Ultrasound diagnosis apparatus and ultrasound imaging method

An ultrasound diagnosis apparatus includes a transmitter, a generator, and an output controller. The transmitter transmits, from an ultrasound probe, push pulses that cause displacement of body tissue according to an acoustic radiation force and transmits, from the ultrasound probe, tracking pulses for observing the displacement of body tissue, which is caused according to the push pulses, in a given scanning area. The generator generates transmission area image data displaying a position to which the push pulses are transmitted. The output controller outputs the generated transmission area image data such that the transmission area image data is superimposed onto medical image data that contains the transmission area.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2013-188776, filed on Sep. 11, 2013, the entire contents of all of which are incorporated herein by reference.

FIELD

Embodiments described herein relate generally to an ultrasound diagnosis apparatus and an ultrasound imaging method.

BACKGROUND

Elastography is a known modality in which the hardness of body tissue is measured and the distribution of the measured hardnesses is then visualized. Elastography is used to diagnose diseases, such as liver cirrhosis, in which the hardness of body tissue changes according to the advancement of lesions. In elastography, there are two main methods to evaluate hardness, and in both methods the body tissue is displaced.

In the first method, the relative hardness of body tissue is visualized by using the magnitude of distortion at each point along a scanning cross-section that is observed when pressure is applied to the body tissue from the body surface with an ultrasound probe and the pressure is then released. In the second method, an acoustic radiation force or mechanical oscillations are applied from the body surface, shear waves then cause displacement of the body tissue, and the displacement is observed at each point along a scanning cross-section over time. This displacement is used to determine the propagation speed of the shear waves and the elasticity is then determined. In the former method, the local magnitude of distortion depends on the dynamic force due to an ultrasound probe being manually moved and an evaluation is made of whether an area of interest is hard or soft relative to the areas around the area of interest. On the other hand, in the latter method, the absolute elasticity of an area of interest can be determined.

In the latter method, a characteristic of shear waves is that they are reflected at the interfaces between tissues of different hardnesses. When displacement due to reflected shear waves is thus observed, the displacement can lead to inaccurate determination of the propagation speed of the shear wave and accordingly an artifact can occur in the hardness image displaying the hardness of body tissue. Consequently, various types of technologies have been proposed that will suppress these artifacts that are attributable to reflected shear waves.

DETAILED DESCRIPTION

An ultrasound diagnosis apparatus according to an embodiment includes a transmitter, a generator, and an output controller. The transmitter transmits push pulses that cause displacement in body tissue according to an acoustic radiation force from an ultrasound probe and transmits tracking pulses for measuring the displacement in the body tissue in a given scanning area, which is the displacement caused according to the push pulses, from the ultrasound probe. The generator generates transmission area image data displaying an transmission area to which the push pulses are transmitted. The output controller outputs the generated transmission area image data such that the generated transmission area image data is superimposed onto medical image data that contains the transmission area.

Ultrasound diagnosis apparatuses and imaging methods according to embodiments will be described with reference to the accompanying drawings.

First Embodiment

A configuration of an ultrasound diagnosis apparatus according to a first embodiment will be described first.FIG. 1is a block diagram of an exemplary configuration of the ultrasound diagnosis apparatus according to the first embodiment. As illustrated inFIG. 1, the ultrasound diagnosis apparatus according to the first embodiment includes an ultrasound probe1, a monitor2, an input device3, and an apparatus main unit10.

The ultrasound probe1includes multiple oscillators (e.g. piezoelectric oscillators) that generate ultrasound according to a drive signal that is supplied from a transmitter11of the apparatus main unit10, which will be described below. The multiple oscillators of the ultrasound probe1also receive reflected waves from a patient P and convert the reflected waves into electric signals. The ultrasound probe1includes a matching layer that is provided to the oscillators, a backing member that prevents backward ultrasound propagation from the oscillators.

When ultrasound is transmitted from the ultrasound probe1to the patient P, the transmitted ultrasound is sequentially reflected on a surface of tissue of the patient P where acoustic impedance discontinuity occurs and is received as reflected-wave signals by the multiple oscillators of the ultrasound probe1. The amplitude of the received reflected-wave signals depends on the difference in acoustic impedance on the discontinuity surface on which ultrasound is reflected. The reflected-wave signals resulting from reflection of the transmitted ultrasound pulses on the flowing blood or the surface of, for example, the heart wall have a frequency shift due to the Doppler effects depending on the velocity components of the moving object in the direction in which ultrasound is transmitted.

In the first embodiment, the ultrasound probe1shown inFIG. 1can be used in any of a case where the ultrasound probe1is a one-dimensional ultrasound probe in which multiple piezoelectric oscillators are arranged in a row, a case where the ultrasound probe1is a one-dimensional ultrasound probe in which multiple piezoelectric oscillators that are arranged in a row are caused to mechanically oscillate, and a case where the ultrasound probe1is a two-dimensional (2D) ultrasound probe in which multiple piezoelectric oscillators are arranged two-dimensionally in a matrix.

The input device3includes a mouse, a keyboard, a button, a panel switch, a touch command screen, a footswitch, a trackball, a joystick, etc. The input device3receives various setting requests from an operator of the ultrasound diagnosis apparatus and transfers the received various setting requests to the apparatus main unit10.

The monitor2displays a graphical user interface (GUI) for the operator of the ultrasound diagnosis apparatus to input various setting requests by using the input device3and displays ultrasound image data that is generated by the apparatus main unit10, etc.

The apparatus main unit10is an apparatus that generates ultrasound image data on the basis of the reflected-wave signals that are received by the ultrasound probe1. As shown inFIG. 1, the apparatus main unit10includes a receiver12, a signal processor13, an image generator14, an image memory15, an internal storage unit16, and a controller17.

The transmitter11controls directivity of transmission of ultrasound. Specifically, the transmitter11includes a rate pulser generator, a transmission delay unit, a transmission pulser and supplies a drive signal to the ultrasound probe1. The rate pulser generator repeatedly generates rate pulses for forming ultrasound transmitted at a given rate frequency (pulse repetition frequency (PRF)). The rate pulses apply a voltage to the transmission pulser in a state where the rate pulses pass through the transmission delay unit and thus have different transmission delays. In other words, the transmitter delay unit gives, to each rate pulse generated by the rate pulser generator, a transmission delay for each oscillator necessary to focus the ultrasound generated by the ultrasound probe1into a beam and to determine the transmission directivity. The transmission pulser applies a drive signal (drive pulses) to the ultrasound probe1at a timing based on the rate pulses. The transmission direction or the transmission delay is stored in the internal storage unit16, which will be described below, and the transmitter11refers to the internal storage unit16and controls the transmission directivity.

The drive pulses are transmitted to the oscillators in the ultrasound probe1via cables from the transmission pulser and then are converted from electric signals into mechanical oscillations. The mechanical oscillations are transmitted as ultrasound in a living subject. The ultrasounds with different transmission delays of the respective oscillators converge and propagate in a given direction. By changing the transmission delay to be given to each rate pulse, the transmission delay unit arbitrarily adjusts the direction of transmission from the surface of the oscillator. The transmitter11gives transmission directivity by controlling the number and positions (transmission apertures) of the oscillators used to transmit ultrasound beams and the transmission delays corresponding to the positions of the respective oscillators constituting the transmission apertures. For example, the transmission delay circuit of the transmitter11gives a transmission delay to each rate pulse generated by the pulser circuit, thereby controlling the position of the point of convergence (transmission focus) in the depth direction of ultrasound transmission.

The transmitter11has a function of changing the transmission frequency, transmission drive voltage, etc. in order to implement a given scan sequence according to an instruction from the controller17, which will be described below. Specifically, changing the transmission drive voltage is implemented by using a linear-amplifier transmitter circuit that can switch its value instantaneously or a mechanism for electrically switching between multiple power units.

The reflected waves of the ultrasound transmitted by the ultrasound probe1reach the oscillators in the ultrasound probe1and are then converted by the oscillators from the mechanical oscillations into electric signals (reflected-wave signals) and the electric signals are input to the receiver12.

