Patent Publication Number: US-11653898-B2

Title: Ultrasound diagnostic apparatus, ultrasound image display method and computer-readable recording medium

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     The entire disclosure of Japanese Patent Application No. 2018-190444 filed on Oct. 5, 2018 is incorporated herein by reference in its entirety. 
     BACKGROUND 
     Technological Field 
     The present invention relates to an ultrasound diagnostic apparatus, an ultrasound image display method and a program and specifically relates to a technique that is useful when a treatment instrument is inserted into the body of a subject under ultrasound guidance and treatment is performed. 
     Description of Related Art 
     Conventionally, as one of medical image diagnostic apparatuses, an ultrasound diagnostic apparatus that transmits ultrasound toward a subject, receives waves reflected by the subject and performs predetermined signal processing on the reception signal to visualize a shape, a condition or behavior of the inside of the subject in the form of an ultrasound image is known. An ultrasound diagnostic apparatus can obtain an ultrasound image with a simple operation of applying an ultrasound probe to a body surface or inserting the ultrasound probe into the body and thus is safe and puts a smaller burden on the subject. 
     For example, an ultrasound diagnostic apparatus is used for treatment by inserting a treatment instrument into the body of a subject under ultrasound guidance to, for example, suck soft tissue in a treatment region of interest. In such treatment, a surgeon such as a doctor can insert the treatment instrument and perform treatment while viewing an ultrasound image obtained by the ultrasound diagnostic apparatus to confirm the treatment region of interest. 
     Where treatment is performed under ultrasound guidance, in order to grasp a correct position and range of a treatment region of interest, it is preferable that the treatment region of interest be clearly reflected in an ultrasound image (B-mode image). However, injection of fluid (for example, saline) from a treatment instrument inserted inside the body or ultrasound irradiation may cause generation of noise (hereinafter referred to as “spray pattern”) in the ultrasound image, resulting in a decrease in visibility of the treatment region of interest. 
     In an ultrasound treatment apparatus disclosed in Japanese Patent Application Laid-Open No. 2000-229098, when treatment is performed using a treatment instrument, a live image during the treatment and a still image picked up, for example, before the treatment are displayed to ensure visibility of a treatment region of interest. 
     However, in the ultrasound diagnostic apparatus disclosed in Japanese Patent Application Laid-Open No. 2000-229098, a still image, for example, one before treatment, is displayed in response to an input of a driving start signal from a treatment instrument and the ultrasound diagnostic apparatus needs to include an interface for signal transmission/reception to/from the treatment instrument. 
     Also, a still image picked up, for example, before treatment is displayed as it is and thus identification of a treatment region of interest may be difficult depending on the level of skills of the surgeon. 
     SUMMARY 
     An object of the present invention is to provide an ultrasound diagnostic apparatus, an ultrasound image display method and a program that enable ensuring visibility of a treatment region of interest with no need for a special interface for connection with a treatment instrument. 
     Another object of the present invention is to provide an ultrasound diagnostic apparatus that enables identifying a treatment region of interest easily irrespective of a level of skills of a surgeon. 
     To achieve at least one of the abovementioned objects, according to an aspect of the present invention, an ultrasound diagnostic apparatus reflecting one aspect of the present invention is an apparatus for generating and displaying an ultrasound image corresponding to reflected ultrasound reflected inside a subject, the apparatus comprising a hardware processor that 
     generates a B-mode image based on a reception signal corresponding to the reflected ultrasound, 
     analyzes the B-mode image and determines an operation status of a treatment instrument used for treatment, 
     displays, based on a result of the determination, a first display image including a current B-mode image and a second display image including a B-mode image obtained when the treatment instrument is in a non-operating state in such a manner that the first display image and the second display image are aligned. 
     To achieve at least one of the abovementioned objects, according to an aspect of the present invention, an ultrasound image display method reflecting one aspect of the present invention is a method for generating and displaying an ultrasound image corresponding to reflected ultrasound reflected inside a subject, the method comprising: 
     generating a B-mode image based on a reception signal corresponding to the reflected ultrasound; 
     analyzing the B-mode image and determining an operation status of a treatment instrument used for treatment; and 
     displaying, based on a result of the determination, a first display image including a current B-mode image and a second display image including a B-mode image obtained when the treatment instrument is in a non-operating state in such a manner that the first display image and the second display image are aligned. 
