Abstract:
The dynamic property of a blood flow in a superficial blood vessel of a living body are constructed. 
     A physical stimulus is given to the blood flow, and an ultrasonic response from the blood flow to the physical stimulus is measured and evaluated, which allows the blood property to be evaluated noninvasively and dynamically. Therefore, a medical check and a lifestyle-related diseases prevention effect are promising.

Description:
CLAIM OF PRIORITY 
       [0001]    The present application claims priority from Japanese application JP 2007-153491 filed on Jun. 11, 2007, the content of which is hereby incorporated by reference into this application. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to an apparatus for measuring and evaluating a blood flow in a superficial blood vessel using a high-frequency ultrasound. 
         [0004]    2. Description of the Related Art 
         [0005]    Recently, lifestyle-related diseases including hyperlipidemia, high blood pressure, diabetes, and visceral fat obesity becomes an issue, and there is an increasing need for early detection or prevention of the lifestyle-related diseases. 
         [0006]    There is an ultrasonic B-mode imaging technique for evaluating a degree of blood cell aggregation which is a potential risk factor of incidence or progression of arterial sclerosis, or thrombus formation (for example, see Japanese Patent Application Laid-Open No. 2005-110724). There is a study on simulation for frequency dependence of ultrasonic back scattering on a difference in degree of red blood cells aggregation (for example, see David Savery and Guy Cloutier, “A point process approach to assess the frequency dependence of ultrasound back scattering by aggregating red blood cells”, J. Acoust. Soc. Am. 110(6), 2001). 
         [0007]    In the method disclosed in Japanese Patent Application Laid-Open No. 2005-110724, a dynamic property of the blood cannot be evaluated. Although an apparatus to measure the dynamic property of the red blood cells in vitro exists, its measurement results do not indicate blood flow kinetics in the living body. That is, currently the method for invasively measuring and evaluating the dynamic property of the blood flow in human beings in vivo is not established. 
         [0008]    In David Savery and Guy Cloutier, “A point process approach to assess the frequency dependence of ultrasound back scattering by aggregating red blood cells”, J. Acoust. Soc. Am. 110(6), 2001, coagulation time of pig&#39;s blood sample is assumed to represent red blood cell aggregation rate, the degree of back scattering in high frequencies of 12.5 MHz or more is estimated by simulation based on experimental data in relatively low frequencies of 3.5 MHz to 12.5 MHz. 
         [0009]    Human skin is acoustically different individually, therefore it is difficult to measure the blood flow in human skin under the same condition without the influence of individual differences. 
         [0010]    An object of the invention is to provide means for measuring and evaluating the dynamic property of the blood flow in the superficial blood vessels of human beings in vivo. Another object of the invention is to provide a method for measuring the ultrasound wave under the same condition irrespective of the influence of individual differences. 
       SUMMARY OF THE INVENTION 
       [0011]    In order to solve the problem, the present invention is a blood flow measuring and evaluating system including a signal processing unit for transmitting and receiving an ultrasound to and from the superficial blood vessel of the living body to process the acoustic received signal. 
         [0012]    In accordance with an aspect of the invention, an ultrasonic radiation apparatus includes an ultrasonic radiation unit for irradiating a test specimen with an ultrasonic signal; a reception unit for receiving an ultrasound from the test specimen; an image data processing unit for producing plural pieces of image data based on a signal received by the reception unit; a blood vessel signal estimating unit for estimating a range of a blood vessel corresponding portion of the test specimen from the image data; a computing unit for performing Fourier transform to the blood vessel corresponding portion; and an evaluation unit for evaluating blood state information on the test specimen based on computation result of the computing unit. 
         [0013]    In the typical effect of the present invention disclosed in the present application, the dynamic property of the blood can noninvasively be evaluated. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]      FIGS. 1A and 1B  show an ultrasonic data obtaining apparatus aimed at measurement of a superficial blood vessel in a living body; 
           [0015]      FIG. 2  shows an example of a B mode image of a blood flow in the superficial blood vessel; 
           [0016]      FIG. 3  is a flowchart showing a sequence for measuring a blood state; 
           [0017]      FIG. 4  shows a result example of FFT computation processing of the B mode image in stimulus response; 
           [0018]      FIG. 5  shows an example of a change in evaluating ultrasonic signal intensity in the stimulus response; 
           [0019]      FIGS. 6A and 6B  show examples of stimulus given to evaluate the blood state; 
           [0020]      FIG. 7  shows a method for reducing measurement variations according to individual differences or a measurement region and a measurement condition of the same subject; 
           [0021]      FIG. 8  shows flowchart showing a noise reducing method; 
           [0022]      FIG. 9  is a flowchart showing a method for measuring reflection intensity by specifying an A mode measurement position in the B mode image; 
           [0023]      FIG. 10  is a flowchart for measuring and evaluating a degree of blood cell aggregation in the A mode; 
           [0024]      FIG. 11  shows measured data of a reflection echo from an auricle of a rabbit in the A mode; 
           [0025]      FIG. 12  shows an example of an apparatus configuration; 
           [0026]      FIG. 13  shows an example of the apparatus configuration; 
           [0027]      FIGS. 14A and 14B  show an example of the apparatus configuration; 
           [0028]      FIG. 15  shows a schematic view of a blood-cell spatial frequency distribution; and 
           [0029]      FIGS. 16A ,  16 B and  16 C show tables for evaluating a blood property and a table of measured data of blood test. 
       
