JP2022036721A - Creation method for ultrasonic tomographic image - Google Patents

Abstract

To provide an ultrasonic image creation method capable of emphasizing visualization of the bone by paying attention to difference between reflection characteristic in the bone and scattering characteristic in muscular tissue.SOLUTION: A reflection characteristic group {RR (θ; z, φ)} from a plane and a scattering characteristic group {RS (θ; z)} from a point are measured in advance. Next, a signal P (x, z) is measured with respect to an object. Amplitude characteristic R (θ; P (x, z)) is calculated with respect to a signal P (x, z). The obtained amplitude characteristic R (θ; P (x, z)) is compared with the reflection characteristic group {RR(θ; z, φ)} from the plane measured in advance and the scattering characteristic group {RS (θ; z)} from the point, so as to determine which of reflection or scattering, the signal is derived from, and an angle φ is identified in the case of reflection. An obtained result is displayed overlapping an ultrasonic tomographic image (a B mode image).SELECTED DRAWING: Figure 7

Description

The present invention relates to a method for creating an ultrasonic tomographic image in an ultrasonic diagnostic apparatus, and to a method for creating an ultrasonic image in which bone is emphasized in a situation where bones, muscle tissues, and organs in a living body are mixed.

Epidural anesthesia is one of the widely used local anesthesia methods in clinical practice. An anesthetic needle is injected into the epidural space of the patient to continuously inject the anesthetic. This anesthesia method has the following three advantages over general anesthesia. The first is that in surgery on the lower limbs and lower abdomen, the stress response during the operation can be suppressed and the immune system can be maintained. The second is that postoperative pain can be alleviated by continuously administering an anesthetic even after surgery. Third, the frequency of postoperative complications can be reduced. Therefore, epidural anesthesia can greatly contribute to reducing the burden on patients during and after surgery.

In order to perform epidural anesthesia, the position of the epidural space where the anesthesia needle is punctured must be identified and the needle must be punctured accurately. Needles must be passed from the back to the spinal gap, but the spinal gap in the epidural space is very narrow and the identification of the gap depends on the experience and palpation of the physician. In particular, the thoracic spine has a narrow gap, making it difficult to identify its position. Images by medical ultrasound are used as an aid to puncture, but general ultrasonic tomographic images do not have sufficient depiction ability to accurately identify the puncture position. The causes include specular reflection of ultrasonic waves on the bone surface and the influence of shallow muscle tissue. That is, this anesthesia method has a problem that it is difficult to specify the puncture position of the anesthesia needle because the surface structure of the spine is complicated.

As a related technique, in Patent Document 1 below, the trabecula direction is determined by relatively rotating the living body in a plane intersecting the wave transmission direction of ultrasonic waves. In this case, since the living body is rotated, it cannot be used in real time during the operation of epidural anesthesia.

In Patent Document 2, an image in which the inside of a tissue and a bone are emphasized separately is obtained by imaging using a plurality of frequency components. However, when determining the shape of the bone on the bone surface, the specular reflection on the bone surface is not taken into consideration, and the shape of the thoracic spine surface, which is a complicated structure, cannot be accurately depicted.

Patent Document 3 discloses a method for identifying the shape of a bone using ultrasonic waves. However, it is necessary to send and receive ultrasonic waves multiple times according to the shape of the bone, and even in this case, it cannot be used in real time during the operation of epidural anesthesia.

Patent No. 3888744 Patent No. 4713112 Patent No. 6231547

W. Kroebel, K.-H. Mahrt, “Recent results of absolute sound velocity measurements in pure water and sea water at atmospheric pressure,” Acustica, Vol. 35, pp. 154-164 (1976). Hashimoto, Mori, Arakawa, Onishi, Yamauchi, Kanai, "Study on Differences in Reflective Characteristics of Surface Structures and Scattering Characteristics of Point Structures Aiming at Visualization of Human Thoracic Vertebrae by Ultrasound," Proceedings of the 2020 Acoustical Society of Japan Spring Meeting Shu, pp. 71-74 (2020).

It is an object of the present invention to pay attention to the difference between the reflex property in bone and the scattering property in muscle tissue, and to provide an ultrasonic image creating method capable of emphasizing the depiction of bone.