     To achieve at least one of the abovementioned objects, according to an aspect of the present invention, a non-transitory computer-readable recording medium reflecting one aspect of the present invention is a medium storing a program for causing a computer in an ultrasound diagnostic apparatus for generating and displaying an ultrasound image corresponding to reflected ultrasound reflected inside a subject, to perform: 
     first processing for generating a B-mode image based on a reception signal corresponding to the reflected ultrasound; 
     second processing for analyzing the B-mode image and determining an operation status of a treatment instrument used for treatment; and 
     third processing for displaying, based on a result of the determination by the second processing, a first display image including a current B-mode image and a second display image including a B-mode image obtained when the treatment instrument is in a non-operating state in such a manner that the first display image and the second display image are aligned. 
     To achieve at least one of the abovementioned objects, according to an aspect of the present invention, an ultrasound diagnostic apparatus reflecting one aspect of the present invention is an apparatus for generating and displaying an ultrasound image corresponding to reflected ultrasound reflected inside a subject, the apparatus comprising a hardware processor that 
     generates a B-mode image based on a reception signal corresponding to the reflected ultrasound, 
     determines an operation status of a treatment instrument used for treatment, 
     displays, based on a result of the determination, a first display image including a current B-mode image and a second display image including a B-mode image obtained when the treatment instrument is in a non-operating state in such a manner that the first display image and the second display image are aligned, and highlights a treatment region of interest in the second display image. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       The advantages and features provided by one or more embodiments of the invention will become more fully understood from the detailed description given hereinbelow and the appended drawings which are given by way of illustration only, and thus are not intended as a definition of the limits of the present invention: 
         FIG.  1    is a diagram illustrating an outer appearance of an ultrasound diagnostic apparatus according to an embodiment; 
         FIG.  2    is a diagram illustrating a configuration of an ultrasound probe; 
         FIG.  3    is a block diagram illustrating a major part of a control system in the ultrasound diagnostic apparatus; 
         FIGS.  4 A and  4 B  are diagrams illustrating an example of a B-mode image when a treatment instrument is in a non-operating state and an example of a B-mode image when the treatment instrument is in an operating state, respectively; 
         FIG.  5    is a diagram illustrating an example of ultrasound image display processing; 
         FIGS.  6 A to  6 C  are diagrams for describing a method for determining an operation status of the treatment instrument based on a brightness distribution; and 
         FIGS.  7 A and  7 B  are diagrams illustrating example display images when the treatment instrument is in an operating state (during treatment) and example display images when the treatment instrument is in a non-operating state (after treatment). 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
     Hereinafter, one or more embodiments of the present invention will be described with reference to the drawings. However, the scope of the invention is not limited to the disclosed embodiments. 
     An embodiment of the present invention will be described in detail below with reference to the accompanying drawings. 
       FIG.  1    is a diagram illustrating an outer appearance of ultrasound diagnostic apparatus  1  according to an embodiment of the present invention.  FIG.  2    is a diagram illustrating a configuration of ultrasound probe  20 .  FIG.  3    is a diagram illustrating a major part of a control system in ultrasound diagnostic apparatus  1 . 
     Ultrasound diagnostic apparatus  1  is used together with a treatment instrument and visualizes a state of the inside of a subject in the form of an ultrasound image to support treatment using the treatment instrument. When treatment is performed using a treatment instrument, a treatment mode is selected in ultrasound diagnostic apparatus  1 . 
     Examples of the treatment instrument include one that creates a pressure-reduced portion at a distal end of a puncture part using the Venturi effect and sucks soft tissue of a treatment region of interest from the pressure-reduced portion to perform treatment (for example, TenJet (product name) manufactured by HydroCision, Inc.). The treatment instrument is equipped with a driving operation section, for example, a foot pedal, and can be activated/deactivated by operating the driving operation section. 
       FIG.  4 A  is a diagram illustrating an example of an ultrasound image obtained in a non-operating state in which a treatment instrument is not activated and  FIG.  4 B  is a diagram illustrating an example of an ultrasound image obtained in an operating state in which the treatment instrument is activated. Note that in each of  FIGS.  4 A and  4 B , for ease of recognition of the inserted treatment instrument, puncture part N of the treatment instrument is illustrated with a line drawing superimposed thereon. The same applies to  FIGS.  7 A and  7 B  referred to later. 