    
    
     DESCRIPTION OF REFERENCE NUMERALS 
       [0000]    
       
           101 : Human hand 
           102 : Target blood vessel such as superficial blood vessel 
           103 : Transducer 
           104 : Antenna 
           105 : Radio wave 
           106 : Ultrasonic measuring apparatus 
           107 : Control unit for transmitting signal 
           108 : Signal processing unit for processing received wave signal 
           109 : Storage unit 
           110 : Skin 
           111 : Blood property determination unit 
           112 : Image data processing unit 
           113 : Pressure applying unit 
           114 : Time measuring unit 
           115 : Warning unit 
           201 : Example of B mode image of blood flow in normal individual 
           202 : Example of B mode image of blood flow in WHHL Rabbit 
           203 : Blood vessel wall 
           301 : Blood flow is stopped by pressing blood vessel 
           302 : Temporal imaging of B-mode still image in a process of releasing press 
           303 : Determination of blood flow area whose data is processed 
           304 : FFT computation processing 
           305 : Computation of integrated signal value 
           306 : Quadratic differential processing 
           307 : Computation of maximum value 
           308 : Display of result 
           601 : Blood flow is stopped by applying pressure on superficial blood vessel 
           602 : Increased blood cell aggregation 
           603 : Pressure on blood vessel is released 
           604 : Decreased blood cell aggregation in a process of restart of the blood flow 
           605 : Stimulus such as lifting of arm is given to blood flow 
           606 : Blood pressure is locally increased by gravity 
           607 : Blood flow velocity is increased 
           608 : Detection of target size being reduced by blood cell aggregation decrease 
           701 : Hair 
           702 : Intercalated portion 
           800 : Start measurement 
           801 : Control pressure-applying method on blood vessel 
           802 : Perform B mode imaging 
           803 : Estimate blood vessel position 
           804 : Measure reflection intensity 
           805 : Blood vessel position is largely changed? 
           806 : N-time measurements is ended? 
           807 : Perform noise reduction processing 
           808 : M-time measurements is ended? 
           809 : End measurement 
           810 : Perform B-mode imaging and select raster 
           811 : Perform A-mode imaging 
           901 : Input unit 
           902 : A/B mode switching unit 
           903 : Memory 
           904 : Blood vessel position estimating unit 
           905 : Blood flow signal selecting unit 
           906 : Spatial frequency computing unit 
           907 : Blood property estimating unit 
           908 : Raster control unit 
           909 : Display unit 
           1000 : CCD camera 
           1001 : Display image 
           1002 : Camera image 
           1003 : Transducer position display 
       
