun to spread. A diagnostic device that uses ultrasonic waves measures the speed of sound and attenuation when the ultrasonic waves propagate through bone tissue,
The bone density and the elastic modulus (elastic strength) of the bone are estimated, and if a low estimated value is obtained, it can be considered that calcium has escaped from the bone, so that osteoporosis is diagnosed. For example, in the diagnostic device disclosed in Japanese Patent Application Laid-Open No. 2-104337, one ultrasonic transducer emits an ultrasonic impulse toward the bone tissue of the subject, which is the measurement site, and the ultrasonic pulse transmitted through the bone tissue is detected. The ultrasonic wave is received by the other ultrasonic transducer to measure the speed of sound in the bone tissue, and the slower the speed of sound in the bone tissue is, the more it is diagnosed that osteoporosis is progressing. This is because the diagnostic apparatus operates on the assumption that the speed of sound is proportional to the bone density in bone tissue.

[0004]

However, the theoretical basis for linking the bone density with the speed of sound is uncertain. Strictly speaking, the speed of sound in bone tissue is not proportional to the bone density, Elastic modulus / bone density]. Moreover, since the elastic modulus of bone and the bone density contribute to the speed of sound in such a way that the elastic modulus of bone increases as the bone density increases, the speed of sound in the bone tissue increases as the bone density increases. It cannot respond sensitively, and the correlation coefficient between sound speed and bone density in bone tissue is never high. Therefore, it has been impossible to obtain a highly reliable diagnosis from a conventional diagnostic device that estimates the bone density and the elastic modulus of the bone from the measurement results of the sound velocity and the attenuation of the ultrasonic wave in the bone tissue.

The present invention has been made in view of the above-mentioned circumstances, and despite the fact that it is a simple type without fear of radiation exposure, it can estimate the bone density much more accurately than in the past and has a highly reliable diagnosis. An object of the present invention is to provide an ultrasonic reflex-type osteoporosis diagnostic device capable of performing the following.

[0006]

In order to solve the above problems, the osteoporosis diagnosing method according to the invention of claim 1 applies an ultrasonic transducer to the skin surface covering the lower part of the tibia of the subject, and the ultrasonic impulse is applied to the skin surface. Emitted repeatedly to the cortical bone of the lower tibia, receives the echo returning from the surface of the cortical bone to measure the echo level, and further extracts the maximum echo level from the measured echo levels, A feature of the present invention is that osteoporosis is diagnosed by performing a predetermined arithmetic processing based on the extracted maximum echo level.

Further, in the invention according to claim 2, the ultrasonic transducer is applied to the skin surface covering the lower part of the tibia of the subject, and ultrasonic impulses are repeatedly emitted toward the cortical bone of the lower part of the tibia to generate a cortex of the lower part of the tibia. An ultrasonic reflex-type osteoporosis diagnostic device for diagnosing osteoporosis by receiving the echo returning from the bone surface and measuring the echo level, and extracting the maximum echo level from the measured echo levels. Maximum echo level extraction means for performing, and a reflection coefficient calculation describing a processing procedure for calculating an ultrasonic reflection coefficient at the interface between the soft tissue of the subject and the cortical bone of the lower tibia based on the maximum echo level. A program and a processing procedure for calculating the density of the cortical bone of the subject by using a predetermined regression equation regarding the ultrasonic reflection coefficient of the density of the cortical bone are described. And bone density calculating program,
A memory for storing various processing programs including the reflection coefficient calculation program and the bone density calculation program, and temporarily storing various data including the measured echo level and the extracted maximum echo level, and the reflection coefficient calculation By executing a program and the bone density calculation program, the ultrasonic reflection coefficient is calculated based on the maximum echo level extracted by the maximum echo level extraction means, and then the calculated ultrasonic reflection coefficient is calculated. And a bone density calculating means for calculating the density of the cortical bone of the subject based on the above.

According to the invention of claim 3, the ultrasonic transducer is applied to the skin surface covering the lower tibia of the subject, and ultrasonic impulses are repeatedly emitted toward the cortical bone of the lower tibia, and the cortex of the lower tibia. An ultrasonic reflex-type osteoporosis diagnostic device for diagnosing osteoporosis by receiving the echo returning from the bone surface and measuring the echo level, and extracting the maximum echo level from the measured echo levels. Maximum echo level extraction means for performing, and a reflection coefficient calculation describing a processing procedure for calculating an ultrasonic reflection coefficient at the interface between the soft tissue of the subject and the cortical bone of the lower tibia based on the maximum echo level. A program and an acoustic impedance that describes a processing procedure for calculating the acoustic impedance of the cortical bone based on the ultrasonic reflection coefficient A calculation program, a bone density calculation program describing a processing procedure for calculating the density of the cortical bone of the subject using a predetermined regression equation relating to the acoustic impedance of the density of the cortical bone, the reflection coefficient calculation program, and the above. A memory for storing various processing programs including the acoustic impedance calculation program and the bone density calculation program, and temporarily storing various data including the measured echo level and the extracted maximum echo level, and the reflection coefficient calculation program By executing the acoustic impedance calculation program and the bone density calculation program, the ultrasonic reflection coefficient is calculated based on the maximum echo level extracted by the maximum echo level extraction means, and then calculated. Based on the ultrasonic reflection coefficient Calculates the acoustic impedance of quality bone, then it is characterized by comprising a bone density calculation means for calculating the density of the cortical bone of said subject based on the calculated the acoustic impedance.