     In the above-described treatment instrument, a significant amount of fluid is ejected from a suction port provided in the pressure-reduced portion, high-brightness spray pattern SP spreading downward from a distal end of puncture part N of the treatment instrument is shown in the ultrasound image (see  FIG.  4 B ). 
     When the treatment instrument is inserted toward a treatment region of interest to perform treatment under ultrasound guidance, ultrasound diagnostic apparatus  1  displays a live image during the treatment as a first display image and a still image during a non-treatment period as a second display image, in response to a change in operation status (for example, activation/deactivation) of the treatment instrument. Since no spray pattern SP is shown in the second display image, visibility of the treatment region of interest is ensured. 
     Note that ultrasound diagnostic apparatus  1  has no need to include an interface for transmission/reception of a driving signal to/from treatment instrument, but may include such interface. 
     As illustrated in  FIG.  1   , ultrasound diagnostic apparatus  1  includes ultrasound diagnostic apparatus body  10  and ultrasound probe  20 . Ultrasound diagnostic apparatus body  10  and ultrasound probe  20  are connected via cable  30 . Note that ultrasound probe  20  may be connected to ultrasound diagnostic apparatus body  10  via wireless communication. 
     Ultrasound probe  20  transmits ultrasound to a subject, receives an ultrasound echo resulting from reflection of the ultrasound by the subject, converts the ultrasound echo into a reception signal and transmits the reception signal to ultrasound diagnostic apparatus body  10 . For ultrasound probe  20 , any electronic scanning probe such as a convex probe, a linear probe or a sector probe or a mechanical scanning probe such as a mechanical sector probe can be employed. The ultrasound probe  20  may include a puncture needle guide portion to which a puncture needle is attached, the puncture needle guide portion guiding a direction of puncture. 
     As illustrated in  FIG.  2   , ultrasound probe  20  includes acoustic lens  21 , acoustic matching layer  22 , transducer array  23  and backing material  24  in the order mentioned from the ultrasound transmission/reception side. Note that a protective layer may be disposed on a surface of acoustic lens  21  (ultrasound transmission/reception surface). 
     Acoustic lens  21  is a lens that converges ultrasound in a slice direction (direction orthogonal to a scanning direction in which a plurality of transducers are aligned), and for example, when a material, a sound propagation speed of which is lower than that of a living body, is used for the acoustic lens, generally has a semicylindrical shape in which a central portion in the slice direction thereof bulges. 
     Acoustic matching layer  22  is an intermediate substance for making ultrasound efficiently enter the subject and matches an acoustic impedance of the transducers (not illustrated) and an acoustic impedance of the subject with each other. 
     Transducer array  23  is formed of, for example, a plurality of strip transducers arranged in a single row in the scanning direction. In other words, ultrasound probe  20  is what is called a single-row probe. 
     Backing material  24  attenuates unwanted vibration caused by transducer array  23 . 
     Ultrasound diagnostic apparatus body  10  visualizes a shape, a condition or behavior of the inside of the subject in the form of an ultrasound image (B-mode image), using the reception signal from ultrasound probe  20 . 
     As illustrated in  FIG.  3   , ultrasound diagnostic apparatus body  10  includes, for example, operation input section  11 , transmission section  12 , reception section  13 , image processing section  14 , image storage section  15 , image display section  16 , display section  17  and system control section  18 . 
     Each of transmission section  12 , reception section  13 , image processing section  14 , image storage section  15  and image display section  16  is formed of, for example, a dedicated or general-purpose hardware (electronic circuit) for relevant processing, such as a DSP (digital signal processor), an ASIC (application-specific integrated circuit) or a PLD (programmable logic device), and provides a relevant function in cooperation with system control section  18 . 
     Operation input section  11  receives an input of, for example, a command for providing an instruction to, for example, start an examination or information relating to the subject. Operation input section  11  is formed of, for example, an operation panel including a plurality of input switches, a keyboard and a mouse. Note that operation input section  11  may be formed of a touch panel integrated with display section  17 . 
     Transmission section  12  generates a transmission signal (driving signal) and outputs the transmission signal to ultrasound probe  20  according to an instruction from system control section  18 . Although not illustrated, transmission section  12  includes, for example, a clock generation circuit, a pulse generation circuit, a pulse width setting section and a delay circuit. 
