JP6133130B2 - Thickness measuring method and thickness measuring apparatus - Google Patents

Description

  The present invention relates to a technique for measuring the thickness of a measurement object using ultrasonic waves or the like.

  Conventionally, the thickness of the cortical bone has been used as one of the indexes greatly related to the bone strength. For example, a tomographic image of a bone can be generated based on the principle of CT (Computed Tomography) using X-rays, and the thickness of the cortical bone can be measured based on the tomographic image.

  However, a measuring apparatus using X-rays is expensive and has a problem of exposure. Therefore, various techniques for measuring the thickness of cortical bone using safe ultrasonic waves have been proposed.

  For example, Patent Documents 1 and 2 transmit ultrasonic signals toward cortical bone and measure the thickness of the cortical bone based on the time difference between the reflected wave from the surface of the cortical bone and the reflected wave from the back surface. The technology to do is disclosed.

  Non-Patent Documents 1 to 3 disclose techniques for deriving cortical bone thickness by spectral processing of ultrasonic echoes.

JP 2010-057520 A US Pat. No. 7,601,120

Keith A. Wear, 'Autocorrelation and Cepstral Methods for Measurement of Tibial Cortical Thickness', IEEE transactions on ultrasonics, ferroelectrics, and frequency control, Vol. 50, No. 6, June 2003, pages 655-660. Janne P. Karjalainen, Ossi Riekkinen, Juha Toyras, Heikki Kroger, Jukka Jurvelin, 'Ultrasonic Assessment of Cortical Bone Thickness In Vitro and In Vivo', IEEE transactions on ultrasonics, ferroelectrics, and frequency control, Vol. 55, No. 10, October 2008, pages 2191-2197. Janne P. Karjalainen, Juha Toyras, Jukka S. Jurvelin, 'Cepstrum method enables accurate assessment of thickness of cortical bone layers-Potential improvement for analysis of ultrasound backscatter from underlying trabecular matrix', Proceedings of 20th International Congress on Acoustics, ICA 2010, Australia, August 2010, 23-27.

  When measuring cortical bone using ultrasonic waves, the reflected wave from the cortical bone may be disturbed due to the roughness of the cortical bone surface or the presence of pores in the cortical bone. In the case of the configurations of Patent Documents 1 and 2, when the reflected wave from the cortical bone is disturbed, it becomes difficult to detect the peak of the echo on the front surface or the echo on the back surface. As a result, the time difference between the echoes on the front surface and the back surface cannot be accurately detected, and the measurement accuracy of the cortical bone thickness is lowered.

  When obtaining the spectrum of an ultrasonic echo as in Non-Patent Documents 1 to 3, ideal conditions (such as that the front and back surfaces are parallel, the surface is smooth, and the bone is homogeneous) are required. Therefore, it is difficult to measure the thickness of actual cortical bone (having voids and complicated shapes). For example, in the method using the cepstrum process, there is a possibility that the distance between the cortical bone surface and the hole is erroneously calculated as the cortical bone thickness.

  Conventionally, in order to obtain a good reflected wave from the cortical bone, an ultrasonic signal may be transmitted and received using a single sensor with an acoustic lens 101 as shown in FIG. However, when such an acoustic lens is used, transmission waves are concentrated at the focal position, so that it is easily affected by the cortical bone shape at the focal position. In particular, in the case of an elderly person, the shape of the back surface 15 of the cortical bone 10 is rough, and many holes exist in the cortical bone 10. For example, when the back surface 15 is rough as shown in FIG. 15B, the reflected wave is scattered when the back surface 15 is focused, and it becomes difficult to receive the reflected wave from the back surface 15.

  As described above, since the conventional technique is easily affected by the roughness of the surface of cortical bone and pores, it has been difficult to accurately and stably measure the thickness of the cortical bone.

  Further, in the case of a single sensor using the acoustic lens 101 as shown in FIG. 15, since the distance to the focal point is fixed, it is necessary to use the stand-off 102 (for example, Non-Patent Documents 1 and 2), and measurement is inconvenient. . Further, when the soft tissue and the cortical bone surface are not parallel, it is necessary to adjust the direction of the sensor so as to be perpendicular to the cortical bone surface, which is also inconvenient in measurement.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a technique capable of easily and robustly measuring the thickness of an object to be measured.

Means and effects for solving the problems

  The problems to be solved by the present invention are as described above. Next, means for solving the problems and the effects thereof will be described.

According to the viewpoint of this invention, the thickness measuring method for measuring the thickness of a to-be-measured body through a medium is provided as follows. That is, this thickness measuring method includes a transmitting step, a receiving step, a delay time setting step, a beam forming step, and a thickness detecting step. In the transmission step, a transmission wave is transmitted from the element array having a plurality of elements capable of transmitting and receiving signals toward the measurement object via the medium. In the receiving step, a reflected wave from the measurement object is received by the element array. In the delay time setting step, the delay time of each element is set. In the beam forming step, a reception beam signal is formed by synthesizing a reception signal output from an element that has received the reflected wave by delaying the delay time set for the element. In the thickness detection step, the thickness of the measurement object is detected based on the intensity of the received beam signal. In this thickness measuring method, the beam forming step is performed by changing the delay time set in the delay time setting step so as to change a focal length when the reflected wave is emitted from a focal point. By repeating, a scanning step of forming a plurality of received beam signals is included. In the thickness detection step, the thickness of the measurement object is detected based on the intensity of the plurality of received beam signals.

Thus, by setting an appropriate delay time for each element, the phases of the reception signals output by each element can be made uniform. Since the S / N ratio can be improved by synthesizing a plurality of reception signals having the same phase, the peak of the reflected wave from the measurement object can be detected robustly. Therefore, with the above configuration, the thickness of the measurement object can be detected robustly. Further, by repeating the beam forming process while changing the delay time, the received beam signal can be formed with the phases of the reflected waves aligned.

  In the thickness measurement method, it is preferable that in the delay time setting step, a maximum delay time is set for a specific center element, and a smaller delay time is set for an element far from the center element.

  That is, the reflected wave from the object to be measured arrives the earliest to the element (center element) that is closest to the object to be measured, and the element farther from the center element until the reflected wave arrives. Takes time. Therefore, by setting the delay time as described above, the phase of the waveform of the reflected wave included in each received signal can be made uniform.

  In the thickness measuring method, it is preferable that there is a hyperbolic relationship between the delay time set for each element in the delay time setting step and the distance from the element to the central element.

  When the cross-sectional ring shape of the object to be measured is regarded as an arc shape, the above relationship is established. Thereby, the delay time of each element can be set appropriately.

  The thickness measuring method is preferably performed as follows. That is, the measured object has a first surface. This thickness measuring method includes an inclination angle detecting step of detecting the inclination angle of the first surface by performing transmission / reception a plurality of times with different transmission angles for transmitting transmission waves from the element array. In the transmission step, the transmission wave whose transmission angle is adjusted based on the inclination angle detected in the inclination angle detection step is transmitted.

  By this inclination angle detection step, it is possible to detect in which direction the first surface of the measurement object is located. In the transmission step, by transmitting the transmission wave in consideration of the inclination angle of the first surface, the transmission wave can be reliably applied to the first surface.

  The thickness measuring method is preferably performed as follows. That is, the measured object has a first surface and a second surface. The thickness measuring method includes a combining process step of combining the plurality of received beam signals generated in the scanning step to form a combined beam signal. In the thickness detection step, the thickness of the object to be measured is based on the time difference between the peak of the reflected wave from the first surface and the peak of the reflected wave from the second surface included in the combined beam signal. Is calculated.

  By combining a plurality of received beam signals, a combined beam signal including the peak of the reflected wave from the first surface and the peak of the reflected wave from the second surface can be obtained. Based on the time difference between the peaks of the first surface and the second surface, the thickness of the object to be measured can be accurately measured.

