Abstract:
When a tomographic image is displayed, the operator of an ultrasonic diagnostic apparatus is allowed to know the timing to optimize the image quality and decide by him- or herself whether optimization needs to be done now or not. 
     The ultrasonic diagnostic apparatus includes: an ultrasonic probe for sending out an ultrasonic wave toward a vital tissue and receiving a reflected wave of the ultrasonic wave reflected from the tissue; an image constructing section for constructing an image frame representing a tomographic image of the tissue by calculating the magnitudes of displacements at multiple measuring sites on the tissue based on the reflected wave; a display section for displaying the image frame thereon; and a processing section for analyzing an image feature quantity of the image frame and comparing the image feature quantity to a predetermined reference feature quantity. Based on a result of the comparison, the apparatus gives a notification that it is time to decide whether its operator wants the image quality of the image frame to be optimized now or not.

Description:
TECHNICAL FIELD 
     The present invention relates to a technology for displaying an image on an ultrasonic diagnostic apparatus and more particularly relates to a control technique for optimizing display of a tomographic image on an ultrasonic diagnostic apparatus. 
     BACKGROUND ART 
     An ultrasonic diagnostic apparatus is used to display a tomographic image representing an internal tissue of a subject&#39;s body. The tomographic image is generated based on an ultrasonic wave that has been sent out from an ultrasonic probe and then reflected from the internal tissue. 
     In this case, the tomographic image displayed will look incessantly different every time either the ultrasonic probe or the subject moves. For that reason, they say that some kind of processing for adjusting the image appearance by either increasing or decreasing the luminance of the tomographic image (which is so-called “optimization processing”) should be carried out. 
     Some methods for carrying out such optimization on an ultrasonic diagnostic apparatus by determining the best timing are proposed in Patent Documents Nos. 1 and 2, for example. 
     According to Patent Document No. 1, a variation in the pixel intensity histogram of a series of image frames is monitored. And if the feature quantity of that histogram has been stabilized for a certain period but if a significant variation has been sensed in the feature quantity of the pixel intensity histogram of the latest image frame, the computer decides that the ultrasonic probe has moved and gets the image optimized automatically. 
     On the other hand, according to Patent Document No. 2, ultrasonic images are sampled periodically and each of those ultrasonic image sampled is divided into a number of blocks. And if a difference in feature quantity between one block of the previous sampled image and its associated block of the current sampled image has exceeded a threshold value, then it is decided that some significant change has occurred and image optimization is carried out automatically. 
     CITATION LIST 
     Patent Literature 
     Patent Document No. 1: Japanese Patent Application Laid-Open Publication No. 2001-187057 
     Patent Document No. 2: Japanese Patent Application Laid-Open Publication No. 2007-98142 
     SUMMARY OF INVENTION 
     Technical Problem 
     According to the methods disclosed in Patent Documents Nos. 1 and 2, however, whenever any variation is sensed in the image, optimization is automatically done by the device. That is why the operator cannot know in advance exactly when optimization needs to be done but has no choice but to confirm that the optimization has already been done by sensing a significant change of the image. This means that the optimization could be done at an unwanted timing for him or her. 
     On top of that, even if the quality of the image that has been optimized is not up to the operator&#39;s expectations, he or she has to look at that tomographic image continuously, which is very inconvenient for him or her. 
     It is therefore an object of the present invention to allow the operator of an ultrasonic diagnostic apparatus to know the timing to optimize the image and also let him or her decide whether optimization needs to be done or not. Another object of the present invention is to allow the operator who has opted to optimize the image but who has sensed that the resultant optimized image is not to his or her expectations to change the current method of displaying the image. 
     Solution to Problem 
     An ultrasonic diagnostic apparatus according to the present invention includes: an ultrasonic probe for sending out an ultrasonic wave toward a vital tissue and receiving a reflected wave of the ultrasonic wave that has been reflected from the vital tissue; an image constructing section for constructing an image frame representing a tomographic image of the tissue based on the reflected wave; a display section for displaying the image frame thereon; and a processing section for analyzing an image feature quantity of the image frame and comparing the image feature quantity to a predetermined reference feature quantity. Based on a result of the comparison, the apparatus gives a notification that it is time to decide whether its operator wants the image quality of the image frame to be optimized now or not. 