     The clock generation circuit generates a clock signal based on which a pulse signal transmission timing and a transmission frequency are determined. The pulse generation circuit generates a bipolar rectangular-wave pulse having a preset voltage amplitude in a predetermined cycle. The pulse width setting section sets a pulse width of rectangular-wave pulses to be output from the pulse generation circuit. The rectangular-wave pulses generated in the pulse generation circuit are separated into different wirings for the respective transducers of ultrasound probe  20  before or after being input to the pulse width setting section. The delay circuit delays the generated rectangular-wave pulses according to transmission timings for the respective transducers and outputs the generated rectangular-wave pulses to the respective transducers. 
     Reception section  13  receives the reception signal from ultrasound probe  20  and outputs the reception signal to image processing section  14  according to an instruction from system control section  18 . Although not illustrated, reception section  13  includes, for example, an amplifier, an A/D conversion circuit and a phase-adjustment/addition circuit. 
     The amplifier amplifies reception signals corresponding to ultrasounds received by the respective transducers of ultrasound probe  20  at a predetermined amplification ratio set in advance. The A/D conversion circuit converts the amplified reception signals into digital data at a predetermined sampling frequency. The phase-adjustment/addition circuit provides delays to the respective reception signals resulting from the A/D conversion for the respective wirings for the transducers to adjust time phases of the reception signals and adds up the reception signals (phase-adjustment and addition). 
     Image processing section  14  includes B-mode image generation section  141  and image analysis section  142 . Also, although not illustrated, image processing section  14  includes a DSC (digital scan converter) that performs coordinate conversion and pixel interpolation according to the type of ultrasound probe  20 . 
     B-mode image generation section  141  generates a B-mode image indicating a state of the inside of the subject based on the reception signal, in accordance with an instruction from system control section  18 . When the treatment instrument is inserted inside the subject, puncture part N of the treatment instrument is shown in the B-mode image (see  FIGS.  4 A and  4 B ). Also, spray pattern SP spreading from the distal end of puncture part N toward a deep part is shown in a B-mode image during treatment in which the treatment instrument is active (see  FIG.  4 B ). 
     Image analysis section  142  analyzes a B-mode image and determines a change in operation status of the treatment instrument. For example, image analysis section  142  determines whether the treatment instrument is in an on-state (during treatment) or in an off-state (during a non-treatment period). A method for determination of a change in state of the treatment instrument will be described later. 
     Image storage section  15  is formed of, for example, a non-volatile semiconductor memory (what is called a flash memory) or a hard disk drive. Image storage section  15  may be a disk drive that drives an optical disk such as a CD (compact disc), a DVD (digital versatile disc) or a BD (Blu-ray disc (“Blu-ray” is a registered trademark)) or a magneto-optical disk such as an MO (magneto-optical disc) to read/write information. 
     Image storage section  15  stores image data generated in B-mode image generation section  141  on a frame-by-frame basis. The image data stored in the image storage section  15  is read out according to an instruction from system control section  18  and used for analysis by image analysis section  142  or used for display on display section  17 . 
     Image display section  16  converts data of a B-mode image generated in image processing section  14  (which may be data stored in image storage section  15 ) into a display signal that is compatible with display section  17  and outputs the display signal according to an instruction from system control section  18 . In the present embodiment, when ultrasound diagnostic apparatus  1  is used together with a treatment instrument, image display section  16  provides two-screen display in which two B-mode images are aligned (see  FIGS.  7 A and  7 B ). In the two-screen display, first display image D 1  is a current B-mode image and second display image D 2  is a B-mode image obtained when the treatment instrument is in a non-operating state. 
     Display section  17  is formed of, for example, a liquid-crystal display, an organic EL display or a CRT display. Display section  17  displays a display image based on a display signal from image display section  16 , in accordance with an instruction from system control section  18 . 
     System control section  18  performs overall control of ultrasound diagnostic apparatus  1  by controlling operation input section  11 , transmission section  12 , reception section  13 , image processing section  14 , image storage section  15 , image display section  16  and display section  17  according to the respective functions. 
