Ultrasound diagnostic equipment

Abstract

To facilitate proper imaging of the contrast agent over a wide range of depths within the subject, or to obtain transmission conditions suitable for contrast-enhanced ultrasound examination of each subject. [Solution] The ultrasound diagnostic device 10 includes a bioparameter calculation processing unit 1042 that performs a pilot transmission to acquire a bioparameter set representing the ultrasound propagation state within the subject 300, a sound pressure distribution simulation execution unit 1102 that estimates the sound pressure distribution by performing a sound pressure distribution simulation using one transmission parameter set extracted from the ultrasound transmission condition storage unit 118 as transmission conditions and the bioparameter set as input, a sound pressure distribution analysis unit 1104 that analyzes multiple sound pressure distributions estimated by multiple sound pressure distribution simulations using different transmission parameter sets to select a transmission parameter set that yields the optimal contrast-enhanced image, and determines the selected transmission parameter set as the transmission conditions to be used in contrast-enhanced ultrasound examination.

Description

Technical Field

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[0001] The present invention relates to an ultrasonic diagnostic apparatus, particularly an ultrasonic diagnostic apparatus used for contrast-enhanced ultrasound examination.

Background Art

[0002] Contrast-enhanced ultrasound examination (CEUS) is a technique that enables imaging of blood vessels in a living body by vibrating a contrast agent injected intravenously into the living body greatly with an ultrasonic beam and extracting non-linear components such as harmonic waves from the received echo. The bubble-like contrast agent has three types of dynamics: reflection, resonance, and collapse due to ultrasonic irradiation, and these dynamics depend on the sound pressure of the transmitted ultrasonic beam. In order to display blood vessels with high contrast and good images, it is preferable to keep the sound pressure of the ultrasonic wave within the entire depth direction of the subject between the contrast threshold as the lower limit threshold that can image with a certain tissue contrast or more and the breakdown threshold as the upper limit threshold where the contrast agent can exist without breaking. Since the sound pressure of the transmitted ultrasonic beam depends on the transmission conditions, it is necessary to adjust the transmission conditions so that they fall between the above respective thresholds.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, even when contrast-enhanced ultrasound is performed under the same transmission conditions, the vibration state of the contrast agent will differ depending on factors such as the subject's body type. Furthermore, even with the same subject, the vibration state can dynamically change depending on the location of the contrast agent in the tissue, as well as the subject's condition at the time of examination, such as blood pressure and body temperature. Therefore, in order to generate ultrasound images that show good contrast agent distribution over a wide range of depths within the subject, it is necessary to appropriately set the transmission conditions used in contrast-enhanced ultrasound each time.

[0005] The purpose of this disclosure is to facilitate proper imaging of contrast agents over a wide range of depths within a subject. Alternatively, the purpose of this disclosure is to obtain transmission conditions suitable for contrast-enhanced ultrasound examinations of each subject. [Means for solving the problem]

[0006] The ultrasound diagnostic apparatus according to this disclosure comprises a processor, the processor selects a provisional measurement condition from among a plurality of measurement conditions that generate different transmission beams, performs simulation or preliminary transmission and reception based on the provisional measurement condition to generate an intensity distribution of sound pressure distribution along the depth direction within a specific subject or a distribution of harmonics that reflects the sound pressure distribution, calculates an evaluation value representing the size of the portion in the intensity distribution that satisfies the appropriate intensity conditions for contrast agent imaging, selects a main measurement condition from among the plurality of measurement conditions based on a plurality of evaluation values ​​corresponding to each of the plurality of measurement conditions, and performs transmission and reception for contrast-enhanced ultrasound examination based on the main measurement condition to generate an ultrasound image representing the contrast agent distribution within the specific subject based on the received information obtained from the specific subject.

[0007] Furthermore, the appropriate intensity conditions include a lower intensity threshold to ensure the lowest contrast of the ultrasound image and an upper intensity threshold to avoid contrast agent destruction, and the portion that satisfies the appropriate intensity conditions may be the portion of the sound pressure distribution that falls between the lower intensity threshold and the upper intensity threshold.

[0008] Furthermore, the measurement conditions may also be a set of transmission parameters that serve as transmission conditions for generating the transmission beam.

[0009] Furthermore, the processor may perform preliminary transmission and reception to determine a set of bio-parameters representing the ultrasonic propagation state within the specific subject based on the received information obtained from the specific subject, and then estimate the sound pressure distribution along the depth direction within the specific subject by executing the simulation using the transmitted parameter set and the bio-parameter set as input parameters.

[0010] Furthermore, the appropriate intensity condition has an intensity lower threshold to guarantee the desired contrast of the ultrasound image, and the portion that satisfies the appropriate intensity condition may be the portion of the harmonic distribution that is equal to or greater than the intensity lower threshold.

[0011] Furthermore, the measurement conditions may be a combination of a transmission parameter set that serves as the transmission conditions when performing the preliminary transmission and reception and the transmission and reception for contrast-enhanced ultrasound examination, and a reception parameter set that serves as the reception conditions.

[0012] Furthermore, the processor may calculate the evaluation value based on the display range of the ultrasound image or the range of interest in the depth direction within the specific subject. [Effects of the Invention]

[0013] According to this disclosure, contrast agents can be properly imaged over a wide range of depths within the subject. Alternatively, according to this disclosure, transmission conditions suitable for contrast-enhanced ultrasound examination of each subject can be obtained. [Brief explanation of the drawing]

[0014] [Figure 1] This is a block diagram showing the schematic configuration of the ultrasound diagnostic device in Embodiment 1. [Figure 2] This is a flowchart showing the method for determining the transmission conditions in Embodiment 1. [Figure 3] (a) is a diagram showing the sound pressure distribution in the depth direction of the subject in two dimensions, and (b) is a diagram showing the level of the sound pressure obtained from the sound pressure distribution shown in (a). [Figure 4] (a) is a diagram showing a specific example of a site to be examined of the subject, and (b) is a diagram showing the level of the sound pressure obtained from the sound pressure distribution obtained by performing a sound pressure distribution simulation on the site shown in (a). [Figure 5] It is a block diagram showing a schematic configuration of the ultrasonic diagnostic apparatus in Embodiment 2. [Figure 6] It is a flowchart showing a method for determining transmission / reception conditions in Embodiment 2. [Figure 7] (a) is a diagram schematically showing the harmonic power distribution in the depth direction of the subject, and (b) is a diagram showing the level of the harmonic power obtained from the harmonic power distribution shown in (a).