The receiver12controls the directivity of reception of ultrasound. Specifically, the receiver12includes a pre-amplifier, an A/D converter, a reception delay unit, and an adder and performs various types of processing on the reflected-wave signals that are received by the ultrasound probe1to generate reflected-wave data. The pre-amplifier amplifies the reflected-wave signals per channel to perform gain correction processing. The A/D converter performs A/D conversion on the gain-corrected reflected-wave signals and the reception delay unit gives a reception delay necessary to determine the reception directivity per channel. The adder sums the reflected-wave signals (digital signals) to which the reception delays are given and generates reflected-wave data. The summing by the adder enhances the reflection components from the direction corresponding to the directivity of reception of reflected-wave signals. The reception direction or reception delays are stored in the internal storage unit16, which will be described below, and the receiver12refers to the internal storage unit16and controls the reception directivity. The receiver12according to the first embodiment is capable of parallel simultaneous reception.

The signal processor13performs various types of signal processing on the reflected-wave data generated from the reflected-wave signals by the receiver12. The signal processor13performs logarithmic amplification, envelope detection processing, etc. on the reflected-wave data to generate data (B-mode image data) displaying the signal intensity at each sample point by luminance intensity.

The signal processor13also generates data (Doppler data) obtained by extracting the momentum information from the Doppler effects of the moving object at each sample point in the scanning area from the reflected-wave data received from the receiver12. Specifically, the signal processor13generates Doppler data obtained by extracting the average velocity, variance, power value, etc. at each sample point as the momentum information on the moving object. The moving object is, for example, the blood flow, tissue of, for example, the heart wall, or a contrast agent.

The ultrasound diagnosis apparatus according to the first embodiment is an apparatus capable of performing elastography in which the distribution of measured hardnesses is visualized. Specifically, the ultrasound diagnosis apparatus according to the first embodiment is an apparatus capable of performing elastography by applying an acoustic radiation force and thus causing displacement of body tissue.

In other words, the transmitter11according to the first embodiment transmits, from the ultrasound probe1, displacement-causing burst waves (push pulses) that cause displacement due to shear waves generated by an acoustic radiation force. The transmitter11according to the first embodiment transmits, from the ultrasound probe1, observation pulses (tracking pulses) for observing the displacement caused by the displacement-causing burst waves for multiple times in each of multiple scanning lines of the scanning area. In other words, the transmitter11transmits, from the ultrasound probe, push pulses that cause displacement of body tissue according to the acoustic radiation force and transmits, from the ultrasound probe, tracking pulses for observing the displacement of body tissue in a given scanning area caused according to the push pulses. The observation pulses are transmitted in order to observe the propagation speed of the shear waves, which are generated by the displacement-causing burst waves, at each sample point in the scanning area. The observation pulse is normally transmitted in each scanning line of the scanning area for multiple times (e.g. for 100 times). The receiver12generates reflected-wave data from the reflected-wave signals of the observation pulses transmitted in each scanning line of the scanning area. The displacement-causing burst waves are an example of displacement-causing ultrasound. The observation pulses are an example of observation ultrasound.

The signal processor13analyzes the reflected-wave data of the observation pulse that is transmitted for multiple times in each scanning line of the scanning area and calculates hardness distribution information displaying the hardness distribution in the scanning area. Specifically, by measuring the propagation speed of the shear waves generated by the displacement-causing burst waves at each sample point, the signal processor13generates information on the hardness distribution in the scanning area.

For example, the signal processor13analyzes the frequency of the reflected-wave data of the observation pulses. Accordingly, the signal processor13generates momentum information (tissue Doppler data) over multiple time phases at multiple sample points in each scanning line. The signal processor13performs time integration on the speed components of the tissue Doppler data over multiple time phases that are acquired at each of the multiple sample points in each scanning line. In this manner, the signal processor13calculates the displacement at each of the multiple points in each scanning line over multiple time phases. The signal processor13then determines a time at which the maximum displacement is caused at each sample point. The signal processor13acquires the time at which the maximum displacement is caused at each sample point as the time at which the shear waves reach each sample point. The signal processor13then performs spatial differentiation on the time at which the shear waves reach each sample point to calculate the propagation speed of shear waves in each sample point. Hereinafter, a “propagation speed of shear waves” is referred to as a “shear wave speed” below.

The signal processor13generates hardness distribution information by color-coding the shear wave speed and mapping the color-coded shear wave speed at sample points. Hard tissue has a high shear wave speed and soft tissue has a low shear wave speed. In other words, the value of shear wave speed indicates the value of hardness (elastic modulus) of tissue. In the above-described case, observation pulses serve as tissue Doppler transmission pulses. The shear wave speed may be calculated by the signal processor13from the cross-correlation of displacement of tissue between adjacent scanning lines, not based on the time at which the maximum displacement is caused at each sample point.

The signal processor13may calculate a Young's modulus or a shear modulus from the shear wave speed and generate hardness distribution information from the calculated Young's modulus or shear modulus. Each of the shear wave speed, Young's modulus, and shear modulus can be used as a physical quantity that indicates the hardness of body tissue. A case will be described below where the signal processor13uses the shear wave speed as a physical quantity indicating the hardness of body tissue.

The shear waves that are generated by one transmission of displacement-causing burst waves propagate and attenuate. When observation of shear wave speed over a wide area is attempted, the shear waves that are generated due to the displacement-causing burst waves transmitted in a specific scanning line attenuate as they propagate and then cannot be observed at a sufficient distance from the position to which the displacement-causing burst waves are transmitted.

In such a case, it is required to transmit displacement-causing burst waves at multiple positions in the orientation direction. Specifically, the scanning area (or a region of interest) is divided into multiple areas along the orientation direction. Before transmission/reception observation pulses to/from each area (hereinafter, “divided area”), the transmitter11transmits displacement-causing burst waves at different scanning line positions so that shear waves are generated. Typically, the position to which displacement-causing burst waves are transmitted is set near each divided area. If the simultaneous parallel receptions are limited to a small number, the transmitter11performs processing for transmitting displacement-causing burst waves once and then transmitting observation pulses in each scanning line of a divided area for multiple times sequentially along the orientation direction in each of the multiple divided areas.

The image generator14generates ultrasound image data from the data generated by the signal processor13. From the B-mode image data generated by the signal processor13, the image generator14generates B-mode image data that displays the intensity of reflected waves by luminance. Furthermore, from the Doppler data generated by the signal processor13, the image generator14generates Doppler image data that displays the moving object information. The Doppler image data is, for example, speed image data, distribution image data, power image data, or a combination thereof.

From the hardness distribution information generated by the signal processor13, the image generator14generates hardness image data that displays the hardness of body tissue by colors. For example, the image generator14generates, as hardness image data, the shear wave speed image data obtained by plotting, in each point in the scanning area, a pixel value corresponding to the shear wave speed at each point in the scanning area.

The image generator14generally coverts the scanning line signals of ultrasound scanning into scanning line signals in a video format represented by a TV format etc. (i.e., performs scan conversion) and generate ultrasound image data to be displayed. Specifically, by performing coordinate conversion according to the mode of ultrasound scanning by the ultrasound probe1, the image generator14generates the ultrasound image data to be displayed. Furthermore, in addition to scan conversion, the image generator14performs various types of image processing, such as image processing (smoothing processing) for reproducing a luminance-averaged image and image processing (edge enhancing processing) that uses a differential filter in an image, by using multiple image frames after scan conversion. The image generator14combines additional information (textual information of various parameters, scale mark, body mark, etc.) with the ultrasound image data.

In other words, the B-mode image data, Doppler data, and hardness distribution information are ultrasound image data prior to scanning conversion and the data generated by the image generator14is ultrasound image data posterior to scan conversion to be displayed. If the signal processor13generates three-dimensional (3D) data (3D B-mode image data, 3D Doppler data, and 3D hardness distribution information), the image generator14performs coordinate conversion according to the mode of ultrasound scanning by the ultrasound probe1, thereby generating volume data. The image generator14then performs various types of rendering to generate 2D image data to be displayed.

The image memory15is a memory that stores image data to be displayed, which is generated by the image generator14. The image memory15may store data that is generated by the signal processor13. The B-mode image data, Doppler data, and hardness distribution information that are stored in the image memory15can be accessed by the operator, for example, after diagnosis and serve as ultrasound image data to be displayed via the image generator14.

The internal storage unit16stores control programs for performing ultrasound transmission/reception, image processing, and display processing, diagnostic information (e.g. patient IDs and doctor's opinions), and various types of data such as diagnosis protocols and various body marks. The internal storage unit16is, as required, used to store the image data stored in the image memory15. The data stored in the internal storage unit16can be transferred to an external device via an interface unit (not shown).