     System control section  18  includes, for example, CPU (central processing unit)  181 , which serves as an arithmetic/control device, and ROM (read-only memory)  182  and RAM (random access memory)  183 , which serve as a main memory device. A basic program and basic setting data are stored in ROM  182 . Also, a treatment support program to be executed in the treatment mode is stored in ROM  182 . CPU  181  performs centralized control of operation of the respective functional blocks (transmission section  12 , reception section  13 , image processing section  14 , image storage section  15 , image display section  16  and display section  17 ) of ultrasound diagnostic apparatus body  10 , by reading a program according to the content of processing from ROM  182 , loading the program to RAM  183  and executing the loaded program. 
     In the present embodiment, the functions of the respective functional blocks are fulfilled by cooperation between the respective pieces of hardware forming the functional blocks and system control section  18 . Note that some or all of the functions of the respective functional blocks may be fulfilled by execution of programs by system control section  18 . 
       FIG.  5    is a flowchart illustrating an example of ultrasound image display processing where ultrasound diagnostic apparatus  1  is used together with a treatment instrument. This processing is fulfilled, for example, by execution of a predetermined program (treatment support program) stored in ROM  182  by CPU  181  in response to enabling of the treatment mode in ultrasound diagnostic apparatus  1 . The enabling of the treatment mode is performed by, for example, mode selection via operation input section  11 . 
     In step S 101 , system control section  18  controls transmission section  12  to transmit ultrasound from ultrasound probe  20 . 
     In step S 102 , system control section  18  controls reception section  13  to acquire a reception signal corresponding to reflected ultrasound (ultrasound echo) received by ultrasound probe  20 . 
     In step S 103 , system control section  18  controls image processing section  14  (B-mode image generation section  141 ) to generate a B-mode image based on the reception signal and store the B-mode image in image storage section  15 . 
     In step S 104 , system control section  18  controls image display section  16  and display section  17  to display a current B-mode image (live image) as first display image D 1 . Note that second display image D 2  is not specifically limited before a start of treatment using the treatment instrument (except resumption of treatment). For example, as second display image D 2 , a B-mode image before insertion of the treatment instrument may be displayed or the current B-mode image may be displayed. 
     In step S 105 , system control section  18  controls image processing section  14  (image analysis section  142 ) to analyze a brightness distribution in the generated B-mode image. More specifically, system control section  18  generates a graph of brightness values in a predetermined region (see  FIGS.  6 A and  6 B ).  FIG.  6 A  is a graph when the treatment instrument is in a non-operating state and  FIG.  6 B  is a graph when the treatment instrument is in an operating state. 
     Here, it is preferable that the predetermined region that is subject to the analysis of the B-mode image be, for example, a deep region (region DR surrounded by the dotted line in each of  FIGS.  4 A and  4 B ) in the B-mode image. When the present function is used, a user sets a display depth in such a manner that a treatment region of interest is displayed in an upper part with reference to a center of the screen. Therefore, the deep region (for example, a lower region corresponding to 20% of the B-mode image) is displayed as a relatively-low brightness (black display) image. Then, upon high-brightness spray pattern SP being shown, a change occurs in brightness distribution. Therefore, detection of a change in brightness distribution of the deep region is favorable for determination of a change in operation status of the treatment instrument, more specifically, determines whether the treatment instrument is activated or deactivated. Note that an entirety of the B-mode image may be subject to analysis or a particular region other than the deep region may be subject to analysis. 
     Next, in step S 106  in  FIG.  5   , system control section  18  controls image processing section  14  (image analysis section  142 ) to determine whether or not the operation status of the treatment instrument has changed, based on a result of the analysis. 
     As illustrated in  FIGS.  6 A and  6 B , in a case where the treatment instrument has been switched from a non-operating state to an operating state, high-brightness spray pattern SP is shown, causing an increase of high brightness-side frequencies. On the other hand, in a case where the treatment instrument has been switched from an operating state to a non-operating state, high-brightness spray pattern SP disappears, causing a decrease in high brightness-side frequencies. Therefore, comparison between a brightness distribution obtained last time and a brightness distribution obtained the present time enables determination of whether or not the operation status of the treatment instrument has changed. 