Mode for Carrying Out the Invention

[0015] Hereinafter, embodiments according to the present disclosure will be described based on the drawings.

[0016] Embodiment 1. (Configuration of Ultrasonic Diagnostic Apparatus) FIG. 1 is a block diagram showing a schematic configuration of an ultrasonic diagnostic apparatus 10 in the present embodiment. The ultrasonic diagnostic apparatus 10 in the present embodiment includes an apparatus main body 100 and a probe 200. The apparatus main body 100, also called a "console", has an operation unit 112 and a display unit 114, which will be described later as user interfaces. The probe 200 is a device that transmits and receives ultrasonic beams for ultrasonic diagnosis. Inside the probe 200, a vibration element array 202 configured by arranging a plurality of vibration elements is built in. Each vibration element performs mutual conversion between an electrical signal and an ultrasonic signal by the piezoelectric effect. There are several types of probes 200, such as a linear type, a sector type, and a convex type.

[0017] The ultrasonic diagnostic apparatus 10 can also be referred to as an ultrasonic diagnostic system. The ultrasonic diagnostic apparatus 10 has a function of performing ultrasonic diagnosis using the probe 200. The ultrasonic diagnostic apparatus 10 in the present embodiment particularly has a contrast ultrasonic examination function. The contrast ultrasonic examination is an examination that greatly vibrates the bubble-like contrast agent injected into the living body by an ultrasonic beam and detects non-linear signals to depict blood vessels with high contrast against the living tissue.

[0018] In the following description, "imaging in the contrast mode" refers to imaging using a contrast agent, and in the case of the present embodiment, it is synonymous with imaging of the contrast agent in the contrast ultrasonic examination. Also, "contrast" in an image refers to the difference between the bright part and the dark part of the image, and "high contrast" means that the difference is large. "High contrast" as referred to in the present embodiment means that the difference in brightness between the part where the contrast agent is injected and the part where it is not is large, and the ultrasonic image representing the contrast agent distribution can be clearly displayed. In other words, contrast can also be said to be the ratio of the intensity of the harmonic component from the contrast agent to the intensity of the harmonic component from the living tissue.

[0019] The transmission / reception control unit 102 controls the transmission and reception of ultrasonic waves by each vibration element in the probe 200. This control includes, for example, supplying an electrical transmission signal to each vibration element and amplifying the electrical reception signal from each vibration element. The transmission beamformer 1022 forms an ultrasonic transmission beam by controlling the supply timing of the transmission signal to each vibration element. The reception beamformer 1024 performs coherent addition processing on the reception signals from each vibration element in the probe 200. The reception beam is formed by this coherent addition processing. The reception beamformer 1024 outputs echo data obtained along the reception beam as a result of the coherent addition processing.

[0020] The signal processing unit 104 performs various signal processing on the echo data output by the receiving beamformer 1024, including gain correction, logarithmic amplification, envelope detection, and filtering. This forms beam data corresponding to each echo data.

[0021] In this embodiment, the signal processing unit 104 includes a bio-parameter calculation processing unit 1042. The bio-parameter calculation processing unit 1042 calculates bioacoustic parameters (hereinafter simply referred to as "biological parameters") used in the sound pressure distribution simulation calculation performed by the transmission condition determination unit 110. More specifically, the bio-parameter calculation processing unit 1042 acquires a set of multiple bio-parameters (hereinafter referred to as "biological parameter set") representing the ultrasonic propagation state within the subject by pilot transmission, which corresponds to preliminary transmission and reception.

[0022] As will be described in detail later, in this embodiment, the optimal transmission conditions are determined to obtain an ultrasound image that shows good contrast agent distribution. In this process, the accuracy of the sound pressure distribution is crucial. The sound pressure distribution is affected by parameters set in the transmission conditions, such as the transmission frequency and the input voltage to the probe, but it also changes significantly depending on the above-mentioned biological parameters which depend on the subject 300. In particular, the acoustic attenuation rate and sound velocity included in the biological parameters greatly change the shape of the sound pressure distribution, so it is desirable to be able to input them into the sound pressure distribution simulation. Therefore, in this embodiment, a biological parameter calculation processing unit 1042 is provided so that a set of biological parameters can be obtained and input into the sound pressure distribution simulation.

[0023] Furthermore, the method for estimating the acoustic attenuation rate can be, for example, the technology described in Japanese Patent No. 6457107, and the method for estimating the speed of sound can be, for example, the technology described in Japanese Patent No. 7493481.

[0024] The image processing unit 106 has coordinate transformation and interpolation functions, and forms a display frame, i.e., an ultrasound image, based on multiple beam data output from the signal processing unit 104. The beam data from the signal processing unit 104 is coordinate system data for beam scanning, and consists of multiple data points along the beam direction corresponding to the beam data. For example, the image processing unit 106 transforms the signal value of each data point of the beam data into the display coordinate system, i.e., the coordinate system of the ultrasound image (generally a Cartesian coordinate system represented by a pair of x and y coordinates). The image processing unit 106 also interpolates the value of a pixel with no value from the values ​​of surrounding pixels. Through such coordinate transformation and interpolation, the image processing unit 106 forms an ultrasound image such as a B-mode tomographic image. When performing contrast-enhanced ultrasound examinations, the image processing unit 106 generates an ultrasound image representing the contrast agent distribution using CHI (Contrast Harmonic Imaging), a method of selectively displaying harmonic signals generated by nonlinear effects on ultrasound incident on an ultrasound contrast agent (generally microbubbles). The image formed using CHI will be referred to as a "contrast-enhanced image" in the following description. As described above, the transmission / reception control unit 102, the signal processing unit 104, and the image processing unit 106 work in coordination to generate a contrast-enhanced image of the subject 300 based on the received information obtained from the subject.

