WO2018037600A1

WO2018037600A1 - Ultrasound imaging apparatus and ultrasound image generation method

Info

Publication number: WO2018037600A1
Application number: PCT/JP2017/009765
Authority: WO
Inventors: 悠史坪田; 川畑　健一; 崇秀寺田; 文晶武; 一宏山中
Original assignee: 株式会社日立製作所
Priority date: 2016-08-22
Filing date: 2017-03-10
Publication date: 2018-03-01
Also published as: JP6539620B2; JP2018029653A

Abstract

The present invention reduces the influence exerted by a background factor on an ultrasonic CT image so as to facilitate recognizing the progression of a lesion. An ultrasonic element transmits ultrasonic waves to a region of a subject to be imaged, and obtains a reception signal by receiving the ultrasonic waves in the form of transmitted waves that have transmitted through the subject. An image generation unit processes the reception signal so as to generate an image representing a distribution of a given physical property value in the subject. The image generation unit uses the subject's temperatures measured at the time of transmission and reception of ultrasonic waves so as to generate a standard temperature conversion image that represents a distribution of the physical property value in the case when the subject's temperature is at a given standard temperature.

Description

Ultrasonic imaging apparatus and ultrasonic image generation method

The present invention relates to an ultrasonic imaging apparatus and an ultrasonic image generation method.

An ultrasonic CT (Computed Tomography) device is a method for irradiating a subject in a medium with ultrasonic waves from a plurality of directions and receiving the ultrasonic waves transmitted through the subject from the transmission signals obtained from the physical properties (sound speed and It is a device that obtains a distribution of transmission signal attenuation rates) and generates a tomographic image. Ultrasonic waves are generated using an ultrasonic element that converts an electrical signal such as a piezoelectric element into ultrasonic waves. The ultrasonic wave transmitted through the subject is received again by the ultrasonic element and converted into an electric signal to obtain a transmission signal. The ultrasonic elements are arranged in a ring array, for example, and a subject is inserted into the opening of the ring to shoot.

Patent Document 1 discloses a basic configuration and imaging technique of ultrasonic CT.

Japanese Translation of National Publication No. 08-508925

The ultrasonic CT apparatus is expected to be a breast cancer screening apparatus that can be applied to younger people because it does not have radiation exposure unlike mammography. In order to measure the degree of progression of breast cancer using an ultrasonic CT apparatus and lead to early diagnosis and early treatment, it is necessary to accurately discriminate changes in a plurality of images obtained by imaging the same subject multiple times in time series. However, since various background factors other than the progression of breast cancer change the physical property value and are reflected in the image, whether the change in the image indicates a change in the physical property value due to the progression of breast cancer or the background. It is difficult to determine whether a change in physical property value due to a factor is present, making early diagnosis difficult.

An object of the present invention is to reduce the influence of background factors on an ultrasound CT image and to easily grasp the degree of progression of a lesion.

In order to achieve the above object, according to the present embodiment, an ultrasonic element that transmits an ultrasonic wave to an imaging region of a subject, receives a transmitted wave of the ultrasonic subject, and outputs a reception signal; There is provided an ultrasonic imaging apparatus including an image generation unit that processes a signal and generates an image indicating a distribution of predetermined physical property values in a subject. The image generation unit uses the body temperature of the subject at the time of transmission and reception of ultrasonic waves to generate a standard body temperature image that generates a standard body temperature converted image indicating a distribution of physical property values when the body temperature of the subject is a predetermined standard body temperature Includes a generator.

According to the present invention, an ultrasonic CT image excluding the influence of a change in body temperature, which is one of background factors, can be obtained, so that it is easy to grasp the temporal change of the subject.

1 is a block diagram showing a schematic configuration of an ultrasonic imaging apparatus (ultrasonic CT apparatus) according to Embodiment 1 of the present invention. Sectional drawing which shows schematic structure of the ring array of the apparatus of FIG. 1 is a flowchart showing the operation of the ultrasonic CT apparatus according to the first embodiment. Body temperature acceptance screen example of the ultrasonic CT apparatus of the first embodiment Graph showing the temperature dependence of the sound speed of water (A) Explanatory drawing which shows an example of the information displayed on the header of the display screen of an ultrasonic CT apparatus, (b) Explanatory drawing which shows an example of the display area of a display screen of an ultrasonic CT apparatus, and a selection reception area | region. A block diagram showing composition of an image generation part of Embodiment 2. The graph which shows the kind of living tissue of Embodiment 2, and the range of the sound speed and attenuation factor which those can take 7 is a flowchart showing the operation of the ultrasonic CT apparatus according to the second embodiment.

An ultrasonic imaging apparatus according to an embodiment of the present invention will be described.