[0009]

In the configuration of the present invention, the acoustic impedance of cortical bone is represented by the square root of [elastic modulus × density] of cortical bone, so that the elastic modulus increases with increasing bone density.
Since it receives a synergistic effect, it responds sensitively above the speed of sound and significantly increases. On the contrary, when the bone density is decreased and the elastic modulus is decreased, the acoustic impedance undergoes these synergistic effects, and the acoustic impedance significantly decreases in response to the sound velocity and higher. In addition, since the measurement site is limited to the cortical bone of the lower tibia where there is less noise, it is possible to measure the echo level with good reproducibility, and along with this, the maximum echo level can be extracted more accurately. became. Therefore, the acoustic impedance of the cortical bone below the tibia is a good index for determining the bone density. For example, when the acoustic impedance of the lower tibia is significantly smaller than the average value of the age group, it can be seen that cortical osteoporosis is aggravated.
It should be noted that, according to the experiment, even in the cortical bone of the lower tibia, noise is significantly reduced particularly in the range of 40 mm to 100 mm above the ankle. Therefore, of the cortical bone under the tibia, 40 mm to 100 mm above the ankle
The range of is most suitable as the measurement site.

Further, instead of using the acoustic impedance of cortical bone in the lower tibia as an index of bone density, the ultrasonic reflection coefficient at the interface between soft tissue and the cortical bone in the lower tibia is a monotonically increasing function of the acoustic impedance of cortical bone. Even if is used as an index of bone density, the same effect as described above can be obtained.

[0011]

Embodiments of the present invention will be described below with reference to the drawings. The description will be specifically made using an embodiment. First Embodiment FIG. 1 is a block diagram showing an electrical configuration of an osteoporosis diagnostic apparatus according to a first embodiment of the present invention, FIG. 2 is a schematic external view showing the external appearance of the apparatus, and FIG. , FIG. 4, FIG. 5, and FIG. 6 are explanatory diagrams used to explain the operation of the apparatus, and FIG.
Is a flow chart showing the flow of the operation of the device,
FIG. 8 is a graph showing a regression line relating to the acoustic impedance Zb of the density ρ of cortical bone, and is a diagram used for explaining a bone density calculation subprogram that constitutes the same apparatus.
As shown in FIGS. 1 and 2, the osteoporosis diagnosing device of this example responds to each time a half-wave impulse electric signal is input in a predetermined cycle, in response to the electric signal of the half-wave impulse. An ultrasonic impulse is emitted toward the cortical bone (hereinafter also simply referred to as the lower tibia), and the echo (reflected wave) returned from the surface of the lower tibia is received and converted into a received signal (electrical signal). And an ultrasonic transducer (hereinafter, simply referred to as a transducer) 1 for supplying a half-wave impulse electric signal to the transducer 1 and processing the received signal output from the transducer 1 to process an echo level from the lower surface of the tibia. Device body 2 for diagnosing osteoporosis by extracting (amplitude of reflected wave)
And a cable 3 for connecting the transducer 1 and the apparatus body 2 to each other.

The transducer 1 is mainly composed of an ultrasonic vibrator 1a having electrode layers on both sides of a disk-shaped thickness vibrating piezoelectric element such as lead zirconate titanate (PZT). In order to remove the effect of transmission reverberation on one electrode surface (transmission / reception surface of ultrasonic impulse),
An ultrasonic wave delay spacer 1b such as polyethylene bulk is fixed. Here, in order to perform a highly accurate measurement, it is desirable that an ultrasonic wave impulse close to a plane wave can be radiated from the wave transmission / reception surface of the transducer 1 toward the cortical bone, and an echo close to a plane wave returns from the cortex bone to the wave transmission / reception surface. Therefore, as the transducer 1, it is preferable to use a piezoelectric element having a relatively large disc radius so that the transmitting / receiving surface is as wide as possible.