[0025] The display processing unit 108 synthesizes various informational images or characters onto the ultrasound image formed by the image processing unit 106 to form display screen data. Information synthesized onto the ultrasound image includes, for example, the ROI (Region of Interest) representing the display range of various display modes such as color Doppler mode, and lines indicating the sample volume and beam location for pulsed Doppler mode. The display screen data formed by the display processing unit 108 is displayed on the display unit 114.

[0026] The transmission condition determination unit 110 determines the transmission conditions for transmission beamforming. In this embodiment, the transmission condition determination unit 110 determines transmission conditions particularly suitable for imaging in contrast mode. As will be described in detail later, in this embodiment, the transmission condition determination unit 110 uses a plurality of transmission parameter sets that are pre-set and registered in the ultrasonic transmission condition storage unit 118 as transmission conditions. The transmission condition determination unit 110 includes a sound pressure distribution simulation execution unit 1102 and a sound pressure distribution analysis unit 1104.

[0027] The sound pressure distribution simulation execution unit 1102 estimates the sound pressure distribution by executing a sound pressure distribution simulation using a transmission parameter set as the transmission conditions and a bio-parameter set calculated by the bio-parameter calculation processing unit 1042 (hereinafter, the transmission parameter set and the bio-parameter set are collectively referred to as "input parameters") as input. The sound pressure distribution simulation outputs a sound pressure distribution assuming that contrast agent has been injected into the subject 300. In particular, in this embodiment, by using the bio-parameters of the subject 300 to be examined as input to the sound pressure distribution simulation, it is possible to estimate the sound pressure distribution along the depth direction within the subject. The sound pressure distribution simulation execution unit 1102 obtains multiple sound pressure distributions by executing multiple sound pressure distribution simulations using different transmission parameter sets as transmission conditions.

[0028] The sound pressure distribution analysis unit 1104 selects transmission conditions that are estimated to be optimal for contrast-enhanced ultrasound examination performed on the subject 300 by referring to multiple sound pressure distributions obtained by the sound pressure distribution simulation execution unit 1102. Basically, it selects transmission conditions that increase the range in which good contrast is estimated to be obtained in the depth direction of the subject 300 (referred to as the "appropriate range" in this embodiment). In contrast-enhanced ultrasound examination, transmission beamforming is performed using the transmission conditions determined by the transmission condition determination unit 110. In this embodiment, "depth direction" refers to the direction from the body surface of the subject 300 toward the inside of the body unless otherwise specified.

[0029] The operation unit 112 is a device operated by an operator (hereinafter also referred to as "user") to input parameters and control the display in ultrasound diagnosis. The display unit 114 is a device that displays images and is composed of, for example, a liquid crystal panel or an organic EL panel. The display unit 114 displays display screen data formed by the display processing unit 108. The control unit 116 controls the execution of ultrasound diagnostic processing by controlling the operation of each component included in the main unit 100.

[0030] The ultrasonic transmission condition memory unit 118 stores multiple transmission parameter sets as measurement conditions, which are used when performing transmission beamforming through sound pressure distribution simulations and the like. A transmission parameter set is created by combining multiple transmission parameters. The transmission parameters themselves included in the transmission parameter set can have the same configuration as the transmission parameters specified in general transmission beamforming. Specifically, transmission parameters include the input voltage to the probe 200, frequency, wave thread length, ultrasonic shape (sine wave or sum of multiple sine waves, etc.), apodization, aperture diameter, and focal point. By changing the setting value of at least one of these transmission parameters, multiple transmission parameter sets are set whose setting values ​​do not exactly match those of other transmission parameter sets. Multiple transmission parameter sets with different settings result in transmission conditions that produce different transmission beams. Note that since the transmission parameter set is used as the transmission condition when performing transmission beamforming, it may also be referred to as "transmission conditions" for convenience.

[0031] The functions provided by each component 102 to 116 in the main unit 100 are realized through the coordinated operation of a computer installed in the main unit 100 and a program running on a processor installed in the computer. The computer may be equipped with multiple processors and configured to appropriately distribute the functions provided by each component 102 to 116 among the processors. The multiple processors may include processors specialized for specific processing functions. The control unit 116 may be implemented with a single processor or multiple processors. The ultrasonic transmission condition storage unit 118 is implemented with a storage device such as an HDD (Hard Disk Drive) installed in the main unit 100. Alternatively, it may be implemented using an external storage device via a network.

[0032] The configuration of the ultrasound diagnostic device 10 described above using Figure 1 may be basically the same as the previous hardware configuration.

[0033] (Method for determining transmission conditions) As mentioned above, in contrast-enhanced ultrasound, a contrast agent is intravenously injected into the living body (i.e., "subject 300"), and the contrast agent is vibrated significantly by an ultrasound beam. The nonlinear signal from this vibration is received as reception information to visualize the blood vessels of subject 300. However, even if contrast-enhanced ultrasound is performed under the same transmission conditions, the bubble-like vibration state of the contrast agent will differ depending on differences in subject 300's body type, etc. Furthermore, even with the same subject 300, it can dynamically change depending on the location of the tissue where the contrast agent is present, and also depending on subject 300's condition such as blood pressure and body temperature at the time of the examination. Therefore, it is preferable to set transmission conditions that are suitable for the differences in subject 300, or the subject 300's physical condition, and perform transmission beamforming to obtain good contrast-enhanced images as a result.

