Patent Publication Number: US-2015063057-A1

Title: Ultrasonic measurement apparatus, ultrasonic imaging apparatus, and ultrasonic measurement method

Description:
BACKGROUND 
     1. Technical Field 
     The present invention relates to an ultrasonic measurement apparatus, an ultrasonic imaging apparatus, and an ultrasonic measurement method. 
     2. Related Art 
     JP-A-2003-175035 discloses an ultrasonic diagnostic apparatus that determines units whose operation can be stopped or restricted according to an operating condition of the apparatus that is notified from a control unit, selects a power save method from a plurality of power save methods including power off, clock off, reducing clock frequency, switching to sleep mode, and the like, based on characteristics of the units that are determined to be able to stop or restrict operation, and executes operation restriction control for implementing power saving with the selected power save method. 
     JP-WO-A-2010/53008 discloses an ultrasonic diagnostic apparatus that is provided with an ultrasonic probe for transmitting and receiving ultrasonic waves, a transmission unit for providing a signal to the ultrasonic probe and causing the ultrasonic probe to form an ultrasonic beam, a reception unit for receiving a reception signal that is obtained by transmitting the ultrasonic beam toward a subject, a signal processing unit for forming an ultrasonic image based on the reception signal, a display unit that displays the ultrasonic image, and a control unit for controlling the transmission unit, the reception unit, the signal processing unit and the display unit, and that sets an operating mode of the transmission unit to a low power consumption operating mode or a high spatial resolution operating mode. 
     With the invention disclosed in JP-A-2003-175035, low power consumption of the ultrasonic diagnostic apparatus is achieved by turning off the power supply and the clock in units of circuit modules such as the transmission unit and the reception unit. For example, power supply to the transmission module which does not need to operate at the time of reception is stopped during the reception period. Accordingly, there is a problem with the invention disclosed in JP-A-2003-175035 in that power consumption at the time of image generation cannot be reduced. 
     With the invention disclosed in JP-WO-A-2010/53008, there is a problem in that spatial resolution deteriorates in the low power consumption mode, since power consumption is reduced in the low power consumption mode at the cost of the linear operation of the linear transmission amplification circuit. 
     SUMMARY 
     An advantage of some aspects of the invention is to provide an ultrasonic measurement apparatus, an ultrasonic imaging apparatus, and an ultrasonic measurement method that are able to achieve low power consumption together with high resolution. 
     An ultrasonic measurement apparatus according to a first aspect of the invention is provided with an ultrasonic transducer device that includes channels constituted by ultrasonic transducer elements that transmit and receive an ultrasonic wave; a reception processing unit that performs, when information showing a normal mode or a low power consumption mode shows the normal mode, processing for receiving a first number of ultrasonic echoes from among ultrasonic echoes relating to the transmitted ultrasonic wave that are acquired from the channels, that performs, when the information shows the low power consumption mode, processing for receiving a second number of ultrasonic echoes that is less than the first number from among ultrasonic echoes relating to the transmitted ultrasonic wave that are acquired from the channels, and that outputs reception signals obtained from the reception processing; and an image processing unit that receives input of the reception signals output from the reception processing unit, that adds together the first number of the reception signals with a weight that is computed in advance and performs image generation based on the reception signal obtained from the adding, when the information shows the normal mode, and that adds together the second number of the reception signals with a weight that depends on the reception signals and performs image generation based on the reception signal obtained from the adding, when the information shows the low power consumption mode. 
     According to this aspect, an ultrasonic wave is transmitted from channels that are constituted by ultrasonic transducer elements. Processing for receiving a first number of ultrasonic echoes, from among ultrasonic echoes relating to the transmitted ultrasonic wave that are acquired from the channels, is performed when information showing a normal mode or a low power consumption mode shows the normal mode, processing for receiving a second number of ultrasonic echoes that is less than the first number, from among the ultrasonic echoes relating to the transmitted ultrasonic wave that are acquired from the channels, is performed when the information shows the low power consumption mode, and reception signals obtained from the reception processing are output. When the information shows the normal mode, the first number of reception signals are added together with a weight that is computed in advance and image generation is performed based on the reception signal obtained from the adding, and when the information shows the low power consumption mode, the second number of reception signals are added together with a weight that depends on each reception signal, and image generation is performed based on the reception signal obtained from the adding. In the case of the low power consumption mode, the number of channels can thereby be reduced and low power consumption can be achieved. Also, in the case of the low power consumption mode, high resolution can be achieved by adding together the reception signals with a weight that depends on the reception signals. That is, low power consumption can be achieved together with high resolution. 
     An ultrasonic measurement apparatus according to a second aspect of the invention is provided with an ultrasonic transducer device; a transmission processing unit that transmits an ultrasonic wave of a predetermined wavelength toward an object from a first number of channels of the ultrasonic transducer device; a channel selection unit that acquires information showing a normal mode or a low power consumption mode, and selects channels to be used so as to acquire, from the first number of channels, reception waves of ultrasonic echoes relating to the transmitted ultrasonic wave, when information showing the normal mode is acquired, and to acquire, from a second number of channels that is less than the first number, reception waves of ultrasonic echoes relating to the transmitted ultrasonic wave, when information showing the low power consumption mode is acquired; a reception processing unit that performs processing for receiving the reception waves of the ultrasonic echoes relating to the transmitted ultrasonic wave that are acquired from the first number of channels or the second number of channels, and outputs a reception signal of each channel obtained from the reception processing; and an image processing unit that adds together the reception signals of the channels output from the reception processing unit with a weight that is computed in advance, when information showing the normal mode is acquired, adds together the reception signals of the channels output from the reception processing unit with a weight that depends on the reception signals, when information showing the low power consumption mode is acquired, and performs image generation based on the reception signal obtained from the adding. 
     According to this aspect, an ultrasonic wave of a predetermined wavelength is transmitted from a first number of channels of the ultrasonic transducer device toward an object, reception waves of ultrasonic echoes relating to the transmitted ultrasonic wave are acquired from the first number of channels, when information showing the normal mode is acquired, and reception waves of ultrasonic echoes relating to the transmitted ultrasonic wave are acquired from a second number of channels that is less than the first number, when information showing the low power consumption mode is acquired. Processing for receiving the reception waves of the ultrasonic echoes relating to the transmitted ultrasonic wave that are acquired from the first number of channels or the second number of channels is performed, and a reception signal of each channel obtained from the reception processing is output. The reception signals are added together with a weight that is computed in advance, when information showing the normal mode is acquired, the reception signals are added together with a weight that depends on the reception signals, when information showing the low power consumption mode is acquired, and image generation is performed based on the reception signal obtained from the adding. When information showing the low power consumption mode is acquired, the number of channels can thereby be reduced and low power consumption can be achieved. Also, when information showing the low power consumption mode is acquired, high resolution can be achieved by adding together the reception signals with a weight that depends on the reception signals. That is, low power consumption can be achieved together with high resolution. 
     Here, the channel selection unit may, when information showing the low power consumption mode is acquired, select the second number of channels that are located in a central portion of the first number of channels. The occurrence of grating lobes can thereby be suppressed, particularly in the case where the frequency is high. 
     Here, the channel selection unit may, when information showing the low power consumption mode is acquired, select the second number of channels such that an interval between adjacent channels in the second number of channels is the largest interval that satisfies the condition of being less than half the wavelength of the transmitted ultrasonic wave. The occurrence of grating lobes can thereby be suppressed, particularly in the case where the frequency is low. 
     Here, the channel selection unit may acquire information showing the relationship between the frequency of the transmitted ultrasonic wave and the second number of channels, and select the second number of channels based on the acquired information. The second number of channels can thereby be appropriately selected according to the frequency. 
     Here, the channel selection unit may, when information showing the low power consumption mode is acquired, select the second number of channels by adding together a plurality of channels among the first number of channels to serve as one channel. The number of channels can thereby be reduced while maintaining the sound pressure of the signals. 
     Here, the image processing unit may derive the weight that depends on the reception signal of each channel of the second number of channels, so as to minimize the variance of the result of multiplying the output signal of each channel of the second number of channels after a delay time that depends on the linear distance from the object to the channel by the weight that depends on the reception signal of the channel. The weight of each channel can thereby be changed according to the incoming wave. 
     Here, the image processing unit may, when information showing the low power consumption mode is acquired, derive the weight of each channel after extracting a plurality of sub apertures from an aperture constituted by the second number of channels and taking respective averages thereof. Deterioration of the azimuth estimation accuracy due to the influence of interference waves having correlativity can thereby be prevented. 
     An ultrasonic imaging apparatus according to a third aspect of the invention is provided with an ultrasonic transducer device; a transmission processing unit that transmits an ultrasonic wave of a predetermined wavelength toward an object from a first number of channels of the ultrasonic transducer device; a channel selection unit that acquires information showing a normal mode or a low power consumption mode, and selects channels to be used so as to acquire, from the first number of channels, ultrasonic echoes relating to the transmitted ultrasonic wave, when information showing the normal mode is acquired, and to acquire, from a second number of channels that is less than the first number, ultrasonic echoes relating to the transmitted ultrasonic wave, when information showing the low power consumption mode is acquired; a reception processing unit that performs processing for receiving the ultrasonic echoes relating to the transmitted ultrasonic wave that are acquired from the first number of channels or the second number of channels, and outputs a reception signal of each channel obtained from the reception processing; an image processing unit that adds together the reception signals of the channels output from the reception processing unit with a weight that is computed in advance, when information showing the normal mode is acquired, adds together the reception signals of the channels output from the reception processing unit with a weight that depends on each reception signal, when information showing the low power consumption mode is acquired, and performs image generation based on the reception signal obtained from the adding; and a display unit that displays the generated image. Low power consumption can thereby be achieved together with high resolution. 
     An ultrasonic measurement method according to a fourth aspect of the invention includes transmitting an ultrasonic wave of a predetermined wavelength toward an object from a first number of channels of an ultrasonic transducer device; acquiring information showing a normal mode or a low power consumption mode, and selecting channels to be used so as to acquire, from the first number of channels, ultrasonic echoes relating to the transmitted ultrasonic wave, when information showing the normal mode is acquired, and to acquire, from a second number of channels that is less than the first number, ultrasonic echoes relating to the transmitted ultrasonic wave, when information showing the low power consumption mode is acquired; performing processing for receiving the ultrasonic echoes relating to the transmitted ultrasonic wave that are acquired from the first number of channels or the second number of channels, and outputting a reception signal of each channel obtained from the reception processing; and adding together the output reception signals of the channels with a weight that is computed in advance, when the information showing the normal mode is acquired, adding together the output reception signals of the channels with a weight that depends on each reception signal, when information showing the low power consumption mode is acquired, and performing image generation based on the reception signal obtained from the adding. Low power consumption can thereby be achieved together with high resolution. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will be described with reference to the accompanying drawings, wherein like numbers reference like elements. 
         FIG. 1  is a perspective diagram showing a schematic configuration of an ultrasonic measurement apparatus 1 according to a first embodiment of the invention. 
         FIGS. 2A to 2C  show an exemplary schematic configuration of an ultrasonic transducer element. 
         FIG. 3  shows an exemplary configuration of an ultrasonic transducer device (element chip). 
         FIGS. 4A and 4B  show exemplary ultrasonic transducer element groups UG (UG1 to UG64), with  FIG. 4A  showing the case where there are four element columns, and  FIG. 4B  showing the case where there is one element column. 
         FIG. 5  is a block diagram showing an exemplary functional configuration of a control unit. 
         FIG. 6  illustrates a signal delay at each channel. 
         FIG. 7  illustrates sub apertures in spatial averaging. 
         FIG. 8  shows an exemplary schematic configuration of a control unit  22 . 
         FIG. 9  is a flowchart showing the flow of the overall processing by the ultrasonic measurement apparatus 1. 
         FIG. 10  is a flowchart showing the flow of processing in a normal mode of the ultrasonic measurement apparatus 1. 
         FIG. 11  is a flowchart showing the flow of processing in a low power consumption mode of the ultrasonic measurement apparatus 1. 
         FIGS. 12A and 12B  illustrate use configurations of the channels, with  FIG. 12A  showing the case of the normal mode, and  FIG. 12B  showing the case of the low power consumption mode. 
         FIGS. 13A and 13B  illustrate use configurations of the channels, with  FIG. 13A  showing the case of the normal mode, and  FIG. 13B  showing the case of the low power consumption mode. 
         FIG. 14  is an exemplary channel selection table showing the relationship between frequency and channels to be used. 
         FIG. 15  is a block diagram showing an exemplary functional configuration of a control unit in an ultrasonic measurement apparatus 2 according to a second embodiment of the invention. 
         FIG. 16  is a flowchart showing the flow of processing in a low power consumption mode of the ultrasonic measurement apparatus 2. 
         FIGS. 17A and 17B  illustrate use configurations of the channels, with  FIG. 17A  showing the case of the normal mode, and  FIG. 17B  showing the case of the low power consumption mode. 
     