<< Embodiment 1 >>
Since the physical property value (especially the sound velocity value) of the living tissue depends on the temperature, in this embodiment, the influence of temperature is removed as one of the background factors that affect the ultrasonic image of the subject. Since the body temperature of the subject varies depending on the temperature of the medium with which the imaging site is in contact, the physiological cycle of the subject itself, and the like, in this embodiment, the body temperature of the subject is set to a predetermined standard body temperature using the body temperature information of the subject. The standard body temperature conversion image which shows distribution of the physical-property value in the case of being is generated.

FIG. 1 is a schematic configuration diagram of the ultrasonic imaging apparatus (ultrasonic CT apparatus) of the present embodiment, and a cross-sectional view of the ultrasonic element array of FIG. The ultrasonic imaging apparatus of the present embodiment includes a plurality of ultrasonic elements 13 and an image generation unit 11 as shown in FIGS. The ultrasonic element 13 transmits ultrasonic waves to the imaging region of the subject 1, receives the ultrasonic waves transmitted through the subject 1, and outputs a reception signal. The image generation unit 11 processes this received signal to generate an image indicating a distribution of predetermined physical property values in the subject 1. At this time, the image generation unit 11 includes a standard body temperature image generation unit 12, and the standard body temperature image generation unit 12 uses the body temperature of the subject 1 at the time of transmission and reception of the ultrasonic wave so that the body temperature of the subject 1 is predetermined. A standard body temperature converted image showing a distribution of physical property values in the case of the standard body temperature is generated.

For example, the standard body temperature image generation unit 12 calculates the physical property value at the body temperature at the time of reception of the ultrasonic wave using the received signal, and calculates the calculated physical property value between the physical property value of the imaging region and the temperature obtained in advance. Based on the relationship, it is converted into a physical property value at standard temperature. And the standard body temperature image generation part 12 produces | generates a standard body temperature conversion image using the converted physical property value.

Hereinafter, the ultrasonic CT apparatus of the present embodiment will be specifically described. Here, an ultrasonic CT apparatus suitable for using the breast as an imaging site in breast cancer screening or the like will be described.

In addition to the ultrasonic element 13 and the image generation unit 11 described above, the ultrasonic CT apparatus includes a bed 2 on which the subject 1 is placed, a water tank 4 having a cylindrical side surface, a spare tank 5, a control unit 6, and an image generation unit 11. A built-in signal processing unit 7, a storage unit 8, and an input / output unit 9 are provided.

Note that the storage unit 8 may be connected to an external server connected via a network. Thereby, all or a part of the data stored in the storage unit 8 can be transferred or copied to an external server and saved.

The bed 2 has an opening so that the chest can be inserted, and a cylindrical water tank 4 is attached to the opening. The bed 2 includes a bed driving mechanism (not shown) that moves the bed 2 up and down. Inside the water tank 4, as shown in FIG. 2, an array (hereinafter referred to as a ring array) 3 in which ultrasonic elements 13 are arranged in a ring shape is provided. Further, the ring array 3 is provided with an array drive mechanism (not shown) that enables parallel movement in the axial direction of the water tank 4.

The ultrasonic element 13 is a piezoelectric element or the like, and is an element that converts an electric signal into an ultrasonic wave and transmits it, and converts the reached ultrasonic wave into an electric signal. The water tank 4 is filled with warm water. The reserve tank 5 purifies the hot water in the water tank 4, heats it to a predetermined temperature, deaerates it, and supplies it to the water tank 4 again.

Thermometers

114a and 114b are attached to the lower part of the water tank 4 and the reserve tank 5 to monitor the water temperature.

The input / output unit 9 includes a touch panel and a keyboard. The imaging conditions of the ultrasonic CT apparatus are set by the user via the input / output unit 9. The set shooting conditions and the like are stored in a memory of the storage unit 8, a hard disk drive, or the like.

The signal processing unit 7 includes a processor (for example, a CPU (Central Processing Unit)) and a memory in which a program is stored in advance, and the function of the signal processing unit 7 is read and executed by the processor. Is realized by software. Note that part or all of the signal processing unit 7 may be realized by hardware. For example, the signal processing unit 7 is configured by using a custom IC such as ASIC (Application Specific Integrated Circuit) or a programmable IC such as FPGA (Field-Programmable Gate Array), and the operation of the image processing unit 11 and the like described later is performed. A circuit design may be performed so as to realize it.

The signal processing unit 7 generates a control signal based on the imaging conditions and the like, and sends it to various controllers constituting the control unit 6. The controller performs transmission / reception and switching of ultrasonic signals, control of vertical movement of the array drive mechanism of the ring array 3 and the bed drive mechanism of the bed 2, water pressure control of the reserve tank 5, feedback control of hot water temperature, and the like. The received signal is recorded in the storage unit 8 and is subjected to image processing calculation by the image generation unit 11 of the signal processing unit 7 to generate a cross-sectional image indicating the distribution of physical property values of the subject 1. The generated image is displayed on a monitor of the input / output unit 9 or the like.