[0034] Therefore, in this embodiment, immediately before performing a contrast-enhanced ultrasound examination, preliminary ultrasound transmission and reception is performed to obtain biological parameters as information indicating the state of the subject 300 to be examined, and a sound pressure distribution simulation is performed using these biological parameters as input. This embodiment is characterized in that, by using a set of biological parameters and various different sets of transmission parameters as transmission conditions, the transmission conditions for obtaining the optimal contrast-enhanced image for the subject 300 in the contrast-enhanced ultrasound examination are determined by the sound pressure distribution simulation. The optimal contrast-enhanced image here is a high-contrast, good contrast-enhanced image along the depth direction of the subject 300 within the imaging field of view. Furthermore, a high-contrast, good contrast-enhanced image basically corresponds to the sound pressure distribution obtained by ultrasound transmission and reception falling within the range of the contrast threshold and the breakdown threshold within the imaging field of view, as will be described later. In this embodiment, the appropriate intensity condition is that the sound pressure level falls within the range of the contrast threshold and the breakdown threshold, and when this appropriate intensity condition is met, it is considered that a high-contrast, good contrast-enhanced image has been obtained. Incidentally, the "contrast threshold" is the lower intensity threshold to guarantee the minimum contrast of the ultrasound image. The "breakdown threshold" is the upper intensity threshold to avoid contrast agent breakdown. The contrast threshold and the failure threshold can be determined using known methods.

[0035] The method for determining the transmission conditions in this embodiment will be explained below using the flowchart shown in Figure 2.

[0036] First, the ultrasound diagnostic device 10 acquires biological parameters representing the physical condition of the subject 300, such as body shape, and its current condition. Specifically, the ultrasound diagnostic device 10 performs a pilot transmission at a first ultrasound frequency towards a predetermined area of ​​the subject 300, such as a tumor on an organ (step S110). The first ultrasound frequency may be any frequency used for normal ultrasound diagnosis. For example, the first ultrasound frequency may be 2 to 20 MHz.

[0037] The bioparameter calculation processing unit 1042 calculates bioparameters from the received signal obtained by pilot transmission (step S120). The bioparameters are, for example, the acoustic attenuation rate, sound velocity, and subcutaneous fat thickness at a predetermined part of the subject estimated from the received signal. In this embodiment, a bioparameter set is obtained by combining these bioparameters.

[0038] Once the biological parameter set is obtained, the sound pressure distribution simulation execution unit 1102 selects one transmission parameter set to be used for the sound pressure distribution simulation from among the transmission parameter sets registered in the ultrasonic transmission condition storage unit 118 (step S130).

[0039] As mentioned above, the ultrasonic transmission condition storage unit 118 stores multiple transmission parameter sets, each with at least one transmission parameter having a different parameter value. The sound pressure distribution simulation execution unit 1102 reads a transmission parameter set from the ultrasonic transmission condition storage unit 118 that has not yet been used to run the simulation. Reading this transmission parameter set is equivalent to selecting a provisional measurement condition for running the sound pressure distribution simulation from the measurement conditions registered in the ultrasonic transmission condition storage unit 118.

[0040] Then, the sound pressure distribution simulation execution unit 1102 uses the read-out transmission parameter set as the transmission conditions, and estimates the sound pressure distribution by executing a sound pressure distribution simulation using these transmission conditions and the bio-parameter set calculated by the bio-parameter calculation processing unit 1042 as input parameters (step S140). In this embodiment, a sound pressure distribution indicating the intensity of sound pressure is generated as an intensity distribution.

[0041] Thus, once a sound pressure distribution is obtained through a single sound pressure distribution simulation performed with a single set of transmission parameters as the transmission conditions, the sound pressure distribution analysis unit 1104 analyzes this sound pressure distribution to extract and determine the range from the entire depth range in which a high-contrast, good contrast-enhanced image can be obtained in the depth direction of the subject 300 (step S150). The range determined here will be referred to as the "suitable range," as will be described later. Details of the processing in the sound pressure distribution analysis unit 1104 will be described later.

[0042] Next, the sound pressure distribution simulation execution unit 1102 proceeds to step S170 if it has executed a sound pressure distribution simulation using all transmission parameter sets registered in the ultrasonic transmission condition storage unit 118 that are candidates for transmission conditions (Y in step S160). If there are transmission parameter sets that have not yet been used to execute the sound pressure distribution simulation (N in step S160), it proceeds to step S130 and repeatedly executes steps S140 to S150 described above.

[0043] Here, we will explain the processing in the sound pressure distribution analysis unit 1104.

[0044] Figure 3(a) schematically shows the sound pressure distribution obtained by performing a sound pressure distribution simulation. Figure 3(b) shows the sound pressure level obtained from the sound pressure distribution shown in Figure 3(a).

[0045] Figure 3(a) shows the sound pressure distribution in the depth direction in two dimensions, obtained by transmitting and receiving an ultrasonic beam from the vibrating element array 202. In Figure 3(a), darker colored areas indicate higher sound pressure. That is, when an ultrasonic beam is transmitted from the vibrating element array 202, the sound pressure increases as it approaches the focal point, i.e., as it goes deeper. After passing the focal point, it can be seen that it then decreases.

[0046] Figure 3(b) shows the sound pressure level extracted in one dimension along the central axis indicated by the dashed line C, from the two-dimensional sound pressure distribution shown in Figure 3(a). In Figure 3(b), sound pressure S represents the sound pressure level, with the level increasing towards the right of the figure.

[0047] Figure 3(b) shows the contrast threshold t1 and the breakdown threshold t2. When the sound pressure S falls within the range SR between these two thresholds, a high-contrast, good contrast-enhanced image is obtained. Since a high-contrast, good contrast-enhanced image is a useful and suitable image for contrast-enhanced ultrasound examination, it will be referred to as a "suitable image" for convenience in the following explanation.