From the same viewpoint, it is preferable to use cortical bone, which has a large radius of curvature and can be regarded as a flat surface and is close to the surface of the skin, as the measurement site. Therefore, the inventors of this application, as a result of measuring the cortical bone of various parts of the human body, in cortical bone other than the lower tibia, the cause of the occurrence of the echo from the cortical bone in a part other than the cortical bone is unknown. It was found that the echoes of the same tended to overlap, and the measurement reproducibility was not very good. On the other hand, as shown in FIG. 3, such noise is rarely mixed in the lower tibia Mb. Especially, Ankle Mc
It was found that in the range K of 40 mm to 100 mm above, the noise was hardly mixed, and the frequency of extracting only the echo from the lower tibial Mb alone was much higher than that of the cortical bone in other regions. Therefore, in this embodiment, the measurement site is limited to the cortical bone of the lower tibia where the noise is less mixed, and particularly 40 mm to 1 above the ankle Mc.
The range of 00 mm was set as the optimum measurement site K.

The device body 2 includes a pulse generator 4, a matching circuit 5, an amplifier 6, a waveform shaper 7, an A / D converter 8, a ROM 9, a RAM 10, and a CPU (central processing unit). 11, a level meter 12, and a display unit 13. The pulse generator 4 is connected to the transducer 1 via the cable 3 and has a center frequency of approximately 2.5.
An electric signal of a half-wave impulse of MHz is repeatedly generated at a predetermined cycle (for example, 100 msec) and transmitted to the transducer 1. The matching circuit 5 performs impedance matching between the transducer 1 connected via the cable 3 and the apparatus body 2 so that signals can be transmitted and received with maximum energy efficiency. Therefore, the received signal is output from the transducer 1 every time the ultrasonic transducer 1a of the transducer 1 receives the echo from the lower tibia,
Through the matching circuit 5, the amplifier 6 without loss of energy
Is input to The amplifier 6 amplifies the received signal input via the matching circuit 5 with a predetermined amplification degree and then inputs it to the waveform shaper 7. The waveform shaper 7 is composed of a band-pass filter having an LC structure, performs a filtering process on the received signal amplified by the amplifier 6, and linearly shapes the noise to remove a noise component, and then the A / D converter 8 To enter. A
The / D converter 8 includes a sample hold circuit (not shown), a sampling memory (SRAM), and the like, and the waveform shaper 7 to be input according to the sampling start request of the CPU 11 is input.
Output signal (waveform-shaped analog received signal) is sampled at a predetermined frequency (for example, 12 MHz) and sequentially converted into a digital signal, and the obtained digital signal is temporarily stored in its own sampling memory, and then the CPU 11 Send to.

The ROM 9 is, in addition to the operating system (OS), various processing programs of the CPU 11, specifically, a maximum echo level extraction subprogram, a reflection coefficient calculation subprogram, an acoustic impedance calculation subprogram, and a bone density calculation subprogram. Etc. are stored.
The maximum echo level extraction sub-program is a procedure for fetching a digital signal from the sampling memory of the A / D converter 8 for each one pulse and detecting the echo level for each echo, and the procedure for detecting the echo level for each echo. The processing procedure for extracting the maximum echo level from the echo levels is written. The reflection coefficient calculation sub-program is based on the value of the maximum echo level given by the maximum echo level extraction sub-program, and the ultrasonic reflection at the almost vertical reflection at the interface between the soft tissue of the subject and the lower tibia (measurement site) The processing procedure for calculating the coefficient R is written.

In the acoustic impedance calculation subprogram, the calculation procedure of the acoustic impedance Zb containing the equation (1) is written based on the calculated value of the ultrasonic reflection coefficient R given by the reflection coefficient calculation subprogram. .

## EQU1 ## Zb = Za (R + 1) / (1-R) (1) Za: Acoustic impedance of soft tissue Formula (1) is derived from Formula (2). When the surface of the lower tibial Mb can be regarded as a plane, the ultrasonic impulse emitted from the transducer 1 can also be regarded as a plane wave, and the wavefront is parallel to the surface of the lower tibial Mb (when the light is incident almost vertically). , The echo level is expressed by equation (2). As will be described later, the echo level becomes maximum when the wavefront of the plane wave and the surface of the lower tibia Mb are parallel. Therefore, the echo level given by equation (2) is the maximum echo level.

## EQU2 ## R = (Zb-Za) / (Zb + Za) (2)

Further, the bone density calculation subprogram is based on the calculated value of the acoustic impedance Zb given by the acoustic impedance calculation subprogram, and the bone density of the subject (the density of cortical bone in general) containing the expression (3). The procedure for calculating ρ is described. Where equation (3)
Is a regression equation regarding the acoustic impedance Zb of the bone density ρ, and is obtained by carrying out a sample survey in advance, as shown in FIG.