  In the thickness measurement method, in the synthesis processing step, the synthesized beam signal can be formed by integrating the plurality of received beam signals.

  In this way, by integrating the received beam signals, the peak of the reflected wave from the first surface and the peak of the reflected wave from the second surface can be combined into one combined beam signal.

  In the thickness measuring method, in the synthesis processing step, a maximum intensity value is obtained from the plurality of received beam signals at each time, and the maximum value is arranged in the time axis direction to form the synthesized beam signal. You can also

  As a result, it is possible to obtain a combined beam signal that leaves a strong peak included in each received beam signal.

According to another aspect of the present invention, a thickness measuring method for measuring the thickness of an object to be measured through a medium is provided as follows. That is, this thickness measuring method includes a transmitting step, a receiving step, a delay time setting step, a beam forming step, and a thickness detecting step. In the transmission step, a transmission wave is transmitted from the element array having a plurality of elements capable of transmitting and receiving signals toward the measurement object via the medium. In the receiving step, a reflected wave from the measurement object is received by the element array. In the delay time setting step, the delay time of each element is set. In the beam forming step, a reception beam signal is formed by synthesizing a reception signal output from an element that has received the reflected wave by delaying the delay time set for the element. In the thickness detection step, the thickness of the measurement object is detected based on the intensity of the received beam signal. The measured object has a first surface and a second surface. This thickness measurement method determines that the minimum thickness of the object to be measured can be measured when the reflected wave from the first surface and the reflected wave from the second surface are returned from the same direction. A minimum thickness determination step is included .

  That is, since the minimum thickness exists in a place where the first surface and the second surface are parallel, it is determined that the minimum thickness can be measured when the front surface reflected wave and the back surface reflected wave return from the same direction. it can.

  In the thickness measuring method, the medium is a soft tissue, the measured object is a cortical bone, and the transmission wave can be an ultrasonic signal.

  Thus, the thickness of cortical bone in soft tissue can be measured by transmitting and receiving ultrasonic signals.

  In the thickness measurement method, the transmission wave is preferably a plane wave.

  In this way, by setting the transmission wave as a plane wave, the transmission wave does not concentrate on a specific portion of the measured object, and thus a reflected wave from the measured object can be stably obtained. This enables a robust measurement.

According to another viewpoint of this invention, the thickness measuring apparatus for measuring the thickness of a to-be-measured object through a medium is provided. That is, the thickness measuring apparatus includes an element array, a delay time setting unit, a beam forming unit, and a thickness detecting unit. The element array includes a plurality of elements capable of transmitting and receiving signals, and transmits a transmission wave toward the measurement object via the medium and receives a reflected wave from the measurement object. The delay time setting unit sets a delay time of each element. The beam forming unit forms a reception beam signal by synthesizing a reception signal output from an element that has received the reflected wave by delaying the delay time set for the element. The thickness detection unit detects the thickness of the measured object based on the intensity of the received beam signal. In this thickness measuring apparatus, the delay time set by the delay time setting unit is changed so as to change a focal length when the reflected wave is emitted from a focal point. A scan processing unit that forms a plurality of reception beam signals by repeating the formation of the reception beam signals is provided. The thickness detector detects the thickness of the measured object based on the intensity of the plurality of received beam signals.

  In the thickness measuring apparatus, it is preferable that the delay time setting unit sets a maximum delay time for a specific center element, and sets a smaller delay time for an element farther from the center element.

  The thickness measuring device is preferably configured as follows. That is, the measured object has a first surface. The thickness measuring device includes an inclination angle detection unit that detects an inclination angle of the first surface by performing transmission / reception a plurality of times with different transmission angles for transmitting transmission waves from the element array. The transmission angle is adjusted based on the inclination angle detected by the inclination angle detection unit and the transmission wave is transmitted to the measurement object. Based on the reflected wave obtained at this time, the beam forming unit receives the reception wave. Form a beam signal.

  The thickness measuring device is preferably configured as follows. That is, the measured object has a first surface and a second surface. The thickness measuring apparatus includes a synthesis processing unit that combines the plurality of reception beam signals formed by the scan processing unit to form a synthesized beam signal. In the thickness detector, the thickness of the object to be measured is determined based on the time difference between the peak of the reflected wave from the first surface and the peak of the reflected wave from the second surface included in the combined beam signal. calculate.

According to another viewpoint of this invention, the thickness measuring apparatus for measuring the thickness of a to-be-measured object through a medium is provided. That is, the thickness measuring apparatus includes an element array, a delay time setting unit, a beam forming unit, and a thickness detecting unit. The element array includes a plurality of elements capable of transmitting and receiving signals, and transmits a transmission wave toward the measurement object via the medium and receives a reflected wave from the measurement object. The delay time setting unit sets a delay time of each element. The beam forming unit forms a reception beam signal by synthesizing a reception signal output from an element that has received the reflected wave by delaying the delay time set for the element. The thickness detection unit detects the thickness of the measured object based on the intensity of the received beam signal. The measured object has a first surface and a second surface. This thickness measuring apparatus determines that the minimum thickness of the object to be measured can be measured when the reflected wave from the first surface and the reflected wave from the second surface are returned from the same direction. A minimum thickness determination unit is provided.

  In the thickness measuring apparatus, the medium is a soft tissue, the measured object is a cortical bone, and the transmission wave can be an ultrasonic signal.

  In the thickness measurement apparatus, the transmission wave is preferably a plane wave.

1 is a block diagram of an ultrasonic diagnostic apparatus according to an embodiment of the present invention. The schematic diagram which shows a mode that an ultrasonic signal is transmitted / received with respect to a cortical bone. The figure explaining the process in a beam formation part. The figure which shows the model in which the reflected wave is transmitted from the single reflection point. The graph which shows the delay time set to each element at the time of using the model of FIG. The figure which shows an example of the model which the present inventors examined. The figure which shows the propagation path at the time of transmitting a plane wave to a circular mirror. The flowchart of the thickness measuring method. Theta-t graph explaining the detection method of the inclination angle in an inclination angle detection process. The figure explaining the process in a scanning process part and a synthetic | combination process part. The flowchart of the thickness measuring method which concerns on another embodiment. The figure explaining the process in a scanning process part and a synthetic | combination process part in another embodiment. The figure which shows the case where the minimum thickness can be measured. The figure which shows the case where the minimum thickness cannot be measured. The figure explaining the measurement by the conventional single sensor.

  Next, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram of an ultrasonic diagnostic apparatus 1 as a thickness measuring apparatus according to an embodiment of the present invention.

  The ultrasonic diagnostic apparatus 1 of the present embodiment uses a cortical bone 10 of a human body as a diagnosis target (measurement target). As shown in FIG. 1, the cortical bone 10 is covered with a soft tissue (medium) 11 such as fat or muscle. Further, the cancellous bone 13 exists inside the cortical bone 10. The cortical bone 10 has a surface (first surface) 14 that contacts the soft tissue 11 and a back surface (second surface) 15 that contacts the cancellous bone 13.

  The ultrasonic diagnostic apparatus 1 of the present embodiment is configured to measure the thickness of the cortical bone 10 via the soft tissue 11. The thickness of the cortical bone 10 refers to the distance between the front surface 14 and the back surface 15. The measured thickness can be used as a measure of bone strength.

  As shown in FIG. 1, the ultrasonic diagnostic apparatus 1 includes an ultrasonic transducer 2 and an apparatus main body 3.

  The ultrasonic transmitter / receiver 2 transmits and receives ultrasonic waves. The ultrasonic transducer 2 includes an abutment surface 2 a that abuts against the surface (skin) of the soft tissue 11 at the measurement site, and an element array 22. The element array 22 includes a plurality of elements 24 arranged in a line at equal intervals along the contact surface 2a.