[0048] For example, in Figure 3(b), the sound pressure S when the depth from the vibrating element array 202 has not reached depth d1 does not reach the contrast threshold t1, indicating that sufficient contrast is not obtained, i.e., a suitable image cannot be obtained.

[0049] The sound pressure S at a depth from the vibration element array 202 between depths d1 and d2 is greater than or equal to the contrast threshold t1 and does not reach the failure threshold t2. In other words, it falls between the contrast threshold t1 and the failure threshold t2, indicating that a suitable image can be obtained in this range L1.

[0050] The sound pressure S from the vibration element array 202 between depths d2 and d3 is above the failure threshold t2, indicating that the contrast agent has broken down and a suitable image cannot be obtained.

[0051] The sound pressure S from the vibration element array 202 at depths d3 to d4 is greater than or equal to the contrast threshold t1, similar to range L1, and does not reach the failure threshold t2. In other words, it falls between the contrast threshold t1 and the failure threshold t2, indicating that a suitable image can be obtained in this range L2.

[0052] Furthermore, when the depth from the vibration element array 202 exceeds depth d4, the sound pressure S does not reach the contrast threshold t1, indicating that sufficient contrast is not obtained, i.e., a suitable image cannot be obtained.

[0053] As described above, in this embodiment, ranges L1 and L2 are extracted as the range from which a suitable image can be obtained in contrast-enhanced ultrasound examination (hereinafter referred to as the "suitable range"). The suitable range can also be described as the length in the depth direction, and the longer this length in the depth direction, the better the suitable image that can be obtained.

[0054] The sound pressure distribution analysis unit 1104 analyzes the sound pressure distribution obtained from a single sound pressure distribution simulation and calculates the suitable range as an evaluation value representing the size of the portion of the sound pressure distribution that satisfies the appropriate intensity conditions for contrast imaging, i.e., generating a contrast-enhanced image. In other words, the sound pressure distribution analysis unit 1104 defines the appropriate intensity condition as the sound pressure level S falling between the contrast threshold t1 and the breakdown threshold t2, and calculates the portion that satisfies this appropriate intensity condition, i.e., the suitable range. In this embodiment, the evaluation value is obtained as many times as the number of times steps S130 to S150 are repeated, or in other words, as many times as the number of transmission parameter sets registered in the ultrasonic transmission condition storage unit 118.

[0055] The transmission condition determination unit 110 then determines the transmission condition that yields the best evaluation value, i.e., the sound pressure S that maximizes the total length of the suitable range in the depth direction (i.e., the transmission parameter set), as the transmission condition to be used in contrast-enhanced ultrasound examination (step S170). Determining the transmission condition to be used in contrast-enhanced ultrasound examination based on the suitable range is equivalent to selecting this measurement condition from among multiple transmission parameter sets (i.e., measurement conditions) registered in the ultrasound transmission condition storage unit 118.

[0056] Once the transmission conditions are determined as described above, the ultrasound diagnostic device 10 performs a contrast-enhanced ultrasound examination using those transmission conditions. By using these transmission conditions, a suitable image, i.e., a high-contrast, good contrast-enhanced image, can be displayed during a contrast-enhanced ultrasound examination.

[0057] (modified version) Figure 4(a) shows specific examples of areas of the subject 300 that are to be examined. Figure 4(a) schematically illustrates the subcutaneous fat layer 302, muscle 304, and organs such as the liver 306. It is shown that organs 306 contain a tumor 308 and large blood vessels 310. The areas of the subject 300 shown in Figure 4(a) are the targets for the transmission and reception of the ultrasound beam shown in Figure 3(a), and are the target areas for sound pressure distribution simulation.

[0058] In Figure 4(a), the illustration of the sound pressure distribution as shown in Figure 3(a) is omitted. However, in Figure 4(b), the sound pressure level is extracted in one dimension along the central axis indicated by the dashed line C shown in Figure 4(a). The fitting range in Figure 4(b) can be determined using the method shown in Figure 3(b). That is, when the sound pressure S falls within the range SR between the contrast threshold t1 and the distortion threshold t2, the range L3 in Figure 4(b) is the fitting range.

[0059] Incidentally, in the above explanation, the fit range was calculated based on the entire display range of the contrast-enhanced image, and a longer fit range was considered to indicate a better contrast-enhanced image. However, in contrast-enhanced ultrasound examinations, users may prefer a clearer display of a specific range of the subject 300, even if it means a slightly shorter fit range. The transmission conditions may be selected to accommodate such user requests.

[0060] For example, by inputting a preset (such as organ names like liver or pancreas, or broad body part names like abdomen or lower limbs), the user's desired observation range, or in other words, their area of ​​interest (hereinafter referred to as the "range of interest"), is determined to some extent. For example, in the case of a Japanese male's liver, the average distance from the epidermis to the liver surface is 3-4 cm, and to the diaphragm is 12-15 cm, so the 3-15 cm range containing the liver is the imaging range to be drawn. Thus, having the user input a preset is one way to specify the range of interest in the depth direction within the subject.

[0061] Alternatively, the user may be allowed to specify a region of interest from within the entire display range of the contrast-enhanced image. For example, if the user wants to visualize only the area containing tumor 308 in Figure 4(a), the user may be allowed to manually specify the region of interest A as the range from depth d6 to depth d7.

[0062] If a range of interest is specified, the sound pressure distribution analysis unit 1104 calculates the percentage of the range (length) that includes the range of interest within the fitted range. Here, the percentage of the range of interest that overlaps with the fitted range is referred to as the "overlap rate." For example, in the example shown in Figure 4, the range of interest A overlaps with the fitted range L3 by 100%, so the overlapping range (length) is A, and the overlap rate in the range of interest A can be calculated as overlapping length (=A) / range of interest (=A) = 100%.