    
    
     DESCRIPTION OF EXEMPLARY EMBODIMENTS 
     Embodiments of the invention will now be described with reference to the drawings. 
     Configuration of First Embodiment 
       FIG. 1  shows a general view of an ultrasonic measurement apparatus 1 according to a first embodiment of the invention. The ultrasonic measurement apparatus 1 is, for example, a compact ultrasonic measurement apparatus. The ultrasonic measurement apparatus 1 primarily includes an ultrasonic probe  10  and an ultrasonic measurement apparatus main body  20 , with the ultrasonic probe  10  and the ultrasonic measurement apparatus main body  20  being connected by a cable  15 . Note that the ultrasonic measurement apparatus 1 is not limited to being a compact ultrasonic measurement apparatus, and may be, for example, a stationary ultrasonic measurement apparatus, or an integrated ultrasonic measurement apparatus in which the ultrasonic probe is built into the main body. 
     Also, the ultrasonic measurement apparatus 1 uses an ultrasonic element array that enables linear scanning and sector scanning, and employs electronic focusing. In the case of linear scanning, the aperture is divided, transmission and reception are performed with the resultant apertures, and lines are generated. Also, in the case of sector scanning, lines are generated, while changing the transmission timing (delay time) of respective channels of the full aperture, and changing the beam direction. Hereinafter, the case where the ultrasonic measurement apparatus 1 performs linear scanning will be described as an example. 
     The ultrasonic probe  10  has an ultrasonic transducer device  11 . The ultrasonic transducer device  11  transmits an ultrasonic beam toward an object while scanning over the object along a scan surface, and receives ultrasonic echoes resulting from the ultrasonic beam. 
     Taking a type that uses piezoelectric elements as an example, the ultrasonic transducer device  11  has a plurality of ultrasonic transducer elements  12  (ultrasonic element array; refer to  FIGS. 2A to 2C , etc.) and a substrate in which a plurality of apertures are disposed in an array. 
       FIGS. 2A to 2C  show an exemplary configuration of the ultrasonic transducer elements  12  of the ultrasonic transducer device  11 . In the present embodiment, a monomorph (unimorph) structure in which thin piezoelectric elements and a metal plate (vibration film) are stuck together is employed as the ultrasonic transducer elements  12 . 
       FIGS. 2A to 2C  show an exemplary configuration of an ultrasonic transducer element  12  of the ultrasonic transducer device  11 .  FIG. 2A  is a plan view of an ultrasonic transducer element  12  formed on a substrate (silicon substrate)  60  viewed from an element formation side in a direction perpendicular to a substrate  60 .  FIG. 2B  is a cross-sectional view showing a cross-section along A-A′ in  FIG. 2A .  FIG. 2C  is a cross-sectional view showing a cross-section along B-B′ in  FIG. 2A . 
     The ultrasonic transducer element  12  has a piezoelectric element part and a vibration film (membrane, supporting member)  50 . The piezoelectric element part primarily includes a piezoelectric layer (piezoelectric film)  30 , a first electrode layer (lower electrode)  31 , and a second electrode layer (upper electrode)  32 . 
     The piezoelectric layer  30  is formed using a PZT (lead zirconate titanate) thin film, for example, and is provided so as to cover at least a portion of the first electrode layer  31 . Note that the material of the piezoelectric layer  30  is not limited to PZT, and materials such as lead titanate (PbTiO 3 ), lead zirconate (PbZrO 3 ) and lead lanthanum titanate ((Pb, La)TiO 3 ), for example, may be used. 
     The first electrode layer  31  is formed on an upper layer of the vibration film  50  with a metal thin film, for example. This first electrode layer  31  may be an interconnect that extends to outside the element formation area as shown in  FIG. 2A , and is connected to an adjacent ultrasonic transducer element  12 . 
     The second electrode layer  32  is formed with a metal thin film, for example, and is provided so as to cover at least a portion of the piezoelectric layer  30 . This second electrode layer  32  may be an interconnect that extends to outside the element formation area as shown in  FIG. 2A , and is connected to an adjacent ultrasonic transducer element  12 . 
     The lower electrode of the ultrasonic transducer element  12  is formed by the first electrode layer  31 , and the upper electrode is formed by the second electrode layer  32 . Specifically, the portion of the first electrode layer  31  covered by the piezoelectric layer  30  forms the lower electrode, and the portion of the second electrode layer  32  covering the piezoelectric layer  30  forms the upper electrode. That is, the piezoelectric layer  30  is provided so as to be sandwiched between the lower electrode and the upper electrode. 
     An aperture  40  is formed by etching such as reactive ion etching (RIE) or the like from the back surface (surface on which the element is not formed) side of the substrate  60 . The resonance frequency of ultrasonic waves is determined by the size of the aperture  40 , with the ultrasonic waves being emitted to the piezoelectric layer  30  side (in a direction from far to near in  FIG. 2A ). 
     The vibration film  50  is provided so as to close the aperture  40  using a two layer structure consisting of a SiO 2  thin film and a ZrO 2  thin film, for example. This vibration film  50  supports the piezoelectric layer  30  and the first and second electrode layers  31  and  32 , and produces ultrasonic waves by vibrating in accordance with the expansion and contraction of the piezoelectric layer  30 . 
       FIG. 3  shows an exemplary configuration of the ultrasonic transducer device (element chip). The ultrasonic transducer device of this exemplary configuration includes a plurality of ultrasonic transducer element groups UG1 to UG64 and drive electrode lines DL1 to DL64 (broadly, 1st to mth drive electrode lines, where m is an integer of 2 or more) and common electrode lines CL1 to CL8 (broadly, 1st to nth common electrode lines, where n is an integer of 2 or more). Note that the number (m) of drive electrode lines and the number (n) of common electrode lines are not limited to the numbers shown in  FIG. 3 . 
     The plurality of ultrasonic transducer element groups UG1 to UG64 are disposed in 64 columns in a second direction D2 (scan direction). Each of the ultrasonic transducer element groups UG1 to UG64 has a plurality of ultrasonic transducer elements that are disposed in a first direction D1 (slice direction). 
       FIG. 4A  shows an exemplary ultrasonic transducer element group UG (UG1 to UG64). In  FIG. 4A , the ultrasonic transducer element group UG is constituted by first to fourth element columns. The first element column is constituted by ultrasonic transducer elements UE11 to UE18 that are disposed in the first direction D1, and the second element column is constituted by ultrasonic transducer elements UE21 to UE28 that are disposed in the first direction D1. The third element column (UE31 to UE38) and the fourth element column (UE41 to UE48) are also similarly constituted. The drive electrode line DL (DL1 to DL64) is commonly connected to the first to fourth element columns. Also, the common electrode lines CL1 to CL8 are connected to the ultrasonic transducer elements of the first to fourth element columns. 
     The ultrasonic transducer element group UG in  FIG. 4A  constitutes one channel of the ultrasonic transducer device. That is, the drive electrode line DL is equivalent to the drive electrode line of one channel, and the transmission signal of one channel from a transmission circuit is input to the drive electrode line DL. Also, the reception signal of one channel constituted by the ultrasonic transducer element group UG is output from the drive electrode line DL. Note that the number of element columns constituting one channel is not limited to four columns as shown in  FIG. 4A , and may be less than four columns or greater than four columns. For example, one channel may be constituted by a single element column, as shown in  FIG. 4B . 
     Returning to the description of  FIG. 3 , the drive electrode lines DL1 to DL64 (1st to mth drive electrode lines) are laid in the first direction D1. An ith drive electrode line DLi of the drive electrode lines DL1 to DL64 (where i is an integer such that 1≦i≦m) is connected to the lower electrode of the ultrasonic transducer elements UE of the ith ultrasonic transducer element group UGi. 
     Transmission signals VT1 to VT64 are supplied to the ultrasonic transducer elements UE via the drive electrode lines DL1 to DL64 in a transmission period for emitting ultrasonic waves. Also, reception signals VR1 to VR64 from the ultrasonic transducer elements UE are output via the drive electrode lines DL1 to DL64 in a reception period for receiving ultrasonic echo signals. 
     The common electrode lines CL1 to CL8 (1st to nth common electrode lines) are laid in the second direction D2. The second electrode of the ultrasonic transducer elements UE is connected to one of the common electrode lines CL1 to CL8. Specifically, as shown in  FIG. 3 , for example, a jth common electrode line CLj (where j is an integer such that 1≦j≦m) of the common electrode lines CL1 to CL8 is connected to the upper electrode of the ultrasonic transducer elements that are disposed in the jth line. 