     Also, in the graphs in  FIGS.  6 A and  6 B , when the treatment instrument is in an operating state (see  FIG.  6 B ), a mean and variance of brightness values are large in comparison with a case where the treatment instrument is in a non-operating state (see  FIG.  6 A ). Therefore, whether or not the operation status of the treatment instrument has changed can be determined using a mean and variance of brightness values calculated from a brightness distribution. For example, as illustrated in  FIG.  6 C , whether the treatment instrument is in an operating state or in a non-operating state can be determined according to a linear discriminant using a set of a mean and variance of brightness values (means, variance). Also, for example, whether treatment instrument is in an operating state or in a non-operating state may be determined by comparing one of the mean and the variance of brightness values with a threshold value for the one. 
     In a case where the operation status of the treatment instrument has changed (“YES” in step S 106 ), the processing proceeds to the processing in the step S 107 . In a case where the treatment instrument has been activated from an inactive state and treatment (suction) has been started or in a case where the treatment instrument has been deactivated from an active state and the treatment has been finished (which may be a temporary end), the processing in step S 107  is performed. In a case where the operation status of the treatment instrument has not changed (“NO” in step S 106 ), the processing proceeds to the processing in step S 101 . In this case, the treatment instrument is kept inactive or kept active, display of second display image D 2  is maintained and only the live image displayed as first display image D 1  is updated. 
     In step S 107 , system control section  18  controls image storage section  15  to read out a B-mode image obtained during a non-treatment period in which the treatment instrument is a non-operating state. 
     More specifically, in a case where the treatment instrument has been switched from a non-operating state to an operating state, a B-mode image before treatment is read out. In this case, the read-out B-mode image is preferably one immediately before the treatment instrument enters the operating state. 
     Also, in a case where the treatment instrument has been changed from an operating state to a non-operating state, a B-mode image after the treatment is read out. For example, in step S 106 , arrangement is made so as to, in a case where the status has been maintained for a certain period of time after the change in brightness distribution in the predetermined region, determine that the operation status of the treatment instrument has changed, enabling reading out a still image during a non-treatment period (after treatment) in which no spray pattern SP is shown. 
     In step S 108 , system control section  18  controls image display section  16  and display section  17  to display the read-out B-mode image (still image during a non-treatment period) as second display image D 2 . Then, the processing returns to step S 101  and repeated until completion of the treatment. 
     In a case where the treatment instrument has been switched from a non-operating state to an operating state, display section  17  provides two-screen display of first display image D 1  (live image) and second display image D 2  (still image before the treatment) (see  FIG.  7 A ). Since no spray pattern SP is shown in second display image D 2 , treatment region of interest TR can easily be identified. A surgeon can perform treatment while confirming treatment region of interest TR by comparing first display image D 1  and second display image D 2 . 
     Also, in a case where the treatment instrument has been switched from an operating state to a non-operating state, display section  17  provides two-screen display of first display image D 1  (live image) and second display image D 2  (still image after the treatment) (see  FIG.  7 B ). Since no spray pattern SP is shown in second display image D 2 , treatment region of interest TR can easily be identified. Also, since second display image D 2  is a still image after treatment, the surgeon can confirm a status of progress of the treatment regarding to which extent the treatment region of interest remains, and thus can properly perform the treatment until the treatment region of interest is fully removed. 
     Note that in a case where the treatment instrument has been switched from an operating state to a non-operating state and then switched to an operating state, that is, in a case where treatment is resumed after an interruption, a still image immediately before the resumption of the treatment is displayed as second display image D 2 . Then, in a case where the treatment instrument has been switched from the operating state to a non-operating state, a new B-mode image (still image after an end of the resumed treatment) is read out by the processing in steps S 107  and S 108  and second display image D 2  is thereby updated. 
     In the above-described ultrasound image display processing, it is preferable that when second display image D 2  is displayed in step S 108 , the treatment region of interest is highlighted. Examples of the highlighting include coloring. As illustrated in  FIGS.  7 A and  7 B , treatment region of interest TR in second display image D 2  is shown more clearly than treatment region of interest TR in first display image D 1 . 
     Since a treatment region of interest is softer or more slurry than the surrounding bone and body tissue, the treatment region of interest is shown with a brightness that is lower than the surroundings. Therefore, it is possible to analyze a B-mode image, detect a tissue region, identify a low-brightness region in the tissue region as a treatment region of interest and highlight treatment region of interest TR. 