     The processing section may adopt, as the predetermined reference feature quantity, a result of the analysis on the previous image frame displayed. 
     The ultrasonic diagnostic apparatus may further include an interface section for receiving an instruction from the operator. If after the apparatus gives the notification that it is time to decide whether the operator wants the image quality of the image frame to be optimized now or not, the interface section is instructed to control the image quality, the processing section may determine a parameter for setting the image quality to be a predetermined reference value based on a result of the analysis, and the image constructing section may reconstruct the image frame in accordance with the parameter. 
     The ultrasonic diagnostic apparatus may further include an interface section for receiving an instruction from the operator. If after the apparatus gives the notification that it is time to decide whether the operator wants the image quality of the image frame to be optimized now or not, the interface section is instructed not to control the image quality, the processing section may change the predetermined reference feature quantity. 
     If after the image constructing section has reconstructed the image frame in accordance with the parameter, the interface section is instructed not to control the image quality, the image constructing section may reconstruct the image frame without adopting the parameter determined. 
     If the interface section is instructed not to control the image quality, the processing section may replace the predetermined reference feature quantity with the image feature quantity of the image frame. 
     The processing section may analyze, as the image feature quantity, a luminance related feature quantity of each of multiple areas that have been defined in the image frame. 
     The interface section may be a piece of hardware that allows the user to instruct the apparatus to control the image quality. 
     The interface section may also be a piece of hardware that allows the user to instruct the apparatus not to control the image quality. 
     The display section may display a sign on its screen to give the notification that it is time to decide whether the operator wants the image quality of the image frame to be optimized now or not. 
     The ultrasonic diagnostic apparatus may further include a light-emitting device for giving the notification, based on a result of the comparison, the operator that it is time to decide whether the operator wants the image quality of the image frame to be optimized now or not. 
     Advantageous Effects of Invention 
     According to the present invention, the operator is notified that it is time to decide whether the operator wants the image quality of the image frame to be optimized now or not. That is to say, since the image quality is not changed suddenly without notice while the apparatus is used, the operator never feels unnaturalness. On top of that, by instructing the apparatus whether the image quality of the image frame needs to be optimized or not, the operator can decide by him- or herself whether the image quality should be controlled now or not. 
     Also, if the operator has instructed the apparatus not to control the image quality now, the reference feature quantity that was used when the operator was notified of that timing is changed. That is why the operator will be told the time to get the image quality optimized using a different reference after that. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  illustrates the appearance of an ultrasonic diagnostic apparatus  100  as a specific preferred embodiment of the present invention. 
         FIG. 2  is a block diagram illustrating an internal configuration for the ultrasonic diagnostic apparatus  100  of this preferred embodiment. 
         FIG. 3  is a flowchart showing the processing to get done by a processor  107  to determine whether it is the optimization timing or not. 
         FIG. 4  illustrates two sub-areas that overlap with each other. 
         FIG. 5  is a flowchart showing the procedure of the processing to get done after the operator has been notified. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Hereinafter, preferred embodiments of an ultrasonic diagnostic apparatus according to the present invention will be described with reference to the accompanying drawings. 
       FIG. 1  illustrates the appearance of an ultrasonic diagnostic apparatus  100  as a specific preferred embodiment of the present invention. Using an ultrasonic probe  101 , the ultrasonic diagnostic apparatus  100  displays a tomographic image of an internal body tissue as an image frame on a monitor  108  in real time. At that time, the user can control the image quality and other settings using various buttons on this ultrasonic diagnostic apparatus  100  (e.g., buttons  111  and  112  on a control panel). 
       FIG. 2  is a block diagram illustrating an internal configuration for the ultrasonic diagnostic apparatus  100  of this preferred embodiment. 
     The ultrasonic diagnostic apparatus  100  includes an ultrasonic probe  101 , an A/D converter  102 , a beam former  103 , a detecting section  104 , an image constructing section  105 , a frame memory section  106 , a processor  107 , a monitor  108 , a parameter storage section  109 , an optimization enter button  111  and an optimization cancel button  112 . 
     The ultrasonic probe  101  sends out and receives an ultrasonic beam as described above. 