     A common voltage V COM  is supplied to the common electrode lines CL1 to CL8. This common voltage V COM  need only be a constant direct current voltage, and not 0V, that is, not ground potential. 
     In the transmission period, a difference voltage between the transmission signal voltage and the common voltage is applied to the ultrasonic transducer elements UE, and ultrasonic waves of a predetermined frequency are emitted. 
     Note that the arrangement of the ultrasonic transducer elements UE is not limited to the matrix arrangement shown in  FIG. 3 , and may be in a so-called houndstooth arrangement in which the elements of any two adjacent columns are disposed so as to zigzag alternately. Also, in  FIGS. 4A and 4B , the case is shown where a single ultrasonic transducer element is used as both a transmission element and a reception element, but the present embodiment is not limited thereto. For example, ultrasonic transducer elements for use as transmission elements and ultrasonic transducer elements for use as reception elements may be provided separately, and disposed in an array. 
     Also, the ultrasonic transducer elements  12  are not limited to a configuration that uses piezoelectric elements. For example, transducers that use capacitive elements, such as capacitive micro-machined ultrasonic transducers (cMUTs) may be employed, or bulk transducers may be employed. 
     Returning to the description of  FIG. 1 , a display unit  21  is provided in the ultrasonic measurement apparatus main body  20 . The display unit  21  displays image data for display generated by a control unit  22  (refer to  FIG. 5 ). A liquid crystal display, an organic electroluminescence display or electronic paper, for example, can be used for the display unit  21 . 
       FIG. 5  is a block diagram showing an exemplary functional configuration of the control unit  22  provided in the ultrasonic measurement apparatus main body  20 . The control unit  22  includes a transmission processing unit  110 , a reception processing unit  120 , an image processing unit  130 , a transmission/reception changeover switch  140 , a digital scan converter (DSC)  150 , a control circuit  160 , and a channel selection unit  170 . Note that, in the present embodiment, the control unit  22  is provided in the ultrasonic measurement apparatus main body  20 , but may be provided in the ultrasonic probe  10 . 
     The transmission processing unit  110  performs processing for transmitting ultrasonic waves toward an object. The transmission processing unit  110  includes a transmission pulse generator  111  and a transmission delay circuit  113 . 
     The transmission pulse generator  111  applies a transmission pulse voltage to drive the ultrasonic probe  10 . 
     The transmission delay circuit  113  performs transmission focusing control, and the ultrasonic probe  10  emits an ultrasonic beam corresponding to the generated pulse voltage toward the object. Thus, the transmission delay circuit  113  provides a time difference between channels with regard to the application timing of the transmission pulse voltage, and causes the ultrasonic waves produced by the plurality of vibration elements to converge. It is thus possible to arbitrarily change the focal length by changing the delay time. 
     In the case of linear scanning, the full aperture (64 channels in the example shown in  FIG. 3 ) is divided, and transmission and reception is performed with the resultant apertures (use apertures) to generate individual lines. The eight elements constituting the use aperture among the 64 channels constituting the full aperture are changed over by a multiplexer (MUX) that is not illustrated. Specifically, the 1-8th, 2-9th, 3-10th, . . . , 57-64th channels are sequentially connected to the transmission processing unit  110  by the multiplexer (MUX). One line is then respectively formed by 1-8th, 2-9th, 3-10th, . . . , 57-64th channels. In the present embodiment, 57 lines are formed (i.e., 64 (total number of channels)−8 (number of channels of the use aperture)+1=57). 
     In the present embodiment, the transmission processing unit  110  transmits ultrasonic waves using all the channels of the use aperture (e.g., eight channels). This is because beam width narrows and azimuth resolution increases with enlargement of the use aperture. The full number of channels constituting the use aperture is equivalent to the first number of channels of the invention. (Note that processing at the time of reception differs from at the time of transmission in that at least a portion of the eight channels of the use aperture are used. This will be discussed in detail later.) 
     The transmission/reception changeover switch  140  performs changeover processing of ultrasonic wave transmission and reception. The transmission/reception changeover switch  140  protects the reception processing unit  120  from input of amplitude pulses at the time of transmission, and allows signals at the time of reception to pass through to the reception processing unit  120 . 
     The reception processing unit  120  performs reception processing to acquire reception waves of ultrasonic echoes relating to a transmitted ultrasonic wave received by the ultrasonic probe  10  (hereinafter, reception waves). The reception processing unit  120  includes a reception circuit  121 , a filter circuit  123 , and a memory  125 . 
     The reception circuit  121  converts the reception wave (analog signal) for each channel into a digital reception signal, and outputs the reception signal to the filter circuit  123 . Note that processing for focusing the reception waves is performed with the image processing unit  130  which will be discussed later. 
     The filter circuit  123  performs filtering on the reception signal using a bandpass filter and removes noise. 
     The memory  125  is for storing reception signals output from the filter circuit  123 , and the functions of the memory  125  can be realized by a HDD, a memory such as RAM, or the like. 
     The functions of the reception processing unit  120  can be realized by, for example, an analog front end (AFE) that is constituted by a low noise amplifier (LNA), a programmable gain amplifier (PGA), a filter unit, an analog/digital converter (A/D convertor), and the like. 
     Note that the configuration of the reception processing unit  120  is not restricted to the illustrated example. For example, the filter circuit  123  may be provided in the image processing unit  130  (discussed in detail later) or immediately before an MVB processing unit  131  (discussed in detail later). Also, the functions of the filter may be realized with software. 
     The image processing unit  130  processes the reception signal output from the reception processing unit  120 . The image processing unit  130  primarily includes the MVB (minimum variance beamforming) processing unit  131 , a detection processing unit  136 , a logarithmic transformation unit  137 , a gain and dynamic range adjustment unit  138 , and a sensitivity time control (STC)  139 . 
     The MVB processing unit  131  performs MVB processing, which is directionally-constrained adaptive beamforming. Adaptive beamforming is processing that involves dynamically changing the sensitivity characteristics so as to not have sensitivity to unwanted waves, by changing the weight of each channel according to the incoming wave. Even if an ultrasonic beam is transmitted so as to have high sound pressure in a frontal direction, ultrasonic waves also reach reflectors that exist in directions other than directly in front, since ultrasonic waves are characterized by spreading spherically. When unwanted waves reflected by reflectors other than the target are received, azimuth resolution deteriorates due to the influence of the unwanted waves. In contrast, adaptive beamforming places a constraint on direction so as to not have sensitivity to unwanted waves, thus enabling the problem of a decrease in azimuth resolution due to unwanted waves to be remedied. 
     The MVB processing unit  131  primarily includes a reception focus processing unit  132 , a spatial averaging processing unit  133 , a weight calculation unit  134 , and a weighted addition unit  135 . 
     The reception focus processing unit  132  performs processing for focusing reception waves. Specifically, the reception focus processing unit  132  provides a delay time D m  to the signal received by each channel so that the signals received by the respective channels are in phase, and computes the output signal of each channel after provision of the delay time. Since the reflective wave from a given reflector spreads spherically, a delay time is provided so that arrival time at the reception circuit  121  and at each vibrator is the same, and the reflective waves are added together taking into account the delay time. 
     In the case where the total number of channels is M, an output signal X m  of the mth channel is derived with equation (1). Also, the output signal of each channel is given by equation (2) when expressed in vector notation. Here, x m  is the reception signal of the mth channel, and n shows the sample number (namely, depth in the image). 
     