     
       DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0091]    Preferred embodiments of the present invention will be described below with reference to the drawings. 
       First Embodiment 
       [0092]    In a first embodiment, a measurement target is a human being. However, the measurement target is not limited to the human being, but the invention can be used for not only a human body such as an experimental animal but also measurement and evaluation for a property of a fluid flowing in a relatively superficial part of a certain substance. 
         [0093]      FIGS. 1A and 1B  show a configuration of an ultrasonic data obtaining apparatus aimed at measurement of a superficial blood vessel in a living body.  FIG. 1A  shows the configuration of the apparatus, and  FIG. 1B  particularly shows a configuration of an ultrasonic transducer. An ultrasonic transducer  103  is put on a skin  110  and an ultrasound is transmitted to a target blood vessel  102  such as the superficial blood vessel of a living body  101  and received the signal from it. The ultrasonic transducer  103  receives a control signal for transmitting the ultrasound from an ultrasonic measuring apparatus  106  and send an acoustic signal received from the measurement object to the apparatus  106  in the form of a wireless signal  105  through an antenna  104 . However, the control signal and the acoustic reception signal are not limited to the wireless signal  105 , but the ultrasonic transducer  103  and the ultrasonic measuring apparatus  106  may be connected to each other with a cable to transmit and receive the signals. 
         [0094]    In addition to a method for fixing the ultrasonic transducer  103  by human hands, movement and positioning of the ultrasonic transducer  103  can be performed by attaching the ultrasonic transducer  103  to a jig such as an xyz stage which enables three-dimensional positioning. In addition to position-fixing of the ultrasonic transducer  103  to the superficial blood vessel by checking with eyes, there is also method using optical measurement technique. Hemoglobin in the blood has relatively high near-infrared absorbance in body tissue, and reflection intensity of visible light (such as green light) is high in a region where the superficial blood vessel exists. Therefore, the ultrasonic transducer  103  can be positioned by detecting the region where the superficial blood vessel exists. 
         [0095]    The ultrasonic measuring apparatus  106  includes a control unit  107  used to transmit and receive the ultrasound, a signal processing unit  108  used to process the acoustic signal received from the measurement object, a storage unit  109  in which data is stored, and a display unit  909  used to display measurement results. 
         [0096]    The signal processing unit  108  includes a blood property determination unit  11 . In the case of a B mode, the signal processing unit  108  includes an image data processing unit  112 . 
         [0097]    The display unit  909  displays the received signal and signal processing result in the case where the ultrasonic measuring apparatus is in an A mode, and the display unit  909  displays an image generated by the image data processing unit  112  in the case where the ultrasonic measuring apparatus is in the B mode. An electronically scanning method in which a well-known phased array is used may be adopted to take a B-mode image, or a mechanically scanning method in which, with the use of one-channel transducer and the accompanied control circuit and signal processing circuit, the transducer is mechanically scanned with a motor may be adopted to take a B-mode image. Advantages of the electronically scanning method are that not a continuous raster but a discrete sample volume can be specified in lateral direction and a focal position can be controlled in a depth direction. On the other hand, the mechanically scanning method can realize miniaturization of the apparatus, low power consumption, and low cost. 
         [0098]    A specific method for measuring and evaluating the dynamic property of the blood will be described below. In the ultrasound, as a frequency is high, the smaller object can be visualized, while a distance in which the ultrasound reaches the inside of the living body becomes shallower. In the ultrasonic frequency with which the living body is radiated, the ultrasound having high frequencies of about 30 MHz or more is effectively used in measuring the blood flow of superficial blood vessel. 
         [0099]      FIG. 2  shows an example of the B mode image of the blood flow in the actual superficial blood vessel. A rabbit is the measurement target.  FIG. 2  shows an example  201  of a blood flow image in a normal individual and an example  202  of a blood flow image in a WHHL Rabbit (Watanabe heritable hyperlipidemic rabbit). The WHHL Rabbit has a genetically deficiency of LDL (low-density lipoprotein) receptor, hypercholesterolemia appears from birth in the WHHL Rabbit, and serum triglyceride level of the WHHL Rabbit is over ten times higher than that of the normal individual. In  FIG. 2 , a blood vessel wall  203  is observed as a layer having higher brightness values in the image. The high-brightness portion in the blood mainly represents the existence of the red blood cells. It is found that the blood is observed in higher brightness in the individual of hypercholesterolemia which has red blood cells aggregation, compared to the normal individual. The samples of blood having different properties are dynamically measured and evaluated by the following procedure. 
         [0100]      FIG. 3  is a flowchart showing a sequence for dynamically measuring and evaluating the blood property. The blood flow is temporarily stopped by applying a physical stimulus such as the pressure on the superficial blood vessel (S 301 ). The manipulation is effectively performed using a pressure applying unit  113  which stimulates a position far away from a blood flow observation region by using the ultrasonic transducer  103 . Although an avascularization band may be used in blood collection,  FIG. 1  shows the ultrasonic transducer  103  including the pressure applying unit  113 . The pressure applying unit  113  can be attached to not the ultrasonic transducer  103  but the ultrasonic measuring apparatus  106 , and the first embodiment is not limited to the configuration shown in  FIG. 1 . 