With such a configuration, a tomographic image of the physical property value of the subject 1 in the aquarium 4 is displayed.

FIG. 3 is a flowchart showing the operation of each unit for obtaining a standard body temperature converted image by the ultrasonic CT apparatus of the present embodiment. Hereinafter, the operation of each unit will be described.

When the subject 1 or the operator presses the start button of the input / output unit 9, the signal processing unit 7 displays an inquiry table for the subject 1 on the monitor of the input / output unit 9, and the input / output unit 9 Prompts the user to input an answer, and displays a prompt to change to examination clothes and to measure body temperature using the armpit method, radiation thermometer, etc. Thereafter, the signal processing unit 7 displays on the monitor of the input / output unit 9 a screen for accepting input of the name or ID (identification) of the subject 1, the body temperature T ₁ of the subject ₁ , and the desired standard body temperature T _0. Then, the input from the subject 1 or the operator is accepted (step 101). FIG. 4 is an example of an input reception screen for standard body temperature and the like. The input reception screen 40 in FIG. 4 includes an area 41 that receives an input of a subject ID number, an area 42 that receives an input of a body temperature of the subject, and an area 43 that receives an input of a standard body temperature. The signal processing unit 7 stores the received body temperature and standard body temperature in the storage unit 8.

Subsequently, the signal processing unit 7 displays on the input / output unit 9 a display that prompts the subject 1 to lie down on the bed 2 and insert one breast into the aquarium 4 (step 102). If the signal processing unit 7 grasps that the breast of the subject 1 has been inserted into the water tank 4 by the operation of the input / output unit 9 by the subject 1, the signal processing unit 7 operates the spare tank 5. A control signal is output to the control unit 6. The control unit 6 controls the reserve tank 5 to take in the temperature of the water in the reserve tank 5 with the thermometer 114b and heats the water until the temperature of the water reaches a predetermined temperature (about body temperature). After deaeration, the pump is driven and moved to the water tank 4. Thereby, the water tank 4 is filled with the deaerated water adjusted to a predetermined temperature (step 103).

Next, the signal processing unit 7 controls the control unit 6 to transmit / receive ultrasonic waves as follows. Here, it is assumed that a 2048 channel piezoelectric element (ultrasonic element 13) with a pitch of 0.5 mm is arranged in a ring shape to form a ring array 3 having a diameter of 326 mm. The axial thickness of the water tank 4 of the piezoelectric element is 1 mm. The center frequency of the ultrasonic wave irradiated from the ring array 3 is 1.5 MHz (the wavelength of the ultrasonic wave in water is about 1 mm).

The control unit 6 delivers the transmission signals delayed by a predetermined delay amount to the continuous 512-channel piezoelectric elements of the ring array 3. Thereby, the ultrasonic wave of the plane wave which aligned the phase is irradiated from the piezoelectric element of 512 channels. Then, the reflected wave reflected by the imaging region (breast) of the subject 1 is received by the same 512-channel piezoelectric element. In addition, a transmitted 512-channel piezoelectric element is received by a continuous 512-channel piezoelectric element located opposite to the transmitted 512-channel. As a result, a field of view (Field of view, Field of view, 230 mm) can be secured. The control unit 6 repeats the irradiation operation and the reception operation while shifting the 512-channel piezoelectric elements that irradiate ultrasonic waves on the ring array 3 by 4 channels, so that a slice (cross section) of the water tank 4 has a certain depth. ), A transmitted wave and a reflected wave signal from 360 degrees around the water tank 4 are obtained in 512 views by 0.7 degrees (step 104).

The controller 6 moves the ring array 3 in the depth direction that is the axial direction of the water tank 4, for example, at a pitch of 0.5 mm, while moving (displaces) the ring array 3 at each depth until the predetermined depth is reached. Is repeated (steps 105 and 106). Therefore, when the ring array 3 is repeated until it is displaced by, for example, 20 mm, reception signal data for 40 slices of the imaging region is obtained. With the above procedure, three-dimensional information (received signal) of the breast of the subject 1 is obtained for a predetermined depth range.

The image generation unit 11 of the signal processing unit 7 receives the received signals of the transmitted wave and the reflected wave, processes them as follows, and an image based on the transmitted wave of the subject 1 from the received signal of the transmitted wave (transmitted wave image). Then, a reflection boundary image is generated (reconstructed) as an image of the physical property value distribution and an image based on the reflected wave of the subject 1 (reflected wave image) from the received signal of the reflected wave (steps 107 and 108).

The physical property value distribution specifically assumes a sound velocity distribution and / or attenuation rate (coefficient) distribution, but may be replaced by an equivalent physical quantity. For example, a refractive index or “slowness” may be imaged instead of the speed of sound. “Slowness” is the reciprocal of the speed of sound.