[Formula 3] ρ = αZb + β = 1.80 × 10 ⁻⁴ Zb + 766 (3) ρ: Density of general cortical bone [kg / m ³ ] Zb: Acoustic impedance of lower tibia [kg / m ² sec] α: Bone Regression coefficient of density to acoustic impedance [s
ec / m] β: intercept [kg / m ³ ]

In the above-mentioned sample investigation, the acoustic impedance Zb is measured for the cortical bone under the tibia by applying the ultrasonic reflection method, and the density ρ of the cortical bone Mb is the X-ray (for the bone of the arm) of the radius (arm bone). QCT). As a result of this sample survey, acoustic impedance Zb and X-ray (QC
The bone density ρ measured in T) was found to have a high correlation (r = 0.67). As a result of performing the statistical hypothesis test, when the value of the acoustic impedance Zb of the lower tibia of any subject is Zb, the probability (reliability) that the bone density ρ of the subject falls within the range of ρmin to ρmax is 95%. is there. Therefore, the risk rate is 5%. Here, ρmin is the equation (4)
Thus, ρmax is given by the equation (5).

## EQU4 ## ρmin = (1.80 × 10 ^-4 -30%) Zb + (766-16%) (4)

## EQU00005 ## .rho.max = (1.80 × 10 ^-4 + 30%) Zb + (766 + 16%) (5)

The RAM 10 has a working area in which a work area of the CPU 11 is set and a data area for temporarily storing various data. In the data area, the echo level detected most recently (hereinafter referred to as the echo level this time). ) And an echo level memory area that stores the maximum echo level, an echo waveform memory area that stores the most recently detected echo waveform (current echo waveform) and the maximum echo waveform, and a measurement continuation flag that stores information as to whether or not to continue the measurement. Etc. are set.

The CPU 11 executes the above-mentioned various processing programs stored in the ROM 9 by using the RAM 10 to control the pulse generator 4, the A / D converter 8 and other parts of the apparatus, and 1 pulse 1 The echo level is detected for each echo, the maximum echo level is further extracted from the echo level, and the bone density ρ of the subject is calculated based on the value of the extracted maximum echo level to diagnose osteoporosis.

The level meter 12 is controlled by the CPU 11 and indicates the current echo level stored in the RAM 10 as the deflection of the liquid crystal pointer pattern 12a indicated by the broken line in FIG. 2 and the largest echo detected so far. The maximum echo level, which is the level, is simultaneously displayed as the deflection of the liquid crystal pointer pattern 12b shown by the solid line in the figure. The display 13 is composed of a CRT display or a liquid crystal display, and under the control of the CPU 11, measured values such as echo level, ultrasonic reflection coefficient R, acoustic impedance Zb, calculated value of bone density ρ, and echo waveform are displayed on the screen. To be done.

Next, the operation of this example (the flow of processing of the CPU 11 at the time of diagnosing osteoporosis) will be described with reference to FIGS. When the device is powered on, C
The PU 11 waits for the measurement start switch to be pressed down after presetting each part of the apparatus, initializing counters, various registers, and various flags (step SP10 (FIG. 7)). Here, the operator, as shown in FIG. 4, selects one of the left and right lower tibial parts of the lower tibial Mb on one side.
Surface of soft tissue Ma covering (optimum measurement site K between 40 mm and 100 mm above ankle Mc) (skin surface X)
A state in which the ultrasonic gel 14 is applied diagonally to the front side (between the front side and the inner side), the transducer 1 is pressed against the surface X of the skin via the ultrasonic gel 14, and the transmitting / receiving surface is directed to the lower tibial Mb. Then, turn on the measurement start switch. When the measurement start switch is turned on (step SP11), C
The PU 11 writes "1" in the measurement continuation flag to set the measurement continuation flag, and then starts the diagnostic operation according to the processing procedure shown in FIG. 7 (mainly, the procedure described in the maximum echo level extraction subprogram). To do.

The CPU 11 first sets the pulse generator 4 to 1
A pulse generation command is issued (step SP12). When the pulse generator 4 receives a one-pulse generation command from the CPU 11, the pulse generator 4 outputs a half-wave impulse electric signal to the transducer 1.
Send to When the transducer 1 receives the electric signal of the half-wave impulse from the pulse generator 4, the transducer 1 emits an ultrasonic impulse Ai close to a plane wave toward the lower tibia Mb of the subject. The emitted ultrasonic impulse Ai is
As shown in FIG. 5, it is injected into the soft tissue Ma from the surface X of the skin and propagates toward the lower tibia Mb. Then, a part is reflected on the surface Y of the lower tibia Mb to become an echo Ae, a part is absorbed by the lower tibia Mb, and the rest is the lower tibia Mb.
b is transmitted. The echo Ae follows the path opposite to that of the incident ultrasonic wave Ai, and is received again by the ultrasonic transducer 1a of the transducer 1. In the transducer 1, when the ultrasonic impulse Ai is emitted toward the lower tibia Mb, as shown in the figure, first, the transmission reverberation An ₁ is followed by the echo An ₂ from the surface X of the skin with a slight delay. ,
The echo Ae from the lower tibia Mb is received by the ultrasonic transducer 1a and converted into a received signal (electrical signal) corresponding to the waveform and amplitude of the ultrasonic wave. The received signal generated is passed through the cable 3 to the device body 2 (matching circuit 5).
Input to the amplifier 6, amplified by the amplifier 6 with a predetermined amplification degree, and linearly shaped by the waveform shaper 7,
It is input to the / D converter 8.