The method for creating an ultrasonic image according to the present invention is
(A) The process of measuring the signal P (x, z) derived from the reflection or scattering of ultrasonic waves applied to the object to be imaged, and
(B) The step of calculating the amplitude characteristic R (θ; P (x, z)) based on the signal P (x, z), and
(C) Reflection characteristic group {R _R (θ; z, φ) obtained by measuring the reflection signal of the ultrasonic waves irradiating the surface reflector acquired in advance with the amplitude characteristic R (θ; P (x, z)). )} And the scattering characteristic group { _RS (θ; z)} obtained by measuring the scattering signal of the ultrasonic waves applied to the point scatterer, the signal P (x, z) is a reflected signal or scattering. The step of identifying whether it is one of the signals, and when it is identified as a reflected signal, the step of identifying the angle φ of the image pickup target, and
(D) A step of correcting a B-mode ultrasonic tomographic image of an imaged object based on the angle φ, and
It is a method of creating an ultrasonic image including.

The method for creating an ultrasonic image according to the present invention is the above method, and the correction is an ultrasonic wave applied to a surface reflector previously acquired in the amplitude characteristic R (θ; P (x, z)). Reflection characteristic group _{ R _R (θ; z, φ)} obtained by measuring the reflection signal of In comparison with z)}, normalized intercorrelation is used to identify whether the signal P (x, z) is either a reflected signal or a scattered signal, and if identified as a reflected signal, said. It is a method characterized by identifying the angle φ of an object to be imaged.

The method for creating an ultrasonic image according to the present invention is the above method, in which the correction sets an angle θ = θ _MAX at which the amplitude is maximum in the amplitude characteristic R (θ; P (x, z)). The ratio of the average amplitude in the group {θ _M } with the high amplitude and the average amplitude in the group {θ _m } with the low amplitude including the angle θ farthest from θ _MAX was obtained, and the above ratio was exceeded in the B mode. It is a method characterized by multiplying the pixel value of each pixel in a sound wave tomographic image.

The system for creating an ultrasonic image of the present invention is
(A) A measuring unit that measures the signal P (x, z) derived from the reflection or scattering of ultrasonic waves applied to the object to be imaged, and
(B) An amplitude characteristic acquisition unit that calculates the amplitude characteristic R (θ; P (x, z)) based on the signal P (x, z), and
(C) Reflection characteristic group {R _R (θ; z, φ) obtained by measuring the reflection signal of the ultrasonic waves irradiating the surface reflector acquired in advance with the amplitude characteristic R (θ; P (x, z)). )} And the scattering characteristic group { _RS (θ; z)} obtained by measuring the scattering signal of the ultrasonic waves applied to the point scatterer, the signal P (x, z) is a reflected signal or scattering. An analysis unit that identifies whether it is one of the signals, and if it is identified as a reflected signal, an analysis unit that identifies the angle φ of the image pickup target.
(D) An image processing unit that corrects a B-mode ultrasonic tomographic image of the object to be imaged based on the angle φ, and an image processing unit.
It is a system equipped with.

The program for creating an ultrasonic image of the present invention is
(A) The step of inputting the signal P (x, z) derived from the reflection or scattering of the ultrasonic wave applied to the object to be imaged, and
(B) A step of calculating the amplitude characteristic R (θ; P (x, z)) based on the signal P (x, z), and
(C) Reflection characteristic group {R _R (θ; z, φ) obtained by measuring the reflection signal of the ultrasonic waves irradiating the surface reflector acquired in advance with the amplitude characteristic R (θ; P (x, z)). )} And the scattering characteristic group { _RS (θ; z)} obtained by measuring the scattering signal of the ultrasonic waves applied to the point scatterer, the signal P (x, z) is a reflected signal or scattering. The step of identifying whether it is one of the signals, and if it is identified as a reflected signal, the step of identifying the angle φ of the image pickup object,
(D) A step of correcting a B-mode ultrasonic tomographic image of an imaged object based on the angle φ, and
Is a computer program for making a computer execute.

As described above, according to the present invention, it is possible to acquire an ultrasonic image emphasizing bone for a living body in which bone, muscle tissue, and organ are mixed, and anesthesia when performing epidural anesthesia. It helps to identify the puncture position of the needle.

