JPH06327674A - Measurement method for sound velocity in tissue - Google Patents

Abstract

PURPOSE:To measure a sound velocity in a matched material by eliminating the outer factors in a measurement of a sound velocity in tissue using ultrasonic wave. CONSTITUTION:Water 22 acoustically equivalent to a soft tissue 22 of a testee body 24 is contained in a water tank 20. The testee body 24 is not put into the water tank 20 in a preliminary measurement process, and the real sound velocity is measured by transmitting and receiving ultrasonic wave to water 22. On the other hand, an estimated sound velocity is obtained from the water temperature based on a temperature function 50. A function correction circuit 46 corrects the sound velocity function by the difference between the real sound velocity and the estimated sound velocity. Thus, a sound velocity in a bone 26 is executed using the corrected sound function.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a method for measuring the velocity of ultrasonic waves in tissue.

[0002]

2. Description of the Related Art As a device for diagnosing a living tissue using ultrasonic waves, for example, an ultrasonic diagnostic device is known. Since the velocity of ultrasonic waves (hereinafter referred to as “sound velocity”) is considered to change according to the properties of the living tissue, measuring the sound velocity in the tissue is of great significance for diagnosing the living body.

Here, bone is also one of the tissues, and the speed of sound in the bone is considered to depend on the properties (strength, structure, etc.) of the bone. Therefore, the present applicant has proposed a bone evaluation device in Japanese Patent Application No. 4-127551. In such a device,
In addition to bone mineral content measurement by X-ray, bone acoustic velocity measurement by ultrasonic waves is performed on the foot, and a bone evaluation value is calculated from the two measurement results.

By the way, in the measurement of the speed of sound in the tissue, if an air layer is present on the path from the transmitting oscillator to the receiving oscillator, ultrasonic waves are reflected and attenuated. A water tank or the like is used. That is, the matching material (water) is put in the measuring tank (water tank), and the living tissue is submerged in the matching material to transmit ultrasonic waves.

[0005]

In calculating the sound velocity in the tissue, it is essential to know the sound velocity in the matching material as a premise.

In view of the fact that the speed of sound depends on the temperature, a sound speed function indicating the relationship between the temperature of the matching material and the speed of sound in the matching material is stored or tabulated in advance, and when calculating the sound speed in the tissue, It is conceivable to obtain the sound velocity in the matching material by referring to the sound velocity function.

However, the sonic velocity function only shows a general relationship between temperature and sonic velocity, and if environmental factors such as atmospheric pressure and degree of deaeration differ, different sonic velocities will occur even at the same temperature. The speed of sound is not uniquely determined. Therefore, if the sound velocity is calculated without any correction to the sound velocity function, the accuracy of the sound velocity in the tissue as a final calculation result will be reduced.

The present invention has been made in view of the above conventional problems, and an object thereof is to eliminate external factors and to accurately measure the sound velocity in a matching material, and thus to accurately measure the sound velocity in tissue. An object of the present invention is to provide a tissue-medium sound velocity measurement method that can be performed.

[0009]

In order to achieve the above object, the present invention provides a first wave transmitting / receiving step of transmitting an ultrasonic wave only to a matching material, and an ultrasonic wave in the first wave transmitting / receiving step. An actual sound velocity measurement step of calculating an actual sound speed in the matching material from the propagation time, a correction step of correcting the sound speed function based on the actual sound speed, and a second step of transmitting ultrasonic waves to the tissue in the matching material. A tissue for calculating the sound velocity in the tissue based on the wave transmitting / receiving step, the propagation time of the ultrasonic wave in the second wave transmitting / receiving step, and the sound velocity in the matching material obtained using the corrected sound velocity function. And a medium sound velocity calculation step.

[0010]

According to the above construction, it is possible to first obtain the actual sound velocity of the matching material and correct the sound velocity function by the actual sound velocity.

That is, the actual sound velocity is a true sound velocity under the environment, which is measured by directly measuring the propagation time. Therefore, if the difference (sound velocity error) from the sound velocity (estimated sound velocity) obtained by referring to the sound velocity function is obtained from the temperature of the matching material at that time, then the sound velocity function can be easily corrected.

When calculating the speed of sound in the tissue,
The sound velocity in the tissue can be accurately obtained by using the accurate sound velocity in the matching material specified by the corrected sound velocity function. In addition, the correction of the sound velocity function,
Or it can be done at the same time.

[0013]

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

(1) Principle of Measurement of Medium Sound Velocity In FIG. 1, the tissue 10 is placed inside a measuring tank 14 filled with a matching material 12. On both sides of the tissue 10,
A pair of ultrasonic transducers 16 and 18 are arranged, and the ultrasonic wave 100 is transmitted and received through the tissue 10. The distance L between the ultrasonic transducers 16 and 18 is known, and the thickness d of the tissue 10 is set such that the ultrasonic wave is transmitted to the tissue 10 and then the reflected wave is received by the same ultrasonic transducer. It can be easily measured by measuring the time until the wave is generated on both sides of the subject. In the above-mentioned Japanese Patent Application No. 4-127551, the thickness d
Various measurement methods of are proposed.