[0063] If there are multiple transmission parameter sets that maximize the overlap ratio, one can be selected from among them, one can be selected based on some selection criteria, or the user can be allowed to select it. As a selection criterion, for example, the transmission parameter set that maximizes the matching range can be selected. Alternatively, for example, in the diagram shown in Figure 4(b), the transmission parameter set that maximizes the area enclosed by depths d6, d7 corresponding to both ends of the region of interest A, contrast threshold t1, and sound pressure S can be selected. Conversely, the transmission parameter set that minimizes the area enclosed by depths d6, d7, break threshold t2, and sound pressure S can be selected. Alternatively, a threshold t3 can be set separately between the contrast threshold t1 and the break threshold t2, and the transmission parameter set that maximizes the range (length) exceeding threshold t3 can be selected.

[0064] In this embodiment, the transmission conditions used for contrast-enhanced ultrasound examination are determined as described above. The contrast-enhanced ultrasound examination itself can be performed using the same method as before, so its explanation will be omitted. However, by performing the contrast-enhanced ultrasound examination using the transmission conditions determined by the method described above, a good contrast-enhanced image can be displayed.

[0065] In this embodiment, when performing the sound pressure distribution simulation, all transmission parameter sets registered in the ultrasonic transmission condition storage unit 118 were used, but the user may be allowed to select a transmission parameter set.

[0066] Furthermore, each transmission parameter has a defined range of possible values. Therefore, the user may be allowed to select the values ​​of the transmission parameters to be used for sound pressure distribution simulation from within this range. In other words, this is equivalent to providing the user with a function to manually create the transmission parameter set itself. The transmission parameter set created by the user may or may not be registered in the ultrasonic transmission condition storage unit 118. Alternatively, the information may be managed separately from the ultrasonic transmission condition storage unit 118 as customized data.

[0067] In this embodiment, a good contrast-enhanced image can be magnified in the depth direction for evaluation and display. Furthermore, by performing a pilot transmission before the contrast-enhanced ultrasound examination, the state of the subject 300 at the time of the contrast-enhanced ultrasound examination (i.e., the "biological parameters" mentioned above) is acquired. This makes it possible to determine transmission conditions that are suitable for the subject 300 at the time of the contrast-enhanced ultrasound examination, and by using these transmission conditions, a good contrast-enhanced image suitable for the subject 300 can be displayed during the contrast-enhanced ultrasound examination.

[0068] In this embodiment, we have focused on the sound pressure distribution along the central axis, i.e., the sound pressure distribution in one dimension, but the suitable range may also be obtained by comprehensively considering the sound pressure distribution in two or three dimensions.

[0069] Embodiment 2. (Configuration of an ultrasound diagnostic device) Figure 5 is a block diagram showing the schematic configuration of the ultrasound diagnostic device 10 in this embodiment. The configuration of the ultrasound diagnostic device 10 in this embodiment is basically the same as in Embodiment 1. The ultrasound diagnostic device 10 in this embodiment has the same internal configuration as the signal processing unit 104 and a transmission / reception condition determination unit 120 instead of the transmission condition determination unit 110. In addition, in Embodiment 1, only the transmission parameter set was registered in the ultrasound transmission condition storage unit 118, but in this embodiment, the ultrasound transmission / reception condition storage unit 122 registers both the transmission parameter set and the reception parameter set.

[0070] In this embodiment, the signal processing unit 104 includes a harmonic component extraction processing unit 1044. The harmonic component extraction processing unit 1044 extracts harmonic components from the sound pressure distribution estimated from the received signal obtained by pilot transmission and reception, which corresponds to preliminary transmission and reception.

[0071] In this embodiment, the transmit / receive condition determination unit 120 determines the transmit conditions for transmit beamforming and the receive conditions for receive beamforming. The transmit / receive condition determination unit 120 includes a harmonic power distribution creation unit 1202 and a harmonic power distribution analysis unit 1204. The harmonic power distribution creation unit 1202 creates a harmonic power distribution based on the harmonic components extracted by the harmonic component extraction processing unit 1044. The harmonic power distribution creation unit 1202 creates one harmonic power distribution for each pilot transmit / receive operation. The harmonic power distribution analysis unit 1204 analyzes each of the multiple harmonic power distributions created by the harmonic power distribution creation unit 1202 to select the transmit / receive conditions that yield the optimal contrast-enhanced image.

[0072] The transmission parameter set registered in the ultrasonic transmission / reception condition storage unit 122 may be the same as that of the ultrasonic transmission condition storage unit 118 in Embodiment 1. The receiving parameters themselves to be included in the receiving parameter set may have the same configuration as the receiving parameters specified in general receiving beamforming. Specifically, the receiving parameters include apodization, bandpass filter threshold (cutoff frequency when extracting harmonics), number of receiving channels, aperture diameter, etc. Only one receiving parameter set may be prepared. Alternatively, similar to the transmission parameter set, multiple receiving parameter sets may be prepared in which the setting values ​​do not exactly match those of other receiving parameter sets by changing the setting value of at least one of the receiving parameters. The harmonic power distribution creation unit 1202 selects one of the transmission parameter sets registered in the ultrasonic transmission condition storage unit 118 as the transmission condition, and also selects one of the receiving parameter sets registered in the ultrasonic transmission condition storage unit 118 as the reception condition, and creates a harmonic power distribution.

[0073] (Method for determining transmission and reception conditions) As mentioned above, the vibration state of contrast agent bubbles injected intravenously into subject 300 can dynamically change depending on differences in subject 300's body type, and even in the same subject 300, depending on the location of the tissue where the contrast agent bubbles are present and the subject 300's condition. Therefore, it is desirable to perform contrast-enhanced ultrasound examinations that are suited to the differences in subject 300 or the subject 300's physical condition. In this embodiment, the optimal transmission conditions were determined using sound pressure distribution simulation. In this embodiment, the set of transmission and reception conditions to be used in contrast-enhanced ultrasound examinations (hereinafter collectively referred to as "transmission and reception conditions") is determined by actually performing a pilot transmission and reception, which is a preliminary transmission and reception, on subject 300.

