JPH08613A - Surface-of-bone position detecting method - Google Patents

Abstract

PURPOSE:To easily select the peak of a signal representing the surface of a bone, in a received signal obtained by an ultrasonic receiving wave. CONSTITUTION:The received signal 100 obtained by an ultrsonic receiving wave being applied to the heel is inputted into a function multiplier 34. A function generator 36 produces a surface-of-bone probability function 102, and in the function generator 34, the surface-of-bone probability function 102 is multiplied by the received signal 100. The weighted received signal is sent to a surface-of-bone detector 38 for detecting the peak of the surface of the bone. By detecting the peak of the surface of the body in a surface-of-body detector 50, on the basis thereof, the surface-of-bone probability function may be determined, or on the basis of the information on a testee, the surface-of-bone probability function may also be determined.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for detecting the surface position of bone using ultrasonic waves.

[0002]

2. Description of the Related Art Recently, a bone evaluation apparatus for preventing and diagnosing bone diseases has been proposed. The bone evaluation device transmits and receives ultrasonic waves to and from a living body, and evaluates the bone from the data obtained at that time. As the bone evaluation device, for example, the one proposed by the present applicant in Japanese Patent Application No. 5-135610 can be mentioned.

In the bone evaluation, it is necessary to measure the width (thickness) of the bone in order to calculate the bone density, the sound velocity in the bone, and the like. For that purpose, the bone surface positions must be detected on both sides of the bone.

In the conventional bone surface position detecting method, the bone surface position is detected based on the received signal obtained by receiving the reflected ultrasonic waves. That is, as is well known, since ultrasonic waves are reflected at the boundary where the acoustic impedance is different,
Since a plurality of peaks appear in the received signal, the boundaries of the tissue (body surface, bone surface) can be determined from the positions of the peaks. In that case, in the conventional bone surface position detecting method, for example, the received signal is compared with a predetermined threshold value, and the position of the signal exceeding the threshold value is recognized as the tissue boundary.

[0005]

However, depending on the patient, keratinization of the body surface may progress, and the reflected wave from the body surface may be extremely strong, which may cause the body surface to be erroneously determined to be the bone surface. was there. On the other hand, when the signal contains a lot of noise, a large number of peaks may be generated and it may be difficult to determine the bone surface peak.

The present invention has been made in view of the above conventional problems, and an object thereof is to provide a method for easily selecting a signal (peak) representing a bone surface.

Further, the present invention is not confused by body surface signals,
The purpose is to reliably detect bone surface signals.

Another object of the present invention is to reliably detect the bone surface even when the subject moves. Further, the present invention provides
The purpose is to accurately detect the bone surface according to the individual difference of the subject.

[0009]

To achieve the above object, the invention according to claim 1 transmits and receives ultrasonic waves to and from a living body, and determines the position of the bone surface based on the amplitude value of the received signal. A method of detecting, a transmitting step of transmitting an ultrasonic wave to a living body, a receiving step of receiving a reflected wave from the living body,
It is characterized by including a weighting step of multiplying a received signal obtained by the received wave by a bone surface probability function, and a position detection step of detecting a bone surface position from the weighted received signal.

The invention according to claim 2 is characterized by including a step of detecting a body surface position and a step of determining the bone surface probability function with reference to the body surface position.

Further, the invention according to claim 3 is characterized in that the body surface position is detected based on the received signal.

Further, the invention according to claim 4 is characterized by including a step of inputting subject information and a step of determining the bone surface probability function based on the subject information.

[0013]

According to the structure described in claim 1, first, the ultrasonic wave is transmitted to the living body and the reflected wave is received. As a result, a reception signal is obtained, and the reception signal includes a body surface peak, a bone surface peak, noise, and the like.

In order to emphasize only the bone surface peaks, in the present invention, the received signal is multiplied by the bone surface probability function, so-called weighting is performed. This bone surface probability function indicates the magnitude of the existence probability of the bone surface, and by multiplying the function, the body surface peak in the received signal is reduced, and the bone surface peak appears. In addition, there is a noise reduction effect in a place where the weighting is low.