First, the image generation unit 11 performs Hilbert transform on the transmitted wave reception wave signal in the time direction to generate the sound velocity distribution image, obtains the timing of the maximum amplitude of the reception wave, and generates the attenuation rate distribution image. If so, the maximum amplitude of the received wave is obtained. When generating the sound velocity distribution image, the image generation unit 11 determines the arrival time difference between the reception signals at which the amplitudes of the reception waves before and after insertion of the subject 1 are maximum, and when generating the attenuation rate distribution image. The logarithmic difference of the maximum amplitude before and after insertion of the subject 1 is calculated for each view and each reception channel. This collection of data is called a sinogram. A sinogram is obtained for each slice. The image generation unit 11 processes the sinogram of the difference between the received signals and the sinogram of the logarithm difference of the maximum amplitude by a filtered back projection method (Filtered Back Projection, FBP) widely used in the field of X-ray CT, respectively. By doing so, a tomographic image is reconstructed. From the sinogram of the difference in arrival time of the received signal, a distribution image (tomographic image) of the difference in ultrasonic “slowness” before and after insertion of the subject 1 is obtained. A distribution image (tomographic image) of the difference in attenuation rate before and after insertion of the subject 1 is obtained from the sinogram of the logarithmic difference of the maximum amplitude. The image generation unit 11 uses the sound velocity and attenuation rate of water at the temperature measured by the thermometer 114a, so that the distribution image of the difference of the “slowness” and the distribution image of the difference of the attenuation rate of the subject 1 can be obtained. Images of sound velocity distribution and attenuation rate distribution are generated. The image generation unit 11 performs the above processing on the received signal of the transmitted wave for each slice, and generates an image of the sound velocity distribution and the attenuation rate distribution for each slice (step 107). The image generation unit 11 stores the generated sound speed distribution image and / or attenuation rate distribution image in the storage unit 8.

Next, the image generation unit 11 performs Hilbert transform in the time direction on the received signal of the reflected wave. The image generation unit 11 determines the time (timing) at which the reflected wave from the subject 1 returns to the ultrasonic element 13 after irradiating the ultrasonic wave from the ultrasonic element 13 from the transmitted ultrasonic element 13 to the target pixel ( The sum of the distance to the point 1 in the subject 1 and the distance to the ultrasonic element 13 received from the target pixel is divided by the ultrasonic speed of sound (for example, the speed of water). Alternatively, this timing is obtained in advance and stored in the storage unit 8. Then, the image generation unit 11 adds the signals received by each ultrasonic element 13 at the timing when the reflected wave reflected by the target pixel in the subject 1 reaches each ultrasonic element 13 that performs reception, and adds the signals. The later signal intensity is taken as the value of that pixel. This method is called a delay addition method (Delay and Sum, DAS). By performing this for all pixels in the field of view, a B-mode image widely used in ultrasonic echo inspection can be obtained. By adding the B-mode images obtained at each irradiation angle (view), a reflection boundary image of a slice of the subject 1 is obtained. By performing this process on the reception signal of the reflected wave for each slice, the image generation unit 11 generates a reflection boundary image for each slice (step 108). The image generation unit 11 stores the generated reflection boundary image in the storage unit 8.

Next, the standard body temperature image generation unit 12 in the image generation unit 11 performs an operation for converting the physical property value of the physical property value distribution image generated in Step 107 into a physical property value when the body temperature of the subject 1 is the standard body temperature. Perform (step 109). The human body changes its body temperature depending on the circadian rhythm, menstrual cycle and physical condition. The physical property value (especially the speed of sound) of the subject biological tissue depends on the temperature. FIG. 5 shows a graph of the temperature dependence of the sound speed of water. The vertical axis of this graph represents sound velocity [m / s], and the horizontal axis represents temperature [° C.]. As shown in FIG. 5, the sound speed of water has a slope of about 1.6 m / s / ° C. around 40 ° C., and the sound speed increases as the temperature rises. Therefore, in this embodiment, in order to accurately evaluate properties such as tumor hardness over time, a standard body temperature converted image obtained by removing the influence of temperature as a background factor and converting the physical property value into a physical property value at a standard body temperature is used. Generate as follows.

In the storage unit 8, a function indicating the relationship between the physical property value of the imaging region and the temperature obtained in advance, specifically, the relationship between the physical property value (here, the speed of sound) of the imaging region (breast tissue) and the temperature T. g (T) is stored in advance. The standard body temperature image generation unit 12 reads the function g (T) indicating the relationship between the physical property value (sound speed) of the imaging region (breast tissue) and the temperature T from the storage unit 8, and the subject 1 received in step 101. Using the body temperature T ₁ and the standard body temperature T ₀ , and the following equation (1) or equation (2), the sound velocity value of each pixel of the sound velocity distribution C (T ₁ , X) of the sound velocity distribution image generated in step 107 is calculated. , in terms of sound speed value in the standard temperature _{T 0,} the sound velocity distribution _C in the standard body temperature _{T 0} _(T 0, X) to produce a (standard body temperature in terms of image) (step 109). The standard body temperature image generation unit 12 stores the generated standard body temperature converted image in the storage unit 8.
C (T ₀ , X) = C (T ₁ , X) − {g (T ₁ ) −g (T ₀ )} (1)
C (T ₀ , X) = C (T ₁ , X) / {g (T ₁ ) / g (T ₀ )} (2)
X represents the three-dimensional position coordinate (x, y, z) of the pixel of the sound velocity distribution image. Either formula (1) or formula (2) may be used.