Now, assuming that the propagation time of the transmitted ultrasonic wave until it is transmitted through the tissue 10 and received is t, the velocity V of the ultrasonic wave in the tissue is V = d / {(L- Vw) -t (L-d) / L} (1) is calculated. However, Vw is the speed of sound in the matching material.

Therefore, if the sound velocity Vw in the matching material is known,
Immediately, the sound velocity V in the bone is calculated. In other words, if the sound velocity Vw is not accurate, the accuracy of V will decrease.

(2) Principle of the Present Invention Generally, it is considered that the sound velocity Vw in the matching material depends on the temperature Tw of the matching material. Therefore, if a sound velocity function for obtaining the sound velocity from the temperature is prepared, it is possible to cope with the temperature fluctuation of the matching material.

FIG. 2 shows the sound velocity function F as a graph. The sound velocity function F can be converted into a numerical calculation formula or a table. As shown in FIG. 2, when the temperature of the matching material is around 30 to 36 degrees, the temperature T
The relationship between w and the sound velocity Vw is linear with an almost constant gradient.

However, this sound velocity function F is just a typical one, and the sound velocity Vw varies due to other factors (for example, atmospheric pressure).

Therefore, in the present invention, ultrasonic waves are transmitted / received only to the matching material, the sound velocity of the matching material is measured, and the actual sound velocity is used to correct the sound velocity function. That is, as shown in the figure, when the actual sound velocity is V1 and the sound velocity obtained from the temperature Tw at that time is V2, the difference ΔV becomes the correction coefficient for the sound velocity function F. That is,
By subtracting ΔV from the sound velocity function F, the corrected sound velocity function F ′ can be obtained. Strictly speaking, ΔV may be different at each temperature, but in the temperature range shown in FIG.
It can be considered that ΔV is almost the same at each temperature. That is, it is understood that the correction of the sound velocity function F may be performed by moving the straight line up or down by ΔV.

Actually, the same result can be obtained even if ΔV is stored and ΔV is subtracted (or added) from the sound velocity obtained by the correction function F, which is also theoretically possible. Is the correction of the sound velocity function.

When the sound velocity in the tissue is measured, the temperature of the matching material at that time is detected again, the sound velocity Vw of the matching material is obtained based on the corrected sound velocity function F ', and finally in the tissue. The sound velocity V of is calculated.

The correction of the sonic velocity function can be performed not only in the preparation step but also in the subsequent tissue in-sound velocity measuring step, but in any case, it is common in that the temperature function is corrected from the actual sonic velocity.

(3) Description of Embodiments of the Present Invention FIG. 3 shows the structure of a tissue intermediate sound velocity measuring device according to the present invention. This device measures the speed of sound in bone.

In FIG. 3, water 22 as a matching material is put inside a water tank 20 as a measuring tank. A subject 24 is placed inside the aquarium 20, and the subject 24 is composed of bone 26, which is hard tissue, and soft tissue 28. Note that, for example, the part below the ankle is put in the water tank 20.

Since the device of this embodiment is a device for measuring the speed of sound in the bone, the target tissue is of course the bone 26, and as a matching material, it is acoustically equivalent to the soft tissue 28 ( Water 22 having a similar acoustic impedance is used. That is, in the measurement, the soft tissue 28 can be seen as a part of the water 22 as the matching material.

A pair of ultrasonic transducers 30 and 32 are arranged on both sides of the subject 24. A transmission / reception unit 34 for transmitting and receiving is connected to these ultrasonic transducers 30 and 32.

A temperature sensor 36 for measuring the temperature of the water 22 is arranged in the water tank 20, and the temperature detection signal 102
Is being output.

Ultrasonic waves are radiated from the ultrasonic transducer 30,
The time until the ultrasonic wave passes through the bone 26 and is received by the ultrasonic transducer 32 is measured by the time measuring unit 38 that receives the trigger pulse of the transmission / reception unit 34. Then, the time measurement signal is supplied to the second calculation unit 40 that performs the calculation of the speed of sound in the bone, the actual sound speed calculation circuit 42, and the bone width calculation circuit 44.

The actual sound velocity calculation circuit 42 calculates the actual sound velocity of the water 22 based on the ultrasonic wave propagation time t when ultrasonic waves are transmitted and received while the subject 24 is not placed in the water tank 20. The signal indicating the actual sound velocity is output to the function correction circuit 46.

On the other hand, the temperature detection signal 102 is supplied to the first calculator 48 for calculating the sound velocity Vw in water. A memory 50 storing a sound velocity function is provided in the first calculation unit 48.

That is, the first calculator 48 calculates the sound speed Vw in water from the temperature T of the water according to the sound speed function.

In the preparatory measurement step which will be described in detail later, the actual sound velocity calculation circuit 42 obtains the actual sound velocity, while the first calculation unit 48 calculates the sound velocity before correction (estimated sound velocity) from the sound velocity function. The two are compared by the function correction circuit 46, and the sound velocity difference ΔV shown in FIG. 2 is calculated. This ΔV is added to or subtracted from the sound velocity function.