The internal storage unit16further stores information on the shear wave speed image data acquired by image capturing. For example, the internal storage unit16stores the time at which shear waves reach each sample point regarding the shear wave speed image data acquired by image capturing.

The controller17controls the whole processing performed by the ultrasound diagnosis apparatus. Specifically, according to various setting requests that are input by the operator via the input device3and various control programs and various types of data that are read from the internal storage unit16, the controller17controls processing performed by the transmitter11, the receiver12, the signal processor13, and the image generator14. The controller17puts control such that the monitor2displays the ultrasound image data to be displayed, which is stored in the image memory15.

The transmitter11and the receiver12incorporated in the apparatus main unit10may be configured by using processor hardware (CPU (Central Processing Unit), MPU (Micro Processing Unit), integrated circuit, etc.) or may be configured by using a program of a software module.

The general configuration of the ultrasound diagnosis apparatus according to the first embodiment has been described. The ultrasound diagnosis apparatus according to the first embodiment having the above-described configuration transmits displacement-causing burst waves and visualizes the hardness of body tissue.

In this method, generally, after shear waves are generated, changes in displacement near each point (sample point) are observed over time and the time at which the peak of displacement is caused is determined as the time at which the shear waves reach. By obtaining a spatial differential of the time at which the shear waves reach, a local shear wave speed can be determined. However, it is known that the time at which shear waves reach is not necessarily calculated properly because generated shear waves are reflected at the interfaces (structure boundary) between tissues of different hardnesses and this results in time-displacement curves different from expected ones, and thus an artifact can occur in a hardness image (shear wave speed image or elasticity image) that is displayed eventually.

FIGS. 2A to 2Cillustrate a problem.FIG. 2Ashows an exemplary B-mode image. The hatched oval area positioned at the center of the image represents tissue whose hardness is different from those of other areas. In other words, the outline of the hatched area corresponds to a structure boundary. Furthermore, a burst wave transmission position represents the position to which displacement-causing burst waves are transmitted and an observation point corresponds to a sample point at which displacement that is caused due to displacement-causing burst waves is observed.FIG. 2Bshows exemplary time-displacement curves containing reflected components andFIG. 2Cshows exemplary time-displacement curves obtained by excluding the reflected components from the curves shown inFIG. 2B. The horizontal axis and vertical axis shown inFIGS. 2B and 2Cindicate the time and magnitude of displacement, respectively.

As shown inFIG. 2A, when displacement-causing burst waves are transmitted, shear waves propagate from the burst wave transmission position. The shear waves that propagate rightward from the burst wave transmission position inFIG. 2are observed at Observation point1and then at Observation point2. The shear waves that further propagate are reflected at the shear wave reflected position shown inFIG. 2Aand then propagate leftward. The shear waves that are reflected and propagate are observed at Observation point1and then at Observation point2. The time-displacement curves at Observation point1and Observation point2are shown inFIG. 2B.

As shown inFIG. 2B, the displacement due to shear waves that propagate directly (without being reflected) from the burst wave transmission position is at peak at Observation point1at first and then is at peak at Observation point2. Thereafter, the displacement due to the shear waves that are reflected at the shear wave reflection position is at peak at Observation point2and is then at peak at Observation point1. For example, the time at which shear waves reach is observed as the time at which displacement of the shear waves that directly propagate from the burst wave transmission position is at peak. As shown inFIG. 2B, when the time-displacement curve contains the peak of displacement due to the reflected shear waves, for example, the peak time is erroneously observed and thus an artifact occurs in the shear wave speed image.

For example, has been proposed a technology for suppressing artifacts that are attributable to reflection of shear waves by excluding the components of shear waves propagating in a given direction by using the spatial distribution of time-displacement curves. According to this technology, the time-displacement curves shown inFIG. 2Care acquired by excluding the components of the reflected shear waves from the time-displacement curves (reflected components) shown inFIG. 2Band this prevents erroneous observation of reflected components. However, this method cannot exclude the effects of the reflected shear waves propagating in the same direction. This aspect will be described below with reference toFIGS. 3A and 3B.

FIGS. 3A and 3Billustrate the problem.FIG. 3Ais an exemplary B-mode image. As shown inFIG. 3A, the oval hatched area positioned at the center of the image represents tissue whose hardness is different from those of other areas and, compared toFIG. 2A, the burst wave transmission position and the shear wave reflection position are close to each other.FIG. 3Brepresents exemplary time-displacement curves containing reflected components. The horizontal axis and vertical axis shown inFIG. 3Bindicate the time and magnitude of displacement, respectively.

As shown inFIG. 3A, when displacement-causing burst waves are transmitted, shear waves propagate from the burst wave transmission position. The shear waves that propagate rightward from the burst wave transmission position inFIG. 3Apropagate from the burst wave transmission position directly to Observation point1and Observation point2. On the other hand, shear waves that propagate leftward from the burst wave transmission position are reflected at a near shear wave reflection position and then propagate to Observation point1and Observation point2. In this manner, when displacement-causing burst waves are transmitted at a position near the interface, is observed displacement in which shear waves that propagate from the position where the shear waves are generated directly to the observation points are followed by shear waves that are reflected at the interface and then propagate. In this case, because the directly-propagating shear waves and the shear waves that are reflected and then propagate propagate in the same direction, the reflected components cannot be excluded by using the above-described method.

Furthermore, in general, displacement of tissue that is caused due to displacement-causing burst waves is minute and thus is susceptible to various noises. For example, when the time at which the displacement is at maximum as shown inFIG. 3Bis detected as a reach time, the earlier one of the two peaks, i.e., the reach time corresponding to the shear waves that directly propagate, should be detected. However, if there is an external cause, such as body motion or hand jiggling, the latter peak has greater amplitude so that the latter peak time is detected as the time at which shear waves reach. If an error occurs in detection of a reach time, the error may appear as a significant artifact when a shear wave speed is calculated by performing a spatial differential on the time at which shear waves reach. In order to solve such a problem, when multiple peaks are found, may be contrived a reach time detection method in which, for example, the first peak is detected as a reach time or a general time difference is detected on the basis of the cross-correlation, not by detecting a maximum value, to determine a reach time. However, such methods are susceptible to disturbance (variation in the time-displacement curves due to power noise or motion of the body) resulting from a cause other than reflected shear waves and there is a possibility that the reach time cannot be detected robustly. Furthermore, the latter method increases the calculation costs and thus lowers the real-time property.

The above-described problem tends to occur when there is a structure boundary near a position to which displacement-causing burst waves are transmitted. The structure boundary may be confirmed sufficiently in a B-mode image. In such a case, it is assumed that, if the operator can avoid inclusion of a structure boundary near a position at which displacement-causing burst waves are transmitted (transmission area), artifacts due to reflected components can be suppressed. However, in a conventional ultrasound diagnosis apparatus, displacement-causing burst waves are generally transmitted to multiple spots in a shear wave speed image area but at which positions displacement-causing burst waves are transmitted is not represented to the operator. For this reason, the operator cannot know to which parts displacement-causing burst waves are transmitted and, even when the operator understands that artifacts typically occur as described above, the operator cannot positively avoid such a situation.

For this reason, the ultrasound diagnosis apparatus according to the first embodiment includes a display unit that clearly displays positions at which displacement-causing burst waves are transmitted before or while a shear wave speed image is acquired. For example, when a region of interest (ROI) for displaying a shear wave speed image is set in the B-mode image, multiple positions at which displacement-causing burst waves are transmitted are displayed simultaneously. Furthermore, for example, when at least one of the positions at which displacement-causing burst waves are transmitted is near the interface between tissues of different hardnesses, the position to which displacement-causing burst waves are transmitted can be changed or the number of positions at which displacement-causing burst waves are transmitted can be changed.

The following descriptions refer back toFIG. 1. In the ultrasound diagnosis apparatus according to the first embodiment, the controller17includes a transmission controller171, a generator172, an output controller173, and a changing unit174.