Therefore, if the bone surface peak detection is performed on the weighted received signal, the bone surface position can be easily specified. According to the present invention, since the bone surface position can be accurately detected, for example, the accuracy of measuring the bone width can be improved, and the reliability of the bone evaluation result can be improved.

According to the above-mentioned structure, the bone surface probability function is relatively determined with reference to the detected body surface position. That is, the distance between the body surface position and the bone surface position is
Since it is approximately constant for each person, if the bone surface probability function is determined on the basis of the body surface, that function can be made appropriate. In particular, it is effective when the position of the subject is displaced from the normal position or when the subject moves.

According to the third aspect of the invention, the body surface position is determined from the ultrasonic wave reception signal. That is, since the body surface is in contact with the matching material such as water and the signal peak is relatively clear, the body surface peak can be detected reliably and easily. In this way, the body surface peak is detected using the received signal, and the bone surface probability function is determined accordingly. Then, the received signal is weighted and the bone surface peak is further detected.

According to the structure of claim 4, the height,
An appropriate bone surface probability function for the subject is determined based on the subject information such as weight and sex.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT A preferred embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 shows the overall structure of a bone evaluation apparatus to which the bone surface position detecting method according to the present invention is applied. First, each component of this device will be described.

In FIG. 1, this apparatus is for evaluating the bone of the calcaneus 12, and a pair of transducers 16a and 16b are arranged on both sides of the heel 10 including the calcaneus 12. The vibrators 16a and 16b are mounted on the scanning unit 14, and the scanning unit 14 can be freely moved by driving a motor 18. Scanning unit 1
4 is controlled by the scan control unit 20. The heel 10 is placed in, for example, a water tank (not shown), and water is present between the vibrators 16a and 16b and the heel 10.
Each of the transducers 16a and 16b includes a transmission / reception unit 22 and 24.
Transmission and reception are controlled by. The received signal is converted into a digital signal by the A / D converter 26, and then output to the control device 30 via the measurement control unit 28. here,
The measurement control unit 28 controls the transmission / reception units 22 and 24.

As will be described later, the control device 30 detects the position of the bone surface based on the received signal, calculates the bone width based on this, and finally obtains the bone evaluation value. An input device 32 for inputting various kinds of information is connected to the control device 30.

FIG. 2 shows a configuration relating to bone surface detection in the control device 30. The received signal 100 is input to the function multiplier 34. On the other hand, the bone surface probability function 102 generated by the function generator 36 is also input to the function multiplier 34. In the function multiplier 34, the received signal 100 is multiplied by the bone surface probability function 102, weighted by this, and then the received signal is sent to the bone surface detector 38,
As will be described later, the bone surface peak of the received signal is detected, and the bone surface position is obtained from this. The result is sent to the bone width calculator.

FIG. 3 shows a heel 10 and a pair of vibrators 16a, 1
The relationship with 6b is shown. The heel 10 shown in FIG. 3 is the right heel, and the distance between the left and right bone surface positions (bone width) is, for example, 3 cm, and the distance between the left and right body surface positions (heel width) is , For example, 6 cm. The distance between the transducer 16a and the left bone surface position is about 4 cm.

In such a state, the left vibrator 1
When an ultrasonic pulse is transmitted from 6a toward the heel 10, the ultrasonic wave is reflected by the boundary surface of the tissue such as the body surface and the bone surface, and the reflected wave is received by the transducer 16a. The received signal at this time is shown in FIG. In FIG. 4, the body surface peak (a) appears at about 24 μs, and the bone surface peak (b) appears at about 50 μs. Here, the body surface peak (a) has a relatively large amplitude, and if the bone surface peak is detected in this state, the body surface peak (a) is erroneously detected.
May be determined to be the bone surface peak.

Therefore, in the present invention, for example, by multiplying the received signal by the bone surface probability function shown in FIG.
The received signal is weighted. The resulting weighted received signal is shown in FIG. As shown, the bone surface peak (b) clearly appears, while the body surface peak (a) disappears.

