JP2007209551A - Ultrasonograph - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an ultrasonograph capable of appropriately evaluating kinetic properties of the bone. <P>SOLUTION: This ultrasonograph acquires an interpolation line 52a indicating the shape of the bone surface based on echo signals acquired by transmitting ultrasonic beam onto the surface of the bone applied with a load. The outside diameter ψ of the bone input by a user is previously stored. This ultrasonograph calculates a shrinkage degree in the axial direction of the bone surface due to the application of the load as a strain ε based on the interpolation line 52a and the bone outside diameter ψ. In concrete terms, assuming that the length of the bone surface (the length of the interpolation line 52a) is (x) and the length of the neutral axis of the bone is x+dx, then the strain ε is ε=x/(x+dx)=r/(r+dr)=r/(r+1/2ψ). <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an ultrasonic diagnostic apparatus, and more particularly to an ultrasonic diagnostic apparatus that evaluates mechanical properties of bone.

  In order to diagnose bone metabolic diseases such as osteoporosis, determination of ease of fracture, and quantitative diagnosis of bone fusion after fracture treatment, simple and quantitative measurement of bone strength is desired.

  Currently, the evaluation of bone formation and bone fusion is highly dependent on radiographs. However, it is not only difficult to quantitatively diagnose bone strength by X-ray photography, but also invasiveness to the subject by X-ray irradiation is a problem.

  Therefore, in recent years, it has been proposed to evaluate the mechanical characteristics of bone using ultrasonic waves. For example, in Patent Document 1, an ultrasound beam is transmitted to and received from a bone of a subject to acquire shape data of the bone, and based on the obtained shape data, the amount of bone distortion due to load addition is calculated. An ultrasonic diagnostic apparatus is disclosed. The obtained strain amount is used as a reference for determining the strength of the bone and the degree of fusion of the fractured bone. In this ultrasonic diagnostic apparatus, since the amount of distortion that appears as a clear numerical value can be used as a bone evaluation criterion, bone strength can be measured quantitatively.

JP 2004-298205 A

  However, in this patent document 1, the position change rate in the radial direction of the bone is calculated as the amount of distortion. That is, when the length of the measurement range is L and the maximum amount of displacement in the radial direction of the bone (ie, the maximum amount of deflection) due to the load is Δd, the strain amount ε is ε = Δd / L. That is, Patent Document 1 considers only changes in the shape of the bone surface, and does not consider circumstances such as bone thickness and cross-sectional shape. Therefore, it was impossible to simply compare measurement results between subjects with different bone thicknesses. As a result, there is a problem that, for example, if there is no strain amount data of a healthy bone having the same thickness as the bone to be evaluated, an error may occur in the evaluation of the degree of healing of the fractured bone.

  Therefore, an object of the present invention is to provide an ultrasonic diagnostic apparatus that can more appropriately evaluate the mechanical characteristics of bone.

  The ultrasonic diagnostic apparatus of the present invention is an ultrasonic diagnostic apparatus for diagnosing mechanical characteristics of a bone based on an echo signal obtained by transmitting an ultrasonic beam to a bone in a subject, Based on an echo signal obtained by transmitting an ultrasonic beam to the bone surface, means for acquiring position information on the bone surface when a load is applied to the bone, and bone shape data including at least bone thickness information Storage means for storing, and means for calculating, as a strain amount, a rate of change in the length of the bone in the axial direction with respect to a load, based on bone surface position information and bone shape data.

  In a preferred aspect, the rate of change in the length of the bone in the axial direction is calculated as a ratio between the radius of the arc drawn by the neutral axis of the bone and the radius of the arc drawn by the bone surface when a load is applied. In this case, it is desirable that the bone shape data further includes bone cross-sectional shape information, and based on the bone cross-sectional shape information, the calculation method of the arc radius drawn by the neutral axis is variable. It is also desirable that the type of bone to be diagnosed is cross-sectional shape information of the bone.

  According to the present invention, the amount of distortion is calculated based on bone shape data including bone thickness information. Therefore, a distortion amount reflecting individual differences such as bone thickness can be obtained, and the mechanical characteristics of the bone can be evaluated more appropriately.

  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 ultrasonic diagnostic apparatus according to an embodiment of the present invention. This ultrasonic diagnostic apparatus is suitable for diagnosing the mechanical characteristics of bone. In this embodiment, a load is applied to the bone to be diagnosed, and the amount of bone distortion at that time is used as an index of the mechanical characteristics. The ultrasonic diagnostic apparatus is used to measure the amount of distortion of the bone.

  The probe 10 of the ultrasonic diagnostic apparatus is an ultrasonic probe used in contact with the body surface 50 of the subject. Of course, an ultrasonic probe used by being inserted into the subject may be used. The probe 10 forms an ultrasonic beam 40 toward the bone 52 in the body of the subject.