The signal processing unit 7 displays the standard body temperature converted image generated by the standard body temperature image generation unit 12 in step 109 on the display unit of the input / output unit 9. FIG. 6A is an example of information displayed in the header of the display screen, and FIG. 6B shows an image display area 51 such as a standard body temperature converted image and a display method from the subject 1 or the user. An example of the selection reception area 52 for receiving selection is shown. As shown in FIG. 6A, the header displays a unique ID number, body temperature, water temperature, standard body temperature, imaging date, and the like of the subject 1. Information displayed in these headers is stored in the storage unit 8 or an external server connected to the storage unit according to a predetermined standard (for example, DICOM (Digital Imaging and Communication Communication in Medicine)). In addition, a sound velocity distribution image, an attenuation rate distribution image, a standard body temperature converted image, and a relationship g (T) between a physical property value (for example, sound velocity) of an imaging region (breast tissue) and a temperature T, or a physical property value photographed in the past The distribution image and the standard body temperature converted image are also managed in an integrated manner and stored in the storage unit 8 or an external server.

As shown in FIG. 6B, the signal processing unit 7 receives the type of image to be displayed in the display area 51 in the selection receiving area 52, and stores the selected type of image and the image of the same subject ID. The data is read from the unit 8 or an external server and displayed on the display unit of the input / output unit 9. For example, by selecting a shooting date and a shooting number, image data for each shooting is displayed. Specifically, for example, the sound speed distribution image and the standard temperature-converted image (sound speed) are displayed side by side with the current imaging and the past shooting date. The cross-sectional position (slice depth) of each image can be changed by the slider bar 53 and the mouse wheel. Thereby, it is possible to compare the current and past captured images side by side. In the screen example of FIG. 6B, when the depth is changed by the slider bar 53, the switch 55 is selected. The tomographic positions of all displayed images may be changed synchronously (linked) in accordance with the operation of the slider bar 53. In the screen example of FIG. 6B, whether or not to interlock is switched by the switch 54. Further, as in the screen example of FIG. 6B, the direction of the display section may be selectable from a sagittal image, a coronal image, and an axial image, which are typical MPR (multi-planar reconstruction) sections.

As another display method, the standard temperature conversion images may be sequentially displayed in the order of photographing date in one image display area in accordance with the operation of moving the slider bar 53 by the user. Thereby, a change with time can be easily grasped. In the screen example of FIG. 6B, when the date is changed by the slider bar 53, the switch 56 is selected.

As yet another display method, in order to compare the difference between the left and right breasts, corresponding cross sections of the left and right breasts may be displayed on the screen. For example, the left-right difference of the sagittal section including the nipple can be confirmed.

Also, selection of a reference image may be accepted from the user, and a difference image from the current image may be displayed.

Further, images of different physical property values, that is, a sound speed distribution image, an attenuation rate distribution image, and a reflection boundary image may be displayed side by side for a certain cross section. As a result, the structure and properties of the tissue can be confirmed in association with each other.

Alternatively, only pixels included in a specific sound velocity value range and attenuation rate value range may be extracted and the corresponding area of the reflection boundary image may be displayed in color. For example, it is possible to provide diagnostic support for a radiogram interpreter by coloring a pixel in a high sound velocity and high attenuation rate area suspected of being a malignant tumor in red.

∙ Allow the user to select whether or not to display the standard body temperature converted image in each of the above image display methods.

Further, the set value of the standard body temperature T ₀ may be changed on the display screen.

In the present embodiment, in an ultrasonic CT apparatus that is a non-invasive and quantitative breast cancer screening system, images can be compared with standard body temperature converted images from which the influence of temperature as a background factor is removed. It becomes easy to increase the effectiveness of screening.

In the equations (1) and (2) of step 109, if there is a constant deviation δ between the breast temperature T and the temperature T ′ indicated by the thermometer, it is corrected as T = T ′ + δ and the sound velocity value Conversion may be performed.