It is a schematic diagram of a water tank experiment, A is a schematic diagram when measuring reflection characteristics, and B is a schematic diagram when measuring scattering characteristics. It is the measurement result of the reflection characteristic when φ = 0 ° with respect to the acrylic block, A is the B mode image, B is the amplitude distribution of the element data used for image formation on the broken line (x = 20 mm) in FIG. 2A, and C is. It is a reflection characteristic. Reflection characteristics when φ is changed from 0 ° to 15 ° every 1 ° with respect to the acrylic block. It is the measurement result of the scattering characteristic for the tungsten wire, A is the B mode image, B is the amplitude distribution of the element data used for image formation on the broken line (x = 17 mm) in FIG. 4A, and C is the scattering characteristic. Correlation value between the reflection characteristic of φ = 7 ° in FIG. 3 and the reflection characteristic of the angle φ from 0 ° to 15 °. A, B, C, and D are the measurement results of the reflection characteristics for the acrylic block when φ = 8 °, A is the B mode image, B is the reflection characteristics at the points marked with x in FIG. 6A, and C is the reflection. The emphasized image, D, is the amplitude on the white dashed lines in FIGS. 6C and 6A. E, F, G, and H are the measurement results of the scattering characteristics for the tungsten wire, E is the B mode image, F is the scattering characteristics at the points marked with x in FIG. 6E, G is the image in which the scattering is suppressed, and H is the figure. 6G and the amplitude on the white dashed line in FIG. 6E. Flow chart for obtaining an ultrasonic tomographic image that emphasizes bones

In the present invention, an ultrasonic array probe in which a plurality of ultrasonic generation / detection elements (hereinafter, abbreviated as elements) are arranged is used for transmitting and receiving ultrasonic waves. An ultrasonic array probe is connected to an ultrasonic diagnostic device, ultrasonic waves are transmitted using a plurality of elements, and reflection / scattering signals from an object are received by the plurality of elements. By comparing the angular characteristics of the amplitude of the received signal with the reflection characteristics measured for the surface reflector and the scattering characteristics measured for the point scatterer in advance, whether the object is a surface reflector or a point scatterer. Or, in the case of a surface reflector, identify the angle φ with respect to the ultrasonic probe.

In the measurement of the reflection characteristic group {R _R (θ; z, φ)} from the surface, a flat substance such as an acrylic plate is submerged in water, and the angle φ of the acrylic plate surface with respect to the ultrasonic probe is changed from the surface. It can be obtained by measuring the reflected signal of.

In the measurement of the scattering characteristic group { _RS (θ; z)} from a point, a wire whose diameter is sufficiently smaller than the wavelength of the ultrasonic wave is stretched parallel to the elevation direction of the ultrasonic probe, and the scattering from the wire is performed. It can be obtained by measuring the signal.

The signal P (x, z) from the object is measured under the same conditions as when the reflection characteristic group and the scattering characteristic group were measured.

When the lateral position of the ultrasonic beam to be transmitted is x _m = 0, the scattered wave from the point scatterer at the position (x, z) = (0, z _s ) is sent to the element at the position x _m . The propagation time T _s (m) until reception is expressed by Eq. (1), where c _w is the speed of sound from the ultrasonic probe to the object.

The procedure for obtaining the amplitude characteristic R (θ; P (x, z)) for the signal P (x, z) is as follows. First, the envelope amplitude is obtained for the signal P (x, z). For the target point, find the amplitude at the time along the ideal delay time distribution in Eq. (1). From the values of x and z, find the angle θ from the angle θ = tan ^-1 (x / z), and use it as the value of R (θ; P (x, z)).

Next, the reflection characteristic group {R _R (θ; z, φ)} from the surface where the obtained R (θ; P (x, z)) was measured in advance and the scattering characteristic group {R _S (θ;) from the point. Compare with z)}. For example, normalization cross-correlation is used to compare and identify whether it is reflection or scattering, and in the case of reflection, the angle φ.

By superimposing the obtained result on the ultrasonic tomographic image (B mode image) and displaying it, it is determined which part is the bone on the B mode image.