  The element 24 of the present embodiment is an ultrasonic transducer, and when an electric signal is given, its surface vibrates to generate ultrasonic waves. The element 24 is configured to generate and output an electrical signal (received signal) when receiving an ultrasonic wave on the surface thereof. That is, each element 24 can transmit and receive ultrasonic waves.

  The apparatus main body 3 is connected to the ultrasonic transducer 2 by a cable, and is configured to be able to transmit and receive signals to and from the ultrasonic transducer 2. The apparatus main body 3 includes a transmission circuit 31, a plurality of reception circuits 33, a transmission / reception separation unit 34, a calculation unit 35, and a display unit 32.

  The transmission circuit 31 is configured to generate an electric pulse signal and to apply the electric pulse signal to each element 24. The center frequency of the electric pulse signal is, for example, about 1 to 10 MHz. The transmission circuit 31 is configured to apply an electric pulse signal at an arbitrary timing to each of the plurality of elements 24 of the element array 22. As a result, transmission waves can be transmitted from the plurality of elements 24 all at once or at individual timing.

  The element array 22 transmits an ultrasonic signal (transmission wave) via the soft tissue 11 toward the cortical bone 10 (FIG. 2A). The transmitted wave propagates through the soft tissue 11 and is reflected by the surface 14 of the cortical bone 10 to generate a surface reflected wave (FIG. 2B). Further, a part of the transmission wave enters the cortical bone 10, propagates through the cortical bone 10, and is reflected by the back surface 15 to generate a back surface reflected wave (FIG. 2C). The back surface reflected wave is emitted again into the soft tissue 11. The front surface reflected wave and the back surface reflected wave are received by at least some of the plurality of elements 24.

  The plurality of receiving circuits 33 are respectively connected to the plurality of elements 24 constituting the element array 22. Each receiving circuit 33 receives an electrical signal output when the element 24 receives ultrasonic waves, and receives a digital received signal obtained by performing amplification processing, filtering processing, digital conversion processing, etc. on the electrical signal. It is configured to generate and transmit to the calculation unit 35.

  The transmission / reception separation unit 34 is connected between the element array 22 and the transmission circuit 31 and the reception circuit 33. The transmission / reception separation unit 34 prevents an electrical signal (electrical pulse signal) sent from the transmission circuit 31 to the element array 22 from flowing directly to the reception circuit 33, and also sends an electrical signal ( This is for preventing the reception signal) from flowing to the transmission circuit 31 side.

  The calculation unit 35 is configured as a computer including hardware such as a CPU, a RAM, and a ROM, and can execute various types of calculation processing on the reception signals output from the elements 24. The calculation unit 35 has functions as a thickness measurement unit 50 and a reception angle correction unit 57.

  The thickness measuring unit 50 measures the thickness of the cortical bone 10 based on the received signal. The thickness of the cortical bone 10 measured by the thickness measuring unit 50 is appropriately displayed on the display unit 32. With the ultrasonic diagnostic apparatus 1 configured as described above, the thickness of the cortical bone 10 can be measured. The detailed configuration of the thickness measuring unit 50 will be described later.

  The reception angle correction unit 57 is configured to correct a shift in reception timing derived from the arrival angle of the reflected wave. For example, when a reflected wave arrives from a direction orthogonal to the element array 22 (when a reflected wave having a wavefront parallel to the element array 22 arrives), each element 24 receives the reflected wave at the same timing. However, when a reflected wave arrives from an oblique direction with respect to the element array 22 as shown in FIG. 2B, for example, the timing at which the reflected wave is received by each element 24 is shifted. Therefore, the reception angle correction unit 57 is configured to correct a shift in reception timing due to the arrival of the reflected wave from the oblique direction with reference to the case where the reflected wave arrives from the direction orthogonal to the element array 22. Specifically, the reception angle correction unit 57 corrects the timing shift by delaying each reception signal output from each element 24 by a delay time corresponding to the angle at which the reflected wave arrives.

  Since the direction from which the reflected wave actually arrives is unknown, the reception angle correction unit 57 is the direction in which the element array 22 transmits the transmission wave (the direction of the transmission angle θ shown in FIG. 2A). Assuming that a reflected wave has returned from the above, the reception timing is corrected. Unless otherwise specified, in the following description, description of the processing by the reception angle correction unit 57 is omitted, and it is assumed that the reception timing of the reception signal output from each element 24 is corrected by the reception angle correction unit 57.

  Subsequently, characteristic points of the present embodiment will be described in detail.

  In the conventional sensor shown in FIG. 15, the transmission wave is concentrated on the focal point by the acoustic lens 101. Therefore, when the back surface 15 is rough at the focal point position or there is a hole or the like, the reflected wave is reflected. The thickness of the cortical bone 10 cannot be measured stably.

  Therefore, the ultrasonic diagnostic apparatus 1 of the present embodiment is configured not to concentrate the transmission wave at a specific point of the cortical bone 10.

  That is, in the ultrasonic diagnostic apparatus 1 according to the present embodiment, as shown in FIG. 2A, a plane wave having a certain width is transmitted from a plurality of elements 24 of the element array 22 toward the cortical bone 10 (transmission). Process). The plane wave hits an area having a certain width of the surface 14 of the cortical bone 10 to generate a surface reflected wave (FIG. 2B). Further, the plane wave hits an area having a certain width of the back surface 15 of the cortical bone 10 to generate a back surface reflected wave (FIG. 2C). The front surface reflected wave and the back surface reflected wave are respectively received by the plurality of elements 24 (receiving step).

  Thus, since the transmission wave from the element array 22 is a plane wave, the transmission wave does not concentrate on one point on the front surface 14 or the back surface 15. Thereby, it becomes difficult to be affected by the roughness of the front surface 14 and the back surface 15 and the presence of holes in the cortical bone 10, and the surface reflected wave and the back surface reflected wave can be stably received by the element array 22. In addition, since it is not necessary to concentrate the transmission wave at a specific point (focal point), the stand-off that is necessary when a fixed-focus acoustic lens is used is not required, and the measurement is simplified.

  The thickness measuring unit 50 of the ultrasonic diagnostic apparatus 1 according to the present embodiment includes a beam forming unit 42 in order to stably detect the peak of the reflected wave from the cortical bone 10.

The beam forming unit 42 is configured to form a received beam signal _Sacc by integrating and synthesizing the received signals S output from the plurality of elements 24 that have received the reflected waves. FIG. 3 schematically shows how the reception beam signal S _acc is formed. By accumulating a plurality of received signals S, the waveform of the reflected wave included in the received signal S is strengthened and the S / N ratio is improved, so that the peak of the reflected wave is easily detected.

However, only when the effect of the S / N ratio is improved is that obtained, a plurality of phases of the reflected waves of the waveform included in the received signal S is integrated are aligned. Therefore, the beam forming unit 42 includes a delay time setting unit 43 and a delay processing unit 48, as shown in FIG.

  The delay time setting unit 43 is configured to set the delay time of each element 24. The delay processing unit 48 is configured to delay the reception signal S output from each element 24 by the delay time set by the delay time setting unit 43. Therefore, if the delay time of each element 24 is set appropriately, the delay processing unit 48 delays each reception signal S, so that the phases of the reflected waves included in each reception signal S are aligned.

The beam forming unit 42 includes an integration processing unit 44. The integration processing unit 44 is configured to integrate the reception signal S delayed by the delay processing unit 48 to form the reception beam signal _Sacc .

For example, if the phase of the surface reflected wave waveform is the same in each received signal S delayed by the delay processing unit 48, the waveform of the surface reflected wave is strengthened by integrating them, so that the received beam signal S _acc The intensity of the peak of the included surface reflection wave increases (the state shown in FIG. 3). That is, since the S / N ratio of the surface reflected wave is improved, it is easy to detect the peak of the surface reflected wave. Note that the amplitude of the envelope (indicated by a dotted line in FIG. 3) of the received beam signal S _acc is sometimes simply referred to as “intensity” of the signal.