         [0101]    Applying pressure on the superficial blood vessel is not performed for more than one minute, because sometimes the long-time avascularization causes the blood coagulation to form hematoma. Therefore, the apparatus including a time measuring unit  114  such as a timer is effectively formed such that a warning unit  115  provided a warning after one minute or such that the pressure applied blood vessel is released. The time measuring unit  114  is provided on the side of the ultrasonic measuring apparatus  106 , and only a command signal for releasing the pressed blood vessel is effectively transmitted through a cable or a wireless signal  105  to manipulate the pressure applying unit  113 . Alternatively, the time measuring unit  114  may be provided on the side of the ultrasonic transducer  103  or pressure applying unit  113 . From the start of pressure applying on the blood vessel to the pressure release, plural images are captured with time (S 302 ). For example, the images in the following three states are obtained. (a) The state in which pressure is applied on the blood vessel to stop the blood flow. (b) The state in which the blood begin to flow when the pressure is released. (c) The state in which a predetermined time elapsed after the pressure is released. 
         [0102]    A blood flow area (rectangular or raster) to process is determined in the captured image using the blood vessel position estimating unit and the blood flow signal selecting unit (S 303 ). The processing is performed as follows. An arbitrary size of rectangular area (or raster) is determined by checking visually the B-mode image. In this case, it is effective that software of the apparatus has the function. Then, the position where the pixel values are changed in the image is detected by differential processing, because the pixel values are largely changed at a boundary between the blood vessel and the blood (blood vessel portion has the high intensity pixel values and the blood has the low intensity values). This process enables the blood vessel position to be identified and the rectangular area (or raster) for data processing to be selected inside the blood vessel. 
         [0103]    The spatial frequency computing unit performs FFT processing in the selected area (S 304 ). FFT may be performed two-dimensionally or one-dimensionally.  FIG. 4  shows an example of the one-dimensional processing result. As can be seen from the result of  FIG. 4 , a difference in blood between the Normal Rabbit and the WHHL Rabbit can be detected by a time course of a component near a spatial frequency of 0.3/pixel. A wavelength corresponding to about three pixels is a detection limit size of a blood speckle as the current measurement target, and the blood property can dynamically be evaluated by observing a variation of the component. In the current measurement, because the one pixel corresponds to 20 micrometers, the three pixels do to 60 micrometers, namely the aggregation which size is about eight times diameter of the largest blood cells, red blood cell, is observed. 
         [0104]    The speckle size is a result of two-dimensional convolution between a spatial distribution of measurement objects and a point response function of the measuring system. In the case where a shape of the point response function of the measuring system is not changed, the spatial distribution of objects represents the speckle size. In the WHHL Rabbit, the blood flow is not largely changed by the pressure applying and release because blood cells aggregation increases basically. On the other hand, in the Normal Rabbit, the aggregation does not increase basically. However, the aggregation increases when the blood flow is interrupted by applying pressure on blood vessel, and the aggregation disappears when the blood flows again by pressure release. In the measuring system, it is estimated that the size of the aggregated blood-cell cluster is substantially equal to magnitude of the point response function, so that the change caused by the aggregation appears most remarkably at the limit of the speckle size.  FIG. 15  is a schematic view explaining the aggregation of the blood cells. A horizontal axis represents the spatial frequency. When the aggregation of the blood cells increases, the spatial frequency distribution of the blood cell is shifted toward the low-frequency side (arrow in  FIG. 15 ). When a skirt portion of a sensitivity distribution of the received signal exists in an area surrounded by a dotted line, the change of aggregation can be analyzed with high sensitivity by processing the signals in the area surrounded by the dotted line. 
         [0105]    Therefore, the degree of blood cell aggregation can be investigated by focusing on the signal of the skirt portion of the spatial frequency distribution of the signal shown in  FIG. 4 . Obviously, the ultrasound frequency is increased to decrease the speckle size, and the sensitivity to a change of aggregation can be increased. However, attenuation of the ultrasound is increased to hardly receive the ultrasonic signal. From the standpoints of the ultrasonic attenuation and sensitivity to the change of aggregation, it is necessary that the optimum frequency be selected according to a distance from a body surface to the blood vessel. 
         [0106]    As used herein, the spatial frequency shall mean fineness of a periodic structure constituting the image. The spatial frequency is represented by the number of periods having sine intensity distributions in unit length. The Fourier transform is performed to the image to break down the image into the spatial frequency components, which enables the image to be evaluated. The upper limit of the spatial frequency which becomes the measurement target is set not lower than the blood cell size, and desirably the upper limit of the spatial frequency is set to about ⅛ (μm −1 ) of an inverse number of the blood cell. Although the rabbit used in the current experiment is in the congenitally disease state, practically it is necessary to detect the change in blood property before the disease is developed. Therefore, the spatial frequencies higher than 1/60 (μm −1 ) which is of the experimental detection limit shown in  FIG. 4  is required for the lower limit of the spatial frequency. Thus, from the standpoint of the spatial frequency, desirably the apparatus has the measurement range of 1/60 to ⅛ (μm −1 ). On the other hand, the spatial frequency in a depth direction and the spatial frequency in a lateral direction are discussed as follows. First, as to the depth direction, in the ultrasonic imaging, an envelope of the received signal is detected in order to ensure a wide dynamic range, and logarithm compression is performed to the envelope of the received signal to produce the image. The spatial frequency is determined by multiplying a center frequency of the actual acoustic transmission wave by the number of cycles of the acoustic transmission wave in order to detect the envelope of the received signal. Second, as to the lateral direction, a beam width determining the spatial frequency can be obtained by the following equation. Because directionality of a rectangular transducer is expressed by sin(ka·sin θ)/(ka·sin θ), sin(ka·sin θ)/(ka·sin θ)=0.5 is substantially obtained in the case of ka·sin θ=1.9. Where k is a wave number, 2a is a bore diameter, and θ is a directivity angle. Assuming that L is a beam width, F is a focal distance, f is an ultrasonic frequency, and v is an acoustic velocity in the living body, L satisfying Formula 1 is expressed as follows. 
         [0000]    
       