Hereinafter, an example of how to obtain the relationship g (T) between the physical property value of the imaging region (breast tissue) and the temperature T will be described. Pack the breast tissue of a surgically removed person or animal in a polyethylene cuboid holder. A weight is attached to the bottom surface of the holder and submerged in the water tank 4. The opening on the upper surface of the water tank 4 is closed with a heat insulating material. While monitoring the water temperature with the thermometer 114a at the bottom of the water tank 4, the sample waits until the sample reaches thermal equilibrium with the water temperature. A plane wave is irradiated in a direction perpendicular to the surface of the rectangular parallelepiped, and the transmitted wave signal is measured. Thus, similar to the transmitted wave signal processing, the difference in arrival time of the received signal with and without the holder and / or the difference in logarithm of the maximum amplitude is obtained, and the average sound velocity of the breast tissue is determined using the size (known) of the holder. And / or determining the decay rate. By repeating this measurement at different water temperatures, a function g (T) indicating the temperature dependence of the physical property value can be obtained. In order to reduce statistical errors, it is desirable to average the function g (T) obtained from a plurality of different samples.

The function g (T) is stored in the storage unit 8 as a data table or in the form of a coefficient when it is approximated by a polynomial or the like.

<< Embodiment 2 >>
In the first embodiment, the function value g (T) indicating the temperature dependence of the average physical property value of the breast tissue is used to convert the physical property value obtained by imaging into the physical property value at the standard body temperature. Varies by In order to obtain a physical property value at a standard temperature with higher accuracy, in the second embodiment, a different temperature dependency function is used for each living tissue.

FIG. 7 is a block diagram of the image generation unit 11 of the ultrasonic CT apparatus according to the second embodiment. As shown in FIG. 7, in addition to the standard body temperature image generation unit 12, the image generation unit 11 includes a biological tissue determination unit 15 that determines the type of biological tissue from the distribution image of physical property values. Further, the storage unit 8 stores in advance the relationship between the physical property value of the imaging region and the temperature obtained in advance for each type of tissue constituting the imaging region. Further, the storage unit 8 stores each living tissue (water, fat, mammary tissue, cyst, malignant tumor (cancer), and the like), a range of sound velocity values and a range of attenuation rate values that each living tissue can take. . FIG. 8 shows an example of each living tissue (water, fat, mammary tissue, cyst, malignant tumor (cancer), etc.), and the range of sound velocity values and attenuation rate values that each living tissue can take. The vertical axis of this graph represents the sound velocity [m / s], and the horizontal axis represents the attenuation rate [dB / cm / MHz].

FIG. 9 shows a processing flow of the signal processing unit 7 from measurement to image display in the case of using different temperature dependent functions for each tissue. Steps 101 to 108 are the same as in the first embodiment, and the arrival time and intensity of the ultrasonic wave are analyzed for the received signal obtained for the subject 1 by transmission and reception of ultrasonic waves. Based on such information, the image generation unit 11 performs an image reconstruction process, and a distribution image and a reflection boundary image of the physical property values (sound speed value and attenuation rate) of the subject 1 are obtained.

Next, in step 201, the living tissue discriminating unit 15 in the image generating unit 11 obtains the sound speed value and the attenuation rate of the corresponding pixels of the sound speed distribution image and the attenuation rate distribution image, and is stored in the storage unit 8. By referring to the range of sound velocity values and attenuation rate values that can be taken by the biological tissue, the biological tissue of each pixel is classified into water, fat, breast tissue, cyst, malignant tumor (cancer), etc. ( Identify).

Next, in step 202, the standard body temperature image generation unit 12 reads the relationship between the physical property value corresponding to the identified type of biological tissue and the temperature (function g (T)) from the storage unit 8, and uses that function. For each living tissue, the physical property value (for example, sound velocity value) of the pixel is converted into the physical property value at the standard body temperature T ₀ to generate a standard body temperature converted image. By using the temperature dependence function of the physical property value of the living tissue corresponding to each pixel, the physical property value at a standard body temperature with high accuracy can be calculated. By performing this operation for all the pixels, a standard body temperature converted image in which physical property values are accurately converted for each living tissue can be created.

At this time, the living tissue discrimination section 15, at step 201, on the image showing the distribution of physical properties at body temperature T ₁ of the ultrasound at the time of reception generated in step 107, by setting the physical property value of a predetermined range The region (region) in the set range is identified as a different biological tissue. The standard body temperature image generation unit 12 converts the physical property value of the biological tissue in the identified region range into a physical property value at the standard temperature T ₀ using a temperature dependence function corresponding to the biological tissue of the region.

Further, the biological tissue discriminating unit 15 may accept the setting of the range (boundary) of the site (region) of the biological tissue from the user via the input / output unit 9 on the physical property value (for example, sound velocity) distribution image. .