The function generator 36 shown in FIG.
2 generates a bone surface probability function, and the function multiplier 34 shown in FIG. 2 multiplies the bone surface probability function by the received signal.

The bone surface probability function shown in FIG. 5 is determined as follows, for example. As shown in FIG. 3, when the right heel is set at an appropriate position, the distance from the left transducer 16a to the bone surface is about 4 cm on average, and the bone surface is based on that distance. When the position of the peak is calculated, the time when the peak of the bone surface is captured is about 2 × (0.
04/1500) = 53 μS. However, the speed of sound in water is 1500 m / s. That is, the function that gives the maximum weight value to the average bone surface position is the bone surface probability function shown in FIG. As a result, it is possible to focus on the time around the peak of the bone surface, so that the bone surface peak can be detected easily and accurately.

Similar bone surface peaks are detected on the right side of the heel 10, and the bone width is calculated to be, for example, 3 cm from the bone surface positions obtained by these detections.

FIG. 7 shows a bone surface probability function of Gaussian distribution type. With such a function, it is possible to perform weighting more faithful to the existence probability of the bone surface. Further, FIG. 8 also shows a Gaussian bone surface probability function. In this function, 0.5 is also applied to the position where the body surface peak appears.
The weighting value of is given.

FIG. 9 shows still another bone surface probability function. In the function shown in FIG. 9, 1 is set as the weighting value within a fixed period, and 0.5 is set otherwise.

FIG. 10 shows a received signal when ultrasonic measurement is performed on the left heel from the left side. Although it is basically the same as the received signal shown in FIG. 4, since the shape of the calcaneus 12 is targeted, the position of the body surface peak (a) and the position of the bone surface peak (b) are different between the two. There is. Therefore, it is desirable to use the input device 32 shown in FIG. 1 to input whether the measurement target is the right heel or the left heel, and to use the bone surface probability function matching the input.

FIG. 11 shows a bone surface probability function that meets the measurement conditions shown in FIG. 10. In this example, the function is constructed with an average bone surface position of 40 μs.

FIG. 12 shows a weighted received signal obtained by multiplying the received signal shown in FIG. 10 by the bone surface probability function shown in FIG. As shown,
The bone surface peak (b) is clearly visible.

In the above embodiment, a plurality of fixedly set bone surface probability functions are stored in advance and selected according to the case. However, the subject information such as physique, age, sex, etc. is further stored. Accordingly, an appropriate bone surface probability function can be formed individually and adaptively. That is, the size of the calcaneus is
Since each person is different, such a subject information is used to determine an optimal bone surface probability function for each person.

The physique, age, and sex of the subject are input by the input device 32 shown in FIG. Then, in this embodiment, the function generator 36 has the function shown in FIG. 13 as a basic function. Here, a trapezoidal function is adopted as the function, the center of which is the point A and the half-width thereof is B.

The function generator 36 predicts the bone surface position by calculation from the physique (height / weight), age, and sex given as the subject information. Then, point A is aligned with the predicted bone surface position. Further, the function generator 36 calculates the degree of obesity from the height and the weight, and predicts the degree of thickness of soft tissue such as fat on the heel from the degree of obesity. Then, the half width B is determined based on the thickness of the soft tissue.

As a result, as shown in FIG. 13, since the bone surface probability function is determined, the function generator 36 outputs the determined bone surface probability function to the function multiplier 34. It is desirable to set B small for a person who is thin and set B large for a person who is fat. As described above, if the bone surface probability function is determined based on the measured data regarding the body type of the person, the bone surface position can be detected more accurately.

By the way, the thickness of the heel is measured with, for example, a caliper, and the measured value is input to obtain the above-mentioned B.
The value of may be determined. In either case, it is desirable to adaptively determine the optimal bone surface probability function according to the structure of each person's heel.

In the above-mentioned embodiment, it is premised that the heel to be measured is set at an appropriate position. However, in reality, the heel may be displaced from the normal position, and an embodiment for that purpose will be described below.

In this embodiment, the bone surface probability function for detecting the bone surface peak (b) is relatively determined based on the body surface peak (a) which is relatively clear in the received signal.