The CPU 11 sends a 1-pulse generation command to the pulse generator 4 (step SP12), and then the transmission reverberation An ₁ by the ultrasonic transducer 1a of the transducer _1.
Is received, and then an echo An ₂ from the surface X of the skin is received.
Is received, a sampling start command is issued to the A / D converter 8 at the time when the echo Ae from the lower tibia Mb returns to the wave transmission / reception surface of the ultrasonic transducer 1a of the transducer 1. Step SP13). When the A / D converter 8 receives a sampling start command from the CPU 11, the A / D converter 8 performs waveform shaping from the waveform shaper 7 and then receives the received echo signal from the lower tibia Mb at a predetermined frequency (for example, 12 MHz). ), It converts into a digital signal, and the obtained N sample values (digital signal for one echo) are temporarily stored in its own sampling memory. After that, when there is a transfer request from the CPU 11, the N sample values stored in the sampling memory are sent to the CPU.
11 is sequentially sent. The CPU 11 sequentially takes in N sample values from the A / D converter 8 and stores them as the current echo waveform in the echo waveform memory area of the RAM 10 and extracts the largest value from the N sample values. As a result, the echo level is detected this time, and the detection result is stored in the echo level memory area of the RAM 10 (step SP14). The current echo level stored in the echo level memory area of the RAM 10 is displayed on the level meter 12 by the liquid crystal pointer pattern 1 as shown by the broken line in FIG.
It is displayed as a shake of 2a (step SP15).

Next, the CPU 11 reads the current echo level and the maximum echo level from the echo level memory area in the RAM 10 and determines whether or not the value of the current echo level is larger than the value of the maximum echo level ( Step SP16). At this time, it is the first judgment, and the maximum echo level value remains the initial setting value "0".
The U11 judges that the value of the current echo level is larger than the value of the maximum echo level, rewrites the value of the maximum echo level stored in the echo level memory area of the RAM 10 with the value of the current echo level, and further, the RAM10
The maximum echo waveform stored in the echo waveform memory area of is rewritten to the current echo waveform (step SP1).
7). Then, the updated maximum echo waveform is displayed on the display unit 1.
3 and the updated maximum echo level is displayed on the level meter 12 as the deflection of the liquid crystal pointer pattern 12b as shown by the solid line in FIG. 4 (step S).
P18).

Next, the CPU 11 looks at the measurement continuation flag in the RAM 10 (step SP19), and if the measurement continuation flag is set (when the content of the measurement flag is "1"), the CPU 11 determines that the measurement is continued. After making a determination and repeating the above-described one-pulse emission and one-echo reception (steps SP12 to SP15), in step SP16, RA
The current echo level and the maximum echo level are read from the echo level memory area in M10, and it is determined whether or not the value of the current echo level is larger than the value of the maximum echo level. If the result of this determination is that the current echo level is not higher than the maximum echo level this time, the update process is not performed and the process directly goes to step SP19 to check the measurement continuation flag. The content of the measurement continuation flag is kept at "1" unless the operator presses the measurement end switch, and the CPU 11
1 pulse emission and 1 echo reception (step SP12-
SP15), maximum echo level extraction work (step S
Repeat P16 to step SP19).

While the CPU 11 repeats the above-described processing (steps SP12 to SP19), the operator indicates the arrow R in FIG.
, The transducer 1 is applied to the surface X of the skin and directed toward the lower tibial Mb, which is the measurement site, and sometimes a circle is drawn like a precession motion of a coma, and sometimes diagonally like a seesaw in front, rear, left and right directions. While shaking or changing the direction of the transducer 1, the direction in which the liquid crystal pointer patterns 12a and 12b of the level meter 12 are shaken to the maximum, that is, the direction in which the maximum echo level is detected is searched. Level meter 12
The maximum deflection of the liquid crystal pointer patterns 12a and 12b is when the normal line of the lower tibial Mb and the normal line of the wave transmitting / receiving surface of the transducer 1 coincide with each other, as shown in FIG. 6 (a). This is when the wavefront of the plane-wave ultrasonic impulse Ai and the surface Y of the lower tibia Mb are substantially parallel (when the plane-wave ultrasonic impulse Ai is substantially perpendicular to the surface Y of the lower tibia Mb). Because, when both normals coincide with each other, the surface Y of the lower tibia Mb as shown in FIG.
Since the echo Ae that is vertically reflected at returns to the wave transmission / reception surface of the transducer 1 perpendicularly, the wave front of the echo Ae is also aligned substantially parallel to the wave transmission / reception surface. Therefore, the echo due to the difference in the wave reception position on the wave transmission / reception surface. This is because the phase shift of Ae is minimized, so that the received signal is less likely to cancel the peaks and troughs, and therefore the echo Ae having the maximum echo level is received. On the other hand, when the two normals do not match, the wavefront of the echo Ae is not uniform on the transmitting / receiving surface as shown in FIG. 6B, so the received signal is small because the peaks and troughs cancel each other out. Become.