         
           
             
               
                 
                   
                     
                       
                         2 
                          
                         π 
                          
                         
                             
                         
                          
                         fa 
                       
                       v 
                     
                      
                     
                       sin 
                        
                       
                         ( 
                         
                           
                             tan 
                             
                               - 
                               1 
                             
                           
                            
                           
                             L 
                             
                               2 
                                
                               F 
                             
                           
                         
                         ) 
                       
                     
                   
                   = 
                   1.9 
                 
               
               
                 
                   [ 
                   
                     Formula 
                      
                     
                         
                     
                      
                     1 
                   
                   ] 
                 
               
             
           
         
       
     
         [0107]    That is, Formula 2 can be obtained. 
         [0000]    
       
         
           
             
               
                 
                   L 
                   = 
                   
                     2 
                      
                     F 
                      
                     
                         
                     
                      
                     
                       tan 
                       ( 
                       
                         
                           sin 
                           
                             - 
                             1 
                           
                         
                         ( 
                         
                           v 
                           
                             π 
                              
                             
                                 
                             
                              
                             fa 
                           
                         
                         ) 
                       
                       ) 
                     
                   
                 
               
               
                 
                   [ 
                   
                     Formula 
                      
                     
                         
                     
                      
                     2 
                   
                   ] 
                 
               
             
           
         
       
     