[0074] The method for determining the transmission and reception conditions in this embodiment will be explained below using the flowchart shown in Figure 6.

[0075] First, for example, the harmonic power distribution creation unit 1202 in the transmission / reception condition determination unit 120 selects one transmission parameter set from the transmission parameter sets registered in the ultrasonic transmission / reception condition storage unit 122 that is not used in the pilot transmission / reception described later. It also selects one arbitrary reception parameter set from the reception parameter sets registered in the ultrasonic transmission / reception condition storage unit 122 (step S210).

[0076] Next, the harmonic power distribution generation unit 1202 uses the selected transmission parameter set as the transmission condition and the selected reception parameter set as the reception condition to perform pilot transmission and reception (step S220). Thus, in this embodiment, when a set of transmission and reception parameter sets registered in the ultrasonic transmission / reception condition storage unit 122 is used as the measurement condition, the set of transmission and reception parameter sets selected from the ultrasonic transmission / reception condition storage unit 122 is used as the provisional measurement condition to perform pilot transmission and reception.

[0077] Next, the harmonic component extraction processing unit 1044 extracts the harmonic components originating from the contrast agent from the sound pressure distribution estimated from the received signal obtained by pilot transmission and reception (step S230). Then, the harmonic power distribution creation unit 1202 creates a harmonic power distribution by referring to the harmonic components extracted by the harmonic component extraction processing unit 1044 (step S240). The harmonic power distribution is a distribution of harmonics that reflects the sound pressure distribution and corresponds to the intensity distribution.

[0078] Thus, once a single harmonic power distribution is obtained through one pilot transmission and reception using a single set of transmission and reception parameters as the transmission and reception conditions, the harmonic power distribution analysis unit 1204 analyzes this harmonic power distribution to extract and determine the range in the depth direction of the subject 300 in which a high-contrast, good contrast-enhanced image can be obtained, i.e., the suitable range, from the entire depth direction (step S250). Details of the processing in this harmonic power distribution analysis unit 1204 will be described later.

[0079] Next, the harmonic power distribution generation unit 1202 proceeds to step S270 if it has performed a pilot transmission and reception using all the transmission parameter sets registered in the ultrasonic transmission / reception condition storage unit 122 that are candidates for transmission conditions (Y in step S260). If there are transmission parameter sets that have not yet been used in the simulation (N in step S260), it proceeds to step S210 and repeatedly executes steps S210 to S250 described above.

[0080] For example, if m transmission parameter sets and n reception parameter sets are registered in the ultrasonic transmission / reception condition storage unit 122, the harmonic power distribution creation unit 1202 will perform m × j (j=1 to n) pilot transmissions and receptions. The combination of transmission parameter sets and reception parameter sets used for pilot transmissions and receptions may be selected by the user.

[0081] Here, we will explain the processing in the harmonic power distribution analysis unit 1204.

[0082] Figure 7(a) schematically shows the harmonic power distribution created by performing pilot transmission and reception. Figure 7(b) shows the harmonic power levels obtained from the harmonic power distribution shown in Figure 7(a).

[0083] Figure 7(a) shows the harmonic power distribution in the depth direction in two dimensions, obtained by transmitting and receiving an ultrasonic beam from the vibrating element array 202. In Figure 7(a), darker colors indicate stronger harmonic power. That is, when an ultrasonic beam is transmitted from the vibrating element array 202, the harmonics increase with depth and gradually become undetectable as the bubble-like contrast agent begins to break down.

[0084] Figure 7(b) shows the harmonic power levels extracted in one dimension along the central axis indicated by the dashed line C, from the two-dimensional harmonic power distribution shown in Figure 7(a). In Figure 7(b), the harmonic power P represents the power, or in other words, the intensity level of the harmonics, with higher levels indicating greater intensity towards the right of the diagram. Intensity can also be considered sensitivity.

[0085] Figure 7(b) shows the harmonic threshold t3. The harmonic threshold t3 is the lower intensity threshold that indicates the lower limit of intensity required to guarantee the desired contrast in the contrast-enhanced image. When the harmonic power P is greater than or equal to the harmonic threshold t3, a high-contrast, good contrast-enhanced image, i.e., a fitted image, is obtained.

[0086] Incidentally, considering that the contrast of the contrast mode and the breakdown of the contrast agent can be determined from the harmonic values, a contrast threshold t1 and a breakdown threshold t2 are not set as in Embodiment 1, and instead a harmonic threshold t3 is set. The harmonic threshold t3 is a threshold above which it is estimated that the desired contrast can be obtained if harmonics are obtained. Note that if the contrast agent vibrates appropriately, more harmonics can be obtained. Also, if the contrast agent is broken down, the value of the harmonic component will be low.

[0087] For example, in Figure 7(b), the harmonic power P when the depth from the vibrating element array 202 has not reached depth d8 has not reached the harmonic threshold t3, indicating that sufficient contrast is not obtained, i.e., a suitable image cannot be obtained.

[0088] The harmonic power P from the vibration element array 202 at depths d8 to d9 is greater than or equal to the harmonic threshold t3, indicating that a suitable image can be obtained in the range L4 from depth d8 to depth d9.

[0089] Furthermore, when the depth from the vibration element array 202 exceeds depth d9, the harmonic power P does not reach the harmonic threshold t3, indicating that sufficient contrast is not obtained, i.e., a suitable image cannot be obtained.

[0090] Based on the above, in contrast-enhanced ultrasound examination, in the example shown in Figure 7(b), a suitable image can be obtained in range L4. Furthermore, the longer the length of range L4 in the depth direction, that is, the larger the total amount of the suitable range, the better the suitable image can be obtained.