The transmission controller171controls transmission of displacement-causing burst waves and transmission/reception of observation pulses performed by the transmitter11. For example, the transmission controller171receives an instruction for determining an ROI from the operator. According to the received instruction, the transmission controller171sets positions at which displacement-causing burst waves are transmitted, the number of transmission positions, the position of ROI, the area (size) of ROI, the number of ROIs, etc. for generating shear wave speed image data corresponding to the ROI. Under the control of the transmission controller171, the transmitter11transmits displacement-causing burst waves from the ultrasound probe1. Under the control of the transmission controller171, the transmitter11further transmits, for multiple times, observation pulses for observing displacement that is caused due to the transmitted displacement-causing burst waves from the ultrasound probe1in each of multiple scanning lines of the scanning area.

The generator172generates transmission position image data displaying burst wave transmission positions (push pulse lines) and a scanning area image data displaying the position of the scanning area. For example, the generator172acquires the burst wave transmission position that is set by the transmission controller171. The generator172then generates linear image data (indicator) indicating the acquired burst wave transmission position as transmission position image data. Furthermore, the generator172acquires the position and size of ROI that are set by the transmission controller171. The generator172then generates, as scanning area image data, rectangular-frame image data displaying the acquired position and size of ROI.

The output controller173outputs the generated transmission position image data and scanning area image data such that the generated transmission position image data and scanning area image data are superimposed onto the ultrasound image data. For example, the output controller173displays transmission position image data and scanning area image data, which are generated by the generator172, such that the transmission position image data and scanning area image data are superimposed onto a B-mode image.

The changing unit174receives change instructions for changing the position to which displacement-causing burst waves are transmitted, the number of transmission positions, the position of scanning area, the area of scanning area, or the number of scanning areas. According to the received change instructions, the changing unit174changes the position at which the transmitter11transmits displacement-causing burst waves, the number of transmission positions, the position of scanning area, the area of scanning area, or the number of scanning areas.

FIGS. 4A and 4Bare flowcharts of a procedure taken by the ultrasound diagnosis apparatus according to the first embodiment. With reference toFIGS. 5A to 5D, the procedure taken by the ultrasound diagnosis apparatus according to the first embodiment will be described.FIGS. 5A to 5Dillustrate the processing performed by the ultrasound diagnosis apparatus according to the first embodiment.

As shown inFIG. 4A, the transmission controller171of the ultrasound diagnosis apparatus according to the first embodiment determines whether a start instruction for starting a hardness image generation mode for generating a hardness image is received from an operator (step S101). The hardness image generation mode is, for example, a state where an ROI for generating a hardness image is set and, after the ROI is set, displacement-causing burst waves are transmitted and thus a hardness image is generated. When a start instruction is not received (NO at step S101), the controller17waits until a start instruction is received.

On the other hand, when a start instruction is received (YES at step S101), the monitor2displays an ROI setting GUI under the control of the transmission controller171(step S102). The ROI setting GUI that is displayed on the monitor2will be described here with reference toFIG. 5A. As shown inFIG. 5A, for example, a B-mode image51that is obtained by scanning with the ultrasound probe1is displayed on the monitor2. The monitor2displays, on the B-mode image51, an ROI52that specifies an area in which a shear wave speed image is generated. The size and position of the ROI52is pre-set. The transmission controller171receives instructions for changing the size and position of the ROI52from the operator and changes the size and position of the ROI52according to the received instructions.

The transmission controller171determines whether the ROI52is determined (step S103). For example, the transmission controller171determines whether the ROI52is determined according to whether an instruction for determining the ROI52is received from the operator. When an ROI is not determined (NO at step S103), the transmission controller171waits until an ROI is set. On the other hand, when the ROI52is determined (YES at step S103), the transmission controller171divides the determined ROI52into divided ROIs (step S104) and calculates burst wave transmission positions corresponding to the ROIs, respectively (step S105).

The reason for diving the ROI52into divided ROIs will be described here. In elastography, for example, displacement-causing burst waves are transmitted at an end of the ROI52, propagation of the shear waves thus generated to the other end of the ROI52is observed, and the speed of propagation is displayed by an image. In this case, because displacement caused by the displacement-causing burst waves is generally minute in few to few tens of micrometers and furthermore the shear waves from the displacement attenuate while propagating, only few millimeters of shear waves can be observed. For this reason, in order to acquire a shear wave speed image of a relatively wide area, displacement-causing burst waves are transmitted to multiple spots, a shear wave speed image of few millimeters of shear wave propagation occurring in each of the spots is generated, and the multiple shear wave speed images are combined when displayed eventually. Thus, when the ROI52is determined, the transmission controller171divides the ROI52into small areas (divided ROIs) according to the size of the specified ROI52. The transmission controller171then determines positions at which displacement-causing burst waves are transmitted that correspond to the respective small areas.

The processing at steps S104and S105will be described below. For example, the transmission controller171calculates a required number of divided ROIs on the basis of the lateral width of the ROI52, which is determined at step S103, and the upper limit value of the width of ROI. The upper limit value of the ROI width is, for example, previously stored in the internal storage unit16. For example, if the width of the ROI52that is set as shown inFIG. 5Ais 2.7 cm and the upper limit value of the ROI width is 1.0 cm, three ROIs each having a width of 0.9 cm (divided ROIs53,54and55) are set. Alternatively, for example, two divided ROIs each having a width of 1.0 cm and a divided ROI having a width of 0.7 cm may be set.

The transmission controller171then determines a position to which displacement-causing burst waves are transmitted for observing the shear wave speed in each divided ROI. Because, in general, the shear wave speed cannot be determined properly at a position where displacement is caused, it is preferable that displacement-causing burst waves be transmitted to the outside of the area about which a shear wave speed image is acquired. For example, an offset value that defines the distance between a burst wave transmission position and a divided ROI is stored in the internal storage unit16. The transmission controller171calculates a position that is distant, by the offset value, from the left end of each of set divided ROIs as a burst wave transmission position. In the example shown inFIG. 5B, the transmission controller171calculates burst wave transmission positions56,57, and58as transmission positions for observing a shear wave speed in the respective divided ROIs53,54, and55.

As described above, the transmission controller171divides the ROI52into the divided ROIs53,54, and55and calculates the burst wave transmission positions56,57, and58corresponding to the divided ROIs53,54, and55, respectively. For the embodiment, the case has been described where the ROI52is divided and the divided ROIs53,54, and55are set. Alternatively, for example, it is not necessary to divide the ROI52if the width of the determined ROI52is smaller than the upper limit value.

The generator172then generates transmission position image data and divided ROI image data (step S106). For example, as shown inFIG. 5B, the generator172acquires the burst wave transmission positions that are set by the transmission controller171. The burst wave transmission positions represent transmission areas to which push pulses are transmitted from the ultrasound probe1and are also referred to as push pulse lines. The generator172then generates transmission position image data (transmission area image data) displaying the acquired burst wave transmission positions. The generator172then acquires the position and size of ROI that is set by the transmission controller171. The ROI includes small areas (divided ROIs) corresponding to the burst wave transmission positions. The generator172then generates scanning area image data displaying the acquired position and size of ROI.

FIG. 5Billustrates the case where the burst wave transmission positions are displayed by linearly image data. Alternatively, for example, a burst wave transmission position may be displayed by an arrow image data indicating, in addition to the position to which push pulses are transmitted, the direction of the transmission. Alternatively, a burst wave transmission position may be displayed by data of an image in a shape that narrows toward the focus position and expand rearward with respect to the focus position (a shape with a narrow part).

The output controller173displays the transmission position image data and divided ROI image data such that the transmission position image data and divided ROI image data are superimposed onto the B-mode image data (step S107). For example, as shown inFIG. 5B, the output controller173acquires, from the generator172, the transmission position image data displaying each of the burst wave transmission positions56,57, and58and the divided ROI image data displaying each of the divided ROIs53,54, and55, which are generated by the generator172as shown inFIG. 5B. The output controller173then superimposes the acquired transmission position image data displaying each of the burst wave transmission positions56,57, and58and the divided ROI image data displaying each of the divided ROIs53,54, and55onto the B-mode image data and displays the superimposed data on the monitor2.

According to change instructions from the operator, the changing unit174then changes the burst wave transmission position and the divided ROI (step S108). When the changing unit174receives no change instruction, the processing at step S110may be performed, without performing the processing at steps S108and S109.

The processing performed by the changing unit174will be describe with reference toFIGS. 5B to 5D. A case will be described here where the display image shown inFIG. 5Bis displayed by the processing before step S107.