By the way, in the diagnostic apparatus of this example, in order to improve the diagnostic accuracy, the echo Ae returned by vertical reflection is used.
Is assumed to be extracted. This is because, in the acoustic impedance calculation subprogram described above, the equation (1) for deriving the acoustic impedance Zb from the ultrasonic reflection coefficient R at the time of substantially vertical reflection is, as described above, the substantially vertical reflection from the lower tibial Mb and the echo Ae. This is because it is an expression that holds when returning. Therefore, the operator is
If the echo level is maximized when the angle of is changed near the normal to the lower tibial Mb, it is considered that the echo Ae reflected almost vertically on the surface Y of the lower tibial Mb returns to the transmitting / receiving surface of the transducer 1. You can The liquid crystal pointer patterns 12a and 12b of the level meter 12 change sensitively when the normal line of the lower tibial Mb and the normal line of the transmitting / receiving surface change significantly, but when both normal lines substantially match. , It is relatively easy to find the echo Ae of the vertical reflection because the change becomes dull.

When the operator looks at the shake of the liquid crystal pointer patterns 12a and 12b of the level meter 12 and determines that the maximum echo level can be extracted, he depresses the measurement end switch. When the measurement end switch is pressed, the CPU 11
Resets the content of the measurement continuation flag to "0" and lowers the measurement continuation flag by interrupt processing. When the measurement continuation flag is cleared, the CPU 11 causes the next 1 and subsequent 1
The pulse emission is stopped (step SP19). And
The maximum echo level stored in the echo level memory area of the RAM 10 is read and displayed on the display 13 (step SP20).

After that, the CPU 11 executes the reflection coefficient calculation sub-program so that the maximum echo level V1 stored in the echo level memory area of the RAM 10 is reached.
And the complete echo level V0 previously written in the reflection coefficient calculation subprogram, the ultrasonic reflection coefficient R at the interface between the soft tissue Ma of the subject and the lower tibia Mb is calculated (step SP21), and the calculated value is calculated. Is displayed on the display 13 (step SP22). Here, the ultrasonic reflection coefficient R is the perfect echo level V when completely perpendicularly reflected.
Ratio of 0 to maximum echo level V1 [R = V1 / V0]
Is derived from The complete echo level V0 can be theoretically calculated, but can also be found by preparing a dummy block of plastic or the like and measuring the echo level.

Next, the CPU 11 substitutes the value of the ultrasonic reflection coefficient R given by the reflection coefficient calculation subprogram into the equation (1) according to the acoustic impedance calculation subprogram, and substitutes the acoustic impedance Z of the lower tibia Mb.
b [kg / m ² sec] is calculated (step SP23), and the calculation result is displayed on the display 13 (step SP24).

Next, the CPU 11 substitutes the value of the acoustic impedance Zb of the lower tibia Mb given by the acoustic impedance calculation subprogram into the equation (3) according to the bone density calculation subprogram to calculate the bone density ( In step SP25), the calculation result is displayed on the screen of the display 13 (step SP26).

According to the above construction, since the echo Ae of vertical reflection in which the level change of the echo from the lower tibia is blunted with respect to the displacement (vibration of the transducer 1) is utilized, the maximum echo level can be easily extracted, and Can be extracted with good reproducibility. In addition, since the liquid crystal pointer pattern 12a constantly displays the echo level this time and the liquid crystal pointer pattern 12b also permanently displays the maximum echo level on the level meter 12, it is easier to search for the maximum echo level. Becomes Therefore, the acoustic impedance Zb of the lower tibia Mb can be accurately obtained.

Acoustic impedance Zb of lower tibial Mb
Is represented by the square root of [elastic modulus × density] of the lower tibial Mb, and therefore the elastic modulus increases as the bone density increases. Increase to. On the contrary, when the bone density decreases and the elastic modulus decreases, the acoustic impedance Zb receives these synergistic effects and responds sensitively above the speed of sound, and decreases significantly. Therefore, the acoustic impedance Zb of the lower tibia Mb
Is a good indicator for determining bone density. Therefore, the operator operates the lower tibia M displayed on the display unit 13.
The progress of osteoporosis can be accurately estimated from the value of the acoustic impedance Zb of b. For example, when the acoustic impedance is significantly smaller than the average value of that age group, it can be seen that osteoporosis is aggravated.