     In step S 108 , as a result of the treatment region of interest in second display image D 2  being subjected to highlighting processing, the surgeon can confirm to which extent the treatment has been performed and whether or not the treatment has correctly been performed, by comparing the images before and after the treatment and thus can perform the treatment properly. In other words, the surgeon can easily identify a treatment region of interest irrespective of the level of his/her skills and thus can more properly perform the treatment. 
     As described above, ultrasound diagnostic apparatus  1  according to the embodiment is an ultrasound diagnostic apparatus for generating and displaying an ultrasound image corresponding to reflected ultrasound reflected inside a subject, the apparatus including: B-mode image generation section  141  that generates a B-mode image based on a reception signal corresponding to the reflected ultrasound; image analysis section  142  (determination section) that analyzes the B-mode image and determines an operation status of a treatment instrument used for treatment; and image display section  16  that based on a result of the determination by image analysis section  142 , displays first display image D 1  including a current B-mode image and second display image D 2  including a B-mode image obtained when the treatment instrument is in a non-operating state in such a manner that first display image D 1  and second display image D 2  are aligned. 
     Also, the ultrasound image display method according to the embodiment is an ultrasound image display method for generating and displaying an ultrasound image corresponding to reflected ultrasound reflected inside a subject, the method including: a first step of generating a B-mode image based on a reception signal corresponding to the reflected ultrasound (step S 103  in  FIG.  5   ); a second step of analyzing the B-mode image and determining an operation status of a treatment instrument used for treatment (steps S 105  and S 106  in  FIG.  5   ) and a third step of, based on a result of the determination in the second step, displaying first display image D 1  including a current B-mode image and second display image D 2  including a B-mode image obtained when the treatment instrument is in a non-operating state in such a manner that first display image D 1  and second display image D 2  are aligned (steps S 107  and S 108  in  FIG.  5   ). 
     Also, the program according to the embodiment causes system control section  18  (computer) in ultrasound diagnostic apparatus  1  for generating and displaying an ultrasound image corresponding to reflected ultrasound reflected inside a subject, to perform: first processing for generating a B-mode image based on a reception signal corresponding to the reflected ultrasound (step S 103  in  FIG.  5   ); second processing for analyzing the B-mode image and determining an operation status of a treatment instrument used for treatment (steps S 105  and S 106  in  FIG.  5   ); and third processing for, based on a result of the determination by the second processing, displaying first display image D 1  including a current B-mode image and second display image D 2  including a B-mode image obtained when the treatment instrument is in a non-operating state in such a manner that first display image D 1  and second display image D 2  are aligned (steps S 107  and S 108  in  FIG.  5   ). 
     This program is provided via, for example, a computer-readable removable storage medium (which may be an optical disk, a magneto-optical disk or a memory card) with the program stored therein. Also, for example, this program can be provided by being downloaded via a network from a server that holds the program. 
     According to ultrasound diagnostic apparatus  1 , the ultrasound image display method and the program according to the embodiment, even when visibility of treatment region of interest TR is lowered by spray pattern SP in first display image D 1  including a live image, no spray pattern SP is shown in second display image D 2  including a still image during a non-treatment period, the still image being obtained when the treatment instrument is in a non-operating state, and thus visibility of treatment region of interest TR is ensured. Therefore, a surgeon can properly perform treatment while confirming treatment region of interest TR in second display image D 2 . 
     Also, the operation status of the treatment instrument is determined by means of image analysis and thus there is no need to provide a special interface for connection with the treatment instrument in ultrasound diagnostic apparatus  1 . Therefore, reduction in cost of ultrasound diagnostic apparatus  1  can be achieved. 
     Also, in ultrasound diagnostic apparatus  1 , image analysis section  142  (determination section) determines whether the treatment instrument is activated or deactivated. Consequently, ultrasound diagnostic apparatus  1  can properly respond to a case where noise (for example, spray pattern SP) is shown in a B-mode image depending on the operation status of the treatment instrument. 
     Also, in ultrasound diagnostic apparatus  1 , image analysis section  142  (determination section) determines a change in operation status of the treatment instrument. Consequently, proper second display image D 2  can be displayed according to a case where the treatment instrument has been switched from a non-operating state to an operating state or a case where the treatment instrument has been switched from an operating state to a non-operating state. 
     Also, in ultrasound diagnostic apparatus  1 , image analysis section  142  (determination section) determines the operation status of the treatment instrument based on a change in brightness distribution in a predetermined region in a B-mode image. 