  The transmission / reception unit 12 controls the probe 10 to electronically scan the ultrasonic beam 40 in the tomographic plane. When the probe 10 is a linear probe, for example, 120 ultrasonic beams 40 are electronically scanned one after another, and an echo signal is acquired for each ultrasonic beam 40. The transmission / reception control unit 14 appropriately controls the transmission / reception unit 12 in accordance with an instruction from the user input via the operation panel 16.

  The plurality of echo signals acquired by the transmission / reception unit 12 are output to the tomographic image forming unit 18. The tomographic image forming unit 18 forms a tomographic image (B-mode image) of bone based on a plurality of echo signals. The echo signal acquired by the transmission / reception unit 12 is also output to the echo tracking processing unit 20. The echo tracking processing unit 20 performs so-called echo tracking processing that extracts and tracks a bone surface portion from each echo signal. As the echo tracking process, for example, a technique detailed in Japanese Patent Laid-Open No. 2001-309918 can be used. For example, three tracking echo signals are used for the echo tracking process. The tracking echo signal may be selected from echo signals (for example, 120 echo signals) used for tomographic image formation, or dedicated to three tracking signals transmitted by interrupting tomographic image formation. An echo signal may be used.

FIG. 2 is a diagram for explaining how the surface portion of the bone 52 is tracked by three echo signals. Each echo signal 68 corresponding to each of the three ultrasonic beams 40 directed toward the bone 52 exhibits a large amplitude (amplitude maximum portion 69) at a portion corresponding to the bone surface. The echo tracking processing unit specifies the bone surface position based on the position of the amplitude maximum portion 69 (waveform acquisition time). In addition,
200602091832399680 __________ AL1-3524 ____________________ APH_0
Although FIG. 2 shows an example in which there are three echo signals for echo tracking, a plurality of signals other than three can be measured. In this echo tracking process, a tracking point 42 is a surface point tracked for each echo signal, that is, for each ultrasonic beam 40.

  The interpolation line generation unit 22 (see FIG. 1) generates an interpolation line that connects these tracking points 42. That is, an interpolation line is generated by performing curve interpolation on the plurality of tracking points 42 using spline interpolation, least square interpolation, or the like. The interpolation line generated here is a curve indicating the bone surface shape. This interpolation line can be made closer to the original bone surface shape by increasing the number of echo signals for echo tracking processing. The generated interpolation line is temporarily stored in the memory 24 and used for calculating the distortion amount ε described later.

  The strain amount calculation unit 28 calculates a bone strain amount ε due to the load addition. This distortion amount ε is calculated based on the generated interpolation line and bone shape data input from the user via the operation panel. A method for calculating the strain amount ε will be described in detail later.

  Here, the bone shape data is data including thickness information and cross-sectional shape information of the bone to be diagnosed. FIG. 3 is an example of a screen display when inputting bone shape data. When diagnosing the mechanical characteristics of the bone, the user inputs in advance the subject name, the subject ID, the thickness of the bone to be diagnosed, and the cross-sectional shape of the bone to be diagnosed according to the screen display shown in FIG. . The input bone shape data is temporarily stored in the memory 24 and used for the calculation of the strain amount calculation unit ε.

  The bone thickness may be acquired in advance using an image diagnostic apparatus (such as X-rays or CT) using X-rays, or calculated based on a B-mode image obtained by the ultrasonic diagnostic apparatus. May be. On the other hand, the cross-sectional shape of the bone is almost the same for each bone type, and there is almost no individual difference. For example, it is known that the cross-sectional shape of the femur is a substantially circular shape, and the cross-sectional shape of the tibia is a substantially equilateral triangle. Therefore, the user may select a shape corresponding to the type of bone to be diagnosed as the cross-sectional shape of the bone. Alternatively, the display screen may be configured as shown in FIG. 4, and the bone type may be selected instead of the cross-sectional shape of the bone. In this case, the ultrasonic diagnostic apparatus determines the cross-sectional shape of the bone based on the selected bone type.

  The display image forming unit 32 forms an image to be displayed on the display 34 as a diagnosis result. The display image forming unit 32 includes a tomographic image formed by the tomographic image forming unit 18, a strain amount ε calculated by the strain amount calculating unit 28, a load value measured by the load measuring device 36 and added to the bone, and the like. Is entered. The display image forming unit 32 outputs an image obtained by graphing the distortion amount ε and the load value alone or with a B-mode image and outputs it as a display image to the display 34.