The operator recognizes that the burst wave transmission position57corresponding to the divided ROI54from among the three divided ROIs43,54, and55is close to the oval structure boundary. The operator selects the burst wave transmission position57here by using the input device3and gives an instruction for changing the burst wave transmission position57. For example, the operator makes an adjustment to shift the burst wave transmission position57toward or distant from the left end of the divided ROI54. In another example, the changing unit174may be configured to select a position distant from the left end of the divided ROI54by the offset value or a position distant from the right end of the divided ROI54by the offset value such that the operator selects any one of the positions. In other words, the changing unit174may set a limit on the positions that the operator can select. This is because if, for example, a burst wave transmission position is set at a position away from a divided ROI by a certain distance or more, the shear waves generated at the position attenuate completely before reaching the target divided ROI and displacement sufficient to determine the shear wave speed in the target divided ROI cannot be obtained. On the other hand, if a burst wave transmission position is set at a position close to a target divided ROI with a certain distance or less or is set in the target ROI, the shear wave speed cannot be determined properly near that position. Alternatively, the operator may arbitrarily set a burst wave transmission position to some extent and the size of a small area and the number of small areas may be automatically changed according to the set position.

For example, as shown inFIG. 5C, the changing unit174receives a change instruction for changing the burst wave transmission position57to a burst wave transmission position59from the operator. According to the received change instruction, the changing unit174changes the burst wave transmission position57to the burst wave transmission position59.

For example, as shown inFIG. 5D, upon receiving a change instruction for changing the burst wave transmission position57to a burst wave transmission position60from the operator, the changing unit174automatically changes the position and size of divided ROI and the number of divided ROIs in accordance with the burst wave transmission position60to which the burst wave transmission position57is changed. Specifically, when the burst wave transmission position57is changed to the burst wave transmission position60, the changing unit174shifts leftward the position of the left end of the divided ROI54corresponding to the burst wave transmission position57such that the distance between the left end of the divided ROI54and the burst wave transmission position60is equal to the offset value. The changing unit174then shifts leftward the position of the right end of the divided ROI54such the width of the divided ROI54is within the upper limit value of the ROI width. Accordingly, the width of the divided ROI55exceeds the upper limit value of the ROI width. For this reason, the changing unit174further divides the divided ROI55. In the example shown inFIG. 5D, the right area of the divided ROI55is allocated as another divided ROI61and accordingly the widths of all divided ROIs can be equal to or less than the upper limit value of the ROI width. In accordance with the change of the position of the left end of the divided ROI55(the right end of the divided ROI54), the changing unit174also shifts the burst wave transmission position58leftward by a distance equal to the distance by which the left end of the divided ROI55is shifted (leading to a burst wave transmission position62). The changing unit174further determines a burst wave transmission position63corresponding to the divided ROI61and generates and displays transmission position image data in the determined position.

For the example shown inFIG. 5D, the case has been described where, in accordance with the burst wave transmission position to which a burst wave transmission position is changed, various parameters, such as other burst wave transmission positions, the number of burst wave transmission positions, the position of divided ROI, the area of divided ROI, or the number of divided ROIs, are automatically changed. Alternatively, in response to a change in any one of the parameters, the changing unit174may automatically change other parameters on the basis of the offset value and ROI width upper limit value. Accordingly, the operator can easily change various parameters and furthermore can prevent the changed parameters from deviating from the offset value or ROI width upper limit value. Furthermore, the changing unit174may change all parameters according to the operator's discretion. In other words, the changing unit174receives change instructions for changing various parameters and, according to the received change instructions, changes the parameters. In this case, because the operator can change all parameters to arbitrary values the operator's discretion can be reflected to details. Furthermore, for example, when there is no significant structure in an ROI and it can be assumed that reflection or refraction of shear waves will not occur, by increasing the number of positions in which displacement-causing burst waves are transmitted, shear wave propagation can be observed only in an area where sufficient displacement is caused and consequently the image quality can be improved.

In the example shown inFIG. 5B, it is not necessary to change the burst wave transmission position58because the structure boundary near the burst wave transmission position58is almost perpendicular to the burst wave transmission position58and there is a low risk that reflected shear waves that propagate in the same direction as that of shear waves are caused.

As described above, the changing unit174receives change requests for changing various parameters, such as the position to which displacement-causing burst waves are transmitted, the number of transmission positions, the position of scanning area, the area of scanning area, or the number of scanning areas. According to the received change instructions, the changing unit174then changes various parameters.

The following descriptions refer back toFIG. 4A. The output controller173displays the post-change transmission position image data and divided ROI image data such that the post-change transmission position image data and divided ROI image are superimposed onto the B-mode image data (step S109). For example, when the changing unit174shifts the burst wave transmission position, the output controller173shifts the transmission position image data corresponding to the shifted burst wave transmission position and displays the transmission position image data on the monitor2. Furthermore, for example, when the changing unit174adds a divided ROI, the changing unit174causes the generator172to generate divided ROI image data corresponding to the added divided ROI and displays the generated divided ROI image data on the monitor2.

By performing the above-described processing, N sets of transmission position image data and N sets of divided ROI image data are displayed on the B-mode image51. In other words, the transmission controller171sets N separated positions to which burst waves are transmitted in order to scan the whole area of the ROI52and N divided ROIs for observing shear waves generated by the transmitted burst waves.

The transmission controller171determines whether a request for starting image capturing to acquire shear wave speed image data is received from the operator (step S110). When no image capturing start request is received (NO at step S110), the transmission controller171waits until an image capturing start request is received.

In contrast, when an image capturing start request is received (YES at step S110), the transmission controller171performs processing for generating shear wave speed image data (step S111). The processing for generating shear wave speed image data will be described here with reference toFIG. 4B.

As shown inFIG. 4B, the transmission controller171makes a setting of “n=1” (step S201). Under the control of the transmission controller171, the transmitter11transmits displacement-causing burst waves from the ultrasound probe1at an n-th burst wave transmission position (step S202). Under the control of the transmitter11and the receiver12, the ultrasound probe1transmits/receives observation pulses in a divided ROI corresponding to the displacement-causing burst waves (step S203). For example, observation pulses are transmitted/received to/from a scanning line (raster) in the divided ROI for multiple times (about 100 times). Accordingly, changes in displacement over time at each point (each sample point) are calculated. If a system that can perform multiple receptions corresponding to a single pulse is used, changes in displacement over time over the area of the ROI can be known from one transmission of displacement-causing burst waves. However, if the number of simultaneous receptions is limited, multiple transmissions/receptions of observation pulses are performed for multiple times in different raster positions. In that case, each time when observation pulses are transmitted in a different raster position, displacement-causing burst waves are transmitted.

The signal processor13then calculates the displacement at each point (each sample point) of the divided ROI and generates hardness distribution information (step S204). To calculate the displacement, a method of calculating a Doppler shift between two echo signals, a method of calculating a cross-correlation, etc. can be used. On the basis of the changes in displacement over time at each point, the signal processor13calculates the time at which shear waves reach each point and calculates the shear wave speed at each point.

The image generator14then generates shear wave speed image data corresponding to the n-th burst wave transmission position (step S205). The transmission controller171then determines whether “n=N” is satisfied (step S206). When “n=N” is not satisfied (NO at step S206), the transmission controller171increments “n” to satisfy “n=n+1” (step S207) and the transmitter11returns to step S202and transmits displacement-causing burst waves from the ultrasound probe1at the n-th burst wave transmission position.

On the other hand, when “n=N” is satisfied (YES at step S206), the transmission controller171ends the process for generating shear wave speed image data. The above-described processing generates N sets of shear wave speed image data.

The following descriptions refer back toFIG. 4A. According to an instruction from the transmission controller171, the image generator14combines the N sets of shear wave speed image data to generate composite image data (step S112). Under the control of the transmission controller171, the monitor2displays the composite image data that is the shear wave speed image data on the whole ROI (step S113). The image capturing processing for acquiring shear wave speed image data ends here.

If the request that is input by the operator is request for image capturing to acquire a video image of shear wave speed image data, the processing from step S111to step S113is repeated under the control of the transmission controller171until image capturing end request is received.

For the above-described procedure, the case has been described where the burst wave transmission position or the divided ROI is changed before receiving a request for starting image capturing to acquire shear wave speed image data from the operator. However, embodiments are not limited to this. For example, the burst wave transmission position or the divided ROI may be changed after the shear wave speed image data is acquired by mage capturing. In this case, the operator can change the burst wave transmission position while viewing the shear wave speed image that is update in realtime.