  Also, for example, by setting a delay time different from that for the front surface reflected wave to each element 24, it is possible to improve the S / N ratio of the back surface reflected wave by aligning the phase of the back surface reflected wave waveform. (Illustration omitted). This makes it easier to detect the peak of the back surface reflected wave.

  As described above, according to the configuration of the ultrasonic diagnostic apparatus 1 of the present embodiment, the peak of the front surface reflected wave and the back surface reflected wave can be detected stably, so that the thickness of the cortical bone 10 can be obtained robustly.

  By the way, in order to align the phase of the waveform of the reflected wave (front surface reflected wave or back surface reflected wave) from the cortical bone 10, it is necessary to appropriately set the delay time of each element 24. Next, a method for setting the delay time of each element 24 in the delay time setting unit 43 will be described.

  First, as a simple model of the propagation path of the reflected wave, the model shown in FIG. The model of FIG. 4A is a model in which a reflected wave radiated from a single reflection point 53 is received by each element 24 of the element array 22.

  In the model of FIG. 4A, the element 24 where the reflected wave arrives earliest is set as the central element 24 c of the element array 22. The distance from the central element 24c to the reflection point 53 is Z, the propagation time until the reflected wave from the reflection point 53 arrives at each element 24, the distance from the element 24 to the central element 24c is ΔX, and the ultrasonic wave Assuming that the sound velocity of the medium propagating is SOS, the following relationship is established. As the SOS, an empirical value of sound velocity in soft tissue can be used.

The propagation time T _c of the reflected wave from the reflection point 53 to the central element 24c can be obtained by the following equation by substituting ΔX = 0 into the above equation 1.

The difference between the propagation time T _c of the reflected wave to the central element 24 _c and the propagation time T of the reflected wave to the other element 24 is defined as a delay time ΔT of the reflected wave to each element 24. The delay time ΔT of the reflected wave up to each element 24 can be obtained by the following Equation 3.

  If the formula 3 is modified, the following formula is obtained.

  Equation 4 above has the same form as the hyperbolic equation. As is well known, the hyperbolic equation can be expressed by Equation 5 below. Accordingly, it can be said that the relationship between the position ΔX of each element 24 and the delay time ΔT of the reflected wave to the element 24 is a hyperbola. Therefore, if the delay time ΔT is plotted against the position ΔX of each element 24, a hyperbolic graph as shown in FIG. 4B is obtained.

  In order to align the phases of the reflected waves included in the reception signal S output from each element 24, the delay time of each element 24 may be set so as to cancel out the delay time ΔT. Therefore, the delay time to be set for each element 24 by the delay time setting unit 43 can be represented by a hyperbola graph (FIG. 5) obtained by vertically inverting the graph of FIG. Therefore, it can be said that there is a hyperbolic relationship between the delay time set for each element 24 and the position ΔX of each element 24 (distance from the central element 24c). As shown in the graph of FIG. 5, the delay time set for the central element 24c is the longest, and the delay time becomes smaller as the element 24 is farther from the central element 24c.

  That is, in the model of FIG. 4A, the time until the reflected wave arrives earlier at the element 24 closer to the central element 24c, the reflected wave from the reflection point 53 arrives earlier, and the element 24 farther from the central element 24c arrives. It takes. Therefore, a larger delay time is set for the element 24 closer to the central element 24c. If the delay time of each element 24 is set as described above, when the reflected wave is radiated from the reflection point 53 of FIG. Can be aligned.

  The delay time set by the delay time setting unit 43 has been described above with reference to the model of FIG. 4A as a simple model of the propagation path of the reflected wave. However, as described above, in the ultrasonic diagnostic apparatus 1 according to the present embodiment, since the transmission wave is not concentrated on a specific point of the cortical bone 10, the reflected wave (surface reflection wave or back surface reflection) is reflected from the specific reflection point 53. Waves) are not expected to be emitted. Therefore, the model of FIG. 4A is not suitable as a model of the propagation path of the front surface reflected wave and the back surface reflected wave in this embodiment.

  Therefore, the present inventors examined a model shown in FIG. This model is obtained by modeling the shape of the cortical bone 10 with the cross-sectional shape of the front surface 14 of the cortical bone 10 being an arc having a radius R1 and the cross-sectional shape of the back surface 15 being an arc having a radius R2. The distance from the central element 24c of the element array 22 to the front surface 14 is Z1, and the distance from the back surface 15 is Z2.

  The actual cortical bone 10 has a complicated curved surface as a whole, but if it is limited to a partial region (local site) of the cortical bone 10, the shape of the cortical bone 10 is sufficiently approximated by the above model. it can. As shown in FIG. 2A, the ultrasonic diagnostic apparatus 1 of the present embodiment emits a plane wave from a part of the elements 24 of the element array 22 toward a part of the cortical bone 10 (local part 12). Configured to send. Thus, in this embodiment, since the area | region which applies an ultrasonic wave is limited to the one part area | region of the cortical bone 10, it may be considered that approximation by the model of Fig.6 (a) is materialized. When transmitting a transmission wave from a part of the element array 22 in this way, the part is referred to as a sub-array 25.

  Next, the delay time ΔT of the back surface reflected wave to each element 24 in the model of FIG.

  In the model shown in FIG. 6A, if the radii R1, R2, distances Z1, Z2, and the sound speeds of the cortical bone 10 and the soft tissue 11 are set, the back-surface reflected wave generated when a plane wave is transmitted from the element array 22 is set. The propagation path to each element 24 can be obtained by simulation using Snell's law. An example of the propagation path obtained by the simulation in this way is shown in FIG. Based on the propagation path of the back surface reflected wave obtained in the simulation, the delay time ΔT of the back surface reflected wave to each element 24 can be calculated. An example of the delay time ΔT obtained based on the simulation is shown in the graph of FIG.

  The inventors of the present application conducted extensive research and found that the graph of the delay time ΔT in FIG. 6B is very similar to the graph of the delay time ΔT in FIG.

  Therefore, when the inventors of the present application examined in detail, even when the combination of the six parameters in the model of FIG. 6A is varied, the delay time ΔT of the back reflection wave obtained by the simulation based on the model is different. Thus, it was found that the delay time ΔT calculated by the above-described equation 3 was well matched. In the range studied by the inventors of the present application, the graph of the delay time ΔT of the back-surface reflected wave obtained by the simulation using the model of FIG. This graph (FIG. 4B) can be approximated with a similarity of about 99%.

  Next, the delay time ΔT of the surface reflected wave to each element 24 in the model of FIG.

  In the case of the model of FIG. 6A, since the cross-sectional shape of the surface 14 is an arc, the surface 14 can be regarded as a circular mirror. As is well known, in a circular mirror, if the aperture area is sufficiently small, a focal point 51 can be assumed as shown in FIG. If a plane wave is transmitted toward the cortical bone 10 (circular mirror), the surface reflected wave generated by the reflection of the plane wave by the surface 14 (circular mirror) is transmitted through the propagation path as if radiated from the focal point 51. It is received by the element 24 (FIG. 7).

Therefore, the delay time ΔT of the surface reflected wave to each element 24 in the model of FIG. 6A can be calculated on the assumption that the surface reflected wave is emitted from the single focal point 51. More specifically, if the distance from the center element 24c to the focal point 51 and the focal length Z _f, by substituting the focal length Z _f a distance Z in Equation 3 already described, the surface reflection of each element 24 The wave delay time ΔT can be calculated. In this way, the delay time ΔT of the surface reflected wave to each element 24 can be calculated using Equation 3.

  As described above, it is clear from the research by the inventors of the present application that the delay time ΔT of the front surface reflected wave and the back surface reflected wave generated when a plane wave is transmitted from the element array 22 can be approximately calculated by Equation 3, respectively. became.