Here, an acrylic block is taken up as a substance that imitates bone, an example of measuring the reflection characteristic group { _RR (θ; z, φ)} from a surface, and a tungsten wire is taken up as a substance that simulates a point scatterer. Then, an example of measuring the scattering characteristic group {R _S (θ; z)} from a point will be described.

FIG. 1 shows a schematic diagram of the aquarium experimental system. The object was submerged in a water tank, and the received signal from the object was acquired using an ultrasonic linear array probe. As shown in FIG. 1 (a), a bone was simulated by an acrylic block installed so as to have an angle φ with respect to the surface of the ultrasonic probe as an object for reflecting ultrasonic waves. Similarly, as shown in FIG. 1 (b), a point scatterer was simulated by stretching a tungsten wire having a diameter of 10 μm parallel to the elevation direction (y-axis) of the ultrasonic probe.

The ultrasonic diagnostic equipment used was Prosound α10 manufactured by Hitachi Aloka, Ltd., and the sampling frequency was 40 MHz. The linear array probe used had a number of elements of 192, an element spacing of 0.2 mm, an effective aperture width of 19.2 mm, and a center frequency of transmitted ultrasonic waves of 7.5 MHz. The water temperature was 19.0 ° C, and the speed of sound in water was determined to be 1482 m / s by the method described in Non-Patent Document 1. The reflection / scattering characteristics obtained from the focused beam formed by multiple spherical waves generated from 96 elements were investigated. The depth of the object with respect to the probe surface was 30 mm. When transmitting ultrasonic waves, a transmission delay was applied to each element so that the depth of the surface of the object coincided with the focal point of the transmission beam. Amplitude was not weighted to each element during transmission and reception.

Normally, when acquiring an ultrasonic tomographic image (B mode image), multiple elements receive reflection / scattering signals from an object for a single ultrasonic beam generated by using multiple elements. .. Using the assumed sound velocity, the delay time difference according to the distance from a certain point to each element is obtained, the delay time is adjusted so that the delay time difference becomes constant, and then the radio frequency received by multiple elements (Radio Frequency:). The delay addition process of adding RF) signals and acquiring one RF signal is performed. By performing this measurement and processing while changing the transmission position of the ultrasonic beam, it is possible to obtain RF signals for multiple ultrasonic beams, and by performing envelope processing on the RF signals, the amplitude is obtained and each position is obtained. A B-mode image can be obtained by displaying as a brightness distribution corresponding to.

In this patent, the RF signal received by each element before this delay addition processing, so-called element data, is used.

FIG. 2 shows the results of the reflection characteristics measured with φ = 0 ° for the acrylic block. 2A shows the amplitude distribution of the element data used to form the B-mode image on the broken line (x = 20 mm) of FIGS. 2A and 2A. Using Eq. (1), calculate the ideal delay time for each element (dashed line) based on the time when the envelope signal obtained by the central element becomes maximum, and obtain the amplitude at that time. The reflection characteristics were calculated. The results of the obtained reflection characteristics are shown in FIG. 2C. In FIG. 2C, the simulation values of the reflection characteristics are also shown by dotted lines. The simulation method followed the method described in Non-Patent Document 2.

In FIG. 2B, the spread of the received waveform was observed in a time domain earlier than the ideal delay time distribution due to scattering calculated by the equation (1) shown by the dotted line. Further, the delay time distribution when the envelope amplitude in each receiving element is maximized is in agreement with the ideal delay distribution from the scatterer.

In the region where the absolute value of the angle is larger than 10 ° with respect to the measurement result of the reflection characteristic in FIG. 2C, the amplitude is greatly reduced. The tendency of the measured value of the reflection characteristic and the theoretical value was almost the same.

FIG. 3 shows the results of obtaining the reflection characteristics while changing the angle φ of the acrylic block with respect to the surface of the ultrasonic probe. When the angle φ increased by 1 °, the angle at which the amplitude of the reflection characteristic peaked shifted by 2 °.

