JP2000287968A - Osteoporosis measuring apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To accurately and correctly measure an acoustic impedance of lumbar vertebrae. SOLUTION: A plurality of transducers T1, T2... and T64 making up a transducer array 2 are arranged at a position in a radial direction from one point (focus FP) and at a fixed distance from the point on the radiation side of an ultrasonic wave to realize the focusing of a beam of an ultrasonic pulse. The focused ultrasonic pulse is admitted between plicas of a lumbar vertebrae to be radiated to the lumbar vertebrae.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to osteoporosis by radiating an ultrasonic pulse toward a predetermined part of a subject and measuring the reflectance of an ultrasonic wave (echo) reflected at an interface between soft tissue and bone. The present invention relates to an ultrasonic reflection type osteoporosis measuring device for obtaining information.

[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 a disease in which calcium comes out of bones and becomes faint and easily breaks even with a slight shock, which is one of the causes of so-called bedridden elderly people. Physical diagnosis of osteoporosis is mainly performed by precisely measuring bone density using a diagnostic device such as DXA or QCT using X-rays. However, physical diagnosis using X-rays requires a large-scale device. In addition, there is a risk of exposure.

[0003] Therefore, as a simple device that can be handled without exposure, an osteoporosis diagnostic device using ultrasonic waves has become widespread. A diagnostic device using ultrasonic waves measures the speed of sound and attenuation when the ultrasonic waves propagate through bone tissue, estimates the bone density and the elastic modulus (elastic strength) of the bone, and obtains a low estimated value. If you are diagnosed with osteoporosis.

[0004] For example, in a diagnostic apparatus described in Japanese Patent Application Laid-Open No. 2-104337 (US Patent Application No. 193295), two ultrasonic transducers face each other across a subject's bone, which is a measurement site, and one ultrasonic transducer is used. The ultrasonic pulse is emitted from the transducer toward the bone tissue of the subject, and the ultrasonic pulse transmitted through the bone tissue is received by the other ultrasonic transducer, so that the speed of sound in the bone tissue is measured. It is diagnosed that osteoporosis is progressing as the speed of sound at is slower. This is based on an empirical rule that the processing algorithm of the diagnostic device indicates that the speed of sound is proportional to the bone density in bone tissue.

However, the theoretical basis for linking bone density and sound speed is uncertain. Strictly speaking, the speed of sound in bone tissue is not proportional to bone density, but rather [elastic modulus of bone / bone density]. Given by the square root of In addition, the elasticity and density of bone contribute to the speed of sound in such a way that the elasticity of bone increases as the density of bone increases. Can't respond sensitively to the increase,
The correlation between the speed of sound in bone tissue and bone density is by no means high. Also, the rationale for linking bone density and ultrasound attenuation is uncertain.

Therefore, a highly reliable diagnosis is required for a conventional ultrasonic transmission type diagnostic apparatus for estimating bone density and elasticity of bone from measurement results of sound speed and ultrasonic attenuation in bone tissue. That is impossible.

As means for solving such inconveniences,
Applicants have used ultrasonic transducers to repeatedly emit ultrasonic pulses toward flat surface bone tissue,
Receives the echoes returned from the bone tissue, extracts the maximum echo that can be regarded as a vertical reflection echo from the received echoes, and based on the extracted maximum echo, calculates the reflectance and acoustic impedance. An ultrasonic reflection type osteoporosis diagnostic apparatus which calculates and diagnoses osteoporosis based on these calculated values has been proposed (Japanese Patent Application No. 8-34100).
issue).

[0008] Further, in order to enable more accurate measurement, the applicant has provided a beam of ultrasonic pulses radiated from a plurality of transducers toward a measurement site on a transmitting / receiving surface of the transducer. An osteoporosis diagnostic apparatus has been proposed which has a structure in which the acoustic impedance is measured by focusing on an ultrasonic delay spacer and focusing on a measurement site (Japanese Patent Application No. 9-241173).
issue).

[0009]

The problem to be solved by the present invention is disclosed in Japanese Patent Application No. Hei.
According to the osteoporosis diagnostic apparatus described in Japanese Patent No. 241173, the number of transducers is insufficient, so that only an effect of reducing the angle dependence when measuring the acoustic impedance of flat bone can be obtained. It is difficult to measure a target and curved bone. For example, the lumbar vertebrae correspond to local and curved bones because the folds are present at certain intervals.

[0010] Here, the lumbar vertebra is an important part for diagnosing osteoporosis because fractures are liable to occur. If the acoustic impedance of the lumbar vertebra can be measured accurately, medical effectiveness will be increased. Is desired.

The present invention has been made in view of such circumstances, and an object of the present invention is to provide an osteoporosis measuring apparatus capable of reliably and accurately measuring the acoustic impedance of a lumbar spine.