  That is, in order to obtain the delay time ΔT of the reflected wave (surface reflected wave or back surface reflected wave) by simulation using the model of FIG. 6A, six parameters (radius R1, R2, distance Z1, Z2, and It is necessary to set the sound velocity of the cortical bone 10 and the soft tissue 11). Empirical values can be used for the sound velocity of the soft tissue 11, but the other five parameters are unknown. Thus, it is conceivable to search for five unknown parameters by trial and error. However, since five independent parameters are searched for by trial and error, the calculation load becomes enormous and is not realistic.

  In this respect, since there is only one unknown parameter (distance Z) in Equation 3, it is simpler than the model of FIG. 6A in which there are five unknown parameters. Therefore, if Equation 3 is used when calculating the delay time ΔT of the reflected wave (front surface reflected wave or back surface reflected wave), it is compared with the case where the delay time ΔT is calculated by simulation using the model of FIG. Thus, the calculation load can be greatly reduced.

  Based on the above, the thickness measurement method of the present embodiment will be specifically described with reference to the flowchart of FIG.

In this thickness measurement method, first, the inclination angle _θsurf of the surface 14 of the cortical bone 10 is detected (step S101, inclination angle detection step). Note that the inclination angle _θsurf is an angle formed by the tangent to the surface 14 of the cortical bone 10 and the direction in which the elements 24 are arranged in the element array 22 (see FIG. 2A).

  The thickness measurement unit 50 includes an inclination angle detection unit 45. The inclination angle detection unit 45 is configured to transmit a plane wave at a certain transmission angle θ from a part of the element array 22 (subarray 25) toward a part of the cortical bone 10 (local site 12). The transmission angle θ is an angle formed by a direction orthogonal to the direction in which the elements 24 of the subarray 25 are arranged and the traveling direction of the plane wave (see FIG. 2A).

The plane wave transmitted from the subarray 25 is reflected by the surface 14 of the cortical bone 10 to generate a surface reflected wave (see FIG. 2B). This surface reflected wave is received by each element 24 of the element array 22. The inclination angle detection unit 45 integrates the reception signals S output from the elements to form a reception beam signal _Sacc .

For example, as shown in FIG. 2A, when the transmission angle θ and the inclination angle θ _surf coincide with each other, the surface reflected wave returns from the direction in which the plane wave is transmitted (direction of the transmission angle θ) (for example, FIG. as shown in b)). In this case, since the deviation in timing at which the surface reflected waves are received by the respective elements 24 is appropriately corrected by the reception angle correcting unit 57, the intensity of the peak of the surface reflected waves in the received beam signal _Sacc increases. On the other hand, when the transmission angle θ and the tilt angle _θsurf do not match (not shown), the surface reflected wave returns from a direction different from the direction in which the plane wave is transmitted (the direction of the transmission angle θ) (or returns completely). Not come) In this case, since the deviation in timing at which the surface reflected waves are received by the respective elements 24 cannot be corrected appropriately by the reception angle correction unit 57, the intensity of the peak of the surface reflected waves in the received beam signal _Sacc becomes small.

As described above, when the transmission angle θ is different, the intensity of the peak of the surface reflected wave included in the reception beam signal S _acc is also different. The inclination angle detection unit 45 is configured to perform transmission / reception of the plane wave a plurality of times with different transmission angles θ. As a result, a plurality of received beam signals S _acc with different transmission angles θ are obtained.

If the intensity of each received beam signal S _acc is plotted against the transmission angle θ, a θ-t graph as shown in FIG. 9 is obtained. In FIG. 9, it is shown that the intensity of the received beam signal S _acc is higher as the dot pattern density is higher. In the θ-t graph, a portion having a high intensity (a portion having a high dot pattern density) is referred to as an “echo image”.

The tilt angle detection unit 45 is configured to obtain the coordinates (θ _max , t _max ) of the point where the intensity of the echo image of the surface reflected wave is maximum on the θ-t graph (FIG. 9). It can be determined that the transmission angle (transmission angle θ _max ) at this time matches the inclination angle θ _surf of the surface 14 of the local region 12. That is, the inclination angle θ _surf = θ _max of the surface 14 of the local region 12. As described above, the tilt angle detection unit 45 can detect the tilt angle _θsurf of the surface 14 of the local region 12.

Next, the thickness measuring unit 50 transmits a plane wave from the subarray 25 toward the local site 12 (step S102, transmission process). In this transmission step, the thickness measurement unit 50 adjusts the transmission angle θ of the transmission wave so as to coincide with the inclination angle θ _surf detected by the inclination angle detection unit 45, and transmits the transmission wave. Thereby, since the plane wave hits the surface 14 of the local region 12 perpendicularly, the plane wave can be reliably applied to the surface 14.

  The plane wave generates a surface reflected wave on the surface 14 of the cortical bone 10. The plane wave is incident on the cortical bone 10 and generates a back-surface reflected wave on the back surface 15. The front surface reflected wave and the back surface reflected wave are received by the plurality of elements 24 of the element array 22, respectively (step S103, reception process).

  The thickness measurement unit 50 of this embodiment includes a scan processing unit 49. The scan processing unit 49 is configured to repeatedly perform the delay time setting process (step S104) and the reception beam forming process (step S105) (loops of steps S104 to S105, scan process).

  In the delay time setting step (step S104), the delay time setting unit 43 obtains the delay time ΔT of the reflected wave to each element 24 based on Equation 3. In order to calculate the delay time ΔT, the value of the distance Z, which is a parameter of Formula 3, is required. However, an appropriate value to be set for the distance Z is unknown. Therefore, the delay time setting unit 43 is configured to calculate a delay time ΔT for each element 24 by substituting an appropriate value for the distance Z in Expression 3 in step S104.

  Then, the delay time setting unit 43 sets the delay time of each element 24 so as to cancel the obtained delay time ΔT. As already described, there is a hyperbolic relationship as shown in FIG. 5 between the delay time of each element 24 set based on Equation 3 and the position ΔX of each element 24.

In the beam forming step (step S <b> 105), the delay processing unit 48 delays the reception signal S output from each element 24 by the delay time set in the element 24. The integration processing unit 44 integrates the reception signals S delayed by the delay processing unit 48 to form a reception beam signal _Sacc (step S105, beam forming step).

  Then, the scan processing unit 49 repeatedly performs the delay time setting process and the reception beam forming process described above (loop of steps S104 to S105, scan process).

  Note that the delay time setting unit 43 is configured to vary the value to be substituted for the distance Z in Formula 3 for each repetition in the scanning process. Accordingly, in the scanning process, the delay time setting process and the beam forming process are repeatedly executed while changing the value of the distance Z. In this way, repeating the process while changing the value of the distance Z may be simply expressed as “scanning the distance Z”.

Through the above scanning process, a plurality of received beam signals S _acc with different values of the distance Z are obtained (FIG. 10).

As described above, the delay time ΔT of the surface reflected wave to each element 24 can be approximately calculated by Equation 3. Although the value of the distance Z necessary for calculating the delay time ΔT of the surface reflected wave is unknown, in the above scan processing step, the distance Z that is the only unknown parameter of Equation 3 is scanned. In some cases, the delay time ΔT of the surface reflected wave can be calculated appropriately. At this time, in the beam forming step, the phase of the waveform of the surface reflected wave included in each received signal S can be made uniform. Therefore, the S / N ratio of the surface reflected wave is generated in the received beam signal S _acc generated at this time. Should have improved.