Second Embodiment Next, a second embodiment of the present invention will be described. In the second embodiment, a reflection coefficient calculation subprogram (algorithm) different from that in the first embodiment is adopted. Except for this, the configuration is substantially the same as that of the first embodiment. That is, in the reflection coefficient calculation subprogram of the second embodiment, the ultrasonic reflection coefficient R at the time of substantially vertical reflection at the interface between the soft tissue Ma and the lower tibia Mb can be regarded as the plane wave of the ultrasonic impulse Ai and the echo Ae. , And the attenuation of the ultrasonic wave in the soft tissue Ma can be ignored, and is calculated by the equation (6).

[0036]

## EQU00006 ## R = Ve / P.Q.B.Vi (6) where P: When a unit electric signal (voltage, current, scattering parameter, etc.) is applied to the transducer 1, it is substantially perpendicular to the transducer 1. Sound pressure of ultrasonic impulse Ai output in the direction Q: Amplitude B of the received signal (electrical signal) output from transducer 1 when echo Ae of unit sound pressure is incident on the transmitting / receiving surface of transducer 1 substantially vertically : Product of amplitude amplification of amplifier 6 and amplitude of waveform shaper 7 Vi: Amplitude of electric signal applied to transducer 1 from pulse generator 4 Ve: Maximum echo level P, Q, B, Vi , Are both functions of frequency, but here, the component at the center frequency (for example, 2.5 MHz) is used. Regarding P, Q, B and Vi,
These measured values and set values are written and stored in the ROM 9 (reflection coefficient calculation subprogram in this example).

Equation (6) is derived as follows. First, the amplitude Vi from the pulse generator 4 to the transducer 1
Is applied, the ultrasonic wave impulse Ai of the sound pressure PVi is output from the transmitting / receiving surface of the transducer 1 toward the lower tibia Mb. Therefore, the echo Ae of the sound pressure RPVi returns perpendicularly to the transmitting / receiving surface of the transducer 1. Therefore, the maximum echo level Ve is given by the equation (7).

## EQU00007 ## Ve = Q.R.P.B.Vi ... (7) From equation (7), equation (6) is derived.

As described above, also with the configuration of the second embodiment, the CPU 11 causes the soft tissue Ma and the lower tibia Mb to be operated.
Since the acoustic impedance Zb of the lower tibial Mb is calculated from the ultrasonic reflection coefficient R at the interface with, it is possible to obtain substantially the same effect as in the first embodiment described above.

Although the embodiment of the present invention has been described in detail with reference to the drawings, the specific configuration is not limited to this embodiment, and there are design changes and the like that do not depart from the gist of the present invention. Is also included in the present invention. For example, the ultrasonic transducer forming the transducer is not limited to the thickness vibration type, but may be the bending vibration type. The acoustic impedance of the soft tissue Ma is 1.5 × 10 ⁶ of the acoustic impedance of water.
Since it is close to [kg / m ² sec], the acoustic impedance of water may be used instead of the acoustic impedance of the soft tissue Ma in the calculation of the ultrasonic reflection coefficient by applying the formula (1). Further, various processing programs of the CPU 11 are RO
Instead of storing it in M9, it may be stored in an external storage device such as a hard disk if necessary.

The method of calculating the ultrasonic reflection coefficient R is not limited to the method described in the above embodiment. For example, when one end face of the transducer 1 is set as a free end and an echo from the one end face is observed. Since the ultrasonic wave is completely reflected at one end face, the reflection level at this time becomes equal to the level of the incident wave. Therefore, the ultrasonic reflection coefficient R can also be obtained as the ratio of the level of this incident wave and the echo level from the cortical bone Mb. Further, instead of using the acoustic impedance Zb of the lower tibia Mb as an index of the bone density ρ, the ultrasonic reflection coefficient R at the interface between the soft tissue Ma and the lower tibia Mb, which is a monotonically increasing function of the acoustic impedance Zb of the lower tibia Mb, is determined by the bone. As an index of the density ρ, it is possible to obtain substantially the same effect as that of the first embodiment.

[0041]

As described above, according to the structure of the present invention, the acoustic impedance of cortical bone is represented by the square root of [modulus of elasticity × density] of cortical bone. Due to the synergistic effect of increasing the elastic modulus, it responds sensitively above the speed of sound and significantly increases. vice versa,
When the bone density is decreased and the elastic modulus is decreased, the acoustic impedance undergoes these synergistic effects, and the acoustic impedance is significantly decreased in response to the sound velocity and above. In addition, since the measurement site is limited to the cortical bone of the lower tibia where there is less noise, it is possible to measure the echo level with good reproducibility, and along with this, the maximum echo level can be extracted more accurately. became. Therefore, the acoustic impedance of the cortical bone below the tibia is a good index for determining the bone density. For example, when the acoustic impedance of the lower tibia is significantly smaller than the average value of the age group, it can be seen that cortical osteoporosis is aggravated.