         [0108]    The information on the blood cell property is obtained by determining the focal distance F, the ultrasonic frequency f, and the bore diameter width a, and the apparatus can be configured so as to suitably estimate the blood cell property. 
         [0109]    The state of  FIG. 4  is evaluated by the following method. An integration value is computed for the signal near the spatial frequency of 0.3 (in this case, 0.275 to 0.3) (S 305 ). The integration value is computed in each of the states (a), (b), and (c) for  302 .  FIG. 5  and Table of  FIG. 16A  show result examples. The WHHL Rabbit has the small change in signal intensity compared with the Normal Rabbit. The blood property is evaluated based on the change in signal intensity. 
         [0110]    In evaluating the blood property, the pieces of information on the blood cell property and blood property are obtained from the information on the blood cell property obtained by the FFT computation processing. That is, the information on the blood cell property and the corresponding pieces of information on the blood cell property and blood property are read from a blood cell property and blood property information table stored in the blood property estimating unit. 
         [0111]    The following processing is performed to evaluate the state of the change with time. Quadratic differential filtering processing of a=[1 −2 1] is performed to a one-dimensional array (in this case, numerical values of (a), (b), and (c) in Table 1A) of the change with time of the computed integration value (S 306 ), and the maximum absolute value of the result is determined (S 307 ). It is assumed that a SS value is the maximum absolute value. Table of  FIG. 16B  shows an example of the result. A property of the blood flow in the living body can be evaluated by the comparison of the values in Table 1B, and the all the conditions such as the aggregation state of the blood cell and viscosity represent the property of the blood flow. For example, when a threshold is set to zero, the state of the blood flow can be evaluated such that probably the blood is not healthy. In addition, there is a method for evaluating mean gradient. Table of  FIG. 16C  shows a reference data of the result of the blood test for the WHHL Rabbit and Normal Rabbit used in the experiment. In the WHHL Rabbit, the total cholesterol exhibits about ten times the Normal Rabbit. In the lipid-rich blood, because the blood cells are easily aggregated, the sluggish response to pressure release, is observed and therefore the SS value is zero or lower. 
         [0112]    The evaluation result of the blood flow obtained based on the measurement result is displayed on the data display unit  909  of the ultrasonic measuring apparatus (S 308 ), and the evaluation result is stored in the storage unit  109  if needed. 
         [0113]    The method for performing the evaluation with three points of data obtained with time is described by way of example. However, the time scale used is not limited to the range of the three points, but longer time course from the pressure release to the steady state may be measured to perform the evaluation. 
         [0114]    In the above-described method, the pressure is used as the physical stimulus related to the blood flow velocity such that the degree of blood cell aggregation is increased as shown in  FIG. 6A . The blood flow is stopped by applying pressure on the superficial blood vessel using the pressure applying unit  113  (S 601 ). That is, the degree of blood cell aggregation is increased (S 602 ). Then, the pressure on the blood vessel is released (S 603 ), and the increased blood cell aggregation begins to be decreased in the process of restart of the blood flow (S 604 ). A method for measuring and evaluating the blood flow in the middle of the transient response is shown. Applying the pressure on the blood vessel, it is necessary that the region of pressure applying is located away from the blood flow measurement region to an extent. That is, it is necessary that the pressure applying unit  113  and the ultrasonic transducer  103  is disposed with a predetermined distance. When the blood vessel position in the measurement region is largely moved, the measured section is shifted, which possibly results in disadvantages. On the other hand, as shown in  FIG. 6B , the stimulus can be applied such that blood cell aggregation is decreased. When the stimulus such as the lifting of an arm is applied (S 605 ), the blood pressure is locally increased by gravity (S 606 ). In the case where the blood has small viscous resistance to the blood cell (so-called runny), the blood flow velocity is largely changed when the hand is raised. On the other hand, in the case where the blood has large viscous resistance to the blood cell (so-called sticky), the blood flow velocity is not so changed. The difference in change can similarly be evaluated by the above-described method. 
         [0115]    The case in which measurement variations caused by the individual differences or the measurement region and measurement condition even in the same subject are decreased will be described below with reference to  FIG. 7 . When the signal is measured from the blood vessel in the living body by the ultrasonic echo method, the state of propagation path has a large influence on the signal intensity or frequency characteristics. A pulse transmitted from the ultrasonic transducer  103  enters the living body through the intercalated portion  702  between the transducer and surface of the body. The pulse propagates while being attenuated and scattered in the skin  110  and the living body tissues located between the skin  110  and the target blood vessel  102 , and the pulse reaches the blood vessel  102 . As used herein, the intercalated portion  702  shall means an acoustic propagation path which is formed by an ultrasound gel between the skin  110  and the ultrasonic transducer  103 , and the