     The A/D converter  102  converts the ultrasonic reflected wave received into a digital signal. The beam former  103  performs a delayed combination on the ultrasonic wave reflected wave that has been A/D converted. And the detecting section  104  carries out an envelope detection on an ultrasonic echo signal that has been subjected to the delay combination. 
     The image constructing section  105  subjects the ultrasonic echo signal detected to signal processing, thereby constructing a tomographic image frame representing the tissue. 
     The frame memory section  106  accumulates image frames of the tomographic image. What is accumulated in the frame memory section  106  may be nothing but tomographic image frames, which may be accumulated there either for a predetermined amount of time or in a predetermined number. 
     The processor  107  is a so-called central processing unit (CPU) and analyzes the tomographic image frames, thereby determining whether a currently presented image needs to be processed or not. For example, the processor  106  may analyze a series of tomographic image frames to detect any variation between them. And on sensing that the luminance value has decreased to a threshold value or less, the processor  107  may determine whether the luminance of the image should be increased or not. 
     The monitor  108  displays the tomographic image on it. 
     The parameter storage section  109  stores image quality control parameters and results of image analysis. 
     The optimization enter button  111  conveys the operator&#39;s image optimization enter instruction to the processor  107 . On the other hand, the optimization cancel button  112  conveys the operator&#39;s image optimization cancel instruction to the processor  107 . 
     This ultrasonic diagnostic apparatus  100  operates in the following manner. 
     An ultrasonic beam is sent out toward the subject by the ultrasonic probe  101 , reflected by his or her internal body tissue, and then received by the ultrasonic probe  101 . The A/D converter  102  converts an analog signal representing the ultrasonic reflected wave received into a digital signal. And the beam former  103  performs a delay combination on that ultrasonic reflected wave. 
     The detecting section  104  performs an envelope detection, thereby removing transmitted wave components (i.e., carrier components) from the received signal and outputting it as an ultrasonic echo signal to the image constructing section  105 . 
     The image constructing section  105  subjects the input ultrasonic echo signal to filtering, total gain application processing, TGC application processing, LGC application processing, frame gain application processing, scan conversion and other kinds of processing, thereby constructing an ultrasonic tomographic image frame, getting it stored in the frame memory section  106  and presenting it on the monitor  108 . 
     The processor  107  retrieves an image frame from the frame memory section  106  and analyzes the feature quantity of that image. As used herein, the “feature quantity” may refer to the luminance value of each of multiple regions that have been defined in the image or their standard deviation, for example. 
     Furthermore, the processor  107  compares the result of this analysis to the result of the previous analysis that has been obtained from the parameter storage section  109 , thereby determining whether or not there is any significant difference (such as a variation in luminance value, of which the magnitude exceeds a predetermined threshold value) between those two image frames. In this case, the “result of the previous analysis” refers to the result of the analysis that was performed on an image frame when the optimization enter button  111  was pressed by the operator last time. 
     And if there is any significant difference between them, the processor  107  decides that the time has come when the operator has to decide whether he or she wants the image quality to be controlled (or optimized) now or not (such a timing will be referred to herein as an “optimization timing”) and gives a notification to him or her or that by displaying a sign on the monitor. Instead of displaying such a sign on the monitor  108 , the operator may also be notified by blinking a light-emitting device such as an LED built in the optimization enter button  111  on the control panel or an LED (not shown) that is provided separately from the button. 
     It should be noted that the terms “control” and “optimization” herein have the same meaning. The “optimization processing” to be described later is a kind of processing for improving the image quality. That is why after the optimization processing has been done, it can be said that the image quality is higher than ever. For that reason, such a state in which the image quality has been improved to the maximum degree up to a certain point in time will be referred to herein as either an “optimized” state or a “controlled” state. 
       FIG. 3  shows the sequence of the processing to get done by the processor  107  to determine whether it is the optimization timing or not. 
     First of all, in Step  201 , the processor  107  divides a given image frame into a number of sub-areas, each having a width M and a height N that may have been set to be arbitrary values in advance. In this preferred embodiment, those sub-areas are defined to be completely separate ones that never overlap with each other. However, this is just an example and those sub-areas could overlap with each other.  FIG. 4  illustrates two sub-areas that overlap with each other. The respective sub-areas may also be defined in this manner, too. 