       
         
           
             
               
                 
                   
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     As shown in  FIG. 6 , the ultrasonic wave reflected from a reflection object (object) that is located in a depth direction Z from the ultrasonic transducer device  11  arrives at each channel as a spherical wave. Accordingly, the time taken for the reflection signal to arrive at the element of each channel is determined by a linear distance q m  from the reflection object to the channel, with the ultrasonic wave taking longer to arrive as the distance of the element from the reflection object increases. An arrival time D′ m  for each element depends on the linear distance from the object to each channel of the use aperture, and is determined geometrically, as shown in equation (3). p m  is the position of the ultrasonic transducer element  12 , Z is the depth distance, and c is the sound velocity (fixed value). 
         q   m =√{square root over ( p   m   2   +Z   2 )}
 
         D′   m   =q   m   /c   (3)
 
     Note that the reception focus processing is the same in the case of both the normal mode and the low power consumption mode (the normal mode and low power consumption mode will be discussed in detail later). The output signals computed by the reception focus processing unit  132  are output to the spatial averaging processing unit  133 . 
     The spatial averaging processing unit  133  performs processing known as spatial averaging that involves extracting a plurality of sub apertures from the aperture constituted by the M channels and taking respective averages thereof. Spatial averaging is performed in order to prevent azimuth estimation accuracy from deteriorating due to the influence of correlated interference waves when the value of each channel is used directly. 
     For example, consider the case where K sub apertures (K=M−S+1) each consisting of S channels are extracted from the aperture of a total number of channels M, as shown in  FIG. 7 . In this case, the input vector of each sub aperture can be represented as shown in equation (4). 
     