  Next, the strain amount ε as a bone diagnosis index will be described. The strain amount ε is a value indicating the expansion / contraction characteristics of the member deformed by receiving a load, and is used as an index for determining strength. In this embodiment, the expansion / contraction ratio in the axial direction is calculated as the strain amount ε. For example, consider a case where a load W is applied to the upper surface 100a of the rod 100 having a circular section as shown in FIG. It is assumed that the upper surface 100a of the bar 100 contracts due to this bending and the length thereof changes from D + α to D. At this time, the strain amount ε in the bar upper surface 100a can be expressed as a ratio of the expansion / contraction amount α due to the load addition to the length D + α before the load addition. That is, the strain amount ε is ε = α / (D + α).

  Here, when bent by applying a load, the upper surface of the bar is reduced and the lower surface of the plate is expanded. On the other hand, in the middle part of the bar, there is a part whose length does not change. The portion where the length does not change is called a neutral axis. The position of the neutral shaft 100b varies depending on the cross-sectional shape of the member, but when the cross-sectional shape is circular, a line passing through the center of the circle is the neutral axis.

  Since the neutral shaft 100b does not expand and contract, the length of the neutral shaft 100b is equal to the length of the bar upper surface 100a before expansion and contraction. Therefore, the strain amount ε (ε = α / D) can be obtained based on the length of the neutral shaft 100b and the length of the upper surface 100a of the bar when a load is applied. In this embodiment, the strain amount ε of the bone subjected to the load is calculated using this principle.

  Specifically, the calculation of the amount of bone strain ε will be described using a femur having a substantially circular cross section as an example. FIG. 6 is a schematic view of a femur that is bent under a load. When calculating the strain amount ε, the position of the tracking point obtained by calculating the position of the tracking point present on the surface of the bone is calculated based on the echo signal obtained by transmitting the ultrasonic beam to the surface of the bone. Is interpolated to obtain an interpolation line 52a (a bold solid line in FIG. 6) indicating the surface shape of the bone.

  Here, the length L of the measurement section and the amount of bending h of the bone measured by the ultrasonic diagnostic apparatus are sufficiently shorter than the total length of the bone. Therefore, the bending shape of the bone in the measurement section can be assumed to be an arc having a certain curvature.

  Now, assuming that the length of the bone surface (the length of the interpolation line 52a) in the measurement section is x and the length of the neutral axis of the bone (the line indicated by the alternate long and short dash line in FIG. 6) is x + dx, It is represented by 1.

  ε = dx / (x + dx)... Formula 1

Here, since the bending shape of the bone can be assumed to be an arc, dx and x + dx in Equation 1 can be converted into arc equations, respectively. That is, if the radius of the arc drawn by the bone surface (interpolation line: thick solid line) is r, and the radius of the arc drawn by the bone neutral axis 52b (thick one-dot chain line) is r + dr, dx = r · K, x + dx = (r + dr)・ It can be set to K (K = 2π · θ / 360 °). If this is substituted into Equation 1, Equation 2 is obtained.
ε = r / r + dr Equation 2

Furthermore, when the cross-sectional shape of the bone is substantially circular, the neutral axis 52b is the center point of the circle. Therefore, if the outer diameter of the bone is φ,
dr = φ / 2 Formula 3
It becomes.

In FIG. 2, when attention is paid to the right triangle shown by the dotted line, Expression 4 is obtained from Pythagorean's theorem.
r ² = {(L / 2) ² + (r−h) ² }
r = (L ² + 4h ² ) / 8h Expression 4

Then, when Expressions 3 and 4 are substituted into Expression 2, Expression 5 is obtained.
ε = r / r + dr
= 4hφ / (L ² + 4h ² + 4hφ) Equation 5

  In Equation 5, all the right sides are known values. That is, the bending amount h and the measurement section length L can be obtained from an interpolation line or the like, and the bone outer diameter φ is designated by the user in advance. Therefore, according to Equation 5, the distortion amount ε can be calculated using a known value.

  Here, in the prior art, for example, Patent Document 1, the ratio (h / L) of the deflection amount h to the measurement section length L is used as an index for evaluating the mechanical characteristics of the bone. In the ratio (h / L) of the bending amount h, the individual difference of bone, for example, the thickness of the bone is not considered. Therefore, the ratio (h / L) of the amount of deflection is unsuitable for comparison of measurement results between subjects with different bone thicknesses. As a result, for example, if there is no ratio (h / L) of the amount of flexion of healthy bones of the same thickness, the accuracy of diagnosis such as the degree of bone fracture or bone disease (false indirect or osteomalacia) decreases. It was inconvenienced.

  On the other hand, in this embodiment, the strain amount ε as an index for diagnosis is a value reflecting the thickness of the bone (outer diameter φ) as is clear from Equation 5. Therefore, the measurement results (distortion amount ε) can be compared between subjects with different bone thicknesses. As a result, the degree of fracture fracture and the diagnosis of bone disease are facilitated.