[0012]

SUMMARY OF THE INVENTION An osteoporosis measuring apparatus according to the present invention comprises: a transducer array in which a plurality of transducers for radiating an ultrasonic pulse into a living body and receiving an echo from the inside of the living body are arranged; An ultrasonic transducer connected to each of the
The echo signal received by each transducer is represented by A
Calculating means for obtaining information on osteoporosis by obtaining the reflectance of ultrasonic waves at the boundary between soft tissue and bone based on the echo signals after A / D conversion, A plurality of transducers of the transducer array are characterized by being arranged in a radiation direction from one point on the ultrasonic wave radiation side and at a fixed distance from the point.

According to the osteoporosis measuring apparatus of the present invention, the plurality of transducers constituting the transducer array are arranged in a radiation direction from one point on the ultrasonic wave radiation side and at a position at a fixed distance from the point. Therefore, focusing (focusing) of the beam of the ultrasonic pulse can be easily realized, and the focused ultrasonic pulse can be made incident between the folds of the lumbar spine and emitted to the lumbar vertebra. Thereby, the acoustic impedance of the lumbar spine can be measured reliably and accurately. Further, since the acoustic impedance can be accurately measured, it is also possible to accurately determine the area density distribution of the bone (lumbar vertebra).

[0014]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram showing a configuration of an embodiment of the present invention, and FIG. 2 is a diagram schematically showing a use state of the embodiment.

First, the osteoporosis measuring apparatus according to the present embodiment converts an electric pulse signal into an ultrasonic pulse, radiates the ultrasonic pulse to a predetermined measurement site of a subject, and reflects ultrasonic waves (reflected from the measurement site). Echoes) and convert them into electrical signals by a plurality of transducers T1, T2,.
A transducer array 2 in which T64 are arranged, and an electric pulse signal is supplied to the transducers T1, T2,..., T64, and each transducer T1, T2,.
The apparatus main body 1 that takes in the received wave signal (echo signal) from T64 and performs digital analysis processing to be described later to measure osteoporosis, and the cable 3 that connects the transducer array 2 and the apparatus main body 1 It is configured as a subject.

What should be noted in the present embodiment is the structure of the transducer array 2. That is, the transducer array 2 used in the present embodiment
As shown in FIGS. 3 and 4 (a) and (b), the array of transducers T1, T2,.
The transducers T1, T2,..., T64 are located at a point (focus F
It is characterized in that the ultrasonic pulse beam can be focused on the focal point FP by arranging it in a direction radiating from P) and at a certain distance from the focal point FP (spherical arrangement).

The transducers T1, T2,..., T64
For example, a piezoelectric element having a thickness vibration type such as lead titanium zirconate (PZT) having electrode layers formed on both surfaces is used. Further, the transducers T1, T2,..., T64 are supported by a substantially spherical support plate (not shown) or the like. Ultrasonic delay spacers (not shown), such as polyethylene bulk, are attached as needed.

Next, details of the osteoporosis measuring apparatus of the present embodiment will be described below. As shown in FIG. 1, the apparatus main body 1
, T64,..., T64 via the cable 3 and the A / D converters 17 connected to the respective receivers 16. , CPU (Central Processing Unit)
11, ROM 12, RAM 13, and display 1
5 and so on.

The transmitter 15 includes a matching circuit, a pulse generator (both not shown), and the like.
An electric pulse signal of 54 to 1.62 MHz (center frequency 1 MHz) is repeatedly generated at a predetermined cycle and supplied to the transducers T1, T2,..., T64.

The receiver 16 includes a matching circuit, an amplifier, a waveform shaping circuit (all not shown), and the like, and amplifies the reception wave signals from the transducers T1, T2,..., T64 at a predetermined amplification degree. Thereafter, the waveform is linearly shaped (such as noise component removal) and supplied to the A / D converter 17. Note that this receiver 16
The matching circuit provided in the transmitter 15 is provided between the transducers T1, T2,.
Impedance matching is performed so that signals can be transmitted and received without energy loss.

The A / D converter 17 includes a sample hold circuit, a high-speed sampling memory (both not shown), and the like, and outputs an output signal (waveform shaped) of the receiver 16 supplied in accordance with a sampling start request of the CPU 11. An analog reception wave signal is converted to a predetermined frequency (for example, 12 MHz).
In step z), the digital signal is converted into a digital echo signal, and the digitized echo signal is temporarily stored in a high-speed sampling memory and then supplied to the CPU 11.

The ROM 12 stores a processing program for causing the CPU 11 to measure osteoporosis. The processing program includes an echo waveform measurement processing program, a reflectance calculation program, a bone acoustic impedance calculation program, and the like.

The RAM 13 includes a working area in which a work area of the CPU 11 is set, and a data area for temporarily storing various data.
Each element of the scattering matrix is temporarily stored in the data area.