       
         
           
             
               
                 
                   
                     
                       
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     Note that, instead of spatial averaging, processing known as temporal averaging that takes the average in a time direction of each channel may be performed. Signals processed by the spatial averaging processing unit  133  are output to the weight calculation unit  134  or the weighted addition unit  135 . 
     Note that the spatial averaging processing unit  133  is not an essential constituent element. In the case where spatial averaging is not performed, signals processed by the reception focus processing unit  132  can be output to the weight calculation unit  134  or the weighted addition unit  135 . 
     The weight calculation unit  134  computes the weight to be applied to the output of each channel, in the case of applying MVB processing. Here, weight calculation will be described. 
     First, the case where spatial averaging is not used will be described. An output z that is output by the weighted addition unit  135  is the result of multiplying a weight w m  of each channel and a signal x m  obtained from delay processing performed on each channel that is output from the reception focus processing unit  132  and summing the multiplication results, and is represented by equation (5). 
     
       
         
           
             
               
                 
                   
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     This is given by equations (6) and (7) when expressed in vector notation. H is a complex conjugate transpose and * is a complex conjugate. 
     
       
         
           
             
               
                 
                   
                       
                   
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     A correlation matrix R is given by equations (8) and (9). 
         R[n]=E[X[n]X[n]   T ]  (8)
 
         E└|z[n]|   2   ┘=w[n]   H   R[n]w[n]   (9)
 
     In order to compute a weight that minimizes the variance of z[n] in equations (8) and (9), conditional minimization problems such as shown in equations (10) and (11) are solved to derive the weight as shown in equation (12). 
     
       
         
           
             
               
                 
                   
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     Here, a is a steering vector. In the present embodiment, phasing has already being performed, so the direction is 0 degrees. Accordingly, a can be set to 1. 
     Next, the case where spatial averaging is used will be described. The correlation matrix can be represented as shown in equation (13). 
     
       
         
           
             
               
                 
                   
                       
                   
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     At this time, the optimal weight is derived by equation (14). 
     
       
         
           
             
               
                 
                   
                     
                       
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     The weighted addition unit  135  adds together the signals of the respective channels using the computed weights in the case where weights are computed by the weight calculation unit  134 , and using weights computed in advance in the case where weights are not computed by the weight calculation unit  134 . That is, an operation using equation (15) is performed to obtain the output z. The signal obtained from the adding by the weighted addition unit  135  is output to the detection processing unit  136 . Note that the weights computed in advance may be a fixed value or may be weight that depends on the number of scan lines, the distance from the object to the channel, or the like. This weight does not, however, vary with the size of the reception signal. 
     
       
         
           
             
               
                 
                   
                       