Although the above description uses a femur having a substantially circular cross section as an example, it can be applied to other bones such as a tibia having a generally triangular cross section. However, in that case, it is desirable to change the value of dr according to the cross-sectional shape of the bone. That is, in the case of a bone having a substantially circular cross section as shown in FIG. 7A, the neutral shaft 52b is a line passing through the center of the circle. On the other hand, in the case of a bone having a substantially equilateral triangle cross section as shown in FIG. 7B, the neutral axis 52b is a line passing through a 2/3 point of a perpendicular line dropped from the apex of the triangle to which a load is applied to the opposite side. Become. In the case of a bone having such a cross-sectional shape, dr is dr = 2 / 3φ, and the strain amount ε is ε = 16hφ / (3L ² + 12h ² + 16hφ). Thus, the reliability of the distortion amount can be further improved by changing the calculation formula of the distortion amount ε according to the cross-sectional shape of the bone.

  Next, a diagnosis example based on the distortion amount ε will be described. Diagnosis using the amount of strain ε includes diagnosis of the degree of fracture fracture. When diagnosing the degree of healing of fractured bones, measure the amount of fracture of the fractures periodically (for example, once every two weeks), and the standard amount of distortion (for example, the amount of distortion of healthy bone without fracture) ). As a result of the comparison, if the strain amount of the fractured bone to be diagnosed and the reference strain amount are substantially the same value, it can be determined that the fusion has been sufficiently performed. Here, the amount of distortion is a value reflecting the thickness of the bone. Therefore, even if the thickness of the fractured bone to be diagnosed is different from that of the healthy bone whose reference strain is calculated, the degree of fusion can be appropriately diagnosed. As a result, it is not necessary to prepare different reference strain amounts for each thickness of the fractured bone, and it becomes possible to diagnose the degree of fracture fusion more easily.

  Furthermore, the progression rate of fusion can be compared by comparing the change in strain over time among a plurality of subjects. By comparing the progression rate of fusion, various diseases that hinder bone fusion can be detected early.

  As described above, according to the present embodiment, the strain amount ε is calculated in consideration of individual differences in bone, for example, differences in thickness. According to this strain amount ε, comparison is possible even between subjects with different bone thicknesses, so that the mechanical characteristics of the bone can be evaluated more appropriately. At that time, since the cross-sectional shape of the bone is also taken into consideration, the reliability of the strain amount ε as an evaluation index can be further improved.

It is a block diagram which shows the structure of the ultrasonic diagnosing device which is embodiment of this invention. It is a figure which shows the mode of a tracking process. It is a figure which shows an example of a bone shape data input screen. It is a figure which shows the other example of a bone shape data input screen. It is a figure which shows the shape deformation | transformation of the bar material by load addition, (A) is before a load addition, (B) shows the shape after a load addition. It is a figure explaining the parameter used for calculation of the amount of distortion of a bone. It is a figure explaining the difference of the neutral axis by shape, (A) is a cross-sectional circle shape, (B) shows the neutral axis of a cross-section equilateral triangle.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 Probe, 12 Transmission / reception part, 14 Transmission / reception control part, 16 Operation panel, 18 Tomographic image formation part, 20 Echo tracking process part, 22 Interpolation line production | generation part, 24 Memory, 28 Distortion amount calculation part, 32 Display image formation part, 34 Display, 36 load measuring instrument, 40 ultrasonic beam, 42 tracking point, 52 bone, 52a interpolation line, 52b neutral axis.

Claims (4)

An ultrasonic diagnostic apparatus for diagnosing mechanical characteristics of a bone based on an echo signal obtained by transmitting an ultrasonic beam to a bone in a subject,
Based on an echo signal obtained by transmitting an ultrasonic beam to the bone surface, means for acquiring position information of the bone surface when a load is applied to the bone;
Storage means for storing bone shape data including at least bone thickness information;
Means for calculating the amount of strain change in the axial length of the bone relative to the load based on the position information of the bone surface and the bone shape data;
An ultrasonic diagnostic apparatus comprising: The ultrasonic diagnostic apparatus according to claim 1,
The rate of change in length of the bone in the axial direction is calculated as a ratio of the radius of the arc drawn by the neutral axis of the bone and the radius of the arc drawn by the bone surface when a load is applied. Ultrasonic diagnostic equipment. The ultrasonic diagnostic apparatus according to claim 2,
The bone shape data further includes bone cross-sectional shape information,
An ultrasonic diagnostic apparatus, wherein a method for calculating an arc radius drawn by a neutral axis is varied based on the cross-sectional shape information of the bone. The ultrasonic diagnostic apparatus according to claim 3,
An ultrasonic diagnostic apparatus characterized in that the type of bone to be diagnosed is cross-sectional shape information of the bone.

Images