FIG. 14 shows a pair of vibrators 16a and 16b.
The received signal is shown when the heel is placed at any position in between. Here, since the body surface peak (a) appears relatively clearly in any of the received signals, the body surface detector 50 shown in FIG. 2 first detects the body surface peak (a). Then, the function generator 36 predicts the position of the bone surface peak (b) with the time t1 of the body surface peak (a) as the reference position, and sets the bone surface probability function based on the prediction. In this example, the time from the body surface peak to the bone surface peak is calculated as 2 × (0.02 / 1500) = 27 μs based on the premise that the bone surface is located at a position approximately 2 cm from the body surface. , Which is the center of the bone surface probability function. The bone surface probability function shown in FIG. 15 is set in this way, and if it is multiplied by the received signal shown in FIG.
As shown in, the weighted received signal is obtained. As a result, the bone surface peak (b) appears clearly, which enables accurate calculation of the bone width.

The shift amount from the reference position, that is, the time difference from the reference position to the center of the bone surface probability function can be calculated based on the subject information such as the physique and sex described above. By doing so, more accurate peak detection can be performed.

[0044]

As described above, according to the invention described in claim 1, by multiplying the received signal by the bone surface probability function indicating the existence probability of the bone surface, the peak of the body surface, noise, etc. are reduced. The bone surface peak can be clarified by using the above-mentioned method, and the bone surface peak detection accuracy can be improved. Therefore, it is possible to accurately calculate the bone width.

According to the second aspect of the present invention, since the bone surface probability function can be determined with the body surface position as a reference, even when the position of the subject deviates from the normal position,
Accurate peak detection is possible. In that case, the body surface position can be determined from the received ultrasonic signal itself.

According to the configuration of claim 4, it is possible to determine an appropriate bone surface probability function for the subject.

[Brief description of drawings]

FIG. 1 is a diagram showing an overall configuration of a bone evaluation device to which a bone surface position detecting method according to the present invention is applied.

FIG. 2 is a block diagram showing a configuration related to bone surface detection in the control device of the bone evaluation device.

FIG. 3 is a diagram showing a relationship between a pair of vibrators and a heel.

FIG. 4 is a waveform diagram showing a received signal.

FIG. 5 is a diagram showing an example of a bone surface probability function.

FIG. 6 is a waveform diagram showing a received signal after weighting.

FIG. 7 is a diagram showing an example of a bone surface probability function.

FIG. 8 is a diagram showing an example of a bone surface probability function.

FIG. 9 is a diagram showing an example of a bone surface probability function.

FIG. 10 is a waveform diagram showing a received signal.

FIG. 11 is a diagram showing an example of a bone surface probability function.

FIG. 12 is a waveform diagram showing a received signal after weighting.

FIG. 13 is a diagram showing a basic form of a bone surface probability function.

FIG. 14 is a waveform diagram showing a received signal at the time of displacement.

FIG. 15 is a diagram showing an example of a bone surface probability function.

FIG. 16 is a waveform diagram showing a received signal after weighting.

[Explanation of symbols]

 10 heel 12 calcaneus 16a, 16b oscillator 30 controller 34 function multiplier 36 function generator 38 bone surface detector 50 body surface detector

Claims (4)

[Claims] 1. A method for transmitting and receiving ultrasonic waves to and from a living body and detecting the position of a bone surface based on the amplitude value of a received signal, the method comprising transmitting the ultrasonic waves to the living body. A receiving step of receiving a reflected wave from the living body; a weighting step of multiplying a received signal obtained by the receiving by a bone surface probability function; and a bone surface from the received signal after the weighting. A position detecting step of detecting a position, and a bone surface position detecting method comprising: 2. The bone surface position according to claim 1, further comprising: a step of detecting a body surface position; and a step of determining the bone surface probability function with the body surface position as a reference. Detection method. 3. The method according to claim 2, wherein the body surface position is detected based on the received signal. 4. The bone according to claim 1, further comprising a step of inputting subject information, and a step of determining the bone surface probability function based on the subject information. Front position detection method.