Further, as described above, the delay time ΔT of the back surface reflected wave to each element 24 can also be approximately calculated by Equation 3. Although the value of the distance Z necessary for calculating the delay time ΔT of the back surface reflected wave is unknown, in the above scan processing step, the distance Z, which is the only unknown parameter of Equation 3, is scanned. In some cases, the back surface reflected wave delay time ΔT can be calculated appropriately. At this time, in the beam forming step, the phase of the waveform of the back surface reflected wave included in each received signal S can be made uniform. Therefore, in the received beam signal S _acc generated at this time, the S / N ratio of the back surface reflected wave has the S / N ratio. Should have improved.

Accordingly, among the plurality of received beam signals S _acc obtained in the scanning process, the received beam signal S _acc with an improved S / N ratio of the _front surface reflected wave and a received beam with an improved S / N ratio of the back surface reflected wave are included. Each of the signals S _acc is considered to be included (FIG. 10).

The thickness measuring unit 50 according to the present embodiment includes a synthesis processing unit 52 that synthesizes a plurality of reception beam signals S _acc formed by the scan processing unit 49 to form a synthesized beam signal S _comb .

The synthesis processing unit 52 first detects the intensity (amplitude of the waveform envelope) of each of the plurality of received beam signals S _acc obtained by the scan processing unit 49. Then, the synthesis processing unit 52, the intensity of each received beam signal S _acc, by sampling at predetermined time intervals, to obtain samples representing the intensity of each received beam signal S _acc for each of the predetermined time. Next, the synthesis processing unit 52 obtains a sample indicating the maximum value among the samples acquired for each received beam signal S _{acc at} each predetermined time. Then, the synthesis processing unit 52 generates a synthesized beam signal S _comb by arranging and connecting the samples indicating the maximum values for each predetermined time along the time axis (step S106, synthesis processing step).

As described above, among the plurality of received beam signals S _acc , the received beam signal having an improved S / N ratio of the back surface reflected wave (the peak of the back surface reflected wave has increased) and the S / And a received beam signal in which the N ratio is improved (the peak of the surface reflected wave is increased). By combining the plurality of received beam signals S _acc by the combining processing unit 52, a combined beam signal S _comb having a large peak of the _front surface reflected wave and a large peak of the back surface reflected wave can be obtained (FIG. 10). ).

The thickness measurement unit 50 includes a thickness detection unit 54 that calculates the thickness of the cortical bone 10 (distance between the front surface 14 and the back surface 15) based on the combined beam signal S _comb . First, the thickness detection unit 54 detects a time t _{1 at} which the peak of the front surface reflected wave appears in the combined beam signal S _comb and a time t _{2 at} which the peak of the back surface reflected wave appears. As described above, in the combined beam signal S _comb , since the S / N ratio of the back surface reflected wave and the surface reflected wave is improved, the times t ₁ and t ₂ can be detected robustly.

The thickness detection unit 54, based on the difference Δt of time t ₁ and time t ₂ (see FIG. 10), it calculates the thickness of the cortical bone 10 (distance of the surface 14 and rear surface 15) (step S107, thickness detection Process). For example, if the speed of sound in the cortical bone 10 is SOS, the thickness of the cortical bone 10 can be obtained by SOS × Δt.

  The thickness measuring unit 50 appropriately displays the thickness of the cortical bone 10 obtained as described above on the display unit 32, and ends the flow.

As described above, according to the thickness measurement method using the ultrasonic diagnostic apparatus 1 of the present embodiment, the thickness of the cortical bone 10 can be measured via the soft tissue 11. The thickness measurement method of this embodiment includes a transmission step, a reception step, a delay time setting step, a beam forming step, and a thickness detection step. In the transmission step, a transmission wave is transmitted from the element array 22 having a plurality of elements 24 that can transmit and receive signals toward the cortical bone 10 via the soft tissue 11. In the reception process, the reflected wave from the cortical bone 10 is received by the element array 22. In the delay time setting step, a delay time is set for each element 24. In the beam forming step, a reception beam signal S _acc is formed by synthesizing the reception signal S output from the element 24 receiving the reflected wave by delaying the delay time set in the element 24. In the thickness detection step, the thickness of the measured object is detected based on the intensity of the received beam signal.

  Thus, by setting an appropriate delay time for each element, the phases of the reception signals output by each element can be made uniform. Since the S / N ratio can be improved by synthesizing a plurality of reception signals having the same phase, the peak of the reflected wave from the measurement object can be detected robustly. Therefore, with the above configuration, the thickness of the measurement object can be detected robustly.

  Next, another embodiment of the present invention will be described with reference to the flowchart of FIG. In the following description, the same reference numerals are given to the element names for the same or similar configurations as those in the above embodiment, and the description is omitted.

  In the above-described embodiment, it is assumed that the plane wave transmitted from the subarray 25 appropriately hits both the front surface 14 and the back surface 15. However, the front surface 14 and the back surface 15 of the cortical bone 10 do not necessarily exist in the same direction when viewed from the subarray 25. Therefore, in the thickness measurement method of the embodiment described below, transmission / reception is performed a plurality of times by changing the transmission angle θ of the plane wave from the sub-array 25. Thereby, a plane wave can be reliably applied to the front surface 14 and the back surface 15.

Also in this thickness measurement method, first, the inclination angle _θsurf of the surface 14 of the cortical bone 10 is detected (step S201, inclination angle detection step).

Next, the thickness measuring unit 50 transmits a plane wave at the transmission angle θ while changing the transmission angle θ (step S204) within a predetermined range centered on the inclination angle _θsurf detected in step S201 (step S204). (S202, transmission process) and the process of receiving the reflected wave from the cortical bone 10 (step S203, reception process) is repeated.

  As described above, since the transmission / reception of the plane wave is repeated while changing the transmission angle θ, the plane wave can be reliably applied to the front surface 14 and the back surface 15.

  Since reflected waves from the cortical bone 10 are received by the plurality of elements 24, a plurality of reception signals S can be obtained in step S203. In the above processing, step S203 is repeated while changing the transmission angle θ, so that a plurality of reception signals S can be obtained for each transmission angle θ.

  Subsequently, the delay time setting unit 43 sets an appropriate value for the distance Z in Expression 3, and obtains the delay time ΔT of the reflected wave to each element 24. Then, the delay time setting unit 43 sets a delay time for each element 24 so as to cancel the obtained delay time ΔT (step S205, delay time setting step).

The delay processing unit 48 delays the reception signal S output from each element 24 by the delay time set in the element 24. The integration processing unit 44 integrates the reception signals S delayed by the delay processing unit 48 to form a reception beam signal _Sacc (step S206, beam forming step).

As described above, in the present embodiment, a plurality of reception signals S are obtained for each transmission angle θ by the processing of steps S202 to S204. Therefore, in the beam forming step in step S206, a received beam signal _Sacc is formed for each transmission angle θ.

The thickness measuring unit 50 of this embodiment includes an image generating unit. The image generation unit samples the intensity of the received beam signal S _acc for each transmission angle θ formed in step S206 at each predetermined time t, and obtains a sample indicating the intensity of each received beam signal S _acc for each time. To do. Here, each sample is considered as one pixel. Since each pixel (sample) is obtained every predetermined time t and every transmission angle θ, two-dimensional image data (θ-t graph) represented by t-θ coordinates is obtained (step). S207). The image data obtained in this way is referred to as an echo image E.

  The scan processing unit 49 of the present embodiment is configured to repeat the processes of S205 to S207 (scanning process). Also in the present embodiment, the delay time setting unit 43 is configured to vary the value to be substituted for the distance Z of Formula 3 for each repetition in the scanning process. Thereby, a plurality of echo images E with different values of the distance Z are obtained (FIG. 12).

The synthesis processing unit 52 of the present embodiment synthesizes a plurality of echo images E generated by the scan processing unit 49 to generate a composite echo image E _comb (step S208, synthesis processing step). Specifically, the composition processing unit 52 obtains the maximum value of the pixel values in the plurality of echo images E for each coordinate (θ, t) of the echo image. Then, the synthesis processing unit 52 generates the synthesized echo image E _comb by plotting the maximum value pixel obtained for each coordinate (θ, t) at the coordinate (θ, t).