     Next, in Step  202 , the processor  107  calculates the feature quantity of every sub-area. In this preferred embodiment, the standard deviation of the luminance values of all pixels in each sub-area is used as the feature quantity. As the feature quantity, not just the standard deviation but also some statistic such as an average, a median, or a coefficient of variation or the sum of power spectra of the images could be used as well. 
     Subsequently, in Step  203 , the processor  107  retrieves the previous sub-area feature quantity from the parameter storage section  109 , calculates the absolute value of the difference between the previous and current feature quantities on a sub-area basis and then calculates the sum of those differences, thereby obtaining a feature quantity difference Diff between the previous and current image frames. 
     Thereafter, in Step  204 , the processor  107  compares a preset threshold value Th to Diff. If the processor  107  finds Diff greater than the threshold value Th, then the processor  107  decides that it is time to update the image quality. Then, the process advances to Step  205 . 
     In Step  205 , the processor  107  notifies the operator that the optimization timing has come. In this processing step, the notification may be made either by displaying a sign on the monitor  108  or by blinking the light-emitting device just as described above. 
     Finally, in Step  206 , the processor  107  stores the feature quantity of each sub-area that has been calculated this time in the parameter storage section  109  so that the feature quantity can be used for analysis next time. 
     When the sign indicating that the optimization timing has come is displayed in Step  205 , the operator can get the image optimized by pressing the optimization enter button  111 . 
     Next, it will be described what processing will be performed after such a sign indicating that the optimization timing has come has been displayed. 
       FIG. 5  is a flowchart showing the procedure of the processing to get done after the operator has been notified. 
     First, in Step  301 , the processor  107  determines whether the operator has pressed the optimization enter button  111  or the optimization cancel button  112 . If the optimization enter button  111  has been pressed, the process advances to Step  302 . On the other hand, if the optimization cancel button  112  has been pressed, then the process advances to Step  307 . 
     If the optimization enter button  111  has been pressed, the processor  107  stores in Step  302  the current image quality control parameters in the parameter storage section  109  just before the settings are changed. And the processor  107  performs a series of processing steps  303  to, thereby calculating image quality control parameters to optimize the image and entering those parameters into the image constructing section  105 . Thereafter, in Step  306 , the image constructing section  105  reconstructs an image frame based on the image quality control parameters entered and then outputs the reconstructed image frame to the monitor  108 . 
     Specifically, those processing steps  303  through  306  are performed in the following manner. 
     First, the image quality control parameters for optimizing the image may be calculated by any of various methods. As an example, the processing of optimizing a TGC (time gain control) value will be described. 
     As used herein, the “TGC” means a control to be performed to reduce a variation in the lightness of an image within an image frame. Generally speaking, if an ultrasonic wave is used, its reflected wave will attenuate more steeply when reflected from a deeper region under the skin than when reflected from a shallower region under the skin. That is why an image representing that deeper region tends to darken. Thus, to overcome such a problem, the ultrasonic diagnostic apparatus  100  of this preferred embodiment classifies the depths under the skin  2  into seven levels, for example, and is ready to control the image lightness for each of those seven grades. As a result, the gain control can be done on a depth-by-depth basis so that an image frame can always be displayed with its lightness controlled according to the operator&#39;s preference, no matter whether the image frame represents a shallow region or a deep region under the skin. For instance, the image frame can always be displayed with its lightness kept constant at each and every depth. Or an image frame representing an internal body tissue that is located deep under the skin may be displayed with an increased lightness. And it is the TGC value that is used in such a depth-by-depth gain control. 
     The processing of optimizing the TGC value may be carried out as follows. Specifically, in Step  303 , the processor  107  calculates the average of luminance values for each depth level under the skin  2  in the image frame. Next, in Step  304 , the processor  107  determines a TGC value, which will be a predetermined reference value when multiplied with the average that has been calculated in the previous step, on a depth-by-depth basis again. In this preferred embodiment, the depths under the skin  2  are classified into seven levels and the image quality may be controlled adaptively according to the depth in question. 
     Then, in Step  305 , the processor  107  enters the TGC value thus determined as an image quality control parameter into the image constructing section  105 . 
     And in Step  306 , the image constructing section  105  reconstructs an image frame based on the image quality control parameters entered and then outputs the image frame thus obtained to the monitor  108 . 