Hereinafter, specific examples of biological tissue identification and physical property value conversion by the biological tissue discrimination unit 15 will be described. Although there are variations due to individual differences in the distribution range of the sound speed and attenuation rate of the main biological tissue included in the breast shown in FIG. 8, tissue identification is performed by providing an appropriate threshold value. The biological tissue determination unit 15 selects a pixel having a predetermined sound speed value and attenuation rate value range, for example, a sound speed of 1570 m / s or higher and an attenuation rate of 1.0 dB / cm / MHz or higher. Thereby, only the cancer tissue is extracted from the sound velocity distribution image. The temperature dependence function g _cancer (T) of the physical property value of cancer, which has been obtained in advance, is stored in the storage unit 8 or an external server as a database. Standard body temperature conversion is performed on the extracted physical property values of the pixels according to the above-described equations (1) and (2). The standard body temperature conversion is similarly performed on the extracted pixels of other tissues. For pixels whose tissue is unknown, for example, a temperature-dependent function of the physical property value of water may be assumed and applied. By fusing the converted physical property values of each pixel, a standard body temperature-converted image that takes into account the temperature dependence that differs for each tissue is obtained.

The relationship between the physical property value of the imaging region and the temperature (temperature dependence function of the physical property value) obtained in advance for each tissue constituting the imaging region stored in the storage unit 8 is received from the user via the input / output unit 9. May be.

When the imaging region of the subject 1 is the breast, the relationship between the physical property value of the imaging region and the temperature is obtained in advance for each tissue having a different mammary gland density of the subject 1 and stored in the storage unit 8. Is desirable. This is because the temperature dependence of physical properties varies depending on the density of the mammary gland. For example, when the mammary gland density of the subject 1 is known to be one of Fatty, Scattered, Heterogeneously, Extremely Dense in the BI-RADS (Breast Imaging Reporting and Data System) classification by imaging such as mammography in advance, The standard body temperature image generation unit 12 selects the corresponding one from the temperature dependence functions of the physical property values obtained in advance for each mammary gland density, and uses them for converting the physical property values of the standard temperature T ₀ .

Furthermore, considering that the appearance of the mammary gland varies depending on the menstrual cycle, the biological tissue discrimination unit 15 may further classify the mammary gland tissue into a follicular phase, an ovulation phase, a secretion phase, and a menstrual phase. The temperature-dependent function of the physical property value of the mammary gland tissue obtained in advance for each menstrual cycle is stored in the storage unit 8, and the standard body temperature image generation unit 12 reads out the function of the corresponding cycle to obtain the standard temperature T ₀ . Used for physical property conversion.

The above-mentioned various temperature dependence relationships are stored in advance in the storage unit 8 of the apparatus, but the user may generate and use their own temperature dependence functions. As for the distribution range of the sound velocity and attenuation rate of the biological tissue in FIG. 8, the user may arbitrarily specify the region and composition, and perform standard temperature conversion according to the setting.

The ultrasonic CT apparatus of the second embodiment described above is the same as the apparatus configuration and operation of the first embodiment except for the configuration and operation described above, and a description thereof will be omitted.

<< Embodiment 3 >>
In the first and second embodiments, it is assumed that the body temperature distribution in the imaging region of the subject 1 is uniform, but generally the body temperature varies depending on the location of the body. For example, when the water temperature of the water tank 4 is higher than the body temperature of the subject 1, a temperature gradient depending on the distance from the body surface is generated. Therefore, the image generation unit 11 calculates the distribution of the body temperature of the imaging region based on the body temperature T1 of the subject ₁ and the distance from the body surface, and the standard body temperature image generation unit 12 serves as a standard body temperature converted image. Then, an image showing the distribution of the physical property values when the body temperature distribution is a uniform standard body temperature T ₀ is generated.

In order to calculate the distribution of the body temperature of the imaging region, the image generation unit 11 adds the body temperature T ₁ of the subject ₁ and the distance from the body surface to the medium (here, water) in contact with the body surface of the imaging region. The temperature, the temperature conductivity of the living tissue at the imaging site, and the time from when the imaging site touches the medium until the ultrasound is transmitted are used.

Specifically, the measured body temperature of the subject 1 is T ₁ , and the temperature of the thermometer 114 a attached to the lower part of the water tank 4 is T ₂ . The distance from the body surface is x, and the temperature conductivity of the body surface tissue is a. The temperature conductivity a is obtained by dividing the thermal conductivity by the specific heat and the density. By solving numerically the heat conduction equation of Equation (3) under the boundary condition where T ₁ and T ₂ are the temperature of the heat bath, the temperature T ( It can be determined how x, t) changes. Here, for simplicity, a one-dimensional model was used without considering heat transfer due to blood flow or convection in the water tank.

The temperature of the tissue in the vicinity of the breast epidermis can be estimated by giving the time t from entering the water and the distance x from the body surface obtained from the reconstructed image.

Based on the calculated temperature distribution inside the breast, using the formula (1) or formula (2), the physical property value is converted into the physical property value of the standard temperature T ₀ , thereby obtaining a more accurate standard body temperature conversion image. Can be generated.