  The plurality of echo images E include an echo image with an improved S / N ratio of the front surface reflected wave and an echo image with an improved S / N ratio of the back surface reflected wave, as shown in FIG. Yes. As shown in FIG. 12, the echo image of the surface reflected wave appears clearly (with high intensity) in the echo image in which the S / N ratio of the surface reflected wave is improved. Similarly, in an echo image in which the S / N ratio of the back surface reflected wave is improved, the echo image of the back surface reflected wave appears clearly (with high intensity).

Therefore, by synthesizing the plurality of echo images E by the synthesis processing unit 52, a composite echo image E _comb having a clear echo image of the front surface reflected wave and a clear echo image of the back surface reflected wave can be obtained. (FIG. 12).

The thickness detector 54 of the present embodiment detects the echo image of the front surface reflected wave and the echo image of the back surface reflected wave included in the synthesized echo image E _comb . The thickness detector 54 determines the time difference Δt between the time t ₁ when the echo image of the _front surface reflected wave is detected in the synthesized echo image E _comb and the time t ₂ when the echo image of the back surface reflected wave is detected (see FIG. 12). Based on the above, the thickness of the cortical bone 10 (distance between the front surface 14 and the back surface 15) is calculated (step S209, thickness detection step).

  By the way, since the thickness of the cortical bone 10 varies depending on the measurement site, it is necessary to measure the thickness (minimum thickness) at the site where the front surface 14 and the back surface 15 are closest to each other in order to obtain a highly reliable measurement result. Therefore, the thickness measurement unit 50 of the present embodiment includes a minimum thickness determination unit that determines whether or not the minimum thickness can be detected.

As shown in FIG. 13A, the minimum thickness h _min of the cortical bone 10 exists at a site where the tangent line (inclination angle θ _surf ) of the front surface 14 and the tangent line (inclination angle θ _back ) of the _back surface 15 are parallel. doing. If the front surface 14 and the back surface 15 are parallel, the front surface reflected wave and the back surface reflected wave return to the sub-array 25 from the same direction, so that the echo image of the front surface reflected wave and the echo image of the back surface reflected wave are combined echo image E _comb. Appear in the same direction θ (FIG. 13B).

On the other hand, for example, as shown in FIG. 14A, the thickness h of the portion where the tangent of the front surface 14 and the tangent of the back surface 15 are not parallel is not the minimum thickness of the cortical bone 10. Thus, when the front surface 14 and the back surface 15 are not parallel, the front surface reflected wave and the back surface reflected wave return to the subarray 25 from different directions, and therefore, the echo image of the front surface reflected wave and the echo image of the back surface reflected wave are combined echo images. E _comb appears in different directions θ (FIG. 14B).

Therefore, the minimum thickness determination unit is configured to determine whether or not the echo image of the front surface reflected wave and the echo image of the back surface reflected wave appear in the same direction θ in the composite echo image E _comb ( Step S210, minimum thickness determination step).

When the echo image of the front surface reflected wave and the echo image of the back surface reflected wave appear in different directions θ in the composite echo image E _comb (in the case of FIG. 14B), the minimum thickness determination unit performs a step. It is determined that the thickness of the cortical bone 10 obtained in S209 is not the minimum thickness. In this case, the thickness measuring unit 50 is configured to move the sub-array 25 to a position where the minimum thickness can be measured (step S211) and repeat the processing from step S201 to step S210. In the case of the ultrasonic diagnostic apparatus 1 of the present embodiment, the movement of the subarray 25 can be realized electronically by switching the element 24 that transmits a plane wave instead of physically moving the subarray 25.

On the other hand, the minimum thickness determination unit, and the echo image of the surface reflected wave echo image of the back surface reflected wave, (case shown in FIG. 13 (b)) if appearing in the same direction θ in the composite echo images E _comb The thickness of the cortical bone 10 obtained in step S209 is determined to be the minimum thickness. In this case, the ultrasonic diagnostic apparatus 1 displays the thickness of the cortical bone 10 obtained in step S209 on the display unit 32 as a final measurement result, and ends the flow.

  According to the above method, the minimum thickness of the cortical bone 10 can be measured accurately and stably.

  The preferred embodiment of the present invention has been described above, but the above configuration can be modified as follows, for example.

  In the above-described tilt angle detection step, in order to detect the tilt angle of the surface 14, it is necessary to perform transmission and reception a plurality of times while changing the transmission angle θ. In the embodiment described with reference to the flowchart of FIG. 11, transmission / reception is performed a plurality of times while changing the transmission angle θ in order to form an echo image (θ-t graph). If the minimum thickness cannot be measured, the sub-array 25 must be moved to repeat transmission / reception. Thus, when transmission / reception from the element array 22 is actually repeated many times, there is a problem that it takes time for measurement.

  Therefore, transmission and reception of signals in the subarray 25 may be performed by calculation by applying a known aperture synthesis method in the field of ultrasonic flaw detectors. The aperture synthesis will be briefly described as follows.

  First, an ultrasonic signal is transmitted from a certain element 24, a reflected wave from the cortical bone 10 is received by each element 24 of the element array 22, and the received signal output by each element 24 is data (received signal data). Remember as. This is repeated while switching the element 24 that transmits the signal, and the received signal data is collected.

  Of the collected received signal data, the received signal data of each element 24 based on the signals transmitted by the plurality of elements 24 constituting the sub-array 25 is synthesized for each element 24, thereby transmitting a transmission wave from the sub-array 25. Sometimes, the received signal S output from each element 24 can be obtained by calculation.

  In this way, by collecting the received signal data in advance, all transmission / reception of signals by the subarray 25 can be performed by calculation. Thereby, since it is not necessary to repeat transmission and reception of signals in the subarray 25, the time required for measurement can be shortened.

  Therefore, in the present invention, when “transmission” and “reception” are used, in addition to the case where signals are actually transmitted and received by the subarray 25, each element 24 of the subarray 25 is synthesized by synthesizing the received signal data collected in advance. Includes a process (aperture synthesis) for obtaining the received signal S output by the calculation.

  In the above embodiment, the combining processing unit 52 forms a combined beam signal by arranging the maximum values of a plurality of received beam signals. However, the synthesis processing unit 52 may form a synthesized beam signal by, for example, integrating the intensity of a plurality of received beam signals every time. In short, it is only necessary to appropriately combine the peak of the front surface reflected wave and the peak of the back surface reflected wave to generate one combined beam signal.

In the above-described embodiment, the ultrasonic diagnostic apparatus 1 is configured to calculate the thickness of the cortical bone 10, but is not necessarily limited thereto. For example, the ultrasonic diagnostic apparatus 1 does not specifically calculate the value of the cortical bone thickness, but only displays the combined beam signal S _comb of FIG. 10 or the combined echo image E _comb of FIG. good. The operator of the ultrasonic diagnostic apparatus 1 obtains the thickness of the cortical bone 10 based on the time difference Δt between the surface reflected wave and the back reflected wave by viewing the displayed synthesized beam signal S _comb or synthesized echo image E _comb. it can.

  In the above embodiment, a plane wave is transmitted from the element array 22 toward the cortical bone 10, but the present invention is not limited to this. Since it is sufficient that the transmission wave does not concentrate on a specific point of the cortical bone 10, for example, a spherical wave having a focal point outside the cortical bone 10 may be transmitted.

  In the above embodiment, the beam forming process is repeatedly performed while changing the value of the distance Z (scanning process). This is because the value of the distance Z is unknown, and therefore the phase of the reflected wave (front surface reflected wave or back surface reflected wave) cannot be aligned in one beam forming step. However, as a possibility, the phase of the front surface reflected wave and the back surface reflected wave may be aligned in the first beam forming step. In this case, since it is not necessary to repeat the beam forming process, the beam forming process may be performed only once.