                   
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     The detection processing unit  136  performs absolute value (rectification) processing, and thereafter applies a low-pass filter to extract an unmodulated signal. 
     The logarithmic transformation unit  137  performs Log compression on the extracted unmodulated signal, and converts the form of expression of the signal, so as to more easily confirm the maximum and minimum signal strengths of reception signals at the same time. 
     The gain and dynamic range adjustment unit  138  adjusts the signal strength and the area of interest. Specifically, in gain adjustment processing, a direct current component is added to the Log-compressed input signal. Also, in dynamic range adjustment processing, the Log-compressed input signal is multiplied by an arbitrary number. 
     The STC  139  corrects the degree of amplification (brightness) according to depth, and acquires an image having uniform brightness across the entire screen. 
     Note that the functions of the image processing unit  130  can be realized by hardware such as various processors (CPU, etc.), an ASIC (gate array, etc.) and the like, computer programs, or the like. 
     The DSC  150  performs scan conversion on B-mode image data. For example, the DSC  150  converts line signals into image signals by interpolation processing such as bilinear interpolation. The DSC  150  then performs scan conversion on the B-mode image data. The DSC  150  outputs the image signals to the display unit  21 . Images are thereby displayed on the display unit  21 . 
     The control circuit  160  performs control of the transmission pulse generator  111 , the transmission delay circuit  113 , the reception circuit  121 , the transmission/reception changeover switch  140 , and the MVB processing unit  131 . 
     Also, a mode switching unit  23  (refer to  FIG. 5 ) is provided in the ultrasonic measurement apparatus main body  20 . The mode switching unit  23 , upon information showing the operating mode (the normal mode and the low power consumption mode will be described in detail later) of the ultrasonic measurement apparatus 1 being input via an input unit that is not illustrated, for example, receives the information showing the operating mode and inputs this information to the control circuit  160 . Here, the information showing operating mode is information showing the normal mode and low power consumption mode. 
     The channel selection unit  170  acquires the information showing operating mode from the control circuit  160 , and selects channels to be used for reception of ultrasonic echoes based on this information. The channel selection unit  170  acquires reception waves from all the channels of the use aperture, when information showing the normal mode is acquired, and selects channels to be used so that reception waves are acquired from at least a portion of the full number of channels of the use aperture, when information showing the low power consumption mode is acquired. The channel selection unit  170  will be described in detail later. 
     Although the main configuration of the ultrasonic measurement apparatus 1 has been described above in describing the features of the present embodiment, the configuration of the ultrasonic measurement apparatus 1 is not limited to the above configuration. The instant invention is not restricted by the classification method or names of the constituent elements. The configuration of the ultrasonic measurement apparatus 1 can also be classified into more constituent elements according to the processing content. One constituent element can also be classified so as to execute more processing. Also, the processing of each constituent element may be executed by one piece of hardware or may be executed by multiple pieces of hardware. 
       FIG. 8  is a block diagram showing an exemplary schematic configuration of at least a portion of the control unit  22 . As shown in the diagram, the control unit  22  is provided with a central processing unit (CPU)  221  which is an arithmetic device, a random access memory (RAM)  222  which is a volatile storage device, a read only memory (ROM)  223  which is a nonvolatile storage device, a hard disk drive (HDD)  224 , an interface (I/F) circuit  225  that connects the control unit  22  with other units, a communication apparatus  226  that performs communication with external devices, and a bus  227  that connects these constituent elements with each other. 
     Each of above functional units is realized by the CPU  221  reading out a predetermined program stored in the ROM  223  to the RAM  222  and executing the read program. Note that the predetermined programs may, for example, be installed in the ROM  223  in advance, or may be downloaded from a network via the communication apparatus  226  and installed or updated. 
     Next, processing by the ultrasonic measurement apparatus 1 of the present embodiment having the above configuration will be described. The ultrasonic measurement apparatus 1 is characterized in that the number of channels that are used and the beamforming processing differ according to the mode. 
       FIG. 9  is a flowchart showing processing for judging the current ultrasonic measurement apparatus 1. The control circuit  160  judges whether the low power consumption mode is active, based on information showing the operating mode input from the mode switching unit  23  (step S 100 ). 
     Here, the operating modes in the present embodiment will be described. In the present embodiment, a normal mode in which normal processing using all the channels of the use aperture is performed (refer to  FIGS. 12A and 13A ; described in detail later), and a low power consumption mode in which processing is performed using at least a portion of the channels of the use aperture (refer to  FIGS. 12B and 13B ; described in detail later) can be set. 
     In the case of an ultrasonic diagnostic apparatus that performs digital processing, the high power consumption of the AFE (equivalent to the reception processing unit  120 ) that performs processing for converting analog signals to digital signals is an issue. Accordingly, in the low power consumption mode, power consumption is reduced by reducing the number of signals input to the AFE. 
     However, there is a problem in that simply reducing the number of signals input to the AFE, that is, the number of channels, results in a decreases in image quality. Therefore, in the present embodiment, image quality is improved by performing MVB processing in the low power consumption mode. 
     If the low power consumption mode is not active (NO at step S 100 ), that is, if the information showing the operating mode input from the mode switching unit  23  is information showing the normal mode, the control circuit  160  performs processing in the normal mode in which reception focusing is performed using the signals of all the channels of the use aperture (step S 102 ). 
     If the low power consumption mode is active (YES at step S 100 ), that is, if the information showing the operating mode input from the mode switching unit  23  is information showing the low power consumption mode, the control circuit  160  performs processing in the low power consumption mode in which reception focusing is performed using the signals of at least a portion of the channels of the use aperture, and performs MVB processing (step S 104 ). 
     The control circuit  160  judges whether a processing end instruction has been input via the input unit or the like that is not illustrated (step S 106 ). If a processing end instruction has not been input (NO at step S 106 ), the processing returns to step S 100 , if a processing end instruction has been input (YES at step S 106 ), the processing is ended. 
     Next, image generation processing in the case of both the normal mode and the low power consumption mode will be described.  FIG. 10  is a flowchart showing the flow of image generation processing in the normal mode. 
     The control circuit  160  initializes the scan line number l which is a number showing the line for generating an image to 1 (l=1) (step S 110 ). The scan line number l is a number showing one of the ultrasonic transducer element groups UG1 to UG64 constituting an ultrasonic transducer device such as shown in  FIG. 3 . For example, the scan line number l of an element group provided at a given end, here, the ultrasonic transducer element group UG1, is set to 1. Also, the scan line number l of the element group that is adjacent to the element group having the scan line number 1, here, the ultrasonic transducer element group UG2, is set to 2. The scan line number l is given to all the element groups in this way. The relationship between the ultrasonic transducer element groups UG1 to UG64 and the scan line number l can be stored in a memory such as the ROM. 
     The control circuit  160  performs transmission of an ultrasonic pulse from all the channels of the use aperture corresponding to the channel having the scan line number l initialized at step S 110  or the scan line number l updated at step S 148  which will be discussed later (steps S 112  to S 116 ). For example, the channels at the time of the scan line number 1 are the ultrasonic transducer element groups UG1 to UG8, and the channels at the time of the scan line number 2 are the ultrasonic transducer element groups UG2 to UG9. 
     Specifically, the transmission pulse generator  111  generates a pulse voltage for transmitting an ultrasonic pulse having a frequency f (f can take any given value) (step S 112 ). The transmission delay circuit  113  performs transmission focusing control (step S 114 ), and the ultrasonic probe  10  emits an ultrasonic beam corresponding to the pulse voltage generated at step S 112  toward the object (step S 116 ). 
     Next, the control circuit  160  performs transmission/reception changeover processing via the transmission/reception changeover switch  140 . The ultrasonic probe  10  receives the reception waves that come back as a result of the emitted ultrasonic beam being reflected by the object with all the channels of the use aperture, and passes the received signals to the reception processing unit  120 . The reception circuit  121  converts the reception wave (analog signal) for each channel into a digital reception signal, and outputs the reception signals to the filter circuit  123  (step S 118 ). 
     The filter circuit  123  performs bandpass filtering on the reception signals (step S 120 ). The control circuit  160  saves the signals output from the filter circuit  123  to the memory  125  (step S 122 ). 
     The MVB processing unit  131  performs processing for rectifying and adding together the signals saved in the memory  125  (step S 124 ). Specifically, the reception focus processing unit  132  derives the output signal of each channel after provision of a delay time that depends on the linear distance from the object to the each channel of the use aperture, and the spatial averaging processing unit  133  performs spatial averaging on the output signal of each channel derived by the reception focus processing unit  132 . The weighted addition unit  135  then adds together the signals of the ultrasonic transducer elements  12  using weights set in advance. 