Further, instead of using the acoustic impedance of the cortical bone of the lower tibia as an index of bone density, the ultrasonic reflection coefficient at the interface between soft tissue and the cortical bone of the lower tibia is a monotonically increasing function of the acoustic impedance of the cortical bone. Even if is used as an index of bone density, the same effect as described above can be obtained.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an electrical configuration of an osteoporosis diagnostic apparatus according to a first embodiment of the present invention.

FIG. 2 is a schematic external view schematically showing the external appearance of the device.

FIG. 3 is an explanatory diagram used for explaining an operation of the device.

FIG. 4 is an explanatory diagram used for explaining an operation of the device.

FIG. 5 is an explanatory diagram used for explaining an operation of the device.

FIG. 6 is an explanatory diagram used for describing the operation of the device.

FIG. 7 is a flowchart showing a flow of operations of the apparatus.

FIG. 8 is a graph showing a regression line relating to acoustic impedance of cortical bone density, and is a diagram used for explaining a bone density calculation subprogram according to the first embodiment.

[Explanation of symbols]

1 Transducer (Ultrasonic Transducer) 4 Pulse Generator 8 A / D Converter (Maximum Echo Level Extraction Means) 9 ROM (Memory) 10 RAM (Memory) 11 CPU (Maximum Echo Level Extraction Means, Bone Density Calculation Means) Ai Ultra Sound wave impulse Ae Echo from lower tibia Ma Soft tissue Mb Lower tibia X Skin surface Y Lower tibia surface

Claims (3)

[Claims] 1. An ultrasonic transducer is applied to the skin surface covering the lower tibia of a subject, ultrasonic waves are repeatedly emitted toward the cortical bone of the lower tibia, and echoes returning from the cortical bone surface are received. The echo level is measured by further, and a maximum echo level is extracted from the measured echo levels, and based on the extracted maximum echo level, predetermined arithmetic processing is performed to diagnose osteoporosis. A method for diagnosing osteoporosis. 2. An ultrasonic transducer is applied to the skin surface covering the lower tibia of a subject, and ultrasonic impulses are repeatedly emitted toward the cortical bone of the lower tibia, and an echo returning from the cortical bone surface of the lower tibia is emitted. An ultrasonic reflex type osteoporosis diagnostic device for diagnosing osteoporosis by receiving and measuring an echo level, comprising: maximum echo level extraction means for extracting a maximum echo level from the measured echo levels. A reflection coefficient calculation program describing a processing procedure for calculating an ultrasonic reflection coefficient at the interface between the soft tissue of the subject and the cortical bone of the lower tibia based on the maximum echo level, and the density of the cortical bone. Bone density calculation program describing a processing procedure for calculating the density of the cortical bone of a subject using a predetermined regression equation regarding the ultrasonic reflection coefficient A memory for storing various processing programs including the reflection coefficient calculation program and the bone density calculation program, and temporarily storing various data including the measured echo level and the extracted maximum echo level, and the reflection By executing the coefficient calculation program and the bone density calculation program, the ultrasonic reflection coefficient is calculated based on the maximum echo level extracted by the maximum echo level extraction means, and then the calculated ultrasonic wave. An osteoporosis diagnosing device comprising: a bone density calculating means for calculating the density of the cortical bone of the subject based on a reflection coefficient. 3. An ultrasonic transducer is applied to the skin surface covering the lower tibia of the subject, and ultrasonic impulses are repeatedly emitted toward the cortical bone of the lower tibia, and an echo returning from the cortical bone surface of the lower tibia is emitted. An ultrasonic reflex type osteoporosis diagnostic device for diagnosing osteoporosis by receiving and measuring an echo level, comprising: maximum echo level extraction means for extracting a maximum echo level from the measured echo levels. A reflection coefficient calculation program describing a processing procedure for calculating an ultrasonic reflection coefficient at the interface between the soft tissue of the subject and the cortical bone of the lower tibia based on the maximum echo level, and the ultrasonic reflection coefficient An acoustic impedance calculation program describing a processing procedure for calculating the acoustic impedance of the cortical bone based on A bone density calculation program that describes a processing procedure for calculating the density of the cortical bone of the subject using a predetermined regression equation relating to the acoustic impedance of the density, the reflection coefficient calculation program, the acoustic impedance calculation program, and A memory for storing various processing programs including a bone density calculation program, and temporarily storing various data including the measured echo level and the extracted maximum echo level, the reflection coefficient calculation program, and the acoustic impedance calculation program And by executing the bone density calculation program, to calculate the ultrasonic reflection coefficient based on the maximum echo level extracted by the maximum echo level extraction means, then to the calculated ultrasonic reflection coefficient Based on the acoustic impedance of the cortical bone Calculates, then osteoporosis diagnostic apparatus characterized by comprising a bone density calculation means for calculating the density of the cortical bone of the subject based on the calculated acoustic impedance.