     More specifically, image analysis section  142  (determination section) determines the operation status of the treatment instrument based on at least one of a mean and variance of brightness values in the predetermined region. 
     Consequently, the operation status of treatment instrument can be determined by relatively simple processing and thus a processing load on system control section  18  can be reduced. 
     Also, in ultrasound diagnostic apparatus  1 , a predetermined region that is subject to image analysis is a deep region in the B-mode image. Consequently, a change in brightness distribution accompanying a change in operation status of the treatment instrument is conspicuously indicated, enabling easy and correct determination of the operation status of the treatment instrument. 
     Also, in ultrasound diagnostic apparatus  1 , when the treatment instrument has been switched from a non-operating state to an operating state, image display section  16  displays second display image D 2  including a B-mode image obtained immediately before the switching. Consequently, no spray pattern SP is shown in second display image D 2  and thus treatment region of interest TR can easily be identified, enabling the surgeon to proceed treatment while confirming treatment region of interest TR by comparing first display image D 1  and second display image D 2  with each other. 
     Also, in ultrasound diagnostic apparatus  1 , when the treatment instrument has been switched from an operating state to a non-operating state, image display section  16  displays second display image D 2  including a B-mode image immediately after the switching. Since second display image D 2  is a still image after treatment, the surgeon can confirm a status of progress of the treatment regarding to which extent the treatment region of interest remains and thus can properly perform the treatment until completion of removal of the treatment region of interest. 
     Also, in ultrasound diagnostic apparatus  1 , image display section  16  highlights the treatment region of interest in the second display image. More specifically, the treatment region of interest has a brightness that is lower than that of a region around the treatment region of interest. Consequently, the surgeon can easily identify the treatment region of interest regardless of the level of his/her skills and can further properly perform the treatment. 
     Furthermore, the present embodiment also discloses an aspect of the invention as follows. 
     Ultrasound diagnostic apparatus  1  according to the embodiment is an ultrasound diagnostic apparatus for generating and displaying an ultrasound image corresponding to reflected ultrasound reflected inside a subject, the apparatus including: B-mode image generation section  141  that generates a B-mode image based on a reception signal corresponding to the reflected ultrasound; image analysis section  142  (determination section) that determines an operation status of a treatment instrument used for treatment; and image display section  16  that based on a result of the determination by image analysis section  142 , displays first display image D 1  including a current B-mode image and second display image D 2  including a B-mode image obtained when the treatment instrument is in a non-operating state in such a manner that first display image D 1  and second display image D 2  are aligned Image display section  16  highlights treatment region of interest TR in second display image D 2 . 
     Consequently, a surgeon can easily identify a treatment region of interest irrespective of the level of his/her skills and thus can properly perform treatment. 
     Note that in this case, the determination section may be configured so as to determine the operation status of the treatment instrument based on a driving signal from the treatment instrument, rather than image analysis. 
     Although an invention made by the present inventor has been described above based on an embodiment, the present invention is not limited to the above embodiment and can be changed without departing from the spirit of the invention. 
     For example, image display section  16  may be configured so as to display information relating to the area of treatment region of interest TR. As the information relating to the area of treatment region of interest TR, for example, the area of a low-brightness region may be indicated by a numerical value in a screen (for example, a lower part of the screen) or may be indicated by a graph. Indication of the area of the low-brightness region before treatment and the area of the low-brightness region after treatment by respective numerical values or graphs enables visually confirming to which extend treatment has been performed. Also, for example, image display section  16  may be configured to indicate a degree of reduction of the area of the low-brightness region after treatment relative to the area of the low-brightness region before the treatment (for example, “−10” when the degree of reduction is 10). Consequently, a result of the treatment can easily be confirmed. 
     Also, a B-mode image obtained during a non-treatment period (before treatment), the B-mode image being read out when the treatment instrument has been switched from a non-operating state to an operating state, may be a B-mode image obtained several frames before the treatment instrument enters the operating state, rather than a B-mode image immediately before the treatment instrument enters the operating state. This is because in the case of the frame immediately before, a spray pattern may be shown slightly. 
     Although embodiments of the present invention have been described and illustrated in detail, the disclosed embodiments are made for purpose of illustration and example only and not limitation. The scope of the present invention should be interpreted by terms of the appended claims.