intercalated portion  702  includes a hair  702  on the body surface. The echo signal reflected from the blood cell in the blood vessel reaches the transducer through the reverse path, and the echo signal is converted into an electrical signal. The acoustic characteristics of the blood vessel wall heavily depends on individual differences in the acoustical path through superficial intercalated portion  702 , the skin  110 , and the living body tissue between the skin and the target blood vessel  102 . Even in the same person, the surface state of the skin depends on the measurement condition, and usually the same surface state is hardly kept. Therefore, the propagation path has a strong influence on the intensity and frequency characteristics of the echo signal derived from the blood cell. It is difficult to remove the influence of the propagation path to obtain only the signal derived from the blood cell property in one-time measurement. Therefore, the blood flow velocity is controlled by applying the pressure on blood vessel or changing the blood pressure, and only the signal component derived from the blood cell property is changed to perform the measurement. This enables the signal derived from the blood cell property to be separated from the influence of the propagation path. 
         [0116]    A noise reduction method will be described with reference to  FIG. 10 . There are two factors which cause the noise or measurement variations. First, when the echo signals from tissues except for the blood cell are mixed, relative sensitivity of the measurement is lowered to the change in blood flow property. Second, in the case where an artery is used as the target blood vessel, density of the blood cell per unit volume fluctuates by pulsation of the artery, which causes the measurement variations. The noise reduction method will be described below with reference to a flowchart of  FIG. 10 . After the measurement start (S 800 ), the blood vessel pressing method is controlled (S 801 ). In this case, pressure-applying method on the blood vessel pressing is controlled using the pressure applying unit  113 . Alternatively, the control may be performed using a device such as a cuff. Alternatively, pressure is applied on the blood vessel temporally to interrupt the blood flow, and the elapsed time since the blood flow restarts again may be used as a parameter. Then, the capturing of the B-mode image is performed (S 802 ), and the blood vessel position is estimated by binarization or a region growing in which an area having an arbitrary shape is extracted (S 803 ). The reflection intensity is measured (S 804 ). The reflection intensity is measured N times, and the data is obtained for an interval not lower than one heart beat. The influence of the measurement variations by the pulsation is decreased by averaging. In N-time measurement, when the blood vessel position is periodically estimated (S 803 ), whether or not the measurement region is largely shifted can be checked by checking the large position shift of the blood vessel position (S 805 ). When the measurement region is largely shifted, the blood vessel position is corrected to take the data or the measurement is started again from the beginning. After the N-time measurements are performed (S 806 ), the averaging processing of N times or only the fluctuation component is extracted. This enables the noise to be reduced (S 807 ). The sensitivity for the signal component reflected by the blood property can be improved by extracting only the fluctuation component. The extraction of the fluctuation component is performed by removing the DC component in the frequency space, or by removing the trend on the temporal axis. The measurement processing is repeated while pressure-applying method on the blood vessel is changed. After the measurement shown in  FIG. 8  or  9  is completed, the blood property can be measured by the ultrasonic echo method. 
       Second Embodiment 
       [0117]    In a second embodiment, an operator specifies the A-mode measurement position from the B-mode image, and the operator performs the measurement of the reflection intensity. The point different from the first embodiment will mainly be described below. Other configurations except for the point described below are basically similar to those of the first embodiment.  FIG. 12  shows a configuration of an apparatus of the second embodiment. In the second embodiment, an A/B mode switching unit  902  can switch between the A mode and the B mode in response to an input from an input unit  901 . When the raster is fixed by the A-mode switching, the acoustic received wave data of the acoustic received wave processing unit  108  is recorded in the memory  903 . In the apparatus configuration of the second embodiment, the data is displayed on the display unit  909  as the computation result concerning the blood property through the blood vessel position estimating unit  904 , blood flow signal selecting unit  905 , spatial frequency computing unit  906 , and blood property estimating unit  907 . 
         [0118]      FIG. 9  is a processing flowchart of the second embodiment. The operator selects the raster at the same time as the B-mode imaging (S 810 ). Because the A-mode imaging is performed with the raster, so that a data sampling interval can be improved to 10 to 100 times, and the various fluctuation-component extracting method described in the first embodiment can be adopted. That is, because the B-mode imaging is a technique of repeating the A-mode imaging by the number of raster lines while the raster is moved, the data sampling interval (not the sampling interval of A/D conversion, but time interval during which data is obtained from a certain sample volume) is decreased by the number of raster lines when focusing attention to one raster. However, in the A-mode imaging, it is necessary that the blood vessel position be correctly estimated to confirm whether or not the echo is precisely obtained from reflection and scattering body in the blood vessel. Therefore, the B-mode imaging is periodically performed and the operator visually confirms that the echo is precisely obtained from reflection and scattering body in the blood vessel. Alternatively, the fluctuation is checked during the sampling time.  