[0091] Thus, in this embodiment, a suitable intensity condition is set such that the harmonic power P is equal to or greater than the harmonic threshold t3. Therefore, the portion that satisfies the appropriate intensity condition is the portion where the harmonic power P is equal to or greater than the harmonic threshold t3, as in range L4. In this embodiment as well, the suitable range is calculated as an evaluation value representing the size of the portion that satisfies the appropriate intensity condition for generating a contrast-enhanced image.

[0092] The harmonic power distribution analysis unit 1204 determines the range in the depth direction of the subject 300 from the harmonic power distribution, as shown in Figure 7(b), in which a suitable image can be obtained. Then, the transmission / reception condition determination unit 120 determines the transmission / reception conditions (i.e., the set of transmission parameter set and reception parameter set) that yield the largest range (i.e., the total length in the depth direction) among the ranges in which a suitable image can be obtained as the transmission / reception conditions to be used in contrast-enhanced ultrasound examination (step S270). Determining the transmission / reception conditions to be used in contrast-enhanced ultrasound examination based on the suitable range is equivalent to selecting the measurement conditions from among multiple transmission / reception parameter sets (i.e., measurement conditions) registered in the ultrasound transmission / reception condition storage unit 122.

[0093] Once the transmission and reception conditions are determined as described above, a contrast-enhanced ultrasound examination is performed using these conditions. In contrast-enhanced ultrasound examinations, a suitable image, i.e., a high-contrast, good contrast image, can be displayed by using these transmission and reception conditions. In this embodiment, instead of displaying the received signal as is, the harmonic components contained in the received signal can be effectively extracted and imaged. In other words, the blood vessel area to be imaged where the contrast agent has been injected can be displayed brightly, while other biological parts can be displayed darkly.

[0094] In this embodiment, although not explained here, the scope of interest may be specified by the user, similar to the case of Embodiment 1. [Explanation of Symbols]

[0095] 10 Ultrasound diagnostic device, 100 Main unit of the device, 102 Transmit / receive control unit, 104 Signal processing unit, 106 Image processing unit, 108 Display processing unit, 110 Transmission condition determination unit, 112 Operation unit, 114 Display unit, 116 Control unit, 118 Ultrasound transmission condition storage unit, 120 Transmit / receive condition determination unit, 122 Ultrasound transmission / receive condition storage unit, 200 Probe, 202 Vibration element array, 300 Subject, 302 Subcutaneous fat layer, 304 Muscle, 306 Organ, 308 Tumor, 310 Large blood vessel, 1022 Transmit beamformer, 1024 Receiving beamformer, 1042 Biological parameter calculation processing unit, 1044 Harmonic component extraction processing unit, 1102 Sound pressure distribution simulation execution unit, 1104 Sound pressure distribution analysis unit, 1202 Harmonic power distribution creation unit, 1204 Harmonic power distribution analysis unit.

Claims

1. Equipped with a processor, The aforementioned processor, Select a provisional measurement condition from among several measurement conditions that produce different transmission beams. By performing simulations or preliminary transmissions based on the aforementioned provisional measurement conditions, an intensity distribution is generated representing the sound pressure distribution along the depth direction within a specific subject, or the harmonic distribution reflecting said sound pressure distribution. An evaluation value is calculated that represents the size of the portion in the aforementioned intensity distribution that satisfies the appropriate intensity conditions for contrast agent imaging. Based on multiple evaluation values ​​corresponding to each of the multiple measurement conditions, the main measurement condition is selected from among the multiple measurement conditions. Based on the aforementioned measurement conditions, transmission and reception for contrast-enhanced ultrasound examination are performed, and an ultrasound image representing the contrast agent distribution within the specific subject is generated based on the received information obtained from the specific subject. An ultrasound diagnostic device characterized by the following features.

2. In the ultrasound diagnostic apparatus according to claim 1, The aforementioned appropriate intensity conditions include a lower intensity threshold to ensure the lowest contrast of the ultrasound image, and an upper intensity threshold to avoid contrast agent destruction. The portion that satisfies the aforementioned appropriate intensity condition is the portion of the sound pressure distribution that falls between the lower intensity threshold and the upper intensity threshold. An ultrasound diagnostic device characterized by the following features.

3. In the ultrasound diagnostic apparatus according to claim 1, The ultrasonic diagnostic apparatus is characterized in that the measurement conditions are a set of transmission parameters that serve as transmission conditions for generating a transmission beam.

4. In the ultrasound diagnostic apparatus according to claim 3, The aforementioned processor, Based on the received information obtained from the specific subject, preliminary transmission and reception are performed to determine a set of biological parameters representing the ultrasound propagation state within the specific subject. By performing the simulation using the aforementioned transmission parameter set and the aforementioned biological parameter set as input parameters, the sound pressure distribution along the depth direction within the specific subject is estimated. An ultrasound diagnostic device characterized by the following features.

5. In the ultrasound diagnostic apparatus according to claim 1, The aforementioned appropriate intensity conditions include an intensity lower threshold to ensure the desired contrast of the ultrasound image. The portion that satisfies the aforementioned appropriate intensity condition is the portion of the harmonic distribution that is equal to or greater than the aforementioned lower intensity threshold. An ultrasound diagnostic device characterized by the following features.

6. In the ultrasound diagnostic apparatus according to claim 1, The ultrasound diagnostic apparatus is characterized in that the measurement conditions are a set of transmission parameters that serve as transmission conditions when performing the preliminary transmission and reception and the transmission and reception for contrast-enhanced ultrasound examination, and a set of reception parameters that serve as reception conditions.

7. In the ultrasound diagnostic apparatus according to claim 1, The ultrasound diagnostic apparatus is characterized in that the processor calculates the evaluation value based on the display range of the ultrasound image or the depth range of interest within a specific subject.

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