FIG. 4 shows the measurement results of the scattering characteristics. FIG. 4A is a B-mode image, and FIG. 4B is an amplitude distribution of element data used for image formation on the broken line (x = 17 mm) of FIG. 4A. In the element data, the ideal delay time distribution of the point scatterer calculated by Eq. (1) is also shown by a broken line. In the element data of FIG. 4B, it was confirmed that the signal was received along the ideal delay time distribution. Based on the time when the envelope signal obtained by the central element is maximized, the ideal delay time is calculated for each element (dotted line) using Eq. (1), and the amplitude at that time is obtained. The scattering characteristics were calculated. The result and the result of the simulation value of the scattering characteristic are shown in FIG. 4C. The simulation method followed the method described in Non-Patent Document 2. The theoretical value of the scattering characteristic is a parabola that reaches its maximum when the angle is 0 °.

FIG. 5 shows the correlation value between the reflection characteristics when the angle φ is 7 ° in FIG. 3 and the reflection characteristics when the angle φ is -15 ° to 15 ° and the matching by the normalized cross-correlation process. .. At this time, using the symmetry of the reflection characteristic R _R (θ; z, φ) with respect to the angle φ, the reflection characteristic with the angle φ from -15 ° to -1 ° has the angle φ from 1 ° to 15 °. It was calculated as R _R (θ; z, φ) = R _R (-θ; z, -φ) using the reflection characteristics. Further, the correlation value by the normalized cross-correlation process with the measured value of the scattering characteristic shown in FIG. 4C was 0.21. As a result, the correlation value was the highest when φ = 7 °.

From the above, it was confirmed that there is a large difference in the angular characteristics of the amplitude between the scattering characteristics and the reflection characteristics. In addition, when the angle φ was different, there was a difference in the angle at which the amplitude of the reflection characteristic peaked. By utilizing these differences, for example, matching using normalized cross-correlation processing, it is possible to identify whether it is reflection or scattering, and in the case of reflection, the angle φ.

A water tank experiment was performed in the same manner as in Example 1. FIG. 6A is a B mode image measured with φ = 8 ° with respect to the acrylic block. FIG. 6B shows the reflection characteristics at the points marked with x in FIG. 6A. FIG. 6E is a B-mode image for the wire. FIG. 6F shows the scattering characteristics at the points marked with FIGS. 6E ×. FIG. 6B and FIG. 6F also show simulation values of reflection and scattering, respectively. In FIGS. 6B and 6F, the experimental values and the simulated values were in good agreement.

Comparing the difference between the maximum value and the minimum value of the amplitude in FIGS. 6B and 6F, the reflection characteristic of FIG. 6B was large and the scattering characteristic of FIG. 6F was small. In order to emphasize the reflected wave using this difference in amplitude between reflection and scattering, the average amplitude in the group {θ _M } with high amplitude including the angle θ = θ _MAX where the amplitude is maximum in FIGS. 6B and 6F. , The ratio of the average amplitudes in the low-amplitude group {θ _m }, including the angle θ farthest from θ _MAX , was taken and images were drawn over the B-mode images of FIGS. 6A and 6E, respectively. The results are shown in FIGS. 6C and 6G, respectively. Further, the luminance values on the white dashed lines in FIGS. 6C and 6G are shown in FIGS. 6D and 6H together with the luminance values on the white dashed lines in FIGS. 6A and 6E, respectively. By this method, the reflector brightness could be emphasized by about 40 dB with respect to the scatterer brightness.

Based on the examples described above, a basic processing procedure for obtaining an ultrasonic tomographic image with emphasized bone according to the present invention will be described below with reference to the flowchart shown in FIG. 7.
Step S1: Measure the reflection characteristic group {R _R (θ; z, φ)} from the surface and the scattering characteristic group {R _S (θ; z)} from the point.
Step S2: The signal P (x, z) is measured with respect to the object.
Step S3: The amplitude characteristic R (θ; P (x, z)) is calculated for the signal P (x, z).
Step S4: The amplitude characteristic R (θ; P (x, z)) obtained in step S3 is obtained from the reflection characteristic group {R _R (θ; z, φ)} from the surface obtained in step S1 and the points. Compare with the scattering characteristic group { _RS (θ; z)} of, and identify whether it is reflection or scattering, and in the case of reflection, the angle φ.
Step S5: The result obtained in step S4 is superimposed and displayed on the ultrasonic tomographic image (B mode image).

In order to perform epidural anesthesia, the position of the epidural space where the anesthesia needle is punctured must be identified and the needle must be punctured accurately. By using the present invention, it is possible to create an ultrasonic image in which bones are emphasized in a situation where bones, muscle tissues, and organs in a living body coexist. Therefore, it can be used as an aid for puncture.