The CPU 11 executes the above-described processing program stored in the ROM 12 by using the RAM 13 so that the transmitters 15... 15 and the A / D converters 17.
7, control of each part of the apparatus such as 7, measurement processing of 8 × 8 echo waveforms, Fourier transform of echo waveforms, calculation of interface reflectance between soft tissue and bone, calculation of acoustic impedance of bone (diagnosis of osteoporosis), etc. I do.

The display 14 is a CRT or LCD, etc., and under the control of the CPU 11, the maximum bone echo level (measured value), the interface reflectance between soft tissue and bone (calculated value), the acoustic impedance of bone (calculated value), This time, the bone echo waveform, the maximum bone echo waveform, and the like are displayed on the screen.

Next, the operation of the present embodiment (flow of processing)
Will be described. In this example, fractures are likely to occur,
The lumbar vertebra, which is an important part in the diagnosis of osteoporosis, is set as the measurement site.

When the apparatus is powered on, the CPU 11
Are presets, counters and various registers of each part of the device,
After the initial setting of various flags, it waits until the measurement start switch is pressed. Here, as shown in the schematic diagram of FIG. 2, the operator determines a bone (lumbar vertebra) Mb which is a measurement site of the subject.
Ultrasonic gel 4 is applied to the surface (cortical surface) of soft tissue Ma covering
Is applied, the transducer array 2 is applied to the surface of the cortical layer via the ultrasonic gel 4, and the measurement start switch is turned on with the transmitting / receiving surface facing the bone Mb. When the measurement start switch is turned on, the CPU 11 starts operating according to the processing procedure (flow chart) shown in FIG.

First, in step SQ1, the CPU 1
1 measures the echo waveform Smn (t) from the bone Mb under the control of the echo waveform measurement processing program.

Specifically, of the 8 × 8 transducers T1, T2,..., T64 of the transducer array 2,
When ultrasonic waves are emitted from the n-th transducer Tn, the echo reflected at the interface between the soft tissue and the bone is received by the m-th (m ≠ n) transducer Tm. .., T64 are executed to measure 8 × 8 echo waveforms Smn (t). These echo waveforms Smn (t) are taken into the CPU 11 via the A / D converter 17.

Next, in steps SQ2 and SQ3, the CPU 11 removes the waveform S which is considered to be an echo from the bone in order to remove noise such as the first reverberation of the transducer and multiple reflection between the echo bone and the transducer.
mn (t) is multiplied by the gate Gmn (t) (Smn
After (t) → Gmn (t) * Smn (t), Fourier transform is performed (Smn (t) → Smn (ω)).

After the Fourier transform processing is completed, the CPU 1
1 are N ′ (N ′ <N = 8) eigenvalues λ of sufficiently large absolute values in the following equation (1) and φn (ω) (n = 1, 2) for each frequency ω. ,..., N) are obtained by the processing described below (steps SQ4 and SQ5).
In this example, it is assumed that N '= 1, that is, a single eigenvalue is obtained.

ΣnSmn (ω) φn (ω) = λφ ^* m (ω) (1) where φ ^* m is the complex conjugate of φm. Also φm
(Ω) is standardized (Σnφn (ω) φ ^* n
(Ω) = 1), and its direction as a vector continuously changes in accordance with a change in frequency.

Lim [Σnφn (ω) φ ^* n (ω + Δω)] = 1 Δω → 0 is satisfied.

In calculating the eigenvalues λ and φn (ω), first, for each frequency ω, a 2N × 2N (N = 8) real symmetric matrix S ′ (ω)

[0036]

(Equation 1)

Is created. In this real symmetric determinant (the eigenvalues are positive / negative symmetric), the positive eigenvalues of S ′ (ω) are set to λn (ω) (n = 1, 2, 3,..., N) in descending order of absolute value. On the other hand, negative eigenvalues are -λn in descending order of absolute value.
It is proved that (ω) (n = 1, 2, 3,..., N) exists. From the absolute values of these eigenvalues, a single (or plural) eigenvalue λ is obtained.

At this time, the eigenvector for the positive eigenvalue λn is φ′n (ω), and the eigenvector for the negative eigenvalue −λn is φ ″ n (ω). .lambda.N '(N'<N), and .phi.n (.omega.) =. phi.'n (.omega.) + j.phi. "n (.omega.). However, for Snn (ω), Snn (ω)
= 0.

For a more detailed description of the processing relating to the eigenvalue, refer to the "eigenvalue problem" described in the specification of Japanese Patent Application No. 9-241173.

The eigenvalue λ obtained as described above is actually a value proportional to the reflectance of the object (the interface between the soft tissue and the bone) because of the frequency characteristics of the transducer and the like. Value) λ is multiplied by a predetermined proportionality constant to determine the interface reflectance between soft tissue and bone.