FIG. 11  shows a reflection echo from an ear of the rabbit in the form of RF data in the A mode. Hereinafter, a continuous set of A modes is referred to as packet. The pieces of data at the same sampling point in the packet are arranged, and the pieces of data is divided into the temporally changed sampling point and the temporally unchanged sampling point, which allows the position of the blood vessel to be estimated. Assuming that a i,N  is A-mode data at a data obtaining number N and a sampling point i, an A-mode data row is expressed by A=(a 1,N , a 2,N , . . . , and a i,N ). A data set Bi=(a i,1 , a i,2 , . . . , a i,N ) in which data is reorganized in each data obtaining number in the packet is produced from the A-mode data row to check the change in data in a data obtaining number direction (N direction). Because the signal from the tissue has the small temporal change while the data from the blood vessel has the large temporal fluctuation component, the inside of the blood vessel can be distinguished from the outside based on whether or not the temporal change is larger than a predetermined threshold, which allows the blood vessel position to be estimated. In the single data, it is difficult to distinguish the inside of the blood vessel from the outside. However, the inside of the blood vessel can be distinguished from the outside by the method of the second embodiment. Alternatively, the inside of the blood vessel is effectively distinguished from the outside by well-known techniques such as a power Doppler method. Thus, the combination of the blood vessel position estimating method and the A-mode measurement can improve a frame rate to sensitively measure the blood property. Body motion and the movement of the transducer other than movement of blood become also troublesome. The signal correlation is obtained in the whole of the depth direction to remove the influence of the motion of the whole image, whereby the measurement accuracy is effectively improved. 
       Third Embodiment 
       [0119]    In a third embodiment, only the A mode is used in the ultrasonic imaging.  FIG. 13  shows a configuration of an apparatus of the third embodiment. The apparatus configuration of the third embodiment is similar to that of the second embodiment except that the raster control unit and the A/B mode switching unit are eliminated.  FIG. 10  shows the flowchart of the third embodiment. When only the A mode is used, one ultrasonic transducer and one associated control and signal processing circuit can be used to realize the miniaturization, low power consumption, and low cost of the apparatus. On the other hand, the disadvantage due to the fact that the plural channels are not provided is that the blood vessel position is hardly estimated. The method of the second embodiment can be adopted in order to respond to the problem. Additionally, because the B-mode is not incorporated, the miniaturization, low power consumption, and low cost of the apparatus can be realized. 
         [0120]    When the depth-direction blood vessel position estimating method is adopted in the first embodiment, the blood vessel position specifying process can be automated although the operator performs the blood vessel position specifying process in the first embodiment. Not only the automation facilitates the handling of the apparatus, but also the blood vessel position can be chased to improve the measurement accuracy when the blood vessel position is moved during the measurement. 
       Fourth Embodiment 
       [0121]    In a fourth embodiment, one-channel ultrasonic transducer and an optical scattering image are used as a method in which the positioning of the measurement is easily performed while cost is reduced. When the apparatus includes the plural ultrasonic transducer and the associated control and signal processing circuits, the apparatus is enlarged or the cost is increased. On the other hand, a compact digital optical microscope having an LED light source and a CCD sensor can be realized at low cost. The hemoglobin of the blood in the living body tissue has the relatively high absorbance in the near-infrared wavelength region, and the reflection intensity of the visible light (such as green light) is high at the site where the superficial blood vessel exists. Therefore, the site where the superficial blood vessel exists can be detected. That is, the digital optical microscope is used as the blood vessel detector which is of the positioning means, and the blood vessel position is optically detected, and the ultrasonic transducer  103  is positioned according to the blood vessel position, so that the measurement can be performed by the one-channel ultrasonic transducer while the accuracy of the blood vessel position estimation is kept constant. Because the apparatus configuration of the fourth embodiment is identical to that of the third embodiment, the description thereof will not be described.  FIG. 14A  shows a configuration of an apparatus of the fourth embodiment. A CCD camera  1000  is fixed adjacent to the ultrasonic transducer  103 . Although not shown, the brightness of the optical image can be adjusted by appropriately disposing LED around the CCD camera  1000 .  FIG. 14B  shows a display example of the image obtained in the fourth embodiment. A camera image  1002  and an ultrasonic transducer position  1003  are displayed in a display image  1001 . At this point, the blood vessel image is monitored in the camera image, and the ultrasonic transducer  103  is moved, whereby the operator can understand that the ultrasonic transducer  103  is placed at the desired position relative to the blood vessel position.