As described above, the ultrasound diagnosis apparatus according to the first embodiment generates transmission position image data and scanning area image data and displays the generated transmission position image data and scanning area image data such that the transmission position image data and scanning area image data are superimposed onto B-mode image data. Accordingly, the operator can confirm by sight the burst wave transmission positions and scanning area. Thus, for example, by confirming the position of a structure boundary where shear waves are likely to be reflected while comparing the B-mode image and the burst wave transmission positions and by handling the ultrasound probe1to change the position or direction of the ultrasound probe1, the user can avoid the situation where an artifact is likely to occur due to reflection of shear waves. In other words, the operator can avoid that the structure boundary is included near the position to which displacement-causing burst waves are transmitted. Consequently, the ultrasound diagnosis apparatus according to the first embodiment can improve the image quality of the hardness image.

Furthermore, for example, the ultrasound diagnosis apparatus according to the first embodiment receives change instructions for changing various parameters, such as the position to which displacement-causing burst waves are transmitted, the number of transmission positions, the position of scanning area, the area of scanning area, or the number of scanning areas. According to the received change instructions, the ultrasound diagnosis apparatus changes various parameters. Accordingly, the operator can avoid a situation where an artifact is likely to occur due to reflection of shear waves even when it is difficult to avoid interfaces between tissues of different hardnesses only by changing the position and direction of the ultrasound probe1.

Furthermore, according to the operator's discretion, the operator can avoid positions in which transmission of displacement-causing burst waves having a great acoustic energy should be avoided, such as the vicinity of a highly-reflective object, e.g. bone, and plaque or tumor that may rupture.

Furthermore, selection of a burst wave transmission position according to the operator's discretion allows the operator to easily investigate and know the connection between the structural characteristic in the vicinity of the burst wave transmission position and an artifact to occur, which eventually allows the operator to positively improve the image quality of the shear wave speed image. On the other hand, when no significant structure is found in the ROI, the image quality can be further improved by increasing the number of burst wave transmission positions.

For the first embodiment, the case has been described where the changing unit174changes various parameters according to change instructions from the operator. However, embodiments are not limited to this. For example, the ultrasound diagnosis apparatus does not necessarily include the changing unit174. In this case, the operations and the apparatus configuration can be simplified. Even in this case, the ultrasound diagnosis apparatus generates and displays transmission position image data and scanning area image data, which allows the operator to confirm by sight burst wave transmission positions and scanning area. Consequently, by changing the position or direction of the ultrasound probe, the operator can avoid a situation where an artifact is likely to occur due to reflection of shear waves.

For the first embodiment, the case has been describe where the ultrasound diagnosis apparatus generates and displays transmission position image data and scanning area image data. However, embodiments are not limited to this. For example, the ultrasound diagnosis apparatus may generate and display only any one of transmission position image data and scanning area image data. In this case, by keeping transmission position image data or scanning area image data sufficiently apart from a structure boundary displayed on the monitor2, the operator can avoid a situation where an artifact is likely to occur due to reflection of shear waves.

Display and non-display of burst wave transmission positions and divided ROIs may be switched according to an instruction from the user. For example, at step S113inFIG. 4A, when composite image data of shear wave speed image data is displayed, the output controller173does not display the burst wave transmission positions and divided ROIs. When the composite image data is not displayed and the B-mode image is displayed, the output controller173re-displays the burst wave transmission positions and divided ROIs.

For the first embodiment, the case has been described where an ROI is divided horizontally (laterally). Alternatively, an ROI may be divided horizontally (in the depth direction).

Second Embodiment

For the first embodiment, the case has been described where the operator confirms by sight and determines whether there is a structure boundary that is likely to reflect shear waves near a burst wave transmission position. However, embodiments are not limited to this. For example, the ultrasound diagnosis apparatus may determine whether there is a structure boundary near a burst wave transmission position. Thus, for a second embodiment, a case will be described where an ultrasound diagnosis apparatus determines whether there is a structure boundary near a burst wave transmission position and, according to the determination result, calls the operator's attention by using a display or outputting a warning sound or a burst wave transmission position is re-set at a position sufficiently away from the structure boundary.

FIG. 6is a block diagram of an exemplary configuration of an ultrasound diagnosis apparatus according to the second embodiment. The ultrasound diagnosis apparatus according to the second embodiment has the same configuration as that of the ultrasound diagnosis apparatus shown inFIG. 1but is different from the ultrasound diagnosis apparatus shown inFIG. 1in that the ultrasound diagnosis apparatus according to the second embodiment includes an extraction unit175and a determination unit176and that the processing performed by the output controller173and the changing unit174is different in part. For the second embodiment, the different aspects from the first embodiment will be described mainly and the same reference numerals as those used inFIG. 1are used to denote the same functions as those of the configuration described for the first embodiment and descriptions for the same functions will not be given here.

The extraction unit175extracts the outline of body tissue from the ultrasound image data. The outline of body tissue is not limited to the outline of internal organs, such as the heart and lever, and includes the outline of various types of tissue that can be confirmed by sight in ultrasound image data. For example, the extraction unit175extracts an outline from the B-mode image data by using a technology for extracting the edge from image data.

On the basis of the outline and a transmission position, the determination unit176determines whether there is a given outline within a given area from the transmission position. For example, the determination unit176determines whether there is a structure boundary that may cause reflected shear waves that propagate in the same direction as that of shear waves near the burst wave transmission position.

The output controller173has the same functions as those described for the first embodiment. Furthermore, the output controller173outputs a warning when it is determined that there is a given outline within a given area. For example, the output controller173displays a warning message on the monitor2or outputs a warning sound via a speaker.

The changing unit174has the same functions as those described for the first embodiment. Furthermore, when it is determined that there is the given outline within the given area, the changing unit174changes at least one of the position to which the transmitter11transmits displacement-causing burst waves, the number of transmission positions, the position of scanning area, the area of scanning area, and the number of scanning areas. For example, the changing unit174changes the burst wave transmission position until no structure boundary that may cause reflected shear waves that propagate in the same direction as that of shear waves exists near the burst wave transmission position. In accordance with the change of the burst wave transmission position, the changing unit174changes other parameters, such as the number of positions to which displacement-causing burst waves are transmitted, the position of scanning area, the area of scanning area, and the number of scanning areas on the basis of the offset value and the upper limit value of the ROI width.

FIG. 7is a flowchart of a procedure taken by the ultrasound diagnosis apparatus according to the second embodiment. With reference toFIGS. 8, 9A, and 9B, the procedure taken by the ultrasound diagnosis apparatus according to the second embodiment will be described below.FIGS. 8, 9A and 9Billustrate processing performed by the ultrasound diagnosis apparatus according to the second embodiment.

As illustrated inFIG. 7, the processing from step S301to step S307is the same as the processing from step S101to step S107illustrated inFIG. 4Aand thus the descriptions thereof will be omitted here. In other words, the processing until the exemplary display image shown inFIG. 5Bis displayed is the same as that of the first embodiment.

The extraction unit175extracts the outline from the B-mode image data (step S308). The processing performed by the extraction unit175will be described with reference toFIG. 8. As shown inFIG. 8, the extraction unit175extracts an outline81of a structure from the B-mode image51shown inFIG. 5B. Many methods have been already proposed for the method of extracting an outline from an image and are widely used for B-mode images (ultrasound images). For example, the extraction unit175extracts the outline81of the oval hatched area shown inFIG. 5Bfrom the B-mode image51by using the technology disclosed in Japanese Laid-open Patent Publication No. 2010-282268. The B-node image51is shown as a white area and the outline81is shown on the image as a matter of convenience. However, practically, an image of the outline81can be displayed such that the outline81is superimposed on onto the arbitrary B-mode image51displayed on the monitor2. Furthermore, the outline81is not necessarily superimposed onto the arbitrary B-mode image51when displayed. For example, when shear wave speed image data has been captured, the outline81may be displayed such that the outline81is superimposed onto the shear speed image data. The case has been described here where the extraction unit175extracts the single outline81. Alternatively, the extraction unit175may extract multiple outlines. The extraction unit175stores the information on a single outline or multiple outlines in the internal storage unit16.