     The logarithmic transformation unit  137  performs logarithmic transformation on the result of adding together the signals of the channels of the use aperture (step S 140 ). The gain and dynamic range adjustment unit  138  adjusts the signal strength and the area of interest (step S 142 ). The STC  139  corrects the degree of amplification (brightness) according to depth (step S 144 ). 
     The control circuit  160  judges whether the scan line number l showing the line for generating an image is less than the number L of scan lines (step S 146 ). The number L of scan lines is the number of ultrasonic transducer element groups UG1 to UG64 constituting an ultrasonic transducer device  11  such as shown in  FIG. 3 , with L being 64 in the example shown in  FIG. 3 . 
     If the scan line number l is less than the number L of scan lines (YES at step S 146 ), the control circuit  160  adds 1 to the current scan line number l to update the scan line number l, and returns the processing to step S 112  (step S 198 ). 
     If the scan line number l is not less than the number L of scan lines (NO at step S 146 ), the scan line number l matches the number L of scan lines, that is, transmission and reception of ultrasonic pulses has ended for all the lines. In this case, the DSC  150  performs scan conversion to generate B-mode image data (image data for display), and outputs the generated image data for display to the display unit  21  (step S 150 ). The display unit  21  displays the generated image data for display (step S 152 ). This ends the processing shown in  FIG. 10 . 
       FIG. 11  is a flowchart showing the flow of image generation processing in the low power consumption mode. Note that the same signs are given to portions that are the same portion as processing shown in  FIG. 10 , and a detailed description thereof will be omitted. 
     The control circuit  160  initializes the scan line number l to 1 (l=1) (step S 110 ). 
     The control circuit  160  performs transmission of ultrasonic pulses from all the channels of the use aperture corresponding to the channel having the scan line number l initialized at step S 110  or the scan line number l updated at step S 148  which will be discussed later (steps S 112  to S 116 ). 
     Next, the channel selection unit  170  selects channels to be used for reception of ultrasonic echoes reflected by the object, from among all the channels of the use aperture from which ultrasonic pulses were transmitted at steps S 112  to S 116  (step S 130 ). Note that the channels selected by the channel selection unit  170  are equivalent to the second number of channels of the invention. Hereinafter, selection of channels will be described in detail. 
       FIGS. 12A and 12B  and  FIGS. 13A and 13B  illustrate the use configuration of the channels included in the use aperture, with  FIGS. 12A and 13A  showing the case of the normal mode, and  FIGS. 12B and 13B  showing the case of the low power consumption mode. In the case of the normal mode, all the channels are used. In contrast, since power consumption is reduced in the case of the low power consumption mode, the number of signals input to the AFE, that is, the number of channels, is reduced. 
       FIG. 14  is a channel selection table showing the relationship between frequency when the interval of the distance (element pitch) between adjacent channels is 300 μm and channels to be used. This table is stored in the ROM  223 , for example. The channel selection unit  170  selects the channels to be used, based on the wavelength of ultrasonic waves that are transmitted, and the channel selection table stored in the ROM  223 . 
     The transmission frequency is often changed when using the ultrasonic measurement apparatus 1. Although resolution increases with an increase in frequency, observation depth decreases. Accordingly, the user of the ultrasonic measurement apparatus 1 selects an optimal frequency to use depending on the depth of the site to be observed. However, the appropriate method for preventing the occurrence of grating lobes which cause image quality deterioration differs depending on the frequency. Accordingly, the channel selection unit  170  stores information showing the relationship between frequency and channels to be used, and channels to be used can be selected based on this information. 
     Note that the information showing relationship between frequency and channels to be used is not limited to the channel selection table shown in  FIG. 14 . 
       FIG. 12B  shows the case where the frequency in  FIG. 14  is greater than or equal to 2.5 MHz. In the case where frequency is high, a portion of the channels are selected, so that the element pitch does not change. In  FIG. 12B , the channel selection unit  170  selects a portion (e.g., four) of the channels that are located in a central portion of the use aperture as channels to be used. Note that it is not essential to select the elements that are located in a central portion of the use aperture, and channels that are located at the edge of the use aperture may be selected. 
       FIG. 13B  shows the case where the frequency in  FIG. 14  is less than 2.5 MHz. The appearance of grating lobe is determined by a wavelength λ (sound velocity/frequency) of the transmission wave and the element pitch. Generally, in the case where ultrasonic waves are transmitted and received in a range of 180 degrees, grating lobes will be suppressed if the element pitch is less than λ/2. Accordingly, the channel selection unit  170  selects channels to be used such that, in the case where the frequency is low, the interval between selected channels is the largest interval that satisfies the condition of being less than λ/2. In  FIG. 13B , the channels to be used are selected every other channel. 
     By thus reducing the number of channels to be used, the number of signals that are input to the reception processing unit  120 , that is, the number of drives of the AFE which has high power consumption, can be reduced, enabling low power consumption to be achieved. Note that although, in the present embodiment, channels to be used were selected based on a channel selection table, the method of selecting channels to be used is not limited thereto. Note also that even when the signals of at least a portion of the channels of the use aperture are passed to the AFE, one line is formed, similarly to the case where all the channels are used. 
     Returning to the description of  FIG. 11 , the control circuit  160  performs processing for changing over transmission/reception via the transmission/reception changeover switch  140 . The ultrasonic probe  10  receives the reception waves that come back as a result of the emitted ultrasonic beam being reflected by the object. The transmission/reception changeover switch  140  passes only the signals received by the channels selected at step S 130  to the reception processing unit  120 . The reception circuit  121  then converts the reception wave (analog signal) for each channel into a digital reception signal, and outputs the reception signals to the filter circuit  123  (step S 131 ). 
     The filter circuit  123  performs bandpass filtering on the reception signals (step S 136 ). The control circuit  160  saves the signals output from the filter circuit  123  to the memory  125  (step S 137 ). This processing is the same as the processing of steps S 120  and S 122 . 
     The MVB processing unit  131  performs so-called MVB processing on the signals saved in the memory  125 , which involves computing weights that differ for each channel, and performing weighted addition using the computed weights (steps S 138  and S 139 ). Specifically, the reception focus processing unit  132  provides a delay time to the signal received by each channel, so that the signals received by the respective channels are in phase, and computes an output signal of each channel after provision of the delay time. The spatial averaging processing unit  133  performs spatial averaging on the output signals computed by the reception focus processing unit  132 . The weight calculation unit  134  then computes a weight to be applied to the output of each ultrasonic transducer element  12  (step S 138 ). 
     The weighted addition unit  135  then adds together the signals of the respective channels, using the weights computed at step S 138  (step S 139 ). This ends the MVB processing. 
     The logarithmic transformation unit  137  performs logarithmic transformation on the result of having added the signals of the respective channels (step S 140 ). The gain and dynamic range adjustment unit  138  adjusts the signal strength and the area of interest (step S 142 ). The STC  139  corrects the degree of amplification (brightness) according to depth (step S 144 ). 
     The control circuit  160  judges whether the scan line number l of the ultrasonic transducer element group targeted for processing in steps S 112  to S 144  is less than the number L of scan lines (step S 146 ). The number L of scan lines depends on the number of ultrasonic transducer element groups UG1 to UG64 constituting an ultrasonic transducer device such as shown in  FIG. 3 . 
     If the scan line number l is less than the number L of scan lines (YES at step S 146 ), the control circuit  160  adds 1 to the current scan line number l to update the scan line number l, and returns the processing to step S 112  (step S 148 ). 
     If the scan line number l is not less than the number L of scan lines (NO at step S 146 ), the scan line number l matches the number L of scan lines, that is, the transmission and reception of ultrasonic pulses has ended in all the ultrasonic transducer element groups UG. In this case, the DSC  150  performs scan conversion to generate B-mode image data (image data for display), and outputs the generated image data for display to the display unit  21  (step S 150 ). The display unit  21  displays the generated image data for display (step S 152 ). This ends the processing shown in  FIG. 10 . 
     According to the present embodiment, power consumption in the low power consumption mode can be suppressed by reducing the number of drives of the reception processing unit, that is, the AFE. Also, since MVB processing is performed in the low power consumption mode, image quality degradation due to reducing the number of channels can be suppressed. 
     Also, according to the present embodiment, B-mode images can be displayed in the normal mode, enabling compatibility with a conventional ultrasonic measurement apparatus to be maintained. 
     Also, according to the present embodiment, appropriate channels are selected in the low power consumption mode depending on the frequency, enabling the occurrence of grating lobes to be effectively suppressed. 