Thereafter, the CPU 11 proceeds to step SQ6 and obtains the acoustic impedance of the bone (lumbar vertebra) by controlling the acoustic impedance program of the bone.

Here, the proportionality constant used for calculating the acoustic impedance is the eigenvalue λ of the object whose reflectance is known.
Is measured and calculated in advance by the same processing as described above, and calculated from the calculated value and the reflectance (known value) of the object.

Specifically, the transducer array 2
(Transducer: 8 × 8, pitch 14 mm, wave source: surface wave source (directivity: 3 dB down 45 degrees), diameter 4
Bakelite sphere of 0mm (reflectance 0.6, density 1.5g
/ Cm ³ , sound velocity 4000 m / sec) and a medium (water:
A density of 1.0 g / cm ³ and a sound velocity of 1500 m / sec) are arranged so that the distance between them is 160 mm (see FIG. 4). (Calculation conditions: frequency 250 kHz to 1.25 MHz: step 5 kHz)
Then, there is a method of obtaining a proportional constant from the calculated value and the reflectance 0.6. In the measurement of the proportionality constant, water is used as the medium because the acoustic impedance of the soft tissue of the subject (person) shows a value close to the acoustic impedance of water.

According to the present embodiment having the above configuration, the plurality of transducers T1, T2,..., T64 constituting the transducer array 2 are positioned in the radiation direction of the focal point FP and at a fixed distance from the focal point FP. Because it is located in
Focusing of the beam of the ultrasonic pulse can be easily realized, and the focused ultrasonic pulse can be made incident between the folds of the lumbar spine and emitted to the lumbar spine. As a result, the acoustic impedance of the lumbar spine can be reliably and accurately measured.

In the present embodiment, the progress of osteoporosis can be determined based on the acoustic impedance of the bone (lumbar vertebra) calculated by the above processing.

That is, the acoustic impedance of the bone is
It is given by the square root of [bone elastic modulus x bone density], and the parameters "bone elastic modulus" and "bone density" are in a relationship that if one increases (decreases), the other increases (decreases). Therefore, as bone density increases (decreases), bone elasticity also increases (decreases), and the acoustic impedance significantly increases (decreases) in a sensitive response due to this synergistic effect.
Therefore, the acoustic impedance of bone is a very good index for determining bone density. For example, if the acoustic impedance of the bone of the subject is significantly smaller than the average value of the age group, the operator knows that osteoporosis of the bone is worse.

Here, in the above embodiment, the number of transducers arranged in the transducer array is 8 ×
Although the number is eight, the number is not limited thereto, and the number can be increased or decreased as necessary. Further, the transducer array is not limited to a two-dimensional structure, and may have a one-dimensional structure in which transducers are arranged in a line. Further, the ultrasonic vibrator constituting the transducer is not limited to the thickness vibration type, may be a flexural vibration type, and the center frequency used for measurement is not particularly limited.

[0048]

As described above, according to the osteoporosis measuring apparatus of the present invention, a plurality of transducers constituting a transducer array are arranged in a direction radiating from one point on the ultrasonic wave radiating side and at a constant distance from that point. Since it is located at a distance, the acoustic impedance of the lumbar spine, which is an important part in diagnosing osteoporosis, can be measured reliably and accurately, making it possible to diagnose osteoporosis with great medical effectiveness. In addition, the bone area density distribution can be measured more accurately than a conventional apparatus using a flat transducer array.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of an embodiment of the present invention.

FIG. 2 is a diagram schematically showing a use state of the embodiment of the present invention.

FIG. 3 is a perspective view schematically showing a configuration of a transducer array applied to the embodiment of the present invention.

FIG. 4 is a plan view (a) and a side view (b) schematically showing the structure of a transducer array.

FIG. 5 is a flowchart showing the contents of a processing operation according to the embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Device main body 11 CPU 12 ROM 13 RAM 14 Display 15 Transmitter 16 Receiver 17 A / D converter 2 Transducer array T1, T2, ..., T64 Transducer 3 Cable

Claims (1)

[Claims] 1. A transducer array in which a plurality of transducers for emitting ultrasonic pulses into a living body and receiving echoes from the inside of the living body are arranged,
An ultrasonic transducer connected to each of the transducers, and an echo signal received by each transducer are taken in through an A / D converter, and based on the echo signal after the A / D conversion, a soft tissue And calculating means for obtaining information on osteoporosis by determining the reflectance of the ultrasonic wave at the boundary between the bone and the bone, wherein the plurality of transducers of the transducer array are radiated from one point on the ultrasonic wave radiation side and in the direction of radiation. An osteoporosis measuring device, wherein the osteoporosis measuring device is arranged at a position at a fixed distance from a point.