1 ... Subject
2 ... Bed
3 ... Ring array 4 ... Water tank
5 ... Reserve tank
6. Control unit
7: Signal processor
8 ... Memory part
9 ... Input / output section
DESCRIPTION OF SYMBOLS 11 ... Image generation part 12 ... Standard body temperature image generation part 13 ... Ultrasonic element 15 ... Biological tissue discrimination | determination part

Claims

An ultrasonic element that transmits an ultrasonic wave to an imaging region of the subject, receives a transmitted wave of the ultrasonic wave of the subject, and outputs a reception signal;
An image generation unit that processes the received signal and generates an image showing a distribution of predetermined physical property values in the subject;
The image generation unit uses the measured or estimated body temperature of the subject at the time of transmission and reception of the ultrasonic waves to indicate the distribution of the physical property values when the body temperature of the subject is a predetermined standard body temperature. An ultrasonic imaging apparatus including a standard body temperature image generation unit that generates a standard body temperature converted image.
The ultrasonic imaging apparatus according to claim 1, wherein the standard body temperature image generation unit calculates the physical property value at the body temperature at the time of reception of the ultrasonic wave using the received signal, and calculates the physical property. An ultrasound imaging apparatus, wherein a value is converted into a physical property value at the standard temperature based on a relationship between the physical property value and the temperature of the imaging region determined in advance.
3. The ultrasonic imaging apparatus according to claim 2, wherein the image generation unit stores a relationship between the physical property value of the imaging part and a temperature obtained in advance for each type of tissue constituting the imaging part. A storage unit;
The standard body temperature image generation unit identifies and identifies a living tissue of a part exhibiting the physical property value within a predetermined range based on the physical property value at the body temperature at the time of reception of the ultrasonic wave obtained from the reception signal. An ultrasonic imaging apparatus, wherein the relationship between the physical property value corresponding to the type of the biological tissue and the temperature is read from the storage unit and used for the conversion of the physical property value for the part of the biological tissue.
The ultrasonic imaging apparatus according to claim 3,
The standard body temperature image generation unit identifies a biological tissue corresponding to the combination of physical property values obtained from the received signal by referring to the value of the physical property value or a combination of value ranges obtained in advance for each biological tissue. An ultrasonic imaging apparatus.
The ultrasound imaging apparatus according to claim 3, wherein the standard body temperature image generation unit generates an image indicating a distribution of the physical property values at the body temperature at the time of reception of the ultrasound, and on the image, the The range of the part showing the physical property value of a predetermined range is set, the biological tissue of the set range of the part is identified, and the physical property value of the biological tissue of the identified range of the part is set as the physical property value at the standard temperature An ultrasonic imaging apparatus characterized by converting.
The ultrasonic imaging apparatus according to claim 1, further comprising a reception unit that receives a setting of the standard body temperature from a user.
The ultrasonic imaging apparatus according to claim 3, wherein a reception is received from a user of a relationship between the physical property value of the imaging part and a temperature obtained in advance for each tissue constituting the imaging part stored in the storage unit. An ultrasonic imaging apparatus further comprising a unit.
5. The ultrasonic imaging apparatus according to claim 4, further comprising a reception unit that receives from the user a value of the physical property value or a combination of value ranges obtained in advance for each living tissue. Imaging device.
The ultrasonic imaging apparatus according to claim 3, wherein the relationship between the physical property value of the imaging region and the temperature is obtained in advance for each tissue having a different mammary gland density of the subject, and is stored in the storage unit. An ultrasonic imaging apparatus.
The ultrasonic imaging apparatus according to claim 2, wherein a plurality of types of the relationship between the physical property value and the temperature of the imaging part determined in advance are prepared according to a physiological cycle of the subject, and the standard The ultrasound imaging apparatus, wherein the body temperature image generation unit selects the relationship corresponding to the physiological cycle of the subject received from the user and uses the relationship for the conversion.
The ultrasonic imaging apparatus according to claim 1, wherein the image generation unit calculates a body temperature distribution of the imaging region based on a body temperature of the subject and a distance from a body surface,
The ultrasonic imaging apparatus, wherein the standard body temperature image generation unit generates an image showing a distribution of physical property values when the body temperature distribution is a uniform standard body temperature as the standard body temperature converted image.
The ultrasonic imaging apparatus according to claim 11, wherein the image generation unit calculates the body temperature distribution of the imaging region in addition to the body temperature of the subject and the distance from the body surface, The temperature of the medium that is in contact with the body surface of the imaging region, the temperature conductivity of the biological tissue of the imaging region, and the time from when the imaging region touches the medium until the transmission of the ultrasonic wave is received are used. An ultrasonic imaging apparatus.
An ultrasonic image generation method for generating an image indicating a distribution of predetermined physical property values in the subject by processing a reception signal obtained by receiving a transmitted wave of an imaging region of the subject to which an ultrasonic wave has been transmitted. There,
Using the body temperature of the subject at the time of transmission and reception of the ultrasonic wave, a standard body temperature converted image showing a distribution of the physical property values when the body temperature of the subject is a predetermined standard body temperature is generated. An ultrasonic image generation method.