The determination unit176determines whether there is a given outline within a given area from the burst wave transmission position (step S309). The given area is, for example, an area of 0.3 cm or less from the burst wave transmission position. The given outline is, for example, an outline including a tangent parallel to the burst wave transmission position. If it is not parallel to the beams of displacement-causing burst waves, there are little effects on propagation of shear waves.

The processing performed by the determination unit176will be described with reference toFIG. 8. For example, the determination unit176compares the position of the outline81that is extracted by the extraction unit175and the displayed burst wave transmission position and determines whether the outline81is within the area of 0.3 cm from the burst wave transmission position. For example, in the example shown inFIG. 8, the determination unit176sets areas82,83, and84having a width of 0.3 cm on the right and left with respect to the respective burst wave transmission positions56,57, and58, i.e., having a width of 0.6 cm and whose centers are at the burst wave transmission positions, respectively. The determination unit176determines whether the areas82,83, and84include the outline81. In the example shown inFIG. 8, the determination unit176determines that the areas83and84include the outline81. The determination unit176then determines whether the outline81within the area83includes a tangent parallel to the burst wave transmission position and whether the outline81within the area84includes a tangent parallel to the burst wave transmission position. In the example shown inFIG. 8, the determination unit176determines that the outline81within the area83includes a tangent parallel to the burst wave transmission position57and determines that the outline81within the area84does not include a tangent parallel to the burst wave transmission position58. Accordingly, the determination unit176determines whether there is a structure boundary that may cause reflected shear waves that propagate in the same direction as that of shear waves near the burst wave transmission position. The above-described given area and given outline are examples only and do not put any limits. For example, the given area may be changed to a value according to the operator's discretion. Furthermore, the given outline can be changed to an outline having an angle according to the operator's discretion.

When it is determined that there is not the given outline within the given area (NO at step S309), the procedure shifts the processing at step S314. On the other hand, when it is determined that there is the given outline within the given area (YES at step S309), the output controller173outputs a warning (step S310). For example, the output controller173displays a warning message on the monitor2or outputs warning sound via a speaker. For example, as shown inFIG. 9A, the output controller173displays the burst wave transmission position57, regarding which it is determined that there is the given outline within the given area from the burst wave transmission position, in a wider line than those of other burst wave transmission positions56and58. For example, as shown inFIG. 9B, the output controller173displays a caution mark86on the upper right on the screen of the monitor2. This does not limit examples of the warning that is output by the output controller173. For example, a line85shown inFIG. 9Amay be displayed in a color different from that of other burst wave transmission positions.

The following descriptions refer back toFIG. 7. The changing unit174determines whether an automatic change instruction that is an instruction for automatically changing the burst wave transmission position and divided ROI is received from the operator (step S311). When no automatic change instruction is received (NO at step S311), the changing unit174waits until an automatic change instruction is received.

When an automatic change instruction is received (YES at step S311), the changing unit174changes the burst wave transmission position and the divided ROI (step S312). For example, the changing unit174shifts the burst wave transmission position57leftward such that the outline81cannot be within an area of 0.3 cm from the burst wave transmission position57. As described for the first embodiment, on the basis of the offset value and the upper limit value of the ROI width, the changing unit174changes other parameters, such as the number of positions to which displacements-causing burst waves are transmitted, the position of scanning area, the area of scanning area, and the number of scanning areas. Accordingly, as illustrated inFIG. 5D, the changing unit174changes the burst wave transmission position such that the given outline is not close to the burst wave transmission position. The embodiments are not limited to the above-described example. For example, the changing unit174may shift the burst wave transmission position57rightward.

The processing from step S313to step S317is the same as the processing from step S109to step S113and thus the descriptions thereof will be omitted here.

Embodiments are not limited to the above-described procedure. For example, the processing for outputting a warning (step S310) is not necessarily performed. In this case, for example, when it is determined the given outline is within the given area (YES at step S309), the changing unit174automatically changes the burst wave transmission position and the divided ROI (step S312).

For example, such automatically changing processing (step S311and step S312) is not necessarily performed. In this case, for example, as described for the first embodiment, the changing unit174changes the burst wave transmission position and divided ROI according to the change instructions from the operator.

As described above, the ultrasound diagnosis apparatus according to the second embodiment determines whether there is a structure boundary near a burst wave transmission position. Upon determining that there is a structure boundary near the burst wave transmission position, the ultrasound diagnosis apparatus outputs a warning. Accordingly, the ultrasound diagnosis apparatus according to the second embodiment can make a notification indicating whether displacement-causing burst waves are to be transmitted in the vicinity of the structure boundary while the operator does not confirm the displayed burst wave transmission position and B-mode image by sight in detail.

The ultrasound diagnosis apparatus according to the second embodiment automatically changes the burst wave transmission position and divided ROI upon determining that there is a structure boundary near the burst wave transmission position. Accordingly, the ultrasound diagnosis apparatus according to the second embodiment can optimize the burst wave transmission position and the position of the divided ROI without additional operation by the operator. The operator can confirm the optimized burst wave transmission position and position of the divided ROI and then practically start generating and displaying shear wave speed image. For example, upon determining that there is a structure boundary near the burst wave transmission position, the ultrasound diagnosis apparatus according to the second embodiment may make a setting such that processing for generating and displaying shear wave speed image is not performed. In this case, for example, the controller17controls the transmission controller171not to collect images even if an image capturing request for acquiring shear wave speed image data is received. Accordingly, the ultrasound diagnosis apparatus according to the second embodiment can avoid image generation in a situation where an artifact due to reflection of shear waves may occur.

For the second embodiment, the case has been describe where the extraction unit175extracts an outline. Alternatively, the extraction unit175may extract the surface of bone or a structure such as plaque or tumor that may rupture. Accordingly, the operator can easily know whether displacement-causing burst waves are to be transmitted to a part regarding which ultrasound signal transmission having a great acoustic energy should be avoided.

Third Embodiment

For the first and second embodiments, the case has been described where, after it is determined whether there is a structure boundary near a burst wave transmission position, the burst wave transmission position and divided ROI are changed and shear wave speed image data is acquired by image capturing. However, embodiments are not limited to this. For example, after shear wave speed image data is acquired by image capturing, the ultrasound diagnosis apparatus may generate reach time color image data corresponding to the time at which shear waves reach in order to confirm whether proper shear wave propagation occurs during the image capturing. For the third embodiment, a case will be described where an ultrasound diagnosis apparatus generates reach time color image data.

The ultrasound diagnosis apparatus according to the third embodiment has the same configuration as that of the ultrasound diagnosis apparatus shown inFIG. 1but is different from the ultrasound diagnosis apparatus shown inFIG. 1in a part of the processing performed by the image generator14and the output controller173. Thus, for the third embodiment, the different aspects from the first embodiment will be described mainly and the same reference numerals as those used inFIG. 1are used to denote the same functions as those of the configuration described for the first embodiment and descriptions for the same functions will not be given here.

The image generator14generates reach time color image data displaying the times at which shear waves reach. The reach time color image data is, for example, image data obtained by plotting, in each point in a scanning area, a pixel value corresponding to the time at which shear waves reach each point. For example, the image generator14generate reach time color image data by plotting, in each point in the scanning area, a color corresponding to the time at which shear waves reach each point in the scanning area.

The output controller173displays the reach time color image data. For example, the output controller173displays the reach time color image data, which is generated by the image generator14, such that the reach time color image data is superimposed onto the B-mode image data.

FIG. 10is a flowchart of a procedure taken by the ultrasound diagnosis apparatus according to the third embodiment. The procedure taken by the ultrasound diagnosis apparatus according to the third embodiment will be described below with reference toFIGS. 11A and 11B.FIGS. 11A and 11Billustrate processing performed by the ultrasound diagnosis apparatus according to the third embodiment.

Here, a case will be described where the display image shown inFIG. 11Ais displayed on the monitor2according to the processing of the first embodiment. The display image contains the B-mode image51, and the divided ROIs53,54, and55where shear wave speed images are displayed, respectively. It is represented that the shear wave speed in the oval structure on the B-mode image51shown inFIG. 11Ais roughly higher than that of the surrounding tissue and parts of irregularly different shear wave speeds can be seen in the divided ROI54. The operator cannot determine, only by watching the display image shown inFIG. 11A, whether the parts accurately reflect the hardness of tissue or the parts result from improper detection of shear wave propagation. For this reason, the ultrasound diagnosis apparatus according to the third embodiment generates and displays reach time color image data.