     Note that, in the present embodiment, since linear scanning was described as an example, channels to be used were selected from among the eight channels of the use aperture in the low power consumption mode. In contrast, in the case of sector scanning, the full aperture is used (the use aperture consists of 64 channels), and lines are generated while changing the beam direction. Accordingly, as long as a configuration is adopted in which channels to be used are selected from the full aperture (e.g., 64 channels), the present embodiment can be applied to sector scanning. 
     Second Embodiment 
     Although the ultrasonic measurement apparatus 1 according to the first embodiment reduces the number of channels by using a portion of the channels and inputs the signals of the channels that are used to the reception processing unit in the low power consumption mode, the method of reducing the number of signals that are input to the reception processing unit is not limited thereto. 
     An ultrasonic measurement apparatus 2 according to the second embodiment reduces the number of signals that are input to the reception processing unit by adding together the signals of a plurality of channels and inputting the resultant signal to the reception processing unit. Hereinafter, the ultrasonic measurement apparatus 2 will be described. 
       FIG. 15  is a block diagram showing an exemplary functional configuration of a control unit  22  provided in an ultrasonic measurement apparatus main body  20  of the ultrasonic measurement apparatus 2. Since a difference between the configuration of the ultrasonic measurement apparatus 2 and the configuration of the ultrasonic measurement apparatus 1 is that the ultrasonic measurement apparatus 2 has adder circuits  142 , whereas the ultrasonic measurement apparatus 1 does not have adder circuits, the adder circuits  142  will be described here. The same signs are given to portions that are the same as the configuration of the ultrasonic measurement apparatus 1, and a detailed description thereof will be omitted. 
     The adder circuits  142  are provided between the transmission/reception changeover switch  140  and the reception processing unit  120 . The adder circuits  142  add together the reception signals received by a plurality of channels, and input the resultant signal to the reception processing unit  120  as the reception signal of one channel. The channels that input to the adder circuits  142  are selected by the channel selection unit  170 . The adder circuits  142  will be discussed in detail later. 
     Hereinafter, the processing that is performed by the ultrasonic measurement apparatus 2 will be described. Since the processing that is performed by the ultrasonic measurement apparatus 1 and the processing that is performed by the ultrasonic measurement apparatus 2 differ in the case of the low power consumption mode, the processing that is performed by the ultrasonic measurement apparatus 2 in the case of the low power consumption mode will be described. Note that the same signs are given to portions that are the same as processing by the ultrasonic measurement apparatus 1, and a detailed description thereof will be omitted. 
       FIG. 16  is a flowchart showing the flow of image generation processing in the low power consumption mode. 
     The control circuit  160  initializes the scan line number l to 1 (l=1) (step S 110 ). 
     The control circuit  160  performs transmission of an ultrasonic pulse from all the channels of the use aperture corresponding to the channel having the scan line number l initialized at step S 110  or the scan line number l updated at step S 148  which will be discussed later (steps S 112  to S 116 ). 
     Next, reception processing is performed (step S 134 ). Hereinafter, the processing of step S 134  will be described. 
     The control circuit  160  performs processing for changing over transmission/reception via the transmission/reception changeover switch  140 . The ultrasonic probe  10  receives the reception waves that come back as a result of the emitted ultrasonic beam being reflected by the object. The channel selection unit  170  passes the signals received by the selected channels (here, all the channels) two at a time to one adder circuit  142 , and the adder circuit  142  adds together the signals of the plurality (here, two) of channels and passes the resultant signal to the reception processing unit  120 . 
       FIGS. 17A and 17B  illustrate the adding of the reception signals of a plurality of channels by the adder circuits  142 , with  FIG. 17A  showing the case where the adder circuits  142  do not add the signals, that is, the case of the normal mode, and  FIG. 17B  showing the case where the adder circuits  142  add together the reception signals of two channels, that is, the case of the low power consumption mode. 
     In the case shown in  FIG. 17A , the reception signal of each channel is input directly to the reception processing unit  120 , without passing through the adder circuits  142 . This is the same as the case shown in  FIGS. 12A and 13A . 
     In the case shown in  FIG. 17B , the adder circuits  142  add together the signals of two adjacent channels, and the resultant signal is input to the reception processing unit  120  as the signal of one channel. Accordingly, the reception signals received by eight channels are input to the reception processing unit  120  as reception signals received by four channels. The number of channels is thereby reduced in a pseudo manner, and the number of signals that are input to the reception processing unit  120  is reduced. 
     Also, in the case shown in  FIG. 17B , the signals obtained from the adding by the adder circuits  142  are input to the reception processing unit  120  as the signal received by one of the two channels which received the signals that were added (right-hand channel in  FIG. 17B ). Channels are thereby selected. 
     By thus reducing the number of signals that are input to the reception processing unit  120 , the number of drives of the AFE having high power consumption can be reduced, enabling low power consumption to be achieved. Also, since the sound pressure of the signals that are input can be maintained by adding the signals together, reception sensitivity can be maintained. 
     Note that although, in  FIG. 17B , the reception signals of all the channels are input to the adder circuits  142 , the signals of all the channels do not necessarily need to be added together, and the reception signals of at least a portion of the channels may be input to the adder circuits  142 . For example, the signals of the four channels in the center of the use aperture may be input directly to the reception processing unit  120 , and the two channels at either edge of the use aperture, that is, four channel in total, may be respectively input to the reception processing unit  120  by the adder circuits  142  as the signal of one channel. 
     Also, although, in  FIG. 17B , the signals of two channels are input to one adder circuit  142 , the signals of three or more channels may be input to one adder circuit  142 . 
     Also, in  FIG. 17B , the element pitch is widened by adding together the signals of a plurality of channels. The number of channels that input to one adder circuit  142  may also be set according to the frequency of the ultrasonic wave that is transmitted, so that the grating lobes do not occur. 
     The reception circuit  121  then converts the reception wave (analog signal) for each channel into a digital reception signal, and outputs the reception signals to the filter circuit  123 . 
     The filter circuit  123  performs bandpass filtering on the reception signals (step S 136 ). The control circuit  160  saves the signals output from the filter circuit  123  to the memory  125  (step S 137 ). This processing is the same as the processing of steps S 120  and S 122 . 
     The MVB processing unit  131  performs so-called MVB processing on the signals saved in the memory  125 , which involves computing weights that differ for each ultrasonic transducer element  12 , and performing weighted addition using the computed weights (steps S 138  to S 139 ). 
     The logarithmic transformation unit  137  performs logarithmic transformation on the result of having added together the signals of the ultrasonic transducer elements  12  (step S 140 ). The gain and dynamic range adjustment unit  138  adjusts the signal strength and the area of interest (step S 142 ). The STC  139  corrects the degree of amplification (brightness) according to depth (step S 144 ). 
     The control circuit  160  judges whether the scan line number l of the ultrasonic transducer element group targeted for processing in steps S 112  to S 144  is less than the number L of scan lines (step S 146 ). 
     If the scan line number l is less than the number L of scan lines (YES at step S 146 ), the control circuit  160  adds 1 to the current scan line number l to update the scan line number l, and returns the processing to step S 112  (step S 148 ). 
     If the scan line number l is not less than the number L of scan lines (NO at step S 146 ), the scan line number l matches the number L of scan lines, that is, transmission and reception of ultrasonic pulses has ended for all the ultrasonic transducer element groups UG. In this case, the DSC  150  performs scan conversion to generate B-mode image data (image data for display), and outputs the generated image data to the display unit  21  (step S 150 ). The display unit  21  displays the generated image data for display (step S 152 ). This ends the processing shown in  FIG. 10 . 
     According to the present embodiment, power consumption can be suppressed in the low power consumption mode by reducing the number of drives of the reception processing unit  120 , that is, the AFE, similarly to the first embodiment. Also, since MVB processing is performed in the low power consumption mode, image quality degradation due to a reduction in the number of ultrasonic transducer element  12  can be suppressed. 
     Also, according to the present embodiment, addition processing is performed to reduce the number of signals that are input to the reception processing unit, the sound pressure of the signals can be maintained, and accordingly reception sensitivity can be maintained. 
     Although the invention has been described above using embodiments, the technical scope of the invention is not limited to the scope given in the above embodiments. A person skilled in the art will appreciate that numerous changes and modifications can be made to the embodiments. Also, it is obvious from the claims that configurations to which changes and modifications are made are included in the technical scope of the invention. Also, the invention is not limited to an ultrasonic measurement apparatus, and can also be provided as an image processing method that is performed in an ultrasonic measurement apparatus, a program that causes an ultrasonic measurement apparatus to perform image processing, a storage medium on which the program is stored, or the like. 
     The entire disclosure of Japanese Patent Application No. 2013-183799, filed Sep. 5, 2013 is expressly incorporated by reference herein.