1 Linear array probe 2 Acrylic block 3 Water tank 4 Water 5 Molybdenum wire

Claims (5)

It ’s a way to create an ultrasound image.
(A) The process of measuring the signal P (x, z) derived from the reflection or scattering of ultrasonic waves applied to the object to be imaged, and
(B) The step of calculating the amplitude characteristic R (θ; P (x, z)) based on the signal P (x, z), and
(C) Reflection characteristic group {R _R (θ; z, φ) obtained by measuring the reflection signal of the ultrasonic waves irradiating the surface reflector acquired in advance with the amplitude characteristic R (θ; P (x, z)). )} And the scattering characteristic group { _RS (θ; z)} obtained by measuring the scattering signal of the ultrasonic waves applied to the point scatterer, the signal P (x, z) is a reflected signal or scattering. The step of identifying whether it is one of the signals, and when it is identified as a reflected signal, the step of identifying the angle φ of the image pickup target, and
(D) A step of correcting a B-mode ultrasonic tomographic image of an imaged object based on the angle φ, and
How to create an ultrasound image including The correction is the reflection characteristic group {R _R (θ; z) obtained by measuring the reflection signal of the ultrasonic wave applied to the surface reflector acquired in advance in the amplitude characteristic R (θ; P (x, z)). , φ)} and the scattering characteristic group { _RS (θ; z)} obtained by measuring the scattering signal of the ultrasonic waves applied to the point scatterer, using the normalized intercorrelation, the signal P The first aspect of the present invention is to specify whether (x, z) is either a reflected signal or a scattered signal, and if it is specified as a reflected signal, to identify the angle φ of the image pickup target. The method described. The correction is the average amplitude in the group {θ _M } with high amplitude including the angle θ = θ _MAX where the amplitude is maximum in the amplitude characteristic R (θ; P (x, z)), and the most from θ _MAX . The claim is characterized in that the ratio of the average amplitude in the low amplitude group {θ _m } including the distant angle θ is obtained, and the ratio is multiplied by the pixel value of each pixel in the B-mode ultrasonic tomographic image. The method according to 1. A system that creates ultrasonic images
(A) A measuring unit that measures the signal P (x, z) derived from the reflection or scattering of ultrasonic waves applied to the object to be imaged, and
(B) An amplitude characteristic acquisition unit that calculates the amplitude characteristic R (θ; P (x, z)) based on the signal P (x, z), and
(C) Reflection characteristic group {R _R (θ; z, φ) obtained by measuring the reflection signal of the ultrasonic waves irradiating the surface reflector acquired in advance with the amplitude characteristic R (θ; P (x, z)). )} And the scattering characteristic group { _RS (θ; z)} obtained by measuring the scattering signal of the ultrasonic waves applied to the point scatterer, the signal P (x, z) is a reflected signal or scattering. An analysis unit that identifies whether it is one of the signals, and if it is identified as a reflected signal, an analysis unit that identifies the angle φ of the image pickup target.
(D) An image processing unit that corrects a B-mode ultrasonic tomographic image of the object to be imaged based on the angle φ, and an image processing unit.
A system equipped with. A program that creates ultrasound images
(A) The step of inputting the signal P (x, z) derived from the reflection or scattering of the ultrasonic wave applied to the object to be imaged, and
(B) A step of calculating the amplitude characteristic R (θ; P (x, z)) based on the signal P (x, z), and
(C) Reflection characteristic group {R _R (θ; z, φ) obtained by measuring the reflection signal of the ultrasonic waves irradiating the surface reflector acquired in advance with the amplitude characteristic R (θ; P (x, z)). )} And the scattering characteristic group { _RS (θ; z)} obtained by measuring the scattering signal of the ultrasonic waves applied to the point scatterer, the signal P (x, z) is a reflected signal or scattering. The step of identifying whether it is one of the signals, and if it is identified as a reflected signal, the step of identifying the angle φ of the image pickup object,
(D) A step of correcting a B-mode ultrasonic tomographic image of an imaged object based on the angle φ, and
A computer program that lets your computer run.

Images