  The thickness measurement method of the present invention is not limited to the measurement of cortical bone thickness but can be widely applied to the measurement of the thickness of other measured objects. For example, the thickness of the blood vessel can be measured by the thickness measurement method of the present invention. By measuring the thickness of the artery, it is possible to detect the thickness of unnecessary components that have precipitated on the inner surface of the blood vessel, and thus can be used for diagnosis of arteriosclerosis.

  Further, the thickness measuring method of the present invention is not limited to the use of a human body as a diagnosis target. For example, in a pipe in which a fluid flows inside, the progress of the corrosion of the inner wall surface varies depending on the pH, temperature, flow method, etc. of the fluid, so it is difficult to determine the degree of deterioration of the pipe. Therefore, by measuring the thickness of the pipe by the thickness measurement method of the present embodiment, the degree of corrosion of the pipe can be monitored.

1 Ultrasonic diagnostic equipment (thickness measuring equipment)
10 Cortical bone (object to be measured)
11 Soft tissue (medium)
14 Surface (1st surface)
15 Back side (2nd side)
22 element array 24 element

Claims (17)

A thickness measuring method for measuring the thickness of a measured object through a medium,
A transmission step of transmitting a transmission wave from the element array having a plurality of elements capable of transmitting and receiving signals toward the measurement object via the medium;
A receiving step of receiving a reflected wave from the object to be measured by the element array;
A delay time setting step for setting the delay time of each element;
A beam forming step of forming a reception beam signal by synthesizing the reception signal output from the element that has received the reflected wave by delaying the delay time set in the element;
A thickness detecting step of detecting the thickness of the measured object based on the intensity of the received beam signal;
Only including,
By changing the delay time set in the delay time setting step so as to change a focal length when the reflected wave is emitted from a focal point, and repeating the beam forming step, a plurality of times Including a scanning step of forming a receive beam signal;
In the thickness detecting step, the thickness of the object to be measured is detected based on the intensity of the plurality of received beam signals . The thickness measurement method according to claim 1 ,
In the delay time setting step,
The maximum delay time is set for a specific center element,
A thickness measuring method, wherein a delay time is set to be smaller for an element farther from the central element. The thickness measuring method according to claim 2 ,
A thickness measurement method, wherein the delay time set for each element in the delay time setting step and the distance from the element to the central element have a hyperbolic relationship. It is the thickness measuring method as described in any one of Claim 1 to 3 ,
The object to be measured has a first surface;
A tilt angle detecting step of detecting a tilt angle of the first surface by performing transmission and reception a plurality of times with different transmission angles for transmitting transmission waves from the element array;
In the transmission step, the transmission wave whose transmission angle is adjusted based on the inclination angle detected in the inclination angle detection step is transmitted. It is the thickness measuring method as described in any one of Claim 1 to 4, Comprising :
The object to be measured has a first surface and a second surface;
Combining a plurality of received beam signals formed in the scanning step to form a combined beam signal,
In the thickness detection step, the thickness of the object to be measured is determined based on the time difference between the peak of the reflected wave from the first surface and the peak of the reflected wave from the second surface included in the combined beam signal. A thickness measuring method characterized by calculating. The thickness measuring method according to claim 5 ,
In the synthesis processing step, the synthesized beam signal is formed by integrating the plurality of received beam signals. The thickness measuring method according to claim 5 ,
Thickness characterized in that, in the synthesis processing step, the combined beam signal is formed by obtaining a maximum value of intensity among the plurality of received beam signals for each time and arranging the maximum values in a time axis direction. Measuring method. A thickness measuring method for measuring the thickness of a measured object through a medium,
A transmission step of transmitting a transmission wave from the element array having a plurality of elements capable of transmitting and receiving signals toward the measurement object via the medium;
A receiving step of receiving a reflected wave from the object to be measured by the element array;
A delay time setting step for setting the delay time of each element;
A beam forming step of forming a reception beam signal by synthesizing the reception signal output from the element that has received the reflected wave by delaying the delay time set in the element;
A thickness detecting step of detecting the thickness of the measured object based on the intensity of the received beam signal;
Including
The object to be measured has a first surface and a second surface;
A minimum thickness determination step for determining that the minimum thickness of the object to be measured can be measured when the reflected wave from the first surface and the reflected wave from the second surface are returned from the same direction; A thickness measuring method characterized by the above. It is the thickness measuring method as described in any one of Claim 1-8 ,
The thickness measuring method, wherein the medium is soft tissue, the object to be measured is cortical bone, and the transmission wave is an ultrasonic signal. A thickness measuring method according to any one of claims 1 to 9 ,
The thickness measuring method, wherein the transmission wave is a plane wave. A thickness measuring device for measuring the thickness of a measured object through a medium,
A plurality of elements capable of transmitting and receiving signals, an element array for transmitting a transmission wave toward the measurement object via the medium, and receiving a reflected wave from the measurement object;
A delay time setting unit for setting the delay time of each element;
A beam forming unit that forms a reception beam signal by synthesizing a reception signal output from an element that has received the reflected wave by delaying the delay time set in the element;
A thickness detector for detecting the thickness of the object to be measured based on the intensity of the received beam signal;
Bei to give a,
The delay time set by the delay time setting unit is changed so as to change a focal length when the reflected wave is emitted from a focal point, and the reception beam signal is formed by the beam forming unit. By repeating the above, a scan processing unit for forming a plurality of received beam signals is provided,
The thickness measuring unit detects the thickness of the object to be measured based on the intensity of the plurality of received beam signals . The thickness measuring device according to claim 11 ,
The delay time setting unit includes:
Set the maximum delay time for a specific center element,
The thickness measuring apparatus is characterized in that the delay time is set smaller as the element is farther from the central element. The thickness measuring device according to claim 11 or 12 ,
The object to be measured has a first surface;
A tilt angle detector that detects the tilt angle of the first surface by performing transmission and reception a plurality of times with different transmission angles for transmitting transmission waves from the element array;
The transmission angle is adjusted based on the inclination angle detected by the inclination angle detection unit and the transmission wave is transmitted to the measurement object. Based on the reflected wave obtained at this time, the beam forming unit receives the reception wave. A thickness measuring apparatus for forming a beam signal. The thickness measuring device according to any one of claims 11 to 13 ,
The object to be measured has a first surface and a second surface;
Comprising a combining processing unit that combines the plurality of received beam signals formed by the scan processing unit to form a combined beam signal;
In the thickness detector, the thickness of the object to be measured is determined based on the time difference between the peak of the reflected wave from the first surface and the peak of the reflected wave from the second surface included in the combined beam signal. A thickness measuring device characterized by calculating. A thickness measuring device for measuring the thickness of a measured object through a medium,
A plurality of elements capable of transmitting and receiving signals, an element array for transmitting a transmission wave toward the measurement object via the medium, and receiving a reflected wave from the measurement object;
A delay time setting unit for setting the delay time of each element;
A beam forming unit that forms a reception beam signal by synthesizing a reception signal output from an element that has received the reflected wave by delaying the delay time set in the element;
A thickness detector for detecting the thickness of the object to be measured based on the intensity of the received beam signal;
With
The object to be measured has a first surface and a second surface;
A minimum thickness determining unit that determines that the minimum thickness of the object to be measured can be measured when the reflected wave from the first surface and the reflected wave from the second surface are returned from the same direction; A thickness measuring apparatus characterized by the above. The thickness measuring device according to any one of claims 11 to 15 ,
The thickness measuring apparatus, wherein the medium is a soft tissue, the object to be measured is a cortical bone, and the transmission wave is an ultrasonic signal. The thickness measuring device according to any one of claims 11 to 16 ,
The thickness measuring apparatus, wherein the transmission wave is a plane wave.

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