As shown inFIG. 10, the image generator14of the ultrasound diagnosis apparatus according to the third embodiment determines whether a display instruction for displaying reach time color image data is received from the operator (step S401). When no display instruction is received (NO at step S401), the image generator14waits until a display instruction is received.

The image generator14acquires, from the internal storage unit16, the times at which shear waves reach corresponding to the displayed shear wave image data (step S402). The internal storage unit16stores, for example, information on the shear wave speed image data that is acquired by image capturing.

The image generator14uses the acquired reach times to generate reach time color image data (step S403). For example, the image generator14generates reach time color image data by plotting, in each point in the scanning area, a color corresponding to the time at which shear waves reach each point in the scanning area. The reach time used here is not limited to the maximum value of displacement. For example, the reach time may be a maximum value of change of displacement over time. Alternatively, the difference between laterally adjacent two points may be calculated by calculating a cross-correlation between time-displacement curves of the two points and the calculated values may be summed from the value of the position where displacement is caused to acquire a reach time at each point.

The output controller173then displays the reach time color image data, which is generated by the image generator14, such that the reach time color image data is superimposed onto the displayed B-mode image data (step S404).FIG. 11Bshows exemplary reach time color image data that is displayed by the output controller173. In this case, shear waves are generated on the left of each of the divided ROIs53,54, and55and the shear waves propagate rightward. For this reason, if the reach time increases from the left to the right in each divided ROI, it can be determined that propagating shear waves are properly detected. In other words, it is expected that the color changes to be deep from the left to the right in each divided ROI. However, in the example shown inFIG. 11B, while such an expected color change can be seen in the divided ROI53and the divided ROI55, the color suddenly changes in the divided ROI54(i.e., the middle color cannot be seen), which indicates that shear waves that move rightward cannot be detected properly.

As described above, the ultrasound diagnosis apparatus according to the third embodiment generates and displays reach time color image data. Accordingly, with the ultrasound diagnosis apparatus according to the third embodiment, after confirming by sight burst wave transmission positions on the B-mode image51, the operator can easily confirm whether shear waves are generated and propagate as expected. For example, when an artifact occurs in a shear wave speed image due to reflection or refraction of shear waves, the cause of the artifact can be identified and it can be determined easily whether the structure displayed on the sheer wave speed image accurately reflects the structure in the patient. Furthermore, when the operator moves the ultrasound probe1or changes the burst wave transmission positions individually, the operator can confirm each time how the manipulation influences the shear wave propagation and highly-reliable shear wave speed image data is generated and accordingly the data can be easily reflected to the manipulation. The divided ROI54shown inFIG. 11Bindicates that shear waves that move rightward are not properly detected. In this case, for example, by switching the display screen on the monitor2to the display image shown inFIG. 5B, the operator can confirm the distance between the burst wave transmission position57corresponding to the divided ROI54(or the position of the divided ROI54) and the oval structure boundary. Furthermore, by experiencing the above-described confirmation when shear waves are not caused and propagate as expected, the operator can learn a proper distance between the burst wave transmission position57and the oval structure boundary, i.e., a distance with which an artifact tends not to occur.

For the third embodiment, the case has been described where, according to the processing of the first embodiment, the display image shown inFIG. 11Ais displayed on the monitor2. Alternatively, for example, the processing according to the third embodiment may be performed according to and the processing of the second embodiment when the display image shown inFIG. 11Ais displayed on the monitor2.

Alternatively, by combining the third embodiment and the first embodiment, the shear wave speed image and the reach time color image may be displayed simultaneously in parallel. Alternatively, the third embodiment and the second embodiments may be combined and, when a given outline is extracted near a burst wave transmission position, a warning may be output and a burst wave transmission position may be optimized.

Fourth Embodiment

For the first to third embodiments, the case has been described where, after the burst wave transmission positions and divided ROIs are displayed, the burst wave transmission positions and divided ROIs are changed or shear wave speed image data is acquired by image capturing. However, embodiments are not limited to this. For example, the ultrasound diagnosis apparatus may change the burst wave transmission positions and divided ROIs before displaying the burst wave transmission positions and divided ROIs. For a fourth embodiment, a case will be described where, before displaying the burst wave transmission positions and divided ROIs, an ultrasound diagnosis apparatus changes the burst wave transmission positions and divided ROIs.

The ultrasound diagnosis apparatus according to the fourth embodiment has the same configuration as that of the ultrasound diagnosis apparatus shown inFIG. 6but is different from the ultrasound diagnosis apparatus shown inFIG. 6in the procedure taken by the ultrasound diagnosis apparatus. Thus, for the fourth embodiment, the different aspects from the second embodiment will be described mainly and the same reference numerals as those used inFIG. 6are used to denote the same functions as those of the configuration described for the second embodiment and descriptions for the same functions will not be given here.

FIG. 12is a flowchart of a procedure taken by the ultrasound diagnosis apparatus according to the fourth embodiment. The processing from step S501to step S505shown inFIG. 12is the same as the processing from step S101to step S105shown inFIG. 4Aand thus descriptions thereof will not be given here. Furthermore, the processing from step S506to step S510is the same as the processing from step S308to step S312shown inFIG. 7and thus descriptions thereof will not be given here.

The generator172then generates transmission position image data and divided ROI image data (step S511). For example, the generator172generates transmission position image data displaying the burst wave transmission positions that are changed by the changing unit174and divided ROI image data displaying the changed positions of the divided ROIs.

The output controller173displays the transmission position image data and divided ROI image data such that the transmission position image data and divided ROI image data are superimposed onto B-mode image data (step S512). The following processing from step S513to step S516is the same as the processing from step S110to step S113and thus descriptions thereof will not be given here.

Embodiments are not limited to the above-described procedure. For example, the processing for outputting a warning (step S508) is not necessarily performed. In this case, when it is determined that there is a given outline within a given area (YES at step S507), the changing unit174automatically changes the burst wave transmission positions and divided ROIs (step S510).

Furthermore, for example, automatic change processing is not necessarily performed (step S509and step S510). In this case, for example, the changing unit174changes the burst wave transmission positions and divided ROIs according to change instructions from the operator as illustrated for the first embodiment.

Furthermore, processing for clearly displaying the transmission position image data and divided ROI image data on a screen (steps S511and S512) is not necessarily performed. In this case, for example, any one of or both of transmission position image data and divided ROI image data is not necessarily generated and displayed.

As described above, the ultrasound diagnosis apparatus according to the fourth embodiment changes the burst wave transmission positions and divided ROIs before displaying the burst wave transmission positions and divided ROIs. Accordingly, without operator's confirming by sight of displayed burst wave transmission positions and the B-mode image in detail, the ultrasound diagnosis apparatus according to the fourth embodiment can optimize the burst wave transmission positions and divided ROIs and then generate and display a shear wave speed image.

For the above-described embodiments, the case has been illustrated where transmission position image data is superimposed onto an ultrasound image, such as a B-mode image. However, embodiments are not limited to this. For example, the output controller173may superimpose the generated transmission position image data and scanning area image data onto various types of medical image data that is acquired by image capturing by an X-ray diagnosis apparatus, and X-ray CT (Computed Tomography) apparatus, an MRI (Magnetic Resonance Imaging) apparatus, etc.

The components of each device illustrated in the drawings for the first to fourth embodiments are functional ideas and are not required to be configured physically as illustrated in the drawings. In other words, specific separation and integration between devices are not limited to those illustrated in the drawings and the devices may be configured in a way that they are entirely or partly separated or integrated functionally or physically according to various types of load or circumstances and according to an arbitrary unit. Furthermore, a part or all of the processing functions implemented by the devices may be implemented by the CPU or a program that is analyzed and executed by the CPU or may be implemented as wired-logic hardware. Each set of processing performed by the ultrasound diagnosis apparatus illustrated for the first to fourth embodiments can be performed by executing a prepared ultrasound imaging program. The ultrasound imaging program may be distributed via a network, such as the Internet. The ultrasound imaging program may be recorded in a computer-readable non-temporary recording medium, such as a hard disk, flexible disk (FD), CD-ROM, MO, or DVD, and may be read from the non-temporary recording medium and executed by a computer.

According to at least one of the above-described embodiments, the image quality of a hardness image can be improved.