     In some cases, even if the operator has pressed the optimization enter button  111 , he or she may press the optimization cancel button  112  after the optimization has been done. 
     In that case, the process advances to Step  307 , in which the processor  107  sees if any parameter is stored in the parameter storage section  109 . As can be seen from the processing step  302 , if the optimization enter button  111  has ever been pressed at least once, some parameter will be stored in the parameter storage section  109 . 
     But if the optimization enter button  111  has never been pressed yet, no parameters will be stored in the parameter storage section  109 . In that case, the processor  107  ends this processing. But if any parameter is stored in the parameter storage section  109 , then the process advances to Step  308 , in which the processor  107  replaces the threshold value Th with the difference Diff in feature quantity between the image frames. As a result, that Diff value will be used as the threshold value when it is determined next time whether or not it is time to make optimization. Then, the image frame on the monitor  108  does not change at all. 
     Next, in Step  309 , the processor  107  retrieves the TGC value just before the optimization from the parameter storage section  109  and enters it as an image quality control parameter into the image constructing section  105 . This means that the optimization processing that has been carried out once has been canceled. Then, in Step  310 , the image constructing section  105  reconstructs an image frame based on the image quality control parameter entered and then outputs the reconstructed image frame to the monitor  108 . 
     It should be noted that this processing step of entering the image quality control parameter just before the optimization into the image constructing section  105  is only an example. Anyway, as the user is not satisfied with the currently presented image, the way of displaying that image is preferably changed again. For that reason, instead of adopting the image quality control parameter just before the optimization, the types of image processing may be changed again and again until the user gets fully satisfied. 
     If the operator has pressed the optimization cancel button  112 , it means that he or she does not want to get the image quality optimized at that point in time. In other words, it indicates that the optimization standard presented at that point in time by the ultrasonic diagnostic apparatus  100  does not agree with the operator&#39;s. Thus, by changing the threshold value as described above, the threshold value can be even closer to the operator&#39;s optimization standard. 
     In the foregoing description of preferred embodiments, the frame storage section  106  is supposed to accumulate image frames of a tomographic image. However, image feature quantities, which are results of analysis on image frames, may be accumulated instead of the image frames themselves. As a result, the space left in the frame memory section  106  can saved. 
     Also, in the preferred embodiment described above, the user interface means that allows the operator to indicate whether or not he or she wants to get optimization done now is supposed to be the optimization enter button  111  and the optimization cancel button  112 , which are pieces of hardware. However, this is just an example. Alternatively, the monitor  108  may be implemented as a touchscreen panel that displays the buttons  111  and  112  thereon. In that case, portions of the touchscreen panel corresponding to the respective display locations of the optimization enter and cancel buttons  111  and  112  are used as the user interface means. Still alternatively, two dialog boxes that perform the same function as the buttons  111  and  112  may be displayed on the monitor  108  so as to be selectively entered with a mouse or a keyboard. In that case, the user interface means is the mouse or the keyboard. 
     The procedures of processing that have been described with reference to the flowchart shown in  FIGS. 3 and 5  may be carried out as a computer program to be executed by the processor  107 . Such a computer program may be circulated on the market by being either stored on a storage medium such as a CD-ROM or downloaded over telecommunications lines such as the Internet. The processor  107  of the ultrasonic diagnostic apparatus  100  may be implemented as a general-purpose processor (i.e., a semiconductor integrated circuit) that can execute the computer program. Alternatively, the processor  107  may also be a dedicated processor in which such a computer program has been installed. 
     INDUSTRIAL APPLICABILITY 
     The ultrasonic diagnostic apparatus of the present invention can notify the user that it may be high time to optimize the image quality of a subject&#39;s tomographic image and prompts the user to decide by him- or herself whether or not the quality of the image presented should be optimized now. Consequently, according to the present invention, the user can check out the image after having its quality controlled according to his or her preference. 
     REFERENCE SIGNS LIST 
     
         
           100  ultrasonic diagnostic apparatus 
           101  ultrasonic probe 
           102  A/D converter 
           103  beam former 
           104  detecting section 
           105  image constructing section 
           106  frame memory section 
           107  processor 
           108  monitor 
           109  parameter storage section 
           111  optimization enter button 
           112  optimization cancel button