Therefore, when the preparatory measurement process is completed,
The sound velocity function corrected under the environment can be stored in the first calculation unit 48.

The bone width calculation circuit 44 calculates the width d of the bone 26. Specifically, for example, at the time from the transmission of the wave on one side of the subject 24 to the arrival of the reflected wave. Based on this, the distance between the bone 26 and one of the ultrasonic transducers is obtained, and the same calculation is performed on the other side,
Finally, the bone width d is calculated from the distance L. Various methods can be applied to the calculation of the bone width.

The second computing section 40 executes the above-mentioned first equation to obtain the sound velocity V in the bone. However, since the sound velocity Vw in water is calculated based on the corrected sound velocity function, it is possible to accurately obtain the final sound velocity in bone.

Next, the method of measuring the sound velocity in tissue according to the present invention will be described with reference to FIG.

In S101, ultrasonic waves are transmitted / received only to the water 22 without putting the subject 24 in the water tank 20.
At the same time, the temperature of the water 22 is detected by the temperature sensor 36.

At S102, the actual sound velocity is calculated by dividing the distance L by the propagation time t measured by the transmission / reception at S101.

In S103, the estimated sound velocity is obtained using the sound velocity function before correction based on the temperature detected in S101.

In S104, the estimated sound velocity is subtracted from the actual sound velocity to calculate the sound velocity error ΔV. Then, in S105, the sound velocity function is corrected by the ΔV. That is, as shown in FIG. 2, the sound velocity function itself obtained by shifting the first reference sound velocity function or its shift amount is the first
It will be stored in the arithmetic unit.

After the above preparatory measurement process is completed, the subject 24 is actually put in the water tank, and ultrasonic waves are transmitted and received in S106. At the same time, the temperature sensor 36 measures the temperature. Thus, the reason why the temperature is measured again is to cope with the temperature fluctuation of water over time.

In S107, the sound velocity Vw in the matching material is calculated from the detected temperature based on the corrected sound velocity function.

Then, in step S108, the second calculator 40 calculates the sound velocity V in the bone based on the first equation.

In S109, it is determined whether or not the bone sonic velocity has been measured at all required measurement points, and if there are remaining measurement points, the process from step S106 is repeated.

As described above, by correcting the reference temperature function based on the actual sound velocity measurement, it becomes possible to accurately measure the tissue medium sound velocity under various environments.

[0047]

As described above, according to the present invention,
Since the actual speed of sound of the matching material can be measured and the reference sound speed function can be corrected based on the actual speed of sound, the speed of sound in the matching material can be obtained with high accuracy, which in turn improves the accuracy of measurement of the speed of sound in the tissue. It becomes possible.

[Brief description of drawings]

FIG. 1 is a principle explanatory view showing a principle of measuring tissue acoustic velocity.

FIG. 2 is an explanatory diagram showing a sound velocity function.

FIG. 3 is a block diagram showing an overall configuration of a tissue intermediate sound velocity measuring device according to the present invention.

FIG. 4 is a flow chart showing a method for measuring the velocity of sound in tissue according to the present invention.

[Explanation of symbols]

 20 Water Tank 22 Water 24 Subject 26 Bone 28 Soft Tissue 30, 32 Ultrasonic Transducer 36 Temperature Sensor 38 Time Meter Side 40 Second Calculation Section 42 Real Sound Velocity Calculation Circuit 46 Function Correction Circuit 48 First Calculation Section 50 Sonic Speed Function Memory Section

Claims (2)

[Claims] 1. A measuring tank containing a matching material, a pair of ultrasonic transducers arranged at a constant interval in the measuring tank, and measuring the propagation time of ultrasonic waves between the ultrasonic transducers. A time measuring unit, a temperature detector that detects the temperature of the matching material, a first calculation unit that calculates the sound velocity in the matching material according to a sound velocity function indicating the relationship between the temperature of the matching material and the sound velocity, A tissue middle sound velocity measuring device including: a second calculation unit that calculates a sound velocity in a tissue according to a sound velocity in a matching material and the propagation time; and a first transmission / reception wave that transmits an ultrasonic wave only to the matching material. A step, an actual sound velocity measurement step of calculating an actual sound velocity in the matching material from the propagation time of the ultrasonic wave in the first wave transmission / reception step, a correction step of correcting the sound velocity function based on the actual sound velocity, and the matching Allows ultrasonic waves to penetrate the tissue in the material The sound speed in the tissue is calculated based on the ultrasonic wave transmission / reception step 2 and the ultrasonic wave propagation time in the second wave transmission / reception step, and the sound speed in the matching material obtained using the corrected sound speed function. A method for measuring tissue sound velocity, comprising: 2. The method for measuring the velocity of sound in tissue according to claim 1, wherein the tissue to be measured is bone, and the matching material is a liquid acoustically equivalent to soft tissue of a living body. .